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Rapid prototyping and rapid manufacturing in medicin
and dentistryWahyudin P. Syam
ab, M. A. Mannan
ab& A. M. Al-Ahmari
ab
aDepartment of Industrial Engineering, College of Engineering , King Saud University ,
Riyadh, 11421, Kingdom of Saudi ArabiabPrincess Fatimah Alnijris's Research Chair for Advance Manufacturing Technology
(FARCAMT)
Published online: 19 Jul 2011.
To cite this article:Wahyudin P. Syam , M. A. Mannan & A. M. Al-Ahmari (2011) Rapid prototyping and rapid manufacturing medicine and dentistry, Virtual and Physical Prototyping, 6:2, 79-109, DOI: 10.1080/17452759.2011.590388
To link to this article: http://dx.doi.org/10.1080/17452759.2011.590388
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Rapid prototyping and rapid manufacturing in medicine anddentistry
This paper presents an overview of recent developments in the field ofrapid prototyping and rapid manufacturing with special emphasis in
medicine and dentistry
Wahyudin P. Syama,b, M. A. Mannana,b* and A. M. Al-Ahmaria,b
aDepartment of Industrial Engineering, College of Engineering, King Saud University, Riyadh 11421,
Kingdom of Saudi ArabiabPrincess Fatimah Alnijriss Research Chair for Advance Manufacturing Technology (FARCAMT)
(Received 15 May 2011; final version received 16 May 2011)
The fundamentals and latest developments of Rapid Prototyping (RP) and Rapid
Manufacturing (RM) technologies and the application of most common biomaterials
such as titanium and titanium alloy (Ti6Al4V) are discussed in this paper. The issues
while fabricating pre-surgical models, scaffolds for cell growth and tissue engineering and
concerning fabrication of medical implants and dental prostheses are addressed. Major
resources related to RP/RM technology, biocompatible materials and RP/RM applica-
tions in medicine and dentistry are reviewed. A large number of papers published in
leading journals are searched.
Besides the titanium and titanium alloys which were established as bio-compatible
materials over five decades ago, other biocompatible materials such as cobalt-chromium
and PEEK have also been increasingly used in medical implants and dental prosthesis
fabrication. For over a decade RP technologies such as Selective Laser Sintering (SLS)
and Selective Laser Melting (SLM) along with the Fused Depositing Modelling (FDM)
are predominantly employed in the fabrication of implants, prostheses and scaffolds.
Recently Electron Beam Melting (EBM) has been successfully employed for fabrication of
medical implants and dental prostheses with complex features. In dentistry crown
restoration, the use of thin copings of Ti6Al4V made by the EBM process is an emerging
trend. This review is based upon the findings published in highly cited papers during the
last two decades. However the major breakthrough in the field of RP/RM for medical
implants and dental prostheses took place in the last decade. The fabrication of medical
implants and prostheses and biological models have three distinct characteristics: low
volume, complex shapes and they are highly customised. These characteristics make them
suitable to be made by RM technologies even on a commercial scale. Finally, currentstatus and methodology and their limitations as well as future directions are discussed.
Keywords: rapid prototyping; rapid manufacturing; medical application; dental
application; implant; scaffolds
*Corresponding author. E-mail: mamannan@ksu.edu.sa
Virtual and Physical Prototyping, Vol. 6, No. 2, June 2011, 79109
Virtual and Physical PrototypingISSN 1745-2759 print/ISSN 1745-2767 online # 2011 Taylor & Francis
http://www.tandf.co.uk/journalsDOI: 10.1080/17452759.2011.590388
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1. Introduction
Rapid Prototyping (RP) and Rapid Manufacturing (RM)
are material increase manufacturing methods. Instead of
removing material like in turning and milling processes,
material is added layer-by-layer until a complete part is
produced. Therefore, this process is also known as layered
manufacturing (LM). Nowadays, this manufacturingconcept is growing significantly since one of the new
perspectives of manufacturing is to save material and
energy (Chryssolouris et al. 2008). Besides, RP/RM can
significantly reduce time-to-market by shortening product
life cycle (Bernard and Fischer 2002). There are many
methods of RP and RM (Wohlers 1995, Pham and Gault
1998,). In general, RP and RM are divided into three
groups based on the raw material they use, which are solid-
based, powder-based, and liquid-based processes. The main
process characteristic of all RP and RM method is they
require a multi axes control system for building a part layer-
by-layer. In most systems, 2D contours are built by x-y
coordinate movement and z depth is built by lowering theapparatus layer-by-layer after a 2D contour is built
completely in each layer. Until recently, the most common
fabrication processes use either a laser beam to sinter or
melt material or a nozzle to extrude and deposit polymeric
material (Santos et al. 2006). The latest method for layer-
by-layer fabrication using metallic powder employs an
electron beam to melt material.
The Computer Aided Manufacturing (CAM) stage in
conventional manufacturing is bypassed in RP and RM.
Highly customised, low volume, and complex shaped parts
are suitable for manufacturing using LM technology
(Vandenbroucke and Kruth 2007). Owing to these char-
acteristics, biocompatible and medical parts are economic-
ally fabricated using LM technologies. Human body parts
such as hip joints, knee joints, teeth, etc, are highly
customised parts. These parts are unique for each person.
A biocompatible material is needed to fabricate these parts.
The characteristics of biocompatible materials are low
density (reduced weight), high specific strength, good
corrosion resistance and good oxidation resistance (Gao
et al. 2009). Titanium and titanium alloys are the main
metallic materials that are predominantly employed to
fabricate biocompatible parts. In the case of polymeric
materials, PEEK is a new type of polymeric material that
has been found to be suitable for medical applications(Schimdtet al.2007). For the medical application of dental
restoration, a zirconium based material is commonly used
because of its fluorescence characteristic. The development
of digital imaging techniques such as Computer Tomogra-
phy (CT) scan and Magnetic Resonance Imaging (MRI),
and reverse engineering technologies such as laser scanning
and probe scanning, increase the use of RP and RM process
in medical applications (Vandenbroucke and Kruth 2007).
2. Rapid prototyping and manufacturing fundamentals
Early applications of RP techniques were mainly focused on
fabrication of a functional model of a designed part. The use
of a functional model is to demonstrate the functionality of
the designed product to understand the product thoroughly
and to improve the product design. RP processes for
functional modelling are based on plastic material. Later,
Rapid Tooling (RT) emerged to produce low volume moulds
for the plastic injection moulding process and dies for the
low volume stamping process. The RT process uses a laser
beam to sinter and to melt metal powder material to form
the designed mould and die. The RM process is an LM
process that produces the final part to be used. Almost all of
the RM processes are based on metallic powder. The most
common methods for RM are Selective Laser Sintering
(SLS) and Selective Laser Melting (SLM). Results so far
have shown that SLS and SLM processes have failed to
produce 100% dense parts. Subsequently additional
processes are applied to increase the final product density
(Levyet al.2003).In conventional manufacturing, when a part is manufac-
tured by means of a metal removal process, the design of the
3D part is done in a Computer Aided Design (CAD) system.
The output of the CAD system is a CAD model in terms of a
CAD file. This CAD file is sent to CAM system to design the
part mould or die. The output of this CAM system is cutter
location (CL)-file, which contains cutter contact (CC)-point
(tool contact points with material) data. The CL-file is in
general tool path generation file format. After that, this CL-
file is sent to a post processor module to be converted to
machine-specific numerical controlled (NC) code. Subse-
quently, this NC code is transferred to a turning or a milling
machine to fabricate the mould or die. The detailed scheme
of conventional manufacturing stages is depicted in Figure 1.
In RP process stages, a CAD file, which contains the part
design or a CAD model, is converted to stereolithography
(STL) file format. The STL file format consists of the
triangulation of the Non-Uniform Rational B-Spline
(NURBS) or parametric surface of the 3D CAD model.
STL file format is the de facto format adopted by RP/RM
industry. This STL file is sent to RP/RM machine specific
software system for the slicing process. After the STL file is
sliced, the file is transferred to the RP/RM machine
controller. Based on sliced STL data file, the RP/RM
machine fabricates a part layer-by-layer until a completepart is obtained. A detailed scheme illustrating different
steps of a RP/RM process is depicted in Figure 2.
