R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

240 Medical modelling
6.92 The framework fi tted to the patient in clinic.
the clasps, and the framework withstood repeated insertion and removal
cycles.
6.14.5 Discussion
Sources of error
Various studies have aimed to assess error in cobalt-chrome partial denture
frameworks made using traditional investment casting techniques (10, 11,
12). However, in the absence of an appropriate intra-oral scanning technology,
the application of CAD/CAM in dental technology depends on the
dental model, which is a plaster cast taken from an impression of the dental
anatomy made by a dentist. Clearly, this study cannot address issues relating
to the quality of the original dental impression or the casting of the
dental model from this impression. In addition, human error in the interpretation
of the dentist’s instructions or in the dental technician’s chosen
design for the framework is not addressed. However, the adoption of CAD/
CAM/RP technologies may incur several process steps that could contribute
to error between the theoretical designs produced using CAD and the
fi nal manufactured item. The effect of these processes will be an accumulation
of tolerances at each technology stage. However, certain levels of care
and skill may still affect the accuracy of these computer-controlled
techniques.
Table 6.2 shows the steps in the process investigated here and indicates
nominal tolerances associated with the technologies used. The accumulation
of tolerances leads to the maximum error that could be expected to
result from the technologies alone, assuming no human error is encountered.
As human skill level and error cannot be attributed a numerical value