Tensile bond strength of single-step self-etch adhesives to Er:YAG laser-irradiated dentin.

OBJECTIVE: The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on the bond strength to dentine of three single-step adhesives (AQ Bond Plus, G-Bond, and Clearfil Tri-S Bond), and one two-step self-etch adhesive (Clearfil Megabond) as a control. BACKGROUND DATA: The vast majority of the numerous reports on resin bonding to Er:YAG-lased dentine have concluded that Er:YAG laser irradiation is less effective in terms of bond strength, because of the sub-surface damage it produces. However, its effect in combination with single-step adhesives on bonding to dentine remains to be clarified. METHODS: Eighty bovine incisors were ground with silicon carbide paper to obtain a flat dentine surface, which 40 were irradiated with an Er:YAG laser. Both lased and unlased dentine was bonded to a resin composite with each adhesive. Tensile bond strength was determined after 24 h of storage in water at 37 degrees C. Failure patterns after tensile bond testing was analyzed by scanning electron microscopy. RESULTS: The two-step self-etch adhesive (Clearfil Megabond) showed the highest bond strength to unlased dentine, but was significantly less effective on lased dentine than the three single-step adhesives. On the other hand, AQ Bond Plus produced an effective bond strength to both lased and unlased dentine, perhaps due to its low viscosity. CONCLUSION: The single-step adhesives tested in this study were as effective in combination with Er:YAG-lased dentine as the two-step self-etch adhesive.

Influence of free-hand vs uniform irradiation on tensile bond strength in Er:YAG-lased dentin.

PURPOSE: To compare effects of free-hand and mechanically applied uniform irradiation on tensile bond strength of 4-META/MMA-TBB resin to Er:YAG laser-irradiated dentin using an X-Y moving stage. MATERIALS AND METHODS: Three different laser conditions were evaluated: 1.0 W, 100 mJ/pulse, 10 pps; 1.0 W, 50 mJ/pulse, 20 pps; 1.0 W, 33 mJ/pulse, 30 pps. Samples of bovine dentin were set on a moving stage and mechanically irradiated with an Er:YAG laser at a scanning speed of 1.0 mm/s or subjected to free-hand irradiation. The lased dentin surfaces were acid conditioned with 10% citric acid/3% ferric chloride for 15 s, rinsed, and dried. The surfaces were bonded to PMMA rods with 4-META/MMA-TBB resin, and mini-dumbbell-shaped bonded specimens were prepared. Tensile bond strength was measured and compared with the results for free-hand irradiated samples obtained under the same conditions in an earlier study. SEM observations of fractured surfaces after tensile bond testing were also performed. RESULTS: A significant difference was found in tensile bond strength among the 3 laser settings in both free-hand and mechanically uniform irradiations. A comparison of free-hand laser irradiation and mechanically performed uniform laser irradiation revealed no significant difference under either laser condition (p > 0.05). SEM observation of the fractured surfaces showed no difference between the two irradiation methods under all laser conditions. CONCLUSION: No significant difference was found in tensile bond strength between free-hand and mechanically irradiated dentin. Significant differences were found, however, with changes in laser setting in both groups.

Tensile bond strength of one-step self-etch adhesives to Er:YAG laser-irradiated and non-irradiated enamel.

This study determined the bond strengths to Er:YAG laser-irradiated and non-irradiated bovine enamel of three one-step self-etch adhesives (AQ Bond Plus (AQP), G-Bond (GB), and Clearfil Tri-S Bond (TS)) and one two-step self-etch adhesive (Clearfil Megabond (MB)). Eighty SiC paper-ground bovine enamel surfaces were used, of which half were laser-irradiated. The enamel surfaces were bonded to a resin composite with each adhesive, and tensile bond strengths were determined after 24 hours. For non-irradiated enamel groups, MB achieved greater bond strength to enamel than GB and TS (p < 0.05), but no significant difference was found between MB and AQP (p > 0.05). For laser-irradiated enamel groups, no significant differences were found among the four adhesives (p > 0.05). Additionally, for each adhesive, no significant differences were found between laser-irradiated and non-irradiated enamel. It was thus concluded that Er: YAG laser irradiation of enamel did not affect the tensile bond strength of one-step and two-step self-etch adhesives.

Nano-hardness of adhesive interface between Er:YAG laser-irradiated dentin and 4-META/MMA-TBB resin.

OBJECTIVE: The purpose of this study was to evaluate the hardness of the adhesive interface between resin and Er:YAG laser-irradiated bovine dentin by nano-indentation. BACKGROUND DATA: It has been reported that laser output energy and pulse repetition rate affect the tensile bond strength in Er:YAG laser-irradiated dentin. MATERIALS AND METHODS: Three laser settings were evaluated at the same total energy level (approximately 1.0 W): 100 mJ/pulse-10 pps (100-10), 50 mJ/pulse-20 pps (50-20), and 33 mJ/pulse-30 pps (33-30). Laser-irradiated dentin in each group was conditioned with 10% citric acid solution containing 3% ferric chloride for 15 sec, rinsed with distilled water for 30 sec, and bonded to PMMA rods with 4-META/MMA-TBB resin. The bonded specimens were sectioned vertically, embedded in epoxy resin, and their nano-hardness measured. A non-irradiated control group was also investigated. RESULTS: The adhesive resin interface in the controls showed the lowest level of hardness, which gradually increased from the top of the hybrid layer (0 microm) through the bottom of the hybrid layer (5 microm) and into the underlying dentin ( approximately 10 microm). Significant differences in hardness were observed between the 5 microm point in the controls, the 10 microm and 15 microm points in the 100-10 group, and the 10 microm point in the 50-20 and 33-30 groups. CONCLUSION: The results suggest that laser settings affect hybrid layer thickness, even when the total energy level is constant.

Resin bonding to dentin irradiated by high repetition rate Er:YAG laser.

OBJECTIVE: This study evaluated the influence of laser irradiation with a high pulse repetition rate on dentin bonding. BACKGROUND DATA: Although resin bonding to erbium:yttrium-aluminium-garnet (Er:YAG) laserirradiated dentin has frequently been investigated, the effects of a high pulse repetition rate have not yet been sufficiently investigated. METHODS: Four groups treated under different laser conditions were evaluated in this study: 100 mJ/pulse-10 pulses per second [pps], 50 mJ/pulse-20 pps, 33 mJ/pulse-30 pps, and the unlased condition as a control. The total energy used to irradiate each group was adjusted to 1.0 W. After bovine dentin specimens were irradiated by an Er:YAG laser, acid conditioners (10% citric acid/3% ferric chloride) were applied to the lased surface. Thereafter, a PMMA rod was bonded to the lased dentin using 4- META/MMA-TBB resin, and mini-dumbbell-shaped specimens were prepared. These specimens were then tested under tensile mode and fractured surfaces were observed under scanning electron microscopy (SEM). RESULTS: The bond strength of the unlased control was significantly higher than those of the three lased groups. Among the three lased groups, irradiation with higher output energy and lower pulse repetition rate tended to affect the higher bond strength. Upon SEM observation of the fractured surface, the lased groups showed the mixture of failure in the hybrid layer in almost part. There was no significant difference among the three lased groups. CONCLUSION: It can be concluded from the results of this study that a higher pulse repetition rate is not effective for resin bonding to laser-irradiated dentin.