Principal axis analysis of dental attrition data

The principal axis method is an age independent analysis method for dental attrition data which avoids many problems associated with earlier methods of analysis, correlation and regression. A principal axis equation is determined from the scatter of M1 on X and M2 on Y, and the slope of the equation can be used to indicate rate of wear. High slopes indicate rapid rates of wear. Because rate of wear rather than degree of wear is the parameter of interest, the procedure is age independent. Confidence regions can be calculated to test the distinctness of the slopes. Dental data from three Amerind skeletal samples, Indian Knoll, Hardin Site and Campbell Site, are used to illustrate the technique. Because least squares fits such as the principal axis solution are strongly influenced by the magnitude of variance in the data, two different methods of ordinal data collection are used in this test: Molnar's 1–8 and Scott's 4–40 scales. The Scott scoring system provides more satisfactory results when used in the principal axis analysis technique because of smaller confidence regions. The testing of the technique on other samples is urged.     

Measurements of tooth wear among Australian aborigines: II. Intrapopulational variation in patterns of dental attrition

The possible implications of variations in dental attrition patterns have necessitated a detailed assessment of the types, ranges, and causes of tooth wear. Hear we employ measurements of postcanine occlusal wear facets from a sample population of extant Australian aborigines. A principal components analysis was applied as a tool in determining common types of attritional patterns. It was concluded that the range of intrapopulational variation in dental wear patterns must be attributed to a multiplicity of sources in addition to such commonly cited causes as dietary variations, gender, age, and developmental eruption sequences.     

Longitudinal study of dental arch relationships in Australian aboriginals with reference to alternate intercuspation

The patterns of age change in dental arch breadths and depths were studied longitudinally in Australian Aboriginals, 92 males and 68 females. Three types of change in relative arch dimensions were recognized: a divergent pattern in which the differences between maxillary and mandibular dimensions increased with age, a convergent pattern in which the differences decreased, and a parallel pattern in which the arch differences remained metrically stable. The feature that best distinguished the Aboriginals from Caucasian groups was the high frequency of subjects, 71% of males and 40% of females, who showed a divergent growth pattern. The association between divergent growth in arch breadths and the development of alternate intercuspation, which is characterized by an inability to occlude the teeth on both sides of the arch at the same time, is discussed.     

Expression of the entoconulid (sixth cusp) on mandibular molar teeth of an Australian aboriginal population

The expression and genetic basis of the entoconulid (sixth cusp) on mandibular molars were examined in a geographically isolated group of aboriginals from Yuendumu in the Northern Territory of Australia. Four grades of trait expression, ranging from trace to small, medium, and large cusps, were defined on dental casts of 399 subjects. Frequencies of occurrence were among the highest reported in human populations. Approximately 80% of dm2s showed the trait, whereas frequencies in the permanent dentition ranged from around 50% on M2 to 70% on M1 and 80% on M3. The degree of expression increased distally along the molar series, with only 3% of dm2s showing large cusps compared with 25% of M3s. Fluctuating asymmetry was highest for M2 and lowest for dm2. No strong evidence for sexual dimorphism in occurrence or degree of expression was found. Based on a quasi-continuous threshold model, a genetic contribution to entoconulid variability was observed that was strongest for M1. Significant associations were noted between entoconulid expression on mandibular molars and metaconule expression on maxillary molars, indicating that similar developmental mechanisms may influence these traits. The entoconulid and the metaconule both provide additional bulk on the distal occlusal surface of molar teeth, an area subjected to early wear during mastication in aboriginals.     

