Input: Nevertheless, the main outcome of the reported experience is the proposed redesign approach for part consolidation using metal AM.

part consolidation

metal AM


Input: The proposed approach is general, well structured, and detailed enough to be immedialtely applicable at industrial level, but it needs further testing on different case studies to prove the benefits.

be

industrial

testing

case studies


Input: An interesting framework to part consolidation and functional integration exploiting AM technologies is presented and validated in.

framework

part consolidation

AM technologies


Input: In a further development of their approach, the authors have recently addressed the relevant problem of detecting the possible candidates for part consolidation, as reported in.

part consolidation

as


Input: Potentially, when dealing with part consolidation, the designer may consider the need of part decomposition.

part consolidation

decomposition


Input: The need to increase the number of parts in a product fabricated by AM may be due to many reasons: printability, productivity, functionality, artistry, and interchangeability.

fabricated

productivity

AM

be

printability


Input: Printability is actually the main reason being related to the limited working envelope of AM machines.

Printability

AM machines


Input: In the part decomposition problem in AM is addressed, but it is the first and unique example of research on this topic.

decomposition

AM

research


Input: 9 Conclusion and future challenges DfAM is about design for the whole AM product life cycle.

design

AM

life cycle


Input: This paper has presented a framework of tools and methods for DfAM and has shown the strong interaction between these life cycle stages and AM product design.

framework

life cycle

tools

AM

design


Input: The state of the art was presented on many of these design tools and their applicability was illustrated using many of the latest examples from research and industry.

art

industry

design

research


Input: 9.1 AM suitability exploration A growing number of companies are exploring the commercial use of AM within their supply chain.

AM

AM

companies

supply chain


Input: For that, better methods and tools are needed to help the designer obtain an overview that identifies the match between functional and economical demands of the intended product and all stages of AM in product development.

tools

AM

product development


Input: Methods for early cost estimation are lacking, while current figures for production cost per cm3 are not based on established calculation methods and lack experimental and industrial verification.

cost estimation

production cost

experimental

industrial


Input: Late life cycle stages of postprocessing, inspection and certification have a significant impact on production cost and general applicability of AM, but these stages are underrepresented in current DfAM approaches.

life cycle

postprocessing

impact

production cost

inspection

AM


Input: Finally, more education on Additive Manufacturing is needed, as the majority of product designers and engineers are still trained to think subtractive.

Additive Manufacturing

subtractive

as


Input: 9.2 Product design for AM goals Topology optimization enables strategies that go beyond lightweight design to include minimizing support usage and thermal deformation, optimizing local heat input, and with that the local material properties, porosity and strength.

Product design

Topology optimization

design

AM

go

lightweight

local heat input

material properties

support

thermal deformation

porosity

strength


Input: TO methods need further enhancement to tackle optimization as a 3D problem while taking all later product development stages into account.

optimization

product development

as


Input: Generative design strategies have the benefit that they generate many possible design solutions, but as is the case with TO, few production and inspection constraints are currently integrated.

Generative design

design

as

production

inspection


Input: Lattice structures show explicit benefits, especially in application fields involving energy absorption and heat conduction.

Lattice structures

energy absorption

heat conduction


Input: They are however computationally intensive, which limits the optimization possibilities for large lattices to a limited set of parameters.

limits

optimization

lattices

parameters

set


Input: When looking at the part interior, specially designed porosity is seen as a promising new feature for internal transport of gasses and fluids.

designed

feature

as

fluids

transport


Input: Both the optimal process settings as well as models for their application need further research to be applicable in everyday product design.

optimal process

as

as

be

research

product design


Input: To fully exploit the benefits of functional material complexity, further research must be conducted on rules and CAD representations of FGM related design intent.

functional material complexity

research

be

CAD

FGM

design


Input: However, the development of design tools and methods is still a matter of basic research and far from industrial application.

design

research

industrial


Input: The future of additive manufacturing is also looking towards 4D applications where those challenges will be even more relevant.

additive manufacturing

be


Input: For the final optimization of geometry so that it combines AM benefits with efficient production and inspection, a lot of research has been conducted.

optimization

geometry

research

AM

production

inspection


Input: At an individual process level design knowledge is available and constantly being extended or refined.

process

design


Input: Further research is needed to enable improved integration in upstream product design steps like TO and generative design.

research

product design

generative design


Input: Integrating processing and manufacturing with design in AM is feasible since the full digital chain is there.

manufacturing

AM

design

digital chain


Input: In current AM practice only a few zones in a product are defined where process settings can be defined, for example for the top and bottom facing surfaces and the bulk of the product in L-PBF.

AM

facing

L-PBF

process settings

be


Input: If machine learning and closed loop control can be used to define the optimal settings for each deposition area, the need for support structures as well as the effects of thermal stresses and deformations are expected to reduce/diminish.

machine

closed loop control

deposition

deformations

be

as

as

area

support structures

thermal stresses


Input: This will have large impact on the AM products and the way they are designed.

impact

AM

designed


Input: A combination of computational and knowledge-based methods would be an optimal solution for DfAM in the future to define qualified AM design solutions.

be

solution

AM


Input: Data analytic methods could be used to explore and discover knowledge from existing validated designs or dig out implicit knowledge from large industrial practice and experimental data sets.

Data

experimental data

be

designs

industrial


Input: A collaborative cloud-based DfAM platform would be more sustainable for the world if people could share their designs and design knowledge as well as other AM processing related data sets.

platform

be

as

as

sustainable

data

designs

design

AM


Input: This would enable and advance wide KBE in DfAM, save a lot of cost and time and improve quality over the trial and error practice in current DfAM.

quality

trial and error


Input: This will result in new application areas, new process constraints and new AM features The main goal of this review is to provide a detailed and comprehensive description of the published work from the past decade regarding AM of ceramic materials with possible applications in dentistry.

areas

process

AM

AM

ceramic materials

dentistry


Input: The main printable materials and most common technologies are also addressed, underlining their advantages and main drawbacks.

materials

technologies


Input: Methods Online databases were consulted on this topic.

databases


Input: Results Ceramic materials are broadly used in dentistry to restore/replace damaged or missing teeth, due to their biocompatibility, chemical stability and mechanical and aesthetic properties.

Ceramic materials

dentistry

mechanical

biocompatibility

chemical stability

aesthetic


Input: Due to their brittleness nature, a very tight control of the manufacturing process is needed to obtain dental pieces with adequate mechanical properties.

brittleness nature

manufacturing process

dental pieces

mechanical properties


Input: Additive manufacturing is an emerging technology that constitutes an interesting and viable manufacturing alternative to the conventional subtractive methods.

Additive manufacturing

manufacturing

conventional subtractive methods

technology


Input: AM enables the production of customized complex 3D parts in a more sustainable and less expensive way.

AM

production

3D parts

sustainable


Input: AM of ceramics can be achieved with an extensive variety of methods.

AM

ceramics

be


Input: Although very promising, AM of ceramic dental materials remains understudied and further work is required to make it a widespread technology in dentistry.

AM

ceramic dental materials

technology

dentistry


Input: In dentistry, as in many other fields, the production of dental pieces is increasingly becoming automated.

dentistry

as

production

dental pieces


Input: Computer aided design and/or computer aided manufacturing have become progressively widespread within the medical and dental fields.

Computer aided design

computer aided manufacturing

medical

dental


Input: These tools are generally used in the manufacture of dental pieces in machining centers, where extra material is removed from a block to obtain the piece with the desired shape.

tools

dental pieces

machining centers

manufacture

material


Input: This technique is known as subtractive manufacturing.

as

manufacturing


Input: Nowadays, a new type of technology is emerging, additive manufacturing, also referred to as 3D printing, that allow building up pieces by adding materials layer-by-layer, based on a computerized 3D model.

technology

materials layer-by-layer

additive manufacturing

3D printing

as

3D model


Input: This type of technology has suffered great developments in a wide range of areas, allowing to produce pieces of all classes of materials, including materials of biological origin.

technology

materials

range

areas

classes of materials


Input: AM focus has been moving from prototype fabrication to rapid manufacturing of small or medium quantities of end-use products.

AM

fabrication

rapid manufacturing

prototype


Input: Among the main areas of AM application stands out:-Aerospace: AM technology is particularly suitable to obtain a limited number of pieces that are usually required for aerospace applications, with complex geometries and made of advanced materials which are difficult, costly and time-consuming to manufacture.

areas

AM

AM technology

Aerospace

aerospace

complex geometries

materials

manufacture


Input: -Automotive: AM technology is an important tool in this industry, since it can reduce the development cycle, manufacturing and product costs of automotive components.

Automotive

industry

automotive

AM technology

manufacturing

tool


Input: It allows producing small quantities of structural and functional parts and thus, is particularly interesting for racing vehicles, where light-weight alloys and composites are used to obtain highly complex structures.

light-weight

alloys

composites

complex structures


Input: -Energy: AM technology allows the fast development and fabrication of prototypes to reduce the cost and lead-time of research and development of new solutions that reduce the fossil energy dependency.

AM technology

fabrication

prototypes

research

lead-time


Input: It increases the design possibilities to improve energy efficiency and/or power density, in alternatives that use renewable and clean energies.

design

power

density


Input: -Biomedical: Recent developments in the biomaterials field, biologic sciences and biomedicine have potentiated the use of AM techniques.

Biomedical

biomedicine

biomaterials field

AM techniques


Input: Customization is a critical factor in this area and AM allows the production of a wide range of products with specific properties and shapes that meet the patient needs.

critical factor

specific properties

area

range

AM

production


Input: For example, it is possible to produce diagnostic platforms, orthopedic and dental implants, drug delivery systems, medical devices, tissue scaffolds and artificial organs.

dental

medical devices

artificial organs

scaffolds


Input: Biofabrication through AM emerged in the recent years as a new alternative to fabricate tissues.

