Adhesive Cementation and the Strengthening of All-Ceramic Dental Restorations

Dental ceramics are extensively used to restore damaged or missing tooth structure but these fracture in service. Finite element analysis and quantitative fractography of failed restorations have demonstrated that all-ceramic crowns fracture due to the extension of pre-existing surface defects that occupy the inner 'fit' surface of the restoration under tensile loading. Clinically the environment of the inner surface defects is influenced by the dental cement used to retain the restoration on the prepared tooth structure. The use of methacrylate resin-based cements is associated with enhanced clinical performance and in vitro laboratory investigations have demonstrated that thin coatings of resin-based cements can significantly increase the flexural strength of a number of all-ceramic crown materials. Mechanisms to account for the apparent strengthening have been proposed including the generation of crack closure stresses, crack 'healing' effects and the creation of a 'hybrid layer' which radically modifies the stress patterns in the region of the critical defect. However, conjecture remains regarding the basis of the strengthening mechanism, thereby preventing the optimisation of resin-based cementation materials and clinical techniques. The aim of the current article is to provide an insight into resin cementation and the mechanisms by which adhesive cements may determine all-ceramic restoration performance. (C) Koninklijke Brill NV, Leiden, 2009