Purpose: To validate the rationale of using a conventional light-curing resin-based composite (RBC) to lute thick indirect restorations by measuring mini-interfacial fracture toughness (mini-iFT).

Materials and methods: Freshly exposed dentin of extracted third molars (n = 64) was immediately sealed with a thin layer of an experimental RBC with a 50 wt% or 75 wt% (IDS) filler load. Two- or 6-mm -thick CAD/CAM composite block s were luted onto IDS using either pre-heated light-cure or dual-cure luting RBC , with the latter having served as control. Samples were cut into sticks, upon which a notch was prepared at the interface between IDS and luting RBC , prior to being submitted to a 4-point bending test to determine mini-iFT. The results were analyzed using a mixed linear model (LME). Failure mode at the fractured interface was determined using scanning electron microscopy (SEM).

Results: LME revealed that mini-iFT was not significantly affected by the composite block thickness (p = 0.39) , but by the luting RBC (p < 0.0001) and the IDS RBC filler load (p = 0.0011). Mini-iFT was higher with 50 wt% filler-loaded RBC IDS and when luted using the light-cur ing RBC.

Conclusion: This work provides the proof of concept that 2- and 6-mm -thick indirect restorations can safely be adhesively luted with pre-heated conventional light-cure RBC under controlled light-irradiation conditions. This strategy even seems beneficial in terms of mini-iFT compared to using a dual-cure luting RBC. IDS with lower filler content also appeared more favo rable.