Biofabrication

AM

fabricate

as


Input: Here, living cells are deposited layer-by-layer in combination with different biomaterials to obtain complex living structures.

cells

layer-by-layer

biomaterials


Input: In the dentistry field, the use of AM to produce endurable dental structures is expected to bring advantages over conventional manufacturing methods, as reported on other fields.

dentistry field

AM

conventional manufacturing

dental structures

as


Input: In particular, it shall:-Allow the production of customized near-net-shape dental pieces with intricate details.

production

near-net-shape

dental pieces


Input: Product complexity shall not add cost to production beyond the design stage, because once the design is set, costs are independent of the shape.

complexity

production

design

design

set


Input: -Allow reduction of dental parts production time and consequently of time-to-market.

reduction

dental

production


Input: Traditional subtractive technologies involve several time-consuming steps, while AM allows a faster direct production starting simply from a 3D scan of the oral cavity.

subtractive

AM

production


Input: -Limit human error relevance in the procedures.

Limit

error


Input: Minor human intervention is required in AM due to the lower number of manufacturing steps.

AM

manufacturing


Input: -Decrease the environmental impact, ensuring a higher manufacturing sustainability.

impact

manufacturing sustainability


Input: Being an additive technique, it reduces material waste and energy consumption and eliminates the use of conventional manufacturing tools.

additive

material

conventional manufacturing


Input: Globally, AM allows moving from mass production to mass customization, with significant efficiency increase and production costs decrease.

AM

mass production

production costs


Input: The expected dissemination of this technology applied to dental prosthesis shall result in equipmentcost decrease.

technology

dental prosthesis


Input: Thus, the reduction of final product price is predictable, increasing the accessibility of dental care to the poorest sectors of the population.

reduction

predictable

dental

population


Input: Due to the recent expiration of the main 3D printing patents, the access to printers became easier and less expensive.

3D printing

printers


Input: Digital dentistry is reported to be one of the fastest growing sectors of the AM technologies.

dentistry

be

AM technologies


Input: There are several possible applications of AM techniques in dentistry, e.g.

AM techniques

dentistry


Input: crowns, bridges, dentures, models, surgical guides, implants and orthodontics materials.

dentures

implants

materials


Input: Several challenges emerge when this technique is considered to produce endurable dental devices.

dental devices


Input: For example, the reliability of the process, surface finishing of the samples and materials density are among the major concerns.

reliability

process

samples

materials

surface finishing

density


Input: Concerning dental materials that can be used in AM, polymers are the most studied and used ones, followed by metals.

dental

be

polymers

metals

AM


Input: AM of ceramic dental materials is still underdeveloped, mainly due to the difficulties to produce pieces with suitable surface finishing, mechanical properties and dimensional accuracy.

AM

surface finishing

ceramic dental materials

mechanical properties

dimensional accuracy


Input: The available literature regarding AM of ceramic materials represents less than 5% of the total AM published related work.

AM

AM

ceramic materials


Input: The studies are even fewer in what concerns ceramic materials for dental applications.

ceramic materials

dental applications


Input: This paper presents a recent overview of published work concerning AM of ceramic materials for dental applications.

AM

ceramic materials

dental applications


Input: A summary of potentially printable dental biomaterials and brief descriptions of the most common digital manufacturing technologies are also provided, highlighting the main features, advantages and drawbacks, to better understand the potential and restrictions of each technology.

dental

biomaterials

digital manufacturing

technology


Input: The used keywords strings were: 3D printing AND Dental; Additive manufacturing AND Dental.

3D printing

Additive manufacturing

Dental

Dental


Input: Additive manufacturing of bioceramics for dental applicationsbut included in the remaining sections to complement this review and provide any additional remarks.

Additive manufacturing

bioceramics

dental


Input: 3 Ceramic dental materials Bioceramics are broadly used in the dental field.

Ceramic dental materials

Bioceramics

dental


Input: These materials have some attractive features/attributes which are similar to natural dentition properties, e.g.

materials

properties


Input: compressive strength, thermal conductivity, radiopacity, colour stability, aesthetics.

compressive strength

thermal conductivity

stability


Input: However, these materials are brittle, hard and sometimes difficult to process.

materials

process

brittle


Input: Bioceramics can be divided in 4 categories, depending on their main system composition: glass-based systems; glass-based systems with fillers, usually crystalline; crystalline-based systems with glass fillers; polycrystalline solids.

Bioceramics

be

glass fillers

composition


Input: Glass-based systems consist of materials that are made mostly of silicon dioxide and can comprise different amounts of alumina.

materials

silicon dioxide

alumina


Input: Feldspars are composed of aluminosilicates, found in nature, containing different quantities of potassium and sodium.

aluminosilicates

sodium


Input: Feldspars can be modified in several ways in order to produce the glass used in the dental area.

be

glass

dental

area


Input: Additionally, synthetic forms of alumina silicate glasses may as well be manufactured for dental ceramics.

alumina

glasses

as

be

ceramics

dental


Input: The glass composition is almost the same as the pure glass category, being that the difference resides in the amount of different types of crystals that can either be added or grown in the glassy matrix.

glass

as

glass

be

composition


Input: Nowadays, the primary crystal types are leucite, lithium dissilicate or fluoroapatite.

leucite

lithium


Input: Intended as an alternative to traditional metal ceramics, crystalline-based systems with glass fillers were developed.

as

metal ceramics

glass fillers


Input: They are composed of glass-infiltrated, partially sintered alumina.

sintered

alumina


Input: Polycrystaline solids are made by directly sintering crystals together, forming a dense, air-free, glass-free, polycrystalline structure.

Polycrystaline solids

directly sintering crystals

forming

polycrystalline structure


Input: In the next sections, a brief description is presented regarding the main properties of the most frequently used bioceramics in dental applications.

properties

bioceramics

dental applications


Input: 3.1 Zirconia Zirconia ceramics were introduced in dentistry in the early nineties, as endosseous implants in dental prosthetic surgery.

Zirconia

ceramics

as

dentistry

implants

dental

surgery


Input: This material is known to have exceptional mechanical properties and ease of machining in the pre-sintering stage through CAD/CAM.

material

mechanical properties

machining

pre-sintering

CAD/CAM


Input: Zirconia is biocompatible with the tissues in the oral cavity and has been reported to be osteoconductive, which means that this ceramic facilitates bone formation when in contact with it.

Zirconia

be

ceramic

biocompatible

bone

contact


Input: Regarding mechanical properties, zirconia ceramics are considered to have high strength, hardness, wear resistance, resistance to corrosion, modulus of elasticity similar to steel, coefficient of thermal expansion similar to iron, and the highest fracture toughness among the most used ceramics.

mechanical properties

corrosion

fracture

zirconia ceramics

steel

iron

ceramics

strength

hardness

wear resistance

resistance

modulus of elasticity

coefficient of thermal expansion


Input: Zirconia-based ceramics can be stabilized in tetragonal or cubic phases depending on the used dopant, its concentration and temperature during the thermal treatments.

ceramics

be

tetragonal

temperature

thermal treatments


Input: For dental applications, zirconia is commonly stabilized with 3 mol% yttria.

dental applications

zirconia

yttria


Input: The excellent mechanical properties of stabilized tetragonal zirconia are related with the stress-induced from tetragonal to monoclinical transformation, which is accompanied by a 4.5% volume increase.

mechanical properties

volume

stabilized tetragonal zirconia

tetragonal


Input: This behaviour leads to the development of compression zone, shielding the propagating crack tip which inhibits further crack propagation, successfully enhancing toughness.

compression zone

crack propagation

toughness


Input: Nevertheless, there are some disadvantageous aspects of zirconia ceramics.

zirconia ceramics


Input: 3.2 Alumina Alumina, also called aluminum oxide, was first introduced in the 1970s.

Alumina

aluminum oxide


Input: However, the initial applications presented a fracture rate of the order of 13%.

fracture rate


Input: This observed failure was related to a higher porosity.

failure

porosity


Input: With further developments, a decade later, a second improved generation of alumina ceramics was presented, characterized by higher density and smaller grains.

alumina

density

grains


Input: This led to a decrease of the fracture rate to less than 5%.

led

fracture rate


Input: Nowadays, there is available a third generation of alumina ceramic components, with properties such as high purity, high density and finer microstructure.

alumina ceramic components

as

properties

density

finer microstructure


Input: Alumina is used in dental applications for fabrication of endodontic posts, orthodontic brackets, dental implants, crowns and bridges and in ceramic abutments.

Alumina

dental applications

orthodontic

dental

fabrication

endodontic posts

ceramic abutments


Input: High purity alumina has usually a purity of 99.99% and has been developed as an alternative to surgical metal alloys for dental applications.

alumina

as

metal alloys

dental applications


Input: According to US Food and Drug Administration, only the high-purity Al2O3 can be used for medical grade ceramics.

be

ceramics

medical


Input: Impurities such as SiO2, metal silicates and alkali metal oxides that form glassy grain boundary phases must be minimized to less than 0.1 wt%, since the in vivo degradation of such glassy phases leads to the appearance of stress concentration sites where cracks can be initiated, leading to the catastrophic failure of the component.

Impurities

as

metal silicates

alkali metal oxides

be

be

grain boundary

degradation

failure

stress concentration

component


Input: It is possible to enhance alumina toughness and fracture strength by controlling the grain size and the porosity.

alumina

fracture

grain size

porosity


Input: This can be achieved using adequate sintering cycles, and adding some additives, zirconium oxide and chromium oxide).

be

additives

zirconium oxide

chromium oxide

sintering cycles


Input: 3.3 Leucite Leucite is a potassium alumina-silicate.

Leucite

potassium alumina-silicate


Input: This material displays a tetragonal structure at room temperature.

material

tetragonal

structure

temperature


Input: At 625 it suffers a displacive phase transformation from tetragonal to cubic, together with a volume expansion of 1.2%.

phase

volume

tetragonal


Input: Leucite has been widely used as a constituent of dental ceramics to modify the coefficient of thermal expansion, which is very important when the ceramic is to be fused or baked onto metal.

Leucite

as

ceramics

ceramic

be

metal

dental

coefficient of thermal expansion


Input: Usually leucite-based materials are used for veneering ceramics in metal-ceramic restorations, also referred to as feldspathic porcelains.

materials

ceramics

as


Input: Leucite is attained by incongruent melting of feldspar at temperatures between 1150 and 1530.

