(1/229) The length and eruption rates of incisor teeth in rats after one or more of them had been unimpeded.

The eruption rate and length of all four incisor teeth in rats were measured under ether anaesthesia by recording the position of marks on their labial surfaces at 2-day intervals, using calibrated graticules in microscope eyepieces. The rats were divided into four groups and either a lower, an upper, both a lower and an upper, or no incisors were unimpeded. This paper describes the changes when the unimpeded incisors returned to the occlusion. Neither the unimpeded nor the impeded incisors simply returned to control values immediately the period of unimpeded eruption ended, but showed transient changes in their lengths and eruption rates. The results confirm that eruption rates are determined by the sum of the lengths of the lower and upper incisors, rather than by their own lengths, with longer teeth erupting more slowly. Specifically, restoring the bevel to the incisors did not slow their eruption below normal impeded rates. The slowing of the eruption of the longer of two adjacent incisors was related to the length differences of the incisors in the same jaw, not to the sum of the differences in both jaws. Contact with the contralateral incisor in the opposite jaw slowed the eruption of an incisor more than contact with the ipsilateral incisor.  (+info)

(2/229) Mouse odontogenesis in vitro: the cap-stage mesenchyme controls individual molar crown morphogenesis.

Day 14 ICR mouse first lower (M1) and upper molars (M1) as well as heterotopic recombinations of M1 epithelium/M1 mesenchyme and M1 epithelium/M1 mesenchyme were cultured for 6, 8 and 10 days on semi-solid medium. Computer-assisted 3D reconstructions were performed to follow the in vitro development of these explants. In vitro culture of cap-stage molars allowed for the emergence of unequivocal morphological features distinctive for M1 versus M1 including the cusp pattern, cusp inclination and tooth specific chronology for odontoblast and ameloblast terminal differentiations. Both M1 epithelium/M1 mesenchyme and M1 epithelium/M1 mesenchyme recombinations developed according to the known developmental fate of the mesenchyme. Our data demonstrate that the cap-stage dental ecto-mesenchyme not only directs tooth class specific morphogenesis, but also individual molar crown features. Furthermore, the mesenchyme apparently also controls the typical mirror symmetry of right and left handed teeth.  (+info)

(3/229) Longitudinal post-eruptive mandibular tooth movements of males and females.

Unbiased estimates of post-eruptive eruption and migration of the mandibular teeth for large representative samples are presently unavailable. The purpose of this study was to evaluate pure tooth movements of untreated children and adolescents longitudinally. Lateral cephalograms of 214 French-Canadians, followed bi-annually between 8 and 15 years of age, were traced, and the positions of the mandibular permanent central incisors and first molars were digitized. Temporal changes in tooth position were evaluated relative to naturally stable mandibular reference structures, using the mandibular reference line for orientation. The statistical analyses included t-tests to assess gender differences and Pearson product-moment correlations to evaluate associations. The results showed that the incisors proclined significantly more for males (6 degrees) than females (3 degrees). The incisor tips displayed early mesial movements that were countered by later distal movements. The incisor apex showed a consistent pattern of distal migration between 8 and 15 years. Mandibular arch length decreased over the 7-year observation period. Rates of mesial molar migration accelerated until 11 years of age and then decelerated. There was no significant change in the mandibular occlusal plane angle between 8 and 15 years of age. Incisor eruption showed the greatest rates during adolescence, attaining peaks at approximately 12 years for females and 14 years for males. The molars erupted approximately 5 mm between 8 and 15 years of age. The greatest gender differences occurred at the older ages, with males showing greater eruption potential than females. It was concluded that the mandibular teeth show significant migration and eruption during childhood and adolescence, with gender differences in the amount, direction, and timing of movement.  (+info)

(4/229) Blood vessel response to pan-endothelium (RECA-1) antibody in normal and tooth loaded rat periodontal ligament.

Immunolabelling of the normal rat molar periodontal ligament (PDL) with RECA-1 antibody, an endothelial cell surface marker, demonstrated the endothelium in the different categories of blood vessels. The intensity of immunolabelling was similar for venous capillaries (VC), post-capillary-sized venules (PCV), and collecting venules (CV). Arterial capillaries (AC) and terminal arterioles (TA) showed a different response, both having a high intensity of endothelium and smooth muscle cell labelling, whether they were located in the PDL or alveolar bone. An experimental, continuous loading of approximately 100 g was applied unilaterally to the mandibular molars for 10 minutes. In the PDL apical compression zone this load resulted in a loss of RECA-1 immunolabelling of the VC, PCV, and CV. Adjacent to the alveolar crest, where shear and tension loads were judged to have occurred, there was enhanced immunoreactivity of VC, PCV, and CV. In the loaded PDL, the AC and TA, irrespective of their location in the ligament or bone, showed strong immunofluorescence of their endothelium and the enveloping smooth muscle layer. Vessel and PDL immunofluorescence were analysed with standardized grey scale densitometry, and the data subjected to ANOVA. Comparison between individual vessel means showed significant differences (P < 0.05). Control teeth showed no immunostaining difference between the coronal and apical region vessels, whereas in the loaded teeth the overall cervical vessel endothelium had a significantly higher value than the apical vessel endothelium (P < 0.001). These findings demonstrate that the endothelium of this microvascular bed can undergo significant immunoreactivity changes when exposed to short-term, continuous, tooth loading.  (+info)

(5/229) The effect of tooth position on the image of unerupted canines on panoramic radiographs.

