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Biomedical subjects

G C Townsend

Publications and source records attributed to G C Townsend.

86 records · Page 5Linked to original sources
PubMed1980

Heritability of deciduous tooth size in Australian aboriginals.

The contributions of genetic and environmental influences to observed variabiliy of deciduous tooth size were quantified in a group of Australian aboriginals. Phenotypic variability was partitioned into four components; between sides, between fathers, between mothers, and between offspring. Results suggested that about 58% of deciduous tooth-size variability was due to additive genetic variance and 15% to common environmental variance. It appears that additive genetic variance is similar in both deciduous and permanent dentitions, but that common maternal effects are more important in determining deciduous tooth-size variability.

Australia↗
PubMed1980

Comparison of mesiodistal crown diameters of the deciduous and permanent teeth in Australian aboriginals.

Mesiodistal crown diameters of corresponding deciduous and permanent teeth were compared in 106 male and 66 female Aboriginal subjects from Yuendumu in the Northern Territory of Australia. On average, the size relationships were similar to those reported for Caucasoid groups but there was considerable variation between subjects, particularly in the deciduous first molar--permanent first premolar comparison.

Australia↗
PubMed1980

Correlations between crown diameters of the deciduous and permanent teeth of Australian Aboriginals.

Correlations between crown diameters of corresponding teeth and tooth groups in the deciduous and permanent dentitions are reported for Australian Aboriginals. Size associations for within-dentition comparisons were stronger than those for between-dentition. Furthermore, correlations tended to be greater for corresponding tooth groups than for single teeth both within and between dentitions. This co-ordination appears to be well marked in Aboriginals compared with other populations.

Australia↗
PubMed1979

Family studies of tooth size factors in the permanent dentition.

Correlations between dimensions of the permanent teeth in Australian Aboriginals were studied by factor analysis to disclose the main sources of shared variability. Findings indicated that in both males and females most of the common variability in the tooth dimensions could be accounted for by factors representing mesiodistal size of anterior teeth, buccolingual size of anterior teeth, generalized size of the premolars and generalized size of the molars. Factor scores derived from the analysis were used to calculate intraclass correlations among brothers and among sisters. These correlations tended to be higher for the factors contributing most to the common variability indicating that the factors might represent fields under direct genetic control. There was no trend for intraclass correlations among siblings derived from multivariate scores to be consistently higher than those based on observed tooth dimensions. The main advantage to the user of factor analysis is the ability to interpret associations between interrelated variables more objectively than is possible by conventional correlation methods.

Cuspid↗
PubMed1978

Inheritance of tooth size in Australian aboriginals.

The purpose of this study was to clarify the question of inheritance of tooth size, with particular reference to the role of the sex chromosomes. Data were obtained from the dental casts of Aboriginals living at Yuendumu in the Northern Territory of Australia, who had participated in a longitudinal growth study extending over 20 years. The compilation and verification of comprehensive genealogical records gathered over a number of years enabled the analysis of family data. Product-moment correlation coefficients between different full-sibling and half-sibling pairs were calculated for permanent tooth size. Values of individual and average correlation for both mesiodistal and buccolingual tooth diameters conformed with the theoretical correlations expected assuming polygenic inheritance. However, no evidence of sex chromosomal involvement was found.

Australia↗
PubMed1978

Heritability of permanent tooth size.

The aim of this investigation was to quantify the relative contributions of genetic and environmental influences to the observed variability of permanent tooth size in a group of Australian Aboriginals. Tooth size data were obtained from dental casts of Aboriginals living at Yuendumu in the Northern Territory of Australia. The custom of polygyny practised by these people enabled the analysis of associations between full-siblings and half-siblings. Phenotypic variability of tooth size was partitioned into four variance components; between sides, between fathers, between mothers and between offspring. From these components, the relative genetic and environmental contributions were quantified and heritability estimates for tooth size derived. Additional estimates of heritability were obtained by regression analysis from a small sample of parent-offspring data. Results of the analyses suggested that about 64% of the total variability of permanent tooth size could be attributed to genetic factors, while a further 6% was due to common environment. Although the findings confirm a relatively strong genetic component, they emphasise the importance of non-genetic influences in the determination of tooth size variability.

