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°, 15°, 30° and 45°) 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° and 15°; 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.