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

Abstract

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 but little research has considered producing these elements using 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 practice and obtaining the opinions of practicing clinicians. Secondly, the qualitative findings are applied to develop a fully CAD/CAM process 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 of fit 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 the prosthesis 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.