The results of this ex vivo study suggest that the self-etch primer should achieve adequate bond strengths when applied to dry enamel surfaces. In addition there should be less retained resin requiring removal at debond.

The problems of ceramic bracket debond have been well documented. A peppermint oil material has been marketed previously as a debonding agent. This study assessed ex vivo the effects of peppermint oil application on the debond behaviour of ceramic brackets compared with ethanol and acetone which are recognized softening agents. Intrigue brackets were bonded to 100 extracted premolar teeth. Groups of 20 bonded teeth were then placed in a test solution, control (distilled water), peppermint oil (5 minutes and 1 hour), acetone (1 hour), and ethanol (1 hour). The teeth were debonded using an Instron. Universal Testing Machine and debond forces recorded. The site of bond failure along with the adhesive remnant index was recorded for each tooth. One hour placement in peppermint oil produced the lowest mean and maximal debond forces (77 and 114 N, respectively). Weibull analysis showed that the probability of failure at 100 N was increased for the 1-hour peppermint group at 88 per cent compared with 52 per cent for the control. Placement in peppermint oil produced the lowest levels of retained resin. There was no evidence of enamel fracture with any of the groups, but bracket fracture remained a problem.

This study assessed bonding of orthodontic brackets to porcelain teeth using two different surface preparation techniques and comparing two bonding systems, Fuji Ortho L.C. and Transbond. Four groups of 20 porcelain premolar teeth were bonded with metal orthodontic brackets (0.022 inch Minitwin, 3M Unitek) according to the following protocol: Transbond with a phosphoric acid etch (group 1), Transbond with a hydrofluoric acid etch (group 2), Fuji Ortho L.C. with a hydrofluoric acid etch (group 3), and Fuji Ortho L.C. with a phosphoric acid etch (group 4). All groups were bonded with a silane coupling agent. The teeth were debonded with an Instron universal testing machine. Bond strength, site of bond failure and adhesive remnant index (ARI) were recorded for each group. Differences between groups were analysed statistically. The composite resin groups (groups 1 and 2) had the highest mean bond strength values at 7.9 and 9.7 MPa, respectively. The resin-modified glass ionomer cement groups (RMGIC; groups 3 and 4) had the lowest mean bond strength values at 6.3 and 1.8 MPa, respectively. The mean bond strength of group 3 was significantly lower than all other groups (P < 0.0001). The Fuji groups had also significantly (P < 0.001) lower ARI scores than the composite groups (groups 1 and 2). Most samples experienced porcelain surface damage, except group 4. In conclusion, the highest bond strength levels were achieved with a conventional composite resin cement (groups 1 and 2). No significant differences in bond strength were found between the hydrofluoric and phosphoric acid etch technique.

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