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Response to Weinstein: public health issues in early childhood caries.

Dr Weinstein's thoughtful overview of public health issues in early childhood caries (ECC) provides an excellent basis for further exploration. For public health to focus on a given problem several factors must be addressed: the disease must be widespread; the etiology or the prevention of the disease or condition must be known; this knowledge is not being applied; and resources for interventions must be available. Currently, appropriate data are not available for ECC and the problem is exacerbated because there is no case definition for the disease. Therefore it is difficult to make public health policy to address this disease. With the knowledge of case definition, prevalence, and efficacy of treatment, we are more likely to engender interest and funding for ECC. Studies in other countries have demonstrated that children who are malnourished, have low birth-weight or both, likely will have hypomineralized primary teeth and thus at risk of ECC. Low birth-weight infants (less than 2500 g) currently constitute over 7% of all US births. The impact of low birth-weight on oral health is not known. Weinstein favors the use of operator-applied preventive agents, yet little evidence is available on the safety and effectiveness of these agents among infants and young children. Further, they are unlikely to be cost-effective and they require frequent appointments, which is often difficult for poor families to manage. Community interventions hold the greatest promise for preventing ECC because larger numbers of people can be reached than in private practice clinical settings.

Birth Weight↗

A radiographic study of mineralization of permanent teeth in a group of children aged 3-7 years.

The purpose of the present study was, by using a standardized radiographic technique, to assess the time of selected mineralization stages of all permanent teeth except the second and third molars in a group of 580 children aged 3-7 years. A complete radiographic examination, consisting of nine intraoral films, was made of each child, using Eggen's film holder. According to degree, mineralization of the teeth was subdivided into nine stages. The cap relation between the two variables, mineralization stage and chronologic age, was calculated by linear regression analysis. The hypothesis of the present study, that linearity exists between the two variables, was confirmed within and close to the investigated age group.

Child↗

Developmental disturbances in permanent teeth after intrusion of their primary predecessors.

The frequency and type of developmental disturbances in the permanent teeth in relation to the child's age at the time of injury were examined in 78 patients with 100 intruded primary incisors. The central incisors were found to be the most frequently affected teeth. Only maxillary teeth were involved. The dominating age group was 1-3 years and intrusion was seldom seen after the age of 4 years. The frequency of disturbed normal development of the permanent teeth was 54%. In eight cases the intruded teeth were removed immediately, 86 teeth reerupted, and six teeth did not reerupt. Internal white enamel hypoplasia was seen frequently; external hypoplasia, seldom.

Age Factors↗

Electronmicroscopic study of mineralization in induced heterotopic bone formation in guinea pigs.

Mineralization of heterotopic bone was studied in a bone induction model using allogenic demineralized dentin implanted in the abdominal wall of guinea pigs. There was a high yield of newly formed osteoid and bone as well as some cartilage together with areas of resorption of the dentin, and fibroblast proliferation. The osteoid contained many matrix vesicles II and less of lysosome-like type I vesicles. Early cartilage formation had more type I vesicles. The implanted dentin contained no matrix vesicles. The first signs of mineralization occurred mainly as irregular clusters of mineral crystals in the matrix close to the surface of collagen fibrils. Crystal-like figures were also found inside some type II matrix vesicles, although most of these vesicles in the mineralization zone had no crystals. The type I vesicles of both bone and cartilage exhibited often crystals near the outer membrane. The mineralizing bone showed a reduction in the size and number of proteoglycan particles. Remineralization of the implanted dentin was also often found and the mineralization pattern resembled the mineralization of bone except for the absence of matrix vesicles. Electron diffraction of selected areas showed that the crystals in the new bone and the mineralized dentin were hydroxyapatite.

Animals↗

Effects of salmon calcitonin on growth of teeth and on extraction socket healing in young rats.

The influence of salmon calcitonin on the growth of teeth and alveolar bone, and on the healing of alveolar sockets has been studied in young male rats. The experimental animals received daily injections of salmon calcitonin 0.5 MRC-U/kg body weight, whereas the control group received the vehicle. The rats were sacrificed at 14 and 28 days after the tooth extractions. Salmon calcitonin had no effect on the dry weight, calcium concentration and mineralization of the maxillary molars and the alveolar bone. Neither were there any significant effects of the hormone on the healing alveolar sockets. All sockets were healed after 4 weeks. The mineralization rate of molar teeth was only a quarter of that of tibiae, which was used as a reference.

Alveolar Process↗

Electron microscopic demonstration of non-mineralized and hypomineralized areas in dentin and cementum by silver methenamine staining of collagen.

An electron microscopic study on silver methenamine staining of hard dental tissues was made on a material that comprised human permanent teeth and primary tooth germs from human and porcine fetuses. It was demonstrated that silver-stained material consisted of collagen fibrils. In predentin and precementum all collagen fibrils were stained, while collagen fibrils of dentin and cementum were unstained except for some fibrils of minor special areas such as Owen's contour lines, interglobular dentin, Tomes's granular layer, and in cementum small "interglobular-like" areas. It is concluded that silver methenamine visualizes collagen fibrils of hypo- and unmineralized areas in dental hard tissues and therefore may be used to demonstrate abnormal patterns of mineralization. Finally variations of silver methenamine stainability in relation to differences in material and methods were studied and discussed.

