Abstract
Objectives: The aim of the study was to assess the influence of cervical margin relocation (CMR) with two different materials (flowable resin composite and light cure resin modified glass ionomer) on marginal integrity of resin nano ceramic composite restoration after thermo mechanical loading (TML). Materials and Method: A total number of (24) standardized MOD cavities with one proximal box (mesial) with cervical margin located one mm beneath the cement- enamel junction (CEJ) were prepared while keeping the distal box supragingival. The division of teeth into two equal main groups (n=12) based on the kind of restorative materials used for (CMR); group (A):- nanohybrid flowable resin composite (Dyract flow) and group (B):- resin modified glass ionomer (Riva). Both groups were restored with direct nanoceramic resin composite (Zenit). After that, each group was split into two equal subgroups (n=6) based on (TML) was done or not. Result: No statistically significant difference in marginal integrity before and after the (TML) regardless of (CMR) was recorded and the flowable resin group showed higher marginal leakage than the mesial resin modified glass ionomer group after the (TML). Conclusions: (CMR) technique seems to promising acceptable technique without compensatory the marginal integrity, marginal integrity in (CMR) was a material-dependent and the (TML) had no significant effect on marginal integrity regardless of (CMR).

Keywords: Cervical margin relocation. Marginal integrity. Thermo mechanical loading