Fluoride-induced developmental changes in enamel and dentine of European roe deer (Capreolus capreolus L.) as a result of environmental pollution

Low-fluoride gels supplemented with nano-sized sodium trimetaphosphate reduce dentin erosive wear in vitro

OBJECTIVE

The study assessed the effect of low-fluoride gels supplemented with micrometric or nano-sized sodium trimetaphosphate (TMP) on dentin erosive wear in vitro.

DESIGN

Bovine dentin blocks (n = 154) were selected by surface microhardness and randomly allocated into seven groups (n = 22/group), according to the gels: Placebo; 4500 ppm F (4500F); 9000 ppm F (9000F); 5% TMP microparticulate plus 4500F (5TMPm+4500F); 2.5% TMP nanoparticulate plus 4500 F (2.5TMPn+4500F); 5% TMP nanoparticulate plus 4500F (5TMPn+4500F); and 12,300 ppm F acid gel (APF). All blocks were treated only once for 60 s and cyclically eroded (ERO, citric acid, 4 × 90 s/day) or eroded and brushed (4 × 15 s/day, five strokes/s, ERO+ABR) over five days (each subgroup n = 11). Dentin wear and integrated hardness loss in depth (ΔKHN) were determined, and the data were submitted to two-way ANOVA, followed by Tukey's test, and Spearman's correlation (p < 0.05).

RESULTS

For ERO, all gels containing 4500F supplemented with TMP significantly reduced dentin wear compared with their counterpart without TMP, reaching values similar to 9000F. For ERO+ABR, 5TMPn+ 4500F gel led to significantly lower wear than all its counterparts, reaching values similar to 9000F and APF. As for ΔKHN, all gels containing TMP promoted superior protective effects compared with 4500F, reaching values similar to 9000F and APF under both challenges. A positive correlation between dentin wear and mineral content in depth was verified.

CONCLUSIONS

Gels containing 4500F supplemented with TMP significantly reduced dentin erosive wear compared with pure 4500F, with additional benefit from the use of nanoparticles.

Fluoride Alters Signaling Pathways Associated with the Initiation of Dentin Mineralization in Enamel Fluorosis Susceptible Mice

Fluoride can alter the formation of mineralized tissues, including enamel, dentin, and bone. Dentin fluorosis occurs in tandem with enamel fluorosis. However, the pathogenesis of dentin fluorosis and its mechanisms are poorly understood. In this study, we report the effects of fluoride on the initiation of dentin matrix formation and odontoblast function. Mice from two enamel fluorosis susceptible strains (A/J and C57BL/6J) were given either 0 or 50 ppm fluoride in drinking water for 4 weeks. In both mouse strains, there was no overall change in dentin thickness, but fluoride treatment resulted in a significant increase in the thickness of the predentin layer. The lightly mineralized layer (LL), which lies at the border between predentin and fully mineralized dentin and is associated with dentin phosphoprotein (DPP), was absent in fluoride exposed mice. Consistent with a possible reduction of DPP, fluoride-treated mice showed reduced immunostaining for dentin sialoprotein (DSP). Fluoride reduced RUNX2, the transcription regulator of dentin sialophosphoprotein (DSPP), that is cleaved to form both DPP and DSP. In fluoride-treated mouse odontoblasts, the effect of fluoride was further seen in the upstream of RUNX2 as the reduced nuclear translocation of β-catenin and phosphorylated p65/NFκB. In vitro, MD10-F2 pre-odontoblast cells showed inhibition of the Dspp mRNA level in the presence of 10 μM fluoride, and qPCR analysis showed a significantly downregulated level of mRNAs for RUNX2, β-catenin, and Wnt10b. These findings indicate that in mice, systemic exposure to excess fluoride resulted in reduced Wnt/β-catenin signaling in differentiating odontoblasts to downregulate DSPP production via RUNX2.

Rethinking the evidence for early horse domestication at Botai

Despite its transformative impact on human history, the early domestication of the horse (Equus caballus) remains exceedingly difficult to trace in the archaeological record. In recent years, a scientific consensus emerged linking the Botai culture of northern Kazakhstan with the first domestication of horses, based on compelling but largely indirect archaeological evidence. A cornerstone of the archaeological case for domestication at Botai is damage to the dentition commonly linked with the use of bridle mouthpieces, or "bit wear." Recent archaeogenetic analyses reveal, however, that horse remains from Botai are not modern domesticates but instead the Przewalski's horse, E. przewalskii-warranting reevaluation of evidence for domestication. Here, we compare osteological traits hypothesized to have been caused by horse transport at Botai with wild Pleistocene equids in North America. Our results suggest that damage observed in Botai horse teeth is likely generated by natural disturbances in dental development and wear, rather than through contact with bridle equipment. In light of a careful reconsideration of the mid-Holocene archaeological record of northern Eurasia, we suggest that archaeological materials from Botai are most effectively explained through the regularized mass harvesting of wild Przewalski's' horses-meaning that the origins of horse domestication may lie elsewhere.

