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At least 235 records · Page 13Linked to original sources
PubMed1982

Differential rates of enamel formation of human tooth surfaces deduced from the striae of Retzius.

Ten permanent maxillary central and mandibular lateral incisor teeth were sectioned in labio-lingual or mesio-distal planes, and the amount of enamel between two striae of Retzius was measured in the vicinity of the dentine-enamel junction. In the initial third of crown formation of central incisors, both the thickness of enamel and the amount of cervical extension of enamel were always greater on the labial than on the lingual surface; the same applied to the thickness of enamel, but not to the amount of cervical extension of enamel, in the lateral incisors. The thickness of enamel together with its cervical extension was greater on the mesial than on the distal surface in the lateral, but not the central, incisors. In the cervical third of the crown, there was a general tendency for the thickness of enamel and its cervical extension to be greater on the lingual and distal surfaces than on the opposite surfaces. For the maxillary central incisors, it saw deduced that the labio-lingual reversion of the rate of development of enamel takes place at approximately the 60 per cent level of the crown formation.

Amelogenesis↗
PubMed1982

Reverse, hormone-dependent sex difference in molar tooth mass in pubertal mice.

The weighed mass of molar teeth of male pubertal (35-day-old) mice was significantly smaller than that of females. X0 females, and chromosomal males (XY) rendered phenotypically female by the testicular feminization gene (Tfm), had high (female-type) molar mass. Chromosomal females (XX or X0) rendered hormonally phenotypically male by the sex reversal gene Sxr, had low (male-type) molar mass. It is concluded that the sex difference was due to hormonal rather than chromosomal factors. Reported sex differences in mammalian tooth size have mainly been in the opposite direction, a discrepancy which may be due to co-existence of opposite dimorphisms of mass and diameter, or to age-specific changes in ontogeny. However, the most likely explanation is that developmental species differences exist.

Animals↗
PubMed1982

Developmental patterns of human dental morphological traits.

A longitudinal series of casts of the deciduous and permanent dentitions of 827 children from Burlington Growth Centre study was examined for 5 traits: shovel-shape of the incisors, cusp six, cusp seven and protostylid of the mandibular molars, and Carabelli trait of the maxillary molars. The changing trait frequencies found support the concept of morphogenetic gradients of expression for non-metric traits from deciduous to permanent teeth. Tests of association showed that if shovelling was present on the deciduous incisors it would usually appear on the permanent successors. Tests of association between the other 4 traits on deciduous second molars and the permanent molars support the view that the second deciduous molar belongs to the total molar tooth district. This gradient expression of morphological traits would fit either the field or clone concepts, but it, and the intra-individual discordances for trait presence, probably reflects the great temporal spacing of dental development seen in man.

Adolescent↗
PubMed1983

Tooth size in children and young adults with trisomy 21 (Down) syndrome.

Mean values and variances of the mesiodistal and buccolingual dimensions of all deciduous and permanent teeth, except third molars, were compared between 147 Down syndrome and 265 control subjects. Permanent tooth dimensions were significantly smaller in the Down syndrome group and also tended to show greater variability. However, for the deciduous dentition, some dimensions were significantly larger in Down syndrome and no systematic differences in variability were noted between the groups. These findings indicate that there may be an initial transitory acceleration in mitotic activity of developing enamel organs in Down syndrome followed by the characteristic generalized retardation in growth.

Adult↗
PubMed1983

The production of developmental defects of enamel in the incisor teeth of penned sheep resulting from induced parasitism.

Thirty-four sheep were infected with nematode parasites (Trichostrongylus spp. and Ostertagia circumcincta) during central incisor formation. The tooth enamel was examined for defects of mineralization at eruption and compared with that of 14 control sheep. The type and number of parasites given, the duration of the infection and the age of the sheep were varied. Sheep receiving high doses of parasites e.g. 200,000 T. vitrinus + 20,000 O. circumcincta showed severe systemic effects (debilitation, scouring and weight loss) which were of short duration (7-10 days) as the infections were terminated by anthelmintic treatment. Hypoplastic enamel (a break in continuity) was induced in all 5 sheep infected at 8 1/4-9 months of age and demarcated opacities (an alteration in the translucency) in 3 out of 4 sheep infected at 10 months of age. Sheep given 150,000 or 40,000 T. colubriformis showed less obvious systemic effects although the weight loss continued in some sheep for up to 54 days. Although opacities of the enamel in the form of parallel lines, sometimes with localized increase in width or with a diffuse opacity superimposed, were seen by microscopic examination (X 10) of teeth in this group, many of the teeth from the control sheep showed similar lesions. Only the hypoplastic lesions can be attributed with confidence to the experimental manipulations.

