Clinical Study on the Influence of Using Separating Medium and Its Type on Indirect Resin Composite Microtensile Bond Strength to Dentin

Purpose: To evaluate the effect of using separating medium and its type on the microtensile bond strength of indirect resin composite restoration to dentin clinically. Materials and methods: Standard 24 MOD cavities were prepared in the upper first premolars for the selected patients by one operator and restored using indirect resin composite (Grandio So Inlay System, VOCO, Germany). Inlays were constructed outside the patient mouth either on silicone die (according to manufacture instructions) or on stone die using two different separating media (glycerin or Vaseline). The fitting surface of the inlay was sandblasted, silanated and bonded before cementation. Teeth were treated with a dual cured adhesive (Futurabond DC, VOCO, Germany) and resin cement (Bifix QM, VOCO, Germany) was used for cementation. After the assigned time (either 24 hours or 3 months) the restored teeth were extracted atraumatically. They were prepared for microtensile bond strength testing which was performed using the universal testing machine. Each restoration yielded 3-4 beams with a total of 90 specimens (15 specimens for each group). Failure mode analysis was done by digital microscope. Collected data were statistically analyzed using One Way-ANOVA and Independent t-test. Results: After 24h silicon die group showed the highest statistical mean microtensile bond strength (29.25±1.57 MPa) followed by stone die (Glycerin) (28.2±1.01 MPa) and then stone die (Vaseline) (24.88±1.17 MPa) at p≤0.001 with an insignificant difference between silicon die and stone die (Glycerin) after 24 h .After 3 months all the values were statistically lower than 24h at p≤0.001.Stone die specimens exhibited predominantly mixed failure and the other two groups commonly had cement/restoration adhesive failure . Conclusion: Fabrication of indirect restoration on silicone die without using separating medium has a great influence on achieving high microtensile bond strength value to the dentin even after 3 months. Vaseline has a deteriorating effect on the microtensile bond strength when it is used as a separating medium for the stone die.