Molar Cusp Research Articles

Evaluation of bone loss due to primary occlusal trauma in two experimental models of occlusal overload

Abstract Introduction Primary occlusal trauma (OT) is an injury of the periodontium with normal height as a result of occlusal forces which exceed their adaptive capacity. Objective To evaluate, histometrically, the alveolar bone loss in the furcation region of rats experimentally submitted to 2 models of occlusal overload. Material and method 45 animals randomly divided into 3 groups: Occlusal Interference (OI, n = 15) - fixing an orthodontic wire segment on the occlusal surface of the first lower molar; Occlusal Overload (OO, n = 15) - wearing of the cusps of the lower contralateral molars, the second and third molars next to the first molar that had its dimensions maintained; Negative Control (NC, n = 15) - evaluation of the initial dimensions of the periodontal ligament (PL). Five animals / group were sacrificed after 14, 21 and 28 days. Result Intergroup evaluation showed significant bone loss in OI (p<0.001) and OO (p<0.01) compared to NC. OI had significantly higher bone loss compared to OO at 14 (p<0.01), 21 (p <0.01) and 28 days (p<0.01). The intragroup evaluation showed no significant influence of time on bone loss in OI and OO, regardless of the technique used (p>0.05). The thickness of the PL remained stable in NC (p>0.05). Conclusion OI and OO were effective in the experimental reproduction of OT, and OI promoted greater alveolar bone loss compared to OO, showing that the impact of occlusal overload in OI increased the extent of the OT injury.

Spatial determinants of the mandibular curve of Spee in modern and archaic Homo.

The curve of Spee (COS) is a mesio-distally curved alignment of the canine through distal molar cusp tips in certain mammals including modern humans and some fossil hominins. In humans, the alignment varies from concave to flat, and previous studies have suggested that this difference reflects craniofacial morphology, including the degree of alveolar prognathism. However, the relationship between prognathism and concavity of the COS has not been tested in craniofacially variant populations. We tested the hypothesis that greater alveolar prognathism covaries with a flatter COS in African-American and European-American populations. We further examined this relationship in fossil Homo including Homo neanderthalensis and early anatomically modern Homo sapiens, which are expected to extend the amount of variation in the COS from the extant sample. These hypotheses were tested using three-dimensional geometric morphometrics. Landmarks were recorded from the skulls of 166 African-Americans, 123 European-Americans, and 10 fossil hominin mandible casts. Landmarks were subjected to generalized Procrustes analysis, principal components analysis, and two-block partial least squares analysis. We documented covariation between the COS and alveolar prognathism such that relatively prognathic individuals have a flatter COS. Mandibular data from the fossil hominin taxa generally confirm and extend this correlation across a greater range of facial size and morphology in Homo. Our results suggest that the magnitude of the COS is related to a suite of features associated with alveolar prognathism in modern humans and across anthropoids. We also discuss the implications for spatial interactions between the dental arches.

ANALYSIS OF MORPHOLOGICAL PARAMETERS OF DENTAL SYSTEM WITH GNATHIC FORM OF MALOCCLUSION CLASS III USING SIMPLYCEPH SOFTWARE (RUSSIA)

Mesiocclusion associated with asymmetric mandibular development is a gnathic form of mesiocclusion characterized by asymmetric deformation of the facial skeleton, requiring detailed examination to perform differential diagnostics. We need to analyze lateral teleroentgenogram of the head using «SimplyCeph» software, frontal teleroentgenogram of the head, multidetector computed tomography. According to scientific data, asymmetric mandibular development is much rarer in clinical practice. Etiology of this abnormality is not determined to date. It is believed that growth zones are activated in condyloid process and mandibular angle for unknown reasons. Aim - to determine the morphological condition of stomatognathic system on the stages of rehabilitation after complex treatment of patients with asymmetric growth of mandible. Materials and methods. We examined 40 patients with malocclusion class III aged from 16 to 40. The examined group included patients with malocclusion class III that corresponded to the certain degree of severity of the abnormality: Grade I - joining of the first permanent molars and canines for Class II Angle, displacement value does not exceed 1/2 of the first permanent molar cusp. Sagittal overjet is absent; the value of anterior crossbite is minimal, moderate or deep. Results. During the stages of rehabilitation of patients with malocclusion class III and asymmetry of the mandible it is necessary to conduct a comprehensive study of facial and gnathic areas of dental system, analyze the results of radiodiagnosis of sagittal, transversal and vertical skull parameters. Conclusion. Method of subcondylar vertical osteotomy helps to normalize the morphological state of dental system. Keywords: malocclusion class III, computer program «SimplyCeph», analysis of lateral teleroentgenogram.

