Towards developing CAD/CAM solutions in the retention of extra-oral facial prosthetics

In the production of removable facial prosthetics, Computer-Aided   Design   and Manufacture (CAD/CAM)is being increasingly explored. This PhD thesis investigates the  application  of  CAD/CAM  in the design  and production  of components  that  retain the  prostheses  to the  anatomy.  Conventional  methods  of hand-crafting the retention elements   are   well   established   butlittle research   has considered   producing these elementsusing  CAD/CAM.  A  fully  digital  prosthetic workflow  has  not  yet  been developed,  and  the  efficacy of  using  CAD/CAM  for  retention  mechanism  design and fabrication remains unclear. This   study firstly focuses on   defining the   requirements   for   designing extra-oral prosthesis  retention  mechanisms,  by mapping  the various  stages of  conventional practiceand obtaining  the opinions  of  practicing  clinicians. Secondly,  the qualitative findings are applied to develop a fully CAD/CAMprocess using existing technologies. Scanning, reverse  engineering,  design  and  fabrication technologies  are  trialled  and samples  of  bar-clip mechanisms  are  produced.  The final  stage focuses on developing objective methods to evaluate aspects of bar-clip design previously limited to subjective evaluation, and to make an initial comparison of conventional and CAD/CAM bar-clip mechanisms.This focuses on measuring surface and dimensional quality, accuracy offit and clip retention forces.This   study   provides an increased   knowledge-base of   current prosthetic practice; CAD/CAM prosthesis production and evaluation methods; and insight into the attitudes of clinicians towards the integration & implementation of CAD/CAM. The  thesis demonstrates that  CAD/CAM  can  be  used to design,produce, and  integrate bar-clip  retention mechanisms  in  all  aspects  of  theprosthesis  production workflow. Digital measurement methods allow an objective evaluation of the important aspects of bar-clip mechanism design,  identifying  a  number  of  inaccuracies/design flaws  that current  evaluation  techniques  fail  to identify.The  study concludes that the  overall CAD/CAM workflow is not yet appropriate for clinical practice but there is potential in the newly developed processes and this drives future work.