34th INTERNATIONAL CONFERENCE ON
PRODUCTION ENGINEERING
29. - 30. September 2011, Niš, Serbia
University of Niš, Faculty of Mechanical Engineering
SOME ASPECTS OF RAPID PROTOTYPING APPLICATIONS IN MEDICINE
Miroslav PLANČAK1, Tatjana PUŠKAR2, Ognjan LUŽANIN1, Dubravka MARKOVIĆ2,
Plavka SKAKUN1, Dejan MOVRIN1
1
Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovica 6, Novi Sad, Serbia
2
Medical faculty Novi Sad, Department of dentistry, Hajduk Veljkova 12, Novi Sad, Serbia
plancak@uns.ac.rs., tatjanapuskar@yahoo.com, luzanin@uns.ac.rs, dubravkamarkovic@yahoo.com,
plavkas@uns.ac.rs, movrin@uns.ac.rs
Abstract: Rapid prototyping (RP) is a term which encompasses a number of modern technologies for
manufacturing of physical models directly from CAD files. Concept of RP offers essential advantages and
benefits in development of a new product: quick transition from first idea to final product (short „time to
market”), lower production costs, improved (optimized) product quality. Application range of RP covers
different fields: production and civil engineering, architecture, medicine etc. Medical RP models are built
mainly by stereolithography, fuse deposition modeling, selective laser sintering and inkjet systems. Main
application in medicine is in orthopedics, soft tissue modeling, dentistry and maxillofacial surgery.
As regard dentistry, RP models enable quick and reliable fabrication of medical devices, visualization,
prosthesis fabrication, implant design and manufacture etc. Current paper gives insight into the RP
techniques which are most commonly employed in dentistry. Furthermore, some new RP techniques and
trends are discussed, while main specificities of RP in dental application are presented.
Key words: rapid prototyping, medicine, dentistry
1. INTRODUCTION
The basic idea underlying Rapid prototyping (RP)
technologies is the possibility of rapidly building
prototypes of a new product designed in a CAD
environment. Prototype making is an important part of
development and manufacturing of products. It helps
testing product design (form, functionality, etc.) before
significant investment in tooling is made. In the past,
model or prototype making was expensive and time
consuming process, which did not allow many
modifications of design. The result of this were products
which were seldom optimised [1], [2], [3].
When RP technologies were developed, primary fields of
application were engineering and design. Applications of
RP in medicine came later, with the development of
modern imaging modalities (Computed Tomography - CT
or Magnetic Resonance Imaging MRI) which provided
input data for model generation in RP [4], [5], [6].
In this paper some RP technologies and their application
in medicine and dentistry are presented.
2. RP IN MEDICINE
RP technologies in medicine and manufacturing differ. In
manufacturing, models are usually designed in CAD
environment and than converted to 3D model while in
medicine and dentistry objects of interest usually exist in
physical form [7], [8]. To create a medical model it is
necessary to acquire data for model building. There are
several ways for data aquisition. Most common are CT –
Computed Tomography and MRI - magnetic resonance
imaging, although CT are widely applied for RP because
image post-processing is less complex. Some other
imaging modalities which can be used for data acquisition
are MDCT – Multidetector Computed Tomography,
CBCT – Cone Beam Computed Tomography, PET –
Positron Emission Tomography, SPECT – Single Photon
Emission Computed Tomography and US –
Ultrasonography [5].
After data acquisition, the next step is image postprocessing which provides data for RP techniques, where
the STL file format is commonly used.
There are a number of RP techniques which can be used
in medicine: Stereolithography (SL), Selective Laser
Sintering (SLS), Fused Deposition Modeling (FDM),
Laminated Object Manufacturing (LOM), Inkjet printing
techniques etc.
Among numerous possible applications of RP in medicine
are:
 possibility to improve diagnostic quality and help in
pre-surgical planning. Simulating complicated
surgical steps in advance using prototype model can
help foresee complications during operation which
may result in reduced procedure time.
 use for implant and tissue design, both for bone
reconstruction and replacement of soft tissues, as rapid
prototyping can be applied on a variety of materials.
 opportunities for scientific research
 use in medical training and education.
Numerous papers have dealt with application of RP in
medicine. In [4], the authors used stereolithography
models in diagnosis and the precise preoperative
simulation of skeleton modifying interventions for
several cases of maxillo-cranio-facial surgery.
A 3D model generated by fused deposition modelling and
used for planning and verification of a surgical procedure
was described in [8]. In this case, the patient required
replacement of left hip joint.
Several applications of RP technologies in soft tissue
facial prosthetics are presented in [15], [16]. Examples
included orbital prosthesis, auricular prosthesis, nasal
prosthesis, etc. Examples were analysed from various
aspects related to RP application: quality, economic
influence and clinical implications.
