Scanning Electron Microscope Image Analysis of Bonding Surfaces following Removal of Composite Resin Restoration Using Er: YAG Laser: In Vitro Study

Abstract

It is impossible to remove tooth-colored restorations by mechanical means without unnecessary damage to the adjacent sound tooth structure. This study is aimed at investigating erbium-doped yttrium aluminum garnet (Er: YAG) laser (Hoya ConBio, VersaWave, CA, USA) in removing composite resin restorations and assessing the change in morphology of bonding surfaces using a scanning electron microscope (EDX, CAMSCANNER, 3200LV, UK). The investigators collected thirty extracted sound human premolar teeth for this investigation, and the conventional design class V cavity was prepared on the buccal surface of each specimen. The specimens were allocated randomly into three groups, according to the procedure used for the ablation of the composite restoration: group A (high-speed diamond fissure bur), group B, and group C (Er: YAG laser) using a different pulse repetition rate of 20 Hz (group B) and 25 Hz (group C). The AutoCAD software program (Autodesk, Inc., 2016) was used to calculate the surface area and the resulting dimensional change of the cavities after restoration removal. The cavities were filled with composite resin and randomly assigned into two groups conforming to the methods applied to eliminate the restoration; diamond turbine fissure bur and laser. In each group, two specimens were selected randomly for scanning electron microscope analysis of bonding surfaces. The least meantime for the composite resin removal was observed in the high-speed diamond bur, significantly less than both Er-YAG laser groups ( $p<0.001$ ). However, at a higher pulse repetition rate, time-consuming decreased. The results showed that laser is more conservative in removing composite resin restoration as the change was most remarkable in group A (0.800 mm), then group C (0.466 mm), and the slightest change is in group B (0.372 mm) ( $p=0.014$ ). The dentin surface of group A showed a smooth surface with no opened dentinal tubule and intact smear layer. In groups B and C, dentin surfaces were irregular, scaly, or flaky, and dentinal tubules were opened without a smear layer. Therefore, Er: YAG laser is effective for composite resin removal considering the parameters chosen in this study with fewer changes in cavity surface area and better microretentive features.