Debonding force and deformation of two multi-stranded lingual retainer wires bonded to incisor enamel: an in vitro study

Two different stainless steel wires were used, 0.016 x 0.022 inch (Bond-A-Braid (R) Reliance Orthodontic Products) and a three-stranded 0.0175 inch wire (Ortho Technology). An in vitro model was used to simulate a vertical force at the interdental wire. Twenty-six pairs of incisors were placed in two groups. A 15 mm length of wire was bonded to the lingual surfaces of each pair of incisors using a common bonding technique. A vertical force was applied to the midpoint of the interdental wire, using an Instron universal testing machine. The failure characteristics examined included the maximum force for debond, the degree of wire deformation, and the site of failure. Significance was predetermined at P <0.05 and multiple comparisons indicated no significant differences (P = 0.147) in the initial mean bond strength between the 0.0175 inch (41.44 N) and 0.016 x 0.022 inch (37.70 N) wires. The main failure type for both the initial and second debond events was fracture of composite bond at the wire-composite interface, cohesive failure. Both wires exhibited similar mean degrees of deflection of 1.30 and 1.51 mm for the 0.0175 inch and 0.016 x 0.022 inch wires, respectively. Rebonding to enamel resulted in significantly lower (P = 0.001) mean bond strength for both wires, 0.0175 inch (13.86 N) and 0.016 x 0.022 inch (14.17 N) in comparison with the initial bond strength. Rebonding to previously bonded enamel may be unpredictable and may lead to higher failure rates of bonded lingual retainers.