Effects Of Different Tooth Preparations On The 3D-Adaption Of Crowns Based On The Reverse Engineeing

Objective:Studying the effects of different tooth preparations on the 3D-adaption of CAD/CAM crowns based on the Reverse Engineering.Methods:Scanning the tooth preparation model of the mandibular first molar to build five different tooth preparations with the NX Imageware13.2 software. Designing the core with the exocad software and cutting 8 resin cores of each group. Finally, the scanning data of each resin core’s inner surface were used to analyze the 3D-adaption with the Geomagic Qualify 12 software.Results:According to the color-coded deviation images, deviation of the heavy chamfer shoulder was the smallest and the most uniform. While the other groups with sharp lines showed large deviation. After statistical analysis, the total deviation of heavy chamfer shoulder,135°shoulder, feather shoulder,90°houlder with lipped margins, and sharp marginal ridges preparation were (16.88±2.83) μm 、(26.88±3.61) μm 、(53.56±4.3) μm、 (51.38±4.46) μm、(47.19±4.62) μm.The heavy chamfer shoulder fits better than the 135°shoulder with statistical significance (P<0.05).The other groups fit poorly with no statistical significance between each group (P>0.05)Conclusion:Three-dimensional analysis with computer is a preferable method to study the 3D-adaption of crowns. Under this experimental condition, the heavy chamfer shoulder and round lines preparation is clinical recommended. While the 90°shoulder with lipped margins, 135°shoulder, sharp marginal ridges should be avoided.