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Relation between cavity design and marginal adaptation in a machine-milled ceramic restorative system.

The purpose of the current study was to evaluate the influence of inclination of the cusp as well as convergence/divergence of the cavity wall on marginal adaptation in a machine-milled ceramic restorative system. Sixty inlay specimens were prepared from a pre-fabricated feldspathic porcelain (Vitablocs Mark 2) by means of a computer integrated manufacturing system (Cerec 2). Specimens were divided into 12 groups according to original cavity preparations consisting of four inclinations of the cusp (0 degree, 15 degrees, 30 degrees and 45 degrees) and three types of cavity form (tapered box, regular box, and undercut box). The restorations were cemented with a dual-activated luting agent (Clapearl DC) and cut into two halves with a low speed cutting saw, after which adaptation at the occlusal surface of each inlay specimen was measured with a microscope. The results showed that the inclination of the cusp did not affect adaptation of the restorations (P > 0.05), whereas the inlay specimens inserted into undercut cavity preparation exhibited significantly poor adaptation as compared with those inserted into regular and tapered cavities in two inclinations of the cusp (0 degree and 15 degrees; P < 0.05). The experimental results suggest that either regular or tapered box form cavity preparation is preferable to the undercut box form to improve occlusal marginal adaptation of the Cerec 2 ceramic restorative system.