AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 62:317-324 (1983) Changing Occlusal Variation in Pima Amerinds ROBERT S. CORRUCCINI, ROSARIO H. YAP POTTER, AND ALBERT A. DAHLBERG Department of Anthropology, Southern Illinois Uniuersity Carbondale, Illinois 62901 (R. S. C.), Indiana University School of Dentistry, Indianapolis, Indiana 46202 (R.H. Yl?), and Uniuersity of Chicago, Chicago Illinois 60637 (A.A.D.) KEY WORDS Dental, Occlusion, Pima, Diet consistency, Malocclusion, Deciduous teeth, Tooth replacement, Arch size ABSTRACT 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. Modern industrialized Western society is characterized by highly variable dental occlusion, often times exceeding limits set by orthodontic consensus for acceptable or good occlusion. Approximately 50% of all American youths show occlusion for which orthodontic treatment is rated mandatory or desirable (Kelley and Harvey, 1977). As with other clinical specialists, orthodontists tend to show more interest in correction than in finding causes. Major textbooks and review articles (cf. Corruccini and Whitley, 1981) concur in considering malocclusion “not abnormal” and predominantly genetic in origin, hence nonpreventable. Various anthropologists or anthropologically oriented dentists have periodically shown that nonindustrialized, nonurbanized populations manifest much lower malocclusion prevalence (see Niswander, 1966; Lombardi and Bailit, 1972; Kaul and Corruccini, 1983 for literature review). The transition from the ancestral state of anatomically ideal occlusion to prevalent bad occlusion has been shown to happen in several groups within one generation upon the acquisition of “modern” (i.e., processed) diet, to annul both the normal-condition and genetic-cause concepts. Similar to heart disease and diabetes which are “diseases of civilization” or “Western dis- 0 1983 ALAN R. LISS. INC eases” (Trowel1 and Burkitt, 1981)that have attained high prevalence in urban society because of environmental factors rather than “genetic deterioration,” a n epidemiological transition (Omran, 1971) in occlusal health accompanies urbanization. Western society has completely crossed this transition and now exists in a state of industrially buffered environmental homogeneity. The relatively constant environment both raises genetic variance estimates (since environmental variance is lessened) and renders epidemiological surveys largely meaningless because etiological factors are relatively uniform. Nevertheless most occlusal epidemiological and heritability surveys are conducted in this population rather than in developing countries currently traversing the epidemiological transition. In this regard, anthropologists have a vital contribution to make in integrating the cross-cultural approach with occlusal epidemiology. Appropriate study populations are disappearing with development. One study sample is the Pima, a reservation Amerindian group from which one of us (A.A.D.) collected about ten thousand dental casts from 1948-1970. Received January 10, 1983; revision received June 30, 1983; accepted July 6, 1983. 318 R.S. CORRUCCINI, R.H.Y. POTTER, AND A.A. DAHLBERG These casts have been studied for evidence of odontometric heritability (Potter et al., 1968, 1983)and differences with fluoride variation in well water. An initial study (Irie and Dahlberg, 1967)presented some occlusal data and concluded that permanent dental occlusion did not change between ages 1216. Extending this comparison to older Pima offers the advantage of assessing occlusal change occurring with dietary change. The Pima traditionally relied on a heavy bean dietary staple grown in their own gardens. Tortillas were also a favorite, the indigenous corn long-cooked and stone-ground. More recently, approximately since 1950, the Pima do not grow their beans, as the all-important country store became the source of commercial beans and processed corn meal. In postwar years the children started receiving good government sponsored dental care, while this has not reached the adults. The dietary transition, considered to be a factor in the dental occlusal epidemiological transition, was fairly subtle in this population, entailing a change from homegrown to commercially purchased versions of the same foods with the latter more refined and more cariogenic. The effect of this and other changes on the Pima occlusion have not yet been considered and are the subject of the present study. MATERIALS AND METHODS A stratified cross-sectional sample from the cast collection was used, in order to represent the various collection times. Records provided exact age, sex, date of casting, and family. If yearly serial casts of the same individual were available, the most recent one (when the individual was oldest) was used. Only those casts were scored that had no missing teeth (congenitally or otherwise), and a t least all but one permanent tooth fully erupted (excluding consideration of M3) such that the full permanent occlusion alone could be assessed. For older individuals (over age 40) it was necessary to allow up to two missing teeth to improve sample size. There were as many as six yearly casts over a nine-year period for younger Pima. Most of the casts of older Pima come from the earlier (1949-1957) series of collections, such that the effects of aging on dentition could be cancelled in the comparison with younger Pima, many of whom were cast between 1963-1969. Average age was 14.7 for young and 27.7 for old Pima. We established lack of correlation of occlusion and age (between 11-30 years) in the young sample, similar to Irie and Dahlberg (1967) and also true of the much larger samples of Kelley and Harvey (1977). Taking 1950 as roughly the cut-off time for traditional Pima diet and considering that dietary effects on permanent occlusion probably act up to 12 years of age, when deciduous premolars are replaced and M2s are erupted, we would expect individuals 30 or younger (by 1969, the last year of casting and the baseline date for this study) to show occlusal effects from dietary change and those over 30 (by 1969) to have developed occlusally during the traditional diet period. The former group was defined as the younger sample and the latter group as the older sample. Every case had two chronological data, the number of years ago born from 1969 (YAB) and actual age at casting. Thus the younger sample consisted of 274 Pima with YAB of 30 or less, and there were 67 older Pima with YAB of 31-50. The minimum age for individuals in the young sample was 11. The variables studied include arch measurements, and measurements and observations of dental occlusal variation (not reflective of “skeletal malocclusion”) taken and modified from the criteria making up the Treatment Priority Index (TPI) described in Kelley and Harvey (1977): Arch Size. Lower arch length (left) was measured from the most anterior point between the cervical margins of the medial incisors to the distobuccal margin of the crown of MI. Upper arch length was from the interincisal point to the distobuccal margin of M1. Arch breadth was measured between the buccal grooves of the MI and M1. Overjet. This is the anterior distance from the most mesial part of the labial surface of the upper central incisor to the labial surface of the opposing lower incisor, measured perpendicular to the coronal plane. Overbite (anterior). With the casts in centric (convenience) occlusion, this is the amount of vertical overlap of the upper central incisor over the lower central incisor taken as a ratio of the total crown height (cervix to incisal edge) of the lower incisor. Cross-bite (posterior). This measures buccal-lingual deviation in occlusion of postcanine teeth (Kelley and Harvey, 197750). Its extent was measured by the distance the mesiolingual cusp of M’ deviated from centric occlusion with the central occlusal fossa of M1 taken as a ratio (in tenths) of the bucco- PIMA OCCLUSAL VARIATION lingual size of the M’ mesiolingual cusp. The measurement was positive if buccal crossbite c M 1 positioned too far to buccal) occurred, and negative when lingual cross-bite was observed, defining crossbite type. The absolute value of this is used to define extent or amount of crossbite. The measure was incremented for bilateral crossbite. Buccal segment relation (BSR). This assesses mesial-distal relations of first molars in centric occlusion (Kelley and Harvey, 1977:49).It was measured as the amount the mesiobuccal cusp of M1 deviated from ideal alignment over the buccal groove of MI, again taken as a proportion of the cusp’s size (that is, a score of 0.5 indicates that the mesiobuccal M1 cusp directly overlies the mesiobuccal cusp of MI). The BSR type measurement was positive for distoclusion (mandibular orthognathism) and negative for mesioclusion (mandibular prognathism), and again absolute value gives BSR extent. Bilateral BSR discrepancy incremented the score. Rotation and displacement (R/D).The rotatioddisplacement score is the sum of the number of teeth rotated or displaced noticeably from ideal alignment, teeth rotated more than 45 degrees or displaced more than 2 mm being counted twice. Anterior and postcanine teeth were considered separately, then added to give the total R/D score. Treatment priority index (TPI). This combined index, designed originally to assess need for orthodontic treatment, is computed according to the method of Kelley and Harvey (1977). However, our only purpose in using it is to derive a n overall measure of occlusal variation that compounds the individual measures. The TPI is only a n epidemiologic variable in the present study and has only internal comparative (not clinical) meaning. With the exception of R/D, all the TPI components are measured along a continuous scale from positive to negative values. Thus, cases of mandibular overjet and of open-bite were entered as negative overjet and negative overbite, respectively. All measurements were made by the same investigator (R.S.C.) with Mitutoyo dial calipers calibrated to 0.02 mm. Like the arch measurements, the occlusal variables constitute ratio-interval data so that parametric statistical techniques may be applied. There was considerable positive skewing in some variables. The one-tailed F 319 test was employed to directionally test the hypothesis that younger and older Pima can be considered a s having been sampled from the same statistical universe regarding variance (frequency and amount of departure from the norm), and the t test was used on the mean values. The