Biofilms are living biological materials that appear when bacteria synthesize and assemble extracellular matrix components after colonizing a surface. They constitute a key feature of bacteria survival in biologically, chemically and/or physically challenging environments. In the mouth, the oral microbial community builds biofilms called dental plaque. Oral biofilms are associated with some of the most common dental diseases, such as caries and periodontitis [1]. Dental calculus is formed when the oral biofilms mineralize in contact with the calcium and phosphate containing oral fluids such as saliva. Supragingival calculus is located above the gingival margin, while subgingival calculus is located below the gingival margin in the periodontal pocket. Dentists observe different material brittleness and adhesion strength to the tooth substrate of supragingival versus subgingival calculus, the mineralization processes leading to these differences are yet only partially understood. In this work, we first aim to understand the differences in microstructure, mineralization and composition of the two types of dental calculus and ultimately derive principles for efficient adhesion from the tooth-calculus-interzone. For this, we characterize dental calculus on native human teeth ethically harvested from consenting donors.

We used microtomography to investigate the overall morphology of the calculus at the mesoscale (Fig. 1a) and microscale, and found differences in micro-porosity. Further characterizations of the interface between mineralized biofilm and tooth at the nanoscale were performed using focused ion beam-scanning electron microscopy (FIB-SEM) (Fig. 1b) and transmission electron microscopy (TEM). Preliminary results revealed the presence of bacteria of different shapes and mineralization degrees in the supragingival versus subgingival calculus. Finally, synchrotron wide angle X-ray scattering data showed significant differences in the crystalline composition and morphologies of the two types of calculus. In the future, combining this structural knowledge with dental calculus adhesion measurements will be key for developing new strategies towards long-lasting interfaces in dentistry.

References

[1] A. Akcali; Periodontology 2000, 2018, 76, 116-115.

Dr. Cécile Bidan