Animals↗
PubMed1983

The influence of crown size dimorphism on sex differences in the Carabelli trait and the canine distal accessory ridge in man.

When the two sexes were contrasted, Pima Indian males showed larger crown dimensions and more pronounced expressions of two morphologic variables, the Carabelli trait and the lower canine distal accessory ridge. In addition, a significant positive relationship was found between crown size and degree of expression of the morphologic traits. When regression analysis was utilized to control for male-female tooth size differences, the moderate dimorphism shown by Carabelli trait was reduced by about half. The more dimorphic distal accessory ridge, related primarily to mesio-distal diameter, also showed a lesser sex difference when crown size effects were held constant. While size dimorphism does contribute to morphologic dimorphism, factors unrelated to crown size still contribute the majority of variance present in trait expression both within and between sexes.

Cuspid↗
PubMed1984

Fluctuating asymmetry in the deciduous dentition of Dominican mulatto children.

An assessment of deciduous tooth-size asymmetry showed no evidence of sex differences. When asymmetry was compared between the various tooth dimensions, the buccolingual dimensions of mandibular incisors consistently displayed high asymmetry values. This finding may reflect a developmental interaction between the deciduous incisor tooth germs and their lingually-placed permanent successors.

Child, Preschool↗
PubMed1984

Histomorphometric evaluation of the dimensional changes in rat-incisor tissues following histological processing and embedding in paraffin wax and glycol methacrylate.

A three-dimensional reconstruction of undemineralized and paraffin wax- or or glycol methacrylate-embedded demineralized rat incisors was made using a computerized histomorphometry. Compared to the undemineralized ground sections, the two demineralizing and embedding procedures grossly distorted the tooth sections. In general, embedding in wax caused shrinkage and in methacrylate caused swelling. Direction and magnitude of the deformation varied in the different tissues of the tooth and its surrounding structures. The distortion was influenced by the ratio between the soft and hard tissues at different cross-sectional levels of the tooth.

Animals↗
PubMed1985

Techniques for choosing reference points from which to measure eruption rates of rat incisors.

Measurements of eruption rates were compared with a computer analysis of measurements of eruption rates from stable and unstable reference points. In the computer analysis, when the measurements were made from unstable reference points, there were correlations between eruption rates and changes in tooth length and between unimpeded and impeded eruption rates. These correlations were not seen in measurements made from stable reference points. The measurements from unstable reference points had greater variances. These correlations were found in measurements made from the gingival margin of the unimpeded incisor but not in measurements from the margin of the impeded incisor. The measurements from the impeded incisor had a lower variance. The ability was demonstrated of these correlations and variance ratios to detect instability of reference points.

Animals↗
PubMed1985

Quantitative assessment of tooth wear, alveolar-crest height and continuing eruption in a Romano-British population.

Although measurements from cement-enamel junction (CEJ) to alveolar crest (AC) have been used in assessing changes in alveolar-crest height as age or chronic inflammatory periodontal disease (CIPD) progresses, there is evidence from ancient populations that the position of AC remains almost constant throughout life and continuing eruption to compensate for attrition may explain why CEJ-AC measurements increase with age. Measurements of occlusal attrition and relationship of CEJ to AC were made on the cheek teeth of 500 Romano-British skulls by direct measurement or by reference to the fixed line of the inferior alveolar canal (IAC) on radiographs. Direct measurements indicated that there were usually no statistical differences between the vertical amounts of tooth substance lost by attrition and the change in the distance CEJ-AC as age progressed. Measurements on radiographs showed that posterior teeth continued to erupt to compensate for attrition and the AC remained static as age progressed. Bone deposition at the AC was seen in the majority of ground sections. Thus tooth wear appears to be compensated by continuing movement of teeth in an occlusal direction. The position of the AC remained almost constant throughout life; AC bone lost by CIPD seemed to be replaced during continuing tooth eruption.

