The clinical challenge of achieving marginal adaptation in direct and indirect restorations

The clinical longevity of tooth-coloured restorations, whether direct or indirect, using composites and ceramics, greatly depends on the quality and stability of their marginal adaptation. In this issue, two interesting studies 7,15 bring this subject and lead us to an exciting discussion. Poor marginal adaptation of direct and indirect restorations exposes the dentin pulp complex to the oral environment, rendering the restorations susceptible to microleakage and plaque retention. This infiltration can lead to recurrent caries, postoperative sensitivity, pathologic pulpal changes, and restoration failures 2. Resin composites have been widely used in direct restorative procedures due to their good esthetics and ability to adhere to tooth structure using adhesive. Despite the development of the resin composites, the conversion of the resin composite monomers into a polymer network is accompanied by a bulk contraction leading to 1.67%-5.68% volumetric polymerization shrinkage 5. When shrinkage stress exceeds the bond strength of the adhesive interface or the tooth's cohesive strength, the interfacial quality of the restoration is damaged, generating gap formation (10–15 μm) 9. Considered as most responsible for the poor adaptation of composite restorations, the polymerization shrinkage is an inherent characteristic of the composites and directly associated to their composition 1,3. To reduce the effects of polymerization shrinkage and the internal/ marginal gap formation, modications in material composition have been suggested modications in material composition (modied methacrylate organic matrixes 7,17 and higher photoinitiator concentrations 1 , for example) as well in restoration techniques 10. The latter includes C-factor control, incremental filling, modulation of the irradiance used for photocuring the composite, use of preheated composite resin, and applying owable composite resin as a liner 10,12,18. In this context and considering the promising results 17 regarding the volumetric shrinkage in methacrylate organic matrixes modified with polyhedral oligomeric silsesquioxane (POSS), Correa Netto, et al. 7 (2015) evaluated the marginal integrity of restorations produced with a model composite based on POSS. To produce the model composite, 25 wt.% of UDMA from the methacrylate organic matrix was replaced by POSS (P25). Surprisingly, the authors observed that the methacrylate organic matrix modied by the addition of 25 wt.% of POSS did not improve the marginal integrity of class I restorations. In addition, this model composite presented the highest volumetric polymerization shrinkage and polymerization shrinkage stress, thus reinforcing the need for future studies on the inuence of other types of POSS molecules on the marginal adaptation and polymerization shrinkage. The potential …