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PubMed1983

Dental size traits within families: path analysis for first molar and lateral incisor.

Previous works on the inheritance of dental traits have traditionally followed Fisher's model for family data under the assumption that phenotypic similarity between relatives is due solely to genetic factors. This study uses recent causal models that incorporate the contribution of nonrandom environmental sources of variation to familial resemblance on dental size. Path analysis was applied to observed interclass and intraclass correlations of sex-specific parent-offspring and sib pairs in 293 Pima Indian families from the southwest United States. The mesiodistal dimension of an early-forming and stable tooth (first molar) was contrasted with a late-forming and variable tooth (upper lateral incisor) for genetic and familial environmental components of variation. Parameters were estimated according to the XTAU models of Rice et al. (1980) and linear constraints placed upon the parameters were tested. The proportion of variance accounted for by genetic and environmental transmissible factors is estimated to be 52% for the first molar and 35% for the lateral incisor. Neither X-linkage nor sex-specific environmental effects are required to explain the transmission of dental size. Nontransmissible environmental effects that account for sibling correlations are detectable. Furthermore, sex differences are found in correlated sibling environments for the lateral incisor but not the first molar, to explain in part male-female differences in the distributions of the upper lateral incisor size.

Female↗

PubMed1989

Appearance of a labial notch in maxillary incisors: a population survey.

A labiogingival notch appearing on the enamel of maxillary central incisors seems to be a potential factor for compromised gingival and dental health. The objective of the survey was to describe the phenomenon and its prevalence in a random Israeli population. One thousand eight hundred eighty children with fully erupted permanent incisors were clinically examined. The appearance of the labiogingival notch on the enamel surface of the maxillary central incisors was determined. Two depth categories of the phenomenon were distinguished by probing. The possible differences in the prevalence of the labial notch appearance, between the sexes as well as between the right and left sides, were statistically evaluated. The prevalence between the right and left sides, were statistically evaluated. The prevalence of the labial notch on at least one incisor in the population examined was 6.5% (5.1% unilaterally and 1.4% bilaterally). No significant difference between the sexes regarding the appearance of this phenomenon was found. The shallow notch was similarly distributed between the right and left sides in both sexes. However, the deeper malformations appeared significantly more on the left side in boys (P less than 0.05) and in girls (P less than 0.01). The gingivae tended to follow the enamel contour; however, only in few cases was gingival inflammation or incipient caries diagnosed. It was concluded that the labio-gingival notch is not a rare phenomenon, and it should be given special attention to prevent possible damage to the dental and gingival tissues.

Anthropology, Physical↗

PubMed2002

Polarized light microscopic analyses of collagen fibers in the rat incisor periodontal ligament in relation to areas, regions, and ages.

We prepared decalcified sagittal sections (20 microm thick) from the incisal, middle, and basal regions of the mandibular incisor of male Wistar rats aged 2, 6, 12, and 24 months, and examined the sections using polarized light microscopy. Most of the birefringent fibers appeared to run obliquely across the periodontal ligament. Birefringent fibers running parallel to the long axis of the incisor were also found in the intermediate area of the ligament. Similar fiber architecture was observed in all four age groups. Quantitative analysis showed that the retardation values of collagen were higher in the bone- and tooth-related areas and lower in the intermediate area of the ligament. The values for the bone- and tooth-related areas increased from the basal toward the incisal regions in all four age groups. Age-related changes in the retardation values were found only in the incisal region of the incisor. In the incisal region, the values for the bone- and tooth-related areas increased markedly from 2-24 months of age, whereas those for the intermediate area increased slightly but significantly with age. Our findings indicate that the degrees of molecular organization and alignment of collagen fibers in the bone- and tooth-related areas of the ligament are higher than those in the intermediate area and increase near the incisal region and with age. It is also suggested that the collagen fibers in the intermediate area remain immature along the long axis of the incisor throughout the life span of the animal.

Age Factors↗

PubMed2001

Effects of dexamethasone on tooth eruption in rats: differences in incisor and molar eruption.

