Syam - Et Al - Rapid Prototyping in Medicine

8/9/2019 Syam - Et Al - Rapid Prototyping in Medicine

1/32

This article was downloaded by: [Gordon Library, Worcester Polytechnic Institute ]On: 04 June 2014, At: 06:43Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House37-41 Mortimer Street, London W1T 3JH, UK

Virtual and Physical PrototypingPublication details, including instructions for authors and subscription information:

http://www.tandfonline.com/loi/nvpp20

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

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of thContent. Any opinions and views expressed in this publication are the opinions and views of the authors, and

are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon ashould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveor howsoever caused arising directly or indirectly in connection with, inrelation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
http://dx.doi.org/10.1080/17452759.2011.590388http://www.tandfonline.com/action/showCitFormats?doi=10.1080/17452759.2011.590388http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditionshttp://dx.doi.org/10.1080/17452759.2011.590388http://www.tandfonline.com/action/showCitFormats?doi=10.1080/17452759.2011.590388http://www.tandfonline.com/loi/nvpp20


2/32

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: [email protected]

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


3/32

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

80 W.P. Syam et al.


4/32

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.

81Virtual and Physical Prototyping


5/32

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.

82 W.P. Syam et al.


6/32

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).



7/32

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).

84 W.P. Syam et al.


8/32

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).



9/32

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).

86 W.P. Syam et al.


10/32

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).



11/32

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).

88 W.P. Syam et al.


12/32

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).



13/32

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).

90 W.P. Syam et al.


14/32

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).



15/32

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).

92 W.P. Syam et al.


16/32

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).



17/32

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).

94 W.P. Syam et al.


18/32

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).



19/32

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).

96 W.P. Syam et al.


20/32

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).



21/32

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).

98 W.P. Syam et al.


22/32

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).



23/32

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).

100 W.P. Syam et al.


24/32

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).



25/32

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).



26/32

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.



27/32

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.



28/32

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.



29/32

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



30/32

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.

References

Arafat, M.T., Lam, C.X.F., Ekaputra, A.K., Wong, S.Y., Li, X. and

Gibson, I., 2011. Biomimetic composite coating on rapid prototyped

scaffolds for bone tissue engineering. Acta Biomaterialia, 7, 809820.

Arcam, AB, 2010. Arcam EBM model A2: Manual book. Guttenberg,

Sweden: Arcam AB.

Bernard, A. and Fischer, A., 2002. New trends in rapid product develop-

ment.CIRP Annals: Manufacturing Technology, 51, 635652.

Booysen, G.F., Barnard, L.F., Truscott, M. and De Beer, D.J., 2006.

Anaesthetic mouthpiece development through QFD and customer

interaction with functional prototypes. Rapid Prototyping Journal, 12,

89197.

Byrne, D.P., Lacroix, D., Planell, J.A., Kelly, D.J. and Prendergast, P.J.,

2007. Simulation of tissue differentiation in a scaffold as a function of

porosity, Youngs modulus and dissolution rate: Application of mechan-

obiological models in tissue engineering. Biomaterials, 28, 55445554.

Cansizoglu, O., Harrysson, O., Cormier, D., West, H. and Mahale, T.,

2008a. Properties of Ti-6Al-4V non-stochastic lattice structures fabri-

cated via electron beam melting. Material Science Engineering A, 492,

468474.

Cansizoglu, O., Harrysson, O.L.A., West, H.A., Cormier, D.R. and Mahale,

T., 2008b. Applications of structural optimization in direct metal

fabrication. Rapid Prototyping Journal, 14, 11422.

Chen, Z., Li, D., Lu, B., Tang, Y., Sun, M. and Wang, Z., 2004. Fabrication

of artificial bioactive bone using rapid prototyping. Rapid Prototyping

Journal, 10, 327333.

Chryssolouris, G., Papakostas, N. and Mavrikios, D., 2008. A Perspective

on manufacturing strategy: Produce more with less. CIRP Journal of

Manufacturing Science and Technology, 1, 4552.

De Beer, D.J., Truscott, M., Booysen, G.J., Barnard, L.J. and van der

Walt, J.G., 2005. Rapid manufacturing of patient-specific shielding

masks, using RP in parallel with metal spraying. Rapid Prototyping

Journal, 11, 298303.

Dowson, D., Hardaker, C., Flett, M. and Isaac, G.H., 2004. A hip joint

simulator study of the performance of metal-on-metal joints. The Journal

of Arthroplasty, 19 (8), 118123.

Durso, P.S., Thompson, R.G. and Earwaker, W.J., 2000. Stereolithographic

(SL) biomodelling in paleontology: A technical note. Rapid Prototyping

Journal, 6, 212215.

Engel., B. and Bourell, D.L., 2000. Titanium alloy powder preparation for

selective laser sintering. Rapid Prototyping Journal, 6, 97106.

Facchini, L., Magalini, E., Robotti, P., Molinari, A., Hoges, S. and

Wissenbach, K., 2010. Ductility of a Ti-6Al-4V alloy produced by

selective laser melting of prealloyed powders. Rapid Prototyping Journal,

16, 450459.

Fantini, M., de Crescenzio, F., Persiani, F., Benazzi, S. and Gruppionio, G.,

2008. 3D restitution, restoration, and prototyping of a medieval damaged

skull.Rapid Prototyping Journal, 14, 318324.

Ganz, S.D., 2005. Presurgical planning with CT-derived fabrication of

surgical guide. Journal of Oral Maxillofacial Surgery, 63, 5971.

Gao, B., Wu, J., Zhao, X. and Tan, H., 2009. Fabricating titanium denture

base plate by laser rapid forming. Rapid Prototyping Journal, 15,

133136.

Geng, L., Feng, W., Hutmacher, D.W., Wong, Y.S., Loh, H.T. and Fuh,

J.F.Y., 2005. Direct writing of chitosan scaffold using a robotic system.

Rapid Prototyping Journal, 11, 9097.

Gopakumar, S., 2004. RP in medicine: A case study in cranial reconstruc-

tive surgery. Rapid Prototyping Journal, 10, 207211.

Harryson, O.L.A., Cansizoglu, O., Marcellin-Little, D.J., Cormier, D.R.

and West II, H.A.W., 2008. Direct metal fabrication of titanium

implants with tailored materials and mechanical properties using electron

beam melting technology. Materials Science and Engineering C, 28,

366373.



31/32

Harrysson, O.L.A., Cormier, D.R., Marcellin-Little, D.F. and Fajal, K.,

2003. Rapid prototyping for trea

Documents

Syam - Et Al - Rapid Prototyping in Medicine