Leucite

feldspar

melting

temperatures


Input: Despite the mechanical properties of feldspathic porcelains being the weakest within ceramic dental materials, their global performance is perceived as quite successful.

mechanical properties

performance

ceramic dental materials

as


Input: 3.4 Lithium dissilicate Lithium silicate-based glass-ceramics were recently introduced as machinable materials to respond to the demanded increased strength, toughness and wear resistance, required for the fabrication of dental pieces.

Lithium

Lithium

as

materials

demanded increased strength

toughness

wear resistance

fabrication

dental pieces


Input: This ceramic material is used in the fabrication of single and multiunit dental restorations, mainly dental crowns, bridges, and veneers, due to its excellent mechanical and optical properties.

ceramic material

fabrication

dental

mechanical

dental crowns

veneers

optical properties


Input: In general, lithium disilicate presents a microstructure constituted by interlocking needle-like crystals embedded in a glass matrix.

lithium

glass matrix

microstructure


Input: As a result of this morphology, cracks are forced to propagate around each individual lithium disilicate crystal.

As

lithium

morphology


Input: This type of microstructure increases both strength and toughness relatively to other commonly used glass-ceramics: they have a strength twice as higher as that of the first generation of leucite-reinforced ceramics.

microstructure

strength

toughness

strength

as

as

ceramics


Input: 3.5 Mica Mica minerals are a group of sheet silicate minerals, or layer type silicates, that consist of varying complex formulae of Si, K, Na, Ca, F, O, Fe and Al.

Mica

sheet

silicates

Si

K

Ca

O

Fe

Al

layer

F


Input: The mechanical properties are dictated by the specific crystal structure formed by the cleavage planes situated along the layers.

mechanical properties

cleavage planes

crystal structure


Input: Crack propagation is more likely to occur along the cleavage planes.

Crack propagation

cleavage planes


Input: Mica-based glass-ceramics are relevant for dental materials due to their good machinability, high strength and resistivity to thermal expansion as well as biocompatibility.

dental

machinability

strength

resistivity

thermal expansion

as

as


Input: 3.6 Others ceramic dental materials Besides the examples mentioned above, there are other ceramic materials used in the dentistry field.

ceramic dental materials

ceramic materials

dentistry field


Input: For over 30 years, calcium phosphate-based formulations are recognized by their good osteoconductivity and biocompatibility in reconstructive surgeries.

calcium phosphate-based formulations

osteoconductivity

biocompatibility


Input: Tricalcium phosphate presents three polymorphs.

phosphate


Input: These include: monoclinic, and hexagonal and rhombohedral form.

monoclinic

hexagonal

rhombohedral form


Input: Hydroxyapatite 62) is the main component of enamel, and is responsible for the bright white appearance and elimination of the diffuse reflectivity of light by closing the small pores of the enamel surface.

Hydroxyapatite 62

enamel

enamel

component

pores


Input: HA can be used as filler in the repair of craniofacial defects or small holes and depressions on enamel surface, as grafting material and as coating in implant dentistry.

be

as

enamel

as

material

as

craniofacial defects

implant

dentistry


Input: Bioactive glasses are silicate-based materials that can form a strong chemical bond with the tissues.

Bioactive glasses

materials


Input: They present great interest in regeneration and healing of bone tissue.

regeneration

bone


Input: Their ability to support osteoblast cells, to bond to both soft and hard tissue and their capability of stimulating angiogenesis in the presence of vascular endothelial growth factor make them an attractive alternative relatively to other scaffold materials.

support

osteoblast cells

vascular endothelial growth factor

soft and hard tissue

angiogenesis

materials

scaffold


Input: Finally, dental impression materials still play a significant role in dentistry.

dental

dentistry

materials


Input: Gypsum products are among the most frequently used materials by dental professionals, since its properties are easily modified by physical and chemical means.

Gypsum

materials

properties

dental


Input: Gypsum may be used as impression material, mold material for processing complete dentures, as binders for silica in gold alloy casting investment, soldering investment, and investment for low-melting-point nickel-chromium alloys.

Gypsum

be

as

material

material

as

silica

gold alloy

alloys

mold

dentures

casting

soldering

low-melting-point


Input: 3.7 Composites A composite material is defined as a combination of two or more materials.

Composites

composite material

as

materials


Input: The resulting combination renders unique properties with characteristics different from the individual components.

properties

components


Input: In dentistry, ceramic composites may comprise combinations such as ceramic-metal, ceramic-polymer, or ceramic-ceramic Examples of current dental ceramic-ceramic composites include aluminacomposites, commercially available as structural ceramics for dental devices.

dentistry

dental devices

ceramic composites

as

ceramic-polymer

dental ceramic-ceramic composites

as

ceramics


Input: These materials, contain either alumina-toughened zirconia or zirconia-toughened alumina, depending on the percentage of the main component.

materials

alumina-toughened zirconia

alumina

component


Input: These composites combine the transformation toughening capabilities of zirconia along with the lower susceptibility to low temperature degradation in biological fluids.

composites

zirconia

biological fluids

toughening

susceptibility

temperature

degradation


Input: More recently, with the development of nanotechnology, the bionanocomposites have emerged.

nanotechnology

bionanocomposites


Input: These materials are expected to mimic native tissue structure, withstand high biting force and harsh oral cavity environment, e.g.

materials

tissue structure

force

mimic


Input: sudden change of temperature or osmotic pressure and invasion of various pathogens.

temperature

osmotic pressure


Input: Possible applications for bionanocomposites in the dental field include dental tissue regeneration or its substitution.

bionanocomposites

dental

dental tissue regeneration


Input: 4 Digital manufacturing CAD/CAM production of fixed prosthetic restorations such as inlays, onlays, veneers, crowns, and fixed partial dentures is a relatively well established technology used by dental health professionals for over 20 years.

Digital manufacturing

CAD/CAM

prosthetic

onlays

fixed partial dentures

dental

as

veneers

technology


Input: All CAD/CAM systems involve three steps.

CAD/CAM


Input: The first one corresponds to the data acquisition, through various scanning technologies that allow to transform the site/product geometry into digital data to be processed by the computer.

data acquisition

scanning

geometry

data

be

computer


Input: This is followed by manipulation and processing of the data set using a CAD software.

data

CAD


Input: Finally, the processed data are used for manufacturing of structures in the desired material through CAM.

processed data

manufacturing

material

CAM


Input: In dentistry, there are three different production concepts available, depending on the location of the steps of the CAD/CAM processes:-chairside production,-laboratory production,-centralized fabrication in a production center.

dentistry

production center

production

production

fabrication

CAD/CAM

laboratory


Input: The production can be carried out through several different technologies, that can be divided into two manufacturing processes: subtractive and additive manufacturing.

production

manufacturing processes

subtractive

additive manufacturing

be

be

technologies


Input: 4.1 Subtractive manufacturing There are several subtractive manufacturing techniques.

Subtractive manufacturing

subtractive manufacturing


Input: The most used in dental ceramics processing is based on milling of pre-sintered or fully sintered blocks, through a computer numeric controlled machine.

dental ceramics processing

milling

pre-sintered

fully sintered blocks

computer

machine


Input: The CAM software automatically translates the CAD model into tool path for the CNC machine.

CAM

CAD model

tool path

CNC machine


Input: This involves computation of the commands series that dictate the CNC milling, including sequencing, milling tools, and tool motion direction and magnitude.

computation

CNC milling

milling

tool motion direction

magnitude


Input: The accuracy of tool positioning has been reported to be within 10.

accuracy

tool

be


Input: The 3-axis milling systems are the most commonly used in dental milling systems.

milling

dental


Input: In such systems, the milling burs move in three axes according to a defined path.

milling burs


Input: SM is extensively used in dentistry for the production of dental pieces such as crowns and bridges.

SM

as

dentistry

production

dental pieces


Input: SM technology allows the processing of materials, which would otherwise be difficult to manipulate.

SM

be

materials


Input: This way, the exhaustive artisanal production techniques are decreased or even eliminated, thus allowing the dental technician to enhance the creative component of his manual manufacturing process.

production

manufacturing process

dental

component


Input: SM is a well-established technology which has the advantage of using intrinsically homogeneous materials which are unaffected by operating conditions.

SM

homogeneous materials

technology


Input: Furthermore, it requires low post-processing and the costs regarding the involved equipment are relatively reduced.

post-processing

equipment


Input: However, this is a wasteful process because the piece is milled from an intact block with a significant loss of material amount.

process

milled

material


Input: Factors such as the objectscomplexity, the dimension of the tooling equipment and the properties of the material can affect and limit the accuracy of this process.

as

material

dimension

tooling

properties

limit

process

equipment

accuracy


Input: 4.2 Additive manufacturing Additive manufacturing, also referred to as solid freeform fabrication, rapid prototyping or 3D printing, involves processing methodologies that are capable of producing structures by depositing materials layer-by-layer resorting to a computer generated design file.

Additive manufacturing

freeform fabrication

3D printing

Additive

as

rapid prototyping

computer

materials layer-by-layer

design


Input: The workpiece is virtually sliced into several two-dimensional layers.

workpiece

two-dimensional


Input: Then, an AM machine generates the tool-path along the x and y directions.

AM machine

tool-path

y


Input: Each material layer is deposited one on top of the other, consecutively, forming a three-dimensional part.

material

layer

forming

three-dimensional


Input: Ceramics present a higher melting point, higher susceptibility to thermal shook and lower sintrerability than the other group of materials.

Ceramics

melting point

susceptibility

sintrerability

materials


Input: Thus, it is quite difficult to obtained fully consolidated parts, without defects, using AM methods that produced directly sintered bodies.

defects

AM

directly sintered bodies


Input: In most of the cases, AM is used to obtain preliminary 3D structures in green that are built from mixture powders with organic or inorganic binder materials and need to be submitted to further steps of debinding and sintering.

