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REDUCED LIGHT ENERGY DENSITY DECREASES POST‐GEL CONTRACTON WHILE MAINTAINING DEGREE OF CONVERSION IN COMPOSITES
Author(s) -
Sakaguchi R.L.,
Berge H.X.
Publication year - 2001
Publication title -
journal of esthetic and restorative dentistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.919
H-Index - 60
eISSN - 1708-8240
pISSN - 1496-4155
DOI - 10.1111/j.1708-8240.2001.tb00440.x
Subject(s) - materials science , composite material , light intensity , polymerization , curing (chemistry) , composite number , light energy , light guide , intensity (physics) , fourier transform infrared spectroscopy , irradiation , degree (music) , optics , light source , polymer , physics , nuclear physics , acoustics
Objective : The purpose of this study was to evaluate the effects of curing‐light energy density on degree of conversion and polymerization contraction stress of a hybrid composite resin. Materials and Methods : Specimens of Bisfil P (Bisco, Inc., Schaumburg, Illinois) were fabricated. The specimens were 5.4 mm in diameter by 1.7 mm in thickness. Five groups of six specimens were cured using different light‐intensity protocols. The control group had the highest light intensity, at 337 mW/cm 2 . Three groups were light‐cured with modified light intensities, which were 71%, 49%, and 34% of the control intensity. In these four groups, the composite was light‐cured for 40 seconds, with only the intensity of the light varying. In the fifth group, specimens were irradiated for 20 seconds with a reduced intensity (241 mW/cm 2 ), followed by 20 seconds at high intensity (337 mW/cm 2 ). A light guide was positioned at 7 mm from the top surface of each specimen during the polymerization. Linear polymerization contraction was measured using electrical strain gauges positioned at the bottom of the specimens. One day after curing, specimens were polished to 600‐grit, and chips were removed with a scalpel from the top and the bottom surfaces of each of the samples to evaluate the degree of conversion using Fourier transform infrared spectroscopy. Results : The control group (337 mWlcm 2 ) had the highest degree of conversion at top and bottom surfaces. The degree of conversion of the specimens cured with the two‐step method was not significantly different from the values of those cured at either higher or lower intensity for 40 seconds. The linear contraction strain for the specimens cured with the two‐step method was not significantly different from that of the sample cured at the lower intensity for 40 seconds. Also, the post‐gel contraction strain increased linearly as the intensity of the light increased. Conclusions : The degree of conversion was more sensitive to changes in light intensity at the bottom of the composite than at the top. Also, strain was linearly related to light intensity (i.e., greater intensity = more strain). Finally, the specimens cured with the two‐step method showed a 21.8% reduction from the contraction strain predicted from a light energy density calculation.