Clinical Relevance

Secondary caries are the main reason for the failure of restorations, class II being the most affected. Techniques that promote less gap percentage are important. Flowable bulk fill composites used at such locations have been shown to decrease gap formation while being a faster procedure than an incremental technique.


To evaluate gap formation of class II restorations, resin-filling techniques using microcomputed tomography (μCT) and scanning electronic microscopy (SEM) are discussed.

Methods and Materials:

Class II cavities were prepared in 30 third molars and analyzed in distal and mesial views. Prime&Bond Universal adhesive was applied in all teeth and divided into five groups (n=6): G1, SS+HIT (Spectra Smart+Horizontal Incremental Technique); G2, SS+OBL (Oblique Incremental Technique); G3, SDR+BFT (Surefil SDR+Bulk Fill Technique); G4, SDR+SS (SDR placed on cervical floors from mesial and distal boxes (not light cured), followed by incremental layering with SS and light curing incrementally with the horizontal technique); and G5, BEZ+BFT (Bulk EZ+BFT). All light-curing procedures were performed with high-mode/1200 mW/cm2, Bluephase Style 20i. Teeth were scanned twice (first scan, empty tooth; second scan, filled tooth after light curing) by μCT. Acquired μCT data were evaluated with software looking for gaps at the external mesial and distal margins and submitted to statistical analysis (one-way analysis of variance and least significant differences post hoc test). Validation of the μCT analysis was performed by SEM.


G5 showed the lowest gap formation percentage, similar to G4 (p=0.20). G4 also showed statistical similarities to G1 and G3 (p>0.05). G2 showed the highest percentages, similar to G1 (p=0.10) but different from the rest of the groups (p<0.05). SEM validated the μCT technique by showing qualitative similar images regarding external marginal gap.


The dual-cure composite and the use of flowable nonpolymerized plus horizontal filling technique showed the best marginal adaptations. The μCT technique was validated for visualization of gap formation after being compared to the SEM technique.

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