Stress analysis of metal-free polymer crowns using the three-dimensional finite element method.
OBJECTIVE
The purpose of this study was to evaluate the stress distribution under various loading conditions within posterior metal-free crowns made of new composite materials.


METHODS
A three-dimensional finite element model representing a mandibular first molar was constructed. Variations of the model had crowns of two types of composite, a glass ceramic, and porcelain fused to metal. A load of 600 N, simulating the maximum bite force, was applied vertically to the crowns. Loads of 225 N, simulating masticatory force, were applied from three directions (vertically, at a 45-degree angle, and horizontally).


RESULTS
The stress distributions in both types of composite crown were similar to that of the glass-ceramic crown. In the test simulating maximum bite force, the maximum tensile stresses on all crowns (17.9 to 18.3 MPa) concentrated around the loading points. In the masticatory force-stimulation test, the specimens experienced maximum tensile stresses of 20.3 to 26.6 MPa under a horizontal load and 10.9 to 11.0 MPa under a vertical load. When the load was applied horizontally, the maximum tensile stress was observed around the loading points on the surface in the case of composite and glass-ceramic crowns, and in the cervical area of the metal coping in the porcelain-fused-to-metal crowns.


CONCLUSIONS
It would appear that the strength of occlusal contact points is important to the integrity of posterior metal-free crowns made of new composite materials and that bite forces applied from the horizontal direction are a critical factor determining success and failure.
Nakamura
T
T
Department of Fixed Prosthodontics, Osaka University Faculty of Dentistry, 1-8 Yamadaoka, Suita, Osaka 5650871, Japan. tnakamur@dent.osaka-u.ac.jp
Imanishi
A
A
Kashima
H
H
Ohyama
T
T
Ishigaki
S
S
D000538:Aluminum Silicates / Q000737:chemistry; D001732:Bite Force; D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003198:Computer Simulation; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry; D020342:Finite Element Analysis; D005898:Glass / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008334:Mandible; D016876:Metal Ceramic Alloys / Q000737:chemistry; D008954:Models, Biological; D008963:Molar; D011108:Polymers / Q000737:chemistry*; D012823:Silicate Cement / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D016474:Weight-Bearing
D000538:Aluminum Silicates; D003188:Composite Resins; D005899:Glass Ionomer Cements; D006047:Gold Alloys; C075815:IPS-Empress ceramic; D016876:Metal Ceramic Alloys; D011108:Polymers; C111131:VMK 68; C111282:dental polyglass; D003776:Dental Porcelain; D012823:Silicate Cement