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PubMed1986

Cemento-fibrous dysplasia of the periodontal membrane (studies of the European hamster maxillary incisor).

The periodontal membrane of European hamster maxillary incisors showed histologic changes consisting of an irregularly orientated, less vascularized connective tissue which included abundant cementicle-like structures. The changes were multifocal and bilateral, growing towards the alveolar bone (Grade 1), causing atrophy of the alveolar bone due to compression (Grade 2) and reaching the periosteal membranes (Grade 3). In a few animals, the lesions were seen after one year. They were seen in 80% of hamsters more than 2 years old. Carcinogenic exposure did not alter the latency and incidence of the alterations. The lesions were thought to be a spontaneously occurring disease representing a nodular cemento-fibrous dysplasia of the periodontium. As, morphologically, no exact attribution to other odontogenic or mesenchymal growth could be made, the entity of this periodontal lesion was considered. Although the changes observed in the periodontal membrane of the maxillary incisors of the European hamster were not exactly comparable to odontogenic cemental lesions in man, they may serve as a model to further clarify the nature of fibro-osseous lesions.

Alveolar Process↗

PubMed1986

Enlargement of rat submandibular salivary gland induced by single amputation of lower incisor teeth. Histological, histometric and ultrastructural studies.

Histological, histometric and ultrastructural studies of rat submandibular salivary glands (SMG) following single amputation of lower incisor teeth were made. The SMG enlargement occurred after the tooth amputation, and its maximal increase of weight was reached 7 days later. The results of histological and histometric observations showed that the enlargement of SMG was due to both hypertrophy and hyperplasia of the acinar cells, and hypertrophic acinar cells were ultrastructurally characterized by well-developed organelles such as rough-surfaced endoplasmic reticulum and Golgi apparatus which filled the entire cytoplasm. Hydropically swollen nerve endings with disappearance of vesicles were frequently found. In later stages, degenerative or necrotic cells were scattered in the acini, and the size and the structure of the remaining acinar cells became gradually similar to those of non-treated glands. The morphological changes seen in the enlarged SMG induced by single amputation of the lower incisor teeth in rat were similar in many ways to those of sialadenosis induced experimentally by active sympathomimetic drugs.

Amputation, Surgical↗

PubMed1990

Postnatal effects of nicotine on incisor development of albino mouse.

Young albino mice, 4-days-old, exposed to 0.1% nicotine sulfate on gestational days 6-20 were compared with untreated pups to determine nicotine's effects on the animals. Pregnant mice were given intraperitoneal injections of nicotine at a dose of 1.67 mg/kg/day. Data of pups weight, CRL, distance between the anterior and posterior limbs, maximum head height and width as well as head circumference were collected. The neonates were then decapitated, their entire mandibles were excised, routinely prepared, sectioned and stained with H and E for histologic examination of the developing incisors. All the parameters were significantly reduced in the treated group. Histologically, the processes of odontogenesis appeared retarded in nicotine treated animals, whereas the control group demonstrated normal dentin and enamel formation. Thus nicotine has a detrimental effect on the development of newborn offspring in general and incisor development in particular. This effect begins prenatally and extends postnatally.

Ameloblasts↗

PubMed1991

Effects of gamma radiation on incisor development of the prenatal albino mouse.

Fetuses of pregnant albino mouse exposed to 400 rad of gamma-irradiation, on the 12th gestational day, were compared with unirradiated fetuses to asses the radiation effect on developing incisors. Pregnant animals were sacrificed on day 18 post coitum, and their fetuses were decapitated. Heads were routinely prepared, frontally sectioned, and stained with hematoxylin and eosin. Histologic examination demonstrated that the development of the maxillary and mandibular incisors was retarded in all the experimental fetuses and were in early bell stage, whereas those of the control animals were elaborated their matrices. It was concluded that gamma-irradiation interferes with cytodifferentiation of the enamel organ and dental papilla and subsequently inhibits normal odontogenesis.

Animals↗

PubMed1975

The ultrastructural localization of iron in rat incisor enamel.

