Kinetics of calcium and fluoride binding to the surface of streptococci and the importance of these ions as mineral reservoirs in dental biofilm

Author(s)

Tarcísio Jorge Leitão

• Document type: Doctoral Thesis
• Press: Piracicaba, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
• Defense date: 2012-06-25

Examining board members

Livia Maria Andaló Tenuta; Cecilia Pedroso Turssi; Fernanda Faot; Carolina Patrícia Aires; Rafael Nobrega Stipp

• Advisor: Livia Maria Andaló Tenuta

Abstract

The study of the retention of mineral ions in dental biofilm and their release to the biofilm fluid is important to understand the role of these reservoirs to interfere with the dental caries process. It is known that fluoride (F) is bound to the biofilm by interaction with calcium (Ca) ions. One type of reservoir formed is Ca-F bridging in bacteria surface and in proteins of the extracellular matrix. When pH drops in dental biofilm after a sugar exposure and a subsaturation state is established, favoring dental demineralization, the ions released from these reservoirs could reduce the potential for mineral loss, but this is unclear in the literature. Furthermore, there is evidence that a Ca pre-rinse increases F retention in biofilm and to evaluate the kinetics of binding and release these ions could be an important strategy to the development of methods that keep them for longer periods in the dental biofilm. Thus, this study aimed to evaluate the kinetics of Ca and F binding and release from bacteria surface as a function of time and pH. Streptococcus mutans IB 1600 was used in all experiments. In vitro studies were conducted to evaluated the kinetics of Ca binding and release using treatments solutions containing 0, 1 or 10 mM Ca. The release capacity also was evaluate after a pH drop. Furthermore, the binding capacity and kinetics of fluoride at 52.6 ?M F (1 ppm F) to bacteria was evaluated. The amount of Ca and F bound to bacteria after equilibrium with treatment solutions was determined in the bacterial pellet after treatment with strong acid, using a colorimetric method and F electrode, respectively. Curves and parameters of binding and release were calculated and treated as biochemical phenomena. Results showed that Ca binding to S. mutans is concentration-dependent and rapid, with maximum saturation achieved in the first minutes. On the other hand, Ca release was shown to be a slower phenomenon, since a significant amount of ions was still bound after 60 min of treatment with Ca-free solution. Moreover, the Ca release seems to be a direct function of media pH and not influenced by the amount of Ca previously bound. F binding to bacteria also shown to be a rapid phenomenon, but independent of Ca concentration in bacteria. Also, Ca binding was not affected by F presence in the treatment solution. In summary, the results suggest that ions bound to bacterial surface could be an important reservoir able to persist for a significant period of time and be released into the biofilm fluid during a pH drop. Furthermore, F binding to bacteria seems not to be influenced by Ca previously bound (AU)

• FAPESP's process: 11/23677-0 - Fluoride retention in dental biofilm: role of bacterial calcium binding and in situ anticariogenic potential
• Grantee: Tarcísio Jorge Leitão de Oliveira
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)