Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel

Objectives The aim of the present study was to investigate in vitro the effect of Er:YAG laser on bonding to enamel, varying the irradiation distance. Method Tensile bond strength of an adhesive restorative system to non-irradiated and irradiated enamel surfaces was evaluated. Thirty caries-free human third molars were sectioned in mesio-distal direction and embedded in acrylic resin. Enamel was flattened, and a 3-mm-diameter bonding area was demarcated. Specimens were randomly assigned into six groups: groups I–V were treated with the Er:YAG laser (80 mJ/2 Hz), varying the irradiation distance (11, 12 mm-focused, 14, 16 and 17 mm, respectively), followed by 35% phosphoric acid etching. Control group (VI) received treatment with phosphoric acid alone. Single Bond adhesive system was applied on the conditioned enamel, and composite resin cones, bonded to enamel, were fabricated with Z250. After storage, samples were tested in tensile to failure (50 kgf and 0.5 mm/min). Results Means in MPa were: I-9.67 (±3.44); II-13.29 (±2.65); III-13.33 (±2.22); IV-14.87 (±3.58); V-16.43 (±4.52); VI-22.90 (±3.03). ANOVA and Tukey test revealed statistically significant decrease of bond strength in group I (P<0.05). Groups II–IV presented similar results, as did groups IV and V. Control group (VI) yielded the best overall performance (P<0.05). Conclusion Er:YAG laser irradiation adversely affected adhesion to enamel. However, bond strength was influenced by the irradiation distance, thus being stronger with the increase of distance to the target tissue.