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At least 1,063 records · Page 59Linked to original sources
PubMed1991

Upper central incisor and canine tooth crown size in 47,XXY males.

Enamel and dentin thicknesses were measured in permanent tooth crowns of 47,XXY (Klinefelter syndrome) males. In 47,XXY males, enamel thickness in maxillary central incisors was significantly greater than that in control males or females, and dentin thickness in incisors and canines was significantly greater than that in control females, but smaller than that in normal males. These findings confirm the concept that human dental growth is affected by sex chromosomes. Amelogenesis is promoted by both X and Y chromosome genes, and sexual dimorphism in average tooth size is evidently determined by a promoting effect of the Y chromosome on dentin growth, probably through cell proliferation. This effect can also explain sex predilection for males in the numbers of supernumerary and ordinary teeth.

Amelogenesis↗
PubMed1992

Histomorphometric study of the periodontal vasculature of the rat incisor.

This study assessed quantitatively the vascular system in the cementum-related periodontal ligament (PDL) along the rat incisor. The lower left incisors of six rats (+/- 200 g) were subjected to routine histological procedures and cross-sectioned serially (2 microns), and the distance between each section and the apex was computed. The PDL of five sections at different levels along the tooth was divided into mesial, lingual, and lateral parts. The number and area of small and terminal arterioles, capillaries (C), sinusoids (S), post-capillary venules (PCV), and connecting venules, as well as the area of the PDL, were established. Blood vessels (BV) occupied 47 +/- 2% of the PDL area in the apical half and 4 +/- 2% at the incisal end. Of the total BV area, 41%, 32%, and 27% were located on the lingual, mesial, and lateral tooth sides, respectively. The majority of BV belonged to the venous system (98.5 +/- 0.6% and 82.5 +/- 3.0% in the apical and incisal parts, respectively). The apical venous system comprised 95.4 +/- 1.6% S and 3.2 +/- 1.0% PCV, reversing to 27.2 +/- 14.2% S and 55.2 +/- 11.3% PCV in the incisal half. The number of arterial profiles increased gradually from 6.8 +/- 1.5 at the apex to 25.3 +/- 2.4 in the incisal part and that of C from 9.0 +/- 1.18 to 25.0 +/- 4.3. The extensive vascularization in the apical half of the PDL is consistent with the high metabolic demands and with the need for protective cushioning of the constantly growing dental and periodontal tissues.2+_

Alveolar Process↗
PubMed1995

Effect of growth hormone on the distribution of decorin and biglycan during odontogenesis in the rat incisor.

Previous studies have shown that growth hormone can influence the expression of N-acetylgalactosamine-containing molecules in the extracellular matrix of developing rat incisors. N-acetylgalactosamine is a principal component of proteoglycans containing chondroitin sulfate and dermatan sulfate, as well as of some glycoproteins. Since chondroitin sulfate proteoglycans are identifiable components in enamel, dentin, and cementum, we have tested the hypothesis that growth hormone modulates their expression in developing rat incisors. The distribution of the chondroitin-sulfate-rich proteoglycans, decorin and biglycan, was investigated. We used the Lewis dwarf rat as a model because their circulating growth hormone levels are markedly reduced. Polyclonal antibodies against decorin and biglycan were used to localize these two proteoglycans. Semi-quantitative assessments of the staining patterns and intensities were made for each proteoglycan within compartments of the developing teeth. In normal Lewis rats, decorin and biglycan differentially expressed throughout the enamel organ, dental papilla, and dental follicle. Decorin displayed a wide distribution throughout all three regions and was closely associated with different cellular components. In contrast, biglycan showed little association with cells and was identified in the predentin and osteoid matrices. The expression of both proteoglycans was dramatically decreased in the growth-hormone-deficient animals. Administration of growth hormone to the dwarf rats markedly elevated the expression of both proteoglycans, approximating the distribution and intensity of staining seen in normal animals. These findings confirm that growth hormone status can modulate the expression of decorin and biglycan, and hence matrix deposition, in the rat tooth.

