Factors affecting the distribution of enamel hypoplasias within the human permanent dentition

Frequencies and morphological and chronological distributions of enamel hypoplasias are presented by tooth type (permanent I1 to M2s), based on a sample of 30 prehistoric Amerindians with complete and unworn dentitions. There is nearly a tenfold variation in frequency of defects by tooth, ranging from 0.13 per mandibular second molar to 1.27 per maxillary central incisor. The six anterior teeth average between 0.70 and 1.27 defects/tooth, whereas the eight posterior teeth average between 0.43 and 0.13 defects/tooth. Earlier developing teeth, such as incisors, have earlier peak frequencies of defects (2.0-2.5 years), while later developing teeth, such as second molars, have subsequent peak frequencies (5.0-6.0 years). These variations are relevant when comparing hypoplasia data based on different teeth. Differences in hypoplasia frequencies among teeth are not solely due to variation in time of crown development, as is usually reported. Rather, there is evidence for biological gradients in susceptibility to ameloblastic disruption. Anterior teeth are more hypoplastic than posterior teeth. More developmentally stable "polar" teeth are more hypoplastic than surrounding teeth. Polar teeth may be more susceptible to hypoplasias because their developmental timing is less easily disrupted. In all teeth, hypoplasias are most common in the middle and cervical thirds. Crown development and morphological factors, such as enamel prism length and direction, may influence the development and expression of enamel surface defects.     

The chronological distribution of enamel hypoplasias from prehistoric Dickson Mounds populations

The chronological distributions of enamel hypoplasias (indicators of nonspecific stress) are assessed for 111 individuals from two prehistoric populations from Dickson Mounds, Lewiston, Illinois. The earlier population (circa A.D. 950-1150) involves a transition from an indigenous gathering-hunting tradition to increasing adoption of Mississippian lifeways. The later population (circa A.D. 1150-1300) is fully Mississippian (MM). Based on the occurrence of hypoplasias on all permanent teeth except third molars, 14 half-year periods from birth to 7.0 years are graded for evidence of hypoplasia-stress. Both populations have a low frequency of hypoplasia which occur before 2 years of age and after 4 years of age. A common peak frequency of hypoplasias between 2.0 and 4.0 years is suggestive of an elevated degree of stress at weaning. The peak frequency of hypoplasias is earlier in the MM (2.5-3.0 years versus 3.0-3.5 years in the pre-Mississippian population). In addition, the rise to and decline from peak frequency occurs approximately 0.5 years earlier in the MM. The earlier and sharper rise to peak frequency suggests earlier and more severe weanling-related stress. Hypoplasias chronologies are undoubtedly influenced by age-related host resistance factors (Sarnat and Schour, 1941). Nevertheless, these data demonstrate that populations may vary in their chronological distribution of hypoplasias and that these variations may provide useful information on age-related patterns of exposure to environmental stressors.     

Prevalence and possible etiology of dental enamel hypoplasia

Two hundred black and white adult human skeletons and 200 living black and white children from the greater Cleveland area were examined for evidence of enamel hypoplasia. Enamel hypoplasia, present in varying expressings (pits, lines and grooves), was found to be more prevalent in both skeletal samples, than in the living groups. In the majority of cases, sex differences between white and black males and females through time and space are highly significant for all tooth catagories. Regardless of the mechanisms behind it, prevalence of enamel hypoplasia for both white and black group has significantly declined through time. No evidence suggesting specific etiologies responsible for enamel hypoplasia can be found. In the majority of previously published reports, the etiology is still idiopathic. The reduction in the prevalence of enamel hypoplasia in the groups examined through time may be related to improved nutritional conditions and the elimination or decline of childhood diseases that have been implicated in this condition.     