F test is more appropriate for measurements of ‘<type’’of occlusal discrepancy and the t test for “extent.” Premature Deciduous Tooth Loss The effect of eruption sequence and premature deciduous tooth loss (PDTL) has caused speculation in discussions of malocclusion etiology. Early shedding of a deciduous tooth, premature eruption of its successor, and a n excessive time lag between those two events are interrelated (Miller et al., 1965; Singh, 1980). Earlier epidemiological results have been quite inconclusive regarding the PDTL factor (Lundstrom, 1955; Miyamoto et al., 1976; Baume, 1973; Corruccini et al., 1983; Anderson et al., 1980). The longitudinal series of Pima casts allows a unique test of PDTL influence in a n occlusally variable population. Teeth lost prematurely due to advanced caries could be identified and considered as a separate category from prematurely lost teeth with no detectable carious involvement. A PDTL score was devised to record noticeable degrees of deciduous tooth exfoliation occurring prematurely from the normal schedule. Due to maturational variation and secular trends (the young sample erupting second molars a year earlier on average than the older sample), it is important to compare tooth succession by a n absolute time schedule and by a relative scale that compares a given tooth to others which ordinarily should be shed earlier or later. Among the younger Pima sample normative ages fell into four categories: permanent incisors replacing deciduous incisors (lower incisors appearing first; central incisors occluding first) a t age 8 or 9, permanent anterior premolar replacing its deciduous predecessor a t age 10, canines and posterior premolars appearing a t age 11 (lower canines appearing first), then by age 11-12 the anterior permanent premolar achieves occlusion, followed by canines and posterior premolars and eruption of the second molars. A deciduous tooth class lost prematurely by one year counted as one point, including maximally 1/2 point counted for a tooth erupting one year earlier than either a normally synchronous antagonist or a n anti- 320 R.S. CORRUCCINI, R.H.Y. POTTER, AND A.A. DAHLBERG BSR type and extent are both significantly more variable in younger Pima, signifying greater average deviation around stipulated norms, and mean BSR extent is significantly larger in the younger Pima. The abnormality is predominantly with mandibular molars being too far anterior, which is usually the case for non-European groups. Only Western European-derived whites tend to show predominant “Class 11” malocclusion with the upper arch displaced anteriorly. When the sexes are separated, differences are still highly significant (x2 = 8.6; d.f. = 1) for males; only eight of 48 older male Pima have cusp-to-cusp or worse BSR anomaly, compared to 96 out of 239 younger males. There is no difference in the much smaller female sample. Postcanine tooth rotation and displaceRESULTS ment is nearly twice as prevalent in the The sexes were very unbalanced with re- young sample with a highly significant difspect to sample size, a total of 287 males and ference between the groups. Displacement of 54 females having been sampled in younger anterior teeth is also less in the older Pima and older groups. The bias resulted from too raised on traditional diet, but more variable few younger females having been cast at a n (A few older Pima had very severely crowded old enough stage of dental maturation (11-12 incisors due to mesial drift.). Although 16.4% years). Every variable was tested for sex dif- of older Pima showed perfect anterior tooth ference, and none was found with the excep- alignment versus 10.6% of the younger, the tion of the metrical arch variables, to agree difference is not significant based on the with Irie and Dahlberg (1967) for Pima, and sample. Total rotation and displacement is Kelley and Harvey (1977)for large American significant between the groups, reflecting the samples. The exception was BSR type, where high incidence of this disorder in the postthe females showed significantly less devia- erior teeth of the younger group. tion from the norm so that this variable was The TPI is smaller, though not significant, compared between old and young samples and less variable in older Pima. Again age with the sexes separated. affects results as some older cases have tooth Table 1 gives basic statistical results. In loss, attrition and mesial migration of teeth terms of incisor overjet, there is a more an- that increases TPI scores, while many others terior maxilla in the younger sample to show maintain remarkably good occlusion. Thus a general trend of modernization (an edge-to- there is a distributional difference, 13 older edge incisor bite actually being the norm in (19.4%)as opposed to 19 younger (6.9%) indiaboriginals). The difference is not significant viduals having perfect TPI scores, i.e., no statistically; the mean of about 3 mm is a t appreciable deviation from ideal anatomical the normative value for American white and occlusion in any variable. The difference is black youths as stipulated by the criteria of significant a t P = .01 by x2 and Kolmogorovthe TPI (Kelley and Harvey, 1977).However, Smirnov tests. older Pima are less variable. The TPI is a valuable method of