Modeling the age-related shift in the mineral content of hard tissues in two Mediterranean deer species

OBJECTIVE

In this paper we aim to provide baseline data and model the changes of Ca, P and Mg throughout life in the mandibular bone, enamel and dentin of red (Cervus elaphus) and fallow deer (Dama dama) in Mediterranean ecosystems.

DESIGN

Through a cross-sectional study of cervids from 1.5 to 20 yrs old, hunted between 1990 and 1997, we apply generalized additive models (GAMs) with data from scanning-electron-microscope with energy-dispersive X-ray (FESEM-EDX) and inductively coupled plasma-mass spectrometry (ICP-MS) analyses.

RESULTS

The mineral content varied in a similar range to that reported for other ruminants. However, we detected lower Ca content values, while more similar results were obtained for P and Mg contents, which led to relatively lower Ca/P ratios and higher Ca/Mg in our deer at that time. A significantly lesser pattern of decreasing mineral content with aging was detected in the fallow deer males, similarities were found between the sexes, and significantly less resistance to demineralization was observed in dentin compared to bone. We discuss how the basic macromineral elements involved in the biomineralization process vary with age throughout life depending on deer species, sex and hard tissues.

CONCLUSION

Allowing for possible inferences of differential changes in the mineralization state at the main stages in life history, our methodological approach opens up new possibilities in zooarchaeological, paleontological, and wildlife research.

Exposure to persistent organic pollutants during tooth formation: molecular mechanisms and clinical findings

Persistent organic pollutants (POPs) constitute a relevant part of environmental pollution. POPs are chemical compounds that persist for a long time in the environment, bio-accumulate in the human body and determine significant adverse consequences to human health. The characteristics of these substances are lipo-affinity, semi-volatility and resistance to the degradation processes. Results deriving from several different studies attest that exposure to the main classes of POPs results in multiple toxic effects on humans and experimental animal models. Among the various alterations caused by exposition to and bio-accumulation of POPs, there are abnormalities in tooth formation and related hard dental tissue structure, especially enamel. This review aimed to describe the close association between the exposure of these compounds during the development of the tooth germ and the occurrence of tooth structural anomalies. Indeed, structural defects of the enamel have as possible consequences higher susceptibility of the tooth to caries disease and higher fragility of the crown to the occlusal trauma.

In vitro study of effects of ELF-EMF on testicular tissues of roe deer (Capreolus capreolus) - FTIR and FT-Raman spectroscopic investigation

Electromagnetic fields (EMF) are classified as an environmental factor affecting living organisms. The aim of the study was to evaluate the effect of EMF at different frequencies (50 and 120 Hz), durations of treatment (2 and 4 h) and with the magnetic induction of 8 m T on testicular tissues of roe deer (Capreolus capreolus) in vitro by comparison with the control samples. Fourier Transform Raman Spectroscopy (FT-Raman) and Fourier Transform Infrared Spectroscopy (FTIR) were utilized in this study to identify the chemical changes in the testicular tissues. The FTIR and FT-Raman spectroscopy methods were used to evaluate differences in spectra of the treated tissues compared to the control group. The results from the analysis of the spectra indicated there were characteristic differences in the testicular tissue compared with the control samples. There was identification of peaks attributed to different biochemical components. Comparing the spectra for different frequencies and treatment times, there was a greater intensity of peaks originating from most of the functional groups in the tissues evaluated. With the FTIR spectra, there were five of 15 peaks, while with the FT-Raman spectra, there were six of ten peaks that were shifted. For FTIR and FT-Raman analyzed spectral ranges, results from the PCA analysis indicate there was no similarity between control groups (2 and 4 h) and samples treated with EMF at a frequency of 120 Hz for 2 and 4 h. In conclusion, therefore, EMF is an environmental factor affecting the testis of roe deer.

Interspecific variation in the diets of herbivores in an industrial environment: implications for exposure to fluoride emissions

Atmospheric fluorides (gaseous and particulate) are deposited on, and absorbed by, vegetation. Ingested fluoride accumulates in calcified tissues of vertebrates, and if it is excessive, it may lead to dental and skeletal fluorosis. The prevalence, form and severity of the effects vary greatly between species. Foraging strategy can be an important determinant of fluoride exposure in herbivores, because foliar fluoride concentrations vary between plant species, for example, according to vertical and lateral position in the vegetation. We combined microhistological analysis of diet and analysis of foliar fluoride levels to examine interspecific variation in dietary fluoride exposure of macropodid marsupials (swamp wallaby Wallabia bicolor, red-necked wallaby Notamacropus rufogriseus and eastern grey kangaroo Macropus giganteus), in the buffer zone of an aluminium smelter in Victoria, Australia. Dietary niche differentiation between species was evident. The swamp wallaby and the red-necked wallaby were browsers or mixed feeders, depending on the classification system used. The eastern grey kangaroo was a grazer, consuming almost entirely grasses. However, foliar fluoride did not vary significantly between the main plant groups consumed. Our results indicate that interspecific variation in diet at this site is unlikely to explain variation in fluoride exposure.

