Metrics for prosthetic cervical margin integrity assessment after dental CAD/CAM milling: a critical analysis from engineering viewpoint.

Abstract

Dental prostheses have significantly evolved due to advances in Computer Aided Design and Manufacturing (CAD/CAM) technology. CAD/CAM systems provide a variety of biomaterials like ceramics, Polymer-Infiltrated Ceramic Network (PICN), and composites, which are preferred for their mechanical and aesthetic properties. However, ceramics, despite their popularity, are brittle and prone to chipping during the machining process, impacting the prosthesis's clinical functions, aesthetics, biological integrity, and mechanical performance. Chipping, especially at thin cervical margin, can cause visible defects, poor sealing, and bacterial growth, reducing prosthesis lifespan. Milling factors influence cervical margin integrity. Chipping assessment involves understanding biomaterial mechanical and machinability characteristics regarding dimensional characterization of milled prosthesis shape. Thus, different type of metrics, based on biomaterial properties or dimensional measurement can be used to assess chipping phenomenon for milled dental ceramics. These metrics are both, based on experimental studies found in literature, and proposed by this paper authors to fill the existing lacks. The brittleness index, based on the ratio between hardness and fracture toughness, predicts susceptibility to chipping after milling. Unidirectional dimensional metrics like the Chipping Factor and weighted Chipping Factor characterize the chipping ratio of the cervical margin. Advanced 2D and 3D metrics, including chip projected area, total weighted chip projected area, and Surface Aspect Ratio, offer more detailed assessments. 3D analysis involves comparing scanned files with CAD models to compute chipped volumes. The aim of this paper is to propose a critical analysis from an engineering viewpoint on metrics used to assess cervical margin integrity for milled dental prosthesis.