AM

sintering

3D structures

debinding

powders

binder

be


Input: Some authors refer to these methods as indirect, contrarily to direct methods where the ceramic powder is sintered during the manufacturing procedure.

as

ceramic powder

sintered

manufacturing


Input: The debinding step depends on the organic components and became diffusion limited by increasing the thickness of the part, leading to higher debinding times The debinding temperature need to be carefully chosen.

debinding

diffusion

debinding

organic components

debinding temperature

be


Input: If is to high the removal rate of the volatile products resulting from the binder decomposition is too high, the pressure may increase and lead to crack formation and/or delamination.

binder decomposition

pressure

delamination

lead


Input: A possible solution to overcome the internal stresses generated during debinding may be the use of plasticizing agents.

solution

debinding

internal stresses

be


Input: The defects can also be avoided through the introduction of open spaces in the structure.

defects

structure

be


Input: That can be achieved by adding compounds able to evaporate/decompose at lower temperature than the debinding process temperature 2.

be

temperature

temperature

debinding


Input: There are several applications for AM in dentistry.

AM

dentistry


Input: One of the earliest is medical modelling, for surgery guide, where anatomical modelsare created.

medical

surgery


Input: The models can also be used as supports for the fabrication of restorations, for example, to help in the addition of veneered materials.

be

as

fabrication

materials


Input: In digital orthodontics, there are systems available that digitally realign the patientteeth to make a series of 3D printed models for the manufacture of aligners.

digital orthodontics

3D printed

manufacture


Input: 3D printing technology can also be used to produce novel titanium dental implants with a porous or rough surface and different types of restorations/components in metallic or polymeric materials.

3D printing technology

be

titanium

metallic

polymeric materials

dental

porous

surface


Input: In the next sections, the main AM technologies available, referred in 1, are described, namely indirect methods, such as binder jetting, material extrusion and jetting and Vat polymerization/stereolitography, and direct methods, which include direct energy deposition and powder bed fusion.

AM technologies

jetting

material extrusion

jetting

Vat polymerization/stereolitography

direct energy deposition

powder bed fusion

as


Input: 4.2.1 Binder jetting Binder jetting uses two materials, a powder-based material and a binder.

Binder jetting

Binder

powder-based material

binder

materials


Input: Usually in the liquid form, the organic binder acts as an adhesive between ceramic powder particles.

binder

as

adhesive

ceramic powder particles


Input: A print head deposits alternated layers of the building material and the binding material, moving horizontally along the x and y axes of the machine.

print head

machine

material

binding material

y


Input: After each layer, the build platform is lowered and the process repeated over the previous layer.

layer

layer

build platform

process


Input: BJ presents several advantages, such as the ability to use a range of materials as well as a large number of combinations powder/binder, being generally a fast printing process.

BJ

printing process

as

as

as

range

materials


Input: The drawbacks of this technology are mainly related to the high porosity and consequent low mechanical properties of the printed pieces.

technology

mechanical properties

porosity


Input: This is due to factors such as the high friction within the powder particles, their random agglomeration and the absence of an external force to compress the powder and improve packaging.

as

powder particles

powder

friction

force


Input: The flowability and spreadability of powders are especially important for BJ.

powders

BJ


Input: Using powders with large particle sizes can enhance the flowability, however it may jeopardize the sinterability and densification behaviour after printing.

powders

particle

sinterability

densification behaviour


Input: Contrarily, very fine particle size may lead to considerable agglomeration and reduced flowability.

particle

lead


Input: Since after sintering, the pieces density rarely exceeds 50% of the theoretical value, this technology seems not to be suitable for structural parts.

sintering

density

theoretical

technology

be


Input: In order to overcome this issue, the printed piece may be infiltered under vacuum with a glass material that penetrates in the pores by capillary effect.

be

glass material

pores

capillary effect


Input: 4.2.2 Material extrusion and jetting Generally, in the material extrusion process the material is heated and extruded through a nozzle.

Material extrusion

jetting

material extrusion

extruded

material

nozzle


Input: The nozzle can move horizontally, and the build platform can move vertically to enable the addition of each subsequent layer.

nozzle

build platform

layer


Input: This process, also known as fused deposition modeling, is the most widespread and inexpensive process within 3D printing technology.

process

deposition modeling

process

as

3D printing technology


Input: However, there are some drawbacks such as not being as fast as other AM processes and presenting an accuracy limited by the nozzle radius, which reduces the final product quality.

as

as

as

AM processes

accuracy

nozzle

product quality


Input: In order to increase the final quality it is necessary to control factors such as extrusion speed and ensure constant pressure and flow.

quality

pressure

as


Input: Another form of AM using material extrusion is material jetting process, where the material is deposited in the form of droplets, instead of filament, to form a 2D pattern.

AM

material extrusion

material jetting

material

filament

droplets

2D pattern


Input: The printed layer is cured using ultraviolet radiation, immediately after the deposition.

layer

cured

ultraviolet radiation

deposition


Input: The process is repeated until the complete 3D part is formed.

process

3D part


Input: 5 shows an example of an occlusal surface of a dental crown produced by this technique from a ceramic suspension of yttria partially stabilized zirconia.

surface

dental crown

ceramic

yttria

partially stabilized zirconia


Input: It is possible to observe surface waviness associated with layer-by-layer deposition.

surface waviness

layer-by-layer deposition


Input: Material extrusion techniques also include robocasting.

Material extrusion

robocasting


Input: In this process, a filament of a paste is extruded through a nozzle while it moves over a platform, building the object layer-by-layer.

process

layer-by-layer

filament

extruded

nozzle

platform


Input: The paste exits the nozzle with a given shape, without being necessary waiting for its solidification or drying to build the next layer.

nozzle

solidification

drying

build

layer


Input: Freeze-form Extrusion Fabrication is another example of extrusion-based AM technology.

Extrusion

AM technology


Input: Contrarily to most of the other extrusion freeform fabrication methods, in FEF, the organic binder content is only 2vol% and the solids loading of the paste can be higher than 50 vol%.

extrusion

fabrication

binder

be


Input: During FEF the piece is built by keeping the surrounding environment of the building platform below the freezing temperature of water.

building platform

temperature


Input: This solidifies the paste after the deposition on each layer during the fabrication process.

deposition

layer

fabrication


Input: FEF enables the production of relatively large parts, when compared with traditional robocasting.

production

robocasting


Input: In extrusion techniques, the mechanical properties can be improved by controlling the crystallographic texture of the materials.

extrusion techniques

mechanical properties

materials

be

texture


Input: This may be achieved by mixing a small number of large particles of anisotropic shape with fine particles.

be

mixing

particles

particles

anisotropic


Input: During extrusion, the anisotropic particles align in the shear direction.

extrusion

anisotropic

shear direction


Input: In a later sintering step, the aligned particles grow absorbing the fine particles, leading to highly textured and dense ceramics.

sintering

particles

particles

ceramics


Input: 4.2.3 Vat polymerization/stereolitography Vat polymerization/stereolitography was created by Chuck Hull in 1986 and was the AM technology pioneer.

Vat polymerization/stereolitography

AM technology

Vat

Chuck


Input: SLA was the first AM to be applied in medicine, which was used to produce surgical models for alloplastic implant surgery in 1994.

SLA

AM

be

medicine

alloplastic implant surgery


Input: In vat polymerization printing, a specific type of light is used to build parts one layer at a time, in a vat containing light-cured photopolymer resin mixed with ceramic powder.

vat polymerization

build

layer

vat

photopolymer resin

ceramic powder


Input: The light travels each layer through the surface of the liquid resin.

layer

surface

resin


Input: Then, the building platform descends allowing that another layer of resin spreads over the surface, and thus repeating the process.

building platform

layer

resin

surface

process


Input: This technology enables a rapid fabrication and allows to create complex shapes with high level of accuracy and good finish.

technology

rapid fabrication

complex shapes

accuracy


Input: The curing depth is a critical parameter that determines the accuracy of the formability.

curing depth

parameter

accuracy

formability


Input: 6 shows a zirconia implant printed trough this method.

zirconia

implant


Input: When compared to conventional polymer-based SLA, using ceramics can affect the line width and the curing depth.

SLA

ceramics

curing depth


Input: Also, since conventional SLA equipment uses dispersions with viscosities lower than 5 Pa.s, the particle size and the solids volume fraction of the ceramics preparations must be adjusted to meet the requirements of both formability and sinterability.

SLA

equipment

particle

volume fraction

ceramics

be

formability

sinterability


Input: To obtain ceramics with a high density, it is essential a fine particle size and a high solids volume fraction.

ceramics

density

particle

volume fraction


Input: Overall, SLA presents excellent surface finishing, but is still considered to be relatively expensive and present a lengthily post-processing time for unprocessed resin removal and additional curing.

SLA

surface finishing

curing

be

resin

post-processing


Input: For ceramics, a final thermal cycle allows to remove the organic resin and sintering the material, increasing its density.

ceramics

resin

material

thermal cycle

sintering

density


Input: 4.2.4 Direct energy deposition techniques Direct energy deposition is a more complex additive printing process, commonly used to repair or add additional material to existing components.

Direct energy deposition

Direct energy deposition

additive

material

process

components


Input: A typical DED machine consists of a nozzle mounted on a multi axis arm, which deposits melted material onto the specified surface, where it solidifies.

DED machine

nozzle

melted

surface

material


Input: The material is heated and melted using a laser, electron beam or plasma arc.

material

melted

electron beam

plasma arc

laser


Input: The piece is lowered by a distance equivalent to the layer thickness.

layer thickness


Input: Although this process typically uses metal, it can also use polymers and ceramics, either provided in wire or powder form.

process

metal

polymers

ceramics

powder


Input: For ceramic materials, it allows achieving almost 100% density and avoids shrinkage or distortion, eliminating the need of debinding or sintering steps.

ceramic materials

density

shrinkage

distortion

debinding

sintering


Input: Wilkes and Wissenbach were pioneer in studying the applicability of this method to manufacture ceramic components for medical applications.

manufacture

ceramic

medical applications


Input: 4.2.5 Powder bed fusion Powder-based printing technologies include selective laser sintering, direct metal laser sintering, selective laser melting and electron beam melting.

