Luting Cement, the Stronghold or the Weak Link in Ceramic Restorations?

A luting agent for fixing indirect dental restorations has to be a sophisticated material as, apart from being biocompatible, it must allow complete seating, provide mechanical support, has to secure the retention and to seal the gap between restoration and tooth structure for many years of function in an aggressive bio-chemical and mechanical environment. Because of their adhesive potential, the latest generations of dental cements, the glass-ionomer and resin-based composites offer improved results. However, a major disadvantage of both classes of materials is their setting, being accompanied by shrinkage, which eventually leads to fracturing of the brittle ceramic. Apparently conflicting interests like being at the same time flexible as well as rigid, hold for luting cements for full ceramic restorations. The interaction between layer thickness, curing shrinkage stress, visco-elasticity, module and strength for a thin adhesive cement layer will be discussed in the perspective of durable functioning of ceramic restorations.