In Figure 3, steps from a CAD file to a sliced file are
illustrated. There are two types of STL files, namely STL
binary files and STL text files (Stroud and Xirouchakis
2000, Luoet al. 2001). The size of the binary file is smaller
than the STL text file. However, a STL binary file is in
machine language format, hence it is more difficult to read
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and process. The STL file is generated by a CAD system or
independent software that converts the CAD model to STL
file format.
Some common steps in preparing the part geometry
information from a CAD file for RP/RM can be seen in the
flow diagram in Figure 4. From a CAD file, a faceting or
triangulation process is done to produce a STL file. After
that, the STL file is sliced by a RP/RM proprietary software
system. Before that, STL manipulation is done for detecting
and repairing STL errors (Szilvasi-Nagy and Matyasi 2003).
This is done by third party software. After that, the sliced
STL file is sent to the machine and the part is fabricated
(Stroud and Xirouchakis 2000, Tong et al. 2004).
RP/RM processes in medical applications can be strongly
interrelated to by 3D imaging technology. Three dimen-
sional imaging techniques such as probe scanning and laser
scanning, provide a point cloud of the model. From the
point cloud of the model, the poly line surface and NURBS
Figure 2. RP stages.
Figure 1. Conventional approach CAD-to final part.
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surfaces are generated and can be converted to a STL file.
CT scan and MRI scan technologies have great impact
for RP/RM in medical applications, because these two
technologies are the most common 3D imaging technolo-
gies in medicine. 3D imaging techniques to get point cloud
data of certain models are known as Reverse Engineering
(RE) techniques. Thus, RP/RM is strongly related to RE
technology.
3. Biocompatible Material
The basic requirement for a material to be selected for any
biomedical application is the capability of a prosthesis
implanted in the body to exist in harmony with tissue
without causing deleterious changes. Another important
factor which needs to be considered is the materials ability
to facilitate osseointegration. Furthermore biocompatible
materials used for bone implant should desirably have a
density not too different from that of the original bone
itself, good corrosion resistance, and high oxidation resis-
tance (Gao et al. 2009). Titanium (Ti) is a commonly used
material for biomedical applications owing to its excellent
bio-compatibility. Ti can be in the form of pure Ti
(unalloyed) and alloyed Ti, which are: a-Titanium, near
a-Titanium, ab-Titanium, and b-Titanium (Sercombe
et al. 2008).
Engel and Bourell (2000) have conducted studies related
to preparing Titanium alloy powder for the SLS process. It
has been found that pre-treatment of titanium powder alloy
has a significant effect on SLS process performance. With-
out pre-treatment, titanium alloy powder will flow poorly
and can create a balling effect, which is the creation ofmolten clumps from laser exposure during the SLS process
rather than wetting and joining together between current
and previous layers. Thus, the part produced had poor
surface finish, poor mechanical property, and poor density
(large porosity). In order to obtain a fully dense and high
performance powder-metal (P/M) part with a good surface
finish, high alloy powder purity and cleanliness should
essentially be maintained. Contamination during the
atomisation process, processing, intermediate handling,
and shipping at normal atmosphere are the major sources
that affect the overall powder quality. The main contami-
nants for Ti-alloy powder are gases, such as argon, oxygen,and nitrogen, and air moisture. These contaminants can
produce porosity, weak grain boundary films, and limit the
bonding force between two powder particles.
The pre-treatment process reported by Engel and Bourell
(2000) was a vacuum annealing process. Vacuum annealing
uses pre-alloyed Ti6Al4V powder. This material was sub-
jected to heat treatment cycles that started at ambient
temperature and ramped to 6508C at a temperature
Figure 3. Steps from a CADfile to a sliced file.
Figure 4. Common steps in preparing the part geometry
information from a CAD file for RP/RM.
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increment rate of about 58C/minute. Argon was the backfill
agent used in bringing the vacuum chamber temperature
back to atmospheric temperature after the heating cycle.
From the process, there are two main gas species: water
vapour and diatomic hydrogen. The graph of partial
pressure peak height for water vapour and diatomic
hydrogen are presented in Figure 5.
As a result of Ti-alloy pre-treatment, the powder particlesbecome more spherical, with a narrower range of size
(denser material and more uniform size). Reduced water
vapour and hydrogen gas contamination has also been
observed. Figure 6 presents Ti-alloy powder before
pre-treatment and after pre-treatment.
Tolochko et al. (2003) studied the mechanism of heat
transfer in the SLS process using Ti powder. Heat transfer
in the SLS process is governed predominantly by thermal
radiation. SLS with a single component powder is harder to
process than with a dual component powder. There are no
difficulties in sintering dual component powder because this
powder is sintered by the liquid-phase binding mechanism.
In single component powder sintering, balling phenomenon
is one of the major and complex problems. Hence an
adjustment of SLS parameters has significant impact.Mechanisms of one-component powder sintering are under
the influence of the laser beam, particle surface melting,
and subsequent joining of the solid non-melted cores of
particles. The liquid-phase sintering mechanism and the
solid-phase sintering mechanism occur at the same time. It
means that SLS and SLM processes run simultaneously. In
this study a continuous wave Nd:YAG laser (l1.06 mm)
Figure 5. (a) Relative water peak height for crucible Ti6Al4V as a function of temperature, (b) Relative diatomic hydrogen
peak height for crucible Ti6Al4V as a function of temperature (Engel and Bourell 2000).
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was employed for processing in a vacuum. A motionless
laser beam, normal to the axis, sinters the powder within 10
seconds. Powder was sintered like a cake (Figure 7).
Inhomogeneity of the sintered zone is primarily caused
by the non-uniformity of the temperature field in the
powder bed under laser irradiation. The sintered structure
consists of a remelted zone around the laser spot below thesurface. In this zone, the neck between particles is wider and
the distance between particle centres is smaller. On the
surface, particle binding is very poor consequently the
surface porosity is high (Figure 8).
Results shown in Figure 8 refer to a hemispherical
sintered sample. In general, this sample consists of a
remelted core and low-sintered zone on the surface area.
Common mechanisms in sintering Ti-alloy powder are
solid-state volume diffusion and surface diffusion.
Sercombe et al. (2008) have done heat treatment of a
component produced by SLM using Ti6Al7Nb powder.
They found that massive acetabular defects occurred in the
hip joint leading to loss of fixation, component fracture,
and hip instability. Heat treatment of a titanium implant
was used to reduce residual stress, and increase ductility,
machinability, structural stability, tensile strength and
fatigue strength. Heat treatment was performed at three
different cooling conditions: air cooling, quenching, and
cooling under flowing argon to 6508C then air cooling.
Better results were obtained after air cooling and cooling in
argon atmosphere, then, air cooling. The pores were
reduced compared to the material condition before heat
treatment. An increase in fatigue strength of the material
has also been exhibited (Figure 9).
Besides titanium and titanium alloys, CoCr has also been
considered as a biocompatible material. Vandenbrouckeand Kruth (2007) optimised and characterised Ti6Al4V and
CoCr materials for SLM processing by testing their
mechanical and chemical properties and comparing process
accuracy and surface roughness of the part produced.
Degradable and undegradable biocompatible materials
were studied by Yan et al. (2003). Undegradable material
is used for permanent planting and replacement as pros-
thetic organs in a human body, for example ear monstros-
ities reconstruction, hip joints, knee joints, etc. Degradable
material is used for structures that induce a humans
regeneration ability of new tissue or organ, for example
cell scaffolds for growing tissue. Polymer polyethylene (PE)
is used for ear monstrosities reconstruction. Materials for
scaffolds fabrication should be biocompatible and have
favourable surface properties for cellular attachment,
differentiation and proliferation (Liu et al. 2007a).
Poly(L-lactid acid), tricalciumphosphate (TCP) composite,
Polyglycolid acid (PGA), Polyanhydrides, Polfumarates
(PF), Polyorthoesters, Polycaprolactones (PCL), and
Figure 7. (a) Side view, (b) Top view (Tolochko et al. 2003).
