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Biomedical subjects

R H Potter

Publications and source records attributed to R H Potter.

At least 37 records · Page 2Linked to original sources
PubMed1983

Dental size traits within families: path analysis for first molar and lateral incisor.

Previous works on the inheritance of dental traits have traditionally followed Fisher's model for family data under the assumption that phenotypic similarity between relatives is due solely to genetic factors. This study uses recent causal models that incorporate the contribution of nonrandom environmental sources of variation to familial resemblance on dental size. Path analysis was applied to observed interclass and intraclass correlations of sex-specific parent-offspring and sib pairs in 293 Pima Indian families from the southwest United States. The mesiodistal dimension of an early-forming and stable tooth (first molar) was contrasted with a late-forming and variable tooth (upper lateral incisor) for genetic and familial environmental components of variation. Parameters were estimated according to the XTAU models of Rice et al. (1980) and linear constraints placed upon the parameters were tested. The proportion of variance accounted for by genetic and environmental transmissible factors is estimated to be 52% for the first molar and 35% for the lateral incisor. Neither X-linkage nor sex-specific environmental effects are required to explain the transmission of dental size. Nontransmissible environmental effects that account for sibling correlations are detectable. Furthermore, sex differences are found in correlated sibling environments for the lateral incisor but not the first molar, to explain in part male-female differences in the distributions of the upper lateral incisor size.

Female↗
PubMed1983

Fluctuating asymmetry in molar dimensions and discrete morphological traits in Pima Indians.

Asymmetry in mesiodistal and buccolingual crown diameters and in eight morphologic crown traits of permanent first and second molars was analyzed in a large Pima Indian sample. Analysis of antimeric differences indicates no consistent evidence for directional asymmetry in Pima molars for either dimensions or morphologic traits. Second molars show greater degrees of metric and morphologic asymmetry than first molars. There is no conclusive evidence for either sex differences in magnitude of asymmetry or relationships between tooth size and morphologic asymmetry. Nonparametric correlations computed between asymmetry in crown dimensions and morphological traits show no significant interaction except where morphological trait development affected crown measurements. The distributions of antimeric differences for dimensional and morphologic traits demonstrate significant leptokurtic deviations from normality. This indicates fluctuating asymmetry in Pima Indians may result from several different sources of developmental variation.

Arizona↗
PubMed1983

Changing occlusal variation in Pima Amerinds.

Occlusal variables and arch measurements have been recorded on 341 Pima Amerinds pertaining to two samples, one of older individuals raised on traditional diets, the other of younger individuals raised on refined commercial foods that are typical of modern urbanized people. Permanent dental occlusion is significantly more variable from defined ideals in the younger sample, despite their fewer deformities resulting from progressive aging. The youths had relatively narrower palates, correlating with a general trend among industrialized populations and also among experimental animals fed soft diets. Relative rate of deciduous tooth loss and replacement did not correlate with any occlusal variable.

Adult↗
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↗
PubMed1982

Professional performance among dental students: a factor analysis.

This study uses factor analysis of dental school performance to extract the underlying factors that are inherent in a set of a student's grades and to evaluate whether a given grade may be associated with more than one factor. Results suggest that overall performance is associated with factors that may be identified as basic science, dental science, and manual skill. The dental science factor appears to be developed during professional training and tends to be less clearly defined that the basic science and manual skills factors, respectively, the associations of clinical course grades with the defined factors are generally low, reflecting the complex involvement of dental clinic performance. It is reasonable to speculate, therefore, that dental school grades, when compounded together as overall GPA across the basic abilities of the students, constitute a likely source of variation that accounts for difficulties in prediction studies when they are used as criterion variables.

Clinical Competence↗
PubMed1982

A derived basic ability criterion for predicting dental students' performance.

This study represents an attempt to develop a valid criterion for predicting students' performance while in dental school. Dental students' overall grade point averages were partitioned into component measures of relevant basic ability clusters in terms of factor scores. The derived indices were used as criterion variables in simple and multiple correlation and regression analyses, with Dental Admission Test (DAT) and predental college scores as predictors. Results showed that basic science abilities were associated with the preprofessional academic predictors, and manual skills with the DAT Perceptual Motor Ability Test (PMAT) scores. None of the presently available preprofessional predictors, taken singly or together, were correlated sufficiently with the factor-associated dental science performance or the nonfactor-associated dental clinical performance for effective prediction. Findings that the development of dental and clinical proficiency at the predoctoral level depends neither on available predictors nor on preprofessional background in the basic sciences have implications for traditional admission policies.