A requirement for tooth eruption is the resorption of alveolar bone. Because bone resorption is stimulated by dexamethasone both in vivo and in vitro, dexamethasone 21-phosphate, a soluble form of dexamethasone, was injected into rats to determine its effect on tooth eruption. Such dexamethasone injections accelerate the time of intra-osseous eruption in rat incisors but do not accelerate the eruption time of rat molars when injected into rats. The injections of dexamethasone 21-phosphate also accelerate the time of eyelid opening in the postnatal rats, as well as retarding growth, as measured by body weight. These effects of dexamethasone 21-phosphate parallel the effects of epidermal growth factor injections, including the absence of an effect on molar eruption. This suggests that the molecular signals for the initiation of tooth eruption (i.e., onset of bone resorption) differ between rat incisors and molars. Given that rat incisors are teeth of continuous eruption whereas rat molars are teeth of limited eruption, as are human teeth, care must be taken in extrapolating results derived from rat incisors to human dentition. In vitro, dexamethasone has no effect on the gene expression of either osteoprotegerin or epidermal growth factor in dental follicle cells derived from molars. Because osteoprotegerin expression during normal tooth eruption is transitorily inhibited early postnatally in the molar dental follicle to allow osteoclast formation, the absence of inhibition of its expression by dexamethasone could explain why dexamethasone does not accelerate eruption in molars.

Animals↗

PubMed2005

Mandibular lateral incisor-canine transposition associated with dental anomalies.

Tooth transposition is a rare positional anomaly that may create many orthodontic problems. Its etiology is an enigma. The occurrence of mandibular canine/lateral incisor transposition is a relatively rare anomaly. Two rooted canine/rotated incisor transposition has not been reported previously in the clinical dental literature. We describe a case with transposition of a mandibular two rooted canine and a lateral incisor with 180 degrees rotation. Possible causes such as trauma and tooth agenesis were absent in this case. Due to the root anomaly, we consider that our case may have a genetic etiology. Although the mandibular lateral incisor and canine were not in their normal anatomic positions, there were no functional or esthetic problems.

Adult↗

PubMed1997

Neandertal incisor beveling.

In discussions of the Neandertals, there has been repeated emphasis on the accelerated rate of attrition and the frequent presence of labial beveling of their incisors. Interpretations of this dental attrition have related it to paramasticatory and dietary uses of their anterior teeth as well as to aspects of their facial morphology. In light of this, we examined the rate of beveling (the angle between the labial and incisal surfaces) of central incisors relative to tooth wear in samples of Neandertals, Inuits and Puebloan Amerindians. I1s show little change in the beveling angle with wear and no significant differences between the samples. I1s, however, exhibit a consistent pattern of increased beveling with dental attrition, progressing rapidly until the crown height approximates its labiolinguinal cervical diameter, and then proceeding at a slower rate. All three samples exhibit a similar pattern. However, the Neandertals have significantly greater beveling in more worn teeth than either recent human sample, and the Inuits have nonsignificantly increased beveling relative to the Puebloans in these more worn I1s. In this, it is the degree of development of beveling, not the pattern of beveling, which differentiates the Neandertals. It is hypothesized that the differences between the Neandertals and recent samples could be the product of: (1) contrast in initial incisor procumbency, (2) a labial separation of the maxillary and mandibular incisal occlusal surfaces during edge-to-edge bite, and/or (3) a greater degree of interproximal wear promoting increased "posterior tipping" of the maxillary incisors. The last appears most likely.

Animals↗

PubMed1978

Incorporation of tetracycline into impeded and unimpeded mandibular incisors of the mouse.

Twenty-four hours after a tetracycline injection, the unimpeded, and more rapidly erupting, mouse mandibular incisor contained 20% to 44% more tetracycline than the contralateral, uncut incisor. It was concluded that the increased tetracycline incorporation reflected a higher rate of mineralization associated with faster tooth formation in the unimpeded tooth. By measuring the amount of tetracycline which became incorporated at different times after an incisor was shortened, it was possible to investigate an early stage of the response of the incisor to cutting. A significant increase in the capacity of the tooth to incorporate tetracycline was detectable 4 h after shortening the tooth, and this was maximal after another 4 h.

Animals↗

PubMed1994

[Retraction of the upper incisors with pseudoelastic treatment elements. Their computational and biomechanical testing and clinical use].

Based on the favorable results achieved by the application of pseudoelastic T loops in the course of canine retraction, this study investigates their application to the retraction of maxillary incisors. A modified Burstone T loop was made of a pseudoelastic orthodontic nickel titanium wire and then subjected to experimental testing. The results obtained were compared with extensive numerical studies. The results of the tests showed that forces and moments generated by the T loop are suitable for the retraction of upper incisors. The clinical application of the pseudoelastic spring was performed using an individualized retraction arch enclosing the whole front segment. Whereas during canine retraction the experimental and clinical results corresponded very well, such was not observed during the retraction of upper incisors. This result implies that the location of the center of resistance of the upper incisors has not been completely clarified. It is thus recommended that this matter should be given further study.

Biomechanical Phenomena↗

PubMed2000

No correlation between primary mandibular anterior crowding and vertical craniofacial configuration or lower incisor inclination.

