1. 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: 
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