Crown diameters of the deciduous teeth in Australian Aboriginals

Mesiodistal and buccolingual crown diameters were measured from dental casts representing the deciduous dentitions of 197 Aboriginal children from the Northern Territory of Australia. Double determination analysis indicated that the semi-automatic recording procedure used was reliable leading to observer errors of no practical significance. Tooth-size was greater in the male subjects but the sexual dimorphism was less marked than in the permanent teeth of the same subjects. The mandibular teeth were more uniform than maxillary with respect to buccolingual size relative to mesiodistal. Extremes of general tooth-size were more marked in the deciduous dentition than in the permanent as a consequence of the relatively large deciduous second molar which in Aboriginals approximates in size the permanent first molar of many other ethnic groups.     

A quantitative analysis of dental attrition rates in the Santa Barbara Channel area

The dentitions of individuals from archaeological sites located along the Santa Barbara Channel were analysed using quantitative methods which allow the accurate assessment of attrition rates. Comparisons of molar wear gradients indicate that attrition rates have decreased significantly through time in the Santa Barbara Channel area.     

Functional relationships between dental attrition and the helicoidal plane

Several quantitative techniques were used to describe and analyze the development of the helicoidal curve of the dentition in a pre-contact sample of 326 native Indians from British Columbia. Results were compared with studies of occlusal patterns in other populations, and anatomical-functional features of the helicoidal pattern were abstracted and generalized. The features that define the helicoidal pattern were found to develop with attrition. The pattern itself, and the complex which produces it, probably have been selected for because they produce an occlusion with an efficient cutting edge and a total complex that provides maximum resistance to the masticatory forces. Studies focusing on the developmental nature of occlusal patterns in early hominid populations would be beneficial in developing a model of the evolution of the helicoidal pattern in modern man.     

Age estimation by dental attrition in an independently controlled early 19th century sample from Zwolle, The Netherlands

This paper reports the investigation of macroscopic aging methods in a skeletal sample from the early 19th century, excavated in The Netherlands and containing a number of individuals of known age and sex. A method is proposed for calibrating age estimations based on dental attrition.     

Ageing and dental attrition in a medieval rural Danish population

The rate of attrition on the permanent molars may depend on culturally and economically determined conditions of living. In order to analyse the relation the probability of having entered the stages of attrition is analysed by means of logistic regression on age at death. It is shown that not all teeth continue to be worn at the same rate throughout life and that there is an association between advanced attrition and risk of dying. The rate of dental attrition does not differ much by sex but there are some indications that male teeth are worn quicker than female teeth. This greater rate of attrition might be due to greater consumption of food in males than in females. The stages of dental attrition give some information on the age at death but they are poor age indicators on their own.     

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.     

Paleoepidemiology of a central California prehistoric population from CA-Ala-329: dental disease

Ala-329 is a prehistoric central California site located on the southeastern margin of San Francisco Bay, dating from approximately 500 AD up to pre-European contact. A large earth mound, Ala-329, has yielded many well preserved burials, approximately 300 of which are included in this study. The most common pathological lesions seen in this population are in the dentition. Advanced attrition is pervasive, affecting all individuals with teeth in occlusion for 2 years or more. Deciduous teeth are involved even in very young children and often show severe wear before replacement. In the permanent dentition, all elements are involved by the second decade; in the oldest age category (41+ years), all individuals show severe wear throughout their dentitions. In fact, by the end of the third decade, the majority of individuals have no enamel remaining. Mild periodontal involvement is found in 74% of adults, socket resorption in 53%, and abscesses in 31% of the relevant sample. Interestingly, although dental abscesses are found more than twice as often among males, socket resorption is seen more often among females. Dental caries are seen in only 10 individuals. The high incidence of periodontal remodeling, socket resorption, and dental abscesses is probably a secondary result of severe dental attrition. It is hypothesized that a large quantity of abrasives in the diet is responsible for the extreme degree of attrition, in fact, among the most severe for any population yet described.     