The aim of the present study was to evaluate the correlation between primary mandibular anterior crowding and vertical craniofacial configuration or sagittal lower incisor inclination. The collective comprised 100 consecutive patients (50 males, 50 females) subject to 4 selection criteria: mandibular anterior crowding > or = 1.0 mm, no previous orthodontic therapy, completely preserved deciduous canines and molars, and lateral cephalograms of good diagnostic quality before initiation of orthodontic treatment. Study casts of all patients were used to measure the mesiodistal width of the incisors and deciduous canines as well as the anterior arch circumference. The difference between the 2 represented the amount of crowding. On all cephalograms 16 parameters of vertical craniofacial configuration and 9 parameters of lower incisor inclination were measured. For error evaluation all measurements were repeated independently on 10 randomly selected study casts and cephalograms. This error amounted for the combined tooth width to 0.51% +/- 0.81, for arch circumference to 0.03% +/- 0.68, and for all cephalometric parameters to 0.38% +/- 4.81. For all parameters, arithmetic means, standard deviations and ranges were calculated. Further, correlation coefficients were calculated between anterior crowding and all 25 cephalometric parameters. The arithmetic mean of crowding was m = 2.0 +/- 1.3 mm with a range of 1.0 to 6.6 mm. The values of all cephalometric parameters were close to well accepted norms in the literature. The correlation coefficients between crowding and all cephalometric parameters varied from r = 0.0 to 0.3. According to this study there is no correlation between primary mandibular anterior crowding and vertical craniofacial configuration or sagittal lower incisor inclination.

Cephalometry↗

PubMed1997

Distribution of the neural cell adhesion molecule (NCAM) during pre- and postnatal development of mouse incisors.

Developmental changes in the distribution of the neural cell adhesion molecule (NCAM) were investigated in mouse incisors by means of the indirect immunofluorescence method. During the prenatal stages of development, NCAM was predominantly found in the dental follicle, but not in the dental papilla; the results were analogous to the distribution of NCAM during molar development. After birth, the expression of NCAM continued in the tissue between the enamel organ and the alveolar bone on the labial aspect. In contrast, the follicular tissue covering the lingual aspect of the incisor gradually lost NCAM immunoreactivity from its outer zone as it differentiated into the highly organized periodontal ligament. The intermediate zone of the ligament continued to express NCAM-immunoreactivity even in mice of 6 weeks of age. This pattern of NCAM expression was different from that found in molar teeth, where the organized peridontal ligament was NCAM-negative. The dental pulp, in which we previously reported that an NCAM-positive area appeared at later stages of molar tooth development, did not express NCAM immunoreactivity even at the latest stage of development covered in this study. These differences in the distribution of NCAM between the incisors and the molars might be related to the fact that rodent incisors continue to grow throughout the life of the animal.

Aging↗

PubMed2006

Urokinase-type plasminogen activator mRNA is expressed in normal developing teeth and leads to abnormal incisor enamel in alpha MUPA transgenic mice.

The urokinase-type plasminogen activator (uPA) is a secreted, inducible serine protease implicated in extracellular proteolysis and tissue remodeling. Here we detected uPA mRNA through in situ hybridization in developing molar and incisor teeth of normal mice at multiple sites of the cap and bell developmental stages. The mRNA was confined to epithelial cells, however, was undetectable in ameloblasts or their progenitor preameloblasts and the inner enamel epithelium. Furthermore, mice of five lines of previously described alphaMUPA transgenic mice, carrying a transgene consisting of the uPA cDNA linked downstream from the alphaA-crystallin promoter, overexpressed uPA mRNA in the same epithelial sites. In addition, alphaMUPA mice showed remarkably high levels of uPA mRNA in ameloblasts, however, exclusively in two specific sites late in incisor development. First, at the late secretory stage, but only on sides of the ameloblast layer. Second, in a limited zone of ameloblasts near the incisal end, coinciding with a striking morphological change of the ameloblast layer and the enamel matrix. In adult alphaMUPA mice, the incisor teeth displayed discoloration and tip fragility, and reduction of the outer enamel as determined by scanning electron microscopy. These results suggest that balanced uPA activity could play a role in normal tooth development. The alphaMUPA tooth phenotype demonstrates a remarkable sensitivity to excessive extracellular proteolysis at the incisor maturation stage of amelogenesis.

Animals↗

PubMed1978

Mucogingival changes resulting from mandibular incisor tooth movement.

