Direct restorations of root filled teeth

Abstract

© 2014 Dr. Nessrin Ahmad TahaRoot filled teeth are weakened by loss of strategic tooth structure through restorative procedures and caries, rather than by the endodontic procedures. In this context, the importance of a restoration which provides cuspal coverage has been highlighted, which incurs further removal of tooth structure and a higher cost. Direct restorations using resin composite materials have been advocated to save time and money while utilizing the bonding ability of these materials to tooth structure. However disadvantages of resin composites including polymerization shrinkage and subsequent problems of leakage, secondary caries and tooth fracture, have limited their adoption as an alternative restorative technique. The purpose of this project was to investigate direct resin composite restoration performance as a permanent filling in root filled teeth, in terms of cuspal movement, strain, microleakage and fracture strength in extracted teeth. In addition, the effect of various test conditions to simulate the clinical environment was investigated: periodontal ligament simulation, thermocycling and mechanical cycling. We also aimed to explore fracture patterns and mechanisms of fracture propagation and approaches to optimize the performance of bonded direct resin composites, including the use of low shrink resin composites, laminate restorations (closed sandwich technique and the open sandwich technique) with conventional and resin modified glass ionomer cements, to find out whether resin composites can restore strength and marginal integrity to serve as a long term functional restoration. It was found that laminate restorations had beneficial effects in terms of reducing cuspal deflection and marginal seal, with acceptable fracture strength. Thermocycling resulted in deterioration of the sealing ability of conventional glass ionomer cements, while neither thermocycling nor periodontal ligament simulation affected the fracture strength. Fracture is a two-step process: firstly interfacial debonding at the buccal or palatal interface, and secondly cuspal fracture beginning at the buccal line angle at the floor of the cavity. Both fracture and failure occurred in a consistent manner regardless of the cavity design, restorative technique (with or without a base) or the loading pattern (cyclic vs. ramped). Failure was predominantly adhesive and biphasic; after debonding the cusp is unsupported and may fracture immediately with the weakest point being the dentine-adhesive interface. Lines of evidence for this phenomenon were derived from load displacement curves, results from staining with methylene blue, micro CT images and crack propagation gauges. Furthermore SEM study of the fractured interface provides strong evidence for propagation of the interfacial crack from gingival to occlusal; with the occlusal interface the last region to fail. Therefore modifications that can reduce or eliminate the stress concentration at the interface may increase the force required to initiate or propagate a crack through this area