High-Strength Porcelain Veneering of Zirconia Prosthetic Mimetic Restorations (PRIMERO) by Cognitive Design and Manufacturing

Esthetic prosthetic restorations, with natural reflection, color from within and color gradients influenced by the internal dentinal core anatomy can best be accomplished by veneered zirconia, rather than with crowns of color and structure graded monolithic zirconia. Concern about the high incidence of chipping with some of the porcelains for zirconia substructures has led to a massive shift from veneered zirconia to the use of monolithic zirconia for crowns and bridges. Because zirconia has four times the hardness of metal, initial concern about antagonist abrasion could with numerous studies be negated. Clinical long-term effects of lack of abrasion of full zirconia crowns, in comparison with 30-75 μm/year for surrounding and opposing dentition is still poorly documented. Massive crack formation in enamel probes has been reported in specimens after in-vitro fatigue testing with opposing monolithic zirconia. In-vitro and clinical studies have shown that only reinforcement of the structure of veneering material can prevent chipping. This article compares the fatigue behavior of three-unit bridges with a substructure of Primero zirconia veneered with Primero Enamel (PR) with bridges with Cercon Base zirconia inner-structure veneered with Ceramco PFZ and Cercon Ceram S (CR1 and CR2) and assess the possibilities and increase their scope to cognitive design and manufacturing of porcelain veneered zirconia crowns and bridges. Fatigue testing of four times eight 3-unit bridges were produced for each of the three porcelains and a reference. The results show that efficient crack-stopping prevented chipping with the PR bridges, while the bridges with conventional porcelains CR1 and CR2, showed failures. We conclude that chipping is mainly porcelain related. Cognitive design and fabrication of the dentin zirconia core will lead to prosthetic mimetic restorations (PRIMERO) with natural esthetics.