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At least 667 records · Page 37Linked to original sources
PubMed2004

Characterization of dental epithelial progenitor cells derived from cervical-loop epithelium in a rat lower incisor.

Dental epithelial progenitor cells differentiate into various cell types during development of tooth germs. To study this mechanism, we produced immortalized dental epithelial progenitor cells derived from the cervical-loop epithelium of a rat lower incisor. The expression patterns of cytokeratin 14, nerve growth factor receptor p75, amelogenin, Notch2, and alkaline phosphatase were examined by immunohistochemistry in both lower and higher cell densities. The patterns of each were compared in the dental epithelium of rat lower incisors. The results demonstrated that these cells could produce ameloblast lineage cells, stratum intermedium cells, stellate reticulum, and outer enamel epithelium. Furthermore, fibroblast growth factor 10 stimulated proliferation of dental progenitor cells and subsequently increased the number of cells expressing alkaline phosphatase. These results suggest that fibroblast growth factor 10 plays a role in coupling mitogenesis of the cervical-loop cells and the production of stratum intermedium cells in rat incisors.

Alkaline Phosphatase↗
PubMed1986

Lower incisor position in treatment planning.

Attention has been focused on the position of the lower incisors in treatment planning. Determination of a stable incisor position around which to plan treatment is an important consideration. In the light of increasing use of fixed appliances in this country it is felt of value to present in detail the various methods available for planning lower incisor position. A brief appraisal of each is given and the literature relating to them discussed. It is concluded that whilst no particular method is ideal, the use of Ricketts' A-Po line in giving an indication of permitted direction of movement, tempered by a cautious approach as advocated by Mills should achieve a compromise between improved aesthetics and stability in most cases. A detailed study is required to assess more fully their practical application.

Cephalometry↗
PubMed1989

A cephalometric study of incisor angulations in a Nigerian population.

This paper has the objective of establishing a standard norm for incisor angulations in a Nigerian population. The upper incisor angle to the Frankfort plane has a biological norm of between 119 degrees and 127 degrees, while the lower incisor angle (to the mandibular plane) is between 96 degrees and 104 degrees. The value for the interincisal angle is between 108 degrees and 116 degrees.

Adolescent↗
PubMed1990

Autotransplantation of premolar teeth to replace missing maxillary central incisors.

Orthodontic treatment decisions when maxillary central incisors are absent or are of poor prognosis, are discussed. Autotransplantation of mandibular first premolars to the incisor region is suggested as an approach in selected cases. The literature is reviewed, surgical technique described and case selection summarized. Cases are reported where autotransplantation of premolars to the maxillary incisor region has produced good functional and aesthetic results.

Adolescent↗
PubMed1990

Effect of the X-linked gene Tabby (Ta) on eyelid opening and incisor eruption in neonatal mice is opposite to that of epidermal growth factor.

Studies on eyelid opening and incisor eruption in 216 neonatal Tabby (Ta)-bearing mice and wildtype controls (35 Ta/Y, 62 + /Y, 30 Ta/Ta, 57 Ta/+ and 32 +/+) showed that in animals hemizygous and homozygous for Ta, the timing of eyelid opening and incisor eruption was significantly delayed (P less than 0.05). It was also observed that once open, the eyes of mutant pups do not remain open for long but soon close again for several days before reopening. An iterative eyes open-eyes closed process seems to continue beyond puberty. Studies in 25 epidermal growth factor (EGF)-treated mutants and 23 saline-treated controls showed that neonatal EGF injections (4 micrograms g-1 body weight per day) reversed the delayed timing of eyelid opening and incisor eruption in hemizygote and homozygote Tabby mice. However, both mutant and wildtype EGF-treated mice also showed the eyes open-eyes closed cycle, whereas untreated nonmutant mice did not. Because Tabby appears to be genetically homologous to the gene for human X-linked hypohidrotic ectodermal dysplasia, these results may have potential clinical significance. The eyes open-eyes closed cycle may involve cycling levels of EGF receptor; since the gene for this receptor shows homology with an oncogene, this system may be useful in studies on genetic control of oncogene function.

