Disturbed enamel mineralization in a rat incisor model

Developmental Enamel Defects in Children from the Southern Region of Ecuador

Developmental defects of enamel (DDEs) are widely observed in children and are related to the appearance of dental caries, malocclusion, tooth sensitivity, and unfavorable esthetic conditions. The objective of this cross-sectional study was to determine the prevalence and distribution of enamel defects present in children aged 6 to 12 years in the provinces located in southern Ecuador. A total of 1606 schoolchildren were examined under the World Health Organization criteria for diagnosis of DDEs. The results are presented using percentage frequency measures and chi-square associations. Some types of DDEs were presented by 50% of the schoolchildren, mainly diffuse opacity, with no statistical differences according to place of residence and/or environment, sex, and age (p > 0.05). In Ecuador, it is necessary to carry out studies on the factors that trigger enamel defects, since they may be associated with the high prevalence of caries already reported in other studies in the country.

Diabetes detrimental effects on enamel and dentine formation

OBJECTIVES

Understanding morphological changes and mineral content of tooth hard tissues may influence dental treatment. In this study, the effect of Type 1 Diabetes Mellitus (T1DM) on tooth structure was examined.

METHODS

Experimental T1DM was induced in 3-week old male Wistar rats (n=10) by a single dose of 60mg/kg body weight of Streprozotocin. All rats were injected with calcein twice during the experiment and sacrificed at the age of 7 weeks old. Micro-computed tomography (micro-CT) was used to determine the mineral density and thickness of enamel and dentine. Also, a histomorphometery study was conducted to detect the rates of dentine mineral apposition and formation. The examined area was in the crown analogue of the rat mandibular incisor parallel to the long axis of the mesial surface of the first molar. All results were compared using Students' t-test (p<0.05).

RESULTS

Results showed that the enamel and dentine thickness were significantly reduced (hypoplasia) and there was a significant reduction of the rate of dentine mineral apposition and formation, while there was no significant effect of the T1DM condition on the mineral density of enamel and dentine.

CONCLUSIONS

T1DM has a detrimental influence on the formation of enamel and dentine in the early growth stage.

CLINICAL SIGNIFICANCE

T1DM condition may alter treatment planning of orthodontic treatment as it is associated with decreased enamel and dentin thickness that may affect teeth size and their resistance to caries.

Prevalence of enamel defects in primary and permanent teeth in a group of schoolchildren from Granada (Spain)

Objective: The purpose of this study was to determine and compare the prevalence and presentations of developmental defects of the enamel (DDE) in the primary and permanent dentitions of a group of healthy schoolchildren residing in Granada (Spain). Study Design: A total of 1,414 healthy schoolchildren were examined using modified DDE criteria for recording enamel defects. Results: The prevalence of DDE of any type was 40.2% in primary dentition and 52% in permanent dentition (p<0.033). Of the 31,820 primary and permanent teeth examined in the study, 699 (4.1%) primary and 1,232 (8.3%) permanent teeth had some form of DDE. Diffuse opacity was the most common type of DDE observed in primary teeth, and demarcated opacity in the permanent teeth. Enamel hypoplasia was the least prevalent defect in both dentition types. Conclusions: The study population showed a high prevalence of DDE in primary as well as in permanent dentition, reflecting the current increasing trend of this condition, which should be considered as a significant public health problem.

Key words:Developmental enamel defects, enamel hypoplasia, demarcated opacity, diffuse opacity.

Effect of high phosphorus diet on tooth microstructure of rodent incisors

Enamel hypoplasia and disruption of dentinogenesis are the most common abnormalities of development and mineralization of human teeth. Several reports are available in the literature on the influence of dietary calcium on the formation of human and rodent tooth; however, the information about the influence of dietary phosphorus on the tooth formation is scarce. The aim of the present investigation was to examine the chronic effect of high phosphorus diet and improper dietary calcium to phosphorus ratio on the mandibular incisor microstructure in a hystricomorph rodent--Octodon degu--using macroscopic observation, histopathological examination, transmission and scanning electron microscopy. The present study shows that enamel and dentin development is disturbed under high phosphorus diet and improper calcium to phosphorus ratio. Disturbed mineral metabolism resulted in enamel depigmentation, enamel hypoplasia, enamel pitting and altered dentin morphology. The results suggest that more attention should be focused on dietary phosphorus content when facing altered tooth structure in young patients with deciduous or permanent dentition. Furthermore, we showed that degus can be used as an experimental animal model for the study of the developmental teeth disturbances.