Powder bed fusion

selective laser sintering

direct metal laser sintering

selective laser melting

electron beam melting

printing technologies


Input: All these technologies use heat to fuse the powdered materials.

technologies

heat

materials

fuse


Input: The differences rely on the energy source and powder materials.

source

powder materials


Input: For instance, SLS, DMLS, and SLM all use lasers, while EBM uses electron beam as energy source In the sintering processes, the powders are not completely melted.

SLS

DMLS

SLM

EBM

sintering

electron beam

processes

melted

as

powders

source


Input: This leads to porous internal structures and rough surfaces.

porous

internal structures

surfaces


Input: In the melting processes, the powders are well fused, creating parts with enhanced mechanical properties and higher densities.

melting

powders

fused

mechanical properties


Input: The process begins with the spreading of a layer of material over the build platform, typically 0.1 mm thick.

process

layer

material

build platform

mm


Input: The energy source fuses the first layer or first cross section of the model.

source

fuses

layer

cross section

model


Input: The build platform is then lowered and a new layer of powder is spread across the previous using a roller.

build platform

roller

layer

powder

spread


Input: 7 shows a dental piece made of alumina-zirconia composite obtained by this process.

dental piece

alumina-zirconia composite

process


Input: The manufacturing time for powder bed fusion based techniques is lower than for other AM techniques.

manufacturing

powder bed fusion

AM techniques


Input: In fact, as it happens with direct energy deposition, since these techniques do not involve the use of binders for the production of intermediate green pieces, it is not required any debinding process.

as

binders

direct energy deposition

production

debinding


Input: However, due to the high heating and cooling rates, thermal shock may occur, which may lead to cracking.

heating

cooling rates

lead

cracking


Input: This may be avoided by pre-heating the powder.

be

powder


Input: 5 Additive manufacturing of bioceramics for dental applications Ceramic materials where only recently considered in AM processing due to their intrinsic properties.

Additive manufacturing

AM

bioceramics

Ceramic materials

dental applications

intrinsic properties


Input: The high melting points of ceramics make them difficult to melt under normal heating methods.

melting points

ceramics

melt

heating


Input: Although it is possible to melt some ceramics, this process can cause new phase formation.

melt

process

phase

ceramics


Input: On the other hand, several factors associated to the processing of the ceramic materials and to the characteristics of the raw materials used may affect the porosity of the final piece.

ceramic materials

raw materials

porosity


Input: An increase of porosity impairs the mechanical properties of the final product.

porosity

mechanical properties


Input: However, it can be favourable for cellular growth or implant fixation, required for specific applications.

be

cellular growth

implant


Input: This section will report published work where different bioceramics, such as zirconia, alumina, calcium phosphates and ceramic composites, with possible applications in dentistry, are processed using various AM technologies.

bioceramics

as

alumina

calcium phosphates

ceramic composites

dentistry

processed

AM technologies


Input: 5.1 Additive manufacturing of zirconia The information concerning the AM of zirconia-based compositions, with possible applications in dentistry is present in 2.

Additive manufacturing

AM

zirconia

zirconia-based compositions

dentistry


Input: Ebert demonstrated the possibility to build dense three-dimensional components of the size of a crown, with its characteristic occlusal surface topography, through material extrusion technology, using zirconia ceramic suspensions.

build

three-dimensional

surface topography

components

crown

material extrusion

zirconia ceramic


Input: The printed and sintered samples were not completely free of process-related defects, mainly due to clogged nozzles during printing.

sintered

samples

defects

clogged nozzles


Input: However, it was possible to obtain specimens with relative density of 96.9%, with mechanical properties comparable to those of conventionally produced 3Y-TZP via cold isostatic pressing.

relative density

mechanical properties

cold isostatic pressing


Input: Moin, established that it is feasible to use high-end digital light processing technology to fabricate a root analogue implant with a certain amount of precision.

digital light processing

fabricate

root analogue

implant

precision


Input: However, the results showed a printed RAI with a 6.67% larger surface area.

surface area


Input: A large number of factors are recognized to influence the precision of this printing technique, namely the resolution of the digital mirroring device and the composition of the ceramic/ photopolymer mixture.

precision

resolution

digital mirroring device

composition

photopolymer


Input: The authors claim that the precise control over spatially grade composition, microstructure design/distribution and shape are potential advantages over milling of unsintered ceramics.

precise control

microstructure

spatially grade composition

milling

unsintered

ceramics


Input: Osman also used a SLA method to efficiently print customized zirconia dental implants with sufficient dimensional accuracy.

SLA

print

zirconia

dental

sufficient dimensional accuracy


Input: The study evaluated among other aspects, the dimensional accuracy, surface topography and mechanical properties.

dimensional accuracy

surface topography

mechanical properties


Input: The authors report that the dimensional accuracy of the printed implant was high and the achieved mechanical properties showed flexural strength close to those of conventionally produced ceramics.

dimensional accuracy

implant

mechanical properties

flexural strength

ceramics


Input: SLA was again used by Xing, to produce ZrO2 complex shaped ceramic components with high dimensional accuracy and proper properties.

SLA

ceramic

dimensional accuracy

properties


Input: The surface roughness of the unpolished ZrO2 showed an anisotropic behavior with values ranging from 0.41 to 1.07 on the measuring direction.

surface roughness

anisotropic


Input: This phenomenon could be eliminated through polishing, reducing Ra to a nanometer scale.

be

polishing

nanometer scale


Input: The sintered ceramics had isotropic mechanical properties close to milled zirconia due to the homogeneity of the grain size.

sintered

milled

ceramics

isotropic

grain size

properties


Input: In the work of Scheithauer, the droplet formation behavior of zirconia suspensions for thermoplastic 3D printing was investigated.

droplet

zirconia

thermoplastic 3D printing


Input: The precise deposition of small adjacent droplets of molten thermoplastic suspensions containing ceramic particles allowed to obtain filament-like structures by coalescence of adjacent droplets.

deposition

droplets

coalescence of adjacent droplets

thermoplastic

ceramic


Input: The researchers introduced the droplet fusion factor in order to calculate the necessary distance between two droplets to produce those filaments.

droplet fusion factor

droplets

filaments


Input: The results showed that filament-like structures with a smooth surface and a nearly homogeneous cross section could be produced for suspensions with a dff of 44% or higher.

smooth surface

homogeneous

cross section

be


Input: In a previous work, the same research group used the same process to print zirconia samples.

research

process

samples

print


Input: They were able to produce ceramic parts with high density and homogeneous microstructures.

ceramic

density

homogeneous microstructures


Input: On one hand the heating rates required for thermal debinding are very low and it must be carried out in a powder bed, increasing the time and complexity of the process.

heating

thermal debinding

be

powder bed

complexity

process


Input: In another work of the same group, the authors combined AM and functionally graded materials to create zirconia-based customizable smart materials.

AM

functionally graded materials

materials


Input: By using T3DP technology, it was possible to selectively deposit two different materials beside each other, offering the prospect of combining suspensions with different contents of a pore forming agents to obtained components with dense and porous areas inside.

technology

materials

pore forming agents

areas

components

dense and porous


Input: The presence of zones with different porosities reduces the elastic modulus, diminishing the stress shielding, which should be benefic for dental implants.

porosities

elastic modulus

stress shielding

be

dental


Input: More, the presence of open pores shall favor the osteointegration.

pores

osteointegration


Input: The work of Shao, showed the possibility of successfully printing ZrO2 ceramic parts by a new extrusion-based process, 3D Gel-Printing.

ZrO2 ceramic

extrusion-based process

3D Gel-Printing


Input: The authors were able to produce printed and sintered cuboid samples with a regular appearance.

sintered

samples


Input: Parameters such as surface roughness, relative density, hardness and transverse rupture strength of printed and sintered samples were compared with those obtained in other 3D printing processes.

Parameters

samples

as

roughness

relative density

hardness

transverse rupture strength

sintered

3D printing


Input: It was found that 3DGP led to samples with higher density, hardness and surface finishing than those obtained by syringe extrusion, and that presented higher transverse rupture strength than others produced by gel casting.

led

samples

density

hardness

transverse rupture strength

surface finishing

extrusion

gel casting

syringe


Input: More, no defects or deformation was observed from outside of the printed samples.

defects

deformation

samples


Input: The authors refer the importance of aspects such as printing conditions, rheological behavior of the slurry as well as the solid loading on the final properties of the printed/sintered samples.

as

slurry

as

as

rheological

properties

samples


Input: Faes combined the advantages of AM extrusion and UV curing into a single 3D printing technique, to obtain pieces with an high shape stability and green strength.

AM

3D printing

UV curing

shape stability

strength


Input: This novel syringe-based AM process, based on the use of a photopolymerizable dispersion, leads to economic benefits since it reduces the raw material consumption.

AM process

photopolymerizable

dispersion

raw material


Input: High shrinkage was observed during sintering, leading to cracking.

shrinkage

cracking

sintering


Input: This must be due to a low load of ceramic particles in the dispersion.

be

ceramic

dispersion


Input: It is suggested to increase the amount of ceramic particles, keeping the rheological behavior, which can be achieved through the introduction of steric repulsive forces in the dispersion, for example using other resins.

ceramic

be

resins

rheological

forces

dispersion


Input: 5.2 Additive manufacturing of alumina 3 gathers the main findings of published work regarding the AM of alumina-based formulations with possible applications in the dental field.

