Light Cure Tip Distance and Shear Bond Strength: Does It have any Clinical Significance?

Aim: The purpose of this study was to assess whether minor change in distance of the light cure tip to the bonding surface produce any significant effect on shear bond strength of composites and resin-modified glass ionomer cement used for bonding brackets. Materials and methods: Ninety therapeutically extracted human premolar teeth were randomly allocated to six groups of 15 specimens each. Resin-modified glass ionomer (GC Fuji Ortho LC) was used to bond brackets to the teeth in three groups with curing light held at three distances from the bracket: 2, 4 and 6 mm. For the other three groups light cured composite resin (Transbond TM XT) was used to bond brackets with curing light held at three distances from the bracket: 2, 4 and 6 mm. After bonding, all samples were stored in distilled water at room temperature for 24 hours and subsequently tested for shear bond strength. Results and conclusion: (1) Light tip distance of 2 or 4 mm does not affect the shear bond strength of composites significantly; however increase in the distance to 6 mm significantly reduces the shear bond strength, (2) There was a significant decrease in the shear bond strength, with the progressive increase in distance of the light source from 2 to 4 and 6 mm in case of resin-modified glass ionomer cement, (3) The mean shear bond strength of light cure composites is higher than resin-modified glass ionomer cement at all the three light source distances compared, i.e. 2 or 4 or 6 mm.