Enamel hypoplasia in deciduous teeth of great apes: do differences in defect prevalence imply differential levels of physiological stress?

This paper presents new data on enamel hypoplasia in the deciduous canine teeth of great apes. The enamel defect under consideration is known as localized hypoplasia of primary canines (LHPC), and is characterized by an area of thin or missing enamel on the labial surface of deciduous canine teeth (Skinner [1986a] Am. J. Phys. Anthropol. 69:59-69). Goals of this study are: 1) to determine if significant differences in the frequency of LHPC occur among three genera of great apes, and 2) to evaluate variation in LHPC prevalence among great apes as evidence of differential physiological stress. Infant and juvenile apes with deciduous teeth were examined at the Cleveland Museum of Natural History (n = 100) and at the Smithsonian Institution, National Museum of Natural History (n = 36). Deciduous teeth were observed under oblique incandescent light, with the naked eye and with a 10x hand lens. Enamel hypoplasia was scored using Federation Dentaire International (FDI)-Defects of Dental Enamel (DDE) standards. Hypoplasias were recorded by drawing defect location and size on a dental chart, and by measuring defect size and location with Helios needlepoint dial calipers. The prevalence of LHPC is reported by genus and sex, using two approaches: 1) the frequency of affected individuals-those having one or more deciduous canine teeth scored positive for LHPC; and 2) the number of canine teeth scored positive for LHPC as a percentage of all canine teeth observed. Variation in defect size and location will be described elsewhere. Localized hypoplasia of primary canine teeth was found in 62.5% of 128 individual apes, and in 45.5% of 398 great ape deciduous canines. As in humans, LHPC is the most common form of enamel hypoplasia in deciduous teeth of great apes, while LEH is rare or absent. The distribution and pattern of expression of LHPC in great apes is similar to that described in humans: side differences are not significant, but mandibular canines exhibit the defect two to five times more often than maxillary canine teeth. Differences in LHPC prevalence by sex are small and not significant. Intergeneric differences are large and non-random: chimpanzees (Pan) exhibit a significantly lower frequency of LHPC (22%, n = 50) by individual count, than either the orangutan (Pongo, 88.0%, n = 25) or the gorilla (Gorilla, 88.7%, n = 53). Tooth count prevalences exhibit a similar pattern of variation and are also statistically significant. These findings suggest that large bodied great apes (gorilla and orangutan) may be under greater physiological stress during perinatal and early postnatal development than the chimpanzee. The size, position, and timing of LHPC lesions are currently under analysis and may yield more insight into the etiological origin of this enamel defect.     

Enamel hypoplasia in the deciduous teeth of early Miocene catarrhines: evidence of perinatal physiological stress

Enamel hypoplasia (EH) is a deficiency in enamel thickness due to physiological insults that compromise ameloblast function during the secretory phase of amelogenesis. The prevalence of EH in the deciduous teeth of nonhuman primates is largely unknown. One exception is the recent discovery of EH in the deciduous teeth of extant great apes which exhibit significant differences in prevalence between genera (Lukacs, 1999 a, 2000 a, Am. J. phys. Anthrop.110, 351-363). EH in deciduous teeth of other primates, living and fossil, remain undocumented. This communication describes a "plane form" type of EH known as localized hypoplasia of primary canines (LHPC) (Skinner, 1986 a, Am. J. phys. Anthrop.69, 59-69) in early Miocene catarrhines from Kenya. Specimens were examined macroscopically, with a 10x hand lens and with a variable power (10-30x) binocular microscope. Fédération Dentaire International (FDI)/Defects of Dental Enamel (DDE) standards were employed in recognition and recording of enamel defects (Fédération Dentaire International, 1982, Int. Dent. J.32, 159-167; Clarkson, 1989, Adv. Dental Res.3, 104-109). Size, shape and location of defects were measured and recorded on an outline drawing of the tooth crown. The Kenya National Museum study sample includes six genera of early Miocene catarrhines (n=66 specimens, with n=80 teeth). Seven deciduous teeth were afflicted with EH, yielding an overall prevalence of 8.75%. Two taxa, Kalepithecus (n=1 deciduous canine) and Proconsul (n=3 deciduous canines), were affected with LHPC. Expression of LHPC in fossil catarrhines is consistent with the expression of EH observed in skeletal samples of extant great apes. This report establishes an approximately 17-23 Ma antiquity for EH among early catarrhines and suggests that the neonatal stage of ontogenetic development was sufficiently stressful physiologically to produce disruption in amelogenesis. These physiological stresses impacted neonates of fossil taxa with a wide range of adult body sizes, from large-bodied Proconsul major ( approximately 75 kg) to one of the smaller-bodied catarrhines, Kalepithecus ( approximately 5 kg).     

