Shear bond strength of a self-adhering flowable composite when used for lingual retainer bonding

The goal of this work was to assess the shear bond strength (SBS) and fracture mode of a self-adhering flowable composite when used after thermocycling for lingual retainer bonding.

A total of 80 human mandibular incisor teeth were categorized into four equal groups: group 1: Vertise™ Flow (VF) without acid etching; group 2: VF with acid etching; group 3: VF with a self-etching bonding agent accompanied by an additional acid etching; group 4: Transbond LR control. Either VF or Transbond LR was applied to the lingual surface of the teeth by packing the material into cylindrical plastic matrices to simulate the lingual retainer bonding area. After all teeth were thermocycled (5000 cycles, 5 and 55 °C), fracture modes were examined under × 20 magnification. The SBS data were assessed via analysis of variance (ANOVA) and Tukey's tests. Fracture modes were analyzed by the χ(2) test at a significance level of 0.05.

Statistically significant differences in SBS values between groups (p < 0.001) were observed. Group 4 exhibited the highest (14.63 ± 1.36 MPa) and group 1 the lowest SBS (2.67 ± 1.35 MPa) values. Statistically significant differences were noted in fracture modes between groups 1, 3, and 4 (p < 0.001). In all the self-adhering flowable composite groups, the adhesive type (tooth-composite interface) fracture occurred more frequently than cohesive and mixed-type fractures.

When applied to bond lingual retainers to unetched enamel or with self-etching bonding agent accompanied by an additional acid etching, Vertise™ Flow resulted in a significant decrease in bond strength.