Figure 6. (a) SEM image of Ti6Al4V powder before pre-treatment, (b) SEM image of Ti6Al4V powder after pre-treatment
(Engel and Bourell 2000).
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Polycarbonates have been used for scaffold fabrication
owing to a number of excellent properties such as bio-
comparability, biodegradation, innocuity, pore rate, mechan-
ical strength, and controllable release performance. These
biodegradable polymers are the most common polymers that
have been used for scaffold studies (Vail et al. 1999).
4. Fabrication of biological implants and pre-surgical models
RP/RM techniques are very suitable for fabrication of
medical implants and prostheses, and biological and
surgical model construction. Biological models are used
for fossil reconstruction which is very useful in archaeology
and palaeontology study. Pre-surgical models are very
useful to help surgeons to plan and design the surgery
process and simulate the process without risk (Hopkins
et al. 2006). It can increase the success rate of the surgery.
RP/RM technologies are also suitable for biomedicalmodels for demonstration and functional models to study
certain aspects of the body mechanism.
Fantini et al. (2008) used integration of Reverse
Engineering (RE), CAD, and RP processes to reconstruct
the missing part of badly damaged medieval skull. 3D laser
scanning was used to capture the complex shape of the skull
and produce point clouds of the model. The point clouds
were processed to get the 3D CAD model of the skull. The
missing part was constructed from the existing CAD model
and then fabricated by Fused Deposition Modelling
(FDM). The missing part of the medieval skull fabricated
using the RP process fit very well with the remaining
existing skeletal part. Reconstruction process steps are
presented in Figure 10.
Bio-modelling in palaeontology using Stereotype Litho-
graphy Apparatus (SLA) was studied by Durso et al.
(2000). Reconstruction of fossils found in palaeontology
was used to study internal and external morphology,
specimen reconstruction, and reconstruction of fragile
specimens. This process highly utilised 3D imaging techni-
ques. The fossilised image was captured by a CT scanner.
This image data acquisition is the most important variable
that affects the bio-model accuracy. A CT scanner resolu-
tion can be set to a high value to obtain a high resolution
image and the specimen could be positioned in several ways,
because radiation exposure does not have any effect on thespecimen. In Figure 11, a bio-model fabricated using 3D
imaging technique and SLA fabrication provides detailed
internal and external morphology.
Zhanget al. (2000) reconstructed the Homunculus skull
from three pieces of the fossil. 3D laser scanning, combined
with the SLA process, was used to reconstruct Homunculus
face and fabricate the model. The scanning process used a
Figure 9. (a) Optical micrograph image of as received microstructure, (b) Microstructure after solution treatment at 10558C
for 1/2 h and subsequent aging for 8 h at 5408C (air cool), (c) Microstructure after solution treatment at 10558C for 1/2 h and
subsequent aging for 8 h at 5408C (slow cool) (Sercombe et al. 2008).
Figure 8. (a) Image of a specimen sintered by laser irradiation under ten seconds, (b) On the left, calculation of relative neck
size (x) distribution and on the right, calculation of thermal distribution corresponding to a-b phase transformation.
Remelted zone is depicted by black colour on the left side (Tolochko et al. 2003).
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Surveyor 3000 3D laser scanner by Laser Design, Inc to get
the point. Overshadowing was unavoidable due to the spike
point induced by light reflection. Rotational scanning and
flat scanning methods were used to enhance data accuracy
and efficiency. Point cloud data from three specimens were
manipulated using DataSculpt software. Using this soft-
ware, the complete face of the Homunculus skull was
reconstructed, and then a STL file was generated for
fabrication in a SLA machine. STL slicing for the SLA
fabrication was done by SLA-250/40 proprietary software,
MAESTRO. The reconstructed model gave meaningful
information to study palaeontology and zoology. The
reconstruction process of the Homunculus skull face is
shown in Figure 12.
De beer et al. (2005) developed a novel procedure to
produce a patient-specific shielding mask using a Minolta
scanner (3D image scanner) and EOS P380 SLS machine
(Figure 13). This mask was used in skin cancer treatment.
The mask covered healthy tissue during radiotherapy
radiation treatment using low energy X-ray (100-250 Kv
or 4-10 MeV) for the cancer tissue. The protection mask
decreased the degree of scatter of X-ray radiation. X-ray
radiation forms were found to be of rectangular, square, or
round shapes, but cancer areas had an irregular form, which
affected an area in healthy tissue between the edge of the
growth and the fields edge. The fabricated mask was found
to be effective and fit to the patient. Besides that, the
process was considerably time-saving and cost-saving as
compared to the lead-mask method.
In a surgery planning applications, Singare et al. (2009)
studied surgery planning and custom implant design using
RP technology. A mandible defect patient was used in this
case study. An image was taken using a CT scanner and a
MRI system. The 2D image resulting from CT/MRI was
Figure 11. (a) 3D volume rendered of CT scan of a 25-million year old juvenile Diprotodontid silvabestus skull, (b) Biomodel
of Diprotodontid Silvabestus (Durso et al. 2000).
Figure 10. Steps in reconstruction of a medieval damaged skull (Fantiniet al. 2008).
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processed by applying segmentation and region growing
techniques. Segmentation separates a soft tissue from a
hard tissue by grey gradient thresholding. After segmenta-
tion, region growing allows segmentation to split thescans. This process produces 2D CT scanned contours
that are stacked upon each other to form a 3D image.
From these 3D references, 3D voxel models are generated
for analysis by a surgeon or a physician. Also, 3D models
can be built for visualisation, consultation and practising,
and model fabrication using RP technology. Process
steps from point cloud until solid model are presented
in Figure 14.
The point cloud data was generated from the 3D voxel
model and loaded to RE software, such as Geomagic todesign the implant. After polygonalisation using wrapping,
the file can be imported as a STL file. But, editing must be
done on polygon model to refine the model and then
convert to a STL file. If the model has to be tested using the
finite element method, then the polygon surface must
be converted to a NURBS surface. Later, a STL file can
Figure 12. Reconstruction process of Homunculus face skull (Zhanget al. 2000).
Figure 13. (a) Photograph image of the patient, (b) 3D generated model of the face, (c) SLS fabricated on left and metal
sprayed mask on right (de Beer et al. 2005).
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be obtained for RP fabrication. A model obtained after the
3D region growing process was converted to a STL file in
order to fabricate the skull for surgery planning. A titanium
implant was produced by investment casting. For the
fabrication of a mould for investment casting, the implant
pattern fabricated by the SLA process was used. The model
and implant fabricated by SLA and investment casting,
respectively, provided an accurate tool for preoperative
planning and surgical simulation (Figure 15).
Canine limb pre-surgical planning has been studied byHarrysson et al. (2003). In their study, 2D images were
derived from CT scanning and converted to a 3D image
using Mimics software (Materialise, NV). From Mimics, a
STL file was created and imported to Geomagic software.
The model was sliced to 11 sections to make the size of the
model fit the SLA apparatus size. The pattern was
prototyped using SLA QuickCast and built and treated in
post curing apparatus (PCA) (Figure 16).
The silicon mould was made by Room Temperature
Vulcanisation (RTV) based upon the SLA pattern. Subse-
quently, polyurethane patterns were cast to the silicon
mould. These models were used for pre-surgical operation
planning and operation rehearsal (Figure 17).
Ganz (2005) illustrated the advantages of CT scan-based
technology to design a pre-surgical guide for implant in
dentistry. From CT scan data, a drilling guide for dental
implants was designed and sent to a 5-axis computer
numerical controlled (CNC) milling machine for fabrication.
5. Fabrication of scaffold for cell growth and tissueengineering and mesh structure for bone implant
Scaffolds are used to grow cells in tissue engineering, such
as musculoskeletal tissue, bone matrix and cartilage. Scaf-
fold mimics the extra cellular matrix for attachment,
migration, and expansion of living cells (Kanungo et al.
