The Effect of Filled Adhesive Application Method and Water Storage on the Retentive Features of a Mechanically Retained Ceramic Orthodontic Bracket to Bovine Enamel

Abstract

Ease of bracket application, durability of enamel bond, and formation of an intact peripheral seal to maintain color stability are goals of esthetic, ceramic orthodontic bracket use. PURPOSE This research examined the effect of three different types of photo-curable resin applications to a commercial ceramic orthodontic bracket base on bond strength and potential for microleakage on bovine enamel following various periods of water storage. METH 0 D S Resin adhesive was applied to polycrystalline orthodontic brackets (Transcend 6000, 3M Unitek, Monrovia, CA) using three methods: 1) manual application of a light-curable adhesive (Transbond, 3M Unitek) to the bracket base (no resin); 2) with a coat of unfilled resin prior to adhesive placement (resin); 3) or with adhesive paste pre-applied by the manufacturer (APC Brackets, 3M'Unitek). Brackets were applied to flattened, acid-etched bovine enamel surfaces using standardized loading conditions. Bonded brackets were stored in phosphate-buffered saline at 37 degrees C for the following durations prior to testing: 1 day, 1 week, and 14 weeks. Following storage, the brackets (17 per test condition) were debonded in shear or were stored in basic fuchsin dye for 24 h prior to sectioning and examination for microleakage under stereo magnification (12 teeth per condition). RESULTS Two-way ANOVA indicated that type of adhesive resin application (p=0.0001) and duration of water storage (p=0.0063) were both significant factors on strength: resin (13.4 MPa) > APC (10.9 MPa) > no resin (9.3 MPa). Water storage decreased bond strength for all groups after 14 weeks storage. The primary debond location for all groups was the adhesive/bracket interface. APC brackets showed greatest microleakage (42%) after 14 weeks, while the other groups each leaked in 33% of specimens. The method of resin application to a ceramic bracket base is shown to affect both strength and potential for micro leakage.