Analysis of CAD-CAM Diamond Burs for Milling Yttrium-Stabilized Zirconia Ceramics

Objectives: The use of Computer-Aided-Design (CAD) / Computer-Aided-Manufacture (CAM) technology in dentistry introduced the automated manufacturing of several types of ceramic restorations such as inlays, onlays, veneers, crowns, and multi-unit fixed dental prostheses. The precision of the design and milling processes can potentially influence the quality of the restorations. CAD/CAM milling units are equipped with pairs of diamond burs, responsible for carving the CAD/CAM block into the final restoration’s anatomy. The aim of this study was to analyze topographical changes of CAD/CAM diamond burs after milling yttrium-stabilized zirconia (YSZ) ceramic frameworks.
Methods: The topographical changes in three groups of diamond burs (n=10) were assessed: 1) new milling burs (control group), 2) step, and 3) cylinder pointed. The burs were divided into three thirds for detailed examination: top, middle and distal. The diamond burs were evaluated under the optical and scanning electron microscope.
Results: Deep grooves, grain detachment, scratches, and brownish colorations were observed under the optical microscope. The scanning electron microscope confirmed but also revealed more features present on the milling bur surfaces as shown in the Figure.
Conclusions: Re-occurring morphological changes were observed in the milling burs used to fabricate long lasting YSZ ceramic restorations. The damage was evident in most locations. The damage on the burs can have detrimental effects on the ceramic structure fatigue strength, as well as on the patient and health-care provider quality expectations of the restoration.