Shear bond strength of lingual brackets on enamel surface submitted to acid-etching or Nd:YAG laser irradiation

Abstract

The patient demand for aesthetic orthodontic solutions is driving for use of lingual brackets and laser irradiation can prevent dental caries in this region. This in vitro study is the first one in literature that aimed to quantify the shear bond strength (SBS) on direct lingual b rackets bonding after different enamel surface pre-treatments. 75 bovine incisor teeth were randomized in 5 groups (n=15): G1- untreated; G2- treated with acidulated phosphate fluoride gel (APF-gel, [F-] =1.23%, pH=3.3 to 3.9); G3- conditioned with 37% phosphoric acid (Condoc 37%, FGM, Brazil) and treated with APF-gel; G4- irradiated with Nd:YAG loser (1064nm, 0.6W, 10Hz- Laser Research) and treated APF-gel; GS- irradiated with Nd:YAG laser + conditioned with 37% phosphoric acid + treated with APF-gel. The positioning of the brackets was standardized during the bonding procedure using a positioner and Transbond XT adhesive (3M Unitek, USA) was used. After bonding, all samples were thermocycled (500 cycles between SoC and 55°C) and submitted to a 48h cariogenic challenge. After cycling, the samples were tested for shear bond strength (SBS) in a universal testing machine (0.5mm/min). SBS test values were statistically higher (p<0.05) in the G3 and G5 groups when compared to the other groups. This study showed that the Nd:YAG loser irradiation improved dental adhesion and increased the mechanical resistance of the enamel because the heating promoted by Nd:YAG laser irradiation changed the morphological and crystallographic properties of enamel; in this way, this treatment also offers the advantage to prevent caries around brackets.