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Biomedical subjects

L C Richards

Publications and source records attributed to L C Richards.

At least 37 records · Page 2Linked to original sources
PubMed1990

Tooth wear and temporomandibular joint change in Australian aboriginal populations.

The masticatory system consists of teeth, temporomandibular joints, and the supporting craniofacial skeleton. The form and function of each of these components of the system can be understood only within the overall context of the system. In a series of studies, the complex relationships between tooth wear and temporomandibular joint morphology and pathology were considered in samples consisting of a total of 58 male and 54 female crania from two Australian Aboriginal populations. The extent and buccolingual direction of tooth wear were assessed using established techniques. Both metric and nonmetric descriptions of temporomandibular joint morphology and pathology were developed. Significant differences in patterns of tooth wear and in the frequencies of various temporomandibular joint changes were evident between sexes and between populations. Furthermore, significant correlations between a number of tooth and joint variables were also evident. In addition, there was clear evidence of relationships between both tooth wear and temporomandibular joint changes and craniofacial morphology. The results of this study provide additional evidence of the complex relationships between the form and function of the masticatory system.

Adult↗
PubMed1990

Dental arch morphology in south Australian twins.

Fourth-order polynomials were used to represent dental arch morphology in 29 monozygous and 19 dizygous like-sexed twin pairs, and in 45 unrelated individuals. The polynomial coefficients provided an accurate description of dental arch morphology with the quadratic (chi 2) and quartic (chi 4) terms reflecting arch shape and the linear (chi) and cubic (chi 3) terms summarizing asymmetry. There were no significant differences between the groups in either the quadratic or quartic terms. Values of correlations between polynomial terms indicated that there was no consistent relationship between maxillary and mandibular arch shape or asymmetry. Intraclass correlations between twins suggested that genetic factors contributed to variation in maxillary arch shape and to a lesser extent to variation in mandibular arch shape but not to arch asymmetry.

Adolescent↗
PubMed1990

Variability of palatal dimensions in South Australian twins.

Estimates of genetic contributions to variability in three palatal dimensions were obtained from a sample of 70 pairs of South Australian twins aged between 11 and 26 years. Palatal width and length were measured directly from dental models, while palatal height was assessed indirectly from moiré contourographs. For each of the three palatal variables there was evidence of significant genetic variance, with heritability estimates for palatal width and height generally exceeding those for palatal length. Furthermore, palatal height measurements displayed greatest relative variability and strongest correlation between monozygous twins (r = 0.95), suggesting that this dimension could be useful as an additional comparative feature in forensic odontological investigations.

Adolescent↗
PubMed1990

Genetic and environmental determinants of dental occlusal variation in twins of different nationalities.

We have compared 10 occlusal traits in 358 monozygous and dizygous twin pairs in 4 different samples and estimated genetic variances for these features. Variable and frequently nonsignificant genetic variance was noted across samples for incisal overbite and overjet, sagittal molar relationship, posterior crossbite, and rotations and displacements of anterior teeth. Heritability estimates (when appropriately calculated) were low in magnitude (0-40%) and erratic, emphasizing the importance of environmental influences on occlusal variation and the variability of apparent genetic determinants with respect to the environment or population in which they are measured.

Adolescent↗
PubMed1989

Discriminant function analysis of clinical and psychological variables in temporomandibular joint pain dysfunction.

Detailed clinical, psychological and illness behaviour information was obtained from 43 patients with temporomandibular joint pain dysfunction. A discriminant function analysis was performed on the multiple variables to test their effectiveness as predictors of a successful response to simple conservative therapy. The questionnaire and statistical methodology employed are described in detail. It was found that clinical, psychological, and illness behaviour factors when used alone were poor predictors (less than 60 per cent) of treatment outcome. However, grouping clinical and psychological factors resulted in over 80 per cent successful prediction.

Adult↗
PubMed1989

[Three-dimensional measurement of the maxillary first molar in Australian whites].

The occlusal surfaces of upper first molars of Australian Whites were measured in three dimensions with the aid of moiré contourography. The dental casts had been collected from Australian White twins who were considered to be of European stock and the casts housed in the Department of Dentistry, The University of Adelaide, South Australia. In the present study, our first aim was to describe the three-dimensional features of occlusal surfaces of molars in Australian whites. One cast was selected from each monozygotic twin pair at random. A total of 24 males and 15 females were photographed. The results obtained in the present study were compared with those of other human populations previously reported. Cusp height of Australian Whites showed intermediate mean values among 8 populations, but mean intercuspal distances were smaller. This feature, such as small size of occlusal surface but relatively high cusps, also found in Dutch and Asiatic Indian. Mean cusp heights in this population of showed similar values between sexes. Mean differences were insignificant as in Asiatic Indian, Australian Aboriginals, and Bantu unlike the Mongoloid, Japanese and Eskimo populations, where there were significant sex differences in cusp heights. This sexual dimorphism in cusp height among human populations is discussed phylogenetically and functionally.

