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PubMed1989

Odontometric asymmetry in Punjabi twins with special reference to methods for detecting spurious genetic variance.

Bilateral human odontometric asymmetry generally shows very little genetic variance. In Indian twins, using the simplest methods, unusual levels of disproportionate monozygous similarity and/or dizygous dissimilarity for asymmetry, giving the appearance of significant genetic determinance, were found. Thus this dental asymmetry constituted an interesting test case for the application of more exact methods for the detection of zygosity bias; these invalidated the spuriously significant genetic variance ratios. Therefore the predominantly environmental influences on bilateral dental asymmetry are confirmed.

Genetic Techniques↗
PubMed1989

A morphometric and quantitative microradiographic study of dental tissues in the hypopituitary dwarf mouse.

In transverse sections the areas of enamel, dentine and pulp were determined using image analysis morphometry, and the mineralization levels of enamel, dentine and alveolar bone using quantitative microradiography and a microphotometric-microdensitometric technique. There were significant differences in the ratios of dentine to pulp area, and in the enamel to total area in the incisors from dwarf and normal animals. The mean dentine to pulp ratio for dwarf incisors was more than six times greater than in normal incisors. There was also a significantly greater variation in the dentine to pulp ratio in dwarfs, which was attributed to their greater variation in pulp size. Values for mineral density of enamel, dentine and bone were similar to those found by other investigators. For example, for normal specimens, the mean mineral density of outer enamel was 2.84 g/cm3 (SD = 0.38), percentage mineralization 92%; outer labial dentine was 1.64 g/cm3 (SD = 0.15), percentage mineralization 52%; and alveolar bone was 1.53 g/cm3 (SD = 0.13), percentage mineralization 49%. The variation in mineralization within each tissue confirmed previous work in rodents. There was a consistent trend for mineralization levels of all hard tissues in the dwarf sample to be less than in the normal sample but the difference was not statistically significant for any one tissue.

Alveolar Process↗
PubMed1989

Spacing in the human deciduous dentition in relation to tooth size and dental arch size.

Dental casts of 243 preschool children, 129 males and 114 females, aged 2.5-5.5 years, were analysed for the presence of interdental spaces, mesiodistal crown diameters, intercanine width, intermolar width and arch length (circumference). The prevalence of primate spaces (diastemata mesial to the upper canines and distal to the lowers) varied from 65 to 90% by arch and sex; it was lowest in the lower arch especially in females, and highest in the upper. These prevalences did not increase with age; however, other spaces which usually occur between incisors may develop towards the end of the deciduous dentition, commonly in arches with primate spaces. Generally, spacing of the deciduous anterior teeth was significantly related to mesiodistal crown diameter and intercanine arch width. The crowns were significantly broader and the arches significantly narrower in cases with no spaces than in those where spaces existed. As the genetic programming for tooth size also normally affects arch size, greater discrepancies between mesiodistal crown diameters of the deciduous anterior teeth and their permanent successors are probably associated with more deciduous arch spacing.

Age Factors↗
PubMed1991

Prolonged effects of hypofunction on the mechanical strength of the periodontal ligament in rat mandibular molars.

The ultimate loads required to extract three mandibular molars in the dissected jaw were examined after elimination of the antagonistic teeth for up to 64 days. The ultimate loads in the experimental first and second molars decreased rapidly in the first few days, while those in the third molar remained low during the same period in both experimental and control groups. The ultimate loads in all three molars of the experimental animals then increased gradually towards the end of the experiment at rates similar to those in controls. Maximum relative reductions of the ultimate load were observed within the first 8 days in all three molars. An increase in the length of roots was also found in all hypofunctional molars. Daily rates of root elongation ranged from 13 to 19 microns/day in the control and from 18 to 26 microns/day in the experimental molars during the whole experiment. The greatest value (80 microns/day) was obtained during the first 8 days in the third molars of both control and experimental animals. Thus the mechanical strength of the periodontal ligament estimated in vitro may be increased by the development of teeth and by non-functional occlusal contacts with the opposing gingiva-covered alveolar ridge deprived of its tooth crowns. The ligament of the third molar was apparently immature at the beginning of the experiment.

Animals↗
PubMed1991

Tooth crown size in 46, X, i (Xq) human females.