Animals↗
PubMed2002

Localization of transcriptional co-activator CBP in the ameloblasts and the other enamel organ-derived cells of the rat incisor.

CREB-binding protein (CBP) was examined in ameloblasts and in other enamel organ-derived cells of the rat incisor, using Western blotting analysis and immunocytochemistry by specific antibodies. Western blotting of labial tissues, including ameloblasts of the incisors, detected a single band with a molecular weight equivalent to the reported value of CBP. In immunocytochemistry, CBP was localized in ameloblast nuclei in the maturation zone but not in the secretion and transition zones. The nuclei of the other enamel organ-derived cells were also positive. Because this protein is suggested to take part in c-Jun-mediated transcription, the present study and the results of a previous report showing c-Jun localization in the nuclei of enamel organ-derived cells suggest that the enamel organ-derived cells, including maturation ameloblasts, undergo active transcriptional regulation.

Ameloblasts↗
PubMed1999

In vivo model for the experimental manipulation of calcified tissues: a surgical approach for accessing the odontogenic organ and associated tissues of the rat incisor.

The tooth organ is extensively used in developmental biology to investigate organogenesis and cell differentiation. It also represents an advantageous system for the study of the various cellular and extracellular matrix events that regulate the formation of both collagenous and noncollagenous calcified tissues. This article describes an in vivo surgical approach to access and experimentally manipulate the tooth organ and supporting tissues of the rat incisor. By use of a dental drill, a "window" was created through the alveolar bone on the buccal aspect of the hemimandible at the apical end of the incisor. It is at this site that epithelial and mesenchymal precursors are situated and undergo cellular differentiation to give rise to cells of the odontogenic organ. Active bone remodeling is also observed in this area to accommodate posterior growth of the tooth. An osmotic minipump connected to the bony window through an outlet catheter was used for controlled and continuous administration of experimental agents over a predetermined period of time. To validate the model, vinblastine sulfate, fetuingold, and dinitrophenylated albumin were thus infused. The animals were then sacrificed and the hemimandibles were processed for histological and immunocytochemical analyses. The effects of the drug and the presence of tracers were restricted to the treated hemimandible and were found in the enamel organ and pulp, as well as in the tooth supporting tissues. Cellular changes typically associated with the administration of vinblastine were obtained, and tracers were localized both in the extracellular milieu and within the endosomal/lysosomal elements of cells. These results suggest that this new surgical approach could serve as an advantageous in vivo model in which various chemical agents, therapeutic drugs, molecular probes are locally administered to study the molecular events that regulate calcified tissue formation.

Animals↗
PubMed1996

Disturbed enamel mineralization in a rat incisor model.

Possession of full-thickness hard enamel appears to be one of the indispensable life-saving characteristics of rats. Previous studies by Suga and his colleagues and by others demonstrated that various types of malformation are evoked in continuously erupting rat incisors. In the current report, we directed our effort to oversee various types of enamel malformation caused experimentally in rat incisors. We surveyed the specimens collected by Suga and his colleagues, as well as specimens we obtained. From the results, it is conceivable that perturbation of the programmed sequential events during enamel development is a major factor in the establishment of enamel malformation. Animal studies with either 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) or a multidentate phosphonic acid (EDTPO) confirmed that dentin mineralization provides a certain inductive effect on the secretion of enamel matrix and subsequent enamel crystallization. Our recent studies using anti-microtubular agents led to the conclusion that the acceleration of mineralization in outer enamel is a type of enamel malformation, most likely due to disruption of the cellular regulation of calcium transport under severe toxic regimens. In future work, experimental approaches combining measurements of kinetic factors with static observation of enamel lesions are required before we can gain a comprehensive understanding of the pathogenesis of disturbed enamel mineralization. The kinetic factors to be considered include the rates of tissue apposition and tooth eruption which determine the total volume of tooth substance formed, and the rate of mineral accretion. Furthermore, information as to the composition, crystallinity, solubility, and mechanical properties of enamel defects is needed before we can assess the susceptibility of teeth having those lesions to caries and other physico-chemical attacks in the oral environment.

