An official website of the United States government
Dental topographic analysis is a suite of measurements designed to capture functional information about occlusal morphology that can be effectively applied to wear series. Recent studies have revealed that some primate folivores exhibit an apparent improvement in dental function (i.e., increased occlusal sharpness) with increased wear—a phenomenon termed ‘dental sculpting.’ While dental sculpting has been identified in a folivorous platyrrhine (Alouatta) and colobine (Presbytis), its prevalence across primate phylogeny and ecomorphology remains underexplored. A wear series of 13 bonobo (Pan paniscus) second mandibular molars were analyzed for dental topography and amount of wear. 3D surfaces were generated in Avizo from μCT data of specimens housed at the Royal Belgian Institute of Natural Sciences representing the broadest range of wear states available. Occlusal sharpness was measured as convex Dirichlet normal energy (DNE) using the R package molaR. Wear was quantified as the dentine exposure ratio (DER) by imaging specimens in occlusal view and measuring the ratio of exposed dentine area to total occlusal area. Linear regression analysis found that DNE declined significantly with increased DER (p= 0.002), with moderate explanatory power (r2= 0.555). These findings suggest that dental sculpting does not occur in Pan paniscus. Our results contrast with those found for the frugivorous platyrrhines Ateles and Plecturocebus, who maintain DNE with wear. Rather, they indicate that bonobos lack compensatory mechanisms to preserve occlusal sharpness across their lifespans and underscore the importance of nutrition gained through relatively soft dietary materials that do not require significant cutting or slicing to efficiently consume.
more »
« less
Dental sculpting and compensatory shearing crests demonstrated in a Wear series of Presbytis rubicunda (Cercopithecoidea, Colobidae) with dental topography analysis
Abstract ObjectivesMaintaining effective and efficient occlusal morphology presents adaptive challenges for mammals, particularly because mastication produces interactions with foods and other materials that alters the geometry of occlusal surfaces through macrowear and/or catastrophic failure (i.e. “chipping”). Altered occlusal morphologies are often less effective for masticating materials of given diet—but not always—some species exhibit dental sculpting, meaning their dentitions are set up to harness macrowear to hone their occlusal surfaces into more effective morphologies (i.e. secondary morphologies). Here we show that dental sculpting is present in the folivorousPresbytis rubicundaof Borneo. MethodsThirty‐one undamaged lower second molars ofP.rubicundaexhibiting various stages of macroscopic wear were micro‐CT scanned and processed into digital surfaces. The surfaces were measured for convex Dirichlet normal energy (vDNE, a measure of surface sharpness), and degree of surface wear. Regression analyses compared surface sharpness with several measures of wear to test for the presence and magnitude of dental sculpting. ResultsPositive correlations between the wear proxies and vDNE reveal thatP.rubicundawear in such a way as to become sharper, and therefore more effective chewing surfaces by exposing enamel‐dentine junctions on their occlusal surfaces and then honing these junctions into sharpened edges. Compared to another primate folivore in which increasing surface sharpness with macrowear has been demonstrated (i.e.,Alouatta palliata), the worn surfaces are similarly sharp, but the dental sculpting process appears to be different. DiscussionThe results presented here suggest that not only do some primates exhibit dental sculpting and the attendant secondary morphology, but that there appear to be multiple different morphological configurations that can achieve this result.P.rubicundahas thicker enamel and a more stereotyped wear pattern thanA.palliata, although both show positive correlations of occlusal surface sharpness (vDNE) with various wear proxies. These findings shed light on the varied approaches for the maintenance of effective and efficient occlusal surfaces in primates.
more »
« less
- PAR ID:
- 10507642
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Biological Anthropology
- ISSN:
- 2692-7691
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
As herbivorous, diphyodont mammals with relatively low-crowned molars, primates experience changes in dental function during their lifetimes as teeth become progressively worn. Maintaining tooth function with wear is thought to pose a particular challenge for folivorous primates whose diets emphasize molar shearing actions. Recent studies using dental topographic methods suggest that certain primate folivores have molar morphology that maintains or increases functional shearing surfaces with tooth wear (‘dental sculpting’). Evidence for this phenomenon has been found in folivorous but not frugivorous New World monkeys, supporting the hypothesis that dental sculpting is an adaptive trait linked to diet. This analysis extends these methods to two sympatric Old World monkeys from Sabah, Malaysia, possessing distinct diets and dental morphologies: the folivorous colobine Trachypithecus cristatus (n=25) and the more frugivorous cercopithecine Macaca fascicularis (n=22). For each species, 3D shear crest lengths and four dental topographic variables (relief index, slope, angularity, and Dirichlet Normal Energy [DNE]) were measured from variably worn lower second molars. Preliminary results indicate that for any given degree of wear, Trachypithecus has longer shear crest lengths and higher relief, slope, angularity, and DNE than Macaca. The two species exhibit different patterns and degrees of change in topography and shearing crest lengths across the wear series. However, these changes do not always match expectations based on their respective diets. Correlations between 3D shear crest lengths and other dental topographic measurements suggests that the type of metric used to assess shearing potential may affect whether or not dental sculpting is detected.more » « less
-
