Designing a Retainer

Designing a Retainer
Introduction
A lot of advances and technological improvements have been made in the field of medicine,
especially dentistry. (Marie B. Teixeira, 2013) (Michael E. Wiklund, 2005)This advances have
greatly helped in this sub field. Thanks to this technological advancements, various medical
appliances have been designed and fabricated which have helped in solving numerous problems
concerning dentistry.
One of the appliances that have designed and fabricated is the retainer. This appliance is
designed by use computer aided (CAD) and computer aided manufacturing (CAD). In addition,
the retainer is then virtually fabricated through either of the two processes; subtractive
manufacturing technology or additive manufacturing technology. Subtractive manufacturing
technology entails milling the appliance to the shape specified from a block of the desired
material, while additive manufacturing technology involves materials layer after layer until the
3D is developed.
In this design we will be using a new technique for integrating cone-beam shaped computed
tomography (OBCT), CAD/CAM, rapid prototyping, stereolithography for the design and
fabrication.
Material and Methods
The first step in designing a retainer is obtaining a digital replica of the teeth from the patient.
Thereafter, the patient’s dental appearance is scanned by CBT. This is done by centralizing the
area of interest in the machine’s focal point.
The patient or client is then directed by the medical officers to bite on two or more tongue blades
in order to separate mandibular teeth from the maxillary teeth. This is to ensure separation of the
dentition on 3D software to be possible.
Then, the CBT data is taken in a DICOM format and the images are imported into the software

This DICOM data is then used to generate a 3D model of the skull. (Faber J, 2006)
This ensures that the threshold required for maximum visualization of the dentition is achieved
all the while eliminating the soft tissues. Thereafter the region of interest is cropped out of the
whole of 3D skull as seen in figure 2
Thereafter the 3D model of the area under study id exported as a file in the stl format which is
later converted to obj format. The data that is in the said format is then opened using another 3D
handling software called Zbrush. In this application, retopology concept is applied. This is
basically creation or modification of an object on surface of another object which forms to the
old object accurately.
As shown in figure 3, ZSphere tool (Pixologic) is used to create a base mesh with clean
topology. The ZSphere starts out with a simple sphere that one can extract from until obtaining
the basic shape of the model to be sculpted on. The topology (surface contour) of the dentition is
drawn via selection of points contoured to the surface of the teeth as it is clearly in figure 4. The
points are placed on the teeth intended for the future retainer and according to the desired
extensions needed to avoid soft-tissue impingement of the future retainer (Fig 5, A). These points