Heat transfer in light activated dental resin composites

Abstract

The objective of this research is to design a satisfactory analytical and experimental model so as to determine the heat generated during the process of polymerization in the light-activated composite dental resin materials in the process of restoration of cavities in teeth. When the curing light is subjected at the top surface of the composite resin, the overall temperature at the pulp-dentine junction increases. This temperature rise is due to the generation of heat within the composite resin. The energy released by the light activation unit along with the exothermic polymerization reaction, which occurs within the monomer molecules of the resin compound, increases the temperature at the pulp-dentin junction. With the increase of the temperature beyond a certain scale (~ 20 oF ),the condition of the nerves and blood vessel at the pulp-dentin junction deteriorates in 60% of cases studied, and the pulp fails to recover from the intra-pulpal temperature increase. A major conclusion is that the restorative resin compound which produces the minimum temperature rise over the time-period of curing, ~ 40 s is the best composite to use for dental restoration purpose. In this paper the temperature rise due to polymerization for the three composite dental resins such as, 3M^TM ESPE^TM Z100^TM Restorative, Filtek^TM LS Low Shrink Posterior Restorative System, and 3MTM ESPETM Filtek Bulk Fill Flowable Restorative (assumed to be made up off 100% resins) are measured. The depth of curing of the restorative resin is equally important as the generation of heat. If the resin is not fully cured, i.e., incomplete polymerization occurs then it can adversely affect the mechanical properties, environmental resistance, wear behavior and biocompatibility with the pulpal tissue of these restorative materials. So, the knowledge of the heat generation and curing depth are essential in determining the effectiveness of a resin from the restoration point of view. To determine the two parameters; the heat generation due to polymerization of the resins and the curing depth, a detailed literature review is done on some relating topics in Chapter 1, so as to create a foundation for the thesis problem. Analysis and experiments have been conducted. The temperature rise versus time and temperature rise versus the curing depth are measured using thermal infrared techniques. Experimental results are compared to an one-dimensional heat conduction model for which the solutions is obtained using the general integral transform method. The comparison between measurement and prediction is good from the trend and shape of the plots point of view but did not agree well on the basis of the values of temperature, time and specimen depth. As the curing depth of the three resins are well beyond 5-6 mm (practical filling depth) , so all of them could be used for the dental restorative purpose. But the results showed the heat generation due to polymerization is highest for 3MTM ESPETM Filtek Bulk Fill Flowable Restorative and lowest for 3M^TM ESPE^TM Z100^TM Restorative. Thus this makes 3M^TM ESPE^TM Z100^TM Restorative the most suitable restorative resin out of the three for dental filling purpose.