Frequency and distribution of enamel hypoplasias in a historic skeletal sample

A skeletal sample of 296 individuals from a 19th century American poorhouse cemetery is examined for the frequency and chronological distribution of linear enamel hypoplasias on the mandibular canines and maxillary central incisors. Dental enamel hypoplasias may be considered to be indicators of increased exposure to health risk at the time of weaning. The purpose of this study is to examine childhood stress and provide a relative measure of that stress, as evidenced by hypoplasias, in a historic sample that represents an industrializing population. The frequency of enamel hypoplasias per individual by tooth ranged from 70 to 73%, with a peak age at stress of 2.5 to 3 years for the maxillary central incisor and 3.5 to 4 years for the mandibular canine. There were no significant differences in the presence of hypoplasias between males and females. The peak age at stress between 2.5 and 4 years in this 19th century sample transects the ranges reported for prehistoric populations (2-6 years) and for modern groups (0-3 years). These results indicate that the stress associated with weaning probably occurred earlier in incipient industrial societies than in prehistoric hunter/gatherers and agriculturalists, yet not as early as in modern industrial groups. The high level of childhood stress in this skeletal sample compared with that of other samples may indicate a change in health, at least among the lowest class, associated with the cultural transition from an agricultural to an industrial society.     

Migration,socio-economic status and age at menarche and age at menopause in the Yucatan,Mexico

The possible effects of migration and socio-economic status (SES) on age at menarche (MENA), age at menopause (MENO), potential reproductive period (PRP), and the correlation between MENA and MENO, were studied in 216 women in the Yucatan, Mexico. They were divided into three groups: migrant from the sisal-growing area on the coast, and sisal and coastal sedentary. Coastal sedentary women, living in the best socio-economic conditions, have the youngest MENA and the oldest MENO. Early migrant women have a significantly younger MENO (p.<0.05) and shorter PRP than Coastal sedentary women. There was no evidence of selective migration for MENA. When the Migrant, Sisal and Coastal sample were divided into cohorts by SES, it was impossible to obtain any clear picture. MENA increases with increased SES for the Coastal and Sisal cohorts, while the Migrant cohorts show an opposite trend. However, only the Low/Middle and High/Middle cohort differences for the Coastal sample are significant (p.<0.05, in both cases). It seems that migration has a limited affect on MENO and the PRP. Contrary to reports in the literature, the correlations between MENA and MENO and migrant status, and migrant socio-economic statuses, are negative, although these correlations were statistically significant in the Coastal sample.     

A microscopic investigation of enamel in wombat (Vombatus ursinus)

Summary A study of the enamel of continuously growing Vombatus ursinus molars was carried out using the techniques of light microscopy, hardness testing, scanning electron microscopy and transmission electron microscopy. From the erupted end to within 8 mm of the growing end, mature enamel was observed and it was found that between comparable areas there were no significant ultrastructural differences in enamel; however, small (12nm diameter), loosely packed needle-like crystals characteristic of developing enamel were observed near the growing end. Mature enamel was found to consist of three optically-translucent regions interleaved with two opaque regions. Opaque enamel was softer than translucent enamel. The opacity and relative softness characteristic of two of the enamel regions was not related to prism pattern or orientation; it was, however, related to the presence of voids (28 nm diameter) in these regions.     

Enamel hypoplasia and age at weaning in 19th-century Florence,Italy

A sample representing a population of the Florence district of middle 19th century was studied to determine the age of occurrence of enamel hypoplasias. The age interval most affected was that between 1.5 and 3.5 years. Historical sources on weaning habits of 19th-century Italian populations indicate a weaning period between 12 and 18 months. This is in agreement with the data on enamel defects, showing that children of post-weaning age are more subject to stress. Wide “grooves”, with prolonged duration, are concentrated between 2 and 2.5 years, whereas “lines” occur primarily between 2.5 and 3 years. We suggest that this distribution could reflect the gradual introduction of dietary supplements until weaning is complete. © 1994 Wiley-Liss, Inc.     

