Differences In Dental Morphology Research Articles

Configuración del surco de los molares mandibulares de los malayos de ascendencia mongoloide

Aim: Variation in dental structures is widely accepted as a combination of multiple factors such as gender, environmental effects and genetics. However, the characterization of similarities and differences in dental morphology has been lacking in relation to the factors mentioned. This study aims to assess and compare the variations in traits in mandibular molars and the influence of gender and ethnicity in affecting these traits amongst the Malaysian population of Mongoloid ancestry. Materials and Methods: Our study population was 180 dental casts of patients, from 15 to 40 years old, comprising 56 Malays and 124 Chinese; 60 were males and 120 were females. Traits like groove pattern, number of cusps, protostylids and deflecting wrinkles were observed, scored, and recorded. Results: This study revealed that the most common mandibular first molar (M1) was characterized by 5 cusps and displayed ‘Y’ groove pattern, while the most common mandibular second molar (M2) had 4 cusps and exhibited a groove pattern that resembled a ‘+’. Notably, all the traits studied were bilaterally symmetrical, except for the groove pattern of M1, while sexual dimorphism was observed in groove patterns of M2. Conclusions: This study found that M1 had a preponderance of 5 cusps with ‘Y’ groove pattern, while M2 were typically 4-cusped with ‘+’ groove pattern. Keywords: Malaysia; Asian people; Ethnicity; Gender; dental anatomy; molar.

Radiographic Identification of Dental Anomalies in Selected Telugu Population of Andhra Pradesh, India

The basic objective of any forensic examination involving unidentified human remains is to identify the individual(s). The forensic significance of teeth can be attributed to their strong resilience to explosive and thermal stress, as well as the possibly unique personal information that can be gleaned from their analysis. Furthermore, the morphology of teeth varies between (and within) populations and sexes. Anomalies in the teeth are a common component of macroscopic dental morphological differences. The current study assesses the incidence of certain dental abnormalities in Population of Andhrapradesh. This study was carried out using Pretreatment records of 630 patients of Andhra Pradesh, India. The Radiographs were reviewed for Dental Anomalies.The anomaly, number of teeth affected, and the location of Anomaly were recorded. To find correlations between dental abnormalities and gender, a Chi-square test was carried out using SPSS software. Of the 630 patients screened 427 (67.7%) presented with at least one anomaly and 203(32.3%) subjects showed no anomaly. Hypodontia is the most prevalent anomaly(38.25%) followed by Impaction(17.30%) and Rotation (17.14%). Anodontia(0.79%) and Hyperdontia(0.95%) are the least prevalent anomalies. Statistical study revealed that dental abnormalities were independent of sex. The prevalence and impact of dental anomalies in various population groups may provide important information for phylogenic and genetic studies, allowing us to comprehend intra and inter-population variation.

Two new species of ektopodontid marsupial from the lower deposits of the Etadunna Formation (latest Oligocene), South Australia and a phylogenetic hypothesis for the Ektopodontidae

Molar morphologies of the latest Oligocene genera, Chunia and Ektopodon, are easy to distinguish, but species determinations are more difficult. As more specimens have been collected, more maxillary fragments with molars and/or alveoli and a portion of the rostrum preserved are available. With a suite of maxillae now known, new ektopodontid features have revealed themselves, including the shortening of the rostrum compared to other families of contemporary possums. The facial angulation represented by the flexure of the rostrum at the boundary between P3 and the molar row results in the rostrum being angled differently than the molar row. Ektopodontids have a significantly greater angulation and thus shorter faces, compared to that seen in contemporary phalangeriform possums. Two new species of the genus Chunia, from the lower Etadunna Formation, South Australia, can be distinguished from the type species, Chunia illuminata, of the Ditjimanka Local Fauna. Differences in molar morphologies and the degree of facial angulation distinguish a new species of Chunia from the lowest faunal zone and the Minkina Local Fauna (facial angulation of 52°) from C. illuminata from the next higher faunal zone (Ditjimanka Local Fauna), which has a greater facial angulation of 63°, while a second new species of Chunia, also from the Dijimanka Local Fauna, has a facial angulation of 58° and intermediate molar traits. The degree of facial shortening is a valid discriminator between species of ektopodontid marsupials as it coincides with the species level differences in dental morphology. Additionally, C. omega from the Tarkarooloo Local Fauna is placed in new genus, Ngathachunia, as it is outside of the hypodigms for both of the previously described genera, Chunia and Ektopodon. A well-supported phylogenetic hypothesis for the family indicates the species of Ektopodon form a monophyletic clade, while the species of Chunia are paraphyletic.Judd A. Case [jcase@ewu.edu], Department of Biology, Eastern Washington University, Cheney, WA 99004, USA. Case, J.A., Month, 202X. Two new species of ektopodontid marsupial from the lower deposits of the Etadunna Formation (latest Oligocene), South Australia and a phylogenetic hypothesis for the Ektopodontidae. Alcheringa XXX, X–X. ISSN 0311-5518.

Enamel chipping and its ecological correlates in African papionins: Implications for hominin feeding behavior.

African papionins are classic paleoecological referents for fossil hominins. Enamel chips on the teeth of baboons and hominins are argued to represent responses to similar dietary habits; however, a comprehensive analysis of modern papionin chipping is lacking, leaving open the question of analog suitability. Here, we investigate patterns of antemortem enamel chipping across a diverse set of African papionin species occupying a range of ecological niches. We compare papionin chipping frequencies to estimates for Plio-Pleistocene hominins to address hypotheses of habitat and/or dietary similarities. Antemortem chips in seven African papionin species were scored on intact postcanine teeth (P3-M3) using established protocols. Chip size was scored on a tripartite scale. Papio hamadryas and Papio ursinus-two common paleoecological referents-display higher levels of chipping than Plio-Pleistocene hominin taxa (Australopithecus and Paranthropus) posited to have similar dietary habits. Papio populations occupying dry or highly seasonal habitats accumulate more large chips than Papio taxa occupying more mesic habitats, and terrestrial papionins chip their teeth more often than closely related taxa occupying arboreal niches. Chipping is present on the teeth of all Plio-Pleistocene hominins; however, chipping in baboons (P.ursinus and P.hamadryas) consistently exceeds most hominin taxa. Chipping frequencies on their own do not reliably sort taxa into major dietary groupings. We conclude that the large differences in chipping frequency may instead reflect habitat use and food processing idiosyncrasies. Less chipping in Plio-Pleistocene hominin teeth compared to modern Papio is more likely attributable to differences in dental morphology rather than diet.

Societal segmentation and early urbanism in Mesopotamia: Biological distance analysis from Tell Brak using dental morphology

The urbanization of Mesopotamia in the 4th millennium BCE led to unprecedented social, economic, and political changes. Tell Brak, located in the Syrian Khabur basin, is one of the best-known early urban sites from this period. Surveys suggest that urban growth at Tell Brak resulted from peripheral expansion driven by the migration of several distinct groups; however, it is not known whether these groups remained recognizably distinct within the newly formed urban center.In the current study, the impact of early urbanization on social organization was explored using non-metric dental data from skeletons excavated from the main site at Tell Brak (n = 111) and its satellite mound Tell Majnuna (n = 179). The Arizona State University Dental Anthropology System (ASUDAS) was employed to examine biodistance between population subsets from the period of early urbanization in the Late Chalcolithic (LC) and the Early Bronze Age (EBA).The results demonstrate differences in dental morphology among the LC groups indicating segmentation within the early urban population at Tell Brak. Patterns of social organization associated with urbanization have thus framed the socio-cultural landscape of even the earliest cities, and bioarchaeological data can be a useful tool for understanding both ancient and modern urbanization.

Development of an online tooth morphology course in response to COVID-19 restrictions.

Tooth morphology, a foundation of clinical and laboratory dentistry, is traditionally taught using lectures supported by study using extracted teeth, plastic replica, wax or chalk carving, or drawing.1 The need to review this model has been highlighted recently by pressures that include the difficulty to obtain and retain good quality teaching specimens, and reduction in teaching hours.1 During academic year 2020–2021, in response to the COVID-19 pandemic and in line with government restriction, our institution curtailed physical presence on campus for staff and students posing additional challenges to the delivery of our tooth morphology course. The delivery of lectures through recordings uploaded to a virtual learning environment (VLE) or remote lecturing using communication platforms cannot fully alleviate the problem. Learning with models (2D or 3D) is preferable to help integrate knowledge acquired in lectures with the 3D structure and appreciate differences in dental morphology. Flash cards offer a potential solution as they provide multiple views of the same tooth and highlight distinguishing features of the teeth. While some learners easily translate 2D information into 3D representations, others struggle with the process.2 In addition, assessment of knowledge in 2D is not aligned with its clinical application. dvantage of the Canvas VLE available at our institution to develop a self-directed tooth morphology learning environment proposing multiple entry points in 2D or 3D to students. We generated interactive FDI (Fédération Dentaire Internationale, FDI World Dental Federation) grids representing permanent or deciduous dentitions. Each button on the grid was linked to a Canvas VLE page containing either a 2D flashcard or a 3D interactive model for each tooth (Figure 1). The dental schools at the University of Dundee and the University of Michigan in Ann Arbor both created a series of 3D dental morphology models for permanent or deciduous dentitions available from the SketchFab website. These models were embedded into Canvas pages, allowing students to access the model in situ without access to external sites. Staff-led interactive sessions were held through Microsoft Teams using unlabeled 3D models loaded to Microsoft PowerPoint. These were screen shared to discuss dental features and quiz students. Each week, lecture notes and recordings were made available (see Supporting Information for full description). Assessment was performed through Canvas quizzes using embedded 3D models that students had not previously seen. Each question required learners to correctly identify a 3D tooth model and answer a question regarding the developmental milestones of the tooth. In response to the problems described above, the solution developed has allowed the continuation of delivery of material for which 3D spatial representation is important. The models were labeled to highlight individual features, providing students with an integrated 3D learning tool that could potentially rival extracted teeth as it offers immediate feedback on feature identification. Examination results for the 2021 cohort (68.7 ± 1.8%) are in line with the average results of the cohorts from 2016 to 2019 (71.5 ± 1.2%, p = 0.237 Student's t-test). The use of 2D and 3D approaches combined with lecture recording, notes, and live sessions for discussions with instant feedback allowed us to cater to different learning modes, and diverse schedules, and gave control to learners, in line with the principles of the Universal Design for Learning.3 While more research will be needed to investigate if students can translate virtual 3D learning to the identification of extracted teeth and if this can be implemented as a replacement for in-person teaching, we believe that this approach offers a strong alternative for students that prefer a self-paced learning environment to directed education. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Distinct tooth regeneration systems deploy a conserved battery of genes

BackgroundVertebrate teeth exhibit a wide range of regenerative systems. Many species, including most mammals, reptiles, and amphibians, form replacement teeth at a histologically distinct location called the successional dental lamina, while other species do not employ such a system. Notably, a ‘lamina-less’ tooth replacement condition is found in a paraphyletic array of ray-finned fishes, such as stickleback, trout, cod, medaka, and bichir. Furthermore, the position, renewal potential, and latency times appear to vary drastically across different vertebrate tooth regeneration systems. The progenitor cells underlying tooth regeneration thus present highly divergent arrangements and potentials. Given the spectrum of regeneration systems present in vertebrates, it is unclear if morphologically divergent tooth regeneration systems deploy an overlapping battery of genes in their naïve dental tissues.ResultsIn the present work, we aimed to determine whether or not tooth progenitor epithelia could be composed of a conserved cell type between vertebrate dentitions with divergent regeneration systems. To address this question, we compared the pharyngeal tooth regeneration processes in two ray-finned fishes: zebrafish (Danio rerio) and threespine stickleback (Gasterosteus aculeatus). These two teleost species diverged approximately 250 million years ago and demonstrate some stark differences in dental morphology and regeneration. Here, we find that the naïve successional dental lamina in zebrafish expresses a battery of nine genes (bmpr1aa, bmp6, cd34, gli1, igfbp5a, lgr4, lgr6, nfatc1, and pitx2), while active Wnt signaling and Lef1 expression occur during early morphogenesis stages of tooth development. We also find that, despite the absence of a histologically distinct successional dental lamina in stickleback tooth fields, the same battery of nine genes (Bmpr1a, Bmp6, CD34, Gli1, Igfbp5a, Lgr4, Lgr6, Nfatc1, and Pitx2) are expressed in the basalmost endodermal cell layer, which is the region most closely associated with replacement tooth germs. Like zebrafish, stickleback replacement tooth germs additionally express Lef1 and exhibit active Wnt signaling. Thus, two fish systems that either have an organized successional dental lamina (zebrafish) or lack a morphologically distinct successional dental lamina (sticklebacks) deploy similar genetic programs during tooth regeneration.ConclusionsWe propose that the expression domains described here delineate a highly conserved “successional dental epithelium” (SDE). Furthermore, a set of orthologous genes is known to mark hair follicle epithelial stem cells in mice, suggesting that regenerative systems in other epithelial appendages may utilize a related epithelial progenitor cell type, despite the highly derived nature of the resulting functional organs.

