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PubMed1985

The chronological distribution of enamel hypoplasia in human permanent incisor and canine teeth.

The frequencies and chronology, based on a standard tooth development chart, of enamel hypoplasia derived from permanent upper central incisors and mandibular canines were compared for 42 prehistoric Amerindians. Between 0.5 and 4.5 years, when the crowns of both these teeth are developing, hypoplasias were 1.36 times more common on the incisors (54 hypoplasias/incisor; 40 hypoplasias/canine). Hypoplasias on incisors occurred earlier (mean = 2.50; median at 2.0-2.5 years) compared to the canine (mean = 3.51; median at 3.5-4.0 years). Differences in published frequencies and chronologies of hypoplasias may be explained, in part, by an indefinable variation in the teeth studied. The highest density of hypoplasias on both tooth crowns was just cervical to the midpoint, suggesting that developmental rates and crown geometry may influence the ability of the crown to record stressful events.

Age Factors↗
PubMed1985

Effects of colchicine and hydrocortisone on unimpeded eruption rates of root-resected mandibular incisors of rats.

A single injection of colchicine and daily injections of hydrocortisone have opposite effects on tooth eruption, respectively causing marked reduction and marked increase in unimpeded eruption rates in the root-resected incisors of rats. Unimpeded eruption rates of both root-resected and normal, non-resected, incisors responded identically to these two drugs, providing support for the view that the eruptive process following root resection is physiological. It was not possible to obtain direct evidence relating to either the hydrostatic pressure or the periodontal fibroblast hypotheses of tooth eruption; the drugs used to affect the eruption rates of resected rat incisors could also affect either the tissue hydrostatic pressure or the motility or contractibility of periodontal fibroblasts or both.

Animals↗
PubMed1986

Penetration of various molecular-weight proteins into the enamel organ and enamel of the rat incisor.

During enamel maturation, most of the organic matrix is removed as the mineral content increases; it is postulated that proteolytic enzymes within enamel break down large proteins into more mobile fragments. To predict how such fragments might leave the enamel, the entry and penetration of various proteins into it was examined. Rats (100 g) were injected via the external jugular vein with 125I-iodinated calcitonin (3600), insulin (5700), epidermal growth factor (EGF; 6100) and albumin (68,000). They were killed after 10 min and radioautographs made to visualize these molecules in the incisor enamel organ and enamel. In addition, dissected incisors were wiped free of their enamel organs, dipped in the iodinated protein solutions for 10 min, and processed for radioautography. In all dipped teeth, except those exposed to albumin, there was a gradient of silver-grain density over the entire thickness of enamel in both the secretion and maturation zones. In all injected animals, enamel labelling in the secretion zone was only slightly above background. In the maturation zone of animals injected with calcitonin and insulin, many grains were over enamel adjacent to smooth-ended ameloblasts but not ruffle-ended ones. Animals injected with EGF and albumin had no labelled enamel in the maturation zone. Thus dipped rat incisor enamel was permeable to proteins with molecular weights as high as 6100. Localization of injected proteins indicates that the enamel organ restricts their passage into enamel, but proteins with molecular weights as high as 5700 may pass into enamel through or between smooth-ended ameloblasts. As exogenous proteins readily diffused into the enamel, it seems likely that enamel proteins of similar size can leave enamel by a similar route.

Animals↗
PubMed1987

The variation in the size and shape of the human speech pattern with incisor-tooth relation.

A mandibular kinesiograph was used to monitor the movement of the lower incisors of young dentate adults reading a standard text. An interface to a microcomputer which recorded and analysed these movements. As the tracings accumulated on the computer monitor, a characteristic pattern was produced. The dimensions of this speech pattern, or envelope of movement, were measured and correlated with the subject's sex and incisor classification. Four distinct patterns were found and these correlated well with incisor classification. Small differences were noted in the dimensions of the speech envelope between men and women, but these were not significant.

Adolescent↗
PubMed1987

An autoradiographic study on the effect of epidermal growth factor on cell proliferation in erupting mouse incisors.

