الفهرس 
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Abstract
Objective: The purpose of the present study was to compare between Laser and conventional technique in class v cavity preparation in gamma irradiated teeth.Methods: A total of 40 extracted human teeth with no carious lesions were used for this study and were divided into two main groups: group I, (n=20) was not subjected to gamma radiation (control) and group II, (n=20) was subjected to gamma radiation of 60 Gray, where standard class V preparation was prepared in buccal and lingual sides of each tooth in both ;where buccal surfaces were prepared by Er,Cr:YsGG Laser(Water Lase I plus) 2780 nm using the gold hand piece with MZ10 Tip in non-contact, H- mode with following parameters during cavity preparation, (power 6 W, frequency 50 Hz, 90٪ water & 70٪ air, then shifting to surface treatment laser parameters of power 4.5 W, frequency50 Hz, 80٪ water & 50٪ air) while lingual surfaces were prepared by the conventional high speed turbine using round diamond bur; then the teeth were sectioned mesio-distally giving up 80 specimens; 40 of them buccal Laser treated Specimens (20 control and 20 gamma irradiated specimens )and 40 lingual conventional high speed bur specimens (20 control and 20 gamma irradiated specimens)Results: Micro-leakage analysis revealed higher scores in both gamma groups compared to the control groups. Chi square test revealed no significant difference between both control groups and gamma groups (p=1, 0.819 respectively). A significant difference was revealed between all 4 groups (p= 0.00018).Conclusion: Both Laser and conventional high speed turbine bur showsgood bond strength in control (non-gamma) group, while also both of two groups shows high degree of micro leakage in gamma group where gamma radiation had a dramatic negative effect on the bond strength in both Laser and bur treated teeth.