Age Factors↗
PubMed1985

A radiographic study of dental development in the hypopituitary dwarf mouse.

Growth in body length, skeletal lengths, incisor lengths and molar root lengths were retarded in dwarf mice. The root lengths of third molars were more severely affected than those of other molars. The crown lengths at the enamel-cementum junction of upper and lower molars of most dwarf mice were significantly shorter than normal. The root canals of dwarf mice were smaller, apical closure was delayed and there was a delay in their eruption to the occlusal level. Although the size of the dentition was markedly affected in the dwarf mice, the functional relationship appeared to be unchanged.

Animals↗
PubMed1987

Quantitative analysis of the molar-size sequence in human prehistoric populations of the Canary Isles.

Percentage frequencies for molar-size sequence of first and second molars, as well as the statistical parameters for the individual differences between the measurements of these molars, were calculated in two human prehistoric aboriginal samples from Gran Canaria and Tenerife Islands using mesiodistal and buccolingual dimensions. Remarkable differences between the two populations, whose cultural and anthropological differences are well established, were observed. The findings support the hypothesis that quantitative analysis of molar size sequence can be useful in establishing phylogenetic relationships between populations.

Atlantic Islands↗
PubMed1987

A hypothetical model of genetic control of tooth-crown growth in man.

Twins and families were investigated to obtain information about inheritance of tooth-crown size. Sixty twin pairs and 100 families were examined using four methods of estimation. The results suggest genetically controlled interactions between tooth germs during their formation. A hypothetical model of odontogenesis is presented.

Humans↗
PubMed1988

Tooth crown size in human females with 45,X/46,XX chromosomes.

Permanent tooth sizes in 15 Finnish females with a 45,X/46,XX chromosome constitution were measured and compared with those of normal females, first-degree female relatives and 45,X females. Mesiodistal crown diameters of the 45,X/46,XX mosaic females were smaller than those of normal females but similar to those of females with pure 45,X chromosome constitution. Labiolingual crown diameters of the 45,X/46,XX mosaics were near normal, being consistently larger than those of 45,X females. The mesiodistal crown sizes are consistent with a decrease in enamel thickness in 45,X/46,XX mosaic females. The difference in labiolingual dimension between teeth of 45,X/46,XX mosaic females and 45,X females may relate to a gradual normalization of growth when normal 46,XX cells are mixed with defective 45,X cells.

Chromosome Aberrations↗
PubMed1988

Principal component analysis of intercusp distances on the lower first molars of three human populations.

The distances between the five main cusps of lower first molars were measured on moiré photographs of casts obtained from Japanese, Dutch and Australian Aboriginal children. Principal component analysis of the intercusp distances, log transformed and standardized so that average tooth size was held constant, revealed three sources of shape variation in cusp topography. All populations were similar for scores on component 1 which was concerned with variations in the position of the hypoconulid. The Dutch had lowest scores on component 2 indicating small buccolingual distances compared with mesiodistal, whereas the Australian Aboriginals had the lowest mean score on component 3, expressing the distances between metaconid, entoconid and hypoconulid.

Asian People↗
PubMed1988

The relationship between mandibular morphology and apical root curvature in man.

Two samples of individuals, a low-angle group and a high-angle group, were selected on the basis of the inclination of the lower border of their mandible, defined by the mandibular plane angle (ML/SNL) in profile radiographs. Apical root curvature of mandibular first and second premolars and molars on panoramic radiographs was compared between the two groups and related to mandibular morphology. In the low-angle group most teeth had more distally curved roots than in the high-angle group. Significant differences were found for the first premolars on both sides (p less than 0.001, p less than 0.05), the right second premolars (p less than 0.05) and the distal root of left first molars (p less than 0.05). Correlations were calculated between root curvature and two variables reflecting mandibular morphology, the mandibular plane angle and the gonial angle. The strongest associations were found between the first premolar roots and the gonial angle (rs = -0.75, p less than 0.001 and rs = -0.56, p less than 0.01, for right and left sides respectively). The association between mandibular morphology and root curvature is probably indirect, caused by tooth migration during root formation.

Bicuspid↗