Of mice and mutations: phenotypic effects of the diabetic db/db and ob/ob mutations on the skull and teeth of mice

AIM

To compare the phenotypic appearance of the skull bones and teeth of wild type C57BL/6J mice with that of diabetic leptin-deficient (ob/ob) and diabetic leptin receptordeficient (db/db) mice used as models for diabetes.

STUDY DESIGN AND METHODS

Skulls were extracted from the carcasses of mice belonging to wild-type C57B/6J mice, db/db mice on a C57BLKS/J background, and ob/ob mice on a C57B/6J background. After removal of overlying tissue, the skulls and mandibles were then left to dehydrate and examined for phenotypic variations in structure and wear.

RESULTS

Bone surfaces of the skulls of wild type mice had a whiter and smoother surface compared with a yellowish colour with a grainy texture in the two mutant strains. The frontal, parietal and occipital bones were translucent in the two mutant strains. Breakages of the zygomatic arches and mandibles were more common in the ob/ob and db/db mice than in the wild type mice. Half of the teeth of the db/db mice and 90% teeth of the ob/ob mice showed considerable wear compared with marginal wear in the wild type mice.

CONCLUSIONS

These observations suggested that the teeth of the two diabetic mutant strains are exhibiting considerable signs of hypomineralization with increased fragility and decreased bone thickness.

Enamel mineral concentration in diabetic rodents

AIM

This was to use x-ray microtomography (XMT), to assess the mineral composition and 3-D structure of enamel and bone in the teeth and skulls of diabetic rodents.

METHODS

Three-dimensional images of the skull were reconstructed using computer generated false colour to highlight different levels of mineralization in bone and enamel.

RESULTS

These showed that diabetic rodents exhibited more wear in their teeth. Deformities were observed in the alveolar process of the mandible and maxilla. Regions of extensive hypomineralization were found in the calvarial bone of skulls. The maximum mineral concentrations and the time constants for diabetic rodents were similar to the controls. The diabetic mice appeared to have random regions of hypomineralization and one diabetic rat had areas of hypoplasia in the mandibular incisors.

CONCLUSIONS

Diabetes may have a detrimental influence on the function of ameloblasts in laying down enamel.

Lead contents in the surface enamel of deciduous teeth sampled in vivo from children in uncontaminated and in lead-contaminated areas

This study aimed to: (1) measure lead contents in the surface enamel of two populations consisting of 4-6-year-old children, one from an apparently uncontaminated area (Ribeirão Preto, São Paulo State, SP, Brazil, n=247) and the other from an area notoriously contaminated with lead (Bauru, São Paulo State, Brazil, n=26); (2) compare biopsy depths between the two populations; (3) correlate biopsy depth with lead content; (4) stratify samples according to biopsy depth to compare lead contents in samples from similar biopsy depths. A surface enamel acid-etch microbiopsy was performed in vivo on a single upper deciduous incisor for each sample. Lead was measured by graphite furnace atomic absorption spectrometry (GFAAS) while phosphorus was measured colorimetrically to establish biopsy depth. Samples from both populations were classified into categories of similar biopsy depths based on biopsy depth quartiles. Median lead contents were statistically different between the Ribeirão Preto population (206 microg/g, range: 5-1399 microg/g) and the Bauru population (786 microg/g, range: 320-4711 microg/g) (p<0.001); however, biopsy depth did not differ between the Ribeirão Preto (3.9 microm, Standard Deviation, SD=0.9) and Bauru (3.8 microm, SD=0.9) populations (p=0.7940). Pearson's correlation coefficient for biopsy depths versus log10 lead values was -0.29 for Ribeirão Preto and -0.18 for Bauru. Lead contents were statistically different between the two populations for all quartiles of biopsy depth. These findings suggest that lead accumulated in the surface enamel of deciduous teeth is linked to the environment in which people reside, indicating that this tissue should be further explored as an accessible biomarker of lead exposure.