Previous studies have shown that the pigmented surface layer of rat incisor enamel contains up to 30% iron but have left the question open as to whether iron is bound to the hydroxyapatite crystals or is present as a separate crystalline phase. Maxillary incisors from adult rats were demineralized for an extended period of time in EDTA. An insoluble membranous structure representing the remaining superficial portion of the enamel was collected and analyzed in the electron microprobe. The analyses showed that the demineralization procedure had removed calcium and phosphorus nearly completely, whereas the iron content of the surface layer had not been appreciably reduced. Electron microscopic examination of these specimens showed that the residual material contained electron-dense particles whose size, form and orientation indicated that they were remnants of the original crystal population. Several other demineralized and undemineralized specimens were also examined electron microscopically. The results indicate that iron is not present as a separate particulate phase but is, probably, bound to the surface of hydroxyapatite crystals.

Animals↗

PubMed1976

Polarized light microscopy of enamel structure in incisors from newborn infants.

Enamel structure in human primary incisors was histologically examined in order to compare the observations with those from recent studies on incipient carious and fluorosed enamel. Ground sections from mandibular incisors of five full-term human infants were examined in polarized light using aqueous media (water, Thoulet's media), alcohols with different refractive indices, and quinoline. Imbibition graphs were made along traverses from the amelodentinal junction (ADJ) to the enamel surface. Quantitative assessments of the birefringence in different media along the traverses indicated a change in the relative volumes of crystallites and surrounding medium with a continuous growth of crystallites toward the ADJ. The influence of organic material is discussed in relation to the differences in calculated form birefringence observed within the specimens. When examined in quinoline, a 30-40-mum-thick surface zone appeared distinct positively birefringent, indicating that the outermost enamel reacted as a molecular sieve. Because of the lower content of minerals the interpretation of this zone differed from that of similar "dark zones" observed in carious and fluorosed enamel.

Dental Enamel↗

PubMed1978

Acute and protracted effects of vinblastine on odontoblasts and dentinogenesis in rat incisors.

The effects of a large dose of vinblastine sulfate (2 mg/kg body weight) on proliferating odontoblast precursors and secretory odontoblasts in the continuously growing rat incisor were studied. The rats were killed 6 h, 24 h, 3 d and 7 d after vinblastine injection. Most cells in the proliferating zone contained arrested mitoses, or had perished after 24 h. After 3 and 7 d, the odontoblasts derived from this zone were reduced in number, and showed altered cell shapes. The odontoblasts had produced irregular dentin. The secretory odontoblasts had displaced nuclei and altered cell shapes after 24 h. Those most affected were opposite early mineralized dentin. In some incisors the cells had perished. In the protracted experiments almost all the odontoblasts were changed and had produced abnormal dentin. In the early mineralized dentin area, accumulations of cells were present after 3 d, and osteodentin-like material after 7 d.

Animals↗

PubMed1978

Histomorphologic investigations of dentinogenesis in incisors of offspring of cyclophosphamide-treated pregnant rats.

Eight days old offspring of six rats treated with single doses of 40 mg/kg and 50 mg/kg of cyclophosphamide on the 20th day of pregnancy constituted two experimental groups. Group 1 (40 mg/kg) comprised 21 animals, Group 2 (50 mg/kg) 14 animals. Histomorphologic investigations of the maxillary and mandibular incisors revealed the following changes: (1) dental constrictions, (2) niche-like dentinal defects, (3) scalloping of the amelodentinal junction, (4) incremental line in the pre-experimental tooth segment, (5) external resorptions, and (6) diffuse edema in the pre-experimental part of pulp. Constrictions and niches qualitatively concurred with those previously observed in adult rats of the same strain, but the lesion frequency was essentially higher in the offspring. Further, the additional change of external resorptions was evinced by the offspring incisors, and changes only rarely observed in adults, such as scalloping of the dentinoenamel junction and a dentinal incremental line, constituted frequent findings in the offspring material.

Animals↗

PubMed1978

Effect of thyroxine and growth hormone on dentin production in maxillary incisors in the rat.