Ameloblasts↗
PubMed1996

Effects of accelerated eruption on the enamel of the rat lower incisor.

The effect of accelerated eruption of the rat lower incisor on enamel was studied in a series of segments obtained when the incisor was cut repeatedly out of occlusion over a five-week period. The segments were ground, cleaned, acid-etched, observed with SEM, and analyzed with EDX. Pigmentation was lost within 11 days. Pigmented superficial enamel was more acid-resistant than the rest of the enamel, but this quality decreased with decreasing iron content. Hypomineralized enamel first appeared in a restricted area at the mesio-labial angle of the tooth in the 6th-7th segment obtained after 11-14 days. Later, hypomineralization became more generalized. All enamel zones were retained throughout the experiment. The geometry of the prism pattern was affected. The angle between prism rows and the enamel-dentin junction increased from 44 degrees to 48 degrees, while the angle of decussation increased from 60 degrees to 70 degrees. The angle between the enamel surface and prisms in the outer enamel was more difficult to assess, but tended to increase from about 25 degrees to 29 degrees. However, the prisms retained their incisal direction. The connection between enamel and dentin was partly disrupted from about the 9th segment onward. The depth of the mesial concavity of the enamel-dentin junction decreased from about the 10th segment onward. Accelerated eruption affects all stages of enamel formation and is a suitable and predictable model for studying regulatory mechanisms in amelogenesis.

Ameloblasts↗
PubMed1996

Dendritic cells: a novel cellular component of the rat incisor enamel organ appearing in the late stages of enamel maturation.

Immunocompetent cells in the enamel organ of rat incisors were examined immunohistochemically using OX6, ED1, and ED2 monoclonal antibodies known to recognize the Class II MHC molecules, a monocyte-macrophage lineage, and residential macrophages, respectively. The OX6 immunopositive cells (MHC cells) were located exclusively in the enamel maturation zone. MHC cells increased in number in the incisal direction and occasionally extended cytoplasmic processes deep into the ameloblast layer. Migration of MHC cells in the ameloblast layer were also encountered. MHC cells lacked phagolysosomes and could be distinguished from typical macrophages. ED2 immunopositive cells were not seen in the enamel organ. ED1 positive cells displayed identical localization to MHC cells except that some appeared in the transitional zone. MHC cells could not be seen in the enamel organ of rat molar tooth germs. Our data confirmed the presence of a large population of "dendritic" immunocompetent cells in the enamel organ of rat incisors and characterized the ultrastructural features of these cells. Biological significance of the immunocompetent cells in the enamel organ during amelogenesis needs to be clarified.

Amelogenesis↗
PubMed2003

Altered pH regulation during enamel development in the cystic fibrosis mouse incisor.

Regulation of pH is necessary to the production of an environment conducive to enamel growth and mineralization. We hypothesize that abnormal extracellular pH in the enamel matrix of mice with the cystic fibrosis gene knocked out (CF mice) results in altered enamel mineralization. The enamel matrix pH during amelogenesis was studied in 10 normal and 10 CF mice. Freshly dissected incisors were immersed in pH indicator or glyoxal bis (2-hydro-xyanil) (GBHA). The normal mouse enamel matrix pH was generally higher and modulated differently than did the CF mouse enamel. GBHA staining showed that normal mice had 2 well-demarcated bands in the maturation zone that correlated to the neutral pH zones, while CF mice showed no staining. These results indicate that CFTR plays a role in pH regulation during enamel development and that a reduced pH results in a lack of calcium influx during enamel maturation and hypomineralization of the CF incisor enamel.

Amelogenesis↗
PubMed2004

C-fos expression in rat brain nuclei following incisor tooth movement.

