Marginal fit and short-term clinical performance of porcelain-veneered CICERO, CEREC, and Procera onlays

Onlay preparations are very complex surfaces for computer surface digitization, CAD, and CAM of all-ceramic onlay cores.

This study tested the hypothesis that onlays can be fabricated with CICERO, CEREC, and Procera core technologies.

Fifteen mandibular and 10 maxillary molars were prepared for onlays in 17 patients (11 women and 6 men). The onlay design was experimental. Molars were prepared with deep gingival chamfers in the proximal boxes and around the functional cusps. The nonfunctional cusps were prepared with broad bevels. Eight stone dies of preparations were measured with a laser beam (CICERO), 10 dies with a light beam (CEREC), and 7 dies with a contact probe (Procera). Two onlay cores were produced for the same stone die. One core was used to analyze fit on the stone die, and the other core was porcelain veneered for optimizing anatomy, esthetics, and fit of the onlay and cemented. The fit of the onlay core on the stone die and the cement width on a stone cast were measured by a microscopic digital imaging system. The onlays were evaluated for function every 6 months for 2 years.

Measurements of the margins by the CICERO system were (1) precise (error <4%) and (2) accurate with an SD of less than 9 microm. The proposed onlay preparation design met the requirement that all points of the surface be visible from a single point of view for optical 3-dimensional mapping by the CEREC system. For the surface measurements by the Procera contact probe, the orientation of the sapphire tip toward the preparation surface was critical, and it was necessary to apply wax to smooth internal edges. The marginal gaps of the CICERO, CEREC, and Procera cores on the stone dies were 74 microm (SD 15), 85 microm (SD 40), and 68 microm (SD 53), respectively. The cement width was 81 microm (SD 64). No fractures occurred.

Marginal gaps for the onlay cores were no more than 85 microm. The cement width of the semicomputer-produced onlays of 81 microm was a favorable measurement value for a clinically acceptable, strong all-ceramic onlay. However, this value as well as anatomy and esthetics of the onlay depended on the craftsmanship of the porcelain veneering by the dental technician.