Permanent tooth crown sizes of six Finnish females with a 46, X, i(Xq) chromosome constitution (isochromosome for the long arm of the X chromosome) were measured from dental casts and compared with those of normal women, first-degree female relatives and 45, X females. Crown diameters of the 46, X, i(Xq) females were not only smaller than in the normal women but even smaller than the 45, X females. These findings can be considered indirect evidence that X chromosome gene(s) for tooth crown growth are most probably located on the short arm.

Chromosome Aberrations↗
PubMed1992

Dental morphology of 45,XO human females: molar cusp area, volume, shape and linear measurements.

A three-dimensional analysis of the maxillary first molars of five 45,XO females and comparison with normal females and males demonstrated a reduction of cusp areas and volumes in the 45,XO females. Mesiodistal and faciolingual dimensions were also reduced. The reductions in basal area and volume were greater in the later developing, distal cusps. In normal females the second X chromosome apparently does not exert an effect on the cusp height but increases the basal area. The results further indicate that the Y chromosome in normal males increases both cusp height and basal area. The steepest cusps were found in 45,XO females while the shallowest were in the control males. Both sex chromosomes thus seem to affect the shape of the cusp but the resulting phenotypes differ.

Female↗
PubMed1992

Relationship between size of distal accessory tubercles and hypocones in permanent maxillary molar crowns of southern Africans.

The relationships between total occlusal crown area and the basal cusp areas of the accessory distal tubercle (C5) and the hypocone were analysed in molars of complete upper tooth rows of a southern African sample. While non-parametric tests between hypocone and C5 sizes did not yield statistically significant results, analyses of metrical data revealed a trend towards compensatory interaction between both cusps. Contrary to previous reports the size of C5 was found to be independent of total crown area. As enamel is thickest on cusp tips there may be a functional reason for the frequency of occurrence of the distal accessory tubercle. The pattern of distribution of the hypocone and C5 within a tooth row may be related to the occlusal wear pattern in Homo, which exhibits a marked lingual slope of wear in anterior molars and a horizontal or even buccal slope in posterior teeth.

Black People↗
PubMed1993

Morphometric variables of developing primary mandibular second molars.

Morphometric variables of second primary molar crowns from birth to completion were examined and measured. An image analysing technique comprising a photographic camera, a monitor, a computer with appropriate software and a digital caliper was used. Strong correlations were found between the 'external' aspect of the crown (mesiobuccal cusp height, mesiodistal and buccolingual dimensions and perimeter), and between all the 'occlusal' measurements of the crown, i.e. all the intercusp distances. However, poor correlations were found between the external and internal measurements of the crown such as the mesiobuccal cusp height and mesiobuccal-mesiolingual cusp-tip distance. It was also found that the mesiobuccal cusp serves as the apex of two triangles, the one formed by mesial cusps, and one formed by the distal cusps. The cusps on the mesial portion of the crown (ML, DB) are on a similar radius from the MB cusp, and the cusps on the distal portion are on a similar radius from the MB cusp. The small sample is a limitation but the results suggest a separate and independent pattern and rate of development of the external and the occlusal morphological variables of the tooth crown. Further research is needed on larger samples.

Humans↗
PubMed1994

Variation in enamel thickness and cusp area within human maxillary molars and its bearing on scaling techniques used for studies of enamel thickness between species.

Thirty-nine unworn maxillary molars (M1 = 18, M2 = 12, M3 = 9), representing 37 individuals of a Slavic population, were sectioned through the mesial cusps in a plane perpendicular to the cervical margin of the crown. Whether the range of variation in enamel cross-sectional area between individuals corresponds to the range of variation found between teeth within a species was investigated. Total tooth crown area, as determined by planimetry, was used as a scaling factor on the basis that a biologically meaningful scaling procedure should take into account both enamel thickness and total tooth crown area, rather than the size of the dentine-enamel junction. Uni- and multivariate statistics revealed that the enamel cross-sectional area of second and third molars is absolutely and relatively larger than it is in first upper molars and that it scales close to isometry with tooth crown area. Conversely, first maxillary molars, with their relatively and absolutely thinner enamel, exhibit positive allometry between enamel and tooth crown area. These patterns were retained even when differences in overall tooth size were adjusted for. Hence, the notion that there exists a 'species-specific' amount of enamel over the tooth crown must be reconsidered, and one should refrain from pooling different tooth types for taxonomic purposes. At least two scaling factors are needed to describe human maxillary molars alone. However, this increase in enamel cross-sectional area from anterior to posterior is not unexpected if one bears in mind that posterior teeth occupy a more advantageous position relative to the chewing muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Austria↗
PubMed1994

Reductions in size and left-right asymmetry of teeth in human oligodontia.

