Effects of different types of light guides on shear bond strength

With the introduction of photosensitive (light cured) restorative materials in dentistry, various methods were suggested to enhance their polymerization including layering and the use of more powerful light-curing devices. The purpose of this study was to determine whether the use of different light guides, specifically the standard curved versus the mini turbo light guides, has different effects on the shear bond strength of orthodontic adhesives immediately after bonding. The light-curing apparatus used was the Optilux 500 (Demetron/Kerr, Danbury, Conn) that has a number of accessories. The two light guides used in the present study were the 11 mm diameter Standard Curved Light Guide (#20898) and the 4 mm diameter curved Mini Turbo Light Guide (#21185). The bonding adhesive system used was Transbond XT (3M Unitek, Monrovia, Calif). Regardless of the light guide used, the adhesive was cured for 30 seconds. The teeth were randomly divided into three groups according to the light guide tip used and the time of bracket removal after the bonding procedure was completed. The findings indicated that the two groups that were debonded within 30 minutes after being light cured with either the Standard (x = 7.6 +/- 3.9 MPa) or Turbo (x = 5.8 +/- 2.8 MPa) Light Guides were not significantly different from each other. On the other hand, both groups had significantly lower shear bond strength than the control group cured with the Standard Light Guide and debonded after 72 hours (x = 12.1 +/- 4.3 MPa). As a result, the use of the Mini Turbo Light Guide did not seem to significantly influence either the shear bond strength or the bracket/adhesive/enamel failure site. Therefore it can be concluded that there is no added advantage in using the Mini Turbo Light over the Standard Light Guide when bonding orthodontic metal brackets.