Optimization of Resilience and Stress Distribution in Porcelain Veneers for the Treatment of Crown-Fractured Incisors
Pascal Magne, DrMedDent/William H. Douglas, BDS, MS, PhD
The present study was conducted to define, when restoring extensive loss of dentin, the configuration of the restoration that will best reproduce the biomechanical properties of the intact original tooth in terms of resilience and stress distribution. The treatment of 1/3-crown fractures and 2/3-crown fractures was investigated using different designs of facial porcelain veneers with and without underlying composite buildup. The stress distribution and tooth compliance were assessed in a numeric model reproducing a 2-dimensional buccolingual cross section of an incisor. A 50-N facial force was applied to simulate an incisal impact situation. The facial surface tangential stresses were calculated, and the maximum displacement (horizontal direction) at the most incisal node of the enamel surface was also recorded and used to calculate the tooth compliance (ie, displacement/load or resilience) for each test condition. Tensile stresses were generated on the facial surface of the porcelain laminates with a similar pattern for all test conditions, the cervical part of the crown being the most quiescent area. Substantial differences appeared in the incisal half of the crown, the lowest stresses being observed for extensively fractured teeth restored without composite buildup (facial peaks at about 33 MPa). Fractured teeth restored with minimal veneers and a dentin-like composite buildup showed stress patterns similar to the intact tooth (facial peaks at about 50 MPa). The natural tooth gave the highest tooth compliance or flexibility. All restorative designs featured increased tooth stiffness. However, the original tooth compliance was almost restored when composite was used to replace the missing dentin, with the porcelain acting only as a facial and incisal enamel substitute. When restoring crown-fractured incisors, tooth compliance and stress distribution can be modulated by the combination of composite and ceramics. Optimized configurations can be reached to reproduce the original biomechanical behavior of the intact tooth. The use of ceramic alone generates low stress concentrations, but also less compliant restored teeth.