Animals↗
PubMed1994

[The effect of doxorubicin on the unimpeded eruption rates of rat mandibular incisors].

We examined the effects of daily injections of doxorubicin, an anti-tumor drug, on unimpeded eruption rates, pulp cells, odontoblasts, periodontal ligament and dentine formation in the rat mandibular incisor. The experimental animals were intraperitoneally injected with 5 mg of doxorubicin/kg body weight/day for a period of 7 days. The eruption rates decreased gradually; and on the seventh day, the mean eruption rate had decreased to 14% of the control value. In addition, we noticed marked destruction of pulp cells and periodontal cells at the basal region of the incisor. The amount of dentine formation was measured using the tetracycline labeling method, but significant decreases in dentine formation were not observed. These results suggest that destruction of the basal tissues is related to inhibition of incisor eruption rates, but that tooth eruption is not related to dentine formation.

Animals↗
PubMed1989

[Effects of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) on the unimpeded eruption rate and the dental hard tissue formation in rat mandibular incisor].

To understand the mechanism of eruption in continuously growing teeth, the relationship between the rate of eruption and formation of dental hard tissues was examined following administration of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP), an inhibitor of hard tissue formation. Three experimental groups of rats received daily subcutaneous injections of 9, 18 or 36 mg P of HEBP/kg, respectively, for 7 days. Tetracycline was also injected to mark the dentine in some animals. To maintain an unimpeded state, all four incisors in each rat were shortened repeatedly during the experimental period. Eruption rates of the mandibular incisors were measured by a photographic method. Transverse sections of the mandibles were cut and histological, microradiographic and fluorescent micrographic examinations were done. Significant decreases of the eruption rates were found in all experimental groups following the administration of HEBP. However, differences were not marked among the three experimental groups. It was also shown that matrix formation and calcification of the dentine were markedly inhibited following the administration of HEBP. Matrix formation and calcification of the enamel were also inhibited by the drug administration. It is assumed that the eruption of the rat incisor is not closely associated with the formation of dental hard tissues and their calcification.

Animals↗
PubMed2004

[Relationship between fetal lead exposure and birth weight--evaluation using deciduous incisor enamel].

OBJECTIVE: The purpose of this study was to examine the relationship between fetal lead exposure and birth weight, using deciduous incisor enamel as a biomarker and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for analysis of lead. METHODS: We asked dental clinics (n=11) and kindergartens (n=11), mainly in the Tokyo metropolitan area and Miyagi Prefecture, and parents to enroll donors of exfoliate deciduous incisors. Donors who consented to this study voluntarily sent deciduous incisors and questionnaires to the authors between March and October, 2003. The Pb/Ca ratios of inner enamel samples were determined by LA-ICP-MS. The relationship between the lead-to-calcium ratio in the enamel and the birth weight was evaluated by stepwise multiple linear regression analysis. RESULTS: One hundred forty-one subjects (male, 72; female, 69) were enrolled in this study. The mean Pb/Ca ratio in the enamel was as low as 0.24 mg-Pb/kg-Ca (SD=0.17). Stepwise multiple linear regression analysis extracted the following maternal variables with a positive coefficient with birth weight: gestational age (p < 0.01), weight gain during pregnancy (p < 0.01), prepregnancy BMI (body mass index, p < 0.01), and parity (p < 0.05). Lead concentration in the enamel was significantly negatively associated with birth weight (p < 0.05). CONCLUSIONS: Our study indicated that lead concentration in the enamel was inversely related to birth weight. This association was found in a population of which the mean blood lead level was estimated to be as low as about 1 microg/dl. We concluded that in utero low lead exposure decreased birth weight, within the normal range of birth weight.

Birth Weight↗
PubMed1994

Ameloblastic fibro-odontoma in the mandibular incisor of a cow.

Odontogenic neoplasm was found in the mandibular incisor area of a 3-year-old Japanese black ox. Macroscopically, the cut surface was white and firm with streaks of hard tissue. Histologically, the tumor was composed of enamel organ structures with odontogenic hard tissue in fibromatous areas. It was diagnosed as ameloblastic fibro-odontoma. The absence of the 4th permanent incisor confirmed by radiography and microscopic examination strongly suggests that this tumor has been originated from the tooth germ tissues of the permanent left 4th incisor.