Prevalence and age at development of enamel hypoplasias in Mexican children

Enamel hypoplasias, deficiencies in enamel thickness resulting from disturbances during the secretory phase of enamel development, are generally believed to result from nonspecific metabolic and nutritional disruptions. However, data are scare on the prevalence and chronological distributions. of hypoplasias in populations experiencing mild to moderate malnutrition. The purpose of this article is to present baseline data on the prevalences and chronological distributions of enamel hypoplasias, by sex and for all deciduous and permanent anterior teeth, in 300 5 to 15-year-old rural Mexican children. Identification of hypoplasias was aided by comparison to a published standard (Federation Dentaire Internationale: Int. Dent. J. 32(2):159-167, 1982). The location of defects, by transverse sixths of tooth crowns, was used to construct distributions of defects by age at development. One or more hypoplasias were detected in 46.7% (95% CI = 40.9-52.5%) of children. Among the unworn and completely erupted teeth, the highest prevalence of defects was found on the permanent maxillary central incisors (44.4% with one or more hypoplasias), followed by the permanent maxillary canine (28.0%) and the remaining permanent teeth (26.2 to 22.2%) Only 6.1% of the completely erupted and unworn deciduous teeth were hypoplastic. The prevalence of enamel defects on the permanent teeth was up to tenfold greater than that found in studies of less marginal populations that used the FDI method. The prevalence of defects in transverse zones suggests a peak frequency of hypoplasias during the second and third years for the permanent teeth, corresponding to the age at weaning in this group. In the deciduous teeth, a smaller peak occurs between 30 and 40 weeks post gestation. The frequency of defects after three years of age is slightly higher in females than males, suggesting a sex difference in access to critical resources.     

Linear enamel hypoplasia in the great apes: analysis by genus and locality

Most studies report a high prevalence of linear enamel hypoplasia (LEH) in the great apes relative to other nonhuman primates and some human populations. It is unclear if this difference is a direct result of poor health status for the great apes, or if it represents differential incidence due to a lower threshold (sensu Goodman and Rose, 1990 Am. J. Phys. Anthropol. [suppl.] 33:59-110) for the occurrence of enamel hypoplasia among great apes. This study uses the Smithsonian National Museum of Natural History's great ape collection to examine the prevalence of LEH, the most common type of hypoplasia observed. Frequencies of LEH are reported, as well as analyses by taxa and provenience. The study sample consists of 136 specimens and includes 41 gorillas, 25 chimpanzees, and 70 orangutans. Analyses of frequencies are presented for both individuals and teeth by taxonomic category and locality. Among the individuals in this study, 63.97% are affected by LEH. Overall, gorillas (29.27%) exhibit lower frequencies of LEH than chimpanzees (68.00%) and orangutans (82.86%). There is a marked difference in LEH frequencies between mountain and lowland gorillas. There is no difference in LEH frequencies between Sumatran and Bornean orangutans. A range of variation for the great apes in enamel hypoplasia frequencies is found when taxon and locality are considered. It is likely that both biological and environmental factors influence the high frequencies of enamel hypoplasia exhibited in the great apes.     