Animals↗

Light and transmission-electron microscopy study of enamel organ cells in germectomized human third mandibular molars.

Using nine serially sectioned germectomized mandibular third molars it was possible to examine light microscopical (LM) and transmission-electron microscopical (TEM) features of maturing human enamel organ cells. The degree of enamel mineralization was estimated by quantitative imbibition studies in polarized light. It was possible to distinguish between three progressive stages of enamel mineralization. The most advanced stage was characterized by external enamel porosity. In the least advanced stages the enamel porosity appeared more extensive beneath a less porous surface layer. Ruffle- and smooth-ended ameloblasts were identified corresponding to the maturing enamel. Smooth-ended ameloblasts were the most frequently observed. However, no preferences for one of the two cell types could be observed in relation to the different stages of enamel mineralization. The maturing human enamel organ cells broadly revealed the same characteristics with respect to morphology features, intracellular organization, and junctional complexes as described in the maturation zone of the rat incisor enamel organ. Our findings therefore add to the view that the basic pattern of amelogenesis is identical in human and rat incisor enamel.

Adolescent↗

Clinical and histologic appearance in enamel of primary teeth in relation to neonatal blood ionized calcium values.

The purpose of this investigation was to study the relationship between low values of blood ionized calcium measured in the first days of life postpartum and the clinical and histologic appearance of enamel of primary teeth. Twenty-five healthy children selected on the basis of optimality with known blood values of ionized calcium from the first days of life participated in a dental examination at the age of 5 yr. Twenty-four of the children contributed one exfoliated tooth each, which was histologically examined. The infants had lower mean values of ionized blood calcium on days 1 and 3 than day 5 postpartum. Thirteen of the 25 children had enamel aberrations, mainly on one tooth each. The histologic examination showed normal overall enamel morphology. The neonatal line was present in all teeth, and these lines were mostly thin. The registered findings about the enamel morphology could not, in any case, be correlated with the measured values of neonatal blood ionized calcium.

Calcium↗

Disturbances of cementum formation induced by single injection of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) in rats: light and scanning electron microscopic studies.

With the rat molar as a model, evidence is presented that dentin mineralization influences formation of acellular cementum. Formation of acellular cementum did not occur on the surface of experimentally induced unmineralized dentin. Instead, an atypical hyperplastic cementum was formed. The disturbance in acellular cementum formation was permanent.

Animals↗

Effects of actinomycin D on developing hamster molar tooth germs in vitro.

The aim of this study was to evaluate the toxic effects of actinomycin D on the developing hamster tooth germ in organ culture. Hamster tooth germs during early secretory amelogenesis were exposed in vitro for 24 h to 10(-9) M-5 x 10(-5) M actinomycin D. Actinomycin D dose-dependently (> or = 10(-7) M) decreased the tooth germ dry weight but mineralization was affected only by doses > or = 10(-5) M. However, the uptakes of TCA-insoluble 32P and [3H]thymidine were significantly reduced dose-dependently from > or = 10(-8) M actinomycin D, indicating that the drug inhibits the synthesis of phosphate-containing macromolecules as well as DNA synthesis. Histologically, 10(-8) M actinomycin D was the lowest dose which was not toxic to any cell type in the developing tooth germ. At 10(-7) M actinomycin D, the most sensitive cells were the proliferating pre-odontoblasts followed by pre-ameloblasts; the mature secretory ameloblasts and odontoblasts appeared unaffected. Higher doses resulted in increased cytotoxicity to the secretory cells and, eventually, total degeneration of most cells. The data suggest that children treated for cancer during tooth development using anti-chemotherapy cocktails containing actinomycin D (serum levels > 10(-7) M) may develop defects later on in the mature dentition as a direct consequence of the toxicity of the drug to the tooth organ.

Ameloblasts↗

Mineralized nodule formation by human dental papilla cells in culture.

Human dental papilla cells were enzymatically separated from deciduous tooth germs of an 8-month-old embryo legally aborted. The second passage cells were cultured up to 35 days in 3 groups. The beta-GP group was cultured in the Dulbecco MEM containing ascorbic acid and beta-glycerophosphate supplemented with 15% fetal bovine serum. The Dex group was in the same medium, in addition containing dexamethasone. The control group contained none of the 3 chemicals. Mineralized nodules were formed after 15 days in the beta-GP and Dex groups. Only in the presence of ascorbic acid and organic phosphate did they mineralize. The addition of dexamethasone caused a significant increase in the number of nodules. By electron microscopy, the nodules contained needle-shaped crystals associated with a network of collagen fibrils. Calcium and phosphorus were detected by energy-dispersive X-ray microanalysis in the nodules. Furthermore, the crystalline material exhibited a pattern consistent with hydroxyapatite and dentin when examined by X-ray diffractometry. Cells showed high levels of alkaline phosphatase activity, which was increased 2-3 times in the presence of the 3 chemicals. These results indicated that human dental papilla cells have the ability to form dentin in culture. The formation of mineralized nodules by human dental papilla in vitro provides a useful model for studying the morphogenesis and differentiation of dental papilla ectomesenchyme.

