Bracket Rebonding: The Influence of Adhesive Removal Method on SBS Yoav Shapinko, Jason Vladimer, Tamar Brosh

Objectives: Spontaneous bracket failure usually requires rebonding of a new bracket, following the adhesive remnants removal from the tooth surface. The aim was to compare different adhesive removal methods prior to rebonding a new bracket in terms of Shear Bond Strength (SBS).
Methods: The buccal surfaces of 40 extracted bovine teeth were etched with 35% orthophosphoric acid for 45-50 sec. followed by applying of primer on the treated surfaces and adhesive composite material (Transbond LT, 3M, USA) on the mandibular premolar brackets meshes. Brackets were then applied on the treated teeth and light cured from the gingival and incisal aspects, using LED light cure unit. Bracket debonding was done after one week storage in water by brass wire-loop engaged around the bracket connected to the universal testing machine (Instron). The maximal force at debonding was registered. Then, all the teeth were randomly divided into two groups according to the adhesive remnants removal method: Group A (N=20): by rough grinding with composite removal bur (Strauss 58). Group B (N=18): by sandblasting with aluminum oxide 50 nm particles. New mandibular premolar brackets were then bonded to the prepared teeth and debonded again according to the previous protocol.
Results: There was no difference between the initial debonding forces between the groups. Group A: 51.16±20.41N. Group B: 50.93±18.73N. After rebonding and repeated debonding, the measured SBS increased significantly: Group A: 61.48±25.08N, Group B: 65.59±19.85N (p<0.05) with no significance differences between the groups.
Conclusions: Full adhesive remnant removal that may compromise the enamel surface is not necessary to achieve acceptable SBS values; it is rather sufficient to grind off the remnants roughly with a composite removal bur or sandblast them before the second bonding.