Dentin production and longitudinal growth of maxillary incisors in female rats, age 60--95 d, were determined by the tetracycline technique in hypophysectomized rats after administration of growth hormone and thyroxine during age 75--95 d. Hypophysectomy was performed at age 60 d. Administration of thyroxine resulted in a considerable increase in dentin apposition and longitudinal growth of the tooth. The same effect, but somewhat lower, was registered for growth hormone. Growth hormone and thyroxine administered simultaneously had an additive synergistic effect. Compared with the effect of hypophysectomy and of hormone administration on longitudinal bone growth and cortical bone remodleing the effect on dentin production and longitudinal growth of the maxillary incisors in the same rats is less pronounced and shows a different pattern in reaction, indicating differences in sensitivity for different cell systems and difference in endocrine control.

Animals↗

PubMed1979

Vincristine's effect on dentinogenesis in rat incisor.

Vincristine was administered to 60 rats in four groups in doses of 0.1, 0.3, 0.5 and 0.7 mg/kg. Histomorphologic investigation of the dentin and odontoblasts in the maxillary incisors after 1, 2 and 3 weeks revealed a moderate to severe disturbance of dentin production in some parts of the incisors. In some of the affected areas the effect seemed to be reversible in that normal-appearing dentin was found pulpal to the dentinal derangements after 2 and 3 weeks. The distribution and severity of the lesions were similar to those previously observed 3 days after injection of the same doses of vincristine.

Animals↗

PubMed1980

Autoradiographic investigation of dentin production in rat incisors after vincristine administration.

0.7 mg/kg VCR was administered intravenously to nine rats in three experimental groups. One hour after VCR injection the animals were injected with 3H-proline. The animals were sacrificed 1.5, 5 and 24 h after the VCR administration, and by comparison with nine control animals similarly injected with sodium chloride solution and 3H-proline, it was shown that VCR causes an early, intracellular retention of labeled proline in the odontoblasts, an abnormal intracellular distribution of labeled material and a generally decreased secretion of dentinal matrix from the odontoblasts in the maxillary incisors. The severity of the effects were shown to vary in different parts of the incisors.

Animals↗

PubMed1981

Colchicine's effects on rat incisor odontoblasts and dentinogenesis.

Colchicine (CLC) in doses of 0.5 and 1.5 mg/kg was administered to 40 female Wistar rats in two equal groups. The animals were sacrificed after 5 h, 24 h, 3 d and 7 d, and the effects of CLC on pulp, odontoblasts and dentin in the continuously growing incisors were studied. With the lowest dose a few arrested mitoses were observed in the germinative part of the pulp after 5 and 24 h. With the highest dose an increasing number of mitoses were observed in the germinative part of the pulp after 5 and 24 h. More incisally the odontoblasts were pale, swollen and granulated after 5 h, and necrotic and disintegrated after 24 h. After 3 and 7 d dentinal derangements, consisting of moderately and severely irregular dentin, osteodentin and a niche-like defect in the labial dentin, were seen. Labially one or two incremental lines traversed the dentin from the apical to the incisal part of the incisors.

Animals↗

PubMed1981

Follow-up study of permanent incisors with enamel fractures as a result of an acute trauma.

The present investigation evaluated the prognosis for vitality after an acute trauma in 2891 permanent incisors with enamel fracture as the only damage, and in 476 incisors with enamel fracture combined with other symptoms on the damaged tooth. Pulpal necrosis developed in 57 teeth (1.7%). Acute treatment in connection with enamel fracture was only performed in half of the cases and had no importance on vitality. The combination of enamel fracture and concussion or mobility resulted in pulpal necrosis in 8.5% of cases, and cases involving both mobility and concussion meant pulpal necrosis in 14% of teeth. The findings clearly illustrated that an enamel fracture is an injury with an extremely favorable prognosis, and that the risk group can be narrowed to cases of combined injuries involving the supportive tissue.

Adolescent↗

PubMed1981

Follow-up study of permanent incisors with enamel-dentin fractures after acute trauma.