The purpose of this study was to evaluate whether panoramic tomograms, which are routinely used in orthodontic practice, can provide adequate information to localize an impacted canine. The effect of changes in position and inclination of an impacted canine on orthopantomograms was investigated in an experimental set-up. An upper canine was removed from a human skull and replaced in a positioning system, enabling simulated positional variations in impactions. In comparison with the image of a contralateral well-aligned canine, the length of the impacted tooth always decreased or remained unchanged, whereas the tooth width increased or remained unchanged. The angulation of the image was unaffected by varying the position of the impacted canine, but altered when the inclination of the tooth in a sagittal or frontal direction was changed. If there was any transversal shift of the impacted canine on the orthopantomogram, it was always towards the mid-sagittal plane. The curvature of the tooth increased after dorsal inclination and decreased after ventral inclination (in comparison with the contralateral well-aligned canine).  (+info)

(6/229) A mathematic-geometric model to calculate variation in mandibular arch form.

A mathematic-geometric model was used to evaluate the variation of mandibular dental arch length with respect to the incisor inclination, but without modifying the intercanine width. In analytical terms, the equations of the curves representing the lower dental arch, before and after incisor inclination of 1 mm and of 1 degree, with controlled and uncontrolled tipping, were studied. The length of the mandibular dental arch changed in the parabolic arch form by 1.51 mm for each millimetre of incisor inclination with respect to the occlusal functional plane, by 0.54 mm for each degree of controlled tipping and by 0.43 mm for each degree of uncontrolled tipping. In the elliptical arch form (e = 0.78), it changed by 1.21, 0.43, and 0.34 mm, respectively, in the hyperbolic form by 1.61, 0.57, and 0.46 mm, in the circular form by 1.21, 0.43, and 0.34 mm, and in the catenary form by 2.07, 0.74, and 0.59 mm. The results show that by changing the arch form without modifying the dimension of the dental arch, different arch lengths can be gained for each millimetre of proclination. In addition, by controlled tipping an inter-incisive arch one-fifth longer than by uncontrolled tipping can be obtained. It would be advisable in orthodontic treatment planning to evaluate the type of dental arch, since the space available or the space required changes depending on the arch form and on the orthodontic tooth movement.  (+info)

(7/229) Dental caries in Quebec adults aged 35 to 44 years.

BACKGROUND: The purpose of this study was to assess the prevalence of dental caries in Quebec adults aged 35 to 44. METHODS: A stratified sample was used. The participation rate was 77% for the questionnaire and 44.5% for the oral examination. A total of 2,110 people were examined. The World Health Organization's caries criteria were used. Examiner agreement with gold standard dentist was excellent at the end of the nine-day training session (Kappa index > 0.8). RESULTS: The level of caries experience is very high in Quebec adults aged 35 to 44. Almost half of dental surfaces (65 of 148) have been affected. These surfaces are mostly missing (39.3) or filled (23.9). However, there were 1.8 decayed surfaces in need of treatment per adult, and more than half the people (55.5%) had no untreated decayed surfaces. Almost three-quarters of decayed surfaces were present in only 14% of the people; lower family income and lower education are risk factors. CONCLUSION: Comparison between Quebec and industrialized countries (United States, England and the Netherlands) shows that in adults 35 to 44, the mean number of decayed teeth is low (between 1.0 and 2.2) and the mean number of filled teeth is relatively similar (between 9.6 and 11.1); however, Quebec has a higher percentage than the United States of edentulous people. As well, in dentate adults, there are 1.6 times more missing teeth among Quebecers than among Americans.  (+info)

(8/229) Effects of hepatocyte growth factor anti-sense oligodeoxynucleotides or met D/D genotype on mouse molar crown morphogenesis.

Hepatocyte growth factor (HGF) is considered to be one of the mediators of epithelio-mesenchymal interactions during early organogenesis and to be also involved in the development of murine molars. In the developing tooth, HGF is expressed in the cells of the dental papillae, and c-Met, its receptor, in the cells of dental epithelia. In order to study the functional role played by HGF in tooth development, we tested the effects of HGF translation arrest by anti-sense phosphorothioate oligodeoxynucleotides on E-14 molars cultured in vitro. We also analyzed the histo-morphogenesis and crown cytodifferentiation of transgenic met E-14 molars cultured in vitro. 3D reconstructions revealed perturbations of the cusp pattern. However, histo-morphogenesis and crown cytodifferentiation were normal at the histological level.  (+info)