In the rat experimental model, molar tooth movement induced by Waldo's method is known to cause a temporally and spatially defined pattern of brain neuronal activation. Since orthodontic correction usually involves the entire dental arch, we used a spring-activated appliance to extend the investigation to incisors, and we included brain regions related to antinociception. Adjustment of the non-activated appliance on incisors resulted in c-fos expression in the dorsal raphe, peri-aqueductal gray matter, and the locus coeruleus, in addition to trigeminal sensory subnuclei and the parabrachial nucleus, where neuronal activation has already been detected in previous studies on molar tooth movement. Appliance activation with a 70-g force resulted in a further increase in Fos-immunoreactive neurons in the trigeminal sensory subnucleus caudalis and in the dorsal raphe. This result suggests that there is a recruitment of neurons related to nociception and to antinociception when tooth movement is increased.

Analgesics↗
PubMed2006

Origin of the deciduous upper lateral incisor and its clinical aspects.

The upper lateral incisor in humans is often affected by dental anomalies that might be explained developmentally. To address this question, we investigated the origin of the deciduous upper lateral incisor (i2) in normal human embryos at prenatal weeks 6-8. We used serial frontal histological sections and computer-aided 3D reconstructions. At embryonic days 40-42, two thickenings of the dental epithelia in an "end-to-end" orientation were separated by a groove at the former fusion site of the medial nasal and maxillary processes. Later, these dental epithelia fused, forming a continuous dental lamina. At the fusion site, i2 started to develop. The fusion line was detectable on the i2 germ until the 8th prenatal week. The composite origin of the i2 may be associated with its developmental vulnerability. From a clinical aspect, a supernumerary i2 might be a form of cleft caused by a non-fusion of the dental epithelia.

Cleft Palate↗
PubMed1980

Effect of glutaraldehyde and decalcifying agents on acid phosphomonoester hydrolase activity in the enamel organ of the rat incisor: a biochemical study comparing enamel organ with liver.

Enamel organs were dissected from the labial surface of unfixed and glutaraldehyde-fixed rat incisors and assayed biochemically at pH 5.0 for acid phosphomonoester hydrolase activity using cytidine 5'-monophosphate (5'-CMP), beta-glycerophosphate (beta GP), phosphorylcholine (PC), and phosphoserine (PS) as substrates. Whole homogenates from unfixed enamel organs showed substantial enzyme activity toward 5'-CMP and beta GP, but 1/4 and 1/8 less activity toward PC and PS, respectively. Perfusion fixation with 2% glutaraldehyde resulted in a net loss of 80% of the enzyme activity toward each substrate. Lineweaver-Burk plots revealed that the fixative depressed the rate of hydrolysis of substrate (decrease in Vmax) and it also lowered the affinity of enzymes for substrate (increase in KM). Hence, fixed tissue generally required two or three times as much substrate to saturate the enzymes, but less substrate was hydrolyzed, as compared to unfixed tissue. Decalcification of fixed incisors with either formic citric acid, ethylenediaminetetraacetic acid (EDTA), or ethyleneglycoltetacetic acid (EGTA) did not further alter enzyme activity in the enamel organ as determined by Lineweaver-Burk plots, However, EDTA and EGTA were found to increase the susceptibility of fixed enzymes to inhibition by lead ions. This chelator-enhanced lead inhibition was greatest following decalcification with EGTA and using PC as substrate. Similar results were obtained for liver.

Acid Phosphatase↗
PubMed1987

Rapid-freezing and malachite green-acrolein-osmium tetroxide freeze-substitution fixation improve visualization of extracellular lipids in rat incisor pre-dentin and dentin.

Rat incisor tissue sections were fixed by a modified version of the malachite green-aldehyde method (MGA) composed of rapid-freezing, malachite green-acrolein staining, and osmium tetroxide freeze-substitution (Fr.MGAO). In the pre-dentin, a thick, dense network of branched fibrous structures was observed. Cryotechniques allowed visualization of complexes about twice as thick and dense as the aggregates visualized on MGA-treated sections. Pretreatment of rapid-frozen samples with methanol before freeze-substitution fixation and staining prevented staining of the complexes otherwise revealed by the Fr.MGAO method. Electron-dense material stained by this procedure resisted de-mineralization with EDTA, while intramitochondrial granules and dentin crystallites were dissolved. EDTA treatment demonstrated unequal distribution of Fr.MGAO staining in dentin in the form of tiny dots underlining the collagen fibers. These results support the concept that rapid-freezing, followed by staining and freeze-substitution fixation, improves preservation of the phospholipids visualized as extracellular matrix components in pre-dentin and dentin of rat incisors.