The present investigation evaluated the prognosis for vitality after an acute trauma in 3144 permanent incisors with enamel-dentin fracture as the only damage and in 923 incisors with enamel-dentin fracture combined with other symptoms on the damaged tooth. The teeth were examined at regular intervals. The observation time was more than 2 years in the case of 78.9% of the material. Pulpal necrosis developed in 250 teeth (6.1%). Pulp death occurred in 3.2% of teeth with enamel-dentin fracture as the only damage. The combination of enamel-dentin fracture and concussion resulted in pulpal necrosis in 5.8% and cases involving both concussion and mobility showed pulpal necrosis in 30.1% of teeth. A registration of the enamel-dentin fracture based on the extent of dentin exposure was undertaken. The relationship between extent of dentin exposure and pulpal necrosis as well as influence of treatment on pulpal necrosis was clearly illustrated. It is concluded that information on damage to the mineralized tissue without details of damage occurring at the same time to supportive tissue is of doubtful value in assessing the prognosis.

Child↗

PubMed1983

Proliferation and migration of rat incisor mesenchymal cells.

Sixty female Wistar rats were injected with tritiated thymidine and killed at intervals between 1 hr and 72 hr after injection. Autoradiographs of paraffin and Vestopal W embedded sagittal sections of the maxillary incisors were prepared. The distribution of labeled cells after 1 hr revealed the basal pulp cells and the preodontoblasts as proliferative cells. The growth rate of the incisor and the migration of the basal pulp cells were established from the position of labeled cells at 72 hr observation time. The number and localization of labeled and unlabeled mitoses were registered in order to determine the duration of the generation cycle of the proliferative cells. The identical cell generation time of preodontoblasts and basal pulp cells and the migration pattern of the latter indicate that the preodontoblasts are renewed by preodontoblast multiplication and not by migration of basal pulp cells.

Animals↗

PubMed1984

Histochemical study of giant tubule content in dentin of unerupted cow incisors.

Incisal dentin of mandible cow incisors was studied by incident light. The material consisted of 12 intact permanent unerupted incisors from 2-yr-old cows removed immediately after bleeding. These specimens were kept in an isotonic EDTA-sucrose solution to be decalcified while maintaining vitality of cellular components. Three of the specimens were successfully dissected in a mesiodistal plane, exposing the giant tubule lumens and their content. By the use of NBT, a compound reduced by the dehydrogenase enzymes of the electron transport in the inner mitochondrial membrane, it was concluded that the giant tubules contained vital cells. The giant tubules were also shown to communicate with the incisal part of the pulp cavity by wide openings.

Animals↗

PubMed1985

Incisor and jaw relationship in 27 persons with osteogenesis imperfecta.

The incisor relation and craniofacial morphology, as evaluated from lateral cephalograms, were studied in 14 women and 13 men with osteogenesis imperfecta. A negative overjet was found in one woman and five men, and for the total material a mesial basal jaw relationship was observed. Data for both women and men indicated that skeletal discrepancies had been partially compensated for by the incisor inclination. Probably, persons with osteogenesis imperfecta may be regarded as a potential high-risk group for development of malocclusion.

Adolescent↗

PubMed1985

Ultrastructure of lingual enamel epithelium in rabbit permanent incisors.

The recent observation that the lingual surface of the permanent rabbit incisor, in contrast to the rodent incisor, is covered with enamel near the initially formed tip, initiated a histologic study of the enamel epithelium in this region. Tooth buds from fetal New Zealand white rabbits aged 27 and 30 days in utero were processed for transmission electron microscopy. Examination of longitudinal and cross-sections revealed a transition of secretory ameloblasts to postsecretory ameloblasts on the facial aspect of the enamel organ. Incisally, the facial ameloblast layer was continuous with postsecretory ameloblasts on the lingual aspect. More apically on the lingual surface, a gradual transition between postsecretory and reduced ameloblasts occurred. This study shows that by day 27 in utero, the ameloblasts on the lingual aspect of the tooth are in the postsecretory and degenerative stages and that, by day 30, the enamel epithelium lingually has been replaced by cementum on the prismatic enamel and by connective tissue.

Ameloblasts↗