The influence of zirconia coping designs on maximum principal stress distribution in all-ceramic premolar crowns: A...

To evaluate the effects of different coping designs on maximum principal stresses in the veneering material using a finite element analysis method.

A maxillary first premolar tooth model was prepared. The primary and prepared tooth model were scanned with a 3D (three dimensional) scanner. Four different coping and veneer models were designed with 3D computer-aided design software: conventional design (DC); design with 3 mm palatal shoulder (DP); design with 1 mm buccal shoulder and 3 mm palatal shoulder (DB); and design with buccal facet (DF). After the models were designed, they were transferred to the finite element analysis (FEA) software for analyses. The middle points of the buccal, mesial, distal and palatal surfaces were determined in the cervical region. For all models, the maximum principal stress distributions and values of porcelain veneer were evaluated under centric occlusion loading and laterotrusive loading conditions with a FEA.

The maximum principal stress area decreased gradually from model DC to model DB on the buccal cervical region under centric occlusion loading. However, models DF and DP showed similar stress distribution. The maximum principal stress at the distal point decreased from DC (14.7 MPa) to DP (13.5 MPa) and DB (9.6 MPa), whereas increased in model DF (33 MPa). Under laterotrusive loading, both the palatal maximum principal stress area and the stress value at the palatal point (model DC: 13.1 MPa, model DP: 3 MPa, model DB: 4MPa) decreased with the palatal shoulder.

Increasing the height of the palatal shoulder may be a practical and efficient approach to reduce the maximum principal stress in all-ceramic crowns. Thus, the clinical failure as chipping in the all-ceramic crowns may be reduced.