2008). According to Hutmacher (2000) scaffold should have
a highly porous 3D structure with an interconnected pore
network in order to facilitate cell growth and nutrient
transportation as well as metabolic waste disposal. A
suitable surface treatment for cell attachment and prolifera-
tion (Hutmacher 2000) is also necessary. Surface treatment
Figure 14. (a) Point cloud data, (b) Polygonal surface, (c) Grid generation, (d) Solid model (Singare et al. 2009).
Figure 15. SLA model, (b) Custom made implant, (c) SLA skull model for preoperative planning, (d) Implantation of the
custom implant (Singare et al. 2009).
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such as coating for scaffolds enable scaffolds to mimic
biochemical properties of native tissue (Arafat et al. 2011).
Tissue engineering (TE) has become a very important
branch of bioengineering owing to its vital role in treating
the damaged tissues while overcoming the limitation
associated with existing clinical practices such as limited
number of organ donors and potential of complication in
allograft tissue (Yeonget al.2006). TE is a technique where
cells are taken from the patient and expanded as well as
seeded on a scaffold (Liu et al. 2007b). Furthermore,
scaffolds are also used to reduce the stress-shielding effect
on a metallic implant in orthopaedic applications. The
stress-shielding effect is due to a mismatch of Youngs
modulus of bulk metallic material and the Youngs modulus
of natural bone. (Heinlet al.2007, Cansizogluet al.2008a,
b, Li et al. 2009). Xiong et al. (2005) proposed a newinterdisciplinary area which is Organism Manufacturing
Engineering (OME) and it deals with indirect and direct cell
assemblies. It is based on the integration of RP technologies
and recent advancement of developmental biology, cell
molecular biology, and biomaterials (metal and non-metal).
A part produced by OME has been reported to have
excellent chemical, physical, and biological characteristics,
and temporal properties, and is highly customisable.
Furthermore, there are a number of functions that OME
should satisfy:
. Manipulate different droplet directly.
. Construct complicated shape and internal structure
using different droplet according to the design.
. The material biological properties should not be affected.
. No toxic materials remain.
. Exhibit high flexibility.
A scaffold has a pore architecture that can facilitate
sufficient supply of blood, oxygen and nutrient for growth of
cells and tissue regeneration. Pore design (channelling, holes
diameter, etc) significantly affects cells and tissue growth. Liet al. (2005a) designed and fabricated calcium phosphate
(CP) scaffold using indirect SLA. Indirect fabrication was
used to make a mould of the scaffold. The material used to
produce the scaffolds was Calcium Phosphate Cement
(CPC) powder that consisted of tetracalcium phosphate
(TECP) Ca4(PO4)2O and phosphate anhydrous (DCPA)
Figure 16. (a) 3D model of the pelvic canine limb using Mimics, (b) SLA model by QuickCast (Harryssonet al. 2003).
Figure 17. (a) Pre-surgical rehearsal, (b) Final frame of the limb, (c) Biomodel in the operation room, (d) Attached ring
fixator (Harrysson et al. 2003).
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CaHPO4. A cylinder having a diameter of 14.5 mm and aheight of 22.6 mm was designed using CAD software.
Subsequently, the mould was designed based on the negative
scaffolds CAD model. In Figure 18 the images of positive
and negative design of the model are presented. The mould
was fabricated using SLA with epoxy resin material. CPC
powder was mixed with Na2HPO4into slurry and to obtain
the CPC paste. This paste was injected to form an epoxy resin
mould. Results showed that the scaffold was non-toxic and
provided excellent cell growth. In Figure 19 images of the
fabricated mould, CPC composite scaffolds, and cell growth
in the scaffold can be seen.
Liuet al.(2007b) fabricated a scaffold mould using the 3D
printer Solidscape T66 (Solidscape, Inc). In their investiga-
tion, they used two proprietary materials named as BioBuild
and BioSupport (supplied by TEOX). Mould design and
steps for scaffold fabrication are illustrated in Figure 20.
They established the following criteria for accessing the
manufacturability of scaffold mould:
. printing deviation (Figure 21a and Figure 21b)
. minimum differentiable space between two adjacent
beams in both horizontal and vertical orientations
(Figure 21c)
. maximum unbroken length of beam and maximum
manufacturability height of isolated feature (Figure 21d)
There are three factors that affect manufacturability and
accuracy of BioBuild and BioSupport materials used for a
scaffold fabrication in their research. These are the thermal
degradation of mould materials, thermal aging of BioSup-
port material, and printer accuracy and printing beam
cross-section. There was a little effect of thermal degrada-
tion (BioBuild was kept in a 1108C reservoir and BioSup-
port was kept in a 808C reservoir) for BioBuild material,
but there was a significant effect on BioSupport material
which exhibited a reduction in molecular weight and
shrinkage of chain length. Thermal aging significantly
affected BioSupport material. The solidification point of
Figure 18. (a) 3D CAD model of a scaffold design, (b) 3D CAD model of a scaffold mould (Li et al. 2005a).
Figure 19. (a) Epoxy resin mould fabricated on SLA, (b) Finished CPC scaffold, (c) SEM image of cell growth in the scaffold
(Liet al. 2005a).
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BioSupport material was lowered by thermal aging. Since
the solidification point of BioBuild was greater than the
solidification point of BioSupport, BioBuild droplets could
penetrate into the support layer to some depth. Accuracy of
the mould was independent of the object size. It was highly
influenced by the printer performance. Relatively higher
accuracy was obtained while printing large features com-pared to while printing small features. With regard to the
effect of the printing beam cross-section, it has been
reported that the manufacturable length increases with an
increases in printing beam cross-section.
Yeonget al.(2006) used the inkjet printing technique for
scaffold indirect fabrication and preliminary characterisa-
tion. A thermal-sensitive natural biomaterial was used for
fabrication. The method used was moulding collagen
scaffold in a dissolvable mould fabricated by RP technol-
ogy. The collagen used was Collagen Type I (Bovine
Achilles tendon, Sigma-Aldrich). The mould was fabricated
using a 3D phase change inkjet printer (Solidscape T612
Benchtop, USA) which utilised the manufacturers proprie-
tary materials, InduraCast and InduraFill. Collagen wascast in the mould and the mould was frozen to 208C.
Subsequently, the mould was removed by immersing it in a
bath of ethanol. After the scaffold was formed, freeze-
drying was used to remove water from the scaffold by
sublimation and desorption. And finally a sterilisation
process was conducted for the scaffold. The result of this
research showed that the characteristic of the scaffold can
Figure 20. Scaffold mould modelling and fabrication steps (Liuet al. 2007b).
Figure 21. Manufacturability criteria (Liuet al. 2007b).
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be manipulated at three different scales: macroscopic scale,
intermediate scale, and cellular scale (Figure 22).
Computer-Aided System for Tissue Scaffolds (CASTS)
was introduced by Naing et al. (2005). They derived
mathematical formulae to design and fabricate tissue
scaffolds. CASTS was integrated with the PRO-E (PTC,
MA, USA) CAD system and provided a parametric library
to design scaffolds. In this method, a 2D image was
captured using a MRI or CT scan. In a commercial
software (MIMIC), scanned 2D data were converted to a
standardised initial graphics exchange specification (IGES)
format. The IGES file was then imported into PRO-E.
CASTS combined the block created in PRO-E with the
patient IGES data and a Boolean operation was performed
to create the patients defect near-net shape scaffold. The
result from observation in the light microscope was that the
scaffold showed regular pre-designed micro architecture.
The, layered scaffold showed good intact struts and well-
defined pores (Figure 23).
A RP method using a robotic system has been developed
by Geng et al. (2005). It was called Rapid PrototypingRobot Dispensing (RPBOD) with a numerically controlled
four axis machine equipped with a multiple dispenser head
(Figure 24).
Extrusion and dispensing are the most widely applied RP
methods in TE research. Acetic acid was neutralised by
sodium hydroxide and precipitated to form a gel-like
chitosan strand. The material used was high-purity chitosan
powder. The chitosan gel was prepared by dissolving 3% w/
v chitosan in 2% v/v acetic acid. NaOH solution was used
as a coagulant and dispensed using a motorised plunger via
another syringe. The result showed that the method can
fabricate chitosan scaffold with pore diameters in the
range of 200500 mm with overall porosity of about 90%
(Figure 25).
