High early bond strength, extended working time for optimal bracket placement, and easy cleanup of excess adhesive are few advantages of visible light-cure orthodontic adhesives. However, the shorter duration of polymerization may lead to polymer shrinkage and eventually microleakage.

To observe and evaluate shear bond strength (SBS) and microleakage of orthodontic brackets bonded to enamel with four commercially available orthodontic adhesives, cured only from incisal direction at various polymerization times.

A total of 160 bovine incisors were randomly assigned to four groups according to adhesive used. Group I: bonded with Transbond XT (3M Unitek™, USA); group II: Enlight (Ormco, USA); group III: Light Bond (Reliance Ortho, USA); and group IV: Discover (Prime Dental, USA). Each group was further divided into four subgroups of A, B, C, and D according to the polymerization duration of 5, 10, 15, and 20 seconds respectively. The bonded teeth were immersed in dye solution. Brackets were then subjected to SBS test on a Universal testing machine. Surface microleakage was observed with the help of optical stereomicroscope.

The SBS was obtained within the range of clinically accepted values, with curing time for Enlight at 5 seconds, Transbond XT and Discover at 15 seconds, and Light Bond at 20 seconds. However, Enlight was demonstrated to provide optimum SBS at least curing time: Minimum duration of 5 seconds achieved adequate SBS ~11 MPa SBS for each of Transbond XT and Enlight. The surface microleakage observed is statistically insignificant among the groups.

From a clinical perspective, a composite resin that needs minimum curing time without compromising on the bond strength is most advantageous. The results for SBS tests showed a better performance for Enlight as compared with the other adhesives: it reached its bond strength of optimum value at curing time of 5 seconds.

Zanke PN, Patni V, Maskarenj M. Comparative Evaluation of varying Photo-polymerization Time on Shear Bond Strength and Microleakage of Four Orthodontic Adhesives: An in vitro Study. J Contemp Dent 2017;7(3):156-160.