Enamel hypoplasia in the Middle Pleistocene hominids from Atapuerca (Spain)

The prevalence and chronology of enamel hypoplasias were studied in a hominid dental sample from the Sima de los Huesos (SH) Middle Pleistocene site at the Sierra de Atapuerca (Burgos, northern Spain). A total of 89 permanent maxillary teeth, 143 permanent mandibular teeth, and one deciduous lower canine, belonging to a minimum of 29 individuals, were examined. Excluding the antimeres (16 maxillary and 37 mandibular cases) from the sample, the prevalence of hypoplasias in the permanent dentition is 12.8% (23/179), whereas the deciduous tooth also showed an enamel defect. No statistically significant differences were found between both arcades and between the anterior and postcanine teeth for the prevalence of hypoplasias. In both the maxilla and the mandible the highest frequency of enamel hypoplasias was recorded in the canines. Only one tooth (a permanent upper canine) showed two different enamel defects, and most of the hypoplasias were expressed as faint linear horizontal defects. Taking into account the limitations that the incompleteness of virtually all permanent dentitions imposes, we have estimated that the frequency by individual in the SH hominid sample was not greater than 40%. Most of the hypoplasias occurred between birth and 7 years (N = 18, X = 3.5, SD = 1.3). Both the prevalence and severity of the hypoplasias of the SH hominid sample are significantly less than those of a large Neandertal sample. Furthermore, prehistoric hunter-gatherers and historic agricultural and industrial populations exhibit a prevalence of hypoplasias generally higher than that of the SH hominids. Implications for the survival strategies and life quality of the SH hominids are also discussed. © 1995 Wiley-Liss, Inc.     

Linear enamel hypoplasia in gibbons (Hylobates lar carpenteri)

This study describes the expression of linear enamel hypoplasia (LEH), a sensitive dental indicator of physiological stress, in Thailand gibbons (Hylobates lar carpenteri). Previous studies of enamel hypoplasia in hominoids have focused on great apes, with little attention given to the expression of this stress indicator in gibbons. In that gibbons differ from both monkeys and great apes in numerous life history features, LEH expression in gibbons might be expected to show significant differences from both. In this study, 92 gibbon specimens from two sites in Thailand were compared with several samples of monkeys and great apes in their expression of LEH. The intertooth distribution of LEH in gibbons was compared to that of chimpanzees and rhesus monkeys. Gibbon populations from both sites exhibit LEH frequencies intermediate between those of the monkey samples, in which LEH prevalence is usually low, and those of the great ape samples, in which LEH prevalence is high. Gibbons differ significantly from monkeys, but not great apes, in the number of individuals whose teeth record multiple stress events. Multiple episodes of stress are rarely recorded in the teeth of monkeys, while multiple stress events occur with higher frequency in gibbons and great apes. Taxonomic variation in the duration of crown formation, the prominence and spacing of perikymata on dental crowns, life history features, and/or experience of physiological stress may explain these patterns. The intertooth distribution of LEH in gibbons is, for different reasons, unlike that of either chimpanzees or rhesus monkeys. The mandibular canines of gibbons have significantly more LEH than any of their other teeth. Aspects of crown morphology, perikymata prominence/spacing, enamel thickness, and crown formation spans are potential causes of taxonomic variation in the intertooth distribution of LEH.     

Linear enamel hypoplasias as indicators of systemic physiological stress: evidence from two known age-at-death and sex populations from postmedieval London

Enamel hypoplasias are useful indicators of systemic growth disturbances during childhood, and are routinely used to investigate patterns of morbidity and mortality in past populations. This study examined the pattern of linear enamel hypoplasias in two different burial populations from 18th and 19th Century church crypts in London. Linear enamel hypoplasias on the permanent dentitions of individuals from the crypt of Christ Church, Spitalfields, were compared to enamel defects on the teeth of individuals from St. Bride's. The method used involves the identification of enamel defects at a microscopic level, and systemic perturbations are detected by matching hypoplasias among different tooth classes within each individual. The pattern of linear enamel hypoplasias was contrasted between individuals from the burial sites of Spitalfields and St. Bride's, between males and females, and between those aged less than 20 years of age and those aged over 20 years at death. Six different parameters were examined: frequency of linear enamel hypoplasias, interval between defects, duration of hypoplasias, age at first occurrence of hypoplasia, age at last occurrence of hypoplasia, and the percentage of enamel formation time taken up by growth disturbances. All individuals in the study displayed linear enamel hypoplasias, with up to 33% of total visible enamel formation time affected by growth disruptions. Multiple regression analysis indicated a number of significant differences in the pattern of enamel hypoplasias. Individuals from Spitalfields had shorter intervals between defects and greater percentages of enamel formation time affected by growth disturbances than did individuals from St. Bride's. Females had greater numbers of linear enamel hypoplasias, shorter intervals between defects, and greater percentages of enamel formation time affected by growth disturbances than males. There were also differences in the pattern of enamel hypoplasias and age at death in this study. Individuals who died younger in life had an earlier age at first occurrence of enamel hypoplasia than those who survived to an older age. The pattern of enamel hypoplasias detected in this study was influenced by tooth crown geometry and tooth wear such that most defects were found in the midcrown and cervical regions of the teeth, and greater numbers of defects were identified on the anterior teeth. Differences in sensitivity of the parameters used for the detection of enamel hypoplasias were found in this study. The percentage of visible enamel formation time affected by growth disturbances was the parameter that identified the greatest number of significant differences among the subgroups examined.     