Additive manufacturing

AM

alumina 3

alumina-based formulations

dental


Input: Work carried out by Scheithauer, showed the possibility of printing dense alumina pieces using 3D printing of high-filled suspensions with thermoplastic binder systems.

alumina

3D printing

thermoplastic binder systems


Input: The authors achieved samples with high densities, homogeneous microstructures and very good bonding between the printed layers.

samples

bonding

homogeneous microstructures


Input: This study also highlights the importance of the rheological properties of the slurries, i.e.

rheological properties


Input: low viscosity allows an easy flow through the needle to form small droplets, which can improve the printing resolution.

viscosity

droplets

resolution


Input: It is concluded that thermoplastic 3D printing presents several advantages over other suspension-based technologies, namely the fact that the green layer solidifying occur by simple cooling, the versatility of ceramic materials that can be used and the applicability in limited areas.

thermoplastic 3D printing

simple

cooling

technologies

layer

areas

ceramic materials

be


Input: It is recognized the potential of the technique to print multimaterial and multifunctional components, as well as to obtain pieces with material and/or property gradients in different dimensions.

print

components

as

as

material

property

dimensions


Input: However, the authors claim that heating rates for thermal debinding must be very low and that the process must be performed in a powder bed.

heating

thermal debinding

be

be

process

powder bed


Input: Dehurtevent, presented a study which provides promising results for manufacturing dense 3D alumina crown frameworks by SLA.

manufacturing

crown

SLA


Input: The authors established a comparison between the physical and mechanical properties of SLA-manufactured alumina ceramics of different compositions and viscosity to those of subtractive-manufactured ceramics.

mechanical properties

alumina

ceramics

viscosity


Input: Their results showed an acceptability window for viscosity of the slurries that allows producing SLA manufactured alumina pieces.

viscosity

SLA

manufactured

alumina


Input: Additionally, the authors were able to achieve a composition that originated a reliable material with the anisotropic shrinkage, high density, flexural strength, and Weibull characteristics suitable for SLA manufacturing.

composition

material

anisotropic shrinkage

density

flexural strength

SLA

manufacturing


Input: Nevertheless, it was observed that although an oversize of 35% allow manufacturing complex morphologies, differential shrinkage led to deformation of the final structure.

manufacturing

complex morphologies

shrinkage

deformation

structure

led


Input: In the work of Maleksaeedi, a powder-bed inkjet 3D-printing and vacuum infiltration process was used for producing alumina parts with high density and improved mechanical properties.

inkjet 3D-printing

vacuum infiltration process

alumina

density

mechanical properties


Input: The authors utilized vacuum infiltration process to enhance the packing of the green parts after printing, by impregnating the 3D-printed parts with highly solid loaded slurries.

vacuum infiltration process

green parts

3D-printed parts


Input: Their results showed that the vacuum infiltration process was able to significantly increase the density, reduce the porosity and increase the strength of the 3D-printed alumina components.

vacuum infiltration process

density

porosity

strength

components


Input: Moreover, the bending strength was improved up to 15 times of the original strength.

bending strength

strength


Input: 5.3 Additive manufacturing of other ceramics The potential of AM has been explored in several dental applications with other ceramic materials.

Additive manufacturing

AM

ceramics

ceramic materials

dental applications


Input: 4 summarizes information regarding various calcium phosphates compositions and other bioceramics, as well as gypsum, mainly for bone regeneration.

calcium phosphates

bioceramics

as

as

bone regeneration


Input: Lopez, produced bioactive tricalcium phosphate scaffolds using a material extrusion technology, robocasting.

tricalcium phosphate scaffolds

material extrusion

robocasting


Input: The printed scaffolds were able to restore critical mandibular segmental defects to levels similar to native bone after a 8 week period implant in an adult rabbit mandibular defect model.

scaffolds

mandibular segmental defects

bone

implant

adult rabbit mandibular defect model


Input: Histological and scanning electron microscopy analysis showed directional bony ingrowth into the scaffold interstices, tracking healing pathway origins to defect walls and marrow spaces.

scanning electron microscopy

directional bony ingrowth

defect

marrow spaces

scaffold interstices


Input: More, it was observed new bone growth and scaffold resorption at bone/scaffold interfaces.

bone growth

scaffold

bone/scaffold interfaces


Input: Another work using robocasting technology is the one carried out by Slots in which porous TCP implants were developed using storable and reusable inks composed of fatty acid/TCP.

robocasting

porous TCP implants


Input: The total fabrication time including ink preparation, printing and sintering was less than 5 h for 8 cm2 of implant.

fabrication time

ink

sintering

implant


Input: The printed implants were able to retain their shape after sintering and were chemically unchanged by the printing and sintering process.

implants

sintering

sintering

process


Input: Mesenchymal stem cells were able to grow on the implants, secrete collagen and alkaline phosphate and mineralize the implant.

Mesenchymal stem cells

collagen

alkaline phosphate

implants

implant


Input: Additionally, they possessed clinically relevant mechanical strength and presented osteoconductive properties.

mechanical strength

osteoconductive


Input: The process demonstrated to be sufficiently simple and effective to enable rapid, on-demand, in-hospital production of patient-specific ceramic implants for treatment of bone trauma.

process

be

ceramic

simple

production

bone


Input: In the study conducted by Fahimipour, a biomimetic porous TCP/alginate/gelatin scaffold containing PLGA) microspheres for slow release of VEGF was processed through extrusion technology.

biomimetic

microspheres

processed

scaffold

PLGA

VEGF

extrusion


Input: The printable ink was selected according to the gel point of different formulations of TCP/alginate/gelatin.

ink

gel point


Input: The process faced some difficulties, for example in what concerns the needle blocking during extrusion if the gel point is above room temperature.

process

blocking

faced

extrusion

gel point

temperature


Input: Nevertheless, it was possible to achieve satisfactory mechanical and biological features supporting cell viability necessary for bone tissue regeneration.Tamimi, prepared customized 3D-printed monetite onlays by binder jetting.

mechanical

onlays

cell viability

bone

binder jetting


Input: The onlays were design to facilitate the diffusion of cells and nutrients from high bone metabolic to low bone metabolic areas.

onlays

cells

design

diffusion

bone

bone metabolic areas


Input: The research showed that bone metabolic activity in onlays is anatomy-dependant and correlates with the ability of bone augmentation.

research

bone metabolic activity

onlays

bone


Input: The authors were able to achieve osseointegration of dental implants in bone augmented with the printed monetite onlays.

osseointegration

dental

bone

monetite


Input: Klammert also used binder jetting technology to produce several specific craniofacial implants of TCP.

binder jetting

craniofacial implants


Input: The printed parts were able to comply with geometric requirements and provide an adequate accuracy of fit, even though the authors did not use a commercial CAD solution.

accuracy of fit

CAD


Input: Fieldint and colleagues face several challenges to adapt and optimize the processing parameters to produce scaffolds using a 3D binder jetting printer and commercially available binders.

face

parameters

scaffolds

3D binder jetting printer

binders


Input: The authors report that the addition of dopants to the ceramic powder decreased the to phase transformation of TCP sintered at 1250 Additionally, the density increased leading to a 250% increase in compressive strength, when compared to pure TCP scaffolds.

dopants

ceramic powder

phase

sintered

density

compressive strength

TCP scaffolds


Input: Shao prepared by extrusion, four groups of bioceramic scaffolds for treatment of bone defects: Mg-substituted wollastonite-based; TCP-based; wollastonite-based; and bredigite-based.

extrusion

bioceramic scaffolds

bone defects


Input: Additionally, CSi-Mg10 printed parts revealed the largest pore dimension but the lowest porosity, mainly due to the considerable shrinkage of the scaffolds during sintering.

pore dimension

porosity

shrinkage

scaffolds

sintering


Input: Asadi-Eydivand, prepared gypsum-based scaffolds also for the treatment of bone defects.

gypsum-based scaffolds

bone defects


Input: They investigated the effect of thermic treatment on the structural, mechanical, and physical properties of samples produced by extrusion/jetting.

mechanical

physical properties

samples


Input: For the lowest temperature, the samples showed adequate mechanical properties, but high cytotoxicity.

temperature

samples

mechanical properties

cytotoxicity


Input: In contrast, temperatures in the range of 500 led to lower cytotoxic scaffolds but insufficient mechanical strength.

temperatures

range

led

cytotoxic scaffolds

mechanical strength


Input: For temperatures higher than 1000 higher compressive strength and greater viability were observed.

temperatures

compressive strength


Input: However, above 1200 decomposition of calcium sulfate occurs, leading to mass loss.

decomposition

calcium


Input: 5.4 Additive manufacturing of ceramic composites 5 gathers the information about AM of ceramic-based composites possible applications in dentistry.

Additive manufacturing

AM

ceramic composites

ceramic-based composites

dentistry


Input: In the work carried out by Goyos-Ball porous robocasted structures made of 10 mol% ceria-stabilized zirconia and alumina composite were produced.

porous

zirconia

alumina composite


Input: The authors found that round lattice structures have compression strength similar to cortical bone, are not cytotoxic and induce osseous differentiation.

round lattice structures

compression strength

cortical bone

cytotoxic


Input: More, the printed parts showed good aesthetics, chemical stability and negligible corrosion and wear.

chemical stability

corrosion

wear


Input: Due to the high structural integrity, the printed parts could be used as scaffolds for load bearing applications during the osteointegration process.

structural integrity

osteointegration

be

as


Input: Rahim established a comparison between composites prepared by extrusion and by injection moulding.

composites

extrusion

injection moulding


Input: The samples were composed of polyamide 12, incorporated with bioceramic fillers, from 10 to 40% content.

samples

polyamide 12

bioceramic fillers


Input: The results of their work showed that the addition of fillers improved or maintained the strength and stiffness of the parts, while reducing toughness and flexibility.

strength

stiffness

toughness

flexibility


Input: Melting behaviour of polyamide 12 did not depend on the processing techniques, but was affected by the addition of fillers and by the cooling rate.

Melting

polyamide 12

processing techniques

cooling rate


Input: Incorporation of fillers improved the thermal stability.

thermal stability


Input: It was found that fuse deposition modelling allows producing medical implants with acceptable mechanical performances for non-load bearing applications.

fuse deposition

medical implants

mechanical

non-load bearing


Input: Jan manufactured ceramic objects by powder bed fusion, using selective laser melting technology.

manufactured

ceramic

powder bed fusion

selective laser melting


Input: The authors were able to produce parts with good mechanical properties, with approximately 100% density, without needing sintering processes or post-processing, which constitutes an advantage.

mechanical properties

processes

post-processing

density

sintering


Input: The study reports some process challenges that need to be overcome, for instance, the thermally induced stresses, caused by the deposition of the new cold powder layers on top of the preheated ceramic, and the surface roughness values.

process

deposition

be

cold powder layers

ceramic

surface roughness


Input: 6 Challenges Additive manufacturing is recognized as a promising technology with advantages not only in the production of customized healthcare products to improve population health and quality of life, but also by its possibility of decreasing environmental impact, enhancing the manufacturing sustainability.