combining Overbite is quite similar among old and different occlusal variables, but carries unyoung, both samples showing average incisor fortunate connotations of clinical assessoverlap of three-tenths of the lower incisor’s ment. Another approach is to combine crown height; again this is within the ortho- occlusal variables by canonical variates analdontic norm. ysis to find whether a statistical combination Crossbite deviations of transverse occlusal that most effectively discriminates older from relations occur mostly with maxilla to the younger samples is significant. This analylingual side, as in all human populations. sis, where the input included all the nonThere is slightly more crossbite in younger metrical variables, resulted in Mahalanobis’ Pima, but the difference is not significant. D = 0.69(F = 2.78, P < .01) and the means mere. Since four categories are recognized and one must be held constant within the sequence against which to gauge the others, this PDTL score ranges from zero to three by 112-pointincrements. The role played by PDTL in creating occlusal variation could be studied only in the younger subsample where longitudinal casts from about ages 6-12 were available; there were 190 such serial cases. Seven classes of PDTL were erected (from zero to three by 1/2point increments) but the zero and the half-point classes were merged to create a minimum sample of 18 in any class. The numbers were normally distributed over these classes. One-way analysis of variance for six groups was conducted for each occlusal variable according to PDTL. PIMA OCCLUSAL VARIATION 32 1 TABLE 1. Descriptive statistics and t and F tests for arch measurements (mm)and occlusal variables Younger Pima (n Variable Overjet Overbite Crossbite (type) Crossbite (extent) BSR (type) BSR (extent) Posterior R/D Anterior R/D Total R/D TPI Mandibular arch length Mandibular arch breadth Maxillary arch length Maxillary arch breadth - X = 274) S.D. 1.43 0.27 0.16 0.29 0.20 0.40 0.98 3.19 4.16 4.71 t F 1.34* 1.09 2.98 0.28 1.23 0.26 1.56 0.30 0.34 0.11 0.34 0.95 1.00 0.24 0.48 0.33 1.06 2.55 2.88 4.38 0.23 - 0.12 0.24 0.55 2.96 3.51 3.89 0.27 0.31 0.23 0.86 2.63 2.86 3.87 1.48 1.58 4.92* 3.45* 0.65 1.67* 1.56 0.89 2.49* 2.07* 1.53* 0.97 1.02 1.37* 42.71 1.80 41.93 1.81 3.12* 1.01 55.71 2.50 56.48 2.91 1.89** 1.36 47.27 1.95 46.14 2.22 3.76* 1.30 59.84 2.75 60.28 2.71 1.16 1.03 - 3.25 0.29 Older Pima (n = 67) X S.D. *Significant a t the .05 level ** .06 > p > .05. being 6.5 standard errors apart on the discriminant vector. Some 68.3% of the old are discriminated from 64.5% of the young individuals, considerably removed from determinative identification but significantly greater (P < .001) than the random expectation of 50%. The coefficients of discrimination emphasized the variables distal R/D and BSR extent in effecting this separation. From the table, arch lengths are significantly greater in younger subjects, while the difference in arch breadths, though larger in the older, is less significant. This is the maxillary shape trend found in all surveyed industrializing groups with rising malocclusion incidences, that is, relative palatal narrowing (and deepening), relating to the “maxillary collapse syndrome” frequent in American youths (Kelley and Harvey, 1977) and to general facial narrowing (Davies, 1972).The relative effect on length and breadth also relates to aging effects: mesial tooth drift, accentuated by some tooth loss and interstitial attrition, reduces arch length with age. Correlation between maxillary arch length and YAB, with effects of chronological age removed by partial correlation, shows zero rather than significantly negative correlation. Among arch measurements, only maxillary breadth correlated significantly (negatively) with TPI. For occlusal variation in relation to PDTL in the younger sample only, analysis of vari- ance showed no significant differences. The highest F-ratio for any measurement or occlusal variation was 1.85 for distal tooth displacement (.lo > P > .05). PDTL scores in the upper half of the range had somewhat higher R/D counts. The only other variable with a relatively high partitioned variance was overbite (F = 1.691, with the biggest increase in occlusal variation again occurring with PDTL scores of 2 or above. The smallest F ratios were associated with arch measurements. Correlations between PDTL and occlusal variables were examined. All correlations were very nearly zero except those for overbite (r = 0.15) and R/D (r = 0.141, both borderline significant correlations indicating slight increase in vertical incisor overlap and in rotated teeth with more PDTL teeth. One major reason for considering PDTL important to increased occlusal variation with urbanization is the possible relation to caries which, if serious, could cause early tooth loss. For cases with macroscopic carious destruction in deciduous teeth (n = 301, a notation was made and these were later removed from the sample (non-carious n = 160).Among the non-carious cases, correlations were consistently larger (though the difference is slight) between PDTL score and occlusal variables than in the carious cases, where PDTL correlations were all near zero. Whatever the relation between tooth succession and occlu- 322 