Evolution of tooth crown shape in Mesozoic birds, and its adaptive significance with respect to diet

Both the evolution of tooth morphology and the relationship between dental features and diet in toothed birds have long been studied. Here we quantify variation in tooth crown shape in 28 key Mesozoic bird species, and examine differences in dental morphology among birds belonging to different taxonomic groupings and inferred to have had different diets. Using geometric morphometric methods (GMM) and phylogenetic comparative methods (PCM), we found few clear differences in tooth crown shape between different taxonomic and ecological categories, and our analysis provides little support for many dietary inferences drawn in previous studies. However, the Solnhofen Archaeopteryx, Jeholornis, Protopteryx, Pengornis, Longipteryx, Tianyuornis, Mengciusornis, Ichthyornis and Hesperornis all were found to possess relatively specialized tooth crown shapes, perhaps reflecting specialized diets such as insectivory, granivory, piscivory and consumption of soft-shelled arthropods. Similarity in tooth crown shape across many Mesozoic birds may indicate the lack of dietary specialization, and the association between tooth form and diet may have been weakened in any case by ‘functional replacement’ of the dentition by a horny beak and, in many cases, gastroliths.

Systematic and paleoecological study of the new remains of Brachypotherium (Rhinocerotidae) from the Middle Miocene Siwaliks (Pakistan)

Newly discovered rhinocerotid remains from the Middle Miocene (14.2–11.2 Ma) of the Siwaliks of Pakistan are described in this paper, adding new data to the existing rhinocerotid fossil record from the Siwalik region. The specimens are identified as belonging to a teleoceratine genus Brachypotherium on the basis of morphometric comparison with the previously known rhinocerotid specimens from the Siwaliks as well as other biogeographic regions. The article provides additional information on the systematics through the dental morphological comparison of the genus Brachypotherium and in particular of Brachypotherium perimense and Brachypotherium fatehjangense. The data indicate an increased teeth size and dental morphological variations in B. perimense by changing environment from the Middle to Late Miocene and morphological differences in B. fatehjangense from B. brachypus. Also, an attempt has been made to clarify the dental morphological differences among different Middle Miocene rhinocerotid species of the Siwaliks. The hypsodonty and thick enamel of the studied samples indicates the presence of grazing communities feeding on coarse grasses during the Middle Miocene of the Siwaliks. The ecological implications of the genus Brachypotherium toward the changing Middle Miocene climatic conditions on the basis of stable isotope and enamel hypoplasia analyses are also discussed. The results of these proxies indicate that the Brachypotherium perimense preferred woodland and ponds, while B. fatehjangense lived in a more forested environment with river system. The transitional pattern of the Middle Miocene Siwaliks of Pakistan from dry to more precipitation and humidity might had some more ecological pressure on B. fatehjangense than on B. perimense.

Expression of Nonmetric Dental Traits in Western European Neanderthals

Neanderthals of Western Europe lived across distinct ecogeographic zones from Marine Iso-tope Stage 7 to 3. Differences in dental morphology from seven Western European sites are compared in terms of ecogeography and chronology.Neanderthals (n = 12) along a north-south gradient were examined. These included the Meuse River Basin of Belgium (Engis 2 and Scladina 1-4A ), Southwest France (Pech de l'Azé 1 and Roc de Marsal), the Pyrenees (Malarnaud and Montmaurin), and the Mediterranean (Hortus). Montmaurin is the oldest, followed by Scladina 1-4A and Malarnaud, whereas the others are younger.Dental casts were prepared from Neanderthal permanent and deciduous dentition. These were de-scribed and scored, according to the ASUDAS. Comparisons of dental traits with respect to ecogeo-graphic regions and chronological categories were constructed.Unusual dental features observed include the anterior fovea, entoconulid, metaconulid, and Cara-belli’s cusp. Dental traits that distinguish ecogeographic regions are the expression of the M1 hypocone and metaconule, whereas the hypoconulid and Carabelli’s cusp separate chronological categories. Dif-ferences are present for the entoconulid and metaconulid in both comparisons.Neither chronology nor ecogeography fully explains the results. Similarities in dental traits exist between Roc de Marsal, Pech de l’Azé 1 and Engis 2, and secondarily within the Hortus assemblage.

