In Vitro Bond Strength Evaluation of Digital Custom Molar Bands

Objectives The aim of this in vitro pilot study was to test the effect of three different bonding protocols on tensile strength of digitally manufactured orthodontic molar bands. Methods Twenty extracted human third molars were mounted through a special designed support into an Instron machine and randomly assigned to three groups, according to three different bonding protocols. Gr1: cleaning with pumice and rotating brush; Gr2: as Gr1 plus 36% phosphoric acid etching for 30 seconds; Gr3: as Gr2 plus adhesive application. The same band cement, RelyX Unicem 2 Automix (3M Espe), the same cementation pressure (measured through an orthodontic dynamometer), and the same light-curing protocol were used for all groups. Tensile loads were applied until tooth-band separation or breakage. One-way ANOVA and post-hoc Tukey test were applied in order to identify possible differences in tensile strength. Results Gr1 (346.90±32.75 N) exhibited significantly (P<0.05) lower tensile strength than Gr2 (614.77±52.67 N) and Gr3 (550±61.22 N); Gr2 and Gr3 exhibited similar tensile strength (P>0.05). Gr1 and Gr3 showed adhesive fracture patterns, between enamel and resin and between resin and inner bands surface respectively, whilst Gr2 showed a mixed pattern of adhesive fracture between the resin and the inner bands surface or between enamel and resin, with some transitional areas of cohesive fracture through the resin cement. No band breakages were recorded. Conclusions The bond strength of customized bands to enamel is higher when the dental surface is etched. The application of an adhesive do not increase significantly the overall bond strength, but it change the fracture pattern leading to a complete retention of the resin cement onto the dental surfaces.