Contours of maxillary molars studied in Australian aboriginals

Distances from the central pit to the perimeter of the crown of permanent upper molars were measured on standardized occlusal photographs of dental casts representing 210 male and 181 female Aboriginals from Yuendumu in the Northern Territory of Australia. In both males and females the first molar was the largest tooth but it showed least variability. Variabilities of the distances tended to be greater for radii constructed in the buccolingual direction than for the transverse mesiodistal radii. The most marked size reduction in the molar series from first to third related to the distolingual part of the crown, which was also the most variable region. Size differences between molars in the mesial contour radii were not marked. Sexual dimorphism was evident in most crown radii, being most marked for the second molar.     

Development and evolution of the helicoidal plane of dental occlusion

The helicoidal plane of dental occlusion is a composite feature involving axial inclination of teeth and effects of dental attrition. Recent studies disagree on its distribution and significance in hominoid primates. The distribution, development, and functional basis of the helicoidal plane are investigated here, based on quantitative analysis of dental morphology and attrition in 667 human and 60 chimpanzee dentitions. Helicoidal planes are nearly universal in the human and chimpanzee dentitions studied. Increasing axial inclination of molars from M1 to M3 is primarily responsible for the helicoidal plane, although attrition acts to increase its expression. In hominoids, increased molar axial tilt appears to be associated with facial shortening and dental reduction. Population and species comparisons suggest a functional relationship with cranial structure. Progressive axial tilt of molars producing a helicoidal plane is found consistently in mammals with cheek teeth positioned partly under the cranium, as in hominids, pongids, some cebids, macropodids, ursids, and sciurids. Facial shortening is an important trend in hominid evolution and axial inclination of molars might be expected to show progressive change from Australopithecus afarensis to recent Homo sapiens.     

Principal axis analysis of gene frequency data

When a set of populations are compared in respect of gene frequencies, and the chi-square test of heterogeneity is found to be significant, it is pertinent to find out whether the heterogeneity can be explained by a few linear combinations of the gene frequencies, and the total heterogeneity chi-square value can be partitioned as the sum of heterogeneity chi-square values contributed by the linear combinations. The present report describes such a method, and the linear combination that explains the maximum heterogeneity is called the principal axis. An application of this method is presented to find clusters of 31 Mongoloid tribal populations of eastern India using ABO gene frequency data.     

Concepts of occlusion: Australian evidence

Longitudinal studies of aboriginal children over a 20-year period have drawn attention to the wide variation in morphological features of the dentition and the way in which occlusal relationships develop. This paper summarizes some important determinants of optimal occlusal development, namely, tooth size relationships within and between dentitions, the patterns of alveolar growth, and tooth migrations during the transition from primary to permanent teeth and the nature of growth changes in the dental arches. Dental occlusion constantly changes throughout life in response to changing functional requirements. Observations limited to cross-sectional material provide an incomplete, and sometimes misleading, concept of dental occlusion and masticatory function.     

Tooth wear in Australian aboriginal populations from the River Murray Valley

The study of tooth wear among prehistoric and recent populations has frequently been concerned with the rate and pattern of wear over the dental arches. In this report we considered the question of tooth wear variation among collections of Australian Aboriginal crania recovered from several sites along the Murray River in Southeastern Australia. These crania represent the remains of relatively recent populations from about 2,000 years ago until the early 19th century. The degree of tooth wear for each dental arch was recorded by an established method of determining the ratio of exposed dentin. The pattern or distribution of wear over each arch was summarized by principal component analysis. The mean wear degree and pattern were compared among four geographical grouping of crania separated by up to 700 miles of river frontage. Our results showed, as expected, a significant difference between the well-defined population at the Lower Murray site (Swanport) and the three upriver groups. However, there were significant differences among these three collections as well. Sexual dimorphism was noted but was only significant in the Lower Murray group; the mean wear was greater and also more variable among the males. At the second of the Middle Murray sites the pattern of wear was different and the degree of wear was significantly less than in the other groups. A possible explanation for this diversity may be environmental and subsistence base differences. The evidence from the Lower Murray supports this possibility, but the differences among the other three groups are not as clearly established. However, our results do suggest that the Murray Black collection, from which these crania were obtained, may not be as homogeneous a group as previously believed.     

