title: Flexural strength and modulus of a step-cured resin composite.
abstract: In an attempt to reduce marginal contraction gaps, a step-curing mode of light polymerization of resin composite has been proposed. It was hypothesized that such an exposure mode, having an initial reduced curing rate, would result in composite having a lower modulus of elasticity than composite exposed in one step. The composite was initially exposed to power density levels of 50, 100, 150, or 200 mW/cm2 for durations of 10, 20, or 40 s. The final exposure and the exposure of the control group were performed at 750 mW/cm2 for 20 s. It was found that certain modes of two-step exposure resulted in a lower flexural modulus than did a one-step exposure of constant, high power density. Regression analysis showed, with statistical significance, that flexural modulus was relatively high following a short initial exposure at low power density or using a long initial exposure at high power density. Conversely, flexural modulus was relatively low following a long initial exposure at low power density or using a short initial exposure at high power density. The results were explained by probable differences in degree of conversion and cross-link density of the polymer network.
authors.affiliation: Department of Dental Materials, School of Dentistry, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark. ea@odont.ku.dk
authors.forename: Erik
authors.initials: E
authors.lastname: Asmussen
authors.forename: Anne
authors.initials: A
authors.lastname: Peutzfeldt
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D004548:Elasticity; D006801:Humans; D008027:Light; D008422:Materials Testing; D018583:Pliability; D011108:Polymers / Q000737:chemistry; D012822:Silicon Dioxide; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D015040:Zirconium
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium