Biology subjects

Towle, I.

Publications and source records attributed to Towle, I..

12 recordsLinked to original sources

bioRxiv2025

Tracking molar wear in captive baboons: sex and age effects using a modified Scott scoring system

ObjectivesThis study evaluates molar wear progression in a captive baboon population under controlled dietary and environmental conditions. By comparing the dentin exposure ratio (DER) with a newly developed quadrant-based modification of Scotts dental wear scoring system (Krueger-Scott method), we evaluate how wear patterns vary by age, sex, and occlusal region. Materials and MethodsMandibular second molars (M2) were assessed at two timepoints, during life and postmortem, in 201 captive baboons from the Southwest National Primate Research Center. Krueger-Scott and DER data were collected from 3D intraoral scans processed in MEDIT Link software. The Krueger-Scott scores assigned ordinal scores (1-10) to four equal quadrants of each M2 based on enamel facet development and dentin exposure. Statistical analyses tested relationships between wear progression, quadrant location, sex, and age. ResultsKrueger-Scott scores and DER values increased significantly between timepoints, indicating wear progression. However, Krueger-Scott scores revealed strong functional patterning: buccal and lingual cusps showed high within-group correlations and weaker cross- group correlations. Males showed significantly higher wear than females, despite being younger on average. The relationship between age and wear progression differed by sex. DiscussionThe Krueger-Scott method provided a more anatomically informative and efficient approach to tracking occlusal wear than DER. It captured regional wear variation and functional asymmetries that DER could not detect. Even under controlled conditions, sex-based differences in wear emerged, likely reflecting behavioral, morphological, or enamel structural variation. These findings offer a comparative baseline and demonstrate the utility of quadrant- level scoring for interpreting wear in extant and extinct taxa.

animal behavior and cognition↗

bioRxiv2024

Assessing tooth wear progression in primates: A longitudinal study using intraoral scanning technology

Intraoral scanners are widely used in a clinical setting for orthodontic treatments and tooth restorations, and are also useful for assessing dental wear and pathology progression. In this study, we assess the utility of using an intraoral scanner and associated software for quantifying dental tissue loss in non-human primates. An upper and lower second molar for 31 captive hamadryas baboons (Papio hamadryas) were assessed for dental tissue loss progression over multiple years (n = 62 teeth). The animals are part of the Southwest National Primate Research Center and were all fed the same monkey-chow diet over their lifetimes. Two molds of each dentition were taken at either two- or three-year intervals, and the associated casts scanned using an intraoral scanner (Medit i700). Tissue loss was calculated in WearCompare by superimposition of the two scans followed by subtraction analysis. Four individuals had dental caries, and were assessed separately. The results demonstrate the reliability of these techniques in capturing tissue loss data, evidenced by the alignment consistency between scans, lack of erroneous tissue gain between scans, and uniformity of tissue loss patterns among individuals (e.g., functional cusps showing the highest degree of wear). The average loss per mm{superscript 2} per year for all samples combined was 0.05 mm3 (0.04 mm3 for females and 0.08 mm3 for males). There was no significant difference in wear progression between upper and lower molars. Substantial variation in the amount of tissue loss among individuals was found, despite their uniform diet. These findings foster multiple avenues for future research, including the exploration of wear progression across dental crowns and arcades, correlation between different types of tissue loss (e.g., attrition, erosion, fractures, caries), interplay between tissue loss and microwear/topographic analysis, and the genetic underpinnings of tissue loss variation.

evolutionary biology↗

bioRxiv2023

Severe enamel defects in wild Japanese macaques

Plane-form enamel hypoplasia (PFEH) is a severe dental defect in which large areas of the crown are devoid of enamel. This condition is rare in humans and rarer in wild primates. The etiology of PFEH has been linked to exposure to severe disease, malnutrition, environmental toxins, and other systemic conditions. Similar defects have also been associated with genetic conditions such as amelogenesis imperfecta. In this study, we examined the prevalence of all types of enamel hypoplasia in several populations of wild Japanese macaques (Macaca fuscata) with the aim of providing context for the severe defects found in macaques from Yakushima Island. We found that macaques from other islands and from the mainland of Japan have low prevalence of the more common types of enamel hypoplasia and none exhibit PFEH. In contrast, 10 of the 21 individuals (48%) from Yakushima Island displayed uniform and significant PFEH, with all 10 living in two adjacent locations in the south of the island. All permanent teeth were affected to varying degrees except for first molars, and the mineral content of the remaining enamel in teeth with PFEH is normal (i.e., no hypo- or hyper mineralization). Given that the affected individuals have smaller first molars compared to non-affected macaques, and that they all underwent dental development during a period of substantial human-related habitat change, we conclude that the PFEH likely resulted from environmental stress. Extreme weather events on the island may also have influenced the formation of these defects. Additionally, it is plausible that a documented recent population bottleneck could have heightened the susceptibility of these macaques to PFEH. Further research on living primate populations is needed to better understand the causes of PFEH in wild primates and to evaluate whether such features can be used to assess the impact of human-related disturbance.

