Evaluation of a reinforced slot design for CEREC system to restore extensively compromised premolars.
OBJECTIVE
The structural stability and adhesive strength of a large-cavity premolar with a CEREC restoration is a frequent problem in long-term use. This study sought to determine whether an additional reinforced slot could increase tooth/ceramic retention using finite element (FE) analysis and fracture testing.


METHODS
The cavity was designed in a typical MODL restoration failure shape when the lingual cusp has been lost. Two FE restored-tooth models with different cavity designs were created using image processing, contour stacking, and mesh generation. Interfacial (normal and shear) stresses were then calculated with and without the slot design for restored teeth under lateral and axial forces and different interfacial conditions (bonded and de-bonding). For validation, a fracture experiment was performed with and without reinforced slot designs for large ceramic CEREC restorations.


RESULTS
The maximum stresses at the buccal wall increased when a lateral occlusal force acted on the restored tooth with a slot design. Conversely, the interfacial stresses decreased when the restored tooth received a uniform axial occlusal force. After de-bonding on the buccal tooth/ceramic interface, the stresses increased by an average factor of three over those obtained with a bonded interface. The fracture forces were consistent with the tendencies predicted in FE analyses.


CONCLUSIONS
An additional reinforced slot for the CEREC restoration of a large cavity could increase retention when a restored tooth receives an axial occlusal load. However, the benefits of a slot seem to be doubtful for a premolar often subjected to a lateral load.
Lin
Chun-Li
CL
Department of Mechanical Engineering, Graduate Institute of Medical Mechatronics, Chang Gung University, 259 Wen-Hua 1st Road, Kwei-Shan, Tao-Yuan 333, Taiwan. cllin@mail.cgu.edu.tw
Chang
Yen-Hsiang
YH
Chang
Wen-Jen
WJ
Cheng
Ming-Hsiang
MH
D000704:Analysis of Variance; D001641:Bicuspid / Q000737:chemistry*; D002516:Ceramics / Q000737:chemistry*; D019245:Compressive Strength; D003737:Dental Cavity Preparation / Q000379:methods*; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D020342:Finite Element Analysis; D006801:Humans; D033081:Shear Strength; D016474:Weight-Bearing
C074543:Cerec