Reconstructing temporal variation of fluoride uptake in eastern grey kangaroos (Macropus giganteus) from a high-fluoride area by analysis of fluoride distribution in dentine

Trace element profiling in the incrementally formed dentine of mammalian teeth can be applied to reconstruct temporal variation of incorporation of these elements into the tissue. Using an electron microprobe, this study analysed fluoride distribution in dentine of first and third mandibular molars of free-ranging eastern grey kangaroos inhabiting a high-fluoride area, to assess temporal variation in fluoride uptake of the animals. Fluoride content in the early-formed dentine of first molars was significantly lower than in the late-formed dentine of these teeth, and was also lower than in both, the early and the late-formed dentine of third molars. As early dentine formation in M1 takes place prior to weaning, this finding indicates a lower dentinal fluoride uptake during the pre-weaning compared to the post-weaning period. This is hypothetically attributed to the action of a partial barrier to fluoride transfer from blood to milk in lactating females and a low bioavailability of fluoride ingested together with milk. Another factor contributing to lower plasma fluoride levels in juveniles compared to adults is the rapid clearance of fluoride from blood plasma in the former due to their intense skeletal growth. The combined action of these mechanisms is considered to explain why in kangaroos from high-fluoride areas, the (early-formed) first molars are not affected by dental fluorosis while the (later-formed) third and fourth molars regularly exhibit marked to severe fluorotic lesions.

Developmental and Post-Eruptive Defects in Molar Enamel of Free-Ranging Eastern Grey Kangaroos (Macropus giganteus) Exposed to High Environmental Levels of Fluoride

Dental fluorosis has recently been diagnosed in wild marsupials inhabiting a high-fluoride area in Victoria, Australia. Information on the histopathology of fluorotic marsupial enamel has thus far not been available. This study analyzed the developmental and post-eruptive defects in fluorotic molar enamel of eastern grey kangaroos (Macropus giganteus) from the same high-fluoride area using light microscopy and backscattered electron imaging in the scanning electron microscope. The fluorotic enamel exhibited a brownish to blackish discolouration due to post-eruptive infiltration of stains from the oral cavity and was less resistant to wear than normally mineralized enamel of kangaroos from low-fluoride areas. Developmental defects of enamel included enamel hypoplasia and a pronounced hypomineralization of the outer (sub-surface) enamel underneath a thin rim of well-mineralized surface enamel. While the hypoplastic defects denote a disturbance of ameloblast function during the secretory stage of amelogenesis, the hypomineralization is attributed to an impairment of enamel maturation. In addition to hypoplastic defects, the fluorotic molars also exhibited numerous post-eruptive enamel defects due to the flaking-off of portions of the outer, hypomineralized enamel layer during mastication. The macroscopic and histopathological lesions in fluorotic enamel of M. giganteus match those previously described for placental mammals. It is therefore concluded that there exist no principal differences in the pathogenic mechanisms of dental fluorosis between marsupial and placental mammals. The regular occurrence of hypomineralized, opaque outer enamel in the teeth of M. giganteus and other macropodids must be considered in the differential diagnosis of dental fluorosis in these species.

Dental fluorosis and skeletal fluoride content as biomarkers of excess fluoride exposure in marsupials

Particulate and gaseous fluoride emissions contaminate vegetation near fluoride-emitting industries, potentially impacting herbivorous wildlife in neighboring areas. Dental fluorosis has been associated with consumption of fluoride-contaminated foliage by juvenile livestock and wildlife in Europe and North America. For the first time, we explored the epidemiology and comparative pathology of dental fluorosis in Australian marsupials residing near an aluminium smelter. Six species (Macropus giganteus, Macropus rufogriseus, Wallabia bicolor, Phascolarctos cinereus, Trichosurus vulpecula, Pseudocheirus peregrinus) demonstrated significantly higher bone fluoride levels in the high (n=161 individuals), compared to the low (n=67 individuals), fluoride areas (p<0.001). Necropsy examinations of all six species from the high-fluoride area near the smelter revealed dental lesions considered characteristic of dental fluorosis in eutherian mammals. Within the high-fluoride area, 67% of individuals across the six species showed dental enamel lesions, compared to 3% in the low-fluoride areas. Molars that erupted before weaning were significantly less likely to display pathological lesions than those developing later, and molars in the posterior portion of the dental arcade were more severely fluorotic than anterior molars in all six species. The severity of dental lesions was positively associated with increasing bone fluoride levels in all species, revealing a potential biomarker of excess fluoride exposure.

