Introduction:
Adhesive restorations in endodontically treated posterior teeth could increase the strength of teeth and decrease the microleakage. The aim of this study was to evaluate the effect of flowable composite as a liner as well as an internal splint agent on bond strength of endodontically treated molars restored with amalgam.
Materials and Methods:
This study was an interventional study which evaluated the fracture resistance of endodontically treated molars in two groups based on cavity preparation of class II MOD or MOD in combination with lingual cusp reduction. Each group was divided into four subgroups and restored with: 1 and 2) Tetric Flow and amalgam with and without prefabricated post. 3 and 4) Copalite and amalgam with and without prefabricated post.  The control group consisted of intact molar teeth. After the restorations were made, the specimens were stored at 37^oC with 100% humidity for 24 hours and then submitted to the load cycling (500,000 cycles) simultaneously with thermal cycling (5^oC and 55^oC). Analysis of data was done by ANOVA and Duncan test with 95% significance level.
Results:
Two factors (Post and cavity preparation) had a statistical interaction with each other (P<0.05). This means that without post, amalgam cuspal coverage restorations were able to increase the fracture resistance of teeth significantly but with post they were not able to do so. Post and Tetric Flow had no effect on fracture resistance individually (P>0.05), and control group showed the most fracture resistance (P<0.05).
Conclusion:
In patients with  suitable  occlusion, lingual cusp reduction and restoration with amalgam without intracanal pin could be an acceptable treatment.