Approx. Filler conc.(wt%) THERMAL STUDIES ON DIFFERENT CLASSES OF CLINICAL DENTAL COMPOSITES S. Sampath*, Riyadh Military Hospital, Saudi Arabia, S.R. Girish, Manipal Institute ofTechnology, India Introduction Dental composites: Highly esthetic materials for restoration of teeth. General Composition Matrix Phase: BisGMA, TEGDMA, UDMA, BisEMA, etc. Filler Phase: Silica, Glass, Quartz, Ceramic, Prepolymerized resin, etc. Silane coupling agent Photoinitiator: Camphorquinone (~470nm). Amine accelerators, pigments, etc. Some Clinical Composites analyzed thermally: Composite Type Resin Matrix Approx. Filler conc.(wt%) Fillers Microhybrid BisGMA with hexamathylene diisocyanate, BisEMA and TEGDMA. 77 Silicate glass particles (<1 µm) and nanosilica (.04 µm) fillers Superior strength Nanocomposite Dimethacrylate resin, Methacrylate modified polysiloxane particles (2-3 nm) 76 Glass filler(1µm), Methacrylate modified SiO2 nanofiller (10nm) Flowable Composite BisGMA(~14%), TEGDMA(~8%), UDMA(~15%). 63 Barium glass, silica, ytterbiumtrifluoride Fluoride Releasing Composite BisGMA(~12%), TEGDMA(~24%), UDMA(~24%). 40 Fluorosilicate glass, silica. Aims Comparing thermal characteristics of different clinical composites. Investigating the quality of polymerization via thermal methods Methods Curing Composite Samples Irradiation of molded pastes with a Halogen curing lamp (500mW/cm2). Curing Time: 20 seconds Final sample weight: ~10mg. Thermal Analyses Thermogravimetric Analysis -to assess thermal stability & weight loss. SHIMADZU DTG-60/60H used. DSC Analysis -to assess any residual reactivities. -Differential Scanning Calorimeter (SHIMADZU DSC-60) used. two heating cycles for every sample from 30C-200C at 5C/min, to assess effect of heat. Results DSC Analyses Glass Transition Temperature (midpoint in the data) 129C for all composite types. Attributable to a highly crosslinked structure in the photocured samples. Enthalpy Changes No exotherms (residual reactivity) noted Signifies complete cure with blue light Endotherms in all composites Structural rearrangements Relaxation of Polymerization Stress Order of Enthalpy Change Largest Endotherm for the Fluoride-releasing composite. Possible greater molecular mobility/mass loss for Fluoride Releasing Composite. Onset Temperatures for Thermal Events Higher Organic Content in Flowable Composite Lower Endothrem Onset. Presence of organically modified polysiloxane particles in the resin matrix of Nanocomposites. TGA Analyses Greater Proportion of Resin (esp Low Viscosity TEGDMA) Higher Weight Loss for Flowable & Fluoride Releasing Composites. Initial Mass Loss (~ 282 C) Total Mass Loss (~500 C) Microhybrid 3.4 ± 1.8% 24.3 ± 0.6% Nanocomposite 4 ± 1.1% 20 ± 0.5% Initial Mass Loss (~ 282 C) Total Mass Loss (~500 C) Flowable Composite 12 ± 1.6% 38 ± 3% F-Releasing Composite 19.1 ± 7% 46 ± 3% References The clinical evaluation of heat-treated composite resin inlay. J. Am. Dent. Assoc. 1990;120: 177–81. M.-H. Chen. Update on Dental Nanocomposites. J Dent Res 2010; 89: 549-560. Thermal characterization of dental composites by TG/DTG and DSC .J Therm Anal Calorim 2010; 102:361–367. Thermal analysis of light-curing composites. J Therm Anal Calorim 2010; 102:107–111. Conclusions Generally high Glass Transitition Temperatures (Tg) for all the tested composites. Fluoride-releasing composite shows higher enthalpy changes and mass losses. Adequate levels of polymerization in this study (high Tg , no exotherms and similar behaviour on second run). *Corresponding Author: Dr.Sheela, Dept. of Dentistry, RMH, PO Box 264, KSA 11944 Email: sheelasamp@gmail.com