Tooth size and left-right asymmetry of tooth dimensions in oligodontia were compared with those of a control group. Both early and late developing teeth were severely affected, and almost all teeth had significant reductions, compared to the control group, in mesiodistal and labiolingual dimensions. Left-right asymmetry of tooth dimensions was also found, but for the mesiodistal dimensions these were not significantly different from the control group. The occurrence of reductions in tooth size and left-right asymmetries suggests that oligodontia is not just an isolated phenomenon. The left-right asymmetry indicates a developmental instability in these individuals. More research is needed, to reveal the aetiology and pathogenesis of oligodontia.

Adolescent↗
PubMed1995

Morphology of the deciduous tusk (tush) of the African elephant (Loxodonta africana).

The tusk of the African elephant is preceded by a deciduous tooth generally known as the tush. Tushes from nine elephant fetuses and six calves younger than 1 year were exposed by dissection and described morphologically. All tushes consisted of a crown, root and pulpal cavity, the formation of which is completed soon after birth. They reached a maximum length of 5 cm, appeared not to erupt through the skin and were pushed aside and resorbed during enlargement of the distally located primordium of the tusk. Dental enamel, which covered the crown, could easily be removed and consisted of rods with an interwoven arrangement; the dentine-enamel junction was flat. Cellular cementum extended for variable distances over the crown and the dentine was tubular in nature. Although the tush apparently has no function, it provides the anlage and orientation for the development of its permanent successor.

Animals↗
PubMed1995

The effect of shortening incisor teeth on the eruption rates and lengths of the other incisors in the rat.

The eruption rates and lengths of all four incisor teeth in rats were measured by recording the position of marks on their labial surfaces at 2-day intervals, using calibrated graticules in microscope eyepieces and ether anaesthesia. When one lower incisor, or both a lower and upper incisor, were unimpeded, the other lower incisor shortened markedly before the next measurement and the uppers slowly lengthened, so that the sum of the lengths of the lower and upper impeded incisors temporarily fell, then returned to control levels. The lower and upper impeded incisors showed temporary accelerations of their eruption when the other incisors were unimpeded. When an upper incisor was unimpeded, the lower incisors lengthened, increasing the sum of the lengths of the lower and upper impeded incisors, and the eruption of the lower and upper impeded incisors was slowed. When there were two impeded incisors in one jaw and only one (left) impeded incisor in the other jaw, the unopposed right impeded incisor tended to be slower and longer than its neighbour and there were significant correlations between the differences in eruption rates and differences in tooth lengths. In all these cases, there are negative relations between eruption and length; increases in length occur with decreases in eruption rate. The simplest explanation for this is that the length changes arise partly from the voluntary behaviour of the rat and also from mechanical problems due to having one impeded incisor in one jaw and two in the other jaw; the length changes cause the eruption-rate changes.

Analysis of Variance↗
PubMed1995

Comparison of the effects of growth hormone, insulin-like growth factor-I and fetal calf serum on mouse molar odontogenesis in vitro.

The effects of growth hormone, its mediator insulin-like growth factor-I (IGF-I), and fetal calf serum on odontogenesis were compared to those of serum-free medium. Explanted, 16-day, fetal mouse first molar tooth germs in early bell stage were grown on semisolid, serum-free medium supplemented with ascorbic and retinoic acids. Recombinant human growth hormone at 50 or 100 ng/ml, IGF-I at 100 or 200 ng/ml, or fatal calf serum at 20% concentration were added to the media. Volumetric changes in serial sections of six tooth germs per treatment over 3 days of treatment (4, 5, 6 days in vitro) were compared by digitized morphometry. Mitotic indices were also compared and the cell densities of the dental papillae recorded. Qualitative ratings of differentiation were ascribed to each tooth germ by light microscopy. Differences in volume, mitotic activity and cell densities were found. The growth hormone-treated tooth germs were not larger than the serum-free ones but had increased mitotic indices and higher cell densities in the dental papillae. IGF-I-treated tooth germs had larger volumes than with all other treatments, e.g. germs treated with 200 ng/ml of IGF-I, after 6 days in culture, were significantly larger than with all other treatments (p<0.01-<0.001). Whilst IGF-I-treated germs displayed the greatest extent of differentiation, growth hormone-treated germs also showed advanced differentiation compared to those on serum-free medium. These results suggest that growth hormone and IGF-I are involved in odontogenesis of murine teeth in vitro by affecting mitotic activity, tissue volume and cell differentiation. In conjunction with previous immunohistochemical studies that show expression of growth hormone receptor and IGF-I in developing teeth, these results provide evidence that both growth hormones and its mediator play a part in odontogenesis.

