Microscopy of tetracycline-induced lesions in the rat incisor enamel organ

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.

Are there structural alterations in the enamel organ of offspring of rats with alloxan-induced diabetes mellitus?

Enamel hypoplasia is the most common developmental defect of human teeth that may be seen in deciduous teeth of babies born to diabetic women. In the present experimental study, we analyzed the enamel organ of the mandibular incisors of the offspring of rats with alloxan-induced diabetes. By light microscopy, no alterations could be found in the enamel organ of rats born to diabetic mothers compared to normal ones, except in one case. In contrast, significant differences were detected with computer-aided morphometry. In the rats born to treated and untreated diabetic mothers, there was thinning of the enamel matrix and of the ameloblasts and the nuclear area of the latter was smaller. In the rats born to treated diabetic mothers, the nuclei of the ameloblasts were more elliptical and there was enlargement of the interstitial area of the stellate reticulum. These results indicate that there are structural defects in the enamel organ of rats born to mothers with alloxan-induced diabetes which could induce the enamel hypoplasia observed by scanning electron microscopy and which may reflect the metabolic alterations seen in this condition. Future studies are needed to determine whether these effects are transitory or permanent.

Morphological and immunocytochemical analyses on the effects of diet-induced hypocalcemia on enamel maturation in the rat incisor

During the maturation stage of amelogenesis, the loss of matrix proteins combined with an accentuated but regulated influx of calcium and phosphate ions into the enamel layer results in the "hardest" tissue of the body. The aim of the present investigation was to examine the effects of chronic hypocalcemia on the maturation of enamel. Twenty-one-day old male Wistar rats were given a calcium-free diet and deionized water for 28 days, while control animals received a normal chow. The rats were perfused with aldehyde and the mandibular incisors were processed for histochemical and ultrastructural analyses and for postembedding colloidal gold immunolabeling with antibodies to amelogenin, ameloblastin, and albumin. The maturation stage enamel organ in hypocalcemic rats exhibited areas with an apparent increase in cell number and the presence of cyst-like structures. In both cases the cells expressed signals for ameloblastin and amelogenin. The content of the cysts was periodic acid-Schiff- and periodic acid-silver nitrate-methanamine-positive and immunolabeled for amelogenin, ameloblastin, and albumin. Masses of a similar material were also found at the enamel surface in depressions of the ameloblast layer. In addition, there were accumulations of glycoproteinaceous matrix at the interface between ameloblasts and enamel. In decalcified specimens, the superficial portion of the enamel matrix sometimes exhibited the presence of tubular crystal "ghosts." The basal lamina, normally separating ameloblasts and enamel during the maturation stage, was missing in some areas. Enamel crystals extended within membrane invaginations at the apical surface of ameloblasts in these areas. Immunolabeling for amelogenin, ameloblastin, and albumin over enamel was variable and showed a heterogeneous distribution. In contrast, enamel in control rats exhibited a homogeneous labeling for amelogenin, a concentration of ameloblastin at the surface, and weak reactivity for albumin. These results suggest that diet-induced chronic hypocalcemia interferes with both cellular and extracellular events during enamel maturation.

A scanning electron and confocal laser microscope investigation of tetracycline-affected human dentine

Because of the well reported dental side-effects of tetracycline administration, the drug should not be administered to children. However, it and its derivatives are often administered over a prolonged period for treatment of acne in young adults. Dental side effects are also noticed in these patients. The aim of this study was to examine with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) the root dentine of a tooth from a young adult affected by tetracycline therapy. The palatal root of an upper third molar, demonstrating distinct areas of tetracycline staining, was removed from the crown and sectioned longitudinally to produce two samples. The pulp tissue was peeled off the dentine and any remaining non-mineralized tissues were removed with sodium hypochlorite. One sample was prepared for SEM and the other as a ground section which was examined with a CLSM. It was demonstrated by SEM that the mineralizing front of unaffected dentine was of a normal calcospherite appearance; in contrast, the mineralizing front of the tetracycline-affected dentine was devoid of calcospherite formation and many surface defects were apparent. In addition, the number of dentinal tubules associated with the defects was reduced. It was shown by CLSM that tetracycline bands were made up of numerous smaller bands and that peritubular dentine not associated with fluorescent bands had incorporated tetracycline. The CLSM examination of the mineralization front of the affected dentine revealed that fluorescence of dentine was restricted to the peritubular dentine. The results confirm that dentine mineralization is affected by systemic tetracycline therapy and that tetracycline can be incorporated into peritubular dentine after mineralization of the primary dentine matrix.

Effects of phosphonoformic acid and 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on distribution of tetracycline in the developing rat molar

Tetracycline was used as a marker to study the effect of phosphonoformic acid and 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on the mineralization of the developing dental hard tissues. Groups of young rats were given a single subcutaneous injection of tetracycline and at the same time were injected with a single dose of either phosphonoformic acid or HEBP (10 mg P/kg b.w.). Alternatively, rats were injected with the tetracycline after different time intervals from the phosphonate injection. Rats were sacrificed at intervals ranging from 1 to 4 days. Frozen-sections were obtained at the level of the maxillary first molar and prepared for light and fluorescence microscopy. The results of the present study indicate that the distribution pattern of tetracycline in the developing dental hard tissues is greatly affected by the pathologic changes induced by phosphonoformic acid and HEBP. Both drugs caused similar changes in the pattern of tetracycline uptake in the developing enamel. There seems to be a direct relation between the presence of developmental defects of enamel and the degree of discoloration induced by tetracycline. Aberrations in the mineralization of dentin were caused only by HEBP. As demonstrated by this study, HEBP is capable of inducing a provisional inhibitory effect on dentin mineralization.

