Fracture Resistance of Different Designs of Zirconia Surveyed Crowns.

Objectives: To assess the fracture resistance of zirconia CAD/ CAM surveyed crowns with two different occlusal rest seat designs.
Methods: Two mandibular second premolar typodont teeth were prepared for full coverage crowns to accommodate a surveyed crown with disto-occlusal rest seat (narrow rest seats), surveyed crown with distal interproximal rest seat (wide rest seats).
The surveyed crowns were prepared with 1 mm rounded shoulder finish line and 1.5 mm occlusal reduction. Tooth preparations were scanned with a chairside intraoral scanner. The scanned restorations and the dies were fabricated using a 3D printer using model resin materials. Crowns were bonded to resin dies using Relyx Luting Cement. Then compression force was applied in a vertical direction using a 4 mm diameter steel bar at the center of each crown using Instron 5569 Universal. Restorations were loaded until fracture, then fracture resistance at maximum load was recorded as the maximum compressive force. The data were analyzed using Wilcoxon signed rank test with an α value of 0.05 using SPSS software.
Results: The mean standard deviation of maximum force was 2250 ± 335 N for narrow rest seat group. The mean standard deviation of maximum force was 2242 ± 293 N for wide rest seat group. Mean fracture resistance among narrow rest seats were higher than those among the wide rest seats but it was not statistically significant.
Conclusions: The use of narrow occlusal rest seat design in CAD-CAM all ceramic surveyed crowns may provide higher fracture resistance.