Enamel hypoplasia in sympatric chimpanzee and gorilla

The prevalence of enamel hypoplasia in 229Pan andGorilla, from the Republic of Cameroon, is described. A substantially higher proportion of gorillas (76%) than chimpanzees (58%) was affected. The incidence of enamel hypoplasia was not a function of sex, body size, or pathology. A study of tooth formation, from radiographs of a further series of immature apes, indicated that the mandibular canine bore 99% of all information about hypoplasia events. In both species a marked regularity of hypoplastic grooving with an interval of about 11.4% of canine crown height was observed. This appears to reflect a semi-annual cycle of stress which is tentatively linked to the twice-yearly rainy season. Uniform spacing of hypoplastic grooves has been observed in a variety of fossil hominids. Readily observable hypoplastic time markers in the teeth have potential for disclosing growth rates in early Hominidae. This is considered important because of the profound significance which prolonged maturation and longevity characteristic of recent human beings have for the transmission of learned behavior and social bonding.     

Environmental stress in the Early Mediaeval Slavic population at Borovce (Slovakia)

Several palaeopathological indicators examined in skeletal samples are caused by stress during childhood and remain visible in adults. In this study, dental enamel hypoplasia was observed in 451 individuals from the Early Mediaeval (8th to beginning of 12th c. AD) Slavic skeletal series at Borovce (Slovakia). The presence of enamel hypoplasia was scored in all types of deciduous and permanent teeth. More than one-fourth (27.2%) of the individuals with preserved permanent teeth showed enamel hypoplasia. No significant differences in the occurrence of the enamel lesions were found between males and females. The age at development of hypoplasias was estimated for 74 individuals by measuring the distance of the defect from the cemento-enamel junction. The hypoplastic defects appeared most frequently between 2.5 and 3.0 years. Following the trends observed in the distribution of age at development of the enamel lesions between subadults and adults, individuals stressed earlier in life had a reduced ability to cope with later insults. High prevalence of enamel hypoplasia, especially among 10–14-year-old growing juveniles, has led to the assumption that the Borovce population lived a considerably long period under conditions of high environmental pathogen load, and probably also suffered from some nutritional deficiencies.     

Gross enamel hypoplasia in molars from subadults in a 16th-18th century London graveyard

Dental Enamel Hypoplasia has long been used as a common nonspecific stress indicator in teeth from archaeological samples. Most researchers report relatively minor linear and pitted hypoplastic defects on tooth crown surfaces. In this work we report a high prevalence and early age of onset of extensive enamel defects in deciduous and permanent molars in the subadults from the post-medieval cemetery of Broadgate, east central London. Analysis of the dentition of all 45 subadults from the cemetery, using both macroscopic and microscopic methods, reveals disturbed cusp patterns and pitted, abnormal and arrested enamel formation. Forty-one individuals from this group (93.2%) showed some evidence of enamel hypoplasia, 28 of them showing moderate or extensive lesions of molars, deciduous or permanent (63.6% of the sample). Scanning Electron Microscope images reveal many molars with grossly deformed cuspal architecture, multiple extra cusps and large areas of exposed Tomes' process pits, where the ameloblasts have abruptly ceased matrix production, well before normal completion. This indented, rough and poorly mineralized surface facilitates both bacterial adhesion and tooth wear, and when such teeth erupt fully into the mouth they are likely to wear and decay rapidly. We suggest that this complex combination of pitted and plane-form lesions, combined with disruption of cusp pattern and the formation of multiple small cusps, should henceforth be identified as "Cuspal Enamel Hypoplasia."     