3. RP IN DENTISTRY
According to [7] there are several areas in dentistry in
which RP can be implemented. Those areas are:
 Manufacture of dental devices – due to a number of
advantages, the most prominent of which is complex
geometry, RP models allow additional functionalities
to dental devices.
 Visualization, diagnostication and education – RP
models offer realistic visual and tactile information
and are used by surgeons to gain knowledge of
anatomical structure. This, in turn, faciliates
communication in surgical teams and between doctors
and patients. In addition, medical students can use RP
models to efficiently learn and practice surgical
procedures
 Surgical planning – RP models allow surgeons to
efficiently plan intricate operations. Moreover, they
can also be used as templateds and guides in operation
rooms. Not only real surgical tools can be applied on
these models to significantly reduce operation time,
but also surgeons are able to see actual location, size
and shape of the problem area in hand. Finally,
anatomical structure can be visualized by using
transparent and/or multicoloured models.
 Customized implant design – In the past, implant parts
used to be selected from standard size parts provided
by manufactures. Thus, in cases of special
requirements, that are outside standard range or
between sizes due to disease or genetics, problems
occured. Standard implants had to be customized for
that specific case, which prolonged operating time and
increased risks of the surgical complication. Besides,
there was also a chance that the implant did not fit
well. RP allows design of individual dental implants,
elliminating majority of the discussed problems.
 Orthotics – RP model can be used to design orthotic
devices with the specific patient’s tooth alignment.
 Prosthetics – So far, dental prosthesis (coping, crown,
bridge, fixture etc.) fabrication has greatly depended
on the skills of dentists and technicians. RP techniques
are increasingly changing this situation for the better,
elliminating the influence of individual skills on the
final result.
 Forensics – RP is a valuable tool in various types of
investigations. Being sufficiently accurate to present
effects of the wounds, RP models can be used to
preserve evidence.
 Biologically active implants – This is a new area of
RP application. Dentistry can successfully exploit RP
technologies to manufacture biologically active
implants such as jawbones that might be damaged or
malformed due to disease.
4. APPLICATION EXAMPLES
As mentioned before, there are many different areas in
dentistry where RP techniques can be applied and
numerous examples can be found in literature related to
this subject.
In [7] a design of a drill guide is presented. In some cases
holes have to be drilled in the patient’s jawbone in order
to position dental implants. A drill guide’s function is to
guide surgeon’s drill to the planned implant location. CT
scan data of the jaw are converted into 3D model which
enables a dentists to go virtualy through the jawbone to
search for the best location for the proposed implants.
Once the designing process is finished, the CAD model of
the drill guide is transferred to an RP system to fabricate
the real drill guide. In addition, the model of the jawbone
is usually fabricated, so the fit of the drill guide and the
treatment planning can be checked and verified. Fig. 1
depicts a bone-supported drill guide, while Fig.2 shows
an RP jawbone model (stereolitography) with mounted
drill guide.
Fig. 1 Schematic of bone-supported drill guide[7]
Fig. 2 Model of jawbone with a mounted drill guide,
manufactured by stereolithography[7]
Stereolitography has also been used for building 3D
models for educational purposes. Teaching cube was
constructed as a teaching device in an operative dentistry
course [9]. At the learning exercise it is required from
students to demonstrate the ability to evaluate simulated
cavity preparation for which purpose the cube was used.
(Fig 3). CAD model of the cube allows changing shape,
number, position and sizes of cavities and making new RP
model for different types of learning exercise.
on the previously solidified ice surface. The most
important advantages of the RFP process are: the process
is cheaper and cleaner, it has potential to build accurate
ice parts with excellent surface roughness, sufficient layer
binding, easiness and no residue for part removal in
molding process, no shrinkage, and, finally, easiness of
material expansion compensation.
Fig. 3 The teaching cube [9]
Application of 3D printing in design and fabrication of
dental prosthesis were presented in [7]. Traditional crown
fabrication includes seven steps (tooth grinding,
imperssion taking, treated tooth extraction, assembly of
biting set, wax pattern making, centrifugal investment
casting with finishing and porcelain sintering and resin
polymerization) and all of these steps depend significantly
on the skills of dental technician. A computer-aided
crown fabrication process simplifies the traditional
fabrication process and accelerates the production period
by using 3D imaging, CAD and RP. In this process CAD
packages are used to construct a crown model, while an
RP system generates the crown model. This procedure
includes four steps: crown inner and outer surface
preparation, CAD crown model construction, crown
model fabrication and investment casting and finishing.