Effects of phosphonoformic and phosphonoacetic acids on developing enamel of rat molars

The effect of a single subcutaneous injection of different dosages of phosphonoformic or phosphonoacetic acid on the developing dental tissues of the rat molar was studied. The substances were injected at different rat ages and effects on the developing teeth were analyzed by means of histochemistry of frozen sections and scanning electron microscopy. Molars of rats injected at the age of 10 or 15 days showed no pathologic changes. Administration of phosphonoacetic acid in a dosage of 10 or 20 mg P/kg b.w. had no demonstrable effect on the dental tissues in any of the animals. Phosphonoformic or phosphonoacetic acid in a dosage of 10 or 30 mg P/kg b.w. respectively induced subameloblastic cysts 24 h after injection to 4-7-day-old rats. The cysts were mainly localized on the mesial sides of the cusps under ameloblasts in the late secretory stage. Calcified depositions were seen in the ameloblastic layer lining the cystic cavities. A thin zone, the staining of which indicated a high mineral content, was seen in the outermost enamel layer under the cysts. A few days later, enamel hypoplasias were seen in areas previously occupied by cysts. A lightly stained line was observed in the enamel matrix demarcating the amount of enamel matrix formed before and after the injection. Hypoplastic lesions were also noted in the enamel surface of newly erupted molars. These findings suggest that the two injected monophosphonates can induce pathologic changes in the developing enamel organ and hypoplasias in the enamel.

Changes of secretory ameloblasts in mini-pig fetuses exposed to ethanol in vivo

After addition of ethanol to the ordinary fodder of pregnant mini-pigs, ultrastructural changes were found in secretory ameloblasts from tooth germs of their mid-term fetuses. Compared with controls, many mitochondria showed abnormal shape and size, and some exhibited deposition of paracrystalline material in the matrix. An abnormal deposition of stippled material intercellularly was also observed. These changes were interpreted as signs of an abnormal secretory function.

Scanning electron microscopy of fluoride-induced disturbances on the enamel surface of rat molars

Rats were given a single high dose of fluoride at the age of 5 days and killed after 24 h, 10 or 15 days. The maxillary first molars were prepared for scanning electron microscopic examination. It was concluded that a single dose of fluoride, preferentially affecting ameloblasts with a high secretory activity, leads to the formation of subameloblastic cysts and enamel hypoplasias covered with granular deposits.

Fluoride-induced cystic changes in the enamel organ of the rat molar

Many substances have been found to cause enamel disturbances in toxic doses, and it has been postulated that these disturbances are linked to the formation of sub-ameloblastic cysts. In the present investigation, fluoride-induced sub-ameloblastic cysts in developing rat molars were related to fluoride dose, age of the animals, and the plasma fluoride level. The sub-ameloblastic cysts, which developed predominantly towards the end of the secretory stage of amelogenesis, appeared shortly after fluoride administration and regressed within 3 days. Hypoplasias and internal defects were found in the enamel under the disturbed ameloblast layer. The highest plasma fluoride levels were found in the youngest animals 24 h after injection. The frequency and size of the sub-ameloblastic cysts were clearly related to the fluoride-dose and age of the animal and, subsequently, to the plasma fluoride level.

The macroscopic appearance and associated histological changes in the enamel organ of hypoplastic lesions of sheep incisor teeth resulting from induced parasitism

Twenty-one penned female sheep were infected with a high dose of nematodes (200,000 Trichostrongylus vitrinus and 25,000 Ostertagia circumcincta) during first incisor development when aged 7-8 months. Three sheep were infected with 200,000 T. vitrinus only; 10 sheep were untreated. Anorexia, lassitude and severe diarrhoea were seen in 14 of the infected sheep after 21-26 days. Anthelmintic was given to sheep showing undue distress to end the infection and to all remaining sheep on day 33. Animals were killed at 3 stages: during the infection, at intervals during later tooth development, and at the time of eruption of the incisor teeth, 7-8 months after the parasites were given. Hypoplasia of the labial enamel of 15 out of 19 teeth from sheep killed after recovery from the infection was classified according to the extent and depth as pits, grooves or larger areas of missing enamel with ledge-formation cervically. The amount of missing enamel related to the severity of the systemic disturbance which affected the secretory ameloblasts. During the period of active infection, some secretory ameloblasts showed vacuolization or were shorter than in controls; some cells were no longer adjacent to the organic matrix; some continued to function but abnormally and later became separated from the retained organic matrix by connective tissue. Cervically-placed ledges resulted either from the recovery and resumption of activity of some ameloblasts or from differentiation of new secretory cells after the infection ended.

Organ culture of murine tooth germs exposed to alloimmune IgG

The effect of H-2 specific alloimmune IgG on mouse molar tooth germs maintained in organ culture was assessed by light microscopy. Histological changes not evident in control incubation material were ascribed to the membrane-mediated effects of alloimmune IgG. A role of H-2 in murine odontogenesis is implicated.