Response of bone and enamel formation to nutritional supplementation and morbidity among malnourished Guatemalan children

The effects of changes in nutritional and health status upon bone and enamel development are examined in a sample of 63 rural Guatemalan children (24 females, 39 males). The number of ossified hand-wrist centers at 3 years and the number of linear enamel hypoplasias (LEH) in ～0–3 year zones of developing teeth were used to monitor the response of bone mineralization and enamel matrix formation to illness and nutritional supplementation. Numbers of ossified centers and LEH were compared across sex, supplementation, and morbidity groups. Enamel matrix secretion responded positively to increased supplementation. Children who received less than 34.25 kcal/day in supplement had more LEH than those who received more supplement. No differences in ossification status were found between supplementation groups. These data suggest that enamel formation may be more sensitive to changes in nutritional status than is bone mineralization. Disruptions of bone and enamel formation were both associated with frequent illness. Children who were ill more than 3.6% of the time had more LEH and fewer ossified hand-wrist centers than children who were less frequently ill. Conclusions regarding relative environmental sensitivity must take into account the specific aspects of dental and skeletal development examined. © 1993 Wiley-Liss, Inc.     

Age at death of the Neanderthal child from Devil's Tower, Gibraltar and the implications for studies of general growth and development in Neanderthals

This study combines traditional methods of assessing dental developmental status based upon modern human standards with new techniques based upon histological observations in order to reassess the age at death of the Gibraltar child from Devil's Tower. The results indicate that the most likely age of this individual at death was 3 years of age. This result is in agreement with an independent assessment of the age of the temporal bone of this specimen (Tillier, AM [1982] Z. Morphol. Anthropol. 73:125-148) and is concordant with dental developmental ages given for modern humans. Moreover, the fact that this specimen appears at the low end of the age scale for calcification stages in modern humans is also supportive of the findings of Legoux (Legoux, P [1970] Arch. Inst. Paleontol. Hum. Mem. 33:53-87) and Wolpoff (Wolpoff, MH [1979] Am. J. Phys. Anthropol. 50:67-114) that dental eruption schedules in Neanderthals were also accelerated. If the cranial bones from Devil's Tower are associated with the dental material, as we believe, they indicate a remarkably precocious brain growth in this individual, which is consistent with what is known about general growth and development in Neanderthals.     

Dental wear in the Libben population: Its functional pattern and role in the determination of adult skeletal age at death

Modal patterns of occlusal attrition are presented for the Libben population based on a sample of 332 adult dentitions. Maxillas and mandibles were reviewed independently by seriation prior to assessment of complete dentitions. The Spearman rank order coefficient for upper and lower dentitions was.96. Wear patterns are very similar to those reported by Murphy (1959a: Am. J. Phys. Anthropol. 17:167–178) for Australian aborigines. There were no significant sexual differences in wear rate. Dental wear is concluded to be a highly reliable and important indicator of adult age at death for skeletal populations if seriation procedures are employed.     

Perinatal stress and increased fluctuating asymmetry of dental calcium in the laboratory rat

Recent studies have consistently reported an increased magnitude of fluctuating dental, long bone, and membranous bone asymmetry as a function of perinatal stress. The present study was designed to test the hypothesis that increases in the fluctuating asymmetry of calcium may be related to the metric changes in these calcium-dependent systems. Pregnant rats were exposed to noise stress from conception through weaning. Bilateral lower first molars were extracted from the neonates, and calcium levels were determined using a standard atomic absorption technique. Levels of fluctuating asymmetry of calcium were found to be significantly increased (p less than .01) in the audiogenic noise-stressed group compared to unstressed, normal controls. These results follow the pattern reported earlier for metric analysis of the dentition and support a stress-induced calcium-transport-disruption hypothesis.     

The Art of Indigeneity: Aesthetics and Competition in Mexican Economies of Culture

On the basis of ethnographic research with woodcarvers in Oaxaca, Mexico, this paper investigates the role that aesthetic practices play in economic competition in cultural markets. I explain how one family has become the most successful artisans in their village by aesthetically referencing the indigenous art that is highly sought after by the North American ethnic art market. By reformulating Bourdieu's analysis of artistic fields, I argue that aesthetic competition should be theorised at the level of genres, which allow insight into how individual aesthetic innovations may transform the fields in which art is produced and circulated. I show that by referencing indigeneity, this successful family not only accesses a new market but also renders their work more authoritative than the carvings of their neighbours, which aesthetically reference Mexican ‘artesanías’ (craftwork). In so doing, they not only earn more money but also change the ways that Oaxacan woodcarvings are valued in general.     

