Effect of photoactivation protocol and radiant exposure on monomer conversion and flexural strength of a resin composite after water and ethanol storage.
The use of soft-start photoactivation to reduce shrinkage stress has become widespread in restorative dentistry. However, an increased susceptibility to ethanol degradation of polymers formed by pulse-delay photoactivation was reported. It was hypothesized that reductions in flexural strength after ethanol storage were related not only to low curing rates, but also to the radiant exposure employed. A commercial composite was subjected to different curing protocols (continuous at high irradiance, continuous at low irradiance, and pulse-delay) and radiant exposures (6, 12, and 24 J/cm2). After 48 h, differences in degree of conversion were minimal and no differences in strength were detected among specimens stored in water. Ethanol storage caused significant strength reductions in pulse-delay and low irradiance specimens that received 6 J/cm2. The results suggest that when low irradiances or pulse-delay methods are used, a relatively high radiant exposure is necessary to originate a polymer network structure similar to that obtained by continuous high irradiance photoactivation.
Gonçalves
F
F
Department of Dental Materials, University of São Paulo, School of Dentistry, Av. Prof. Lineu Prestes, 2227, São Paulo, 05508-900, Brazil.
Calheiros
F C
FC
Witzel
M F
MF
Kawano
Y
Y
Braga
R R
RR
D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D000431:Ethanol / Q000737:chemistry*; D008027:Light; D008422:Materials Testing; D010777:Photochemistry; D018583:Pliability; D013718:Tensile Strength; D014867:Water / Q000737:chemistry*
D003188:Composite Resins; D014867:Water; D000431:Ethanol