This study involved a cephalometric analysis of 1,150 fully treated orthodontic cases evaluated by Kodachrome slides, plaster casts, and cephalometric films to determine changes in the width of keratinized gingiva relative to lower incisor tooth movement and to ascertain the incidence of mucogingival problems in orthodontic patients. It was apparent that in a small percentage of cases visible mucogingival changes occurred and could be statistically correlated with the magnitude and direction of tooth movement. In this group of patients 1.3 percent (sixteen) showed a decrease in the width of keratinized gingiva with either minimal movement or some labial movement of the mandibular incisors; 0.69 percent (eight) had an increase in keratinized gingival width concomitant with significant lingual positioning of the lower incisors. The salient point to be made is that with an initial minimal or inadequate width of keratinized gingiva (0 to 2 mm.), mandibular incisor tooth movement over a period of treatment could significantly affect the final quality of gingival health in the critical mandibular anterior region.

Cephalometry↗

PubMed1983

Long-term effect of intrusive loads of varying magnitude upon the eruptive potential of rat incisors.

The present investigation deals with the functional recovery of the periodontium following application of intrusive loads of varying magnitudes to continuously growing rat incisors. The daily rate of eruption of these teeth served as an indicator of the functional capacity of their periodontal ligament. The left mandibular incisor was shortened to prevent occlusion in thirty experimental and ten control rats. The experimental animals were divided into three groups and constant, calibrated axial loads of 8 Gm./cm.2 (light), 15 Gm./cm.2 (medium), and 26 Gm./cm.2 (heavy) were applied to their incisors by means of closed-coil springs for a period of 2 weeks. The daily eruption rate of all teeth was measured for 80 days following removal of the springs. In all experimental animals, severe and long-lasting impairment of the eruptive potential occurred. The least impairment was seen in the group with the light loads, their eruption rate being fully restored 64 days after removal of the loads, by which time 165 percent of all dental and periodontal tissues was renewed. In the medium-load group, renewal of the tissues reached 140 percent, while a gross impediment in normal eruption rate persisted throughout the entire experimental period. The teeth subjected to heavy loads received a diminished impact of the axially directed loads due to the strong horizontal component of force; consequently, they behaved like the incisors of the light-load group. The light loads proved to cause the least impairment and were the most beneficial to functional recovery.

Animals↗

PubMed1985

Bilateral congenital absence of maxillary lateral incisors: a craniofacial and dental cast analysis.

The dental casts and cephalometric records of forty-three patients exhibiting bilateral congenital absence of maxillary lateral incisors were evaluated to determine the nature and extent of any concurrent craniofacial and dental anomalies. The effects of bilateral orthodontic space closure were evaluated on a subsample of twenty-two cases. The data revealed normal dental arch length, arch width, overjet, and overbite, while significant tooth size discrepancies were found in several anterior and posterior teeth. Craniofacial deviations from normal included smaller maxillary length, smaller mandibular length, smaller anterior cranial base, and nasal bone. Vertical facial dimensions, both anterior and posterior, were significantly less, as was the mandibular plane angle. Soft-tissue examination revealed a 10 degrees greater nasiolabial angle, which was increased a further 5 degrees as a result of a mean incisor retraction of 1.5 mm during space closure. The craniofacial anomalies noted in the present sample were similar to those seen in persons with clefts and may reflect a common etiology related to a developmental disturbance during fusion of the facial processes in utero. In the treatment of patients with bilateral congenital absence of maxillary incisors, mechanotherapy designed to open the mandibular plane, increase the vertical dimension, and move the maxillary posterior teeth forward is recommended in order to prevent worsening the Class III tendency and to minimize maxillary incisor and upper lip retraction. Most cases will require significant mesiodistal reduction in tooth size in order to achieve an optimal occlusion.

Adolescent↗

PubMed1985

Prediction of mandibular incisor and canine crowding changes in the mixed dentition.

To test the hypothesis that preeruptive tooth positions and dental arch parameters might forecast crowding changes, a sample of 47 aboriginal children (26 males, 21 females) was selected stringently on the basis of Class 1 characteristics and an untreated dentition unaffected by caries or attrition. Crowding scores, radiographic relationships of 765E, and dental arch dimensions were evaluated for the mixed dentition (Stage 1, 8.91 +/- 1.05 years) and earliest emergence of the permanent dentition (Stage 2, 12.48 +/- 0.97 years). Changes between the stages were calculated and the sample was divided into two groups, according to an increase (Group 1) or decrease (Group 2) in incisor and canine crowding. Multivariate and multiple regression analyses were used to identify predictors (Stage 1 radiographic and dental arch parameters) of incisor and canine crowding behavior. Dental arch form and tooth size were important factors in measuring the amount of incisor or canine crowding at Stage 1 and Stage 2. Neither the radiographic nor the dental arch predictors proved useful in forecasting crowding changes. Group 2 dental arches tended to be initially narrower, shallower, and more crowded; however, they showed greater molar and canine width expansion and lessened arch depth reduction than Group 1 cases. Many cases showed a reduction in canine crowding from mixed to permanent dentition. This appeared to be largely independent of the observed incisor crowding. Sexual, racial, and individual variations in dentofacial pattern reinforce the need to carefully consider interceptive extraction or space-regaining therapy for each patient because of the unpredictability of crowding behavior during the transition from mixed to permanent dentition.

