Irradiance effects on the mechanical properties of universal hybrid and flowable hybrid resin composites.
OBJECTIVE
A potential problem with high-intensity lights might be failure of polymer chains to grow and cross-link in a desired fashion, thereby affecting the structure and properties of the polymers formed. The purpose of this study was to evaluate mechanical properties of resin composites polymerized using four different light-curing units.


METHODS
A conventional quartz-tungsten-halogen (QTH) light, a soft-start light, an argon-ion laser, and a plasma-arc curing light were used to polymerize disk-shaped (9.0mm diameter x 1.0 mm high) and cylinder-shaped (4mm diameter x 8 mm high) specimens of a universal hybrid and a flowable hybrid composite. Biaxial flexure strength, fracture toughness, hardness, compressive strength, and diametral tensile strength were determined for each composite.


RESULTS
The use of the plasma-arc curing light, a high-intensity light, resulted in significantly lower hardness for the universal hybrid composite compared with the hardness obtained using the conventional QTH and the soft-start units. Hardness was the only mechanical property that was adversely affected by the use of a high-intensity light.


CONCLUSIONS
High-intensity lights might affect some resin composite mechanical properties, but this effect cannot be generalized to all resin composites and all properties.
Department of Restorative Dentistry, Faculty of Dental Medicine, University of Montreal, C.P. 6128, Succursale Centre-Ville, H3C 3J7, Montreal, Que., Canada. annie.st-georges@umontreal.ca
Annie J
AJ
St-Georges
Edward J
EJ
Swift
Jeffrey Y
JY
Thompson
Harald O
HO
Heymann
D003188:Composite Resins / Q000528:radiation effects*; D019245:Compressive Strength / Q000528:radiation effects; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D006219:Halogens; D006244:Hardness / Q000528:radiation effects; D007834:Lasers; D008027:Light; D008422:Materials Testing; D018583:Pliability / Q000528:radiation effects; D019279:Resin Cements / Q000528:radiation effects*; D013718:Tensile Strength / Q000528:radiation effects; D014978:Xenon
D003188:Composite Resins; D006219:Halogens; D019279:Resin Cements; C102735:Revolution (composite resin); C065770:Herculite XR; D014978:Xenon