Additive manufacturing

production

as

technology

quality

impact

manufacturing sustainability

population


Input: However, the inherent challenges of 3D printing should not be overlooked.

3D printing

be


Input: Aspects such as surface quality, dimensional accuracy and the mechanical properties need improvement to allow producing effective high-quality products.

as

quality

mechanical properties

dimensional accuracy


Input: Concerning surface quality, it depends on the AM used technique, processing conditions and raw material characteristics, which affect the thickness of each printed layer.

surface quality

layer

AM

raw material


Input: Powder bed AM leads to lower surface quality than the other AM techniques, due to the presence of large and partially melted powder particles in the printed piecessurfaces.

Powder bed

AM

AM techniques

surface quality

melted

particles


Input: Relatively to the thickness of the printed layers, extrusion techniques typically lead to high layer thicknesses due to the large diameter of the deposition nozzle.

extrusion techniques

lead

layer thicknesses

diameter

deposition


Input: Powder bed fusion and vat polymerization origin lower layer thicknesses due to the ability to precisely focus the energy beam radius.

Powder bed fusion

vat polymerization

layer thicknesses

energy beam radius


Input: Material jetting techniques are the ones that produce the finest layer thickness due to the small jetted droplets.

Material jetting

layer thickness

droplets


Input: Dimensional accuracy is critical in the production of dental pieces, because these must fit tightly the needs of each patient.

Dimensional accuracy

production

dental pieces

fit


Input: A variety of issues affects dimensional accuracy.

dimensional accuracy


Input: The work of Lee summarizes the dimensional accuracy in different manufacturing processes.

dimensional accuracy

manufacturing processes


Input: spreading compaction/densification of the powder within the layers, evaporation of material by laser/heat and shrinkage during solidification.

powder

material

evaporation

shrinkage

solidification


Input: Mechanical properties are influenced by the presence of defects: surface quality and porosity are critical factors.

Mechanical properties

defects

surface quality

porosity

critical factors


Input: Different solutions have been proposed to reduce porosity.

porosity


Input: For example, choosing ceramic powders with an adequate granulometric distribution, adding dopants or a viscous liquid-forming phase, infiltrating the sintered body with vitreous materials and applying cold/hot isostatic pressure to the green body.

ceramic powders

dopants

granulometric distribution

vitreous

phase

infiltrating

materials

green body

sintered

cold/hot isostatic pressure


Input: Shrinkage is also a concern in AM processes since it affects significantly the pieces dimensions and may lead to cracking.

Shrinkage

cracking

AM processes

dimensions

lead


Input: The printing strategy needs to be optimized to prevent the impact of this phenomenon.

be

impact


Input: Possible solutions to minimize this issue are:-Increasing the amount of ceramic particles in the pastes, while keeping the rheological behavior unchanged, which may be achieved adding steric dispersants-Adding to the mixture particles that can expand due to phase transformation or reaction during sintering-Decreasing the sintering temperature, without compromising density-Considering it in the CAD design of the parts.

ceramic

be

steric dispersants

rheological

density

particles

phase

sintering

sintering

CAD


Input: In most of the mentioned studies along this work, the ceramic materials are composed of mixtures of a sacrificial polymeric binder with ceramic particles for the production of the green product.

ceramic materials

binder

ceramic

production

green product


Input: This means that additional post-processing steps, such as sintering, are required to remove the binder and achieve a fully dense ceramic component.

post-processing

as

binder

ceramic

fully dense


Input: This is true for the majority of the AM technologies with few exceptions such as direct selective laser sintering and selective laser melting techniques, where the ceramic particles are directly sintered or melted, respectively.

AM technologies

selective laser sintering

selective laser melting

sintered

as

ceramic

melted


Input: Dental ceramic pieces made by direct ink deposition still present low mechanical properties, compared to other conventional means to produce molded parts.

Dental ceramic pieces

direct ink deposition

mechanical properties


Input: Limitations of this layering technique include poor bonding adhesion between layers and the occurrence of porosity.

bonding

adhesion

porosity


Input: The protocols should be as simple as possible, leading to slurries/inks with appropriate composition, flow consistency and behavior and specific viscoelastic properties.

protocols

composition

consistency

be

as

as

viscoelastic properties


Input: They should contain a high solid volume fraction not only to minimize shrinkage during drying and therefore resist the involved stresses, but also to increase the density of the final product.

solid volume fraction

density

shrinkage

drying


Input: Another important challenge is bacteriological safety of the final products intended to be in close contact with tissues/organs.

bacteriological safety

be

contact


Input: These structures must be able to endure strict sterilization protocols without losing their intrinsic properties.

be

protocols

intrinsic properties


Input: 7 Final considerations Ceramic materials play an important role as dental materials.

Ceramic materials

as

materials


Input: Their high chemical and mechanical resistance, as well as their aesthetic properties, make them an excellent option to replace damaged dental tissues.

mechanical

dental

as

as

aesthetic


Input: Conventional manufacturing methods to produce ceramic dental pieces are generally based on subtractive techniques.

Conventional manufacturing

subtractive

ceramic


Input: These lead to significant material and tool waste and present limitations in the production of parts with complex geometry.

lead

material

tool

production

complex geometry


Input: The rising demand for custom-tailored and patient specific dental products renders dentistry to be one of the rapidly expanding segments of additive manufacturing technologies.

dental

dentistry

be

additive manufacturing


Input: These technologies have been successfully used in many production sectors and present many advantages for processing dental structures, compared with subtracting technologies.

technologies

technologies

production

dental structures


Input: These include less production steps with consequent impact in the total manufacturing time, lower consumables and raw materials consumption, and adequacy to produce very small and complex dental parts.

production

manufacturing

impact

raw materials

dental


Input: It thus opens possibility to mass production of customized dental products, with evident benefit to the patients and/or healthcare systems.

mass production

dental


Input: However, there are still concerns about application of AM to ceramics due to their intrinsically poor mechanical properties, the accuracy of the obtained pieces, their density and surface finishing.

AM

surface finishing

ceramics

mechanical properties

accuracy

density


Input: This comprehensive review shows that, dental bioceramics can be processed through AM by different techniques, e.g.

dental bioceramics

be

AM


Input: material extrusion/jetting, vat polymerization, binder jetting, and powder bed fusion.

material

vat polymerization

binder jetting

powder bed fusion


Input: The first technology is the most widely used.

technology


Input: The studies confirmed that almost any shape could be produced, with different degrees of complexity.

be

complexity


Input: specific mechanical properties, different degrees of porosity and/or density, biodegradability, osteointegration and cytotoxicity.

mechanical properties

degrees of porosity

density

biodegradability

osteointegration

cytotoxicity


Input: Despite the great potential for dental industry, the application of AM to ceramic dental materials is still under study.

dental

AM

ceramic dental materials


Input: In resume, further developments of AM technology are expected to give a significant contribution to bring production costs down, improve manufactured materials properties and render the production processes more efficient and competitive.

AM technology

production

production costs

manufactured

properties

processes


Input: An interesting approach, when printing 3D complex dental ceramic structures, could be to combine the best attributes of AM technologies with conventional surface finishing methods.

dental ceramic structures

be

AM technologies

conventional surface finishing methods


Input: One of the critical issues in orthopaedic regenerative medicine is the design of bone scaffolds and implants that replicate the biomechanical properties of the host bones.

orthopaedic

implants

medicine

design

bone scaffolds

host bones

biomechanical properties


Input: Porous metals have found themselves to be suitable candidates for repairing or replacing the damaged bones since their stiffness and porosity can be adjusted on demands.

Porous metals

be

be

damaged bones

stiffness

porosity


Input: Another advantage of porous metals lies in their open space for the in-growth of bone tissue, hence accelerating the osseointegration process.

porous metals

bone

osseointegration


Input: The fabrication of porous metals has been extensively explored over decades, however only limited controls over the internal architecture can be achieved by the conventional processes.

fabrication

porous metals

be

internal architecture

processes


Input: Recent advances in additive manufacturing have provided unprecedented opportunities for producing complex structures to meet the increasing demands for implants with customized mechanical performance.

additive manufacturing

complex structures

implants

mechanical


Input: At the same time, topology optimization techniques have been developed to enable the internal architecture of porous metals to be designed to achieve specified mechanical properties at will.

topology optimization

internal architecture

porous metals

be

mechanical properties


Input: Thus implants designed via the topology optimization approach and produced by additive manufacturing are of great interest.

implants

designed

topology optimization

additive manufacturing


Input: This paper reviews the state-of-the-art of topological design and manufacturing processes of various types of porous metals, in particular for titanium alloys, biodegradable metals and shape memory alloys.

state-of-the-art

topological design

manufacturing processes

porous metals

titanium alloys

biodegradable metals

shape memory alloys


Input: Bone is a complex tissue that continually undergoes dynamic biological remodelling, i.e., the coupled process whereby osteoclasts resorb mature bone tissue followed by osteoblasts that generate new bone to maintain healthy homeostasis of bone.

Bone

bone

osteoblasts

bone

bone

dynamic

process


Input: This unique feature of bone underpins its ability to remodel itself to repair damage.

feature

bone

damage


Input: However, when a bone defect exceeds a critical non-healable size, external intervention is required to supplement self-healing if the defect is to be bridged.

bone defect

non-healable size

defect

be


Input: Despite recent advances in biomaterials and tissue engineering, repair of such a critical-sized bone defect still remains a challenge.

biomaterials

tissue engineering

bone defect


Input: The optimal choice is to use autograft.

autograft


Input: However, harvesting autograft tissue creates the morbidity associated with a second surgical site.

autograft tissue


Input: The insufficiencies of application of autograft and allograft tissue have led to greater research efforts to identify biomimetic materials and structures that are suitable for skeletal repair without the inherent problems.

autograft

allograft tissue

biomimetic materials

led

research


Input: Metals and alloys have a long history of application as bone implants.