Effect of different dental ceramic systems on the wear of human enamel: An in vitro study

Statement of problemThe wear of tooth structure opposing different advanced dental ceramic systems requires investigation. PurposeThe purpose of this in vitro study was to compare the wear of advanced ceramic systems against human enamel antagonists. Material and methodsFour ceramic systems (IPS e.max Press, IPS e.max CAD, Noritake Super Porcelain EX-3, and LAVA Plus Zirconia) and 1 control group containing human enamel specimens were used in this study (n = 12). All specimens were fabricated as disks 11 mm in diameter and 3 mm thick. The mesiopalatal cusps of the maxillary third molars were prepared to serve as the enamel styluses. All specimens were embedded individually in 25 mm3 autopolymerizing acrylic resin blocks. Wear was measured with a cyclic loading machine and a newly designed wear simulator. All enamel styluses (cusps) were scanned using the Activity 880 digital scanner (SmartOptics). Data from the base line and follow-up scans were collected and compared with Qualify 2012 3-dimensional (3D) and 2D digital inspection software (Geomagic), which aligned the models and detected the geometric changes and the wear caused by the antagonist specimen. One-way ANOVA was used to analyze the collected data. ResultsAfter 125 000 bidirectional loading cycles, the mean loss of opposing enamel volume for the enamel disks in the control group was 37.08 μm3, the lowest mean value for IPS e.max Press system was 39.75 μm3; 40.58 μm3 for IPS e.max CAD; 45.08 μm3 for Noritake Super Porcelain EX-3 system; and 48.66 μm3 for the Lava Plus Zirconia system. No statically significant differences were found among the groups in opposing enamel volume loss (P=.225) or opposing enamel height loss (P=.149). In terms of opposing enamel height loss, Lava Plus Zirconia system showed the lowest mean value of 27.5 μm. The mean value for the IPS e.max CAD system was 27.91 μm; 29.08 μm for the control enamel; 33.25 μm for the IPS e.max Press system; and 34.75 μm for the Noritake Super Porcelain EX-3 system. ConclusionsWithin the limitations of this in vitro study, no differences were found in the linear and volumetric reduction of enamel cusps abraded against enamel disks and all other ceramic specimens. All ceramic systems exhibited high durability and were wear-friendly to opposing enamel.

Residents' journal review

Residents' journal review

Teeth movement in denture and implant-supported prosthesis influenced by microwave flask systems

Background/AimsThis study evaluated the teeth movement in maxillary dentures and mandibular implantsupported prostheses processed by microwave flasks. MethodsA model mounted on articulator was used to manufacture Co-Cr frameworks. Pins were placed for measurements on the incisal edge of upper and lower central incisors (I), buccal cusp of first upper and lower premolars (PM), and mesiobuccal cusps of upper and lower second molars (M). Distances I-I (incisor to incisor), PM-PM (premolar to premolar), M-M (molar to molar), RI-RM (right incisor to right molar), and LI-LM (left incisor to left molar) were measured before and after processing using a microscope (0.0005mm). Vertical misfit between abutment and implant platform was evaluated for regions A (left distal implant), B (left median implant), C (medial implant), D (right median implant), and E (right distal implant) in predetermined labial and lingual sites. Prostheses were divided into groups G1 – conventional flask, and G2 – experimental HH flask. Acrylic resin was microwaved at 1400 W (30% for 3min, 0% for 3min, and 60% for 3min). Horizontal teeth displacement and vertical misfit between abutment and implant platform were considered before and after procedures. Data were submitted to three-way ANOVA and Tukey's test (α=0.05). ResultsExcept for M-M distance, the teeth showed displacements without statistical difference for prosthesis and flask factors. There was no significant difference for vertical misfit values for both flasks. ConclusionDiferente flasks did not cause significant changes in the teeth displacement, except for M-M. Vertical misfit values were not influenced by the flasks.