Differences on the Root and Root Canal Morphologies between Asian and White Ethnic Groups Analyzed by Cone-beam Computed Tomography

IntroductionPopulations from different geographic regions and ethnic backgrounds may present differences in dental morphology. The aim of this study was to compare the differences in root and root canal configurations on Asian and white subpopulations using cone-beam computed tomographic imaging. MethodsInformation from Asian and white patients was retrieved from 2 cone-beam computed tomographic imaging databases in China and Western Europe. Two calibrated observers collected data regarding the number of roots and Vertucci root canal system configuration for all groups of teeth. A total of 15,655 teeth were analyzed. The z test for independent groups was used to analyze differences between the groups. The significance level was considered at a P value < .05. Reliability tests were performed between observers. ResultsDifferences were noted in the number of roots per tooth in 6 groups of teeth. The Asian group showed a higher prevalence of single-root configurations in maxillary first premolars (83.2%) and mandibular second molars (45.4%) when compared with whites with 48.7% and 14.3%, respectively. Moreover, 3-rooted configurations in mandibular first molars were more common in Asians (25.9%) compared with whites (2.6%). Seventeen of the 20 analyzed roots had a higher prevalence of Vertucci type I configuration in Asians. Maxillary first molars with second mesiobuccal root canals were more commonly found in whites than in Asians (71.3% and 58.4%, respectively). A similar situation was found in maxillary second molars. ConclusionsThe Asian ethnic group presented a higher prevalence of Vertucci type I configuration, whereas the white group displayed a higher number of multiple root canal system morphologies. A clinician should be aware of these differences when treating patients from these ethnic groups.

Rethinking the dental morphological differences between domestic equids

Dental morphological differences in the first two mandibular molars of domestic equids have been claimed to possess unique species characteristics and are commonly used to identify archaeological equids to a species level. However, the intraspecific and intra-teeth variability of this morphological trait seems to be largely underestimated and the effects of inter-observer variations are rarely discussed. Therefore, the reliability of such morphological trait is poorly understood. Geometric morphometric (GM) methods can be used to evaluate the level of diversity between different dental morphology and, thus, is a more quantitative and objective approach than visual qualitative observation. This paper aims to examine the intraspecific and intra-teeth variability of lower molar morphology by applying GM analysis on molars from archaeological horses and purported mules as well as modern specimens of known species. The results suggest that other than possible inter-observer variations, the large intraspecific variability deems the dental morphology in lower molars to be unreliable for species identification.

The morphological affinities of the Middle Pleistocene hominin teeth from Pontnewydd Cave, Wales

ABSTRACTSeventeen Middle Pleistocene hominin teeth were excavated at Pontnewydd Cave in North Wales between 1980 and 1995 with a probable age of ∼225 ka, associated with handaxe and levallois artefacts. Their Neanderthal characteristics and their affinities with other European Middle Pleistocene teeth and the major sites of Atapuerca‐SH in Spain and Krapina in Croatia are explored. The Pontnewydd teeth are shown to have a marked similarity to those of Atapuerca‐SH, more pronounced than similarities to teeth from other European Middle Pleistocene sites, and to belong in the pre‐Neanderthal stage of Neanderthal evolution. Distinct dental morphological differences between later European Middle Pleistocene specimens, together with those from Atapuerca‐SH, and European Middle Pleistocene Homo heidelbergensis specimens are identified, contradicting the view that both the Pontnewydd and the Atapuerca‐SH fossils belong in that species. Additionally, the similarities in dental morphology between European and non‐European H. heidelbergensis specimens are demonstrated. We argue that when sites are grouped together for comparative purposes this should be done on morphological grounds, and not by apparent date, in view of the possible contemporaneity of European Middle Pleistocene sites that exhibit different degrees of Neanderthal affinities.