Fabrication of a honeycomb-like scaffold has been
studied by Zeinet al.(2002). In their fabrication, a filament
of bioresorbable polymer poly(e-caprolactone) was
extruded by using a computer control extrusion and
deposition process. They found that scaffolds with fully
interconnected channel networks and controllable porosity
as well as channel size were obtained. The resulting
scaffolds had porosity of 4877%, compressive stiffness of
477 MPa, yield strength of 0.43.6 MPa and yield strain
428%. Moroni et al. (2006) introduced a 3D fibre
deposition technique to produce 3D scaffolds. In their
study, the influence of different pore size and shape was
considered by varying layer thickness, fibre diameter and
spacing as well as orientation. In their results, elastic
properties such as dynamic stiffness and equilibrium
modulus decreased with increasing porosity, but viscous
parameters such as damping factor and creep unrecovered
strain increased.
Cansizoglu et al. (2008a) have studied the properties of
Ti6Al4V non-stochastic lattice structures prepared by
electron beam melting. The study was a preliminary
fabrication of the non-stochastic lattice. The design of the
lattice was essentially the construction of struts that have
different angles respective to base plan (Figure 26).
Figure 22. Scaffold characteristic in different scales: (a) macroscopic scale, (b) Intermediate scale, (c) cellular scale (Yeong
et al. 2006).
Figure 23. (a) Femur segment and fabricated scaffold, (b) Scaffold top view with strut length 1.5 mm, and (c) Bottom view
with strut length 1.5 mm (Nainget al. 2005).
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The angles were 308, 408, 508, 608, 708, and 808.
Compression and flexural tests were conducted and the
test results were compared with finite element analysis
(FEA) results. This comparison showed that all specimens
compressed parallel to the Z-direction (build direction)
failed on shearing at 458relative to the base plan. Elastic
properties were relatively consistent between builds. Com-
pressive strength varied from 2 MPa to 10 MPa and
modulus of elasticity varied from 50 to 225 MPa. Predicted
stiffness and actual stiffness were reasonably acceptable.
Mechanical evaluation of the porous lattice structure
fabricated via electron beam melting had been studied by
Parthasaraty et al. (2010). Using micro-CT, it was found
that the titanium fully interconnected pores struts were well
Figure 25. (a) Step by step process of chitosan-strand scaffold, (b) Final chitosan scaffold, (c) washed and air-dried scaffold,
(d) cell growth on the chitosan scaffold (Geng et al. 2005).
Figure 24. (a) 4-axis robot system set up for scaffold fabrication using dual dispensing and (b) Fabrication of layer of
chitosan-strand scaffold (Geng et al. 2005).
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formed and no evidence of poor interlayer bonding was
found. Murr et al. (2010b) also studied the open cellular
lattice structure fabricated by electron beam melting.
Results showed that plots of relative stiffness versus relative
density were in agreement with the Gibson-Ashby model
for open foam material. A resonant frequency-damping
analysis technique was used to evaluate Youngs modulus
and found that it varies inversely with porosity. Generally,the fabricated open cellular foam has appeared promising
for biomedical applications. Ryan et al. (2008) had fabri-
cated fully interconnected pore network scaffolds by using
indirect casting. The wax master patterns were fabricated
using a 3D printer and subsequently powder metallurgy
was employed to fill the wax master pattern with titanium
slurry. Scaffolds with pore sizes ranging from 200400 mm
were obtained.
The choice of element types for the mesh structure
directly affects the strength and stiffness of the scaffold.
An optimisation of the topology of the beam and truss
structure to generate the mesh structure has been studied by
Cansizoglu et al. (2008b). In their study, they used FEA
equations for the compliance of the structure which was the
objective function. The Quasi-Newton line method was
used for unconstrained optimisation and Sequential Quad-
ratic Programming (SQP) was used for optimisation with
multiple constraints. After the topology optimisation, an
optimisation of the 2D truss or beam was completed.
Subsequently, the 2D elements were converted to a 3D solid
model for RP fabrication. The obtained results can be used
to derive a scaling factor for a future structure. Hollisteri
et al. (2002) studied an image-based homogenisation
optimisation, used to compute relationships between scaf-
fold structure and stiffness, to design scaffold structure andscaffold materials to meet conflicting design requirements
and a minimum porosity threshold was used as a constraint.
Results showed an excellent agreement between scaffold
properties and native bone properties. Byrne et al. (2007)
used a computer simulation technique with a fully three-
dimensional approach for tissue differentiation and bone
regeneration as a function of Youngs modulus, porosity
and dissolution rate. A mechanoregulation algorithm and
three-dimensional random-walk approaches were used to
determine tissue differentiation and bone cell number
respectively. The simulation showed that all these three
variables have critical effects on bone regeneration.
Li et al. (2010) fabricated and tested a Ti6Al4V implant
with a honeycomb-like structure. A honeycomb-like
controlled porous structure was designed and fabricated
by EBM. A scanning electron microscope (SEM) was usedto examine the macro-pore structure and a compression test
was conducted to evaluate mechanical properties. They
found that the fabricated honeycomb-like structure exhibits
a full interconnected open-pore network and the Youngs
modulus is similar to that of the natural bone thus the
stress-shielding effect can be reduced. In vitro bioactivity
tests of lattice structures fabricated by electron beam
melting has been studied by Heinl et al. (2008). Micro-CT
was used for structural analysis of the pore size. Chemical
surface modification using HCL and NaOH induced
apatite formation in the surface. They evaluated the
apatite-forming ability to soak SBF 10 for a bioactivity
test. Results showed that the pore size was suitable for tissueingrowths and vascularisation. The mechanical properties
were similar to human bone and that minimised the stress-
shielding effect. Surface modification by HCL and NaOH
induced in vitro apatite which provided better fixation of
the implant.
6. Fabrication of human and living body prostheses and
implants
Fabrication of human body prostheses has been one of the
most common applications of RP/RM techniques in
medicine. He et al. (2006) studied customised fabricationof a composite hemi-knee joint using SLA. An anatomical
model was scanned using a CT scanner. The binary image
was imported to Mimics software and the femur skeleton
model point cloud data were generated. The point cloud
data was imported to the Surfacer software to obtain a
reconstructed free form model of the femur bone. From the
femur bone model, the hemi-knee joint model was derived.
The model reconstruction process is shown in Figure 27.
Figure 26. Design of non-stochastic lattice structure (Cansizogluet al. 2008a).
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The material of the hemi-knee joint was Ti6AL4V
(titanium alloy) and the material of the femur bone was
b-TCP. For the hemi-knee joint, the master pattern of thepart was fabricated using SLA and the mould was
fabricated using the shell casting technique. The femur
bone master pattern was also fabricated using SLA and the
mould was fabricated using RTV technology. The fabricated
femur bone and hemi-knee joint are shown in Figure 28.
Fabrication of the 3D reconstructed free form model of
the femur bone conformed to the original anatomy within a
maximum deviation of 0.206 mm and the implanted
composite hemi-knee joint matched with surrounding tissue
and bone with sufficient mechanical strength. Fabrication
of bioactive bone has been studied by Chen et al. (2004).
The RP technique was used to replace the traditional way of
fabricating porous scaffold, such as polymer foaming
technique, particulate-leaching, solid-liquid phase separa-
tion, textile technique, and extrusion process. A purpose
made fused deposition model was used where the flow of
extruded material through a nozzle was pneumatically
controlled. A mould of the bone scaffold, using Denature
Sucrose (DS), was fabricated and subsequently the bioma-
terial was cast into it to obtain the final bioactive bone
scaffold. CPC and Bone Morphogenetic Protein (BMP)
were injected into the mould (Figure 29).
The resulting fabricated bioactive bone was thenimplanted together with the animal bone. Twelve weeks
after the implantation, good osseogenesis and bone trans-
formation growth were observed (Figure 30).