Australia↗

PubMed1985

The effect of procedures intended to alter the interstitial fluid pressure in the sockets of resected rat incisors on their eruption rate.

Eruption rates of resected incisors were measured while their sockets were kept open to the mouth. In other resected incisors, hypertonic solutions were placed in the pulp cavity, with the intention of drawing fluid by osmosis across the membrane separating the pulp cavity from the socket, to lower the pressures within the socket. These procedures slowed eruption when control resected incisors were erupting rapidly but not during their initial and final slow phases of eruption. The findings are consistent with there being two factors making resected incisors erupt, tentatively identified as the periodontal ligament and, when eruption is rapid, the interstitial pressures of the tissues in the socket.

Albumins↗

PubMed1995

Instruction by retinoic acid of incisor morphology in the mouse embryonic mandible.

Endogenous retinoids are present in the embryonic mouse mandible and reach a peak in concentration at the time of the formation of the dental lamina. All-trans retinoic acid is present in a 10-fold higher concentration in the future incisor region of the mouse embryonic mandible at day 11.5. It was found here that exogenous all-trans retinoic acid has pleiotropic effects on the pattern of odontogenesis when applied before the formation of the dental lamina. These effects include a change in the pattern of the dental lamina, supernumerary buds and incisors in the diastema region, and replacement of molars with incisors in the molar region. Thus retinoic acid appears to instruct incisor morphology in the mouse embryonic mandible.

Animals↗

PubMed1987

The effect of epidermal growth factor on neonatal incisor differentiation in the mouse.

The effect of epidermal growth factor (EGF) on cellular differentiation of the neonatal mouse mandibular incisor was examined autoradiographically using tritiated thymidine ([3H]TDR) and tritiated proline ([3H]PRO). On days 0 (day of birth), 1, and 2, EGF was administered (3 micrograms/g body wt) sc to neonates. Mice were killed on Days 1, 4, 7, 10, and 13 after birth and were injected with either [3H]TDR or [3H]PRO 1 hr before death. [3H]TDR was used to analyze cell proliferation in eight cell types in the developing mouse incisor including upper (lingual) and lower (buccal) pulpal fibroblasts, preodontoblasts, inner and outer enamel epithelial cells (IEE and OEE), stratum intermedium (SI), stellate reticulum (SR), and periodontal ligament (PDL) fibroblasts. [3H]PRO was used to analyze protein synthesis in ameloblasts, and their secretion products (enamel and dentin), as well as PDL fibroblasts. The selected EGF injection scheme elicited acceleration of incisor eruption with minimal growth retardation. At Day 1, the upper and lower pulp, preodontoblasts, SI, and SR showed a significant decrease in labeling index (LI) 24 hr after a single EGF injection. After multiple injections (Days 0, 1, 2), two LI patterns were observed. In lower pulp, preodontoblasts, IEE, SI, SR, and OEE, a posteruptive change in LI was observed. In contrast, the upper pulp and PDL regions demonstrated a direct temporal relationship with eruption. Autoradiographic analysis with [3H]PRO indicated that EGF treatment caused significant increases in grain counts per unit area in ameloblast, odontoblast, and PDL regions studied. Significant differences were found in all four regions studied (ameloblasts, enamel, odontoblasts, dentin) at the 45-microns-tall ameloblast level as well as ameloblasts and odontoblasts at the 30-microns level at 13 days of age. The PDL demonstrated significant differences at all locations studied (base, 30 microns, 45 microns,) in 4-, 7-, and 13-day-old mice. Morphologically, EGF-treated groups demonstrated premature differentiation of ameloblasts and odontoblasts at the light microscopic level. The data indicate that EGF alters DNA and protein synthesis as well as differentiation patterns during the eruption process. While EGF affects both DNA and protein synthesis, the alteration of differentiation may be secondary to mitogenic effects on proliferative compartments. In order to determine the cellular target for EGF within the newborn mouse incisor, in vivo 125I-EGF binding was analyzed autoradiographically.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