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.
St-Georges
Annie J
AJ
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
Swift
Edward J
EJ
Thompson
Jeffrey Y
JY
Heymann
Harald O
HO
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