ecology↗

bioRxiv2021

Variation in mechanical and structural properties of enamel in primate molars

Mechanical properties of enamel are known to vary across molar crowns in some primates, but the association of this variation with phylogeny, structural properties and tribological behaviour is not well understood. In this study, 20 molars from a range of primate taxa (n=15) were studied using nanoindentation, micro-CT scanning, and SEM imaging. After micro-CT scanning, teeth were sectioned in the lingual-buccal plane through the mesial cusps. Five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral) were studied in three locations (inner, middle, outer enamel regions). The results show middle enamel had the highest hardness and elastic modulus values in all positions. Non-functional molar sides (lingual in lower molars and buccal in upper molars) had higher hardness values than their functional counterparts. Increase in prism size was associated with a decrease in hardness in some tooth positions, and mineral density showed a significant relationship with elastic modulus values. Variation in enamel structure variation (e.g., enamel Schmelzmuster, Hunter-Schreger band thickness), may also be crucial in explaining variation in mechanical properties, with decussation zones associated with higher mechanical properties values. Primate enamel is not a homogeneous material, with variation in mechanical and structural properties across the crown likely associated with functional differences and variation in force distribution. Overall structural and mechanical patterns were similar in the primate species studied despite substantial differences in diet, suggesting these properties are potentially evolutionary conserved.

evolutionary biology↗

bioRxiv2021

Dental caries in wild primates: interproximal cavities on anterior teeth

Dental caries has been reported in a variety of primates, although is still considered rare in wild populations. In this study, 11 catarrhine primates were studied for the presence of caries. A differential diagnosis of lesions found in interproximal regions of anterior teeth was undertaken, since they had been previously described as both carious and non-carious in origin. Each permanent tooth was examined macroscopically, with severity and position of lesions recorded. Two specimens were micro-CT scanned to assess demineralization. The differential diagnosis confirmed the cariogenic nature of interproximal cavities on anterior teeth (ICATs). Overall results show 3.3% of teeth are carious, with prevalence varying among species from 0% to over 7% of teeth affected. ICATs occurred in Pan troglodytes (9.8%), Gorilla gorilla gorilla (2.6%), Cercopithecus denti (22.4%), Presbytis femoralis (19.5%) and Cercopithecus mitis (18.3%). They make up 87.9% of carious lesions on anterior teeth. These results likely reflect dietary and food processing differences among species, but also between the sexes (e.g., 9.3% of teeth of female chimpanzees were carious vs. 1.8% in males). Processing cariogenic fruits and seeds with the anterior dentition (e.g., wadging) likely contributes to ICAT formation. Further research is needed on living populations to ascertain behavioral/dietary influences on caries occurrence in primates. Given the constancy of ICATs in frugivorous primates, their presence in archaeological and paleontological specimens may shed light on diet and food processing behaviors in fossil primates.

zoology↗

bioRxiv2021

Tooth chipping patterns in Paranthropus do not support regular hard food mastication

The paranthropines, including Paranthropus boisei and Paranthropus robustus, have often been considered hard-food specialists. The large post-canine teeth, thick enamel, and robust craniofacial features are often suggested to have evolved to cope with habitual mastication of hard foods. Yet, direct evidence for Paranthropus feeding behaviour often challenges these morphological interpretations. The main exception being antemortem tooth chipping which is still regularly used as evidence of habitual mastication of hard foods in this genus. In this study, data were compiled from the literature for six hominin species (including P. boisei and P. robustus) and 17 extant primate species, to analyse Paranthropus chipping patterns in a broad comparative framework. Severity of fractures, position on the dentition, and overall prevalence were compared among species. The results indicate that both Paranthropus species had a lower prevalence of tooth fractures compared to other fossil hominin species (P. boisei: 4%; P. robustus: 11%; Homo naledi: 37%; Australopithecus africanus: 17%; Homo neanderthalensis: 45%; Epipalaeolithic Homo sapiens: 29%); instead, their frequencies are similar to apes that masticate hard items in a non-regular frequency, including chimpanzees, gibbons, and gorillas (4%, 7% and 9% respectively). The prevalence is several times lower than in extant primates known to habitually consume hard items, such as sakis, mandrills, and sooty mangabeys (ranging from 28% to 48%). Comparative chipping analysis suggests that both Paranthropus species were unlikely habitual hard object eaters, at least compared to living durophage analogues.

