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56 Annals of Dentistry, University of Malaya, Vol. 16 2009Effect of light tip angulation on shear bondstrength of an orthodontic adhesive, Ummu Aiman YusoffDepartment Child,en's Dentistry and OrthodonticsA number of studies have been done in relation to theeffect of different factors affecting the shear bondstrength of orthodontic adhesives, At present there areno studies that have evaluated the effect of light tipangulations while curing the lorthodontic adhesives onthe shear bond strength, The purpose of this study wasto investigate the effect of light curing tip angulationson the shear bond strength of an orthodontic adhesive,Ninety human premolars with brackets bonded ina standardized manner using the light-cure orthodonticadhesive, Transbond XT, were polymerized using a blueLED light curing unit for 40 seconds at three differentangulations of 0 degree, 45 degrees and 90 degrees ata standardized 3 mm distance, The Instron UniversalTesting Machine was used to measure the maximumforce for debonding, The Adhesive Remnant Index(ARI) and evaluation under Scanning ElectronMicroscope (SEM) were done to evaluate the site ofbond failure on tooth and bracket surface, respectively,SPSS version 12,0 was used to analyze the data,The Kruskal-Wallis test was employed to compare theshear bond strength of all groups, Frqm the results, themean shear bond strength values for Group A (0degree), ~roup B (45 degrees) and Group C (90degrees) were 4.15, 4,56 and 6,66 MPa, respectively,The highest mean rank,. was 46,98 for group C. Thestatistical analysis of the study sh6wed'no significantdifference (p = 0.286) of the shear bond strengths oforthodontic adhesives when cured at three differentangulations of the light curing tip, However, the highestshear bond strength was at 90 degrees angulations ofthe light curing tip and its value was within the optimalorthodontic force,if!".. ~-...