Purpose: The aim of this study was to evaluate the marginal adaptation of two different post-obturation restorative materials of premolars with mesio-oclussal-distal MOD cavity.
Materials and Methods: Twenty sound premolars received root canal treatment and MOD cavity. All teeth were divided into 2 groups (n=10). GpA: (Ribbond, polyethylene fiber; USA) inserted in short fiber reinforced resin composite, Ever x Posterior; Japan) followed by nanohybrid Filtek Z250xt; 3M,USA); GpB: (fiber post and core with nanohybrid Filtek Z250xt;3M,USA) then CAD/CAM Emax crown. Marginal adaptation was assessed before and after thermocycling using Stereomicroscope. All teeth were subjected to 5000 cycle's equivalents to 6 months. Dwell times were 25 s. in each water bath with a lag time 10 s. The low-temperature point was 5 0C. The high temperature point was 55 0C. Data were collected and analyzed using one-way analysis of variance was performed followed by Tukey's post-hoc test if showed significance between both groups.
 
Results: Marginal Adaptation was significantly higher before and after thermocycling for GpA (before: 38.12±2.85 µm, after: 42.55±1.19 µm ) than GpB (before: 55.54±1.17 µm, after: 68.24±9.78 µm).
Conclusions: Restored teeth with this conservative approach were able to bear thermocycling. The integration of both fiber reinforced resin composite with ribbond had positive effect on marginal adaptation.