Melbourne Dental School - Theses
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ItemA study of various factors that influence the success of posterior resin-based restorations( 2019)This thesis is centred on the investigation of several physical properties related to bulk-fill resin composites that may influence the success of posterior resin-based restorations. In addition, a test methodology to investigate the fracture toughness of brittle restorative materials was evaluated, including the potential influence of the storage medium. The thesis work begins with a systematic review comparing the clinical success rates of resin composite restorations in posterior teeth, over two time periods, namely 1995-2005 and 2006-2016. It was shown that the main failure reasons for posterior resin composite restorations changed slightly over these periods, with factors related to the material and tooth becoming more significant in the later period, although recurrent caries remained an important reason for failure. Based on the broad findings of the review, three laboratory-based projects were designed to examine the physical properties of resin-based composites, focusing on the recent bulk-fill restorative materials. The experiments also included the effects of polymerising light-curing units, since the new high irradiance (light intensity) units recommend shorter curing times. In addition, a study on fracture toughness of glass -ionomer cements were conducted to determine whether a simple fracture toughness test would provide useful outcomes for a brittle material such as GIC and whether an ion-containing storage medium such as artificial saliva would influence outcomes. The results of these experiments indicated that variations in material composition and curing light devices had a significant influence on the physical properties such as curing stress shrinkage, the combined temperature of polymerisation and curing light radiant exposure (energy), and wear after thermal ageing. A final experiment investigated the effects of the polymerisation shrinkage on the movement of tooth cusps when the resin composite was exposed to two different irradiances curing light devices. This experiment showed that the high irradiance produced greater and more rapid cuspal movement and a greater rise in temperature within the pulp chamber. The results probably cannot provide a direct translation to the clinical situation. However, it would seem that the use of bulk-fill resin composite materials needs to be managed more carefully than perhaps what has been recommended by manufacturers of such materials.