Linear Enamel Hypoplasia Defects Research Articles

More severe stress markers in the teeth of flanged versus unflanged orangutans (Pongo spp.).

We compared an early life stress indicator, linear enamel hypoplasia (LEH), in the canine teeth of two male orangutan (Pongo spp.) morphs. Flanged males have large bi-discoid cheek pads and a laryngeal throat pouch, and they exhibit either the same or higher levels of the stress hormone cortisol throughout development compared with unflanged males, which lack secondary sexual characteristics. Such "developmental arrest" is hypothesized to either reflect a response to experienced high stress (Hypothesis 1), or an adaptation to avoid elevated stress levels and/or having experienced lower stress levels (Hypothesis 2) during early life. As LEH defect depth has been shown to reflect the severity (i.e., intensity and/or duration) of early life stress events, we examined whether unflanged males have shallower LEH defects than flanged males. Flanging status was assessed by measuring the faces of preserved skins. Canine height (N=37) was measured in the same individuals to assess commonality between morphs. LEH defect depths were analyzed using a standardized confocal profilometry method (N=34). Flanged males have significantly deeper LEH defects than unflanged adult males. Canine projected crown heights are similar across males regardless of morph. Evidence from great apes shows that, when comparing canines with similar growth patterns, deeper defects reflect more severe stress events during development. Thus, our results suggest that "developmental arrest" of unflanged males is not a response to having experienced stress, but rather an adaptation to avoid the physiological impacts associated with chronic stress and/or experiencing lower stress levels.

Insights on patterns of developmental disturbances from the analysis of linear enamel hypoplasia in a Neolithic sample from Liguria (northwestern Italy)

ObjectiveTo assess developmental disturbances through the analysis of linear enamel hypoplasia (LEH) frequency and to infer environmental stress and life history within Neolithic communities from Liguria (Italy). Materials43 unworn/minimally worn permanent anterior teeth of 13 individuals recovered from nearby caves and dated to c. 4800−4400 cal. BCE. MethodsLEH defects were identified with high-resolution macrophotos of dental replicas, age at LEH was calculated via perikymata counts. LEH defects matched between two or more teeth were considered as systemic disturbances. LEH frequency by age classes was analyzed via GLZ and Friedman ANOVA. ResultsNumber of matched defects per individual range between 2–12. The mean LEH per individual was highest in the 2.5–2.99 age category, with a significant increase relative to earlier growth stages, followed by a decline. ConclusionLEH may reflect life-history in the local ecology of Neolithic Liguria, where several individuals with osteoarticular tuberculosis have been recorded. Disease burden may have triggered developmental disturbances around the time of weaning. Age at first defect was negatively correlated with age at death and positively with the total number of defects, suggesting that early stress may have affected survivorship. SignificanceThe study contributes to the reconstruction of ecological pressures among Neolithic people of Liguria, and informs on environmental challenges during the Neolithic adaptive expansion. LimitationsThe visual examination of macrophotos is prone to observer error; mid-crown tends to display more visible LEH due to tooth architecture. Suggestions for further researchApply different quantitative methods to examine severity and duration of disturbances.

Dental health status of skeletal remains excavated from an abandoned well at Ajnala, India: a bioarchaeological study

Present study was conducted to assess dental health status of the mid-19th century skeletal remains excavated from an abandoned ancient well and to scrutinize the demographic affiliations of the remains. Thousands of bones, teeth and contextual items were excavated non-scientifically from an abandoned well situated underneath a religious structure at Ajnala (Amritsar, India). Four thousands four hundred and seventy five teeth of each type were examined for presence of dental pathologies of caries, wear and linear enamel hypoplasia (LEH). The frequency distribution of each pathological state was calculated for each tooth type using international dental standards available in the literature. The overall dental status was characteristic of young individuals having low prevalence of dental caries and enamel hypoplasiac lesions.
 Very few teeth had seriously exposed dentine and pulp cavity; indicating consumption of some cariogenic food items. The maxillary and posterior teeth were more affected with dental caries than the mandibular and anterior teeth. LEH defects were found more commonly distributed in the lower canines (44.9%) and upper incisors (34.8%) than their corresponding counterparts and statistically significant differences were noticed in LEH prevalence between anterior and, posterior dentition. The overall percentage of LEH has been found as 15.8%; with 15.4% maxillary and 16.2% mandibular teeth being affected with LEH. The paleodontogical examinations, contextual items and the preliminary molecular findings supported the written versions that victims of Ajnala skeletal remains had sound dental health status and probably belonged to adult males who were killed in 1857 as per written versions.

Quantifying linear enamel hypoplasia in Virunga Mountain gorillas and other great apes.

