Fluoride effect on the secretory-stage enamel organic extracellular matrix of mice

Abstract

The formation of an ordered enamel organic extracellular matrix (EOECM) seems to be a crucial step for the proper formation of the enamel mineral phase. The ordered supramolecular structure of the EOECM in the secretory stage can be analyzed using polarizing microscopy, as it is strongly birefringent. Excessive fluoride (F) ingestion during tooth development can cause enamel fluorosis, leading to increased porosity in mature enamel. We analyzed the effects of F on the birefringence of the EOECM in the A/J, CBA, and DBA/2 strains of mice given 0, 11.25, and 45 ppm of fluoride in drinking water. In the CBA and DBA/2 strains, the 11.25 and 45 ppmF groups presented a significant decrease in optical retardation (OR) when compared with the respective 0 (CBA 11.25 ppmF p = 0.0056 and 45 ppmF p < 0.0001; DBA/2 11.25 and 45 ppmF p < 0.05). ORs in A/J 0 ppmF were significantly higher than in 45 (p < 0.0001). The enamel of the A/J strain was more severely affected by fluoride than it was in the other strains of mice and exhibited the lowest levels of fluoride in plasma, whereas its normal secretory enamel presented a significantly higher protein absorbance than it did in CBA and DBA mice (p = 0.0099 and p = 0.0025, respectively). The results showed that experimental fluorosis can alter the supramolecular organization of EOECM in the secretory stage of amelogenesis and that the susceptibility to dental fluorosis seems to be influenced by the inherent characteristics of the developing enamel.

• amelogenesis
• birefringence
• enamel organic extracellular matrix
• fluoride
• polarizing microscopy

ACKNOWLEDGMENTS

The authors thank Eliene Aparecida Orsini Narvaes, Maria Aparecida Santiago Varella (Department of Morphology), José Alfredo da Silva, and Waldomiro Vieira Filho (Department of Physiological Sciences, Piracicaba Dental School, University of Campinas—UNICAMP) for providing excellent technical assistance, and Dr. Livia Maria Andaló Tenuta for helping with fluoride determinations.

This study was supported by the Brazilian National Research Council (CNPq), FAPESP (grant 04/10994-4) and approved by Committee for Ethics in Animal Research (CEEA—UNICAMP, protocol number 1458-1).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.