Fluoride Action Network

Dental Fluorosis Impacts Dentin in Addition to Enamel

Fluoride Action Network | By Michael Connett

Dental fluorosis is a mineralization defect of tooth enamel marked by increased subsurface porosity. The enamel, however, is not the only component of teeth that is effected. As several studies have demonstrated, dental fluorosis can also impair the mineralization of dentin as well. As noted in one review:

“The fact that human dentin also exhibits hypomineralization in human fluorotic teeth indicates that fluoride exerts its effects on very basic processes involved in biomineralization in general, irrespective of whether crystal formation and growth occurs in mesenchymally or ectodermally derived mineralized tissues. However, relatively little work has been done to identify the mechanisms by which low serum levels of fluoride which result in dental fluorosis affect the development of mineralizing tissues.”
SOURCE: Fejerskov O, Richards A, DenBesten P. (1996). The effect of fluoride on tooth mineralization. In: Fejerskov O, Ekstrand J, Burt B, Eds. Fluoride in Dentistry, 2nd Edition. Munksgaard, Copenhagen. pp. 112-152.

The following are excerpts from studies that have examined fluoride’s effect on dentin mineralization:

“To the authors’ best knowledge, this study is the first to analyze the correlation between dentin [F] and the mechanical and structural properties of dentin. Despite previous work on dentin quality (structural, material and mechanical properties), no studies have evaluated the relationship between dentin mechanical and structural properties and tooth [F]. This relationship is important owing to the increase in F ingestion worldwide (e.g. halo effect, F in dentifrices and other dental products).

In this study, we showed that enamel F concentration does not correlate with any of the parameters tested, while dentin [F] correlates positively with dentin tubule size and negatively with ultrasound velocity. Moreover, the severity of DF [Dental Fluorosis] correlates positively with dentin tubule density and ultrasound velocity. It is known that ultrasound velocity relates to elastic modulus, and that dentin tubule size appears to be related to tooth sensitivity. Dentin sensitivity is believed to be related to dentin tubule permeability, which in turn is related to dentin tubule size. Therefore, one can infer that dentin [F] and/or DF severity, influence dentin elastic modulus and tooth sensitivity.

When analyzing all teeth together, our study showed a positive correlation between dentin [F] and dentin tubule size, demonstrating wider dentin tubules in teeth with higher levels of F in dentin. This is interesting because in humans, histological changes caused by the ingestion of F have more easily been detected in the enamel, but in severe fluorosis the dentin has also shown histological modifications. Fluoride concentration has been shown to influence crystal size, and some evidence indicates that F has an effect on cell function, either directly through interactions with the developing ameloblasts and/or odontoblasts or more indirectly by interacting with the extracellular matrix. Fluoride has been shown to increase bone formation and to increase mineralization lag time in bone, increasing the time between matrix deposition and its mineralization. The F content in the tooth structure may therefore have the same type of action on odontoblast and dentin mineralization (i.e. decreasing the mineralization rate). A hypomineralized enamel and dentin is therefore formed. This action would then explain the positive relationship between dentin tubule size and tooth [F], where hypomineralization, caused by F concentration, would create wider dentin tubules. Another possible hypothesis is that F would influence crystal growth, forming an impaired dental structure with wider dentin tubules.”
SOURCE: Vieira AP, et al. (2006). Fluoride’s effect on human dentin ultrasound velocity (elastic modulus) and tubule size. European Journal of Oral Science 114:83-8.

“Fluoride (F) has been a useful instrument in caries prevention. However, only limited data exist on the effect of its long-term use on dentin mineralization patterns and microhardness… Teeth were analyzed for DF severity, dentin [F], enamel [F], dentin microhardness, and dentin mineralization. Dentin [F] correlated with DF severity; enamel [F] correlated with dentin microhardness and dentin mineralization; DF severity correlated with dentin microhardness.”
SOURCE: Vieira A, et al. (2005). How does fluoride affect dentin microhardness and mineralization? Journal of Dental Research 84:951-7.

“Thus, the present study has demonstrated that exposure of the dentin-pulp complex to higher concentrations of fluoride influences the mineralization process in the transition from predentin to dentin, which may well have a mechanistic basis in the fluoride-induced extracellular matrix changes arising in this region of the tissue. In view of the continued apposition of dentin throughout life, these observations indicate that exposure to high levels of fluoride may exert effects at the cellular level well beyond tooth development during primary, physiological secondary and tertiary dentinogenesis. There are also implications for the regeneration and repair of dentin after injury. The critical importance of growth factors sequestered within the dentin matrix in dentin repair and their association with extracellular matrix components imply that biological repair processes may also be susceptible to the effects of excessive fluoride exposure.”
SOURCE: Moseley R, et al. (2003). The influence of fluoride exposure on dentin mineralization using an in vitro organ culture model. Calcified Tissue International 73:470-5.

“Although the exact mechanisms are unclear, the mineralization of connective tissues such as dentine is apparently altered in the presence of fluoride.”
SOURCE: Milan AM, et al. (2001). Fluoride alters casein kinase II and alkaline phosphatase activity in vitro with potential implications for dentine mineralization. Archives of Oral Biology 46:343-51.

“The sevenfold reduction in phosphate content of DPP isolated from fluorotic dentine evident in the present study will undoubtedly have an influence on the anionic nature of these macromolecules. Such a major change in the biochemical structure of DPP, together with those previously reported for other macromolecules such as proteoglycans, are likely to be important in considering the hypomineralization associated with fluorosis.”
SOURCE: Milan AM, et al. (1999). Altered phosphorylation of rat dentine phosphoproteins by fluoride in vivo. Calcified Tissue International 64:234-8.

“In 1925 Beust called attention to the fact that in adddition to the enamel, the dentin was likewise affected, a condition which he termed mottled dentin.”
SOURCE: Dean HT. (1936). Chronic endemic dental fluorosis (mottled enamel). Journal of the American Medical Association 107: 1269-1273.