immediate versus delayed force application after orthodontic bonding; an in vitro study

statement of problem: bracket de-bonding during initial orthodontic archwire placement immediately after bracket set up or following re-bonding a single bracket can be a clinical concern. purpose: the aim of this in vitro study was to assess the effect of time on the shear bond strength of a no-mix orthodontic composite adhesive. materials and methods: seventy freshly extracted human upper first premolars were collected and stored in normal saline solution. the teeth were cleaned, polished, and randomly separated into 7 groups of 10. first premolar mesh-backed standard edgewise brackets were bonded to all specimens using a no-mix orthodontic composite adhesive. in the first 6 groups, the brackets were de-bonded 2, 5, 10, 15, 30 and 60 minutes after the primary setting time and the shear bond strengths were determined with the universal testing machine. the teeth in group 7 were stored in 100% humidity at 37oc for 24 hours before de-bonding. data were statistically analyzed with one-way anova and the duncan multiple range analyses via spss software. results: the minimum shear bond strength of 14.03 mpa was observed in group 1. a statistically significant difference was found between the shear bond strength of group 1 and the other groups (p<0.05). the shear bond strength increased significantly with time up to the first 5 minutes after bonding, but did not change afterwards. conclusion: the bracket and composite adhesive used in this study demonstrated initial bond strengths of sufficient magnitude to withstand the immediate application of orthodontic forces, even 2 minutes after the primary setting time. therefore, the operator should not be concerned with bracket de-bonding due to primary arch wire placement during the first minutes after bracket set up or following re-bonding a single bracket.