Epidermal growth factor (EGF) is a small polypeptide that induces precocious eyelid opening and incisor eruption in newborn mice; it stimulates cell proliferation in various cell types in vitro and in vivo. EGF was injected twice daily into newborn mice (0.4 microgram/g) and tritiated thymidine was injected subcutaneously 6 h before killing the mice. Longitudinal sections of the lower incisors showed significantly more thymidine-labelled mitoses in the pre-odontoblast and pre-ameloblast layers at the basal ends of incisors in EGF-treated mice than in control mice. Although these results indicate that the EGF-induced precocious tooth emergence is associated with a stimulation of cell proliferation in the root sheath, this tissue may not be the target for the actions of EGF. Earlier studies have shown that root growth is not a factor in the generation of the eruptive force and, as neither the pre-ameloblasts nor pre-odontoblasts express EGF-receptors, the stimulation of cell proliferation in the root-sheath region appears to be a result and not a cause of accelerated tooth eruption, i.e. the increase in root growth may meet the need to maintain the tooth positionally during the accelerated eruptive process.

Animals↗
PubMed1991

The effect of airborne lead on lead levels of blood, incisors and alveolar bone of rats.

Groups of 20 inbred rats were exposed to: (1) "clean air" (0.05 micrograms Pb/m3) for 70 days; (2) 77 micrograms Pb/m3 for 70 days; (3) 249 micrograms Pb/m3 for 28 days; and (4) 1546 micrograms Pb/m3 for 50 days. Half the rats in each group were then killed and the other half kept in "clean air" until the blood lead of groups 1-3 had returned to normal. That half of the incisors which had been completely renewed during the experimental period, as well as the alveolar bone of each rat, were analysed for lead by atomic absorption spectrophotometry. In the rats killed immediately after exposure, the lead levels by atomic absorption alveolar bone showed significant differences (p less than 0.05) among all four groups, except between groups 2 and 3, indicating the importance of the combined effect of airborne lead concentration and length of exposure. For blood, significant differences (p less than 0.05) were found among all groups. For the post-exposure rats, the incisors and blood showed no significant differences (p greater than 0.05) among groups 1, 2, and 3. For alveolar bone, significant differences were not found (p greater than 0.05) between groups 2 and 3. It can be concluded that during lead exposure the alveolar bone transformation was the highest and that of incisor tissue just lower, and that blood lead became supplemented through the process of remobilization from alveolar bone, as reported for other bones.

Aerosols↗
PubMed1991

Morphological and immunocytochemical characterization of cultured rat incisor cervical epithelial cells.

Epithelial cells from the cervical loop of the rat incisor were isolated by co-culture of apical explants with growth-arrested 3T3 fibroblasts. The epithelial phenotype of the expanding outgrowths was confirmed 10 days after the seeding of the explants by phase-contrast microscopy and immunocytochemical identification of cytokeratins. After 3 weeks in culture, the epithelial cells covered the entire surface of the coverslips and were then passaged. Subcultures gave rise to a confluent sheet within 10-12 days. Light and electron microscopy showed that confluent cervical epithelial cells generally reconstituted a bi-layered structure similar to Hertwig's epithelial sheath. Epithelial cells from the rat palate, cultured and subcultured according to the same procedure, organized themselves in 5-6 cell layers, the upper cells having generally a squamous morphology. Synthesis of extracellular matrix molecules by rat incisor cervical epithelial cells was studied with specific antibodies. These cells failed to produce type I collagen, but synthesized all the major basement membrane components (type IV collagen, laminin, heparan sulphate proteoglycan and fibronectin). These observations suggest that the culture conditions allowed the reconstitution of a typical Hertwig's epithelial sheath by rat incisor cervical epithelial cells.

Animals↗
PubMed1992

Calcium movement in vivo and in vitro in secretory-stage enamel of rat incisors.

