Bond Strengths of Orthodontic Primers on Substrate

Objectives: To compare in vitro tensile bond strengths to different substrates between two orthodontic adhesive primers. Methods: Eight non-carious human molars and premolars (E) and eight stainless steel crowns (SS) were sectioned in a mesio-distal direction. Thirty-two amalgam discs (A, 3 x 10 mm) and 16 gold discs (G, 3 x 10 mm) were prepared. The buccal or lingual enamel and stainless steel crown segments along with the gold and amalgam specimens were imbedded in acrylic. The amalgam and gold specimens were polished with 600-grit SiC paper, then all but 8 amalgam (A) specimen surfaces were sandblasted with 110 µm aluminum oxide (MA – micro-etched amalgam). All specimens were then pumiced and air-dried for 5 seconds and divided into 10 groups of 8 specimens and bonded according to manufacturers' directions. Transbond XT Light Cure Orthodontic Adhesive Primer (TXT, 3M Unitek) and Assure Sealant (AS, Reliance) were used to bond a cone of Transbond XT adhesive (3M Unitek) with a diameter of 3 mm on the substrate surface. The teeth were then incubated in a water bath for 24 hours at 37 C. Debonding was performed on an Instron at a crosshead speed of 0.5 mm/min. Data were analyzed by two-way analysis of variance. Results: Means and standard deviations of tensile bond strengths (MPa, n=8) were: E/TXT – 5.8(2.2); E/AS – 7.5(4.3); MA/TXT – 7.4(1.4); MA/AS – 11.0(2.2); A/TXT – 3.4(1.6); A/AS – 6.4(2.2); G/TXT – 13.7(3.6); G/AS – 9.0(2.9); SS/TXT – 2.9(0.9); SS/AS – 5.1(1.8). Fisher's PLSD intervals for comparisons of means among substrates and between adhesives were 1.8 and 1.1 MPa, respectively. Conclusion: AS had higher tensile bond strengths to E, MA, A, and SS. TXT had higher bond strength to G. Several substrates (E, A, SS) had bond strengths less than 8 MPa with both adhesives.