Fluorosed mouse ameloblasts have increased SATB1 retention and Gαq activity

Dental fluorosis is characterized by subsurface hypomineralization and increased porosity of enamel, associated with a delay in the removal of enamel matrix proteins. To investigate the effects of fluoride on ameloblasts, A/J mice were given 50 ppm sodium fluoride in drinking water for four weeks, resulting serum fluoride levels of 4.5 µM, a four-fold increase over control mice with no fluoride added to drinking water. MicroCT analyses showed delayed and incomplete mineralization of fluorosed incisor enamel as compared to control enamel. A microarray analysis of secretory and maturation stage ameloblasts microdissected from control and fluorosed mouse incisors showed that genes clustered with Mmp20 appeared to be less downregulated in maturation stage ameloblasts of fluorosed incisors as compared to control maturation ameloblasts. One of these Mmp20 co-regulated genes was the global chromatin organizer, special AT-rich sequence-binding protein-1 (SATB1). Immunohistochemical analysis showed increased SATB1 protein present in fluorosed ameloblasts compared to controls. In vitro, exposure of human ameloblast-lineage cells to micromolar levels of both NaF and AlF₃ led to a significantly increase in SATB1 protein content, but not levels of Satb1 mRNA, suggesting a fluoride-induced mechanism protecting SABT1 from degradation. Consistent with this possibility, we used immunohistochemistry and Western blot to show that fluoride exposed ameloblasts had increased phosphorylated PKCα both in vivo and in vitro. This kinase is known to phosphorylate SATB1, and phosphorylation is known to protect SATB1 from degradation by caspase-6. In addition, production of cellular diacylglycerol (DAG) was significantly increased in fluorosed ameloblasts, suggesting that the increased phosphorylation of SATB1 may be related to an effect of fluoride to enhance Gαq activity of secretory ameloblasts.

Pronounced reduction of fluoride exposure in free-ranging deer in North Bohemia (Czech Republic) as indicated by the biomarkers skeletal fluoride content and dental fluorosis

Wild deer have been recommended as bioindicators of fluoride pollution. We compared bone fluoride concentrations and prevalence and severity of dental fluorosis in free-ranging European roe deer (Capreolus capreolus) and red deer (Cervus elaphus) from five counties in the northwestern part of the Czech Republic that had been collected by hunters and whose mandibles were presented at trophy exhibitions in the years 1996/1997 ("early period") and 2009 ("late period"). Data on atmospheric fluoride deposition suggested that the deer from the early period had been exposed to markedly higher fluoride levels than those from the late period. We therefore predicted a decline in skeletal fluoride levels and prevalence of dental fluorosis for both species from the early to the late period. Fluoride concentrations were determined in the coronoid process of the mandible, and assessment of dental fluorosis was performed on the permanent cheek teeth. A pronounced drop in fluoride concentrations from the early period (roe deer (n = 157), median: 3147 mg F(-)/kg of dry bone; red deer (n = 127), median: 1263 mg F(-)/kg of dry bone) to the late period (roe deer (n = 117), median: 350 mg F(-)/kg of dry bone; red deer (n = 72), median: 288 mg F(-)/kg of dry bone) was recorded. Prevalence of dental fluorosis also markedly declined from the early to the late period (roe deer: from 93% to 12%, red deer: from 87% to 28%). The reduction of fluoride deposition in the study area and, in consequence, fluoride exposure of the resident deer populations, is attributed largely to the implementation of emission control devices in the brown coal-fired power plants located in North Bohemia from the mid 1990s onwards. The findings of the present study demonstrate that wild deer are well suited for monitoring temporal changes in fluoride pollution of their habitats.

Caries susceptibility of human fluorosed enamel and dentine

OBJECTIVE

Objective of our laboratory study was to determine the impact of dental fluorosis severity on the formation of caries in the human enamel and dentine.

MATERIALS AND METHODS

Thirty-three human molars were grouped according to modified Thylstrup-Fejerskov index (TFI) into normal (N, TFI 0), mild fluorosis (ML, TFI 1-3) and moderate fluorosis (MD, TFI 4-6). Three mesio-distal sections were made in corono-apical axis of the tooth, giving enamel and dentine samples. They were embedded in an epoxy resin, and polished. Half of the polished surface was covered with an acid resistant varnish and immersed in standard acidified buffer solution (pH 4.5) for 48 h to create artificial caries lesions. They were treated with 5% NaOCl for 45 min and sectioned longitudinally along the center into two halves. Cut surfaces were polished and observed under a confocal laser scanning microscope for depth of demineralization. Morphology of the demineralized zones was observed under a field emission scanning electron microscope (FE-SEM). Data were analyzed using one-way ANOVA and Sheffe test (p=0.05).