Animals↗
PubMed2004

Mineral acquisition rates in developing enamel on maxillary and mandibular incisors of rats and mice: implications to extracellular acid loading as apatite crystals mature.

UNLABELLED: The formation rates of mineral in developing enamel were determined by microweighing of incisors of mice and rats. Computations indicated that a large excess of hydrogen ions would result from creating apatite at the calculated rates. Enamel organ cells (ameloblasts), therefore, likely excrete bicarbonate ions to prevent pH in fluid bathing enamel from becoming too acidic. INTRODUCTION: Protons (H+) are generated whenever calcium and phosphate ions combine directly from aqueous solutions to form hydroxyapatite. Enamel is susceptible to potential acid loading during development because the amount of fluid bathing this tissue is small and its buffering capacity is low. The epithelial cells covering this tissue are also believed to form permeability barriers at times during the maturation stage when crystals grow at their fastest rates. The goal of this study was to measure the bulk weight of mineral present in rodent enamel at specific times in development and estimate the amount of acid potentially formed as the apatite crystals mature. MATERIALS AND METHODS: Upper and lower jaws of mice and rats were freeze-dried, and the enamel layers on the incisors were partitioned into a series of 0.5 mm (mouse) or 1.0 mm (rat) strips along the length of each tooth. The strips were weighed on a microbalance, ashed at 575 degrees C for 18-24 h to remove organic material, and reweighed to determine the actual mineral weight for each strip. RESULTS AND CONCLUSIONS: The data indicated that, despite differences in gross sizes and shapes of maxillary and mandibular incisors in rats and mice, the overall pattern and rates of mineral acquisition were remarkably similar. This included sharply increasing rates of mineral acquisition between the secretory and maturation stages, with peak levels approaching 40 microg/mm tooth length. Computer modeling indicated that quantities of H+ ions potentially generated as apatite crystals grew during the maturation stage greatly exceeded local buffering capacity of enamel fluid and matrix proteins. In other systems, bicarbonate ions are excreted to neutralize highly acidic materials generated extracellularly. Data from this study indicate that ameloblasts, and perhaps cells in other apatite-based hard tissues, use similar bicarbonate release mechanisms to control excess acid arising from mineral formation.

Ameloblasts↗
PubMed2005

Gene expression and localization of insulin-like growth factors and their receptors throughout amelogenesis in rat incisors.

Insulin-like growth factors (IGFs) are expressed in many tissues and control cell differentiation, proliferation, and apoptosis. In teeth, the temporo-spatial pattern of expression IGFs and their receptors has not been fully characterized. The purpose of this study was to obtain a comprehensive profile of their expression throughout the life cycle of ameloblasts, using the continuously erupting rat incisor model. Upper incisors of young male rats were fixed by perfusion, decalcified, and embedded in paraffin. Sections were processed for in situ hybridization and immunohistochemistry. mRNA and protein expression profiles IGF-I, IGF-II, IGF-IR, and IGF-IIR mRNA were essentially identical. At the apical loop of the incisor, very strong signals were seen in the outer enamel epithelium while the inner enamel epithelium showed a moderate reaction. In the region of ameloblasts facing pulp, inner enamel epithelium cells were still moderately reactive while signals over the outer enamel epithelium were slightly reduced. In the region of ameloblasts facing dentin and the initial portion of the secretory zone, signals in ameloblasts were weak while those over the outer enamel epithelium were strong. In the region of postsecretory transition, signals in both ameloblasts and papillary layer cells gradually increased. In maturation proper, signals in ameloblasts appeared as alternating bands of strong and weak reactivities, which corresponded to the regions of ruffle-ended and smooth-ended ameloblasts, respectively. Papillary layer cells also showed alternations in signal intensity that matched those in ameloblasts. These results suggest that the IGF family may act as an autocrine/paracrine system that influences not only cell differentiation but also the physiological activity of ameloblasts.