Animals↗
PubMed1995

Phenotypic plasticity in the lower pharyngeal jaw dentition of Astatoreochromis alluaudi (Teleostei: Cichlidae).

The potentially molluscivorous cichlid fish Astatoreochromis alluaudi is known to exhibit a pronounced phenotypic plasticity in its pharyngeal jaw apparatus. Two phenotypes (wild-caught snail-eating specimens and specimens raised on soft food) were examined for differences in the number, size, shape, spacing and wear of functional teeth on the lower pharyngeal jaw. During growth, snail-eating specimens maintain tooth numbers but invest in teeth of a larger size (width and depth). In contrast, specimens fed a soft diet invest in more teeth, their size remaining unchanged except for the central, most posterior teeth. All changes in the dentition must be achieved through successive tooth generations. Serial microradiographs in the caudal area of the lower pharyngeal jaw, a region that is most significant in food processing, indicated that functional teeth in hard-food specimens more often show a successor below. This may be due to more time needed for larger replacement teeth to form and possibly to a shorter replacement cycle linked to the greater wear of the functional teeth. It is hypothesized that maintenance of tooth numbers and increase of tooth size in hard-food specimens is achieved by a one-for-one replacement and expansion of the tooth-bearing region and possibly by closer spacing of the teeth. Increase of tooth numbers in the soft-food specimens is probably achieved through the establishment of new tooth loci at the margins of the dentigerous area in addition to a one-for-one replacement.

Africa, Eastern↗
PubMed1996

Relations between the mesiodistal crown diameters of the primary and permanent teeth of Hong Kong Chinese.

Relations between these diameters were studied on serial dental casts of 112 Hong Kong Chinese (61 males, 51 females) taken at mean ages of 5.68 and 12.31 yr. Size relations were studied in terms of correlation coefficient, difference, and ratio between corresponding pairs of individual teeth and corresponding groups of teeth in both dentitions. The coefficients of correlation were low to moderate (0.2-0.8), with those between groups of teeth consistently higher. As for size differences, incisors and canines were larger in the permanent dentition in both arches by 1.2-2.0 mm. Premolars were smaller than their primary predecessors except for the upper first premolar. When the absolute values of the differences were ranked, the second premolar-second primary molar differences were the greatest (2.0-2.8 mm) while those between the first premolar-first primary molar were the smallest (0.3-0.7 mm). When tooth groups were assessed, the permanent teeth were larger than their predecessors in the anterior segments but smaller in the posterior segments. The leeway space was larger in the mandibular arch (2.2 mm) than in the maxillary arch (0.3 mm). When diameters of five teeth on one side of the arch were combined, the permanent exceeded the primary by 3.5 mm in the upper arch but only 0.5 mm in the lower. The ratios between the permanent and primary tooth sizes showed the same trend as the differences.

Adolescent↗
PubMed1996

Tooth size in relatives of individuals with oligodontia.

Mesiodistal dimensions of teeth in 59 relatives of 26 patients with oligodontia were evaluated and compared with the size of teeth of a control group (n = 66). It was found that the teeth of relatives do show reductions in size even in relatives with a full permanent dentition. In male relatives with a full permanent dentition these reductions were significant for the central and lateral incisors, the cuspids, lower second premolar, upper first molar and lower second molar. For female relatives with a full permanent dentition these reductions were significant for central and lateral incisors, cuspids, first premolars and upper first and second molars. Reductions in tooth size are known to be associated with oligodontia. Therefore, in determining the mode of inheritance, measurements of the size of the teeth of both patients and relatives are important.

Adolescent↗
PubMed1983

An 11-year follow-up of the effects of early bone grafting in infants born with complete clefts of the lip and palate.

This is a report at the age of 11 years of a clinical study of the effects of early bone grafting in infants born with complete clefts of the lip and palate. Matched pairs of similar cleft type were treated according to the same treatment protocol with the exception that only one of each pair received an autogenous rib bone graft at the age of 15 months. The overall impression left by this study is that early bone grafting is not beneficial to the patient.

Bone Transplantation↗