BackgroundComponents of diet known as fallback foods are argued to be critical in shaping primate dental anatomy. Such foods of low(er) nutritional quality are often non-preferred, mechanically challenging resources that species resort to during ecological crunch periods. An oft-cited example of the importance of dietary fallbacks in shaping primate anatomy is the grey-cheeked mangabeyLophocebus albigena. This species relies upon hard seeds only when softer, preferred resources are not available, a fact which has been linked to its thick dental enamel. Another mangabey species with thick enamel, the sooty mangabeyCercocebus atys, processes a mechanically challenging food year-round. That the two mangabey species are both thickly-enameled suggests that both fallback and routine consumption of hard foods are associated with the same anatomical feature, complicating interpretations of thick enamel in the fossil record. We anticipated that aspects of enamel other than its thickness might differ betweenCercocebus atysandLophocebus albigena.We hypothesized that to function adequately under a dietary regime of routine hard-object feeding, the molars ofCercocebus atyswould be more fracture and wear resistant than those ofLophocebus albigena. MethodsHere we investigated critical fracture loads, nanomechanical properties of enamel, and enamel decussation inCercocebus atysandLophocebus albigena.Molars ofCercopithecus, a genus not associated with hard-object feeding, were included for comparison. Critical loads were estimated using measurements from 2D µCT slices of upper and lower molars. Nanomechanical properties (by nanoindentation) and decussation of enamel prisms (by SEM-imaging) in trigon basins of one upper second molar per taxon were compared. ResultsProtocone and protoconid critical fracture loads were significantly greater inCercocebus atysthanLophocebus albigenaand greater in both than inCercopithecus. Elastic modulus, hardness, and elasticity index in most regions of the crown were greater inCercocebus atysthan in the other two taxa, with the greatest difference in the outer enamel. All taxa had decussated enamel, but that ofCercocebus atysuniquely exhibited a bundle of transversely oriented prisms cervical to the radial enamel. Quantitative comparison of in-plane and out-of-plane prism angles suggests that decussation in trigon basin enamel is more complex inCercocebus atysthan it is in eitherLophocebus albigenaorCercopithecus cephus. These findings suggest thatCercocebus atysmolars are more fracture and wear resistant than those ofLophocebus albigenaandCercopithecus. Recognition of these differences betweenCercocebus atysandLophocebus albigenamolars sharpens our understanding of associations between hard-object feeding and dental anatomy under conditions of routine vs. fallback hard-object feeding and provides a basis for dietary inference in fossil primates, including hominins.more » « less
-
Turner, T (Ed.)Advancements in 3D scanning and modeling have transformed dental and dietary analyses, yet studies often focus on whole-crown, unworn teeth, limiting sample sizes and scope due to the challenges of analyzing worn teeth. Here we explore a novel quantitative method using a virtual goniometer to measure occlusal wear angles in over 150 worn mandibular second molars from extant primates, including frugivores, folivores, and hard-object consumers. For the first time, we apply this method to fossil primates: Ekembo, Dendropithecus, and Limnopithecus. Using the Hecate software package, we align and subdivide molars into five patches corre- sponding to the cusps. We segment each patch using the virtual goniometer. This segments the occlusal surface from the corresponding buccal, lingual, mesial, and distal surfaces, providing a normal vector corresponding to the plane of best fit for each segment. We then calculate three key angles that describe the plane orientation. Results suggest the inclination measurement from the virtual goniometer is more robust than the average inclination of points in the occlusal surface. Additionally, we find that, among the fossil sample, wear across cusps does not align with any of the tested extant dietary categories. Paleontology is a versatile field of study, applying methods used across disciplines. Our novel approach provides yet another example in which paleontology makes use of versatile computer application by extending the virtual goniometer’s utility beyond archaeological inquiries to primate dental analysis. Additionally, this application offers valuable insight into evolutionary traits associated with dietary behaviors through the inclusion of extant and fossil primates.more » « less
-
ABSTRACT ObjectivesOdontoblasts lining the pulp cavity deposit dentine throughout life, meaning the volume of the pulp cavity decreases with age. Primates with more abrasive diets have relatively higher molar pulp volume in their unworn molars than those with less abrasive diets. We propose that species with more abrasive diets deposit additional dentine across their lifespans to help resist wear and extend the effective lifespan of their molars. Whereas both age and wear affect dentine deposition, it is unknown which of these two variables has the greater impact. Materials and MethodsWe measured pulp volume and calculated wear from micro‐CT scans of lower first molars of captive‐bredMacaca fascicularis(n = 13) of known age. We used reduced major axis regressions (alpha = 0.05) to test if age or wear was a better predictor of pulp volume. ResultsBoth variables have a significant negative relationship with pulp volume (age:p = 0.004,R2 = 0.546; wear:p < 0.001,R2 = 0.890). A mixed linear model of pulp volume against wear as main effect and age as covariant had a non‐significant interaction effect (p = 0.078) and confirmed that both age (p = 0.030) and wear (p = 0.004) are significantly negatively correlated with pulp volume. DiscussionResults suggest that whereas pulp volume decreases with age, wear is more strongly correlated with decreasing pulp volume. These findings have implications for interpreting odontoblast activity in response to sensory feedback and the relationship between pulp volume and diet. These results also have implications for using molar pulp volume to estimate age at death in humans.more » « less
