In the field of pediatric dentistry the use of Er,Cr:YSGG laser in cavity preparation in deciduous molars has many advantages as fast procedures and patient comfort.The purpose of the present study is to compare between the effect of Er,Cr:YSGG laser and conventional conditioning on the microleakage in cavity class V restored by glass ionomer (GI) and resin modified glass ionomer (RMGI) in deciduous molars. Materials and methods: A standard class V cavity were prepared at the buccal or lingual

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... urface of forty-eight freshly extracted caries-free human deciduous molars which were divided into 2 groups according to the mode of conditioning: group 1: by using Er,Cr:YSGG laser; group 2: by using conventional conditioning. The samples were subjected to thermocycling and dying step. Results: No statistically significant difference between median microleakage scores of the two conditioning methods with RMGI or GI, while RMGI showed statistically significantly lower median microleakage scores than GI. Conclusion: Er,Cr:YSGG laser have adverse effect on the microleakge of cavities restored by RMGI and GI. RMGI showed statistically significantly lower median microleakage scores than GI. Application of the Er:YAG laser, beneath the RMGIs and GI may be an alternative to acid etching