By the inner surface one understands the surface of the
tooth after the preparation or the surface of the standard
die if the tooth is missing, while the outer surface
represents the original surface of the damaged tooth or
teeth. There are two methods for deriving the geometry of
the outer surface. The first method relies on standardized
teeth which are digitized, while in the second method the
surface based on the geometry of the neighboring and
opposite teeth is designed. Construction of the crown
model is performed by combining the inner and outer
surface.
A novel method of pattern fabrication for the investment
casting was proposed by the Liu at al, [11]. They
investigated ice pattern fabrication by rapid freeze
prototyping (RFP). In the investement casting, which has
found application in manufacturing of dental devices, a
wax pattern is usually used. The use of wax patterns is
connected with some technical difficulties such as the
wax pattern expanding, ceramic shell cracking etc. This
new technology employs investement casting with ice
patterns. For that purpose new process and equipment for
RP were developed. In this process, selective depositing
and freezing of the material (water ) layer by layer is used
to produce parts. Basically, two methods are used to
deposit water: continuous deposition and drop-ondemand. deposition (Fig.4).
The build environment is kept at a low temperature which
is below water freezing point. Pure water or colorized
water is extruded or ejected from the nozzle and deposited
Fig. 4 Principle of rapid freeze prototyping [11]
Another new technique developed for metal parts, termed
Selective Laser Melting, is reported in paper [14].
Designed primarily for making non machinable complex
parts for direct use, this technology also found its
application in medical industry. In this process, fully
dense parts are manufactured, creating a fluid phase
which is also known as the ’melt pool’. SLM is a laser
welding process and for that reason all related
phenomena, such as pores, cracks, distortion, warping,
and residual stress, must be taken into consideration. To
avoid or reduce these negative effects to a minimum,
optimization of the basic machine parameters such as the
laser diameter has to be performed. Dental crowns and
bridges can be produced by this method.
5. RP SOFTWARE TECHNOLOGIES
As already noted, application of RP technologies demands
the use of dedicated software and hardware through all
the main stages: (i) design, (ii) process planning, and (iii)
manufacture. Regardless of the particular type of RP
technology, which could be either conventional or novel,
the basic data processing flow remains virtually
unchanged.
The first stage of the data processing flow consists of 3-D
modelling using some of the commercially available CAD
software. Alternatively, model geometry data can be
obtained through reverse engineering, medicinal CTscans, or mathematical modeling.
In order to be efficiently used as input information into
various RP processes, model data must be pre-processed
into some of the neutral data formats. Despite its intrinsic
deficiencies, stereolitography (STL) format is a de facto
standard which is widely accepted by the industry.
However, as a result of intensive research in the domain
of product and model data exchange, numerous
alternative data formats have been developed, such as
STH (Surface Triangles Hinted Format), CFL (Cubital
Facet List ), RPI (Ransellaer Polytechnic Institute
format), G-WoRP (Geometric Workbench for RP), STEP
(STandard for the Exchange of Product data - AP203),
etc.
The process planning stage consists of a number of
specialized tasks which are also performed using
dedicated software solutions: verification of 3-D model
and correction of errors, compensation of STL file,
definition of the direction in which the material shall be
applied, packaging of models into machine’s workspace,
detection of unsolidified residuals, generation of props
and supports, slicing, generation of scanning path, and
generation of control information data file which is
subsequently fed into RP machine’s control unit.
On today’s market there exist numerous dedicated
software tools capable of efficiently performing the
required tasks, such as Bridgeworks (Solid Concepts, Inc,
USA), MagicsSG (Materialise, Belgium), Vista (3D
Systems), etc.
6. CONCLUSION
This paper focused on a review of prototyping
applications in medicine with emphasis on dentistry, i.e.,
dental replacements. An increasing demand for flexible,
cost-effective, and efficient technologies for manufacture
of various types of anatomical replacements in medicine
in general, and dentistry, has stimulated development of a
vast array of rapid prototyping technologies with the
ultimate goal of re-creating them de novo. Presented in
this paper was a succinct review of the state of the art in
this field, accompanied by some relevant application
examples. In the near future, one should expect that the
existing array of RP technologies which still accentuate
the use of predominantly engineering materials such as
polymers, powdered metals, etc., will be augmented by a
nascent technology termed bioprinting. This shall allow
layered manufacturing of various replacements based on
biological materials, thus adding new quality to the ever
expanding domain of rapid prototyping technologies used
in medicine.
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Acknowledgement
Results of investigation presented in this paper are part of
the research realized in the framework of the project
“Research and development of modeling methods and
approaches in manufacturing of dental recoveries with the
application of modern technologies and computer aided
systems“–TR 035020, financed by the Ministry of
Science and Technological Development of the Republic
of Serbia.