Nonretentive Bonded Ceramic Partial Crowns: Concept and Simplified Protocol for Long-lasting Dental Restorations

Purpose: Adhesively luted partial ceramic crowns have been documented to be clinically more durable than direct composite restorations when minimally invasively restoring large defects (replacing two cusps or more) in posterior teeth. The clinical longevity of such restorations is largely determined by the tooth-preparation design, material selection and adhesive luting procedure. The most frequently recorded failure in medium- to long-term clinical trials is fracture of the restoration. The clinical protocol of adhesively luted partial ceramic crowns can be optimized by taking the etiology of these restoration fractures into account. In this article, a simplified nonretentive bonded ceramic partial crown concept is presented that aims to achieve an adhesively luted ceramic restoration - composite cement - residual tooth structure biomechanical unit that maximally resists functional aging. Therefore, the three primary components of the bonded restoration-cement-tooth complex must function in synergy. Methods, Results and Discussion: The clinical protocol starts with a tooth preparation designed to optimally absorb chewing stress. A stable, internally rounded and gently sloping tooth-preparation design with all outer margins inclined towards the tooth center assures a favorable and homogenous stress distribution with low cyclic fatigue subjected to the adhesive interface. This preparation form additionally enables the dental technician to fabricate a well-seating and -fitting ceramic restoration of uniform thickness. As restoration material, monolithic lithium-disilicate glass ceramic is sufficiently strong for the partial crown indication and preferred in order to decrease the fracture risk. Clinically essential for a long-lasting restoration is the optimal bond that can be obtained by combined micromechanical interlocking and chemical bonding of composite cement to hydrofluoric acid-etched and silanized glass ceramic. Conclusion: The clinical effectiveness of this nonretentive bonded ceramic partial crown concept is confirmed by the overall high success rate as well as the very low fracture and debonding rate, as was recorded in long-term clinical trials. Keywords: overlay, onlay, tooth preparation, glass ceramic, indirect restoration