Amelogenesis↗
PubMed2006

Fluoride dentifrice ingestion and fluorosis of the permanent incisors.

BACKGROUND: Fluoride dentifrice is a primary means of preventing childhood caries, but it is also an important risk factor for fluorosis. The authors examine the influence of fluoride dentifrice ingestion on fluorosis of the permanent incisors. METHODS: Participants in the Iowa Fluoride Study received questionnaires at regular intervals concerning fluoride sources. The authors assessed fluorosis using the fluorosis risk index. They estimated daily fluoride ingestion from dentifrice, diet and fluoride supplements and divided the amount by kilograms of body weight. The statistical analysis related fluoride ingestion to fluorosis in the permanent incisors. RESULTS: In bivariate analyses, mild fluorosis was significantly related to ingestion of fluoride dentifrice at ages 24 and 36 months (P = .02 for both). After the authors adjusted for fluoride ingested from dietary sources, logistic regression showed a significant association between fluorosis and dentifrice ingestion at age 24 months (P = .04). CONCLUSIONS: The study results suggest that fluorosis of the permanent incisors is influenced by ingestion of fluoride dentifrice during the first three years of life. Further research is needed to assess total intake of fluoride as a risk factor for fluorosis. CLINICAL IMPLICATIONS: These results support recommendations that young children use only a pea-sized amount of dentifrice. Parents should supervise young children as they brush their teeth with fluoride dentifrice.

Age Factors↗
PubMed2003

Selecting treatment options and sequencing treatment in the replacement of 2 maxillary central incisors with implants: a case report.

This article describes treatment provided to replace 2 maxillary central incisors with implant-supported restorations. The site of a missing maxillary central incisor was treated utilizing a bone expansion technique to augment the labial hard and soft-tissue profiles at the time of implant placement. The adjacent central incisor tooth, although destined to be extracted, was retained to serve as an abutment for a fixed provisional restoration until the first implant was deemed to have successfully integrated. At the appointment to uncover this implant, the fractured tooth was extracted and an implant was immediately placed into the socket. The first implant was then used to support the provisional restoration during the healing phase of the second implant. The techniques utilized resulted in optimum soft-tissue contours, allowed the patient to have a comfortable and esthetic provisional restoration, and minimized the number of surgical procedures.

Adult↗
PubMed2006

Dental development of Didelphis albiventris (Marsupialia): I--incisors and canines.

The formation of incisors and canines in marsupials of D. albiventris was studied at various stages of development. Seventy-six specimens, with ages varying from 0 to 100 days, were used in this investigation. Serial sections of the maxilla were obtained in the transverse plane and stained with hematoxylin and eosin. Histological analyses were made to verify the pattern of teeth development, as well as their chronology of eruption. The period of time from birth to 100 days comprised the entire process of teeth development, from epithelial bud formation to early eruption of the teeth. Oral epithelium thickening gave rise to the functional incisors and canines. In addition, a secondary dental lamina emerged in different phases of development in the outer epithelium of incisors and canines, which degenerated when it reached the bud stage. No evidence of deciduous dentition was observed. The results of this investigation suggest that secondary dental lamina represents remnants of a primitive condition in which secondary dentition used to be present.

Animals↗
PubMed1992

A light and electron microscopic study on pulpal nerve fibers in the lower incisor of the mouse.