The lower incisors of young rats were dissected, immersed in physiological saline containing 45Ca under various conditions, and processed for autoradiography. The data were compared with those from in vivo 45Ca autoradiography. In secretory-stage enamel, wiped free of the enamel organ and immediately immersed in radioactive saline, there was intense labelling in the surface layers. The labelled area expanded only gradually into the deeper layers at a rate similar to that observed in vivo. Labelling in the enamel was similar in pattern but much weaker in intensity when the incisor was identically treated in vitro with the enamel organ attached. Glutaraldehyde pretreatment of the exposed enamel abolished expansion of the labelled area, whereas a hypochlorite pretreatment allowed a rapid diffusion of the isotope into the deeper layers of the secretory-stage enamel. The findings confirm the role of the enamel organ as a diffusion barrier to the penetration of calcium from the extracellular fluid to the secretory-stage enamel, and suggest an intimate correlation between physicochemical properties of the organic enamel matrix and the rate of surface-to-interior diffusion of calcium within the secretory-stage enamel of rat incisors.

Animals↗
PubMed1992

Activation of sympathetic fibres in the pulp by electrical stimulation of rat incisor teeth.

Previous studies of the sympathetic nerve supply of the rat mandibular incisor pulp have shown conflicting results. Here, the neurovascular control of the rat lower incisor pulp was investigated by stimulating the tooth crown and the cervical sympathetic trunk electrically and monitoring blood-flow changes in the pulp by laser Doppler flowmetry. In addition the presence of noradrenaline (NA) in the pulp and gingiva was examined biochemically in untreated and sympathectomized animals by high-performance liquid chromatography. The tissue concentrations of NA in the pulp were 11-fold greater than those of gingiva. Surgical sympathectomy significantly reduced the NA content in the pulp by 76%. Monopolar electrical stimulation of teeth (25-50 microA) for 1 min resulted in a frequency-dependent reduction followed by an increase in pulpal blood flow. At 16 Hz the reduction in blood flow was 65% and the subsequent increase was 9%. After intravenous administration of the alpha-adrenoceptor antagonist phentolamine, the stimulation-induced reduction in pulpal blood flow was diminished by 94% while the increase was significantly enhanced (from 9 to 40%). Infusion of the beta-adrenoceptor antagonists propranolol and timolol significantly reduced this increase in blood flow by 53 and 55%, respectively. Preganglionic sympathetic nerve stimulation also induced a frequency-dependent reduction followed by a slight increase in pulpal blood flow. This reduction in blood flow was almost abolished after alpha-adrenergic blockade and there was no subsequent increase. These findings suggest that there are sympathetic nerve fibres in rat incisor pulp and that they are activated upon monopolar electrical stimulation of teeth resulting in alpha- and beta-adrenoceptor mediated blood-flow responses.

Adrenergic Fibers↗
PubMed1994

Involvement of substance P but not nitric oxide or calcitonin gene-related peptide in neurogenic plasma extravasation in rat incisor pulp and lip.

The possible involvement of the neuropeptides substance P and calcitonin gene-related peptide (CGRP) in the development of neurogenic plasma extravasation in the lower lip, gingiva and incisor pulp was examined in anaesthetized rats by means of the Evans blue method and by using newly developed blockers of substance P (CP-96,345) and CGRP (CGRP8-37). Electrical stimulation of the inferior alveolar nerve (15 V, 2 ms, 10 Hz) for 5 min significantly increased the Evans blue content of the ipsilateral lip, gingiva and pulp by 60 (p < 0.01), 62 (p < 0.01) and 92% (p < 0.05), respectively (n = 8). Pretreatment with CP-96,345 (total dose: 1.5 mg/kg, intravenously) counteracted the dye leakage in the lip and pulp but not in the gingiva (n = 6). The inactive enantiomer (CP-96,344, 1.5 mg/kg, n = 8) or the nitric oxide synthesis inhibitor (N omega-nitro-L-arginine methyl ester hydrochloride, 10 mg/kg, n = 7) did not reduce the stimulation-induced dye extravasation in any of the tissues. Pretreatment with CGRP8-37 (0.3 mg/kg, n = 7) did not significantly influence the development of neurogenic extravasation in the lip and incisor pulp, but it slightly attenuated extravasation in the gingiva. The results indicate that the afferent nerve-induced dye extravasation in the lip and pulp, but not in the gingiva, is to a large extent mediated by substance P acting via neurokinin-1 receptors. There was no evidence for an involvement of nitric oxide or CGRP in neurogenic extravasation in rat incisor and lip.

