Thermal expansion coefficient of dental composites measured with strain gauges.
OBJECTIVE
A simple test method was developed to determine the coefficient of thermal expansion of prevailing restorative resin composites and to study the transient behavior as a function of temperature and repeated thermocycles.


METHODS
Strain gauges were used to determine the thermal expansion for seven commonly used restorative resin composites by measuring the instantaneous strain along with temperature change. The temperature was measured by means of a thermocouple, the tip of which was embedded in the composite. The differences among the test groups were analyzed using ANOVA, followed by Scheffé's multiple comparisons test.


RESULTS
The coefficient of thermal expansion determined for the composites tested was: 22.5 +/- 1.4 x 10(-6)/degree C (Z-100), 23.5 +/- 1.4 x 10(-6)/degree C (P-50), 32.6 +/- 1.6 x 10(-6)/degree C (Herculite XR), 34.1 +/- 1.8 x 10(-6)/degree C (APH), 35.4 +/- 1.4 x 10(-6)/degree C (Conquest), 41.6 +/- 1.5 x 10(-6)/degree C (Silux Plus), 44.7 +/- 1.2 x 10(-6)/degree C (Heliomolar). The coefficient was almost linear in the considered temperature range (26-75 degrees C) for all composites (r > 0.99) and decreased with each consecutive thermocycle (p < 0.1).


CONCLUSIONS
Thermally induced loads, introduced into restored teeth by the mismatch of the coefficient of thermal expansion of the tooth and the restorative material, may be related to microleakage and wear problems. A highly filled hybrid composite such as Z-100 had a coefficient of thermal expansion closest to that of the tooth crown, confirming other studies which demonstrated the benefits of high filler loading in matching the properties of the dental hard tissues.
Versluis
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Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, Minneapolis, USA. antheun@oranje.dent.umn.edu
Douglas
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Sakaguchi
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D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D008422:Materials Testing / Q000379:methods; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013816:Thermodynamics; D015040:Zirconium / Q000737:chemistry
D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; C092421:Conquest composite resin; C513708:Heliomolar; D011140:Polyurethanes; D019279:Resin Cements; C083568:Z100 composite resin; C065770:Herculite XR; C065771:P50 composite resin; C074741:Silux Plus; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium