Influence of light-exposure methods and depths of cavity on the microhardness of dual-cured core build-up resin composites

Keiichi Yoshida,Xiangfeng Meng

doi:10.1590/1678-775720130359

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.

Highlights

Core build-up materials are often required to reconstruct and provide an ideal morphology to severely damaged teeth prior to their preparation for indirect foundation restorations
For the DC Core Plus (DCP), the Knoop hardness number (KHN) was effected by the light-exposure method (p=0.0001; F=1652.29), post-irradiation time (p=0.0001; F=606.09), depth of cavity (p=0.0001; F=1184.99), and all the interactions between all the aforementioned factors (p=0.0001)
For Unifil Core EM (UCE), significant differences were found between the light-exposure methods (p=0.0001; F=201.27), post-irradiation times (p=0.0001; F=857.15), and depth of cavity (p=0.0001; F=488.76); in addition, significant interactions were found between all the aforementioned factors (p=0.0001)

Summary

Introduction

Core build-up materials are often required to reconstruct and provide an ideal morphology to severely damaged teeth prior to their preparation for indirect foundation restorations. Despite substantial documented evidence of the long-term success of large amalgam restorations[26,40], resin composites, since the early days of self-cured materials, have been used for this purpose. Light-cured core build-up materials that are more convenient to use than chemically cured composites have been widely used[33]. Both these materials, have their disadvantages . 12,29 While chemically cured materials do not allow clinicians to adjust the setting time individually, light-cured resin composites do not ensure adequate polymerization in areas with limited access to the curing light. Resin-based composites are associated with polymerization shrinkage, causing stress development under confined conditions[36]. Time limitations when placing core build-up materials

Methods

Results

Discussion

Conclusion