Managing Effects of Manufacturing Variation in Dental Medical Device Treatments - Increasing Geometrical Robustness

Doctoral thesis, 2011

Today, there are many solutions for dental rehabilitation. A damaged tooth can be replaced with a dental crown, and a toothless patient can be rehabilitated with implants and a corresponding bridge set-up. Traditionally, a dental crown is manufactured by veneering porcelain to a metal surface that is obtained through the use of casting principles. Further, implant rehabilitations are carried out based on x- ray pictures and free hand drilling into the jaw bone before implant insertion. However, crown and implant rehabilitations can be provided at a much higher degree of industrialization by means of mass customization. The most common dental rehabilitations are crown restorations for single teeth, while full arch implant rehabilitations are the most comprehensive treatments. It is also these treatment methods that have been used as the bases for the conducted research presented in this thesis. Within mechanical engineering, tolerance analysis and robust design for mass production have been studied closely and developed for decades now. Tolerance analysis studies accumulated variation in mechanical part assemblies, and robust design methods are used to secure the functionality of the product. Therefore, it is of scientific, as well as industrial, challenge to seek answers to how knowledge and methods for tolerance analysis and robust design can be applied for mass customization, especially for dental rehabilitations. The objective of this research is to gain knowledge about, and improve, the product realization processes for dental medical device manufacturing, in order to reduce the influence of geometrical variation in the final treatment. For drill- and implant guided surgery, the focus was initially set on introducing variation simulation principles to the area of dentistry. A methodological approach to finding the greatest contributor and the most sensitive phase to geometrical variation was presented. The simulation method introduced in the first study was also verified compared to actual surgeries conducted on human cadavers. For the crown rehabilitation, a method to increase the geometrical quality was suggested by changing the design, the method is also under industrial implementation process. A method for quantifying the successfulness of a probe scanning was presented. Knowledge of which parameters influence the final variation for the treatment method and an understanding of how parameters can be modeled to increase the robustness for the design has been gained. Finally, a geometry assurance method suitable for medical treatments using mass customized products was suggested. Ultimately, two international patents were also published based on the research.