Biomechanical evaluation of porcelain laminate veneer

Objectives:Evaluation of ceramic veneers with three types of tooth preparation and two kinds of ceramic material by fracture strength test and three dimensional finite element method (3-D FEM). Methods: For the fracture strength test, Seventy maxillary central inciors were randomly divided into seven equal groups. Each group was assigned a tooth preparation as follow:(1)(2) no incisal reduction (type I), (3)(4) 2mm incisal reduction (type L),(5)(6) 2mm incisal reduction and proximal reduction (type U), and (7) unrestored (control). Sixty teeth were prepared .veneers made from: (1)(3)(5) feldspathic porcelain; (2)(4)(6)IPS Empress ceramic. Ceramic veneers were bonded. Fracture loads were recorded with a mechanical testing machine. For 3-D FEM analysis, a three-dimensional finite element model was constructed by means of SCT scanning technology, digital image transfer and transcription. The analysis was performed using the structural analysis program (Ansys 6.1). Location and magnitude of Von Mises Stresses and tensile stresses and stress distribution were calculated in porcelain veneers complex. Results: Mean fracture (SD) loads in N were as follows: Group1: 278.61 (73.86); Group2: 276.55 (95.06); Group3: 295.17 (71.76); Group4: 274.81 (75.12); Group5: 303.42 (96.87); Group6: 353.44 (89.55); Group7: 332.29 (60.06). ANOVA revealed that there was no statistically significant difference among the seven groups. FEM analysis showed that the high stress accumulated under the loading area and the facial cervical third area of porcelain veneer complex. The stress values of type U veneer seemed the highest under loads imitating of protruding and central occlusion. The stress level increased a little with the rising of elastic modulus of the ceramic material. Conclusions: Both feldspathic porcelain and IPS Empress ceramic veneers can restore the original biomechanical behavior of the nature tooth. The facial cervical third area and direct loading area of porcelain veneer complex is the location of maximum comprehensive tensile stresses.