Effect of Er:YAG laser parameters on ablation capacity and morphology of primary enamel.

OBJECTIVE: The purpose of this study was to evaluate the ablation capacity of different energies and pulse repetition rates of Er:YAG laser energy on primary molar enamel, by assessing mass loss and by analyzing the surface morphology with scanning electron microscopy. BACKGROUND DATA: Previous studies have demonstrated the capacity of the Er:YAG laser to ablate enamel substrate. METHODS: Forty-two sound primary molars were bisected in a mesiodistal direction. The enamel surfaces were flattened and their initial mass (in milligrams) was obtained. An area of 4 mm(2) was delimited. The specimens were randomly assigned to 12 groups according to the combination of energy (160, 200, 250, and 300 mJ) and pulse repetition rate (2, 3, and 4 Hz). Er:YAG laser irradiation was performed on each specimen for 20 sec. After irradiation, the final mass was obtained and specimens were prepared for examination with scanning electron microscopy. The data obtained by subtracting the final mass from the initial mass were statistically analyzed using ANOVA and the Tukey test (p < 0.05). RESULTS: The pulse repetition rate of 4 Hz provided greater mass loss, different from that seen with 2 Hz, and similar to that seen with 3 Hz. The energy level of 300 mJ resulted in greater mass loss, similar to that seen with 200 and 250 mJ. Scanning electron photomicrographs showed that there was non-selective enamel removal, with fused and cracked areas in all specimens. CONCLUSION: The parameters of 200 mJ and 2 Hz produced a good ablation rate with fewer surface alterations in primary molar enamel.

Shear bond strength to primary enamel: influence of Er:YAG laser irradiation distance.

PURPOSE: The purpose of this study was to evaluate in vitro the influence of Er:YAG laser irradiation distance on the shear bond strength of an adhesive restorative system to primary enamel. METHODS: Fifty buccal surfaces of extracted human canines were ground and divided into 5 groups (N=10). The control group was etched with 35% phosphoric acid (CA). In the lased groups, the enamel surface treatment was performed with the Er:YAG laser (80mJ/2Hz) by varying the irradiation distance (12, 14, 16, and 17 mm), followed by acid etching. An adhesive agent (Single Bond) was applied on the bonding sites, and resinous cylinders (Filtek Z250) were prepared. Shear bond strength tests were performed in a universal testing machine (0.5 mm/minute). Failure mode was assessed using a X40 magnification stereomicroscope. Data were submitted to statistical analysis by analysis of variance. RESULTS: The means in MPa were: (1) CA=18.76 (+/-6.68); (2) 12 mm=12.73 (+/-5.46); (3) 14 mm=15.9 (+/-6.81); (4) 16 mm=20.1 (+/-6.94); and (5) 17 mm=15.15 (+/-6.81). There was no statistically significant difference (P<.05) among the tested groups. CONCLUSION: The different Er:YAG laser distance irradiations did not influence the adhesive resistance of the resinous system to enamel, even when compared with the control group (acid etching solely).