Metals

alloys

as

implants


Input: Among them, the use of stainless steels, cobalt based alloys, and titanium and its alloys are well established due to their good biocompatibility, satisfactory mechanical strength and superior corrosion resistance.

stainless steels

cobalt

alloys

titanium

alloys

biocompatibility

mechanical strength

corrosion resistance


Input: However, implants made of these materials are usually much stiffer than natural bones, leading to stress shielding-a major source for bone resorption and eventual failure of such implants.

implants

source

implants

materials

bone resorption

failure

stress shielding


Input: Cortical bone has elastic moduli ranging from 3 to 30 GPa, while trabecular or cancellous bone has significantly lower elastic moduli of 0.02GPa.

Cortical bone

elastic moduli

GPa

elastic moduli

cancellous bone


Input: Most current implant materials have much higher moduli than those of bones, e.g., Ti6Al4V has a modulus of around 110 GPa and CoCrMo alloys have a modulus of around 210 GPa.

implant

CoCrMo alloys

GPa

GPa


Input: Therefore, to avoid stress shielding at the bone-implant interface, the equivalent Young's modulus and yield stress have to be adjusted when using these bulk materials.

stress shielding

yield stress

bone-implant interface

be

materials


Input: An effective method is to introduce adjustable porosity or relative density as proposed by Gibson and Ashby for isotropic materials.

porosity

relative density

as

isotropic materials


Input: Traditional methods for fabricating open-cell porous metals include liquid state processing, solid state processing, electro-deposition and vapour deposition.

fabricating

electro-deposition

porous metals

solid state processing

liquid state

vapour deposition


Input: Although the shape and size of the pores can be adjusted by changing the parameters of these manufacturing processes, only a randomly organized porous structure can be achievable.

pores

porous

be

be

parameters

manufacturing processes


Input: However, additive manufacturing technologies can fabricate porous metals with predefined external shape and internal architecture.

additive manufacturing

fabricate

metals

internal architecture


Input: Metal-based additive manufacturing techniques, such as selective laser melting and electron beam melting, are computer controlled fabrication process based on layer-wise manufacturing principles.

additive manufacturing

electron beam melting

fabrication

manufacturing

as

laser

computer


Input: SLM and EBM are increasingly used for the fabrication of porous metals with complex architecture.

SLM

EBM

fabrication

porous metals

architecture


Input: Instead of using electron beam as the energy source in EBM, the SLM technology uses laser beam with adjustable wavelength.

electron beam

laser beam

wavelength

as

source

EBM

SLM


Input: Therefore, EBM can only process conductive metals whereas SLM can process polymer or ceramics as well as metal.

EBM

SLM

process

process

metals

polymer

ceramics

as

as


Input: Furthermore, due to more diffuse energy, EBM process has larger minimum feature size, median powder particle size, layer thickness, resolution and surface finish.

EBM

minimum feature size

layer thickness

resolution

powder particle

surface finish


Input: The robust application of MAM technologies requires extensive material, process and design knowledge, specific to each MAM technology.

technologies

process

technology

material

design


Input: MAM system behaviour is subject to significant stochastic error and experimental uncertainties, requiring that are necessary to simplify the problem.

stochastic error

experimental


Input: Sources of error include: complex and transient heat transfer phenomena, geometric effects with poorly defined powder thermal properties.

error

transient

heat transfer

properties

powder


Input: MAM prediction error can lead to excess melt pool temperature, resulting in undesirable microstructure, residual stress, local porosity, and surface roughness.

prediction error

microstructure

lead

excess melt pool temperature

residual stress

porosity

surface roughness


Input: Understanding the effects of design decisions on temperature related process defects is critically important to the process control.

design

temperature

process defects

process control


Input: Comprehensive reviews of AM technologies can be found elsewhere.

AM technologies

be


Input: Recent successes in orthopaedic regenerative medicine have promised an exciting future of AM technology.

orthopaedic

medicine

AM technology


Input: The world's first additively manufactured mandible was implanted in a patient by Dr. Jules Poukens and his team in 2012 in Belgium.

additively manufactured

implanted


Input: A full lower jaw implant was coated with hydroxyapatite and implanted in an 83 year old lady.

lower jaw implant

coated

hydroxyapatite

implanted


Input: Skull reconstructions with AM parts have been performed successfully by using digital design and AM.

Skull reconstructions

AM parts

design

AM


Input: Mertens successfully reconstructed a class III defect using AM manufactured titanium implants, which provided both midfacial support and a graft fixture.

class III defect

AM

titanium implants

midfacial support

fixture


Input: Jardini in Brazil designed and AM fabricated a customized implant for the surgical reconstruction of a large cranial defect.

designed

AM

implant

reconstruction

cranial defect


Input: Typical design and application approaches of porous metallic implants normally include the design of scaffold, AM and post-processing as illustrated in 1.

design

design

scaffold

porous metallic implants

AM

post-processing

as


Input: This review aims to identify the current status and the future directions of design-oriented AM technology in producing porous metallic structures for bone tissue repair, with a particular emphasis on topological design of internal architecture of porous metals for bone implants.

AM technology

porous metallic structures

topological design

bone tissue repair

internal architecture

porous metals

bone implants


Input: 2 Structure and properties of bone 2.1 Structure of bone Bone is a natural composite containing both organic components and inorganic crystalline mineral, as illustrated in 2.

Structure

properties

Structure

bone

bone

composite

as

organic components


Input: The structure of bone is similar to reinforced concrete that is used in the building industry.

structure

reinforced

bone

concrete

building industry


Input: The function of HA crystals and collagen molecules are like the steel rod and cement to concrete: one part provides flexibility and the other provides strength and toughness.

HA crystals

collagen molecules

steel

cement

concrete

rod

flexibility

strength

toughness


Input: Type-I collagen is a triple helix of nm in diameter and nm in length.

collagen

triple helix

diameter


Input: It is the primary organic components of bone.

organic components

bone


Input: Other non-collagenous proteins include glycoproteins and bone specific proteoglycans.

glycoproteins

proteoglycans

bone


Input: Hydroxyapatite is the inorganic component of bone and is plate-shaped of 50 25 nm in size and 1.5nm thick.

Hydroxyapatite

component

bone


Input: The HA crystals are oriented in a periodic array in the fibrils, preferentially with their c axis parallel to the collagen fibrils.

HA crystals

c

collagen fibrils

fibrils


Input: % of the dry bone.

bone


Input: Bone has a hierarchical structure.

Bone

hierarchical structure


Input: The hierarchical levels of bone include macroscale, microscale, sub-microscale, nanoscale, and sub-nanoscale.

bone

macroscale

microscale

sub-microscale

sub-nanoscale


Input: The macroscale level represents the overall shape of the bone.

macroscale

bone


Input: Bone can be classified as compact bone, and trabecular bone.

Bone

bone

be

as

trabecular bone


Input: Compact bone is almost solid, with only spaces for osteocytes, canaliculi, blood vessels, and erosion cavities etc.

Compact

bone

osteocytes

blood vessels

canaliculi


Input: There are large spaces in trabecular bone.

trabecular bone


Input: The pores in trabecular bone are filled with bone marrow, and the porosity varies between 50 and 90%.

pores

porosity

trabecular bone

bone marrow


Input: The building block of compact bone is the osteons, which are of the size ranging from 10 to 500 whereas the trabecular bone is made of a porous network of trabeculae.

compact

bone

osteons

trabecular bone

trabeculae

porous


Input: At the micron- and nano-scales, aggregated type-I collagen and HA form the collagen fibril.

nano-scales

collagen

collagen fibril


Input: The reinforced collagen fibre is a universal building element for both compact and trabecular bones.

reinforced collagen fibre

element

compact and trabecular bones


Input: 2.2 Mechanical properties of bone Mechanical properties of bone vary significantly with age, anatomical site and bone quality.

Mechanical properties

properties

bone

bone

bone


Input: Among the various biomechanical properties of bone, elastic modulus has attracted the most research interest because of its critical importance for characterizing various bone pathologies and guiding artificial implant design.

biomechanical properties

elastic modulus

bone

bone

research

implant

design


Input: The elastic modulus and strength of bone are anisotropic.

elastic modulus

strength

anisotropic

bone


Input: Compact bone is both stronger and stiffer when loaded longitudinally along the diaphyseal axis than the radial transverse directions.

Compact

bone

diaphyseal axis


Input: Trabecular bone is an anisotropic and porous composite.

Trabecular bone

porous composite

anisotropic


Input: Like many biological materials, trabecular bone displays time-dependent behaviour as well as damage susceptibility during cyclic loading.

biological materials

trabecular bone

as

as

susceptibility

cyclic loading


Input: The mechanical properties of trabecular bone depend on not only the porosity, but also the architectural arrangement of the individual trabeculae.

mechanical properties

trabecular bone

trabeculae

porosity


Input: The physical and mechanical properties of human bone are summarized in 1.

mechanical properties

bone


Input: 2.3 Requirements for the design of orthopaedic implants A successful porous metallic implant would restore the function of bone and promote regeneration of bone tissue at the damaged site.

design

orthopaedic implants

porous metallic implant

bone

bone

regeneration


Input: An ideal bone scaffold should possess the following characteristics: biocompatibility; suitable surface for cell attachment, proliferation and differentiation; highly porous with an interconnected pore network for cell ingrowth and transport of nutrients and metabolic waste; mechanical properties to match the requirements of the surrounding tissues to reduce or eliminate stress shielding, and to meet anatomic loading requirements to avoid mechanical failure.

bone scaffold

biocompatibility

porous

pore

stress shielding

mechanical failure

surface

cell ingrowth

metabolic waste

mechanical properties

cell attachment

transport


Input: Porous metals are implanted to repair bone defects of critical size and, in most cases, serve as load-bearing devices.

Porous metals

as

implanted

bone defects