Clinical Competence↗
PubMed1981

Developmental correlates of crown component asymmetry and occlusal discrepancy.

To improve our understanding of dental asymmetry, more anatomically discriminating measurements than maximum crown dimensions were used. The relation between antimeres and opponents in permanent first molar teeth of 192 twins were studied with respect to crown components measures. Several statistical methods were used to describe asymmetry and discrepancy of occluding units to correlate with developmental stress indicators such as zygosity, birth weight, and congenital disease. To varying degrees, developmental correlates are found to be associated with asymmetry. The amount of occlusal discrepancy seems to be a direct function of bilateral asymmetry. Heterogeneity of MZ-DZ total (among plus within pair) variances occurs fairly consistently for asymmetry but not for discrepancy, implying differential environmental influences between zygosities regarding asymmetry. Genetic variance estimates, designed to be unbiased by differences in environmental variances, are significant for cusp size but not for asymmetry. Our results suggest that asymmetry at the individual cusp level may be an indicator of developmental disruption and that environmental effects, particularly prenatal, may be greater for antimeric units than for occluding units.

Birth Weight↗
PubMed1981

Dimensional characteristics of the Filipino dentition.

This study concerns odontometric analysis of the Tagalog Filipinos in Manila, Philippines. Mesiodistal and buccolingual dimensions of the permanent dentition, a total of 56 variables, were studied in 100 males and 152 females. Results showed that their absolute tooth size was small. Relative tooth size, however, seemed to reflect their Southeast Asian Mongoloid origin. From univariate analysis, considerable male-female differences were shown in most of the variables studied. When correlation effects among the teeth were held constant through multivariate analysis, male-female distance was found to be small and substantial overlapping of the two multivariate distributions was evident. Only four variables could be shown by stepwise discriminant analysis to contribute significantly to the distance. Even the mandibular canine, as the strongest discriminator, could only account for 16.4% of the total multivariate distance. These contrasting findings for sex dimorphism in a set of teeth taken singly and taken jointly indicate that there are factors other than the teeth themselves that are expected to play important roles in determining overall male-female size differences in the set of teeth, and that these differences may not be as clear-cut as univariate analysis suggests.

Adolescent↗
PubMed1981

Variance of occlusion traits in twins.

To reexamine the prevailing concepts of the role of genetic and environmental factors on dental occlusion, individual occlusal traits were studied in 164 pairs of twins. The measured variables were overjet, overbite, crossbite type and extent, buccal segment relationship type and extent, anterior and posterior teeth malalignment, spacing, treatment priority index scores, and the principal components derived from these measures. No association of twin type with the mean of any of the traits could be demonstrated. Further analysis of variance revealed separate sources of twin variance for the set of occlusal variables studied. We were able to detect a significant genetic source of variation for overbite and spacing, and no variance inequality between monozygotic and dizygotic twins. For the majority of the trains (overjet, crossbite, buccal segment relationship, malalignment, and treatment priority index scores), tests of homogeneity of total variance showed inequality between zygosities. The total among-pair and within-pair mean squares were larger for dizygotic than for monozygotic twins. We interpreted the results as evidence for greater environmental influences on the two types of twins. In addition, environmental covariance appeared to be larger for monozygotic than for dizygotic twins with respect to crossbite. In cases where within-pair genetic variance estimates were highly significant, removing the bias due to unequal environmental effects on the two types of twins led to results of no significant genetic variance. These results indicate a further need to explore the sources of environmental variation contributing to the difference. Genetic models that may be used to gain insights into the sources are discussed.

Adolescent↗
PubMed1980

Genetic analysis of occlusal variation in twins.

Orthodontists usually assume that genetic factors are of major significance to the development of malocclusion. Studies of twin similarities have lent support to this concept. Use of the twin model to estimate genetic variance, however, involves the assumptions that there are no mean or total variance inequalities between monozygotic and dizygotic twins. The environmental (including biologic) differences between monozygotic and dizygotic twin development may therefore constitute a source of bias. Genetic variance and heritability were estimated for a series of arch and occlusal traits in sixty twins using recently developed methods that are unbiased by variance heterogeneity between zygosities. Heterogeneity was demonstrated for twenty of the forty traits, suggesting considerable amounts of hidden environmental determinance. Tooth-displacement means differed between monozygotes and dizygotes, indicating bias in that trait's genetic variance analysis. Significant heritability could not be demonstrated for overbite, overjet, buccal segment relation, total tooth displacement, and occlusal discrepancies in arch shape. Arch size, individual tooth displacement scores, and cross-bite show significant genetic variance, averaging only about 36 percent of the total variance of these traits.

