Influence of light-exposure methods and depths of cavity on the
microhardness of dual-cured core build-up resin composites |
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Authors: | Keiichi YOSHIDA Xiangfeng MENG |
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Institution: | 1. Clinic of Fixed Prosthodontics, Nagasaki University Hospital, Nagasaki, Japan.;2. Department of Prosthodontics, The Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing, China. |
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Abstract: | ObjectiveThe purpose of this study was to evaluate the Knoop hardness number (KHN) of
dual-cured core build-up resin composites (DCBRCs) at 6 depths of cavity after 3
post-irradiation times by 4 light-exposure methods. Material and MethodsFive specimens each of DCBRCs (Clearfil DC Core Plus DCP] and
Unifil Core EM UCE]) were filled in acrylic resin blocks with a
semi-cylindrical cavity and light-cured using an LED light unit (power density:
1,000 mW/cm2)at the top surface by irradiation for 20 seconds (20 s),
40 seconds (40 s), bonding agent plus 20 seconds (B+20 s), or 40 seconds plus
light irradiation of both sides of each acrylic resin block for 40 seconds each
(120 s). KHN was measured at depths of 0.5, 2.0, 4.0, 6.0, 8.0, and 10.0 mm at 0.5
hours, 24 hours, and 7 days post-irradiation. Statistical analysis was performed
using repeated measures ANOVA and Tukey''s compromise post-hoc
test with a significance level of p<0.05. ResultsFor both DCBRCs, at 0.5 hours post-irradiation, the 20 s and 40 s methods showed
the highest KHN at depth of 0.5 mm. The 40 s method showed significantly higher
KHN than the 20 s method at all depths of cavity and post-irradiation times,
except UCE at depth of 0.5 mm (p<0.05). The 120 s method did not result in
significantly different KHN at all depths of cavity and post-irradiation times
(p>0.05). In DCP, and not UCE, at 24 hours and 7 days post-irradiation, the
B+20 s method showed significantly higher KHN at all depths of cavity, except the
depth of 0.5 mm (p<0.05). ConclusionKHN depends on the light-exposure method, use of bonding agent, depth of cavity,
post-irradiation time, and material brand. Based on the microhardness behavior,
DCBRCs are preferably prepared by the effective exposure method, when used for a
greater depth of cavity. |
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Keywords: | Composite resins Exposure time Hardness |
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