| Objective:In the daily orthodontic practice, the bonding of orthodontic brackets to enamel is very important, which is a multi-step process. The objective of this test is to evaluate the shear bond strengths (SBS) of different bracket base conditions at different debond times of 5,10,15,30, and 60 minutes and 24 hours.Materials and Methods:Metallic brackets:standard straight wire bracket spherical mesh base (tianmei company, Changsha) and standard straight wire bracket etching base (tianmei company, Changsha). Adhesive resin:orthodontic non-tone-based chemical curing adhesive mixing (3M, the USA).Experiment in vitro:One hundred twenty youth extracted maxillary first premolars were randomly divided into 12 groups (10 per group). In group A1～group A6, standard straight wire bracket spherical mesh base was used:in group B1～group B6, standard straight wire bracket etching base was used. The brackets were bonded to human premolars according to the instructions of adhesive for use. The specimens were stored in artificial saliva at 37℃two minutes later after bonded. The shear bond test of group A1 and B1, group A2 and B2, group A3 and B3, group A4 and B4, group A5 and B5, group A6 and B6 was performed at different debond times of 5,10,15,30, and 60 minutes and 24 hours. Two-way analysis of variance was used to obtain the significant differences among different base conditionsand debond times and their interactions. The chi-squared test was also used to determine significant differences for the ARI scores among the groups (P< 0.05). The enamel surfaces were evaluated according to the adhesive remnant index (ARI) after debonding. The ARI scale has a range from 0 to 3, with 0 indicating no composite left on the enamel; 1, less than half of the composite left; 2, more than half of the composite left; 3, all composite left on the tooth surface. Scanning electronic microscope was used to test the differences between the samples.Results:Lowest shear bond strength was attained with a debond time of 5 minutes for the group A (9.12 MPa) and the group B (8.18 MPa). Highest shear bond strength was obtained with a debond time of 24 hours for the group A (17.32 MPa) and the group B (14.94 MPa). The shear bond strength increased with the bonding time,but statistically significant differences between the groups were not observed for debond times of 5,10,15,30, or 60 minutes.However, the shear bond strength values obtained at 24 hours were significantly different (P<0.001). After adhesive bonding, the difference of the ARI scores between groups A and groups B was not significant. (P> 0.05).4) Before and after adhesive bonding, the scanning electron microscope morphologies of the two brackets'bottoms were significantly different.Conclusion:1 Both the two metal brackets are to meet the clinical needs.2 It is reliable to load the bracket 5 minutes after bonding using 3M UniteTM.3 The factor of bracket base design has significant influence on bracket's bond strength. Metallic bracket with spherical mesh base is more suitable for clinical needs. |
