Bulk fill restoratives: to cap or not to cap--that is the question?

To assess the cuspal deflection and cervical microleakage scores of standardised large mesio-occlusal-distal (MOD) cavities filled with different restoration protocols: (1) conventional resin restoratives, (2) bulk fill flowable base materials 'capped' with a conventional dimethacrylate resin-based composite (RBC) or (3) bulk fill resin restorative materials.

Standardised MOD cavities were prepared in sixty-four sound maxillary premolar teeth and randomly allocated to eight groups. Restorations were placed in conjunction with a universal bonding system and resin restorative materials were irradiated with a quartz-tungsten-halogen light-curing-unit. Restoration protocol (eight oblique increments of conventional resin restorative, bulk fill flowable base and two occlusal 'capping' RBC increments (three increments in total) or bulk fill resin restorative (two increments)) was the dependent variable. A twin channel deflection measuring gauge measured the buccal and palatal cuspal deflections. Teeth were thermally fatigued, immersed in a 0.2% basic fuchsin dye for 24h, sectioned and examined for cervical microleakage score.

Post hoc Tukey's tests highlighted significant differences in the mean total cuspal deflection values between resin restoratives (p < 0.0001) and restoration protocol (p < 0.005). In general (albeit product dependently), an increase in mean total cuspal deflection and concomitant decrease in cervical microleakage score was evident for bulk fill flowable base materials with occlusal 'capping' RBC increments (restoration protocol 2) compared with bulk fill resin restoratives (restoration protocol 3).

Not all bulk fill flowable materials or bulk fill resin restoratives behave in a similar fashion when used to restore standardised MOD cavities in maxillary premolar teeth and material selection is vital in the absence of clinical data.

Poorly performing bulk fill flowable materials or bulk fill restoratives can be identified using the cuspal deflection and cervical microleakage protocol which could save the complications encountered clinically when restoring Class II restorations.