The effect of herbal teas on the shear bond strength of orthodontic brackets

The present study was conducted to evaluate the effects of some types of herbal tea on the shear bond strength (SBS) of orthodontic brackets to enamel surfaces. The brackets were bonded with Transbond XT to 90 extracted human premolar teeth and divided equally into six groups, that is, black, mint-mate herbal, mint-lemon herbal, and rosehip fruit tea and two control groups, Coca-Cola and distilled water. All groups were conditioned for three 5-minute sessions with equal intervening intervals for 90 days. The initial pH, SBS, and adhesive remnant index (ARI) of the groups were evaluated and the data were analysed statistically by Kruskal-Wallis and Mann-Whitney U-tests, one-way analysis of variance, and Duncan and Z-tests, respectively. Rosehip fruit tea (2.4 +/- 0.07) and Coca-Cola (2.5 +/- 0.05) had the lowest pH values. Coca-Cola (6.04 +/- 1.11 MPa) and rosehip fruit tea (7.26 +/- 1.11 MPa) significantly reduced the SBS to enamel (P < 0.001). The SBS results for the other groups were similar (P > 0.05). Except for the Coca-Cola group (ARI score = 0), fracture sites for all other groups were similar with the majority of bond failures at the enamel-adhesive interface (ARI score = 1). Although this experiment could not completely replicate the complex oral environment, it seems to confirm that Coca-Cola and rosehip fruit tea may be a causative factor in bracket-enamel bonding failure.