Abstract: Objective: To investigate the failure mode of porcelain laminates on prepared- and unprepared- anterior teeth in order to compare their longevity and success rate. Methods: Thirty extracted maxillary central incisors were randomly divided into 3 groups regarding their preparation methods. The preparation methods were full-preparation (group A), full-preparation and finishing with fine diamond bur (group B), and no-preparation, only grinding with diamond bur (group C). After conditioning the teeth, ceramic veneers (IPS e.max) were silanated and then cemented with DuoLink luting cement. The shear bond strength was measured for each group and failure mode was determined by stereomicroscopic examination. Results: Group C exhibited the highest shear bond strength. The shear bond strength was significantly different between groups C and B (P< 0.05). However, the difference between group A and C was insignificant, as was the difference between group A and B (P>0.05). Adhesion failure mode was found to be more common than the cohesive mode. Conclusion: Regarding the failure mode of unprepared anterior teeth to porcelain laminate veneers yielded by this study, no-preparation veneers might be used when the enamel is affected by wearing, trauma, or abrasion. It can also be used in patients who refuse the treatments which involve tooth reduction and preparation.

Key words: Veneer, Lithium silicatte glass ceramics, Shear bonding strength, Tooth preparation, Failure mode