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.     

Patterns of dental enamel defects at ancient Mendes, Egypt.

The dental remains of 88 individuals from Old Kingdom, First Intermediate, and Greco-Roman periods at the ancient Egyptian site of Mendes (Tell er-Rub(c)a) were examined for dental enamel hypoplasia, and the results reported here provide some of the first comparative data on enamel defects in ancient Egypt. Overall, 48% of the individuals in the sample have one or more teeth with hypoplasia, with 17% of permanent teeth and 8% of deciduous teeth affected. The permanent teeth account for 87% of the total number of affected teeth, a prevalence over deciduous teeth that is significant at alpha = 0.05. Permanent and deciduous teeth display different patterns of hypoplasia, with the former exhibiting both discrete pitting and linear furrowing, and the latter exhibiting only pits. Teeth with linear defects significantly outnumber those with pits by a factor of more than three to one. Only permanent canines display more than one lesion on a tooth, with a mean of 1.4 defects per affected tooth. Although calculation of the age of insult from lesion position is imprecise, it appears that stress episodes occurred most commonly between approximately 3-5 years of age. The presence of pits in the deciduous dentition, however, suggests that physiological stresses began in utero. There is no statistically significant difference in the frequency of enamel defects between males and females. An observed decrease in the frequency of defects from the Old Kingdom period to the subsequent First Intermediate and Greco-Roman periods is not significant at alpha = 0.05, although such a decrease is expected given epigraphic and other data that refer to prolonged drought and malnutrition in the late Old Kingdom. The calculated chi(2) value of 3.83 is significant at the 0.10 level, however, and since our sample is rather small and the magnitude of the chi-square statistic is a function of sample size, we recommend that future research investigate further the relationship between the frequency of enamel defects and the time period in which they occur.     

Prevalence and etiology of linear enamel hypoplasia in monkeys and apes from Asia and Africa

Ninety-seven specimens of sympatric monkeys and apes from East Malaysia and 115 monkeys and apes from West Africa are examined in order to evaluate the magnitude and nature of the great ape-monkey linear enamel hypoplasia (LEH) 'dichotomy'. This study demonstrates that great apes from both regions have a higher incidence of LEH and repetitive LEH than do gibbons and monkeys. However, the authors find that the dichotomy is not as clear-cut as previous research suggests, since some monkey samples exhibit high LEH frequencies. The authors evaluate the potential influence of great ape-monkey differences in crown height on this dichotomy. They show that canine crown height variation is weakly associated with LEH variation. Differences between monkeys and great apes in their crown formation spans and in their experience of environmental stress may be more likely causes of the dichotomy.     

CRAC channels in dental enamel cells

Enamel mineralization relies on Ca²⁺ availability provided by Ca²⁺ release activated Ca²⁺ (CRAC) channels. CRAC channels are modulated by the endoplasmic reticulum Ca²⁺ sensor STIM1 which gates the pore subunit of the channel known as ORAI1, found the in plasma membrane, to enable sustained Ca²⁺ influx. Mutations in the STIM1 and ORAI1 genes result in CRAC channelopathy, an ensemble of diseases including immunodeficiency, muscular hypotonia, ectodermal dysplasia with defects in sweat gland function and abnormal enamel mineralization similar to amelogenesis imperfecta (AI). In some reports, the chief medical complain has been the patient’s dental health, highlighting the direct and important link between CRAC channels and enamel. The reported enamel defects are apparent in both the deciduous and in permanent teeth and often require extensive dental treatment to provide the patient with a functional dentition. Among the dental phenotypes observed in the patients, discoloration, increased wear, hypoplasias (thinning of enamel) and chipping has been reported. These findings are not universal in all patients. Here we review the mutations in STIM1 and ORAI1 causing AI-like phenotype, and evaluate the enamel defects in CRAC channel deficient mice. We also provide a brief overview of the role of CRAC channels in other mineralizing systems such as dentine and bone.     