Light and electron microscopic studies were made on pulpal nerve fibers in mouse lower incisors, typical continuously growing teeth. Serial sections, from the apex of the odontogenic sheath to the incisal edge of the apical foramen, were examined by light microscopy to identify myelinated fibers passing through the apical foramen. The fine structure of the pulpal nerves was examined by electron microscopy at three sites: 1) the level at the incisal edge of the apical foramen; 2) a level 5 mm incisal from the apex of the odontogenic sheath; and 3) the level where the incisor comes out of the alveolar bone. No myelinated fibers were found passing through the apical foramen; they were also lacking at the three levels of the pulp. At level 2, unmyelinated axons were seen in close contact with smooth muscle fibers of arterioles. At level 3, nerve fibers were difficult to distinguish from processes of fibroblasts and odontoblasts. Degenerating axons were present in Schwann cells, and fine unmyelinated axons running through the odontoblast cell layer were seen. Various types of unmyelinated axons were observed in the apical region (level 1). These axons were classified into 6 types on the basis of their fine structures: Type I, bundles of unmyelinated axons completely or partly ensheathed by Schwann cell cytoplasm (mature type); Type II, bundles of unmyelinated axons in a space formed by a Schwann cell membrane (regenerating type); Type III, bundles of unmyelinated axons ensheathed not by a Schwann cell, but merely by a basal lamina (regenerating type); Type IV, single axons in direct contact with the basal lamina (regenerating or terminal type); Type V, naked, electron-dense axons with many vesicles and mitochondria (growth cone-like type); and Type VI, electron opaque axons, due to loss of axonal organellae (degenerating type). The significance of these structures is discussed in relation to the continuous growth of the rodent incisor.

Animals↗
PubMed1992

Histochemical and immunohistochemical demonstration of macrophages and dendritic cells in the lingual periodontal ligament of rat incisors.

The distribution of macrophages in the lingual periodontal ligament of rat incisors was surveyed by histochemical and immunohistochemical methods. Numerous macrophages showing intense ACPase reactions were located primarily in the shear zone of the periodontal ligament. Immunostaining with an ED1-monoclonal antibody that recognizes various subpopulations of macrophages revealed plentiful positive cells showing flamelike profiles throughout the periodontal ligament, in addition to regular macrophages associated with sinusoidal blood vessels. A similar distribution of flamelike cells expressing Ia antigens was demonstrable with immunostaining using an OX6-monoclonal antibody. A consecutive staining of sections for ACPase histochemistry followed by immunoreactions for Ia antigens revealed the presence of two types of the flamelike cells in the periodontal ligament: one with and the other without distinct ACPase activity, corresponding to the macrophage and the dendritic cell, respectively. Either type of flamelike cells was located in the bone-related and shear zones, whereas only dendritic cells without ACPase activity were restricted to the tooth-related zone. OX6-immunonegative cells showing ACPase reactions were also found in the periphery of the sinusoidal blood vessels. Our data are the first to demonstrate the abundance of macrophages and dendritic cells expressing Ia antigens throughout the lingual periodontal ligament of rat incisors. In addition to regular macrophages, an exclusive localization of macrophages with flamelike extensions has been demonstrated in the bone-related and shear zones of the ligament. The region-specific arrangement of macrophages and dendritic cells with various histochemical and immunological features suggests that the periodontal ligament of rat incisor is a useful model for analyzing the process of differentiation of antigen-presenting cells.

Acid Phosphatase↗
PubMed2002

Clinical evaluation of a patient with single maxillary central incisor.

Hypodontia in permanent dentition is the most common developmental anomaly and frequently found in the second premolar and maxillary lateral incisor In the primary dentition, however, hypodontia appears to be less frequent, with the exception of cases such as ectodermal dysplasia and cleft lip and palate. We report a child with one primary maxillary central incisor at midline. The presence of a single permanent maxillary central incisor was also confirmed by radiological examination. Other intraoral abnormalities were detected including absence of upper labial frenulum and abnormal palatal structure, but no other facial or brain anomalies. Although the condition is exceedingly rare, a thorough examination for more serious anomalies should be conducted since it is suggested to be the mildest feature of holoprosencephaly.

Cephalometry↗
PubMed2002

Impacted primary mandibular central incisors: case report.

Impaction of primary teeth is very rare especially in the maxillary anterior teeth. A tooth that fails to erupt into a normal functional position by the time it normally should, is considered impacted. The purpose of this article is to present a case of a 2 year and 4-month-old male with an impacted primary mandibular central incisors. Clinical examination did not reveal systemic diseases or trauma in the facial region. Clinical and radiographic examinations are described. Treatment consisted of a period of observation for 6 months and the extraction of the impacted primary mandibular central incisors. Eight months after the surgery, the permanent central incisors were erupted in the proper position.

Child, Preschool↗