Machined surface integrity- Application to fixed dental prosthesis

One of the major challenges of restorative dentistry is to rehabilitate dental function by fitting prostheses. The art of dental prosthetics has never ceased to evolve. Improvements in the materials and techniques used in restorative dentistry have always kept pace with technological advances in industrial engineering. In 1973, Professor F. Duret laid the foundations for Computer-Aided Design and Manufacturing (CAD/CAM) applied to dentistry. Duret. The aim of CAD/CAM was to replace "conventional" impression techniques (using thermoplastic pastes) with a completely digital prosthesis manufacturing chain. The design of the prosthetic part, as well as its physical production by machining, become entirely computer-aided. The resulting dental prostheses help restore oral functions (chewing, swallowing, phonation) and maintain the patient's oral health. This modern industrial technique for producing fixed prostheses uses raw biomaterial blocks. These blocks of ceramic, composite or hybrid material (Polymer-Infiltrated-Ceramic-Network (PICN)) are often pressed before being machined by material removal using numerically controlled machine tools (MOCN). The quality of prostheses expected by patients and practitioners is therefore a major public health issue, since today around 50% of the European population has a dental prosthesis (fixed or removable). The most common aspects of expected quality are: aesthetics, mechanical durability, non-adherence of bacterial plaque, bio-compatibility and micromechanical retention of the prosthesis on the prepared tooth. These quality aspects, in line with prosthetic functionalities, call upon various physical or geometric components of the resulting prosthetic surface, linked to the material and its shaping. In engineering, all these components are grouped together under a concept known as surface integrity.

After presenting the concept of surface integrity, this article focuses on its transposition to dental prosthetics. Drawing on experience gained in mechanical engineering, this transposition then establishes correlations between surface integrity, the prosthetic functionalities expected by practitioners and patients, and the machining process implemented in dental CAD/CAM.