Grinding damage assessment on four high-strength ceramics

Current dental practices rely on high-strength ceramics for frameworks and restorations. Yet, the impact of grinding procedures on these materials remains unclear. Prior research has shown that surface damage can reduce mechanical performance, but specific thresholds for damage in CAD-CAM ceramics are lacking. This gap motivated the investigation of grinding effects on four commonly used ceramics. No prior work had resolved how different diamond grits affect chip formation and strength loss. Understanding these relationships is essential for optimizing post-sintering finishing protocols. Manufacturers report flexural strengths, but real-world performance may differ after grinding. This study aimed to bridge the knowledge gap by quantifying damage and estimating strength losses. The results could guide clinicians in selecting appropriate finishing techniques.

The study aimed to evaluate how grinding with different diamond grits affects surface and subsurface damage in four high-strength ceramics. The specific problem is the lack of data on how grinding impacts mechanical integrity. The motivation stems from the need to preserve ceramic strength after shaping. The authors sought to quantify chip depths and estimate strength losses. They focused on clinically relevant materials like 3Y-TZP and alumina-based ceramics. The goal was to determine if certain grits induce critical flaws. The study also aimed to compare materials' responses to grinding. Findings could influence clinical protocols for ceramic finishing.

The researchers used four CAD-CAM ceramics: 3Y-TZP, dense Al2O3, alumina glass-infiltrated, and alumina-zirconia glass-infiltrated. Specimens had mirror-polished surfaces bonded pairwise before grinding. Diamond disks of 75 μm, 54 μm, and 18 μm were used to induce damage. Scanning electron microscopy (SEM) measured chip depths on the bonded interface. Fracture mechanics estimated strength losses based on chip sizes. The method considered chips as critical flaws under tension. Data included average and maximum chip depths for each material and grit size. The approach allowed comparisons of damage across grits and ceramics.

3Y-TZP showed minimal damage with an average chip depth of 12.7±5.2 μm after 75 μm grinding. This induced an estimated 12% strength loss compared to manufacturer values. Dense Al2O3 had the largest chips at 48.2±16.3 μm, leading to a 49% strength loss. Alumina glass-infiltrated had chips of 62.4±19.3 μm, causing a 38% strength loss. Alumina-zirconia glass-infiltrated had chips of 56.8±15.1 μm, resulting in a 34% strength loss. At 54 μm, dense Al2O3 chips were 32.2±9.1 μm, causing a 23% strength loss. Alumina glass-infiltrated showed 42.8±16.6 μm chips and a 25% strength loss. At 18 μm, all materials showed minimal critical damage. The results suggest that 75 μm grinding is most harmful to ceramic strength.

The authors concluded that 75 μm diamond grinding induces significant damage in all four ceramics. 3Y-TZP showed the least strength loss at 12%, while dense Al2O3 had the highest at 49%. Alumina and glass-infiltrated variants also showed notable strength reductions. The findings suggest that 75 μm is too coarse for final shaping. The authors propose using finer grits to minimize damage. They recommend sequential use of finer diamonds after reshaping. Margins and connectors require special attention due to vulnerability. The study implies that current finishing protocols may need revision to preserve ceramic strength.