Influence of Coping Design on CAD/CAM All-Ceramic Crowns Using 3D-FEA

Objectives: The objective of this study was to evaluate, by 3D- FEA, the influence of the various coping materials, coping thickness and biting locations on the stress distribution in CAD/CAM produced all-ceramic crowns.

Methods: The CAD models of multi-layer all-ceramic crowns for maxillary canine produced with CAD/CAM technology were translated into a 3D FEA program. Two kinds of coping materials selected were Zirconia and Alumina. Coping was designed to thin and thick types. The biting locations were on the F1(centric occlusion) or E1( near incisal edge) or G1( near cingulum). The axial angles of the upper and lower canine were built up respectively 20.6° and 14.6° when contact. The force applied from the lower canine to upper canine was 120 N.

Results: (1).When using Zirconia as the coping material, all the highest Mon-Mises stresses no matter on the preparation or coping or veneering porcelain layers were lower than those of using Alumina. (2).As the thick coping was applied, the highest stress was still located on the lingual biting location. Once the thin coping was applied, the highest stress was transferred to the labial cervical third. (3).The more was the biting location near the incisal edge, the more was the stress concentrated in the labial cervical third. As increasing the coping thickness, the highest stress was transferred to the lingual cingulum area.

Conclusions: (1).As a coping material, Zirconia is better than Alumina when the all-ceramic crown was subjected to a higher biting stress. (2).When the coping is thin, the tooth preparation in labial cervical third should be mostly careful for avoiding stress concentration. (3).For avoiding stress concentrated in the labial cervical third, the biting location should be adjusted not near the incisal edge. Also, the dentists could increase the coping thickness for transferring the stress.