RESULTS

Statistically significant difference in depth of demineralization was found between N and MD groups (p=0.046) in the enamel, and between N and ML (p=0.002), N and MD (p<0.001), ML and MD (p=0.029) in dentine. FE-SEM observation of the normal enamel showed direct dissolution with large fissures. Spongy appearance of intertubular dentine gradually disappeared from N to MD.

CONCLUSIONS

Moderately fluorosed enamel showed a significant caries resistance. In contrast, mild and moderately fluorosed dentine was significantly caries susceptible in vitro.

Spatial distribution of dental fluorosis in roe deer (Capreolus capreolus) from North Bohemia (Czech Republic) and its relationships with environmental factors

We assessed the spatial variation of fluoride load on the local ecosystem in the Czech part of the Ore Mountains region and its southern foothills - a heavily polluted part of Europe's "Black Triangle" region. Dental fluorosis in roe deer (Capreolus capreolus) served as a biomarker of fluoride exposure and thus as an indicator of environmental pollution by fluoride. The mean dental lesion index of fluorosis (DLI) calculated from the analyzed mandibles of wild roe deer (>or=2 years of age) was assigned to the hunting ground from which the specimens originated and classified into one of the eight fluorosis categories. Environmental factors potentially related to dental fluorosis (atmospheric deposition of sulfur, concentration of fluoride in and pH of surface waters, geomorphologic features, bedrock and soil type, and vegetation cover), which were represented in the study by GIS layers, were examined to explain the distribution pattern and severity of fluorosis in the roe deer. The study revealed that 75.5% of 616 analyzed mandibles showed dental fluorosis to different extent, with individual DLIs ranging from 0 to 21. The spatial pattern of marked fluorosis on the Czech side continues that found in a previous study on the German side of the Ore Mountains. Together they create a landscape island around several thermal power plants in the region. General Linear Model (GLM) analyses revealed significant relationships between degree of forest damage, soil type, and atmospheric sulfur deposition from air pollution and dental fluorosis, expressed as mean DLI in the roe deer.

Reconstructing impairment of secretory ameloblast function in porcine teeth by analysis of morphological alterations in dental enamel

We studied the relationship between the macroscopic appearance of hypoplastic defects in the dental enamel of wild boar and domestic pigs, and microstructural enamel changes, at both the light and the scanning electron microscopic levels. Deviations from normal enamel microstructure were used to reconstruct the functional and related morphological changes of the secretory ameloblasts caused by the action of stress factors during amelogenesis. The deduced reaction pattern of the secretory ameloblasts can be grouped in a sequence of increasingly severe impairments of cell function. The reactions ranged from a slight enhancement of the periodicity of enamel matrix secretion, over a temporary reduction in the amount of secreted enamel matrix, with reduction of the distal portion of the Tomes' process, to either a temporary or a definite cessation of matrix formation. The results demonstrate that analysis of structural changes in dental enamel allows a detailed reconstruction of the reaction of secretory ameloblasts to stress events, enabling an assessment of duration and intensity of these events. Analysing the deviations from normal enamel microstructure provides a deeper insight into the cellular changes underlying the formation of hypoplastic enamel defects than can be achieved by mere inspection of tooth surface characteristics alone.

Estimation of fluoride distribution in the mandible and teeth of the red deer (Cervus elaphus L.) from industrially polluted areas in Poland

MINI SUMMARY

Animals from areas contaminated by industrial emissions containing fluoride may accumulate it predominantly in hard tissues. Therefore, an analysis was performed for the determination of fluoride content in mandibles and teeth of deer living at large in different areas in Western Pomerania (Poland). Samples of hard tissues obtained with a dental drill, were dissolved in perchloric acid and analyzed for fluoride content with an ion-selective electrode. Using the Generalized Regression Neural Network (GRNN), it was possible to arrange definite variables according to their order of importance concerning the fluoride mean content in investigated bone material. Parametric analysis revealed in which sites of mandibles and teeth the fluoride accumulation was the highest. In our calculation, the traditional statistic as well as artificial neural network was applied.

OBJECTIVE

One of the interesting properties of fluoride is its balancing accumulation in the hard and soft tissues. In this paper, we decided estimate how the changeable doses of fluoride in natural environment influence on fluoride distribution and accumulation in the examined sites of mandible and teeth.