[Osteogenesis imperfecta and dentinogenesis imperfecta: diagnostic frontiers and importance in dentofacial orthopedics]

Osteogenesis imperfecta is a genetic disease that varies in severity and is characterized by fragile bones that fracture easily. Many extra-skeletal manifestations can be noted such as blue sclerotic markings, dentinogenesis imperfecta and impaired hearing or deafness. In most cases, an anomaly of collagen is the cause. It is usually accompanied by a specific Class III type cranio-facial morphology with open bite and increased incidence of impacted permanent molars. Orthodontists called upon to treat the dental aspects of this malady, should be careful to protect their patients against bacterial infection and hemorrhages, and to be well aware of the side affects that can be caused by the biophosphanates that constitute the basis of current medical treatment of osteogenesis imperfecta.

Pb enamel biomarker: deposition of pre- and postnatal Pb isotope injection in reconstructed time points along rat enamel transect

Exposure to lead (Pb) as well as other heavy metals in the environment is still a matter of public health concern. The development of the enamel biomarker for heavy metal exposure assessment is designed to improve studies of dose-effect relationships to developmental anomalies, particularly embryonic dysfunctions, and to provide a time-specific recount of past exposures. The work presented in this paper demonstrates maternal transfer across the placental barrier of the enriched isotope (206)Pb tracer to the enamel of the rat pup. Likewise, injections of (204)Pb-enriched tracer in the neonate rat resulted in deposition of the tracer in the enamel histology as measured by secondary ion microprobe spectrometry. Through enamel, we were able to observe biological removal and assimilation of prenatal and postnatal tracers, respectively. This research demonstrates that enamel can be used as a biomarker of exposure to Pb and may illustrate the toxicokinetics of incorporating Pb into fetal and neonatal steady-state system processes. The biomarker technique, when completely developed, may be applied to cross-sectional and longitudinal epidemiological research.

Defective enamel ultrastructure in diabetic rodents

We investigated six different types of diabetic rodents. Four expressed a genetic obesity resulting in diabetes. One developed diabetes induced by a diet-dependent obesity, and one with genetic diabetes received anti-diabetic medication. The tooth samples were examined under a scanning electron microscope and with an energy dispersive microanalysis (EDX). The electron micrographs showed severe, varying degrees of damage within the six different diabetic animal types, such as irregular crystallite deposition and prism perforations in genetically obese animals compared to less-disordered prism structures in diet-dependent obesity. Anti-diabetic medication resulted in normal enamel ultrastructure. The EDX analysis revealed a reduction in the amount of calcium and phosphorus in all regions affected by diabetes. Based on these animal studies, we suggest that both juvenile diabetes type I (in infants) and adult diabetes type II (in pregnant mothers, affecting the developing foetus) may affect the normal development of teeth in humans.

A comparison between a conventional optical method and image-analysis for measuring the unimpeded eruption rate of the rat mandibular incisor

The impeded/unimpeded eruption rates of the rat incisor have been much studied. The most commonly used optical microscopic method, which has inherent weaknesses, was compared here with an image-analysis method to measure the eruption rate of the mandibular incisor. The study also evaluated the incisal edge as a reference point for the measurement of the unimpeded eruption rate, and the frequency of shortening the mandibular incisor. The image-analysis method was found to be a simple and reliable technique that could replace the optical method. There was no significant difference between the data from the two methods; their kappa coefficients were similar at the 0.99 level. It was concluded that shortening the incisor in the measurement of the unimpeded eruption rate should be done at least every 48 h, and that the incisal edge of the shortened incisor can be used as the reference point for that measurement.