Nitrogen and phosphorus resorption in trees of a Mexican tropical dry forest

Resorption efficiency (RE) and proficiency, foliar nutrient concentrations, and relative soil nutrient availability were determined during 3 consecutive years in tree species growing under contrasting topographic positions (i.e., top vs. bottom and north vs. south aspect) in a tropical dry forest in Mexico. The sites differed in soil nutrient levels, soil water content, and potential radiation interception. Leaf mass per area (g m^–2) increased during the growing season in all species. Soil P availability and mean foliar P concentrations were generally higher at the bottom than at the top site during the 3 years of the study. Leaf N concentrations ranged from 45.4 to 31.4 mg g^–1. Leaf P varied from 2.3 to 1.8 mg g^–1. Mean N and P RE varied among species, occasionally between top and bottom sites, and were higher in the dry than in the wet years of study. Senesced-leaf nutrient concentrations (i.e., a measure of resorption proficiency) varied from 13.7 to 31.2 mg g^–1 (N) and 0.4 to 3.3 mg g^–1 (P) among the different species and were generally indicative of incomplete nutrient resorption. Phosphorus concentrations in senesced leaves were higher at the bottom than at the top site and decreased from the wettest to the the driest year. Soil N and P availability were significantly different in the north- and south-facing slopes, but neither nutrient concentrations of mature and senesced leaves nor RE differed between aspects. Our results suggest that water more than soil nutrient availability controls RE in the Chamela dry forest, while resorption proficiency may be interactively controlled by both nutrient and water availability.     

Enamel hypoplasias as indicators of developmental stress in pongids and hominids

This paper reports the results from a study of enamel hypoplasia in the deciduous dentition of free-living Liberian chimpanzees (Pan troglodytes verus). The entire study collection includes 280 specimens (278 skulls plus two unassociated mandibles), of which 70 are young enough to retain some decidous teeth. Among the subsample of infants, the total frequency of hypoplasia summed over all teeth in any individual reaches 80%, being expressed in the form of pits rather than transverse lines. Hypoplasia of a linear form was common in the permanent dentition, attaining a frequency of 46.7% on maxillary central incisors and 69.7% on mandibular canines.     

Enamel thickness and development in a third permanent molar of Gigantopithecus blacki

A ground section was prepared from a lower right M3 attributed to Gigantopithecus blacki as close as possible to axial plane of the mesial cusps. Daily cross striations were imaged, measured and counted in each cusp using polarised light microscopy. Long-period striae of Retzius were counted in the lateral enamel and their periodicity determined from counts and measurements of daily cross striations between adjacent striae. Cross striation spacings in the cusps were between 3.8 microm at the enamel dentine junction and 6 microm close to the enamel surface. Cuspal enamel formation times were long (800 days in the protoconid and 620 days in the metaconid). Linear enamel thickness was as much as 3.75 mm in the protoconid. There were 63 and 61 long-period striae of Retzius in the mesial aspects of the lateral enamel and the periodicity was 11 days. Lateral enamel formation took 1493 and 1291 days and when summed with cuspal enamel formation times totalled 4 years in the protoconid and 3.5 in the metaconid. Relative enamel thickness was 23, calculated through the mesial cusps. This falls short of that in the so-called 'thick hyper-thick' enamel described in 'robust' australopithecines to which Gigantopithecus blacki has previously been compared in both its dental and mandibular morphology. With respect to enamel thickness, therefore, Gigantopithecus blacki falls squarely among an increasingly large number of Miocene hominoids that can all be described as having 'thick enamel'.     

Effect of growth rate from 6 to 16 months of age on sexual development and reproductive function in beef bulls