Enamel thickness and enamel growth in Oreopithecus: Combining microtomographic and histological evidence

Oreopithecus bambolii, a large-bodied fossil ape, lived in the Tusco-Sardinian archipelago during the Late Miocene, until ca. 6.7Ma. Its dentition, an apparent blend of hominoid and cercopithecoid-like features, has been a matter of discussion since its first description, in 1872. While the height and sharpness of its molar cusps recall some Cercopithecidae, Oreopithecus is currently considered by many as more likely related to dryopithecines. Here, we use microtomographic-based quantitative imaging and histological evidence to link outer and inner tooth structural morphology with enamel development in Oreopithecus permanent teeth. The material consists of 14 teeth/crowns from the sites of Baccinello and Casteani, in Tuscany, and Fiume Santo, in Sardinia. In particular, we add to the record of 2–3D of molar enamel thickness topographic variation and enamel-dentine junction morphology, and using high-resolution replicas of the outer crown and ground sections, comparatively assess molar growth trajectory (crown formation times and enamel extension rates). Our results shed new light on dental development of this “enigmatic anthropoid” and provide additional evidence concerning the still debated question of its evolutionary history.

Shape variation and covariation of upper and lower dental arches of an orthodontic population.

This study aimed to quantify the patterns of shape variability and the extent and patterns of shape covariation between the upper and lower dental arch in an orthodontic population. Dental casts of 133 white subjects (61 males, 72 females; ages 10.6-26.6) were scanned and digitized in three dimensions. Landmarks were placed on the incisal margins and on the cusps of canines, premolars, and molars. Geometric morphometric methods were applied (Procrustes superimposition and principal component analysis). Sexual dimorphism and allometry were evaluated with permutation tests and age-size and age-shape correlations were computed. Two-block partial least squares analysis was used to assess covariation of shape. The first four principal components represented shape patterns that are often encountered and recognized in clinical practice, accounting for 6-31 per cent of total variance. No shape sexual dimorphism was found, nevertheless, there was statistically significant size difference between males and females. Allometry was statistically significant, but low (upper: R(2) = 0.0528, P < 0.000, lower: R (2) = 0.0587, P < 0.000). Age and shape were weakly correlated (upper: R(2) = 0.0370, P = 0.0001, lower: R (2) = 0.0587, P = 0.0046). Upper and lower arches covaried significantly (RV coefficient: 33 per cent). The main pattern of covariation between the dental arches was arch width (80 per cent of total covariance); the second component related the maxillary canine vertical position to the mandibular canine labiolingual position (11 per cent of total covariance). Results may not be applicable to the general population. Age range was wide and age-related findings are limited by the cross-sectional design. Aetiology of malocclusion was also not considered. Covariation patterns showed that the dental arches were integrated in width and depth. Integration in the vertical dimension was weak, mainly restricted to maxillary canine position.