SEM study of the development of rat incisor enamel hypoplasia under hypocalcemia induced by thyro-parathyroidectomy

Several clinical studies have reported the presence of enamel hypoplasia in congenital hypoparathyroidism or hypocalcemia. In previous studies we showed that thyroparathyroidectomy (TPTX) induced perturbations of the ameloblast morphology and secretion, of the rod pattern and of the enamel surface at late secretory stage and beginning of maturation, and limited hypoplasia in the erupted enamel of rat incisor. The aim of the present study was to evaluate by SEM, the extent and evolution of the enamel alterations of thyro-parathyroidectomized rats during the maturation stage. Wistar rats were thyro-parathyroidectomized and sacrificed 57 days later. The incisors were dissected out and processed for SEM. The surface of the incisor was observed from the end of secretion/beginning of maturation to its incisal erupted end. Transverse sections were prepared to study the structural defects and the prism pattern at different stages. The results showed that the surface of the TPTX incisors presented large hypoplastic defects at the end of secretion/beginning of maturation and only small defects in the erupted part. Transverse sections showed that, at the transition from secretion to maturation, the enamel defects extended to the mid-thickness of the tissue. At the incisal end the defects were limited to the outer enamel. As it is difficult to understand how the large apical defects could recover to appear as small hypoplasia at the incisal end, these results raise new questions concerning: (1) the effect of a long term calcium deficiency upon the cellular activity of the ameloblasts, and (2) the capacity of the enamel organ to compensate structural abnormalities.

Intermittent inhibition of dentin mineralization of rat incisors under continual infusion of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) using a subcutaneous mini osmotic pump

The inhibitory effect of the continual administration of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) (8 mgP/kg/day) through a mini osmotic pump on dentin mineralization was examined in relation to the diurnal rhythm of the rat and compared with that of daily injections of same amounts of HEBP known to inhibit dentin mineralization. After daily injections of HEBP, a series of alternating rows of mineralized and non-mineralized dentin islands appeared in the newly formed portion of the crown-analogue of rat incisors. A similar phenomenon occurred under the continual administration of HEBP in rats raised either under regular environmental photofraction or constant lighting conditions. The average distance between the adjacent mineralized dentin islands was 521.0 +/- 51.3 microns in the injected rats. After continual HEBP administration, this was 426.0 +/- 13.2 microns and 416.5 +/- 19.4 microns under ordinary photofraction and constant light, respectively. Although the pattern of individual mineralized dentin islands tended to become irregular in nocturnal rats, no statistical difference was noted between the two values. Rows of mineralized and non-mineralized dentin islands also appeared in the root analogue dentin. No sign of the intermittent inhibition of mineralization was recognized in mesodermal hard tissues other than dentin in the HEBP-affected animals. These data implicate the presence of intrinsic cycles in dentin mineralization at the growing end of rat incisors independent of environmental photofraction as well as the ameloblast function.

Scanning electron microscopy and energy-dispersive X-ray analysis of defects in mature rat incisor enamel after thyroparathyroidectomy

The surface and the structure of the erupted enamel of the continuously growing rat incisor were studied by scanning electron microscopy (SEM) to analyse the effect of thyroparathyroidectomy on enamel formation. Ten male 21-day-old Wistar rats were thyroparathyroidectomized and five sham-operated rats were used as controls. Two months after surgery the rats were perfused with 1% glutaraldehyde and their mandibles dissected. The erupted ends of the incisors were cut off and routinely processed for SEM. An energy-dispersive analysis of X-rays (EDX analysis) was performed for the calcium:iron ratio of the enamel surface defects. Thyroparathyroidectomy induced surface defects and structural abnormalities in the outer layer of the mature erupted enamel. It was established that the surface and structural defects were related. The EDX analysis of the outer enamel showed that the enamel defects were associated with an abnormal elevation of the iron content. The SEM appearance and the EDX analyses indicated that these defects were hypomineralized and rich in iron. The reddish colour of the enamel is due to the high concentrations of iron.