Fabrication of a prosthetic socket was studied by Ng
et al. (2002). Conventional methods for socket prosthetic
fabrication were time consuming and labour intensive. The
main stages of prosthetic socket fabrication are measure-
ment, rectification, and fabrication (Figure 31).
Physical measurements from the amputees records were
noted, and then a plaster wrap cast was taken. Subse-
quently, a positive mould of the amputees stump was
created by filling with plaster of Paris. The rectified shape of
the positive mould was compared with previously taken
shape data on the amputees stump. The refinement process
was carried out until a comfortable shape was achieved.
With new methods, 3D data images of the positive mould
were scanned by Digibot 3D Laser Digitizing System
(Digibotics, Inc). The point cloud data was processed in a
CAD system to obtain a 3D CAD model. A STL file was
generated from the CAD model. For the fabrication
Figure 27. 3D model reconstruction of femur bone and hemi-knee joint (He et al. 2006).
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process, a self-developed FDM machine was employed.
This specialised FDM machine had a nozzle diameter of 3mm which led to a faster process (Figure 32).
From the experiment it was found that, special-purpose
FDM was superior to FDM from Stratasys, Inc, except for
the part weight. Tayet al.(2002) also studied the prosthetic
socket. They introduced the concept of Computer Aided
Socket Design (CASD) and Computer Aided Socket
Manufacturing (CASM). Instead of special-purpose
FDM, they used a commercial FDM machine from
Stratasys, Inc.
Gopakumar (2004) developed a cranial implant for
reconstructive surgery. A patient with a cranial injury on
the frontal region of the skull cage, due to an accident,
was selected. Point clouds of the skull from CT scanswere imported to medical modeller software. CAD
manipulations using a mirroring technique were employed
since the cranial skull has symmetric characteristics.
Subsequently, the designed implant for the damaged
region was derived. A FDM machine was used to
fabricate the implant. The resulting implant was used
as a pattern to make a mould for casting biocompatible
material in a RTV technology based procedure. Heat
curing polymethylmethacrylate (PPMA) was mixed and
poured into the mould. The finished model was perforated
3 mm with 5 mm spacing to provide room for fibrous
Figure 28. (a) Casting of titanium hemi-knee joint, (b) Fabrication of porous bioceramic artificial bone using powder
sintering, (c) Assembly of composite hemi-knee joint and composite hemi-knee joint implantation after three weeks (He et al.
2006).
Figure 29. Process from CAD design until fabrication of the mould and casting of the bone (Chenet al. 2004).
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tissue to grow and to form fibrous encapsulation.
The model reconstruction and implantation is shown in
Figure 33. The designed and fabricated implant had good
fit with the skull which reduced the operation time
significantly.
Singare et al. (2006) fabricated a maxillofacial implant
using a CAD and RP system. The image was obtained from
a helical CT scan. Subsequently, the 3D image of the patient
skull model was used to reconstruct the implant for the
patient. The manual method of implant reconstruction
has been found to be time consuming and the out-
come significantly depends on the surgeons skill. In
their method, the 3D image resulting from the helical
CT scan was manipulated in a CAD system using a
Figure 30. (a) Implant image after surgery, (b) Implant image after 12 weeks (Chen et al. 2004).
Figure 31. (a) Physical measurement, (b) Positive mould, (c) Rectification from positive mould, (d) Final refinement model
(Nget al. 2002).
Figure 32. (a) Start process, (b) In process, (c) After process, (d) Final physical model (Nget al. 2002).
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mirroring technique to reconstruct the mandible implant
(Figure 34).
Then, the SLA process was adopted to fabricate a master
pattern which was directly used in investment casting to
create a plaster mould. The pattern from RP was embedded
with a high temperature resistance phosphate material.
Then it was heated at a temperature ranging from 3008C
to 6008C to obtain a mould for casting the implant.
Subsequently, a customised titanium implant was made
using this mould. Results showed that the mandible
Figure 33. (a) 3D reconstructed image, (b) Designed implant from medical modeller, (c) designed implant fitting in 3D,
(d) Implant fixation during cranioplastic surgery (Gopakumar 2004).
Figure 34. (a) 3D point model of the patient skull, (b) Design of implant in CAD environment, (c) surface model of themandible (Singare et al. 2006).
Figure 35. (a) Titanium implant, (b) Implant implementation to the patient, (c) Patient after mandible reconstruction with
CAD and RP method (Singare et al. 2006).
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implant, fabricated using the RP method, fitted well to the
patient (Figure 35).
Further adjustments were not needed, hence operation
time was reduced significantly. Finally, no complication was
observed during the 14 month follow-up.
A hip stem implant of Ti6Al4V fabricated by electron
beam melting was evaluated by Harryson et al. (2008).A customised hip stem implant was designed by
finite element analysis to determine the shape. Figure 36
shows the design of the hip stem and the fabricated hip
stem.
The lattice (mesh) structure in the hip stem reduces the
modulus of elasticity so that it mimics the stiffness of the
bone to avoid the stress-shielding effect. Orientation of
the part during fabrication was important. The result
showed considerable promise with good mechanical proper-
ties. For the hip joint, between the femoral ball and the
acetabular cup, there should be an interface material or asurface treatment to connect these two implants, because
titanium has the disadvantage of a galling effect that
generates debris inside the joint due to wear (Dowson
et al. 2004).
Figure 36. (a) Designed hip stem implant, (b) Fabricated hip stem implant (Harrysonet al. 2008).
Figure 37. (a) Mock-up of the productsfirst concept by the anaesthetist, (b) Digital design of the mock-up to produce the
first functional part, (c) The 10th design of the model after model refinement process, (d) Final shape (14th model) which meets
all of design criteria (Booysen et al. 2006).
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7. Design and fabrication of dental applications and
prostheses
Anaesthetic mouthpiece development employing QFD
(Quality Function Deployment) and customer interaction
has been reported by Booysen et al. (2006). Booysen et al.
used RP/RM techniques to fabricate a functional model of
the designed prosthesis to interact with and to obtain
feedback directly from the customer. In this way, a customer
can directly try the designed prosthesis and give suggestions
for model improvement before a final mould is made. The
anaesthetist can also interact with the design team and
provide valuable information leading to model refinement.
Undoubtedly, corrections after the final mould has been
made are extremely time consuming and costly and are very
difficult to implement. In Figure 37, a development processaccording to Booysenet al.(2006) is presented.
In each step, a functional model was produced using SLA
technology. The resulting part was used as master pattern to
make a silica mould/tooling employing a process known as
RTV technology. After the final design that met all
customer and anaesthetist requirements, a mould was
produced using a CNC milling machine for mass produc-
tion of the anaesthetic mouth part. In Figure 38, a silica
mould and the final mould for injection moulding are
shown. The cost analysis has also been conducted showing
that a change during the design stage is cheaper and fasterthan a change in the final mould production stage.
Gao et al. (2009) designed and fabricated a titanium
denture base plate using the RM method based on laser
rapid forming (LSR) technology. To date the traditional
lost-wax casting technique remains the most common
technique used in dental prosthetic manufacture. The
method uses a combination of RE and RM technologies.
An impression of the maxillary edentulous was scanned
using laser scanning to acquire point cloud data. Subse-
quently, the point cloud data was processed and a 3D model
was reconstructed and converted to a STL file (Figure 39).
The STL file was then sent to the laser rapid forming
(LRF) machine to be sliced layer-by-layer. In the LRF
machine the titanium powder was sintered until the denture
base plate was finished. Results have shown that a success-
ful denture base plate could be produced using RE and RM
technologies. Finishing and polishing of the denture base
plate using traditional dental laboratory procedures were
carried out. The denture base plate was then fitted to the
patient (Figure 40). The result was judged to be acceptable.
Figure 38. (a) Silica mould for functional prototype, (b) One-half offinal injection moulding tool, (c) Moulded part after
injection moulding process (Booysen et al. 2006).
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Thus, the RM process has good potential to replace the
traditional lost-wax casting technique and still there seems
to be ample room for improvements.