Linear enamel hypoplasia (LEH) is a condition marked by localized reductions in enamel thickness, resulting from growth disruptions during dental development. We use quantitative criteria to characterize the depth of LEH defects and "normal" perikymata in great apes. We test the hypothesis that mountain gorillas have shallow defects compared to other taxa, which may have led to their underestimation in previous studies. Previous attempts to characterize LEH morphology quantitatively have been limited in sample size and scope. We generated digital elevation models using optical profilometry (Sensofar PLu Neox) and extracted 2D coordinates using ImageJ to quantify depths in canines from three great ape genera (N = 75 perikymata; 255 defects). All defect depths fall outside the distribution of perikymata depths. Mountain gorilla defects are significantly shallower than those of other great ape taxa examined, including western lowland gorillas. Females have significantly deeper defects than males in all taxa. The deepest defect belongs to a wild-captured zoo gorilla. Virunga mountain gorilla specimens collected by Dian Fossey exhibit deeper defects than those collected recently. Shallow defect morphology in mountain gorillas may have led to an underestimation of LEH prevalence in past studies. Defect depth is used as a proxy for insult severity, but depth might be influenced by inter- and intra-specific variation in enamel growth. Future studies should test whether severe insults are associated with deeper defects, as might be the case with Haloko, a wild-captured gorilla. Ongoing histologic studies incorporating associated behavioral records will test possible factors that underlie differences in defect morphology.

Frequency and developmental timing of linear enamel hypoplasia defects in Early Archaic Texan hunter-gatherers

Digital photographs taken under controlled conditions were used to examine the incidence of linear enamel hypoplasia defects (LEHs) in burials from the Buckeye Knoll archaeological site (41VT98 Victoria county, Texas), which spans the Early to Late Archaic Period (ca. 2,500–6,500 BP uncorrected radiocarbon). The majority (68 of 74 burials) date to the Texas Early Archaic, including one extremely early burial dated to 8,500 BP. The photogrammetric data collection method also results in an archive for Buckeye Knoll, a significant rare Archaic period collection that has been repatriated and reinterred. We analyzed the incidence and developmental timing of LEHs in permanent canines. Fifty-nine percent of permanent canines (n = 54) had at least one defect. There were no significant differences in LEH frequency between the maxillary and mandibular canines (U = 640.5, n1 = 37, n2 = 43, p = .110). The sample studied (n = 92 permanent canines) had an overall mean of 0.93 LEH defect per tooth, with a median of one defect, and a mode of zero defects. Average age at first insult was 3.92 (median = 4.00, range = 2.5–5.4) and the mean age of all insults per individual was 4.18 years old (range = 2.5–5.67). Age at first insult is consistent with onset of weaning stress—the weaning age range for hunter-gatherer societies is 1–4.5. Having an earlier age of first insult was associated with having more LEHs (n = 54, rho = −0.381, p = 0.005).

Reconstructing patterns of systemic stress in a Jomon period subadult using incremental microstructures of enamel

This study reconstructs systemic stress patterning using incremental microstructures of enamel in a subadult from the Yoshigo cemetery (3200 through 2800 BP), Aichi Prefecture, Japan, with the goal of providing an improved methodological and theoretical framework for interpreting systemic stress among Jomon people. High resolution impressions and replicas were collected for each anterior maxillary tooth. Each replica was studied under 50, 100, or 200× magnification on a measuring microscope. Perikymata spacing and enamel surface profiles were recorded using specialized software. Linear enamel hypoplasia (LEH) defects were identified as accentuated spacing in perikymata combined with a depression in the enamel surface. Each defect was placed within a chronological sequence based on decile location. Stress duration was estimated by counting the perikymata in the occlusal wall of each defect and multiplying that value by the modal periodicity for striae formation. Percentage of enamel growth disruption was estimated by dividing the number of perikymata within the occlusal wall of each matched defect by the total number of perikymata within the imbricational enamel. Eight LEH defects were chronologically matched. Chronology of LEH defects ranged between 1.2 through 3.5 years. Number of perikymata located within the occlusal wall of each defect ranged from one through 20. Estimated durations of stress ranged from 12 through 129.6 days. These durations overlapped with Neandertals, though Point Hope foragers had greater durations of stress with no overlap in interquartile ranges. Disrupted enamel growth ranged from 8.1% in the maxillary left canine to 50.7% in the maxillary right central incisor.

Patterns of systemic stress during the agricultural transition in prehistoric Japan

This study documents and interprets systemic stress during the agricultural transition in prehistoric Japan using linear enamel hypoplasia (LEH) defects and cribra orbitalia (CO) lesions. Middle to Final Jomon cultures (5000-2300 BP) from Honshu Island represent the foraging samples, while Yayoi cultures (2500-1700 BP) represent the early agricultural samples. Jomon foragers from eastern Japan had broad-based, intensive economies. Jomon foragers from western Japan had a greater focus on seasonally available, nutritionally poor resources, while Yayoi people were descendents of migrants from the East Asian continent and introduced wet rice economies to Japan. This study tests the hypotheses that wet rice economies will be associated with a lower prevalence of teeth/individuals affected by LEH defects in western Japan, while few differences in the prevalence of teeth/individuals with LEH defects will be observed between eastern Jomon people and Yayoi farmers. It is further predicted that similar CO prevalence will be observed between Jomon and Yayoi people given environmental similarities. Significantly greater frequencies of teeth affected by LEH defects are observed among western Jomon compared to Yayoi people. The prevalence of teeth with LEH defects is slightly elevated among eastern Jomon foragers compared to Yayoi agriculturalists. Significant differences in CO prevalence are not observed. Systemic stress prevalence in western Japan likely declined following wet-rice agriculture because this crop provided a predictable, renewable resource base. Systemic stress prevalence was similar between eastern Jomon and Yayoi people because both groups practiced intensive subsistence strategies. Similar CO prevalence reflects infectious diseases associated with living conditions.