R.S. CORRUCCINI, R.H.Y. POTTER, AND A.A. DAHLBERG sion may be, it seems to be unconnected to caries. DISCUSSION The older Pima, raised less recently on less refined diets than the younger Pima, are significantly less variable from occlusal ideals in spite of their greater deleterious age changes. The most obvious suspects as causal agents for this difference are dietary change and genetic change. Genetic admixture could only have been extremely slight in the intergenerational time. Orthodontists have often invoked the notion that “race mixture” causes malocclusion (refuted by Chung et al., 1971; Horowitz and Osborne, 1971), in that one may inherit jaw size from one parent which may be disharmonious with tooth size inherited from the other, or malfitting upper and lower jaw profiles from two different ethnic predecessors. Other than this notion, it could also be theorized that the white U S . population has a higher frequency of deleterious alleles for occlusion through accumulating mutations, and that admixture with whites raised the Pima malocclusion prevalence. However, these mechanisms are both very unlikely, due to the short time involved and the lack of evidence of increase in genetic flow. What little admixture that has been documented among Pima seems more toward Mexican mates. In considering environmental correlates of occlusal variation, no single study on humans can offer adequate controls. A crosscultural approach, where many societies urbanizing under different conditions may be examined, holds the most hope for achieving a n understanding of the causes. Other studies documenting a sudden deterioration of occlusal norms have remarked upon the diet, particularly its physical consistency, and how that changes with Western contact. Such study populations have included Eskimos (Waugh, 1937a, 1937b; Williams, 1943; Price, 1936; Wood, 1971), Australian aborigines (Clinch, 1951), Chinese (Liu, 1977; Goose, 1972), Appalachian Americans (Corruccini and Whitley, 1981),Europeans (Lavelle, 1968; Davies, 19721, Asian Indians (Kaul and Corruccini, 1983; Corruccini et al., 1983), Melanesians (Lombardi and Bailit, 1972; Corruccini and Pacciani, 19831, Amerinds (Niswander, 1966), and reviews of several populations (Klatsky, 1948; Price, 1935; Hunt, 1961). In the Pima occlusal transition, dietary consistency and its relation to chewing stress likewise seems to be a possible factor. There is considerable theoretical and experimental support for this concept. It has been shown that vigorous chewing during growth affects midfacial, palatal, and chin growth favorably (Hunt, 1959, 1961) by transmission of forces through the alveolus, and that lessening the biomechanical demands of diet causes a reduction of temporomandibular joint size (Hinton and Carlson, 1979; Corruccini and Handler, 1981). The maxillary narrowing that invariably accompanies occlusal deterioration on a population level has been induced in laboratory rats (Watt and Williams, 1951; Beecher and Corruccini, 1981a), macaques (Beecher and Corruccini, 1981b), and squirrel monkeys (Corruccini and Beecher, 1982; Beecher et al., 1983) fed artificial soft diets. Malaligned teeth and abnormal occlusal contacts were also significantly greater for the soft diet group than hard diet controls in the squirrel monkey study. Other environmental correlates of the maxillary collapse syndrome and related malocclusion which co-occur with urbanization have been suggested. Premature deciduous tooth loss seems a t most to be a minor contributing factor. Chronic allergy, respiratory infection and mouth-breathing (Marks, 1965; Harvold et al., 1973) have a few effects similar to soft diet but respiration and posture lack a logical functional relation to tooth displacement. Interproximal attrition once was thought to increase relative arch space and maintain isomeric dental relationships in the aborigines with gritty diets (Begg, 19541, but the universal applicability of this mechanism is doubtful (Brace, 1977; Lombardi, 1982; Kaul and Corruccini, 1983) especially a s it does not explain crowding in the 12-20 age range prior to significant attrition. In this age range, malocclusion has become the most expensive medical condition in the average American family. It could be that biased sampling operated in the older group, since only individuals with nearly intact dentitions were scored and these may have had better occlusions than excluded cases when younger. Only a n extended longitudinal design could answer this; we hope the facts that most cases age 40-t were excluded, and that the different sample average ages of 15 and 28 span a period of little occlusal change, mitigate this problem. From our data, we conclude that the change in oral function resulting from dietary PIMA OCCLUSAL VARIATION change is a likely factor in deterioration of occlusion in younger Pima. Physical anthropologists and geneticists are suited to test this theory in various rapidly urbanizing societies where more drastic occlusal changes (as well as other increases in chronic noninfectious disease conditions) are shown, especially since dental clinicians are often less than maximally appreciative of cross-cultural data and their implications for preventive therapy. 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