Fluoride-induced alterations of enamel structure: an experimental study in the miniature pig

Abstract

We studied the structural changes in the enamel of mandibular third molars of miniature pigs administered a daily oral dose of 2 mg NaF (approximately 0.9 mg of fluoride) per kg body weight (added to the feed) for 1 year. The treatment period covered most of the secretory stage and the entire post-secretory stage of amelogenesis of the M(3). The enamel of the molars from the fluoride-fed pigs appeared opaque and chalky, and the erupted portions were stained brown. The underlying histopathological change was a pronounced subsurface hypomineralization of the enamel beneath a thin surface rim of higher mineral content. This enamel hypomineralization was attributed to a fluoride-induced impairment of the process of enamel maturation. The most conspicuous finding in the fluorotic enamel was the presence of numerous pit-type hypoplastic defects, denoting a marked fluoride-induced disturbance also of the secretory stage of amelogenesis. Microradiography and scanning electron microscopy revealed an enhanced incremental pattern in the outer enamel of the fluorotic molars. Typically, the bottom of larger hypoplastic defects was underlain by a broad, grossly accentuated incremental line. Occurrence of larger hypoplasias was further associated with the presence of aprismatic enamel, the formation of which was attributed to a loss of the prism-forming (distal) portion of the Tomes' processes of secretory ameloblasts. The findings in the miniature pigs closely parallel earlier observations on fluorotic enamel of free-ranging deer and wild boar from fluoride-polluted areas.

The Impact of Fluoride on Ameloblasts and the Mechanisms of Enamel Fluorosis

“…Mineralization defects in rat incisor maturation-stage enamel can develop during prolonged exposure to fluoridated drinking water at levels as low as 9-10 ppm fluoride (Shinoda, 1975;Angmar-Månsson et al, 1976), and are characterized by the development of a generalized hypomineralized porous subsurface area along the entire crown enamel (Fig. 3a) (Shinoda, 1975;Angmar-Månsson et al, 1976;Whitford, 1982, 1984;Richards et al, 1992;Kierdorf et al, 2004). This type of defect correlates to the porous white opacities seen clinically.…”

“…Whether such lesions erupt as pits (Kierdorf et al, 2004), or develop into pits post-eruptively by mechanical damage of the surface layer that covers the porous subsurface defect (Fejerskov et al, 1994), remains to be investigated. Studies in sheep suggest that both options are possible (Suckling and Thurley, 1984).…”

“…In severe cases, prismless enamel is found within prismatic inner enamel. At these locations, formation of prismatic enamel had been abruptly interrupted during fluoride insult, during which prismless enamel had formed; after recovery, the prismatic enamel continued to form (e.g., Neiman and Eisenmann, 1975;Chen and Eisenmann, 1984;Suckling et al, 1988;Monsour et al, 1989;Kierdorf and Kierdorf, 1997;Kierdorf et al, 2000Kierdorf et al, , 2004.…”

Deposition of cellular cementum onto hypoplastic enamel of fluorotic teeth in wild boars (Sus scrofa L.)

“…The presence of different types of hypoplastic defects denotes a marked impairment of secretory ameloblast function. The grossly enhanced incremental lines in the enamel indicate the location of the surface of the forming enamel at the time of a severe impact on the secretory ameloblasts that caused a permanent or transient cessation of matrix secretion (Kierdorf et al 2000(Kierdorf et al , 2004. Externally visible hypoplastic defects formed when groups of ameloblasts failed to resume their normal secretory function.…”

Developmental defects and postmortem changes in archaeological pig teeth from Fais Island, Micronesia

“…Studies in domestic pigs and wild boar also suggested that histological analysis of developmental defects of enamel enables an assessment of the duration and intensity of stress episodes of different nature that affected enamel formation (Kierdorf et al, 2004(Kierdorf et al, , 2005Witzel et al, 2006).…”