Under restrictive conditions, can the widths of linear enamel hypoplasias be used as relative indicators of stress episode duration?

Linear enamel hypoplasia (LEH), a type of enamel defect reflecting nonspecific physiological stress, has traditionally been used by bioarchaeologists to assess human health. Initially, measurements of defect width were used to estimate the duration of stress episodes. More recently, methods of counting within-defect perikymata (enamel growth increments) were developed to more accurately assess duration. Because perikymata are often not continuously visible within defects, while widths can usually be measured, the primary purpose of this article was to determine if, under restrictive conditions, the widths of LEH defects might be used as relative indicators of stress episode duration. Using a set of dental replicas from the prehistoric Irene Mound (1150-1400 A.D.), this study also investigated potential sources of variation in defect widths and how often defect widths could be measured and within-defect perikymata counted. Of 120 defects, only 47 contained both measurable defect widths and total within-defect perikymata, while 79 had measurable defect widths. Regression analysis revealed that, for these 47 defects, defect widths were more strongly related to the total number of within-defect perikymata than they were to crown region or tooth type. Although wide prediction intervals indicated that a defect's width could not be used to predict the number of within-defect perikymata for an individual, narrower confidence intervals associated with hypothetical mean population widths suggested that mean defect widths might be used to rank populations in terms of relative average stress episode duration.

Brief communication: Comparison of methods for estimating chronological age at linear enamel formation on anterior dentition

Linear enamel hypoplasia (LEH) is an enamel defect that records the effects of physiological stress on tooth formation. Estimating the age at which LEH defects form is integral to the reconstruction of population health in bioarcheological studies. Two principal methods for aging LEH defects have been introduced in the literature. The conventional approach employs regression equations based on a linear model of tooth growth. The newer, Reid and Dean [Am J Phys Anthropol 113 (2000) 135-139] approach, is based upon a histologically derived curvilinear model of enamel development and therefore likely provides more accurate age estimates. However, the extent to which the Reid and Dean method produces estimated ages at defect formation differing from those of the regression equations has not, until now, been determined. This study quantifies the differences between these two methods. Evaluating the degree to which these methods differ is essential for interpreting the accuracy of LEH age estimates given in previous bioarcheological studies. Age estimates of LEH defects on 338 anterior teeth from the Hamann-Todd osteological sample were calculated using both methods. The resulting estimated ages were compared through a randomized block ANOVA. However, the mean differences between the estimated ages yielded by both methods range from 4 months or less depending on the tooth type with an overall average of 2.63 months. The discussion focuses on the degree to which this difference affects answers to bioarcheological questions.

Prevalence and the duration of linear enamel hypoplasia: a comparative study of Neandertals and Inuit foragers

As a dental indicator of generalized physiological stress, enamel hypoplasia has been the subject of several Neandertal studies. While previous studies generally have found high frequencies of enamel hypoplasia in Neandertals, the significance of this finding varies with frequencies of enamel hypoplasia in comparative samples. The present investigation was undertaken to ascertain if the enamel hypoplasia evidence in Neandertals suggests a high level of physiological stress relative to a modern human foraging group, represented here by an archaeological sample of Inuit from Point Hope, Alaska. Unlike previous studies, this study focused specifically on linear enamel hypoplasia (LEH), emphasizing systemic over localized causes of this defect by considering LEH to be present in an individual only if LEH defects occur on two anterior teeth with overlapping crown formation periods. Moreover, this study is the first to evaluate the average growth disruption duration represented by these defects in Neandertals and a comparative foraging group. In the prevalence analysis, 7/18 Neandertal individuals (from Krapina and southern France) and 21/56 Neandertal anterior teeth were affected by LEH, or 38.9% and 37.5% respectively. These values do not differ significantly from those of the Inuit sample in which 8/21, or 38.1% of individuals, and 32/111, or 28.8% of anterior teeth were affected. For the growth disruption duration analysis, 22 defects representing separate episodes of growth disruption in Neandertals were compared with 22 defects in the Inuit group using three indicators of duration: the number of perikymata (growth increments) in the occlusal walls of LEH defects, the total number of perikymata within them, and defect width. Only one indicator, the total number of perikymata within defects, differed significantly between the Inuit and Neandertal groups (an average of 13.4 vs. 7.3 perikymata), suggesting that if there is any difference between them, the Inuit defects may actually represent longer growth disruptions than the Neandertal defects. Thus, while stress indicators other than linear enamel hypoplasia may eventually show that Neandertal populations were more stressed than those of modern foragers, the evidence from linear enamel hypoplasia does not lend support to this idea.