华南化石猩猩前部牙齿釉面横纹与牙冠形成时间研究

釉面横纹的分布与数目可以反映牙齿生长发育的时间和速率变化, 在化石研究中能为复原个体生活史提供重要依据。本研究运用扫描电子显微镜观察华南化石猩猩门齿、犬齿釉面横纹分布与数目, 并估算门齿和犬齿牙冠形成时间, 结果如下: 牙冠从牙尖至牙颈方向釉面横纹分布密度有疏密变化, 牙尖釉面横纹密度小于10条/mm, 中间至牙颈釉面横纹密度较尖部增大, 大约10-15条/mm; 犬齿釉面横纹数目多于门齿, 雄性犬齿釉面横纹数目多于雌性; 根据釉面横纹计数及其生长周期的组织切片观察结果, 估算门齿牙冠形成时间大约为2.97-6.66年, 犬齿雄性长于雌性, 分别为6.25-11.31年和4.28-7.29年。与一些古猿、早期人类、现代人以及现生大猿比较, 华南化石猩猩釉面横纹整体密度稍大于南方古猿和傍人, 小于黑猩猩、大猩猩、现代人和禄丰古猿; 除侧门齿外, 华南化石猩猩釉面横纹数目明显多于南方古猿、傍人和现代人, 与大猩猩接近; 华南猩猩前部牙齿牙冠形成时间与现生大猿、禄丰古猿差别不大, 与现生猩猩最相近, 长于南方古猿和傍人。     

Health of infants in an Imperial Roman skeletal sample: perspective from dental microstructure

This study examines general health in the first year of life of a population of 127 subadults from the Imperial Roman necropolis of Isola Sacra (2nd-3rd century ACE). Health status was determined by analyzing 274 deciduous teeth from these children for Wilson bands (also known as accentuated striae), microscopic defects caused by a disruption to normal enamel development arising from some generalized external stressor. While macroscopic enamel defects, or hypoplasias, have long been used as proxies of general population health, we believe that this is the first population-wide study of microscopic defects in deciduous teeth. We used microstructural markers of enamel to attach very precise chronologies to Wilson band formation that allowed us to calculate maximum prevalence (MAP) and smoothed maximum prevalence (SMAP) distributions to portray what we believe to be a realistic risk profile for a past population of children. There appear to be two periods of high prevalence, the first beginning around age 2 months and continuing through month 5, and the second higher period beginning around month 6 and continuing through month 9. These results are discussed in light of historical records of Roman childhood rearing practices.     

Localized enamel hypoplasia of human deciduous canine teeth: prevalence and pattern of expression in rural Pakistan

Localized hypoplasia of the labial surface of deciduous canine teeth is a widely reported enamel defect, the etiology of which remains enigmatic. Published frequencies for this defect are based on small or biased samples from prehistoric and clinical contexts. In this study I report the prevalence and pattern of expression of this defect among 113 schoolchildren of Harappa village, Punjab Province, Pakistan. The labial surface of deciduous canines of children between the ages of 5 and 8 years was examined using a penlight; age, sex, stature, and socioeconomic status were also recorded. The defect occurs in 34.5% of the subjects studied and in 14.6% of the teeth examined. No significant association was found between the presence of the defect and gender, socioeconomic status, stature, or side of the jaw. The hypoplastic lesion occurs more frequently in the mandible than in the maxilla, and bilateral expressions are less common than unilateral expressions. These results confirm specific aspects of earlier studies and imply that localized (circular) enamel hypoplasia of deciduous teeth, unlike linear enamel hypoplasia, is not a marker of systemic growth disruption.     

Microstructural defects and enamel hypoplasia in teeth of Toxodon Owen, 1837 from the Pleistocene of Southern Brazil

