Optically Assessing Biofilm Distribution in Gaps and Wall Lesion Development

Objectives: This study investigated the distribution of cariogenic biofilm in marginal gaps with multiple patterns by spectral-domain optical coherence tomography (SD-OCT) using an in vitro biofilm model, with the aim to evaluate whether gap size or gap location could affect biofilm formation in gaps and enamel wall lesion development.
Methods: Twenty-four cavities (surface diameter: 2.5mm, bottom diameter: 1.0mm, depth: 1.5mm) were prepared in bovine incisors, restored by Clearfil SE Bond 2 and Clearfil Majesty ES Flow, containing intentional gaps. According to gap location (EA: enamel-adhesive interfacial gap; RA: resin-adhesive interfacial gap) and gap size (40, 80, 120µm), specimens were divided into six groups (EA40, EA80, EA120, RA40, RA80, RA120). Streptococcus mutans (ATCC25175) biofilms were grown within gaps after anaerobic incubation (37°C, 7d). Biofilm distribution in gaps and enamel wall lesion progression were observed by three- and two-dimensional SD-OCT (Thorlabs). Biofilm area (Area), biofilm percentage (Percent) and enamel wall lesion depth (Depth) were measured by Image J and analyzed by Mann-Whitney U test, Kruskal-Wallis test followed by multiple comparisons. All statistics were analyzed at 95% significant level.
Results: Horizontal distribution of biofilm in gaps could be detected by SD-OCT. In Percent, EA40, EA80 were significantly lower than RA40, RA80, separately; in Depth, EA40, EA80, EA120 were significantly higher than RA40, RA80, RA120, separately. EA40 was significantly lower than EA120 in Area and Percent; however, RA40, RA80 and RA120 showed no significant differences in Area, Percent or Depth.
Conclusions: SD-OCT has a potential for biofilm distribution mapping in gaps. Gap size and gap location affect biofilm formation in gaps and enamel wall lesion development. In small gaps, resin-adhesive gaps cause more biofilm formation than enamel-adhesive gaps. However, enamel wall lesions develop less in resin-adhesive gaps than in enamel-adhesive gaps. In enamel-adhesive interfaces, small gaps cause less biofilm formation than large gaps.