الفهرس 
Cover EnglishOnly 14 pages are availabe for public view
 |  | from | 112 |  |  |
| | | from | 112 | | |
Abstract
Seventy five sound premolars recently extracted for orthodontic reasons were carefully selected and stored in distilled water. Teeth were cleaned and crowns were sectioned logitudinally in a mesiodistal direction. Buccal surfaces were embedded in polymethylmethacrylate resin surrounded by polyvinyl chloride ring. Specimens were flattened, etched and prepared to form the sealant-enamel block. Specimens were divided into 3 groups (n=25): group I, the control group. group II, CO2 laser treated. group III, Er,Cr:YSGG laser treated. 20 specimens from each group were subjected to shear bond strength testing (quantitative analysis); examined under the Environmental Scanning Electron Microscope (qualitative analysis) then statistical analyses were performed. The remaining 5 specimens from each group were subjected to vertical cutting in the middle of the sealant block to analyze the effect of laser irradiation on the sealant periphery and sealant center utilizing the ESEM.Results of the shear bond strength testing revealed that the Er,Cr:YSGG laser group (ΙΙΙ) showed the highest shear bond strength values (13.99±3.49MPa) and the difference was statistically significant (P<0.001) than the control (7.65±2.51MPa) and the CO2 laser group (8.97±3.58). However, no statistically significant difference between the control group and CO2 laser group.As regard the ESEM analysis, the control group showed definite termination of the sealant on the enamel surface and the sealant-enamel interface was easily demarcated with the presence of gaps along the sealant-enamel interface. CO2 laser group showed similar results as the control group in relation to the sealant-enamel interface. However, there was an overextension of the sealant on the enamel surface with less frequent gaps than the control group. Er,Cr:YSGG laser group showed that the sealant-enamel interface was not easily distinguished unlike the other groups with a sealant overextension on the enamel surface. Scant gaps were seen between the sealant and the enamel. Observation of the failure modes in the fractured samples revealed that cohesive failure in sealant and mixed mode with more cohesive failure in the sealant were frequently observed in the Er,Cr:YSGG laser group while adhesive and mixed mode with more adhesive failure were predominated in both, the control and the CO2 laser groups.