Australia↗
PubMedDate not supplied

Decline in enamel hypoplasia in relation to fluoridation in Australians.

Enamel hypoplasias are thought to represent calcification disruption indicative of metabolic stress during development. Hypoplasias of permanent maxillary central incisors and mandibular canines have undergone a notable reduction in frequency between Euro-Australian twins born around 1965 and those born ca. 1990. Even when scored very liberally these linear defects are 3.1-4.6 times as prevalent in the earlier Australians, and the discrepancy is proportionately greater among strictly scored defects. Likely correlates of this secular trend logically include reduced childhood fevers and clinical intervention to reduce circum-natal stresses acting on cotwins. However, fluoridation of metropolitan water has emerged as the statistically strongest hypoplasia-preventing factor.

Adult↗
PubMedDate not supplied

Adolescent growth in height of Australian aboriginals analysed by the Preece-Baines function: a longitudinal study.

Adolescent growth in height was studied in 62 Australian Aboriginal children enrolled in a longitudinal study at Yuendumu in the Northern Territory of Australia. A direct-search method for minimization of the Preece-Baines Model 1 function was used to estimate mean constants and biological parameters describing the adolescent growth. There were few differences between Aboriginal and British children in the ages at take-off (TO) and peak height velocity (PHV), in adolescent gain or in the percentages of adult height achieved at TO and PHV. Aboriginal boys, however, were shorter than British boys at TO, PHV and adulthood. PHVs in the Aboriginals, 10.3 cm/yr in boys and 8.4 cm/yr in girls, were higher than in British children. In the light of known levels of infant mortality and morbidity at Yuendumu between 1953 and 1970, it is suggested that the high PHVs may be indicative of 'catch-up' growth following early childhood retardation.

Adolescent↗
PubMedDate not supplied

Size and shape of mandibular first molars in Down syndrome.

The size and shape characteristics of permanent mandibular first molars were compared in a group of young males with Down syndrome (DS) and a control group of normal males. Generalized size was quantified by the log transforms of five intercusp distances and shape by a principal component analysis of the log distances scaled to constant size. On average the DS molars were smaller than the controls by 8%, the most marked reduction being in the distance between the distal and distolingual cusps. The scores on two of the four components of shape also differed between the DS and control teeth. These two shape components, which accounted for over 41% of the total shape variation, were determined specially by the occlusal morphology of the distal crown region. Discriminant function analyses also indicated the importance of the distal regions in discriminating between control and DS molars. Evidence suggests that trisomy 21 is associated with a general retardation in growth. The observed features of DS molars were consistent with decreased cellular activity in the developing tooth germs, producing morphological changes that were more pronounced in the later-forming crown regions.

Adult↗
PubMedDate not supplied

Dental characteristics of patients with Duchenne muscular dystrophy.

A comprehensive assessment of the dental characteristics of 23 patients with Duchenne muscular dystrophy (DMD) was carried out, based on dental records, oral examinations and dental models. Decreasing muscle function was associated with increased plaque and calculus accumulation, leading to gingival inflammation, but caries experience was low. Disturbances in tooth form, number and eruption of the second premolars were observed in 39% of patients. Anterior and posterior open bites were common, associated with lip incompetence, mouth breathing, macroglossia and tongue thrusting. Maxillary and mandibular arch breadths were significantly larger, on average, in the DMD group than in controls. Rather than a normal parabolic arch form, the dental arches in DMD patients tended to be hyperbolic, with the posterior teeth being displaced buccally, consistent with an imbalance between the lingual and facial musculature.

Adolescent↗