Animals↗
PubMed1994

In vitro effects of retinoic acid on mouse incisor development.

The developing dentition is known to express the complete set of retinoic acid (RA) nuclear receptors and cytoplasmic RA-binding proteins (CRABPI and II), and RA is required for in vitro mouse molar morphogenesis, so the role of RA during in vitro mouse incisor development was investigated. Histological procedures, immunocytochemical detection of proliferating cells, immunofluorescence detection of laminin, and in situ hybridization with RNA probes for CRABPI and II were done on the tooth-germ cultures either in the presence or in the absence of RA. RA appeared to control initial morphogenesis, particularly the asymmetrical growth of the cervical loop, and to regulate required differential mitotic activity. RA seemed also to be involved in asymmetrical laminin deposition. The distribution of the CRABP gene transcripts was similar during in vivo and in vitro incisor development. However, CRABPI gene transcript distribution in the labial part of the epithelial loop was detected in vitro only in the presence of RA. A direct role of the CRABPs during tooth development is, however, unlikely because Ch55, a synthetic RA analogue that does not bind to CRABP, had the same effects as RA on in vitro incisor development.

Animals↗
PubMed1995

Response characteristics of periodontal mechanoreceptors to mechanical stimulation of canine and incisor teeth in the cat.

The alveolar bone that overlies the labial aspect of the root of the right lower canine tooth was pared down until paper thin. Thirty-five periodontal mechanosensitive (PM) units sensitive to stimulation of the canine and incisor and to punctate stimulation through the thinned bone of the periodontal ligament of the canine were recorded from the inferior alveolar nerve rostral to the masseter muscle. The units showed a sustained and directionally selective response to pressure applied to the teeth. The optimal directions of stimulation for each tooth in the receptive field were parallel and oriented linguolabially. When the canine was stimulated mechanically in the optimal stimulus direction, the interspike intervals of the responses were relatively regular in most PM units (91%). The conditioning and test stimuli were applied to the adjacent canine and third incisor. The conditioning stimulus (0.10 N) was given to one of these teeth in the optimal stimulus direction. The test stimulus (0.02 N or 0.05 N) was applied to the adjacent tooth in the opposite direction in order to examine the effect of mechanical spreading of the conditioning stimulus on the adjacent tooth. In most PM units, the spike discharges evoked by the conditioning stimulus given to the incisor were stopped by the test stimulus given to the canine. When the given stimuli were reversed, the firings evoked by the conditioning stimulus were slightly depressed by the test stimulus. After removing the spot-like PM receptor site(s) in the paper-thin area of bone, all units but one did not respond to stimulation. These results provide evidence that neurones with multiple-tooth receptive fields and regular spike-interval responses recorded from the inferior alveolar nerve come from the mechanical spreading effect of the stimulation of one tooth on an adjacent tooth through the trans-septal fibre system and that neurones with irregular-interval responses are due to the ramification of PM fibres peripherally.

Alveolar Process↗
PubMed1988

Proportion of unmyelinated axons in rat molar and incisor tooth pulps following neonatal capsaicin treatment and/or sympathectomy.

The occurrence of unmyelinated axons was examined ultrastructurally in rat molar and incisor root pulps of normal rats, of neonatally capsaicin-treated rats, of rats subjected to neonatal capsaicin treatment followed by resection of the superior cervical ganglion and of sympathectomized but otherwise normal rats. Following capsaicin treatment the occurrence of unmyelinated pulpal axons was slightly subnormal. Sympathectomy was largely without effect on the population of unmyelinated axons in tooth pulps of capsaicin-treated rats. In normal rats the proportion of unmyelinated axons in molar pulps was not altered by sympathectomy but it caused a slight decrease in the number of unmyelinated incisor pulpal axons. These findings support the view that most of the unmyelinated axons in rat molar and incisor pulps are sensory, that the parent neurons of these axons differ from nociceptive neurons at other sites by being largely resistant to neonatal capsaicin treatment and that very few unmyelinated tooth pulp axons represent postganglionic efferents.

