Volumetric and dimensional accuracy assessment of CAD-CAM-manufactured dental prostheses from different materials.

STATEMENT OF PROBLEM: In computer-aided design and computer-aided manufacturing (CAD-CAM) dentistry, the CAD of the prosthesis represents the clinical prerequisite design to restore the treated tooth. However, how closely the CAM prosthesis shape matches the CAD, particularly in relation to different materials, is unclear. PURPOSE: The purpose of this in vitro study was to evaluate onlays designed and manufactured with the same CAD-CAM system but manufactured with different materials. MATERIAL AND METHODS: A single standard tessellation language (STL) model was used to produce 6 composite resin onlays, 6 leucite glass-ceramic onlays, and 6 lithium disilicate glass-ceramic onlays. The onlays were digitized by using an X-ray microtomographic protocol with a metrological calibration. The CAD model was then compared with the scans of the different onlays. An analysis by region of interest was then carried out to assess the accuracy and reliability of the dimensional accuracy. RESULTS: The composite resin and the lithium disilicate glass-ceramic had the best dimensional accuracy. The leucite glass-ceramic exhibited a lack of trueness linked to consistent overmilling. The composite resin had less peripheral chipping than the glass-ceramics. CONCLUSIONS: The composite resin and the lithium disilicate glass-ceramic material exhibited satisfactory dimensional accuracy. Milling the glass-ceramic before crystallization considerably improved dimensional accuracy.

Therapeutic strategy for cracked teeth.

The management of cracked teeth represents a difficulty because their diagnosis is complex and there is no consensus concerning their treatment. The present article explains this pathology within enamel and dentin and also focuses on the clinical consequences of crack development in dental tissue. As cracks have both biologic and mechanical implications, a complete review of the literature on the subject has enabled the development of a comprehensive diagnostic approach to identify cracked teeth and optimize their management. The elements of diagnosis are the bite test, transillumination, the pulp sensitivity test, the periodontal test, radiologic examinations, removal of existing restorations, and the use of quantitative light-induced fluorescence. Finally, the management of biologic and mechanical imperatives relating to the treatment of cracked teeth has allowed the proposal of a reliable and reproducible therapeutic strategy based on two pillars: the arrest of bacterial infiltration using immediate dentin sealing, and the limitation of crack propagation using relative cuspal coverage. In this article, the proposed clinical protocol is explained through the use of a decision map and is illustrated by a clinical case example.

Evaluation of the dimensional accuracy of a manufactured dental prosthesis in relation to its computer-aided model.

AIM: Currently, there is no reliable methodology to evaluate the dimensional conformity of dental prostheses manufactured through a digital shaping process. In the CAD/CAM method, the digital design of the prosthesis is considered as a reference, and it is crucial to reproduce it perfectly during the manufacturing process. Therefore, the aim of this study was to offer a comparison between a CAM prosthesis and its design model by superimposing the CAD model with the digitization of the manufactured prosthesis. MATERIALS AND METHODS: The metrological inspection developed in this study and presented in this article involved a comparison of the points cloud obtained by micro-computed tomography (micro-CT) and the CAD model of the prosthesis. First, an estimation of all inspection-method induced measurement errors was carried out, in which the measurement errors were assessed by proceeding to the dimensional inspection of a reference object of known dimensions. Then, the metrological inspection was extrapolated to a dental prosthesis. RESULTS: The estimation of measurement errors presented satisfying results compared with the usual metrological protocols developed by the dentistry research community. The dimensional deviation was estimated at 0.31% and the form deviation at 0.165 µm between the Gaussian sphere and the certified ball. The inspection of the manufactured surfaces revealed under-milled areas on the occlusal face, particularly on the anatomical fossae, and an irregular margin limit compared with its smooth design. CONCLUSION: A reliable micro-CT evaluation of the dimensional accuracy of a manufactured dental prosthesis compared with the CAD model demonstrated the performance level of CAD/CAM systems. The evaluation reliability was confirmed by the estimation of prior measurement errors. This estimation is essential for the metrological analysis.

Mechanical Properties of CAD/CAM Denture Base Resins.

PURPOSE: To evaluate the influence of fabrication processes on the mechanical properties of denture base resins. MATERIALS AND METHODS: Flexural strength, fracture toughness, and Vickers hardness were measured on a conventional pack-and-press resin (PRO), a resin for injection molding (CAP), and a CAD/CAM disc (CAD). RESULTS: For maximal flexural strength, PRO (97.31 MPa) was stronger than CAD (87.98 MPa) and CAP (79.35 MPa). CAD displayed hardness similar to PRO and high fracture toughness. CONCLUSION: CAD/CAM denture base resin mechanical properties result from the evolution of denture base materials, combining high-impact fracture toughness and improved flexural strength and hardness.