Optimization of resilience and stress distribution in porcelain veneers for the treatment of crown-fractured incisors

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 resilienc e and stress distribution. The treatment of 1/3-crown fractures and 2/3-cro wn fractures was investigated using different designs of facial porcelain v eneers with and without underlying composite buildup. The stress distributi on and tooth compliance were assessed in a numeric model reproducing a 2-di mensional buccolingual cross section of an incisor. A 50-N facial force was applied to simulate an incisal impact situation. The facial surface tangen tial stresses were calculated and the maximum displacement (horizontal dire ction) at the most incisal node of the enamel surface was also recorded and used to calculate the tooth compliance (ie, displacement/load or resilienc e) for each test condition. Tensile stresses were generated on the facial s urface of the porcelain laminates with a similar pattern for all test condi tions, the cervical part of the crown being the most quiescent area. Substa ntial differences appeared in the incisal half of the crown, the lowest str esses being observed for extensively fractured teeth restored without compo site buildup (facial peaks at approximate to 33 MPa). Fractured teeth resto red with minimal veneers and a "dentin-like" composite buildup showed stres s patterns similar to the intact tooth (facial peaks at approximate to 50 M Pa). The natural tooth gave the highest tooth compliance or flexibility All restorative designs featured increased tooth stiffness. However, the origi nal 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 complian ce and stress distribution can be modulated by the combination of composite and ceramics. Optimized configurations can be reached to reproduce the ori ginal biomechanical behavior of the intact tooth. The use of ceramic alone generates low stress concentrations, but also less compliant restored teeth .