The Influence of Primer and Its Curing Techniques on Shear Bond Strength of Orthodontic Brackets

Abstract

Aim: To evaluate the effect of primer and its curing techniques on shear bond strength of orthodontic metal brackets and cleaning procedures during debonding of orthodontic adhesive when used with metal brackets. Materials and Methods: A total of 100 freshly extracted human maxillary premolar teeth were cleaned to remove blood and tissue debris and stored in distilled water solution until the time of bonding procedures. The samples were divided into 4 groups in which the teeth were then mounted on self-cured, color-coded acrylic blocks such that the roots were completely embedded into the acrylic block up to cement-enamel junction, and the buccal surface of the crown is perpendicular to the base of the block. In group I, brackets were bonded in a conventional manner with the primer cured before placement of the filled adhesive material. In group II, primer was not pre-cured. In group III, primer was not at all applied. All these 3 groups were bonded with Transbond XT (3M Unitek). Group IV was bonded with no primer adhesive, Heliosit (Ivoclar). After bonding, all the samples were tested for shear bond strength with Instron testing machine in shear or peel mode at a crosshead speed of 1 mm/min. The debonded surfaces were examined for Adhesive Remnant Index (ARI) scores under stereomicroscope at 10x magnification. The obtained values were statistically analyzed. An analysis of variance (ANOVA) test was applied to determine whether significant differences in debonded values existed among the groups. The chi-square test was used to determine significant differences in ARI scores among the different groups. Results: Statistically significant difference ( P value < .001) was observed when group I was compared with groups II–IV. No statistically significant difference ( P value = .559) was observed when group II was compared with group III. No statistical significance was seen ( P value = .521) when group II was compared with group IV. Statistically significant difference ( P value = .042) when group III was compared with group IV. Post hoc test was performed for multiple comparisons of ARI scores between all groups. Chi-square test revealed that the differences in percentage distribution of ARI scores between various groups were statistically significant ( P value < .001). Conclusion: There was a significant difference in the shear bond strength of brackets bonded with Transbond XT and other groups in our study. Even though the average bond strength value of Transbond XT without primer was lower than that of Transbond XT bonded with conventional procedure, it had a low ARI score and eliminated the use of primer. The bond strength values were also considerably greater than the ideal bond strength values required for orthodontic bonding. Hence, the use of Transbond XT without primer made the bonding, debonding and cleaning procedure easy and less time consuming. It also reduced the risk of contact dermatosis in orthodontic personnel and type IV delayed hypersensitivity in patients as the primer was eliminated.