Acrolein↗
PubMed1988

Localization of phosphophoryn in rat incisor dentin using immunocytochemical techniques.

We studied the distribution of the phosphophoryn present in rat incisors by immunolocalization and histochemical techniques. The polyclonal antibody used reacts with both phosphorylated and de-phosphorylated phosphophoryn. Technical problems encountered in immunostaining and in preparing sections from mineralized dentin were resolved by use of peroxidase-conjugated protein A as the "second antibody" in indirect immunostaining reactions and by surface etching of partially demineralized sections. Staining with anti-rat incisor alpha-phosphophoryn antibody showed light staining over the odontoblasts and proximal odontoblastic processes, no stain over the predentin, dense staining over the intertubular dentin, and no stain over the mantle dentin. In the intertubular dentin the stain intensity was directly related to the distribution of mineral. These findings were directly corroborated by staining with Stains All. The mineralization of dentin and the distribution of phosphophoryn within the dentin may be much less uniform than previously supposed.

Animals↗
PubMed1993

Expression of plasma membrane Ca++ pump epitopes parallels the progression of enamel and dentin mineralization in rat incisor.

We investigated the expression of Ca++ pump epitopes during enamel and dentin mineralization in the rat incisor. Secretory and maturation ameloblasts were studied as well as odontoblasts, using a monoclonal antibody (5F10) against human erythrocyte plasma membrane Ca++, Mg(++)-ATPase. A progressive increase in staining intensity in ameloblasts and the odontoblasts was observed beginning with the onset of mineralization. The mainly membrane-related labeling of ameloblasts showed variable intensity depending on the stage of enamel formation, whereas that of the odontoblasts showed even intensity during continued dentinogenesis. Staining of papillary cells was evident only during enamel maturation. Western blot analysis of freeze-dried ameloblasts was also used to determine the molecular weight of the Ca++ pump epitopes as well as the distribution and relative concentration of epitopes at each stage. An immunoreactive band of MW 140 KD and lower molecular weight bands that are more intense in late than in early maturation were demonstrated. Our studies suggest that the expression of plasma membrane Ca++ pump parallels the progression of mineralization in rat incisor enamel and dentin.

Ameloblasts↗
PubMed1984

An unusual lateral incisor.

The conditions of hypodontia, hyperodontia and connation (fusion or gemination) have been outlined. A case has been reported in which there has been failure of development of a normal maxillary lateral incisor on one side, with an unerupted tooth in this region which exhibited characteristics of a supernumerary tooth; a diagnosis of hypo-hyperodontia is suggested. This has occurred in a patient in whom the deciduous incisors in the same quadrant were connate.

Anodontia↗
PubMed1992

A modification to the incisor classification of malocclusion.

During the study of two-hundred orthodontic cases under treatment in the General Dental Service, four clinicians showed only moderate agreement using the British Standard Classification of Incisor Malocclusion. Cohen's Kappa statistic was used to measure the inter-examiner agreement. The 35 cases in which there was high disagreement between the examiners were scrutinized to determine the source of this disagreement. Following discussion, revised definitions were produced which included the introduction of a Class II-intermediate group. After an interval of 2 months these 35 cases were reclassified using the new definitions. Increased inter-examiner agreement was found. Four examiners (three of whom were common to the original study) then used the modified classification to describe the incisal relationship of 100 cases referred for treatment at Bristol Dental Hospital. The inter-examiner and the intra-examiner agreement were both found to be good. It is recommended that the Incisor Classification of Malocclusion be extended to include a Class II-intermediate group.

Humans↗