Abstract

Background: Erbium-doped yttrium aluminum garnet (Er: YAG) laser for preparing dentinal surface alters dentin morphological characteristics which may interfere with bonding. This study aimed to evaluate the effect of different Er: YAG laser energy levels on shear bond strength (SBS) of composite resin to primary tooth dentin and to assess the morphological appearance of dentin by scanning electron microscope (SEM). Materials and Methods: In this in vitro study, 48 primary molars were sectioned mesio-distally (96 samples). About 64 sound buccal or lingual surfaces were randomly divided into 4 groups of 16 samples. Superficial dentin of buccal or lingual surfaces were exposed and polished up to 600-grit of silicon carbide paper. Dentinal surfaces were irradiated with different Er: YAG laser energy levels of 100, 200, 300 mJ/10 Hz. Sixteen specimens were not irradiated to serve as control. The Single Bond adhesive was applied over the acid-etched dentinal surfaces for all tested groups and composite resin cylinders were bonded to the samples. Following thermocycling, SBS of composite resin to dentin were measured and statistical analyses were done using ANOVA and least significant difference tests. For morphological analysis, specimens were examined by SEM. Results: The mean SBS was 15.72 ± 4.05, 23.04 ± 2.81, 34.57 ± 9.63 and 38.39 ± 8.15 megapascals in control, 100, 200, and 300 mJ groups, respectively. There was no significant difference in SBS of 200 and 300 mJ laser energies. SEM images showed that etching after Er: YAG laser irradiation left no smear layer and a few scaly and irregular surfaces were observed, with the widening of dentinal tubules openings. Conclusion: Power output of 200 and 300 mJ in primary tooth dentin preparation yielded highest bond strength but 200 mJ was safer and more effective.