Microbial shift of oral biofilm associated with remineralization of root dentin lesions.

Purpose: To examine the relationship between remineralization of incipient root dentin lesions and the presence of polymicrobial biofilms, as well as examine changes in microbial composition.

Methods: Bovine root dentin disks used as specimens for biofilm formation, were cultured using saliva from a single donor. Amsterdam Active Attachment biofilm model was used to grow biofilms. The culture medium was McBain 2005 with 0.2% sucrose and 0.4 ppm F as sodium fluoride. After cultivation for 48 hours to achieve demineralization, a control group (n=10) was obtained and the other specimens were further cultured for 336 hours in two types of remineralization culture medium, with sucrose (S+) and without sucrose (S-), through continuous anaerobic incubation (10% CO2,10% H2, 80% N2). Then half of the specimens cultured in the S- medium were transferred to the S+ medium for an additional 48 hours resulting in three experimental groups S(+) (n=10), S(-) (n=10), and S(-)de (n=10), respectively. Experiment 1: Transverse microradiography (TMR) analysis - Immediately after respective culture treatments, integrated mineral loss (IML) and lesion depth (LD) in the dentin specimens were analyzed by TMR. Experiment 2: Microbiome analysis - Sequence data of the 16S rRNA gene of each sample was obtained using MiSeq, and partial base sequences were determined. Next-generation sequencing was performed to determine the taxonomic groups of fungi present in the biofilm samples.

Results: Experiment 1: In the control group, formation of dentin demineralization lesions by polymicrobial species biofilms was confirmed. The S(-) group showed significantly decreased IML and shallower LD compared to the control group. The S(-)de group showed a significant increase in IML and LD compared to the S(-) group. Experiment 2: There were statistically significant differences in microbiome between the control group and each of the three experimental groups, both at the genus and species levels. A significant difference in genus was observed between the S(-) group and the S(-)de group.

Clinical Significance: The confirmation of the possibility of microbial shift occurring during the remineralization process of root caries will lead to the development of new remineralization therapies.