Effect of bracket bonding with Er: YAG laser on nanomechanical properties of enamel

Abstract

Background: The aim of this study was to compare the effects of conventional acid etching and

laser etching on the nano-mechanical properties of the dental enamel using nano-indentation test.

Materials and Methods: In this experimental in vitro study, buccal surfaces of 10 premolars were

divided into three regions. One of the regions was etched with 37% phosphoric acid and another

etched with Er:YAG laser, the third region was not etched. The brackets were bonded to both of

etched regions. After thermocycling for 500 cycles, the brackets were removed and the teeth were

decoronated from the bracket bonding area. Seven nano-indentations were applied at 1-31 μm

depth from the enamel surface in each region. Mean values of the hardness and elastic modulus

were analyzed with repeated measures analysis of variance and Tukey HSD tests, using the SPSS

software (SPSS Inc., version16.0, Chicago, Il, USA). P < 0.05 was considered as signifi cant.

Results: The hardness up to 21 μm in depth and elastic modulus up to 6 μm in depth from the

enamel surface for laser-etched enamel had signifi cantly higher values than control enamel and the

hardness up to 11 μm in depth and elastic modulus up to 6 μm in depth for acid-etched enamel

had signifi cantly lower values than the control enamel.

Conclusion: The mechanical properties of the enamel were decreased after bracket bonding with

conventional acid etching and increased after bonding with Er:YAG laser.

Key Words: Elastic modulus, enamel, Er:YAG laser, hardness, nano-indentation test,orthodontic bracket