paleontology↗

bioRxiv2019

Dental caries in human evolution: frequency of carious lesions in South African fossil hominins

Caries frequencies in South African fossil hominins were observed and compared with other hominin samples. Species studied include Paranthropus robustus, Homo naledi, Australopithecus africanus, early Homo and A. sediba. Teeth were viewed macroscopically with Micro-CT scans used to confirm lesions. Position and severity of each lesion were also noted and described. For all South African fossil hominin specimens studied, 16 have carious lesions, six of which are described for the first time in this study. These are from a minimum of six individuals, and include four P. robustus, one H. naledi, and one early Homo individual. No carious lesions were found on deciduous teeth, or any teeth assigned to A. africanus. Most are located interproximal, and only posterior teeth are affected. Caries frequency typically ranges between 1-5% of teeth in non-agricultural human samples, and this pattern seemingly holds true for at least the past two million years in the hominin lineage. Non-agricultural populations significantly above or below this threshold generally have a specialized diet, supporting other dietary evidence that A. africanus likely consumed large amounts of tough, non-cariogenic vegetation. Given the common occurrence of caries in the other hominin species, cariogenic bacteria and foods were evidently common in their collective oral environment. Along with recent research highlighting additional examples of caries in H. neanderthalensis, early Homo and Pleistocene H. sapiens, caries is clearly an ancient disease that was much more common than once maintained throughout the course of human evolution.View Full Text

paleontology↗

bioRxiv2019

Dental abscesses on the maxilla of a two million-year-old early Homo specimen

Abscesses and other periapical lesions are found in abundance in recent archeological samples, yet are scarce in the fossil hominin record. Periapical voids commonly develop after exposure of a tooth’s pulp chamber and are commonly associated with heavy crown wear, trauma or caries. In this study, all available maxilla and mandible fragments from the South African fossil hominin collections were studied, including specimens assigned to Homo naledi, Paranthropus robustus, Australopithicus africanus, A. sediba and early Homo. Only one specimen displayed voids consistent with periapical lesions, and a differential diagnosis of these voids was undertaken. The specimen, SK 847, is described as early Homo and has been dated to 2.3-1.65MA. There is one definite abscess, and likely at least two more with postmortem damage, all on the anterior aspect of the maxilla and associated with the incisors. The abscesses originate from the apices of the incisor roots and are therefore unlikely to represent a systemic disease such as multiple myeloma. They best fit the description of an abscess rather than a cyst or granuloma, with one showing a rounded thickened rim around the lesion. The abscesses highlight that this individual used their anterior dentition extensively, to the point that the pulp chambers were exposed on multiple teeth. This is one of the earliest hominin examples of a dental abscess and shows that this individual was able to cope with several concurrent abscesses, clearly surviving for an extended period. Therefore, this finding adds additional information to the history of dental pathology in our genus.View Full Text

paleontology↗

bioRxiv2019

Root caries on a Paranthropus robustus third molar from Drimolen

Objectives Dental caries is often perceived as a modern human disease. However, their presence is documented in many early human groups, various non-human primates and, increasingly, our hominin ancestors and relatives. In this study we describe an antemortem lesion on the root of a Paranthropus robustus third molar from Drimolen, South Africa, which likely represents another example of caries in fossil hominins.Materials and Methods The molar, DNH 40, is dated to 2.0–1.5 Ma and displays a lesion on the mesial root surface, extending from the cementoenamel junction 3 mm down toward the apex. The position and severity of the lesion was macroscopically recorded and micro-CT scanned to determine the extent of dentine involvement.Results A differential diagnosis indicates root caries, as the lesion is indistinguishable from clinical examples. Although necrotic in appearance, external tertiary dentine is evident on a micro CT scan. Gingival recession and/or continuous eruption of the tooth as a result of extensive occlusal wear would have occurred to facilitate caries formation. Therefore, the lesion is likely linked to relative old age of this individual.Discussion This new example increases the total number of carious lesions described in P. robustus teeth to 12, on occlusal, interproximal and, now, root surfaces. Beyond the consumption of caries-causing food(s), caries formation would have also required the presence of requisite intra-oral cariogenic bacteria in this individual and the species. Of interest, the presence of tertiary dentine on the outward surface suggests the DNH 40 lesion may have been arrested, i.e., no longer active, perhaps relating to a change in diet or oral microbiome just prior to the individual’s death.View Full Text