Analysis of dental attrition and mortality in the Medieval village of Tirup, Denmark

New directions and new questions raised in the study of health in the past justify this reanalysis of the pattern of dental attrition in the Medieval Danish population of Tirup. Dental attrition was scored on all permanent molars from the Tirup skeletal sample. Scores were analyzed by means of logistic regression of the probability of having entered a given stage of wear for a given tooth in a way that is very similar to transition analysis. The primary determinant of dental attrition was age at death. In addition to age, the effects of sex, side, and dating were analyzed. In order to assess the homogeneity of the process of wearing teeth down, a third-order polynomial in age-at-death was also fitted to the transition probabilities. It was found that age is the single most important determinant of dental attrition, and that sex or side did not differentiate the rate of attrition. In several transitions, there was evidence of heterogeneity, indicating both random and systematic interpersonal differences in the rate of attrition and an association between the rate of attrition and age-at-death. It was found that attrition proceeded more quickly after AD 1300 than prior to that date. It is suggested that this was due to a possible general deterioration of living conditions in Northern Europe and an increased reliance on grain for food during the first half of the 14th century. The temporal effect on attrition rate accounts for some but not all the observed heterogeneity wear.     

Microbiological air analysis in dental surgeries: a comparison between two methods

The microbiological quality of indoor air is creating an increasing interest especially as far as places at risk such as hospitals, clinics, medical and odontological surgeries are concerned. Working with the odontologists of our province we have been carrying out a research aimed at preventing cross-infection in odontology. Data obtained from the microbiological analysis of the air in 36 surgeries using S.A.S. were discussed during the V National Congress of Aerobiology. During that congress the need of setting a standardized technique of air sampling in indoor environments emerged and two routes have been identified: (1) the gravimetric technique on open plate exposed for an hour close to the dental unit and (2) the use of the volumetric sampler which gives qualitative data expressed as colonies forming units per cubic metre of air. However, both of these techniques present some problems: using the first a loss of micro-organisms has been noticed due to the variability of the air fluxes and the different weight of the biological particles; using the second one the bacterial charge is also undervalued, because of the stress suffered by the bacteria with the use of the volumetric sampler. In the light of these statements we decided to use both in dental surgeries to be able to compare the results obtained. Our project is expected to carry out at least one inspection and the relative sampling (indoor air, water of the dental unit, air of the syringe, disinfectant solution, surface tampons, biological test of sterility) in each dental surgery in the territory of our health Unit, located in Ferrara, Northern Italy.     

Microbiological air analysis in dental surgeries: A comparison between two methods

The microbiological quality of indoor air is creating an increasing interest especially as far as places at risk such as hospitals, clinics, medical and odontological surgeries are concerned. Working with the odontologists of our province we have been carrying out a research aimed at preventing cross-infection in odontology. Data obtained from the microbiological analysis of the air in 36 surgeries using S.A.S were discussed during the V National Congress of Aerobiology. During that congress the need of setting a standardized technique of air sampling in indoor environments emerged and two routes have been identified: (1) the gravimetric technique on open plate exposed for an hour close to the dental unit and (2) the use of the volumetric sampler which gives qualitative data expressed as colonies forming units per cubic metre of air. However, both of these techniques present some problems: using the first a loss of micro-organisms has been noticed due to the variability of the air fluxes and the different weight of the biological particles; using the second one the bacterial charge is also undervalued, because of the stress suffered by the bacteria with the use of the volumetric sampler. In the light of these statements we decided to use both in dental surgeries to be able to compare the results obtained. Our project is expected to carry out at least one inspection and the relative sampling (indoor air, water of the dental unit, air of the syringe, disinfectant solution, surface tampons, biological test of sterility) in each dental surgery in the territory of our health Unit, located in Ferrara, Northern Italy.