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Biomedical subjects

G C Townsend

Publications and source records attributed to G C Townsend.

At least 73 records · Page 4Linked to original sources
PubMed1986

Metric analyses of the teeth and faces of South Australian twins.

Procedures are described for the acquisition and analysis of data in a study of the dental and facial characteristics of South Australian twins. Comparisons of the mesiodistal diameters of maxillary incisors in MZ and DZ twins revealed heterogeneity of total variances and evidence of inequality of mean values for some dimensions between MZ and DZ twins. Previous estimates of heritabilities for tooth size, relying on classical assumptions in twin research, may be exaggerated. A preliminary analysis of facial shape was undertaken using a procedure for shape matching based on a least squares fit of homologous coordinates. There was evidence of mirror-imaging in some MZ twin pairs and differences in facial asymmetry between male and female DZ twins. Future extensions of the study using methods for three-dimensional shape analysis are described.

Adolescent↗
PubMed1985

Intercuspal distances of maxillary pre-molar teeth in Australian Aboriginals.

Intercuspal distances and mesiodistal and buccolingual crown diameters of maxillary pre-molars were recorded from dental casts of 262 Australian Aboriginals. Although mesiodistal and buccolingual dimensions showed sexual dimorphism, no significant differences were noted between the sexes for intercuspal distances. Intercuspal dimensions showed greater variability and fluctuating asymmetry than did either of the traditional measures. No significant differences in heritability were noted among the three dimensions. Correlations between mesiodistal and buccolingual dimensions were higher than those between buccolingual and intercuspal measures. It appears that the sex differences, which are observed in overall crown dimensions, are established after the cusp tips are localized. Intercuspal distances appear to have a strong genetic component of variability, although they show high phenotypic variability and fluctuating asymmetry. Total tooth size may be subject to more intense selective pressures than the sites of initial calcification.

Australia↗
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

Bruxing patterns in man during sleep.

Nocturnal clenching was monitored using a dedicated microprocessor, appropriate EMG amplification and digitisation. The hardware was located at the subject's bedside and the software provided for the real time recording of clenching bruxism, duration of the episode and the severity in electronic values. Forced clenches before retiring and on arousing provided maximal baseline data against which to compare the severity of sleeping clenches. All ten subjects tested were found to brux and two used intensities of effort while asleep that exceeded their maximal conscious clenches.

Adult↗
PubMed1984

Distribution of nocturnal bruxing patterns in man.

The distribution of nocturnal bruxing patterns in nine subjects was recorded and interpreted in accordance with current concepts of sleep physiology. Few bruxing events were seen in the first 2 h of sleep but peak periods were identified during the night. The findings suggested that bruxism and REM sleep were closely associated and pointed towards a central aetiology for bruxing activity.

Bruxism↗
PubMed1983

Molar size sequence in Australian Aboriginals.

Percentage frequencies for molar size sequence of first and second molars were calculated in a group of contemporary Australian Aboriginals using mesiodistal and buccolingual dimensions, as well as crown areas. Comparisons were made between sexes, arches, and dimensions within the Aboriginal group and also between Aboriginal data and those published for other populations. The frequencies of the M2 greater than M1 molar size sequence in the Aboriginals fell within the range of frequencies reported for other contemporary populations. Differences in the frequencies of the M2 greater than M1 sequence between the sexes and between arches, together with the relatively high frequency of asymmetry in molar size sequence within Aboriginals, supported the notion that local environmental conditions acting during odontogenesis, together with differential responses to other environmental influences, play an important role in determining observed patterns of molar tooth size.

Australia↗
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

Tooth morphology in Down's syndrome: evidence for retardation in growth.

Two dental morphological features, lower incisor shape and Carabelli trait on upper molars, were studied in Down's syndrome (DS) individuals and control groups. Lower incisors were smaller in DS in absolute terms, but showed a relatively greater mesiodistal crown dimension than labiolingual, the opposite relationship to normal. Although the Carabelli trait was present in a high percentage of DS subjects, few showed the cuspal form. These findings are consistent with the concept of a reduction of cellular activity of tooth germs reflecting a general retardation in growth in DS. The altered shape of the lower incisors may influence the pattern of periodontal disease observed in DS subjects.

Down Syndrome↗
PubMed1983

Craniofacial growth in young marmosets (Callithrix jacchus).

A cross-sectional study of craniofacial growth in young marmosets was performed. Selected linear craniofacial measurements were obtained from groups of 5 animals of each sex at 3 monthly intervals from birth to 1 year. These data provide a baseline for comparison with other colonies and in the assessment of teratogens on craniofacial development.

Aging↗
PubMed1983

A comparison of craniofacial growth between two colonies of marmosets (Callithrix jacchus).

General and craniofacial measurements from young marmosets in a recently established Australian colony are presented and compared with similar data published for a long-established colony in the United Kingdom. Statistically significant differences between the colonies were those associated with large error variances, suggesting difficulties in locating certain landmarks rather than real differences in growth. Thus, direct comparison can be made between craniofacial growth studies conducted at these two different marmoset colonies.

Analysis of Variance↗
PubMed1982

The oral effects of prolonged intermaxillary fixation by interdental eyelet wiring.

The oral effects of prolonged intermaxillary fixation were investigated in 106 severely obese patients who had been jaw wired as an aid to weight loss. The principal complications during fixation were episodes of periodontal pain and tooth mobility (40%). After removal of fixation, the principal sequelae were residual periodontal problems (9%) and mandibular limitation (9%). These findings were confirmed in a subgroup of 11 patients who had detailed measurements made of their periodontal index, oral hygiene index and range of jaw movements. These findings were discussed in relation to other methods of management of obesity.

Adult↗
PubMed1981

The effect of locally released oxygen on the development of plaque and gingivitis in man.

An experimental gingivitis study was designed to test the effect of a 5-min twice daily oxygen application on the development of plaque and onset of gingivitis. A method for the local application of medical grade oxygen to the upper anterior teeth was developed, with the lower anterior teeth used as controls. Fourteen periodontally healthy dental students of average age 21.9 years participated in the study. There was no significant effect of oxygen on plaque formation, crevicular fluid flow, or the number of gingival bleeding sites. Experimental and control gingival segments exhibited bleeding on probing at an average of 6.6 days after cessation of mechanical plaque control, much earlier than reported in other experimental gingivitis studies.

Adult↗