[Effect of a nano hydroxyapatite desensitizing paste application on dentin bond strength of three self-etch adhesive...

Objective: To evaluate a nano-hydroxyapatite (nano-HA) desensitizing paste application on the bond strength of three self-etch adhesives. Methods: Three dentin specimens of about 1 mm thick were cut from two teeth. Scanning electron microscope (SEM) was used to evaluate the dentin surfaces without treatment, after citric acid treatment and after nano-HA treatment. Thirty-six intact third molars extracted for surgical reasons were cut to remove the occlusal enamel with isomet, and then were etched with 1% citric acid for 20 s to simulate the sensitive dentin and divided into two groups randomly using a table of random numbers (n=18): the control group (no treatment) and the HA treated group (with nano-HA paste treatment). Each group was divided into three subgroups randomly using a table of random numbers (n=6). Subgroup A, B and C was bonded with G-Bond, Clearfil S(3) Bond and FL-Bond Ⅱ according to the manufacture's instruction separately. At 24 h after bonding procedure, and after water storage for 6 months, microtensile bond strength of the specimens was tested and the failure mode was analyzed. Results: SEM obeservation showed that citric acid could open the dentin tubules to set up the sensitive dentin model, and the nano-HA could occlude the dentin tubules effectively. For subgroup A, bonding strength of specimens treated with nano-HA ([41.14±8.91] MPa) was significantly high than that of the control group ([34.27±6.16] MPa) at 24 h after bonding procedure (P<0.05). However, after 6 month water ageing, the bonding strength of the control group and the HA treated group showed no significant difference (P>0.05). For subgroup B, specimens with nano-HA application showed lower bonding strength ([30.87±6.41] MPa) than that of the control group ([36.73±5.82] MPa) at 24 h after bonding procedure (P<0.05), and after 6 month water ageing, the bond strength of nano-HA application ([25.73±6.99] MPa) was also lower than that of the control group ([32.33±5.08] MPa) (P<0.05). For subgroup C, the bond strength of the control group and the HA treated group have no significant difference either before or after 6 month water ageing (P>0.05). Failure mode analysis showed that more than half of the samples in all groups were adhesive failure. Conclusions: Nano-HA treatment decreased the bond strength of subgroup B, while had no adverse effect on subgroup A and subgroup C.