الفهرس 
ُُEnglish CoverOnly 14 pages are availabe for public view
 |  | from | 120 |  |  |
| | | from | 120 | | |
Abstract
This study was done to compare bond strength of the orthodontic brackets after laser curing composite with that after conventional light curing. One hundred and twenty extracted human premolars teeth divided equally into 3 groups, and every tooth embedded in a block of plaster. Etching and bonding carried out according to the manufacture instructions. group 1: curing done by conventional halogen light curing device for 20 seconds. Group2: curing done by Argon laser device for 20 seconds. Group3: curing done by argon laser device for 5 seconds. Each sample was mounted on the lower fixed compartment of a computer controlled materials testing machine and data were recorded using computer software. Then subjected to a compressive loading and the maximum failure load was recorded. Obtained data were tabulated and statistically analyzed to determine the bond strength between the orthodontic brackets and the teeth. The analysis shows that, the highest bond strength was in group one, followed by group two and lowest bond strength was group three. Conclusion: The wave length 488 nm has a good ability in composite curing and when Argon laser 488nm was used for 20 seconds it gives higher bond strength than when it used for 5 seconds but the results with conventional light when it used for 20 seconds was the best. Research indicates that the argon laser offers a greater depth and degree of polymerization, less time required and an enhancement of the physical properties of composite resins polymerized. These advantages are offset by reports that the increased polymerization caused by the laser results in increased shrinkage, brittleness and marginal leakage which affecting the bond strength between the orthodontic bracket and the tooth enamel. So that it is recommended to use conventional light curing device for 20sec in curing the composite of the orthodontic bracket and not to to use argon laser 488nm for 20 sec.