Adrenergic Fibers↗
PubMed1979

Relationship of the incisive papilla to the maxillary central incisors.

The average distance between the most anterior point of the maxillary central incisors and the most posterior point of the incisive papilla was 12.454 mm with a standard deviation of 3.867 mm. This distance was measured when these two points were projected on a plane which was parallel to the reference plane formed by the tips of three interdental papillae; i.e., the papilla between two central incisors (A), between the first and second molars on the right side (R), and on the left side (L). The average error incurred due to inconsistency of the method employed was less than 3% or less than 0.372 mm for the position of the central incisor. It is believed that the application of this anatomic relation can provide a reliable point for arranging and checking the position of the anterior maxillary teeth for complete dentures.

Denture Design↗
PubMed1992

Denture tooth selection: an analysis of the natural maxillary central incisor compared to the length and width of the face. Part I.

A project was devised by the removable prosthodontic faculty to determine clinically if there is a correlation between the length and width of the maxillary central incisor on a cast and the length and width of the face. A millimeter gauge was used to measure the lengths and widths of the maxillary incisor on a cast. The Trubyte tooth indicator was selected to measure the length and width of the face. This tooth indicator is designed for calibration of the 16 to 1 ratio between facial dimension and maxillary central incisors.

Adult↗
PubMed1975

Double bilateral dens invaginatus in the maxillary incisor region.

Two cases of bilateral double dens invaginatus in the maxillary incisor region have been reported. One of the patients (Case 1), a 12-year-old boy, had double invaginations in both of the erupted teeth in the maxillary lateral incisor region. The other patient (Case 2), a boy 8 years of age, had double invaginations in each of the two partially developed supernumerary teeth that were impacted in the palate in the maxillary central incisor region. Double bilateral dens invaginatus would appear to be a most unusual occurrence.

Child↗
PubMed1978

Clinical significance of supplementary innervation of the lower incisor teeth: a dissection study of the mylohyoid nerve.

In view of the relevance of the mylohyoid nerve to clinical difficulties in achieving deep analgesia of the lower incisors, a dissection study was undertaken. Dissection from twenty-six adult cadavers of both sexes were studied with the aid of a dissecting microscope. The following observations were made: (1) A supplementary branch of the mylohyoid nerve entered the mandible through accessory foramina in the lingual side of the mandibular symphysis in 50% of the cases. (2) It generally arose from the right side (76.9%) and entered the inferior retromental foramen (84.6%). (3) The mylohyoid nerve branch either ended directly in the incisor teeth and the gingiva or joined the ipsilateral or contralateral incisive nerve. In view of this information concerning the high incidence of possible involvement of the mylohyoid nerve in mandibular sensory innervation, it is advisable to block it whenever intervention in the lower incisors is indicated. Routine mylohyoid injection is recommended after mental nerve block. If the inferior alveolar nerve is chosen for anesthetic purposes, additional mylohyoid injection should be given only if pain persists. The mylohyoid injection should be given at the inferior retromental foramen on the median aspect of the inferior border of the mandible through extraoral approach.

Adult↗
PubMed1990

Shovel-shaped incisors and associated invagination in some Asian and African populations.

Shovelling of the incisors is considered to be a polygenic inheritable trait. Shovelling differs considerably between groups of racial populations but is relatively stable within each group. Presence or absence of shovelling helps in racial identification and in exploration of ancestry. Periapical radiographs of patients of several nationalities from Asian and African continents were obtained. Shovelling and invaginations associated with the shovel-shaped incisors was studied according to nationality. Results indicated that the incidence of shovelling in Syrians, Jordanians, Palestinians and Filipinos was 5-6 per cent. In Saudi Arabians, Pakistanis and Indians, the incidence of shovelling was 10-12 per cent. Among Yemenis, Sudanese and Egyptians, the incidence of shovelling was 20-25 percent. The occurrence of invaginations in shovel-shaped incisors was 11 per cent.

Asia, Western↗