Purpose : Marginal shape of abutment is one of the factors to effect on the fitness of zirconia crown. The aim of this study is to help clinicians set up specific guidelines on tooth preparation for CAD/CAM zirconia crown by evaluation of marginal and internal fitness of CAD/CAM zirconia core using abutment model reflecting tip design of diamond burs to be used in a dental clinic.

Material and method : 4 groups consisting of 10 specimens of abutment made with photo-polymerized resin(RC 31, EnvisionTEC, Germany) were fabricated with 3D printer(Ultra 2, EnvisionTEC, Germany). The margin shape of each group’s abutment is designed to reflect 4 types of tip design of diamond burs(torpedo bur, deep chamfer bur, sloped shoulder bur, shoulder bur) to be used in a dental clinic. And then, zirconia cores for abutments of 4 groups were fabricated by same technician with same CAD/CAM system. 5 zirconia cores of each group were adapted on the abutment without cement, and 5 zirconia cores were cemented on abutment with ZPC. After embedding the specimens in resin, we observed marginal and internal fitness on the cross-section of the resin block by recording 200~500 fold magnification.

Result : When experiments without cement, the measured value of the gap in the margin, internal line angle and occlusal surface of torpedo group and deep chamfer group were smaller than sloped shoulder and shoulder group. All result of ZPC cemented groups showed larger values than non-cemented group, especially shoulder group.

Conclusion : Torpedo and deep chamfer bur are clinically acceptable for CAD/CAM zirconia crown. However, sloped shoulder and shoulder bur showed relatively large gap in the finish line and occlusal surface, having large variations within the group.