Effect of different light sources on shear bond strength of brackets bonded with two adhesive systems

This study assesed the shear bond strength and failure site of orthodontic brackets by using 2 adesive systems (Transbond XT [3M/Unitek, Monrovio, Calif], Pad Lock [Reliance Orthodontic Products])and 5 different light sources under same conditions. One hundred and seventy permanent mandibular incisors were randomly divided into 10 groups. Each group consisted of 17 specimens. 170 stainless steel brackets ( Dynalock [3M/Unitek, Monrovio,Calif] )were bonded to teeth. Each adesiv system was light cured with a halogen light (Ortholux XT, 3M/Unitek) for 40 seconds, high intensity halogen (Optilux 500, Demetron) for 20 seconds, high power halogen (Swissmaster, EMS) 6 seconds, high intensity LED (bluephase, Ivoclar) for 20 seconds and plasma arch (BC300) for 6 seconds. After bonding, all sample were stored in distelled water for 3 days and then tested in a shear mode on a universal testing machine. Statistically significant differences were found between light sources and adesive systems when shear bond strengths were evaluated. Shear bond strength of the group bonded with high intensity halogen found significantly lower when compared with the other light sources. Shear bond strength of the groups bonded with Pad Lock were found statistically lower than the groups bonded with Transbond XT. When failure sites were assesed significant differences were found between 10 groups. The results of this study revealed that the plasma arch curing light is a good alternative for light curing polimerization and can be recommended for clinical use due to its reduced chairtime and high performance in terms of shear bond strength values. A new bonding adhesive, Pad Lock, achieved the adequate minimum bond strength for orthodontic brackets but showed lower bond strength then our expectations when compared with Transbond XT.