MATERIAL AND METHOD

The material consist of 103 mandibles of red deer (Cervus elaphus L.) from five forestry districts of Western Pomerania in Poland, which are located near or far away from two major industrial plants: Police Chemical Work and the Dolna Odra Coal Power Plant. Samples (10 mg of powdered bone or tooth) were dissolved in perchloric acid and the fluoride content was determined with an ion-selective electrode. Comparisons were done with the Statistica 5.5 and Statistica Neural Networks.

RESULTS

Animals living in Western Pomerania (Poland) have high fluoride contents in their bones. Fluoride accumulation in mandibles and teeth is irregular. The higher content of fluoride show incisal area, but coronoid process of the mandible was not sensitive to different exposure of environmental fluoride at all. Parametric analysis revealed that the accumulation pattern of fluorine was different in the two groups of deer.

CONCLUSIONS

Many biological and environmental factors may influence on incessant fluoride accumulation in osseous tissue of ruminants living at large. The use of artificial neural networks enables a more accurate insight into the process of fluorine accumulation in the mandible and teeth and helps in the ranking of factors influencing this process.

Fluoride concentrations in antler bone of roe deer (Capreolus capreolus) indicate decreasing fluoride pollution in an industrialized area of western Germany

In order to reconstruct temporal changes in ambient fluoride levels in the industrialized Ruhr area (western Germany), we analyzed the bone fluoride content of 167 antlers of roe deer (Capreolus capreolus) killed between 1951 and 1999 in the northern part of this region. Individual values ranged between 110 and 8,178 mg F-/kg ash, and there was an overall marked decrease over the sampling period. Average bone fluoride concentrations in antlers from the periods 1980 through 1989 (geometric mean [95% confidence interval]: 1,490 [1,193-1,861] mg/kg ash) and 1990 through 1999 (753 [644-882] mg/kg ash) differed significantly (p < 0.001) and were both significantly (p < 0.001) lower than those from the periods 1951 through 1969 (3,720 [3,227-4,288] mg/kg ash) and 1970 through 1979 (2,573 [2,203-3,006] mg/kg ash). The findings are seen as indicative of a progressively reduced atmospheric fluoride deposition into the study area, caused by effective emission-control measures in Germany and neighboring countries. Because antlers are replaced annually, grow during a fixed period of some months, and are regularly collected and kept as trophies, they are well suited as monitoring units for analyzing temporal trends in environmental pollution by fluoride and other bone-seeking pollutants.

Temporal and geographical variation in skeletal fluoride content of roe deer (Capreolus capreolus) from industrialized areas in Germany

In order to study temporal and spatial variation of environmental fluoride levels, we analyzed the mandibular bone fluoride content of 157 roe deer (age range: 1-11 years) from two industrialized regions (Ruhr area: n = 76, sampling period 1955-1998; area W of Cologne: n = 81, sampling period 1983 1998) in the federal state of North Rhine-Westphalia, Germany. Bone fluoride values (dry weight basis) ranged between 150 mg F/kg (2 year-old specimen taken in 1997) and 5724 mg F/kg (10 year-old specimen taken in 1957). In both study areas, a pronounced decline in mandibular bone fluoride concentrations occurred over the respective sampling periods. In consequence, bone fluoride content of animals (both study areas pooled) taken during the period 1990-1998 was significantly (P < 0.00001) lower than that of roe deer from the period 1955 1989, while the two animal groups did not significantly differ in age. These findings are regarded as indicative of a considerable reduction of fluoride deposition into the animals' habitats, due to effective emission control measures. Bone fluoride values for the period 1990-1998 in the roe deer from the Ruhr area significantly (P < 0.005) exceeded those of the individuals from the study area W of Cologne, while the difference in age between the two groups was not significant. In both study areas, a significant (P < 0.00001) positive correlation between age and mandibular bone fluoride content (Ruhr area: rs = 0.601; area W of Cologne: rs = 0.725) was found for animals taken during this period. The present study underscores the suitability of analyzing skeletal fluoride concentrations in wild roe deer in order to monitor the magnitude of environmental contamination by fluoride and thereby to assess the efficiency of measures taken to reduce fluoride emissions from industrial sources.