Enamel hypoplasia is characterized by reduction in the enamel thickness, resulting from a disruption of ameloblast activity due to systemic physiological stress. The euhypsodont teeth of Toxodon, a notoungulate from the Pleistocene of South America, often exhibit signs of enamel hypoplasia, in the form of continuous grooves or a series of pits where the enamel is thinner than in normal areas. These defects alternate with areas of normal enamel, and sometimes more than one form of enamel hypoplasia is present on the same tooth. This study analysed teeth of Toxodon from the Pleistocene Touro Passo Formation and the coastal plain of State of Rio Grande do Sul, Southern Brazil. Six types of enamel hypoplasia were observed. Upper teeth present mainly superficial grooves on the buccal surface, and the defects are less severe than those observed in the lower teeth. In the lower incisors, deep grooves with mesiodistal rows of pits were observed, showing clearly cyclical changes, which to a lesser degree, exist in all teeth. These changes are likely related to the continuous growth of euhypsodont teeth. Seven specimens were analysed under scanning electron microscopy and optical microscopy, which showed the occurrence of microstructural changes associated with the macroscopic enamel defects. Enamel underlying in the vicinity of hypoplastic defects was aprismatic and associated with prominent pathologic striae. These pathological findings might indicate that toxodonts were exposed to some stressing conditions or that their teeth were more easily abraded due to a change in diet items, related to shifting climatic conditions.     

许家窑人幼年个体的釉质发育缺陷

上世纪70年代在许家窑-侯家窑地点发现的人类化石对了解东亚中晚更新世过渡时期古人类的形态演化起到了重要作用。除形态特征外,针对许家窑人病理表现也开展过相关研究,其中许家窑人幼年个体前部牙齿上出现的黄色小坑被认为是患有氟斑牙病的证据,且可能代表世界范围内该牙病的最早实例。然而,经电子显微镜和显微断层扫描显示,这些黄色小坑或凹陷是釉质发育不良表现,而不是代表个体患有氟斑牙病后牙齿受咀嚼压力而产生的物理破损。同步辐射扫描显示,许家窑幼年个体前部牙齿釉质密度均匀,没有出现浅层釉质矿化减小的现象,不支持该个体因釉质矿化过程受影响而患有典型氟斑牙的结论。尽管如此,后部牙齿上大量坑状的釉质缺陷和坑状缺陷底部的加重生长线特征不排除是个体氟摄入过量而影响釉质形成的分泌期而导致的。除表面坑状釉质缺陷外,许家窑幼年个体恒齿不同部位的釉质内部出现缺失（空间结构一般为圆球状）。缺失主要集中在浅层区域,沿齿尖-齿颈方向的密集程度变化与釉质发育不良位置具有一定相关性。釉质内部缺失有时互连并与釉质表面垂直。以上特征显示釉质内部缺失是釉质形成过程受影响所致,且影响因素和发生机理可能与釉质发育不良的类似。许家窑幼年个体不同牙齿在外部釉质缺陷和内部釉质缺失密集程度上的差别可能反映的是个体在发育过程中所需应对的外界扰动因素程度不同。未来研究可对包含许家窑人化石的堆积物中以及许家窑人牙齿中的氟含量进行测定,以进一步研究许家窑人个体的生活环境中是否有过量的氟以及许家窑人是否摄入了过量氟元素,从而对许家窑人的牙齿发育缺陷机理有一个进一步的了解。     

Linear enamel hypoplasia as an indicator of physiological stress in great apes: reviewing the evidence in light of enamel growth variation

Physiological stress, such as malnutrition or illness, can disrupt normal enamel growth, resulting in linear enamel hypoplasias (LEHs). Although ecological factors may contribute to LEH expression, other factors, such as surface abrasion and enamel growth variables, are also likely to be involved. Attention to these other factors is necessary before we can begin to understand what LEH might signify in terms of ecological sources of physiological stress in non-human primates. This study focuses on assessing the contribution of these other factors to variation in LEH expression within and across great ape taxa. Here, we present LEH data from unabraded crown regions in samples of seven great ape species. We analyze these data with respect to lateral enamel formation time and the angles that striae of Retzius make with the enamel surface, as these variables are expected to affect variation in LEH expression. We find that although the duration of enamel formation is associated with sex differences in LEH expression, it is not clearly related to taxonomic variation in LEH expression, and does not explain the low frequency of LEH in mountain gorillas found in this and a previous study. Our data on striae of Retzius angles suggest that these influence LEH expression along the tooth crown and may contribute to the consistently high frequencies of LEH seen in Pongo in this and previous studies. We suggest that future work aimed at understanding species variation in these angles is crucial to evaluating taxonomic patterns of LEH expression in great apes.