Ceramic laminate veneers: effect of preparation design and ceramic thickness on fracture resistance and marginal quality in vitro

Eighty human central incisors were randomly assigned to 10 groups (n = 8) with five different preparation designs: non-prep (NP), minimally invasive (MI) = exclusively enamel-bonded, semi-invasive (SI) = 50% bonded in dentin, invasive (I) = 100% in dentin, and semi-invasive with two additional class III composite resin restorations (SI-C). IPS InLine veneers were fabricated in two thicknesses (L1 = 0.2–0.5 mm; L2 = 0.5–1.2 mm). After adhesive luting (OptiBond FL, Variolink Veneer) with light curing and polishing, specimens were stored in distilled water at 37 °C for 21 days, then thermocycled (2000 cycles between + 5 and + 55 °C), and finally mechanically loaded at the incisal edge at an angle of 45° for 2,000,000 cycles at 50 N und further 1,000,000 cycles at 100 N. Impressions were taken initially, after thermocycling, and after every 250,000 mechanical cycles in order to evaluate cracks and margin quality under a SEM. The veneers were evaluated in a light microscope (× 20) for cracks, chippings, partial, and catastrophic fractures.