paleontology↗

bioRxiv2018

A probable genetic origin for pit defects on the molars of Paranthropus robustus

We report the frequencies of linear enamel hypoplasia (LEH) and, specifically, pitting enamel hypoplasia (PEH) defects in the teeth of Paranthropus robustus, for comparison with four other South African hominin species and three extant nonhuman primate species. Unlike LEH, the lesser known PEH is characterized by multiple circular depression defects across a tooth crown and is often difficult to interpret in terms of developmental timing and etiology. Teeth in all samples were examined macroscopically with type, position and number of defects recorded. Frequencies of teeth with LEH vary among hominin species, but the differences in PEH are considerable. That is, P. robustus has much higher rates of pitting defects, with 47% of deciduous teeth and 14% of permanent teeth affected, relative to 6.7% and 4.3%, respectively, for all other hominin teeth combined; none of the extant primate samples evidence comparable rates. The defects on P. robustus molars are unlike those in other species, with entire crowns often covered in small circular depressions. The PEH is most consistent with modern human examples of amelogenesis imperfecta. Additionally, the defects are: 1) not found on anterior teeth, 2) uniform in shape and size, and 3) similar in appearance/severity on all molars. A possible reason for this form of PEH is as a side effect of selection on another phenotype that shares the same coding gene(s), i.e., a genetic origin. Recent research on the ENAM gene provides one such possibility. Paranthropus likely underwent rapid evolution in the ENAM loci, with changes in this gene contributing to larger posterior teeth and thicker enamel. This same gene is associated with amelogenesis imperfecta; therefore, pleiotropy effects, relating to high selection on this gene during Paranthropus evolution, could have yielded this unique condition.

evolutionary biology↗

bioRxiv2017

Root grooves on two adjacent anterior teeth of Australopithecus africanus

Tooth root grooves and other ante-mortem dental tissue loss not associated with caries found on or near the cementoenamel junction (CEJ) are commonly termed non-carious cervical lesions. Three main processes are implicated in forming these lesions: abrasion, dental erosion, and abfraction. As yet, these lesions have not been described in non-Homo hominins. In this study South African fossil hominin collections were examined for evidence of any type of non-carious cervical lesion. Only one individual shows ante-mortem root grooves consistent with non-carious cervical lesions. Two teeth, a mandibular right permanent lateral incisor (STW 270) and canine (STW 213), belonging to the same Australopithecus africanus individual, show clear ante-mortem grooves on the labial root surface. These lesions start below the CEJ, extend over a third of the way toward the apex, and taper to a point towards the lingual side. Microscopic examination revealed no clear directional striations. The shape of these grooves is extremely similar to clinical examples of dental erosion, with the lack of striations supporting this diagnosis. These are the oldest hominin examples of non-carious cervical lesions and first described in a genus other than Homo; further, the lesions suggest that this individual regularly consumed or processed acidic food items.

paleontology↗

bioRxiv2017

Dietary and behavioral inferences from dental pathology and non-masticatory wear on dentitions from a British medieval town

Dental pathology and wear data can provide valuable insights into diet, cultural practices, and the health of populations. In this study, various dental pathologies and types of wear were recorded for 41 individuals (914 permanent teeth), excavated from the medieval cemetery of St. Owens Church in Southgate Street, Gloucester. Teeth were studied macroscopically with a 10x hand lens to confirm the presence of specific pathologies. Relatively high rates of antemortem chipping on the anterior teeth, and the presence of maxillary central incisor notches, suggested that the Gloucester population commonly used their teeth for non-masticatory activities. Abscessing and antemortem tooth loss fell within previously reported ranges for British medieval sites (2.6% and 6% respectively). However, the sample exhibits extremely high levels of carious lesions and calculus. Nearly 24% of teeth have at least one carious lesion, and the presence of calculus was recorded in 74% of teeth within the sample. Overall caries frequency is similar to sites from later time periods. This frequency may reflect Gloucesters location as a large port town. Remains from the same area, but the earlier Roman period, also shows high rates of both caries and calculus, suggesting a continuation of consuming certain cariogenic foods is likely.

pathology↗