Development and evolution of the unique cetacean dentition

The evolutionary success of mammals is rooted in their high metabolic rate. A high metabolic rate is sustainable thanks to efficient food processing and that in turn is facilitated by precise occlusion of the teeth and the acquisition of rhythmic mastication. These major evolutionary innovations characterize most members of the Class Mammalia. Cetaceans are one of the few groups of mammals in which precise occlusion has been secondarily lost. Most toothed whales have an increased number of simple crowned teeth that are similar along the tooth row. Evolution toward these specializations began immediately after the time cetaceans transitioned from terrestrial-to-marine environments. The fossil record documents the critical aspects of occlusal evolution of cetaceans, and allows us to pinpoint the evolutionary timing of the macroevolutionary events leading to their unusual dental morphology among mammals. The developmental controls of tooth differentiation and tooth number have been studied in a few mammalian clades, but nothing is known about how these controls differ between cetaceans and mammals that retain functional occlusion. Here we show that pigs, a cetacean relative with regionalized tooth morphology and complex tooth crowns, retain the typical mammalian gene expression patterns that control early tooth differentiation, expressing Bmp4 in the rostral (mesial, anterior) domain of the jaw, and Fgf8 caudally (distal, posterior). By contrast, dolphins have lost these regional differences in dental morphology and the Bmp4 domain is extended into the caudal region of the developing jaw. We hypothesize that the functional constraints underlying mammalian occlusion have been released in cetaceans, facilitating changes in the genetic control of early dental development. Such major developmental changes drive morphological evolution and are correlated with major shifts in diet and food processing during cetacean evolution.

Ecological and Evolutionary Determinants of Dental Polymorphism in the Arctic FoxVulpes(Alopex)lagopus

The influence of some ecological and evolutionary factors on the pattern of dental polymorphism across the geographic range of the arctic fox (Vulpes (Alopex) lagopus) was studied. Dental morphotype characters (groups of morphotypes from A to S) in 12 geographically separate populations of the arctic fox were documented. Two evolutionary trends were observed: (1) simplification of the premolars and lower carnassial (M1), and (2) increased complexity of the upper carnassial (P4), third upper incisor (I3), and third lower molar (M3). Differences in dental morphology among arctic fox populations appear to be largely explained by evolutionary history, presence or absence of competition with the red fox (Vulpes vulpes), and diet, with a lesser influence of geography and climate. With respect to morphology, arctic foxes from the mainland populations of Eurasia and North America, are the most similar, followed by the partly-isolated island populations (Greenland, St. Lawrence Island). The most distinct forms are the arctic foxes from Commander Islands, that exist in permanent isolation.

Genetic Variation among Major Human Geographic Groups Supports a Peculiar Evolutionary Trend in PAX9

A total of 172 persons from nine South Amerindian, three African and one Eskimo populations were studied in relation to the Paired box gene 9 (PAX9) exon 3 (138 base pairs) as well as its 5′and 3′flanking intronic segments (232 bp and 220 bp, respectively) and integrated with the information available for the same genetic region from individuals of different geographical origins. Nine mutations were scored in exon 3 and six in its flanking regions; four of them are new South American tribe-specific singletons. Exon3 nucleotide diversity is several orders of magnitude higher than its intronic regions. Additionally, a set of variants in the PAX9 and 101 other genes related with dentition can define at least some dental morphological differences between Sub-Saharan Africans and non-Africans, probably associated with adaptations after the modern human exodus from Africa. Exon 3 of PAX9 could be a good molecular example of how evolvability works.