Vandenbroucke and Kruth (2007) proposed a framework
for a different dental implant application. The method has
been patented. The material used in this framework was a
Cobalt-Chromium based alloy. In their proposal, there was
a metal based structure of the prosthesis and an artificial
teeth support (Figure 41).
An emerging trend in dentistry applications is to fabricate
dental restoration. One dental restoration technique is
metal-ceramic crown restoration which consists of two
layers: metal coping and tooth crown. The challenge is to
fabricate the metal coping with Ti-based material which is
highly reactive to oxygen in elevated temperature by RP/
RM technology.
Densification of porcelain material using a laser has been
studied by Li et al. (2005b). A slurry of dental porcelain
powder was deposited and densified by a laser to obtain
dental restoration. The process is known as Multi Material
Laser Densification (MMLD). MMLD is one of the solid
free form fabrication methods. In conventional prosthoden-
tics, the Porcelain Fused to Metal (PFM) process is
predominantly used, which casts dental restoration from
multi material dental alloy and then coats with several dental
porcelain layers by the firing process in a furnace. The PFM
process is time consuming and costly. Labour cost is around
90% of the final cost and only 5% of the cost is for dental
Figure 40. (a) Fabricated Ti denture base plate, (b) Ti denture base plate was evaluated on original physical cast after
finishing and polishing, (c) completed Ti denture base plate, (d) Completed maxillary Ti denture base plate on patient (Gao
et al. 2009).
Figure 39. (a) Unrestored maxillary edentulous, (b) Plaster 3D model, (c) Denture base plate 3D model (Gaoet al. 2009).
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materials. In MMLD, dental powder paste is extruded layer-
by-layer and subsequently a densification process is carried
out with a laser before extruding the next layer (Figure 42).
The material used in the Li et al. (2005b) study was
dental porcelain powder Ceramco# Silver Body and
consisted of 63.4% SiO2, 16.7% Al2O3, 14.19% K2O,
3.41% Na2O, 1.5%CaO, and 0.8% MgO. The particle size
ranged from 1050 mm as shown in Figure 43.
For the densification process, they used the laser power
control mode. They introduced K parameter:
K 2R
x
(1)
Where 2R is the laser beam parameter and v is width of
the powder line. Ideally, a laser densified line should
possess a near rectangular cross-section so that the
densified line could fit well with previous densified lines.
There are three conditions that the K parameter should
satisfy. First, K should be small when the laser beam
diameter is smaller than the line width. Second, K should
be very large when the laser beam diameter is greater than
the line width. In the third case, K should be in betweenthose two previous conditions. In Figure 44, when K0.5
and the laser size is much smaller than the particle, due to
the Gaussian power intensity profile of the beam, the
centre part has the highest temperature resulting in the
largest shrinkage in the centre and it becomes concave.
When K3, where the size of the laser beam is much
larger than the line width, due to the relatively uniform
laser power intensity, a densification process similar to one
Figure 41. Dental implant framework (Vandenbroucke and Kruth 2007).
Figure 42. MMLD process scheme (Li et al. 2005b).
Figure 43. (a) Dental porcelain powder, (b) Ball-milled
powder (Li et al. 2005b).
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in a furnace takes place and subsequently the balling effect
is observed. When K is in between, the near rectangular
cross-section is formed.
In dentistry, Metal-Ceramic Crown (MCC) restoration isone of the common techniques used in dental restoration.
In MCC, there are two layers. The first is metal coping to
support the crown and the second is the porcelain crown
(Figure 45).
Either casting or milling or both are commonly used
techniques in dental restoration processes using cobalt-
chromium and titanium alloys (Witkowskiet al.2006). The
LM method is a potential technique which can be used to
fabricate a coping. The use of the SLM technique to
fabricate a dental coping of cobalt-chromium alloy had
been studied by Quante et al. (2008). They found that the
accuracy of the internal cavity of the coping was compar-able to that of the internal cavity obtained when using a
conventional technique such as lost-wax casting. Ucar
et al. (2009) studied the fabrication of cobalt-chromium
coping by SLS technique and observed no significant
difference in shape and accuracy of the copings fabricated
by the conventional casting technique and the SLS
technique.
8. Discussion
8.1 Current status and methodology
RP/RM technology is very suitable for low-volume produc-
tion of parts having complex shapes which are highly
customised. These characteristics suit very well for the
fabrication of medical implants and dental prostheses.
There is an obvious connection between RP/RM and RE
technologies. RE technology enables 3D imaging of the
human body parts and thus plays a vital role. CT scans,
MRI, and 3D laser scanning are the most common RE
technologies used for capturing digital images of the human
body parts. Different steps from 3D model building to the
fabrication of an actual implant are presented in Figure 46.
In this figure, images of the limbs, skull, cranial, etc are
captured using a 3D scanner, a CT scanner, or a MRI
system. In CT scanning and MR Imaging a large number of
2D images are captured and combined leading to a 3D
image. The format of the data from CT scanners or MRI
systems is not compatible with systems for RE and RP/RM.
Consequently, it needs to be converted to a format used by
RE software. Before point cloud processing or STL file
generation, 2D segmentation and 3D region growingalgorithms are implemented. Then, a 3D voxel (3D pixels)
model can be generated for analysis by a surgeon or a
physician.
Mimics (Materialise, NV) is one of the leading com-
mercial software packages for generating 3D point cloud
from scanned images. Currently, Mimics is still the leading
software to generate 3D point cloud or STL file from
MRI or CT scanned images. The 3D laser scanner directly
Figure 44. (a) At K0.5, Maragoni effect observed, (b) At K2, near rectangular cross section obtained, (c) At K 3,
balling effect was dominant (Li et al. 2005b).
Figure 45. Schematic view of MCC restoration.
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produces 3D point cloud data. Point cloud data is
processed to obtain a polygon surface model which can
be further edited and refined. The process is commonly
known as wrapping. A STL file can be generated from
the polygon surface model. After the polygonalisation
process and model surface editing and refinement, shaping
algorithms are applied leading to NURBS surfaces and
finally a CAD model. The final CAD model can be used
for FEA.
A large number of software packages are commerciallyavailable forpoint cloud editing, polygon surfacecreation, and
NURBS surface creation. Among them Geomagic, Poly-
works, Rhino, RapidForm, Medical modeler, DataSculpt,
and Surfacer are the leading vendors. The resulting NURBS
surface can be imported to any of the popular CAD software
packages, such as CATIA, Unigraphics NX, Pro-E, Mechan-
ical Desktop, Solid Edge, and SolidWorks using IGES and
Standard for the Exchange of Product Model Data (STEP)
formats or the RE systems provide an option to save the CAD
model ina CAD packages format. Prior to STLfile generation
and slicing for fabrication in a RP/RM system, finite element
method (FEM) based structural analysis or engineering
analysis can be performed to refine the final product such as
creation of a solid object having a certain wall thickness.
In unilateral models, such as face skull, cranium skull,
etc, a mirroring technique to reconstruct the damaged part
or region is used. Since, in unilateral models, there is
symmetry between left and right sides. This can easily beperformed in a CAD system. The cranium reconstruction
of a damaged region of the left side is reconstructed by
mirroring the undamaged region of the right side. By
applying a number of Boolean operations in CAD system
to the images of undamaged and damaged regions, a final
implant design is derived.
The processes for fabrication of metallic implants or their
models can be classified into two main groups: namely
Figure 46. Steps from model building until model fabrication in medical applications.
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direct processes and indirect processes. In the case of direct
processes, the final metallic implant or its model is directly
fabricated in a RP/RM machine, such as SLS, SLM and
EBM machines. In an indirect process a model of the
implant is first produced by creating a positive pattern using
a polymeric material. This positive pattern is then used to
make a negative (impression) mould of the physical model.
RTV technology is commonly used in indirect processes. A
silica mould is produced using the RTV process. From this
silica mould, a final physical model is produced. Besides
RTV, investment casting is rather frequently used, to create
a metallic mould. SLA and FDM are the othermost common RP processes for indirect metallic implant
fabrication.