Disturbed enamel formation in wild boars (Sus scrofa L.) from fluoride polluted areas in Central Europe

The pathological alterations of enamel structure in the teeth of wild boars from fluoride polluted areas in N-Bohemia (Czech Republic) and S-Saxony (Germany) were studied on a macroscopic and a microscopic level. Mandibular bone fluoride concentration (mg F(-)/kg, dry wt; mean +/-SD, individuals <24 months of age) in the specimens from N-Bohemia (754.3+/-149.6) and S-Saxony (490.8+/-135.1) was significantly higher than that of controls (free of dental fluorosis), originating from the western part of Germany (304.7+/-91.0). Fluoride content in bulk enamel (mg F(-)/kg, ash wt) of fluorotic permanent teeth from N-Bohemia (382.1+/-165.2) and S-Saxony (125.0+/-38.3) was likewise significantly increased over that of non-fluorotic control teeth from W-Germany (33.6+/-26.7). Macroscopically, fluorosed wild boar enamel exhibited opacity and discoloration of varying extent, accentuated perikymata as well as hypoplastic and posteruptive surface defects. Microradiographic and scanning electron microscopic analyses revealed enamel subsurface hypomineralization, accentuated Retzius lines and occurrence of broad, hypomineralized incremental bands of abnormal structure underlying hypoplastic enamel surface defects. The presence of zones of aprismatic enamel was associated with these bands. Incremental bands with altered enamel structure and enamel surface hypoplasias, both denoting a severe disturbance during the secretory stage of amelogenesis, have previously been observed in rodents following acute parenteral fluoride dosing. It is concluded that in the chronically fluoride exposed wild boars periods of especially elevated plasma fluoride levels exerted an acute toxic effect on the secretory ameloblasts. A feature not previously reported from fluorosed enamel was the occurrence of canal-like structures that originated at the broad incremental bands and extended into the external enamel. The presence of these canals presumably results from a delay in the resumption of secretory activity by groups of ameloblasts following a fluoride insult. Based on experimental evidence in domestic pigs and in sheep, the overall subsurface hypomineralization of fluorosed wild boar enamel is attributed to a disturbance of enamel maturation. The distribution of fluorotic enamel changes within the dentition of the wild boars could be related to the developmental sequence of tooth formation in the species. Teeth whose crown formation took place prenatally (deciduous teeth) or largely pre-weaning (permanent first molars) exhibited no or only moderate fluorotic enamel alterations. Based on the extension of enamel surface hypoplasias along the coronoapical axes of the tooth crowns, the timing of excess fluoride exposure that caused a marked disruption of enamel matrix secretion was estimated in specimens with a known date of death. The results indicate that the wild boars had been exposed to a particularly severe fluoride impact during autumn and winter of their first year of life.

Monitoring regional fluoride pollution in the Saxonian Ore mountains (Germany) using the biomarker dental fluorosis in roe deer (Capreolus capreolus L.)

The spatial variation of fluoride contamination in the Saxonion part of the Ore mountains (Federal state of Saxony, Germany) was assessed by analysing the prevalence and severity of dental fluorosis in wild male roe deer aged 2 years or more (n = 794) from this region. The study area is exposed to increased atmospheric deposition of fluorides, originating from emission sources in the North-Bohemian brown coal belt. The severity of dental fluorosis in the permanent premolars and molars of one hemimandible per animal was assessed based on a scoring system and a dental lesion index of fluorosis (DLI) assigned to each specimen. On the basis of the mean DLI calculated for the roe deer originating from a certain municipal district, the respective deer sample was assigned to one of seven fluorosis categories, and a map showing the distribution of these categories was produced. Highest fluorosis categories were recorded for roe deer samples from the central and eastern parts of the study area that directly bordered on, or were located near to, the Czech-German border. A close spatial relationship between the main fluoride emission sources in North-Bohemia and the regions with the highest prevalence and severity of dental fluorosis in roe deer was discernible. The observed regional variation of fluoride pollution is in accordance with the results of other studies directly measuring fluoride deposition into the study area or fluoride levels in vegetation. A main advantage of the method used in this study over other ways of recording fluoride contamination of wildlife habitats is that it uses an established and continuously operated system of specimen collection, thereby enabling efficient monitoring with high spatial and temporal resolution at very low cost. Moreover, a clearly recognisable and relevant biological effect is measured which occurs in a dose-dependent manner over a range of environmentally relevant concentrations.

Pathological bone changes in the mandibles of wild red deer (Cervus elaphus L.) exposed to high environmental levels of fluoride

A macroscopic, microscopic and scanning electron microscope study was performed on the pathological bone changes of the mandibles of wild red deer (n = 61) exhibiting severe dental fluorosis. The animals originated from a highly fluoride polluted area in Central Europe (Ore mountains and their southern foreland, Czech-German border region) and constituted 11.2 % of the studied red deer sample (n = 545) from this area. Pathologically increased wear and fracture of fluorosed teeth caused a variety of mandibular bone alterations, including periodontal breakdown, periostitis, osteitis and chronic osteomyelitis. As a further consequence of severe dental attrition, opening of the pulp chamber and formation of periapical abscesses were occasionally observed. In case of severe periodontal breakdown, loss of teeth from the mandibles was found. In addition to the inflammatory bone changes, the occurrence of osteofluorotic alterations was also diagnosed in the specimens with the highest bone fluoride concentrations (> 4000 mg F-/kg dry wt). These changes comprised extended apposition of periosteal bone onto the mandibular cortex as well as deformation of the mandibular body, which was attributed to a fluoride-induced osteomalacia. The present study provided circumstantial evidence that, in addition to fluoride induced dental lesions, the occurrence of marked periodontal disease and tooth loss is an important factor responsible for a reduction of life expectancy in severely fluorotic wild red deer.