The Biomechanics of Partial Symphyseal Fusion in Hapalemur Examined Using Finite Element Analysis

A wealth of research on primate feeding supports the hypothesis that fused mandibular symphyses, ubiquitous among anthropoids, strengthen the joint against “wishboning” stresses that occur as a result of transversely-oriented muscle forces. However, in mammals that include extensive transverse occlusal movements, fusion has been suggested to increase bite forces in the horizontal plane by more efficiently transferring balancing-side muscle forces to the biting side. Some strepsirrhines, including Hapalemur and Propithecus, exhibit varying degrees of partial fusion. Hapalemur feeds extensively on extremely tough bamboo, so increasing transverse bite forces could be selectively important. However, steep molar cusps limit the potential for transverse occlusal movements. We used finite element analysis to examine symphyseal mechanics in Hapalemur. We constructed one completely fused Hapalemur mandible model and five with “symphyseal plates” assigned increasingly stiff elastic moduli (5MPa – 600MPa). Models were constrained at the second molar and loaded with muscle forces. By comparing nodal displacements, we found that modest increases in symphyseal stiffness (0MPa – 50MPa) drastically reduce wishboning, suggesting partially fused symphyses may be nearly as strong as those that are completely ossified. In contrast, we found that stiff/fused symphyses do not increase transverse bite forces.

The role of organic proteins on the crack growth resistance of human enamel

With only 1% protein by weight, tooth enamel is the most highly mineralized tissue in mammals. The focus of this study was to evaluate contributions of the proteins on the fracture resistance of this unique structural material. Sections of enamel were obtained from the cusps of human molars and the crack growth resistance was quantified using a conventional fracture mechanics approach with complementary finite element analysis. In selected specimens the proteins were extracted using a potassium hydroxide treatment. Removal of the proteins resulted in approximately 40% decrease in the fracture toughness with respect to the fully proteinized control. The loss of organic content was most detrimental to the extrinsic toughening mechanisms, causing over 80% reduction in their contribution to the total energy to fracture. This degradation occurred by embrittlement of the unbroken bridging ligaments and consequent reduction in the crack closure stress. Although the organic content of tooth enamel is very small, it is essential to crack growth toughening by facilitating the formation of unbroken ligaments and in fortifying their potency. Replicating functions of the organic content will be critical to the successful development of bio-inspired materials that are designed for fracture resistance.

Mechanics analysis of molar tooth splitting

A model for the splitting of teeth from wedge loading of molar cusps from a round indenting object is presented. The model is developed in two parts: first, a simple 2D fracture mechanics configuration with the wedged tooth simulated by a compact tension specimen; second, a full 3D numerical analysis using extended finite element modeling (XFEM) with an embedded crack. The result is an explicit equation for splitting load in terms of indenter radius and key tooth dimensions. Fracture experiments on extracted human molars loaded axially with metal spheres are used to quantify the splitting forces and thence to validate the model. The XFEM calculations enable the complex crack propagation, initially in the enamel coat and subsequently in the interior dentin, to be followed incrementally with increasing load. The fracture evolution is shown to be stable prior to failure, so that dentin toughness, not strength, is the controlling material parameter. Critical conditions under which tooth splitting in biological and dental settings are likely to be met, however rare, are considered.

Sex assessment efficacy of permanent maxillary first molar cusp dimensions in Indians.

Background:The human first maxillary molar provides clues about evolution and is functionally important. It has four main cusps, and each cusp has an independent growth pattern and different evolutionary background. Though less explored, the analysis based on measurement of each cusp appears to be more meaningful biologically than conventional measurements of the whole crown.Aim:This study aimed to demonstrate the extent of sexual dimorphism in permanent maxillary first molar cusp diameters and their potential utility in sex prediction among Indians using logistic regression analysis (LRA).Materials and Methods:The mesiodistal and buccolingual (BL) crown diameters along with cusp dimensions and cusp indices of right maxillary first molar were measured in an Indian sample (149 males, 151 females; age range of 18–30 years). The possible sex dimorphism in these parameters was evaluated, and LRA was performed to ascertain their usefulness in sex prediction.Results:BL crown dimension and the hypocone (distolingual) cusp showed the highest sexual dimorphism. The combination of metacone and hypocone, i.e., distal cusp diameters among cusp parameters showed the highest accuracy (61.3%). While, on combining all the crown and cusp diameters together the overall accuracy was raised (64.3%).Conclusion:This study supports the ontogeny hypothesis suggesting that early-forming mesial cusps demonstrate less sexual variation as compared to subsequently formed distal cusps in the maxillary molar. Though the sex identification accuracy for cusp diameters of the permanent maxillary first molar in Indians is relatively moderate (≈61%), it can be used as an adjunct for sexing of adult Indians in forensic contexts.

