Bonded ceramic veneers and full crowns restore aesthetically anterior teeth. It is not clear if with this the original strength of teeth may be restored. The influence of the shape and extension of the preparation, is obscure. Objectives: This study investigated in vitro the fracture resistance of restored anterior teeth with increased amount of tissue removal. Methods: 70 intact, extracted, human, maxillary central incisors were divided into 7 groups (n=10): A: intact (control), B: classical veneer, C: ¾ veneer (enamel), D: ¾ veneer (dentin); E: full crown (enamel), F: full crown (dentin); G: veneer on abraded teeth. The removed tooth tissue was determined volumetrically. All IPS-Empress restorations were bonded with Syntac/Variolink II. After water storage for 21 days the teeth were thermocycled (2000x, 5-55°C) and loaded up to fracture (40° inclination, cross head speed 0.5mm/min). Fracture mode was analyzed in the SEM at 200x. Results: Restorations with enamel finishing lines fractured between 980N-1140N (median) and were statistically not different (Kruskal-Wallis test) from intact teeth. Dentin bonded restorations (D, F) fractured significantly earlier (approx. 750N). There was no correlation between the amount of tissue removed and the fracture strength. The predominantly cohesive fracture mode within the tooth structure indicated a stable bond of the restorations. The poorer result with dentin bonded restorations may be explained by the larger difference in modulus of elasticity. Conclusions: Bonded IPS-Empress veneers and crowns are able to restore teeth to their original strength, provided that the finishing line is located in enamel.

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