Alkaline Phosphatase↗

SEM and EDS analysis of calcospherites in human teeth.

The present study was designed to characterize the morphology and composition of calcospherites in the coronal and root predentin of human permanent teeth by scanning electron microscopy (SEM) and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS). Human incisors, premolars, and molars were used. The calcospherites in the coronal predentin were globular and 10-20 microm in diameter. The calcospherites in the root predentin were smaller and their shape was different. Polygonal calcospherites and stellate calcospherites were observed in the intermediate region of the root predentin. Calcospherites were rarely present in the apical region of the root predentin. Calcified matrix fibers were observed in the apical region of the root predentin. The Ca/P molar ratio in crown calcospherites (1.63 +/- 0.27) differed significantly from that in root calcospherites (1.46 +/- 0.28). Sulfur was detected from the cervical region to the root region, but not in the horn region. Odontoblast activity and the local environment of the predentin are thought to determine the shape, size, and composition of calcospherites.

Calcium↗

Involvement of matrix metalloproteinases in the onset of dentin mineralization.

In order to study the involvement of matrix metalloproteinases (MMPs) on dentin formation and mineralization, day 18 embryonic mouse tooth germs were cultured for 10 d in the presence or absence of Marimastat, a general MMP inhibitor, or CT(1166), a more selective inhibitor of gelatinases (MMP-2 and MMP-9) and stromelysin-1 (MMP-3). With Marimastat a dose-dependent increase in thickness of the predentin layer and a decreased mineralization of dentin were observed. At the highest concentration of the inhibitor used, enamel formation had ceased. With CT(1166), these effects were already apparent at the lowest concentration used. Western blot analyses demonstrated that the two inhibitors inhibited the expression of enamelysin (MMP-20). These observations indicate that MMPs (possibly MMP-2, -3, -9 and/or -20) play a role in the onset of dentin mineralization. The lack of enamel formation was possibly due to diffusion of amelogenin from its normal site of apposition. The protein clearly was not retained at the surface of the non-mineralized dentin layer, and immunopositive amelogenin accumulated in the odontoblast compartment. The diffusion of enamel proteins and the accumulation revealed by immunolabeling of two small leucine-rich proteoglycans, decorin and biglycan, in the predentin may have contributed to impaired dentin mineralization.

Amelogenin↗

Effect of calcium, given before or after a fluoride insult, on hamster secretory amelogenesis in vitro.

We tested the hypothesis that high-calcium medium given prior to or immediately after exposure to fluoride (F) reduces the negative effects of F on secretory amelogenesis. Hamster molar tooth germs were grown in organ culture in media with different calcium levels. Deposition of enamel matrix and matrix mineralization were monitored by incorporation of [3H]proline and uptake of 45Ca and acid-soluble 32PO4. Ameloblast structure and the occurrence of a fluorotic enamel matrix were examined by light and electron microscopy. A preculture of explants in high-calcium medium partially prevented the formation of fluorotic (non-mineralizing) enamel matrix, increased matrix secretion but could not prevent F-induced hypermineralization of the pre-exposure enamel. High-calcium medium, applied after F insult, accelerated the recovery of fluorotic matrix, improved ameloblast structure, enhanced amelogenin secretion, and increased enamel thickness. The data indicate that it might be the balance between the amount of mineral deposition and that of matrix secretion which is critical for the mineralization of newly secreted enamel. Exposure to F disturbs this balance by enhancing mineralization of the pre-exposure enamel, probably generating an excess of protons. High calcium may protect against F exposure by enhancing amelogenin secretion into the enamel space, thereby increasing the local buffering capacity at the mineralization front.

Ameloblasts↗

Short exposure to high levels of fluoride induces stage-dependent structural changes in ameloblasts and enamel mineralization.

We tested the hypothesis that the sensitivity of forming dental enamel to fluoride (F-) is ameloblast developmental stage-dependent and that enamel mineralization disturbances at the surface of fluorotic enamel are caused by damage to late-secretory- and transitional-stage ameloblasts. Four-day-old hamsters received a single intraperitoneal dose of 2.5-20 mg NaF/kg body weight and were examined, 24 h later, by histology and histochemistry. A single dose of >or=5 mg of NaF/kg induced the formation of a hyper- followed by a hypomineralized band in the secretory enamel, without changing the ameloblast structure. At 10 mg of NaF/kg, cystic lesions became apparent under isolated populations of distorted late-secretory- and transitional-stage ameloblasts. Staining with von Kossa stain showed that the enamel under these lesions was hypermineralized. At 20 mg of NaF/kg, cystic lesions containing necrotic cells were also found in the early stages of secretory amelogenesis and were also accompanied with hypermineralization of the enamel surface. We concluded that the sensitivity to F- is ameloblast developmental stage-dependent. Groups of transitional ameloblasts are most sensitive, followed by those at early secretory stages. These data suggest that a F-induced increase in cell death in the transitional-stage ameloblasts accompanies the formation of cystic lesions, which may explain the formation of enamel pits seen clinically in erupted teeth.

Ameloblasts↗