Grinding Damage Assessment of YSZ Based Ceramic Frameworks

Objectives: More dentists are using ceramic restorations designed and milled with CAD/CAM systems. In a partially-sintered state, Yttria-stabilized zirconia (YSZ) ceramic restorations are vulnerable to damage from diamond milling burs. This study aimed to assess potential surface damage from milling of YSZ structures.
Methods: Using the MXCL unit, fifteen partially-sintered YSZ frameworks were milled with diamond burs of 64µm grit at 42,000rpm. High-viscosity and low-viscosity polyvinyl siloxane materials (Extrude) were used in two-step impressions of samples. EpoxySet resin and hardener (Allied HighTech Products Inc.) was poured into impressions drop-by-drop, minimizing bubbles. Samples were observed under optical microscope (Keyence) for damage. Samples were affixed to mounting plates with carbon tape and were gold-coated to 4nm thickness. Scanning electron microscope (Zeiss) with EHT=10.00kV allowed quantification of damage, whether visible or non-visible from the optical microscope. Findings were recorded and measured.
Results: Chippings and bur markings were observed near or at the margins of the YSZ structures. Descriptive statistical analysis was used for the chipping and data. The mean depth and width of the chips, as well as data for abnormal bur markings are shown in the table. From sample 1 to 15, the mean size of the chips tended to be larger with longer bur use.
Conclusions: Predominantly, chipping was the damage encountered after milling of partially-sintered YSZ blocks. The damage encountered may cause fracture proneness in YSZ structures, depending on factors such as: residual stress field around chips, and tensile stresses.