Stereolithography: A Recent Tool in Diagnosis, Treatment Planning, and Management of Craniofacial Deformities - Proceedings of All India Seminar on Biomedical Engineering 2012 (AISOBE-2012) - page 2

Fig. 1 Diagram showing the
principle of operation of an
SL system. Winder and bibb.
Medical rapid prototyping
technologies. J Oral
Maxillofac Surg 2005
software in a suitable file format (commonly STL) and transferred to the SL
machine for building. The CAD data file is converted into individual slices of
known dimensions. This slice data are then fed to the RP machine, which guides
the exposure path of the UV laser onto the resin surface. The layers are cured
sequentially and bond together to form a solid object beginning from the bottom of
the model and building up. As the resin is exposed to the UV light, a thin well-
defined layer thickness becomes hardened. After a layer of resin is exposed, the
resin platform is lowered within the bath by a small known distance. A new layer
of resin is wiped across the surface of the previous layer using a wiper blade, and
this second layer is subsequently exposed and cured. The process of curing and
lowering the platform into the resin bath is repeated until the full model is com-
plete. The self-adhesive property of the material causes the layers to bond to one
another and eventually form a complete, robust, 3D object. The model is then
removed from the bath and cured for a further period of time in a UV cabinet
Fig. 2 . The built part may contain layers, which significantly overhang the layers
below. If this is the case, then a network of support structures, made of the same
material, is added beneath these overhanging layers at the design stage to add
support during the curing process. These support structures, analogous to a scaf-
fold, are removed by hand after the model is fully cured. This is a labor-intensive
and time-consuming process. Generally, SL is considered to provide the greatest
accuracy and the best surface finish of any RP technology. The model material is
robust, slightly brittle, and relatively light, although it is hydroscopic and may
physically warp over time (a few months) if exposed to high humidity.
Continued advances in biomodeling can facilitate better diagnosis, treatment
planning, and fabrication of implants for craniomaxillofacial surgeries. Clinically,
these models are used mainly for craniofacial deformities, reconstructive surgeries,
pathologies, and trauma [ 13 ]. Biomodels generated by stereolithography (SL) have
been confirmed to have a higher accuracy compared with milled models and
3-dimensional (3D) computed tomography (CT) visual models [ 14 , 15 ].
The technology allows production of highly accurate and realistic replicas of
the body structures of an individual. The literature has shown some promising