Differential susceptibility of Streptococcus dentisani to dental surfaces: An atomic force microscopy study.

Background: Given frequent dental restorations, understanding the interactions of probiotic Streptococcus dentisani with enamel and dental materials is key, in contrast to the well-studied Streptococcus mutans. This knowledge is vital for the potential applications in promoting oral health of S. dentisani.

Objective: This study aims to evaluate and compare S. mutans and S. dentisani initial adhesion, proliferation, and colonization on dental enamel and commonly used dental materials: nickel-chromium alloy, porcelain, lithium disilicate, autocured, and thermocured acrylics, using atomic force microscopy (AFM).

Methods: The study utilized S. mutans ATCC 35665 and S. dentisani CECT 7746 cultured in brain-heart infusion (BHI) broth. The dental substrates used consisted of enamel obtained from healthy unerupted third molars, nickel-chromium alloy (Ni-Cr), porcelain, lithium disilicate, and both autocured and thermocured acrylics. All simples were cut into 1 cm pieces and subsequently mounted for the AFM analysis. Bacterial suspensions were incubated on these surfaces for 24 h. Surface topography and bacterial adhesion, proliferation, and colonization were analyzed using AFM in contact mode. Roughness parameters (R_a, R_rms, R_Max) were quantified from AFM images using the Nanoscope analysis software.

Results: Atomic force microscopy analysis revealed that after a 24-h incubation, S. mutans demonstrated a superior capacity to adhere, proliferate, and colonize all tested substrates compared to S. dentisani. Streptococcus dentisani was found to be more susceptible to the bactericidal effects of the materials. Notably, porcelain and lithium disilicate surfaces exhibited strong antimicrobial activity. On porcelain, no intact S. dentisani cells were observed, only bacterial debris. Similarly, lithium disilicate showed evidence of bacterial decomposition for both strains, suggesting a potent bactericidal effect.

Conclusion: For the first time, our data revealed that S. dentisani exhibited a reduced capacity for dental surface adhesion, proliferation, and colonization across all tested substrates, compared to S. mutans.