Microleakage Under Class II Restorations Restored With Bulk-fill Materials

Objectives:
To compare microleakage around Class II restorations with a light-cured (Filtek Bulk Fill Posterior) and three dual-cured (Activa, Bulk EZ, Fill-Up!) bulk-fill materials and a conventional light-cured (Filtek Supreme Ultra) material.
Methods: 48 human molars were prepared with Class II slot preparations (5±.5mm height x 4±.5mm width x 2±.5mm depth). Scotchbond Universal (3M ESPE) adhesive, used in the self-etch mode, was applied for 20s, dried, and cured for 10s with an LED curing light (Elipar S10, 3M ESPE, output>1000mW/cm²). For the Fill-Up! group, a dual-cure activator was mixed with the adhesive. A circumferential metal matrix was placed and the teeth (n=8) were randomly restored with A2 shade of each composite. All restorations were placed in a single increment except Filtek Supreme Ultra which was placed in 3 horizontal increments. The specimens were then incubated at 37°C for 48hrs and thermocycled for 10,000 cycles (5°C-55°C, 15s dwell time). An acid-resistant varnish was painted on the tooth leaving a 2mm window unpainted around the restorations. The specimens were immersed in 0.5% toluidine blue (24hrs). Teeth were sectioned in half mesial-distally with a diamond wheel. Microleakage was measured from the external surface at the gingival floor of the restoration along the tooth-restoration interface using a digital microscope (Keyence VHX 600 Series). Percentage of marginal microleakage (stain penetration divided by the depth of the preparation) was compared between different materials using a Kruskal-Wallis test. A Dunn’s test with Bonferroni correction was used for post-hoc comparisons.
Results: Percentage of marginal microleakge (mean±SD) for each group was 12±23%(Filtek Bulk Fill), 17±35%(Activa), 0±0%(Bulk EZ), 26±35%(Fill-Up!), 34±48%(Filtek Supreme in increments), 73±29% (Filtek Supreme in bulk). Significantly less microleakage was produced with Bulk EZ(p<.01), Filtek Bulk-fill(p=.01), and Activa(p=.01) than Filtek Supreme placed in bulk.
Conclusions: Some bulk-fill materials allow less microleakage than conventional composites when placed in bulk.