Australia↗
PubMed1988

Degenerative changes in the temporomandibular joint in two Australian aboriginal populations.

The frequency and severity of degenerative changes in the temporomandibular joints in two Australian Aboriginal populations with different patterns of tooth wear, craniofacial morphology, and temporomandibular joint morphology were examined. The incidence of degenerative changes differed between groups and between sexes and increased with age, ranging from zero in the youngest groups to 65% in the oldest, most severely affected group. Degenerative changes of the fossa were more frequent than condylar changes. Significant associations between degenerative changes and both the pattern of tooth wear and aspects of facial morphology were also evident.

Adult↗
PubMed1987

Temporomandibular joint morphology in two Australian aboriginal populations.

The morphology of the temporomandibular joints in two Australian populations with previously established differences in patterns of tooth wear and craniofacial morphology did not differ significantly from that described in other comparable populations. The relationships between age and linear and angular measures of joint form were generally not significant, but the shape of the mandibular condyle was age-related, with flattening and cavitation of the posterior and medial aspects being more common in older age groups. Comparison of tooth-wear data in groups with different mandibular condylar shapes suggested that rapid anterior tooth wear was associated with flattening or cavitation of the condyle, while relatively rapid posterior tooth wear was more commonly associated with a convex condylar shape.

Adult↗
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

Prediction of mandibular incisor and canine crowding changes in the mixed dentition.

To test the hypothesis that preeruptive tooth positions and dental arch parameters might forecast crowding changes, a sample of 47 aboriginal children (26 males, 21 females) was selected stringently on the basis of Class 1 characteristics and an untreated dentition unaffected by caries or attrition. Crowding scores, radiographic relationships of 765E, and dental arch dimensions were evaluated for the mixed dentition (Stage 1, 8.91 +/- 1.05 years) and earliest emergence of the permanent dentition (Stage 2, 12.48 +/- 0.97 years). Changes between the stages were calculated and the sample was divided into two groups, according to an increase (Group 1) or decrease (Group 2) in incisor and canine crowding. Multivariate and multiple regression analyses were used to identify predictors (Stage 1 radiographic and dental arch parameters) of incisor and canine crowding behavior. Dental arch form and tooth size were important factors in measuring the amount of incisor or canine crowding at Stage 1 and Stage 2. Neither the radiographic nor the dental arch predictors proved useful in forecasting crowding changes. Group 2 dental arches tended to be initially narrower, shallower, and more crowded; however, they showed greater molar and canine width expansion and lessened arch depth reduction than Group 1 cases. Many cases showed a reduction in canine crowding from mixed to permanent dentition. This appeared to be largely independent of the observed incisor crowding. Sexual, racial, and individual variations in dentofacial pattern reinforce the need to carefully consider interceptive extraction or space-regaining therapy for each patient because of the unpredictability of crowding behavior during the transition from mixed to permanent dentition.

Australia↗
PubMed1985

Histopathology of the mandibular condyle.

Histological sections of mandibular condyles surgically removed from 40 female and 12 male patients who failed to respond to conservative management of temporomandibular joint related problems were examined. The proliferation, intermediate and cartilage zones were frequently either partly or completely absent in older subjects confirming previously held views of the functional significance of these zones. There was no obvious sex differences in the histological appearance of the condyle and evidence of inflammatory change was rarely seen.

Adolescent↗
PubMed1985

Dental attrition and craniofacial morphology in two Australian aboriginal populations.

This study considers the craniofacial morphology of two Australian Aboriginal populations with different patterns of tooth wear. Evidence of regional variation in cranial and facial morphology is provided by significant differences in a number of variables. In addition, the intergroup differences in the correlations between attrition and facial variables provide evidence of different adaptive and compensatory changes occurring in each group in response to the different patterns of tooth wear.

Australia↗
PubMed1984

Principal axis analysis of dental attrition data from two Australian Aboriginal populations.

Dental attrition scores from two distinct Australian Aboriginal populations were compared by principal axis analysis. The first group was composed of members of the Narrinyeri group who occupied the river basin and mouth of the River Murray. The second group consisted of members of the Kaurna tribe who occupied the coastal plain to the west of the Narrinyeri. The groups were isolated both physically and culturally and as a result differences in patterns of tooth wear might be expected. In the Narrinyeri sample, attrition tended to be more rapid in females for all but the anterior teeth. The only sex difference in the Kaurna was for the maxillary central incisors, which wore more rapidly in females. Interpopulation differences in the pattern of tooth wear were also evident. The incisors, canines, and premolars of Kaurna subjects tended to wear more rapidly, while the rate of posterior tooth wear tended to be greater in the Narrinyeri. The application of the principal axis method to quantitative attrition data provided a sensitive, objective evaluation of tooth wear. The reasons for the observed differences between the two groups are still not completely clear but may reflect both functional and morphological differences between groups.

Australia↗