Efficacy of Two Methods for Restorative Materials’ Removal in Primary Teeth

This in vitro study aimed to compare the time required for removal, the presence of residues of restorative material, tooth structure loss and dental surface morphology after removal of composite resin and amalgam restorations from occlusal cavities in primary molars using conventional high-speed bur and CVDentus® ultrasonic diamond tips. A total of 37 primary molars were allocated into four groups: Group 1 (n=9)-amalgam restorations removed using high-speed bur; Group 2 (n=10)-amalgam restorations removed using ultrasonic tip; Group 3 (n=8)- composite resin restorations removed using high-speed bur; Group 4 (n=10)-composite resin restorations removed using ultrasonic tip. After being restored, teeth were sectioned and analyzed through stereoscopic microscope images before and after restoration removal. The structural loss was analyzed by software of image analysis, and an examiner assessed for the presence of residues. Scanning electron microscopy was used to evaluate the morphology. Time and structural loss values were compared using ANOVA, and the percentages of samples with residues using Fisher test. There was no statistically significant difference in the tooth structure loss among different methods and restorative materials, as well as in the presence of residues of restorative material. However, diamond burs were faster than the ultrasonic method for both materials. Differences in dental morphology were observed between the methods of restoration removal, but not related to the restorative material. Both conventional high-speed bur and ultrasonic diamond tip methods remove similar amounts of tooth structure, but the removal performed with diamond tips in ultrasonic devices is slower. This study shows that both ultrasonic and conventional high-speed bur methods for removing restorations generate similar loss of sound dental tissue, but the former is slower.

First record of Centrophorus harrissoni from New Zealand, with observations on squamation in centrophoridae (squaliformes)

Three specimens of Centrophorus from the southern Norfolk Ridge, three Kings Ridge, and Kermadec Ridge are provisionally identified as C. harrissoni, extending the species’ known range east to 178°52.1'W. Although apparently rare, C. harrissoni is widely distributed in southern Australian waters and the southwest Pacific between 17°S and 43°S, occurring on continental and insular slopes and oceanic ridges from 450 to 1048 m depth. Differences in dental morphology between juvenile male and female type specimens, a juvenile male from southern Norfolk Ridge and an adult male from the Kermadec Ridge were tentatively attributed to sexual dimorphism. However, additional specimens and research are required to confirm the identity of nominal C. harrissoni from Norfolk Ridge and northern New Zealand. Eight Centrophorus spp., including C. harrissoni, and three Deania spp. were found to differ from C. squamosus in having an area of transverse dermal folds on the ventral surface of the head between the gills. in C. harrissoni and Deania spp. these are naked except for a row of denticles along the top of each fold. in C. harrissoni these denticles are minute and thorn‐like, whereas in Deania spp. they have tridentate crowns on short, straight pedicles.

New populations and biogeographic patterns of the geomyid rodents Lignimus and Mojavemys from the Barstovian of western Montana

ABSTRACT New dental specimens described here from the Barstovian CC South and Flint Creek localities of western Montana are determined to be of two geomyid rodent species, Lignimus transversus and Mojavemys sp. These species were known previously from sparse material and the new samples aid the clarification of their biogeography and evolution. The presence of Lignimus transversus at both localities extends the range of that species to the north. In Mojavemys, a cline of increasing tooth size from south to north is analogous to clines in extant geomyids that correlate with nutritional or climatic gradients. Comparisons of various dental morphologic features of the new material and of the previously described populations of both genera reveal that the examined traits as well as the populations themselves were not genetically linked, and suggest mosaic evolution operated in these species. The differences in dental morphology between the various depositional basins are consistent with the idea of a tectonic influence on mammalian evolution.

New primitive paromomyid from the Clarkforkian of Wyoming and dental eruption in Plesiadapiformes

ABSTRACT Clarkforkian late Paleocene freshwater limestone from the Clarks Fork Basin, Wyoming, has yielded four specimens of the plesiadapiform paromomyid, Acidomomys hebeticus gen. et sp. nov. A. hebeticus has a strong metaconid on p4, a small double-rooted p3, and a very diminutive i2. Presence of p3 and i2 is primitive, and their retention in A. hebeticus suggests that this taxon is part of a previously unknown lineage that diverged from other paromomyids by the early or middle Paleocene. Acidomomys hebeticus is represented by virtually complete upper and lower dentitions, all from less than fully mature individuals, with teeth at one of three stages of development. The dental eruption sequence differs from that of other plesiadapiforms in having p3 erupt before p4 (p3 erupts after p4 in microsyopids, and p3 and p4 erupt simultaneously in plesiadapids). A. hebeticus differs from Plesiadapis and primitive primates, in which the premolars erupt after m3 is in place, in having p3/P3 erupt before or at the same time as that of m3/M3. It is similar to Plesiadapis in having p4 erupt after the molars are in place, a condition considered primitive in primates. While these differences in dental eruption sequence between representatives of Paromomyidae, Microsyopidae, and Plesiadapidae could be phylogenetically significant, they may instead reflect adaptive differences in dental morphology, facial architecture, or life history.