Rapid high-intensity light-curing of bulk-fill composites: A quantitative analysis of marginal integrity

To investigate the effect of rapid high-intensity light-curing on the marginal integrity of four bulk-fill composites, including two materials specifically designed for high-intensity curing.

Class V cavities were prepared on buccal surfaces of intact human molars with simulated pulpal pressure, filled in a single increment and light-cured using a conventional (10 s @ 1,340 mW/cm²) or high-intensity (3 s @ 3,440 mW/cm²) protocol. The restorations were subjected to thermo-mechanical loading (TML) comprising 1,200,000 mechanical loading cycles and 3,000 thermocycles. Quantitative margin analysis was performed before and after TML using a scanning electron microscope, and the marginal integrity was expressed as percentage of continuous margin (PCM).

All PCM values measured before TML were statistically similar regardless of the material and curing protocol (p>0.05). A statistically significant effect of the curing protocol (p = 0.021) was identified only after TML for one material. PCM was significantly diminished by TML (p<0.001) for most combinations of material and curing protocol. The PCM values of the sculptable composites after TML were statistically similar regardless of the curing protocol (p>0.05). Compared to these values, significantly lower PCM after TML was identified for the flowable composites cured with the high-intensity protocol (p = 0.001-0.045).

In most cases, high-intensity and conventional curing generally led to similar marginal integrity. Although all of the investigated composites initially performed similarly well, the flowable composites light-cured using the high-intensity protocol showed a significantly inferior marginal integrity compared to the sculptable composites after loading.

Rapid high-intensity light-curing cannot be recommended for flowable bulk-fill composites since it may compromise the tooth-restoration interface.