Adolescent↗
PubMed1980

Tooth movement and dimensional change of denture base materials using two investment methods.

This in vitro investigation evaluated methods of investing a maxillary denture (1) by using a silicone rubber and gypsum base covering all the artificial teeth and (2) by following the generally accepted procedure of investing in a total gypsum environment. The amount of vertical opening found in dentures processed with silicone investment was approximately the same as for those processed with the all-gypsum technique, the horizontal movement of the teeth was more lingual in the silicone investment technique. Comparing the weight of the residual impression between the denture base of acrylic resin and the master die showed no significant difference between the silicone investments and the gypsum technique. The relined denture base provided a more accurate fit than a heat-cured denture processed in both types of investment, silicone and all-gypsum. Finally, a special device was developed that permitted tooth movement in processed dentures to be measured simply and accurately.

Calcium Sulfate↗
PubMed1979

Association of twin zygosity with the mean and variance of tooth size.

To search for an association of twin zygosity with tooth size, 56 dental variables measured from 65 pairs of twins (43 MZ, 22 DZ) were studied. Results of the t' test for equality of the means showed no association of zygosity with any of the variables in males or in females. Results of the F' test for homogeneity of total variances between zygosities showed evidence for unequal total variances in 15 variables in males and 13 in females. Sex influence was further noted on the association of zygosity with the variance of tooth size. Where total variances were unequal, genetic variance estimates differed when only the within-pair mean squares were used and when combined estimates designed to be unbiased by differences in environmental variances were used.

Female↗
PubMed1977

Semiautomated method for the fluorometric determination of total vitamin C in food products.

A simple method employing simultaneous extraction and oxidation has been developed for the semiautomated determination of ascorbic and dehydroascorbic acids in food products. Recovery studies were conducted on ready-to-eat breakfast cereals and both fresh and canned fruits and vegetables, with average recoveries of 101, 100, and 102%, respectively. Reproducibility data were generated showing a relative standard deviation of 3.5%. The automated method was compared with the manual AOAC fluorometric method and with indophenol titration; correlation coefficients were 0.9960 and 0.9926, respectively. The hydrolysis product of dehydroascorbic acid, 2,3-diketogulonic acid, a reported interference in this method, was prepared and shown not to form an interfering fluorescent derivative.

Ascorbic Acid↗
PubMed1976

A twin study of dental dimension. I. Discordance, asymmetry, and mirror imagery.

Bilateral tooth measurements in twins are partitioned into three orthogonal contrasts, each associated with one degree of freedom, to estimate three parameters: discordance, asymmetry, and mirror imagery. The probability levels of the within-pair variance ratios were used to test for significance of these estimates. The results provided strong evidences for the existence of significant genetic determinants of almost all of the individual tooth dimensions, but little or no evidence for a genetic basis of asymmetry. The analysis gave no indication that monozygotic twinning was associated with an increased degree of either fluctuating asymmetry or mirror imagery, when compared to dizygotic twins. The data on monozygotic twins further suggested that for most variables examined, the increment of environmental discordance resulting from the twinning phenomena was greater than the developmental noise that caused asymmetry within individual cotwins.

Female↗
PubMed1976

A twin study of dental dimension. II. Independent genetic determinants.

To demonstrate the presence of independent genetic determinants of multiple correlated tooth dimensions from twin data, a multivariate analysis was performed on the covariance matrices of monozygotic and dizygotic within-pair differences for mesiodistal and buccolingual dimensions of 28 teeth of the secondary dentition. The results provided strong evidences that the correlation among tooth dimensions is primarily genetic in origin, probably attributable to the pleiotropic action of either independent genes or groups of genes. Among the genetic factors that were identified, one appeared to affect the maxillary teeth in general while a second influenced primarily the anterior mandibular teeth. There was a striking tendency for homologous measurements on the right and left sides to be associated with the same genetic factor. In contrast, genetic determination of the maxillary and mandibular dentition seemed to be independent of each other, and a wider range of genetic factors were found to influence the mandibular than the maxillary teeth, suggesting that a differential degree of evolutionary stability may have been achieved in the teeth of the two jaws.

Female↗