A quantitative backscattered electron imaging study of hypomineralization and hypoplasia in fluorosed dental enamel of deer

Mineral content and distribution of fluorosed and unfluorosed (control) dental enamel of roe deer and red deer cheek teeth were analyzed using digital backscattered electron (BSE) imaging of PMMA-embedded specimens. Compared to the controls, the fluorosed enamel exhibited various aberrations resulting from a fluoride-induced disturbance of the processes involved in enamel formation. Thus, the presence of surface hypoplasias and an enhancement of the incremental pattern in the fluorosed enamel are evidence of a fluoride impact on the secretory ameloblasts, whereas a (subsurface) hypomineralization of different depth and extent is indicative of a fluoride effect on the maturation stage of amelogenesis. The marked variation in the severity of enamel hypomineralization seen along the coronocervical axis of a specimen pointed to a fluoride impact of varying intensity during this period of tooth development. Our observations further indicated that, in some locations, ameloblasts severely affected by fluoride during enamel matrix formation were able to recover from this insult and to function quite normally during the maturation stage of amelogenesis. A major advantage of the BSE imaging technique used in the present study over other methods is that it allows for a combination of micromorphological information with quantitative data on the mineralization of the analyzed tissue, which proved to be very useful for the characterization of fluoride-induced changes in dental enamel.

Determinants and mechanisms of enamel fluorosis

Enamel fluorosis occurs when fluoride concentrations in or in the vicinity of the forming enamel are excessive during its pre-eruptive development. Fluoride concentrations in plasma, enamel and other tissues reflect the difference between intake and excretion, i.e. fluoride balance. In addition to the diet, modern sources of ingested fluoride include a variety of dental products, some of which have been identified as risk factors for fluorosis. Fluoride absorption is inversely related to dietary calcium which, at high concentrations, may cause net fluoride secretion into the gastrointestinal tract. The excretion of absorbed fluoride occurs almost exclusively via the kidneys, a process which is directly related to urinary pH. Thus, fluoride balance and tissue concentrations and the risk of fluorosis are increased by factors such as high protein diets, residence at high altitude, and certain metabolic and respiratory disorders that decrease pH. Factors that increase urinary pH and decrease the balance of fluoride include vegetarian diets, certain drugs and some other medical conditions. Although several other fluoride-induced effects might be involved in the aetiology of fluorosis, it now appears that inhibition of enzymatic degradation of amelogenins, which may delay their removal from the developing enamel and impair crystal growth, may be of critical importance. In addition to the effects of fluoride, disturbances in enamel formation that can be confused with fluorosis are caused by chronic acidosis and hypoxia independently of the level of fluoride exposure.

Mandibular bone fluoride levels and occurrence of fluoride induced dental lesions in populations of wild red deer (Cervus elaphus) from Central Europe

Mandibular bone fluoride concentrations as well as frequency and intensity of fluoride-induced dental lesions were studied in four red deer populations from Czechia and Germany exposed to different levels of environmental fluoride. The degree of fluorosis in the permanent cheek teeth was recorded by a scoring system and the individual mandibles assigned to one of three categories (unfluorosed, slightly to moderately fluorosed, and markedly to severely fluorosed) on the basis of the tooth scores. An increase in the frequency and severity of dental fluorosis was positively associated with an increase in bone fluoride level, which itself was significantly different between the four samples. In all samples, the rate of bone fluoride accumulation was higher in younger than in older deer. The results of this study show that frequency and intensity of dental fluorosis can be used as valid indicators of increased fluoride exposure of deer populations, and thus as a quick, easy, economic and reliable means of monitoring fluoride pollution in areas inhabited by wild deer.

Mandibular bone fluoride accumulation in wild red deer (Cervus elaphus L.) of known age

Mandibular bone fluoride concentration and its relation to age were studied in a sample of 39 red deer of known age (between 2 and 18 years) from an area not exposed to increased fluoride deposition (Harz mountains, Germany). Bone fluoride level ranged from 208 to 1026 ppm dry weight and was positively correlated with age (r = 0.808, P < 0.001), the rate of skeletal fluoride accumulation being higher in younger individuals. This indicates that during the period of skeletal growth, fluoride uptake is more rapid than in later life when accumulation at a lower rate occurs during normal bone turnover. Bone fluoride levels found in the present sample are regarded as resulting from "normal" fluoride exposure in a recent central European red deer population.