SLS and SLM are the two laser based RP processes that
are predominantly used for fabrication of a physical model
from metallic powders. In the case of SLM, nearly 100%
dense parts can be produced. SLM systems that are
common in the market are Sinterstation Pro SLM (3D
Systems, USA), EOSINT (EOS GmBH, Germany), and the
SLM system Concept M3 Linear from Concept Laser
GmBH, Germany which uses a more powerful laser to
achieve higher melting temperature. Yang et al. (2008)
studied the quality of NiTi parts fabricated by the SLM
process in which an appropriate laser mode and scanning
strategy were selected. They concluded that the selection of
an appropriate laser mode and the scanning strategy are the
major factors that affect the quality of NiTi parts produced
by SLM. Facchini et al. (2010) produced fully dense
Ti6Al4V specimens with SLM. In these specimens, small
thermal crack and high residual stress were observed.
Residual stress in the parts fabricated by a SLM system,is one of the main disadvantages of the SLM process
(Shiomi et al. 2004, Mercelis and Kruth 2006, Facchini
et al. 2010). It is caused by a high cooling rate in the
consolidated material after the melting process that creates
misfit between crystals and atoms (Withers and Bhadeshia
2001). In many SLM systems which are currently available
on the market, the fabrication process proceeds under
atmospheric conditions. A RM/RM process to fabricate
Figure 47. Schematic view of EBM.
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titanium and titanium alloy implants, parts and prostheses
free from residual stresses obviously requires it to proceed
in a vacuum chamber where the cooling rate can be
controlled. Furthermore a pre-heating of each layer before
melting leads to favourable results. Consequently any RP/
RM process which does not fulfill the above mentioned
pre-conditions, fails to deliver residual stress free titanium
and titanium alloys parts. EBM is an emerging technology(after several years of hardware and software development
leading to improved quality) to produce parts from metallic
powders. EBM process takes places in a chamber and
primarily focuses on fabrication of medical implants and
aerospace components using Ti and Ti6Al4V powders.
EBM, as well as SLM and SLS, uses powder material.
The parts are fabricated using not only titanium and
titanium alloy, but also other metal powders, such as
aluminium, CoCr, super alloys, stainless still, hard metals,
tool steel powders and technologies to fabricate parts using
powders of copper, niobium, and beryllium have also been
developed.In an EBM system an electron beam is applied to melt
layers of a metallic powder instead of a laser beam.
According to a classification due to Kruth et al. (2005,
2007) EBM is classified as a full melting process. In an
EBM system an electron beam is generated from acceler-
ated electrons which travel nearly at the speed of light, from
a tungsten cathode wire which is heated up to 20008C. The
thermal energy to melt the powder is generated by the
momentum energy generated by accelerated electrons when
they hit the surface of the metallic powder. The power
density of the electron beam can reach 106 kW/cm2 (Arcam
AB, 2010). The electron beam is focused and deflected bymeans of a magnetic lens system, controlled by varying the
current instead of an optical lens that is controlled by a
servo motor such as in SLS and SLM, thus resulting in a
very fast scanning speed which significantly reduces the
build-up time. In this system high beam power and high
scanning speed produce enough heat to completely melt the
metal powder in a short time. The EBM process takes place
in a chamber (2 x 1 03 mbar) under near vacuum
conditions. This condition is suitable for high oxidising
material such as titanium and its alloys. It has been
reported that a Ti6Al4V part fabricated by the EBM
process has strength which is comparable or even superior
to a cast or wrought Ti6Al4V part (Murr 2009a, b).
Emerging titanium alloys such as titanium aluminide
(g-TiAl) have also been found to be suitable for fabrication
in an EBM system (Murr 2010a). Figure 47 depicts a
schematic view of the EBM process.
Some of the limitations that are inherent to most RP/RM
processes used for fabrication of implants and prostheses
can be summarised as follows:
1. The problems in terms of residual stresses and thermal
cracks while fabricating implants and prostheses using
powders of a biocompatible material such as titanium
and its alloys are well known. Therefore casting is still
the most common method used for fabricating implants
of titanium alloys which obviously increases the lead
time as well as adding several steps to the whole process.
2. In most cases rather large values of surface roughness ofthe parts fabricated by RP/RM processes compared with
the surface roughness values obtained in casting and
machining processes limits the use of RP/RM fabrica-
tion processes for medical and dental applications. The
unfavourable surface finish is inherent to the layered
manufacturing process itself, as the average powder
diameter affects the minimum surface finish that can be
obtained. The minimum powder size that is commer-
cially available for layered manufacturing using metallic
powders is around 20mm (EOS GmbH Germany) which
is the minimum value of the layer thickness that can be
achieved. Though several RP machines such as AR-
CAM EBM and EOSINT and several others are capableof maintaining an average distance of 5 mm (positioning
the z-axis) between each layer.
3. Small size and thin walled parts, such as dental coping
and bridges etc, are still difficult to fabricate using RP/
RM technologies. The melting of metallic powder in a
RP/RM process while fabricating small and thin walled
parts is a complex process. Rather large diameter of heat
affected zone (melted-pool diameter) and complex
deformation phenomena, such as swallowing and wrink-
ling due to excessive input of heat energy are the main
issues that need to be addressed.
8.2 Future directions
Issues such as stress-shielding and tissue integration need to
be addressed. The objective is to obtain good tissue
integration and reduce the stress-shielding effect. Though
the stress-shielding effect which is due to a mismatch
between the Youngs modulus of a metallic implant material
and that of the natural bone has been investigated by a
number of researchers, there is still an urgent need to
develop methods for dimensioning and designing metallic
implants.
There seems to be an urgent demand for economic and
customised direct digital fabrication of Ti6Al4V implantsand implants of other biocompatible materials. EBM
technology has proven to be suitable for direct digital
fabrication of implants and prostheses made of titanium
and its alloys with excellent properties. Further research
and development leading to an improved EBM technology
will undoubtedly provide low cost and precise implants,
such as cranium implants, hip joint implants, knee joint
implants, and many others. Current limitations of the SLM
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process such as relatively low speed melting, high residual
stress and resulting thermal cracks as well as porosity in the
fabricated parts can be overcome by this process by
improving the design of currently available systems on the
market.
Research on fabrication of small and thin walled parts
has to be carried out. For example, the fabrication of dental
implants and restoration are the challenges that all RP/RMprocesses face today. An optimisation of process parameters
of SLM and EBM processes leading to an accurate metal
coping for dental restoration with low surface roughness
has to be investigated further.
There are several implants and prostheses in medicine
and dentistry that have rather thin walls and cross-sections
and require a good surface finish. Therefore research on
preparation of smaller diameter biocompatible metallic
powder and development of RP/RM using them needs to
be conducted. Smaller grain size enables the implementa-
tion of a smaller layer thickness that will consequently
enhance the quality of the surface finish.The investigation of the properties of emerging biocom-
patible materials, such as titanium aluminide is another
potential field of research. The properties such as tissue
integration, fatigue life, corrosion resistance, and strength
as well as ductility have to be studied.
9. Conclusion
This paper reviews RP/RM fundamentals and applications
in medicine and dentistry. The biocompatibility of titanium,
titanium alloy, and other materials such as cobalt-chro-
mium and certain polymers has been discussed. Titaniumand its alloys are the most common biocompatible materi-
als that are used thanks to their high strength to weight
ratio, mechanical strength, corrosion resistance, oxidation
resistance, and low density.
Applications in medicine can be divided into four major
groups. Fabrication of biological and pre-surgical models,
fabrication of scaffold for cell growth and tissue engineer-
ing, fabrication of human and living body prostheses and
implants, and design and fabrication of dental prostheses.
RP/RM methods to fabricate physical models or parts for
medical and biological models, such as implants, pros-
theses, and fossils have been successfully employed withgood results. RTV and investment casting are used to
fabricate a mould to produce a physical part or model of it
for indirect RP/RM. The implementation of RP/RM and
RE for dental application and the use of EBM, instead of
the predominant SLM method, for direct metal fabrication
of biocompatible material are the emerging trends. The
crown restoration and dental implant fabrication is another
potential field of RP/RM application in dentistry.
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