Sexual development and reproductive function were studied in 22 Angus × Charolais and 17 Angus bulls from 6 to 16 mo of age. Associations of average daily gain (ADG) and body weight with ages at puberty and at maturity (satisfactory semen quality), scrotal circumference, paired-testes volume and weight, testicular vascular cone diameter and fat thickness, scrotal temperature, sperm production and morphology, and testicular histology, were determined. There were no significant correlations between cumulative average daily gain and any of the end points investigated. Body weight at various ages was negatively correlated with ages at puberty and maturity in Angus × Charolais bulls, positively correlated with paired-testes weight in Angus × Charolais and Angus bulls, and positively correlated with seminiferous tubule volume in Angus bulls (P < 0.05). Semen quality improved gradually with age and the interval between puberty and maturity (mean ± SD; 309.4 ± 29.7 and 357 ± 42 days of age) was approximately 50 days. Age, weight, scrotal circumference, and paired-testes volume were all good predictors of pubertal and mature status, with moderate to high sensitivity and specificity (71.6% to 92.4%). In summary, growth rate between 6 and 16 mo of age did not affect sexual development and reproductive function in beef bulls. However, greater body weight at various ages was associated with reduced age at puberty and maturity, and with larger testes at 16 mo of age, indicating that improved nutrition might be beneficial, but only when offered before 6 mo of age. Average daily gains of approximately 1 to 1.6 kg/day did not result in excessive fat accumulation in the scrotum, increased scrotal temperature, or reduction in sperm production and semen quality, and could be considered “safe” targets for growing beef bulls.     

The effect of rate of eruption on periodontal ligament glycosylaminoglycan content and enamel formation in the rat incisor

The rate of eruption of rat mandibular incisors was either increased by cutting one tooth out of occlusion or eliminated by means of pinning. The effects of such changes in eruption rate on the sulphated glycosylaminoglycan content of the periodontal ligaments was analysed. The length of the enamel secretory zone and the composition of the developing enamel matrix protein was also compared. Sulphated glycosylaminoglycan content of the periodontal ligament increased fourfold (P<0.001) during accelerated eruption but decreased to a corresponding extent (P<0.001) in the absence of eruption, when compared with controls. The length of the enamel secretory zone was also significantly reduced in the immobilised teeth, although the protein content was similar compared with controls. The results demonstrate the differential response to varied eruption rates of the periodontal ligament and enamel, particularly in respect of the extracellular matrix. The data are consistent with the view that the ground substance of the periodontal ligament plays a role in the generation of the eruptive force.     

Phagocytosis and elimination of amelocyte debris by stratum intermedium cells in the transitional zone of the enamel organ of the rat incisor

Summary In the transitional zone of the enamel organ (rat) some of the amelocytes perish. Their debris is phagocytized and digested by stratum intermedium cells and macrophages. These two cell types also seem to remove cytosegresomes expelled from those amelocytes which survive and redifferentiate into transporting amelocytes. Digestion of the amelocyte debris in the stratum intermedium cells is effected rapidly and completely. Degeneration of stratum intermedium cells was not observed in the transitional zone.This work was supported by grants from The Danish Medical Research Council (512-149/69 and 512-1008/71) and The Danish Science Research Council (512-1009/71).     

Dissolved organic carbon affects soil microbial activity and nitrogen dynamics in a Mexican tropical deciduous forest

Seasonal variation of dissolved organic C (DOC) and its effects on microbial activity and N dynamics were studied during two consecutive years in soils with different organic C concentrations (hilltop and hillslope) in a tropical deciduous forest of Mexico. We found that DOC concentrations were higher at the hilltop than at the hillslope soils, and in both soils generally decreased from the dry to the rainy season during the two study years. Microbial biomass and potential C mineralization rates, as well as dissolved organic N (DON) and NH₄⁺ concentrations and net N immobilization were higher in soils with higher DOC than in soils with lower DOC. In contrast, net N immobilization and NH₄⁺ concentration were depleted in the soil with lowest DOC, whereas NO₃⁻ concentrations and net nitrification increased. Negative correlations between net nitrification and DOC concentration suggested that NH₄⁺ was transformed to NO₃⁻ by nitrifiers when the C availability was depleted. Taken together, our results suggest that available C appears to control soil microbial activity and N dynamics, and that microbial N immobilization is facilitated by active heterotrophic microorganisms stimulated by high C availability. Soil autotrophic nitrification is magnified by decreases in C availability for heterotrophic microbial activity. This study provides an experimental data set that supports the conceptual model to show and highlight that microbial dynamics and N transformations could be functionally coupled with DOC availability in the tropical deciduous forest soils. Responsible Editor: Chris Neill