Evaluation of the bond strength of different bracket-bonding systems to bovine enamel

In an experimental study the bond strength of stainless steel, ceramic and plastic brackets to bovine enamel was investigated by tensile testing. The brackets were cemented to the enamel using a conventional two-paste orthodontic bonding resin, a light-cured, fluoride-releasing adhesive, a no-mix-orthodontic bonding resin and a light-curing glass ionomer cement. For evaluation of the experimental data the Weibull analysis was applied. The highest values for the Weibull modulus (m) and the 10 per cent probability of failure (sigma.10) were found in the tested plastic brackets (Dentaurum Edgewise plastic bracket and Spirit bracket) using a no-mix orthodontic bonding resin (System 1). However, the tensile stresses for the 90 per cent probability of failure (sigma.90) were over 10 MPa and carried the danger of enamel fracture. Bracket bonding with glass ionomer cement cannot be recommended because of the low bond strength values for the 10 per cent probability of failure (sigma.10). The most favourable bracket-bonding system concerning the Weibull modulus (m), the 10 and 90 per cent probabilities of failure (sigma.10 and sigma.90) and aesthetics was the ceramic bracket with the silane-treated base (Allure III) using the light-cured, fluoride-releasing orthodontic bonding resin (Sequence). Bond fracture occurred predominantly between bracket and orthodontic bonding resin, with two exceptions. Concerning the ceramic bracket with the silane-treated base (Allure III) using the light-cured glass ionomer cement (Photac Fil), there was no preferential site of failure. Regarding the ceramic bracket with the silane-treated base (Allure III) using the light-cured, fluoride-releasing orthodontic bonding resin (Sequence), bracket fracture was seen more often than bond separation between bracket and enamel. When the bond failure was located at the enamel-orthodontic bonding resin interface enamel prisms could be identified on the adhesive site by scanning electron microscopy.