Validity of intraoral soft tissue landmarks as reference points for orientation of occlusal plane in natural dentition: A clinical study

Introduction: Occlusal plane is the average plane established by incisal and occlusal surfaces of teeth. Various anatomic landmarks are used to determine this missing component of occlusion which is lost with the loss of teeth. However, variation has been observed in the orientation of occlusal plane determined clinically with different anatomical landmarks as references. Objective: This study was undertaken to determine the relation of intraoral anatomic soft tissue landmarks, namely, retromolar pad and parotid papilla with occlusal plane in natural dentition. Materials and Methods: Irreversible hydrocolloid impressions of 100 edentulous individuals (50 males and 50 females) were made to get the models. A 16 gauge wire was extended from mandibular occlusion plane posteriorly up to retromolar pad to establish their relationship. Furthermore, vertical distance of apex of parotid papilla to maxillary molar cusp tip it opposed (distobuccal cusp of maxillary first molar or mesiobuccal cusp of maxillary second molar), and mandibular molar cusp tip (to which parotid papilla apposed) was measured when the teeth were in maximal intercuspal position. Results: This study determined that the natural occlusal plane is oriented posteriorly at the level corresponding with the lower third of retromolar pad. Mean distance of parotid papilla above the corresponding maxillary cusp tip (while in occlusion) was 5.048 mm, and mean distance of Parotid papilla above the corresponding mandibular molar cusp tip (while in occlusion) was determined to be 3.602 mm. The difference in observed means between males and females or between right and left side was not statistically significant.

Three-dimensional analysis of the distal movement of maxillary 1st molars in patients fitted with mini-implant-aided trans-palatal arches.

ObjectiveThe aim of this study was to investigate three-dimensional molar displacement after distalization via miniscrews and a horizontal modification of the trans-palatal-arch (TPA).MethodsThe subjects in this clinical trial were 26 Class II patients. After the preparation of a complete set of diagnostic records, miniscrews were inserted between the maxillary 2nd premolar and 1st molar on the palatal side. Elastic modules connected to the TPA exerting an average force of 150-200 g/side parallel to the occlusal plane were applied. Cone-beam computed tomography was utilized to evaluate the position of the miniscrews relative to the adjacent teeth and maxillary sinus, and the direction of force relative to molar furcation. The distances from the central point of the incisive papilla to the mesiopalatal cusps of the 1st maxillary molars and the distances between the mesiopalatal cusps of the left and right molars were measured to evaluate displacement of the maxillary molars on the horizontal plane. Interocclusal space was used to evaluate vertical changes.ResultsMean maxillary 1st molar distalization was 2.3 ± 1.1 mm, at a rate of 0.4 ± 0.2 mm/month, and rotation was not significant. Intermolar width increased by 2.9 ± 1.8 mm. Molars were intruded relative to the neighboring teeth, from 0.1 to 0.8 mm.ConclusionsDistalization of molars was possible without extrusion, using the appliance investigated. The intrusive component of force reduced the rate of distal movement.

Industrial noise and tooth wear - experimental study.

Tooth wear is a complex multifactorial process that involves the loss of hard dental tissue. Parafunctional habits have been mentioned as a self-destructive process caused by stress, which results in hyperactivity of masticatory muscles. Stress manifests itself through teeth grinding, leading to progressive teeth wear. The effects of continuous exposure to industrial noise, a “stressor” agent, cannot be ignored and its effects on the teeth must be evaluated.Aims: The aim of this study was to ascertain the effects of industrial noise on dental wear over time, by identifying and quantifying crown area loss.Material and Methods: 39 Wistar rats were used. Thirty rats were divided in 3 experimental groups of 10 animals each. Animals were exposed to industrial noise, rich in LFN components, for 1, 4 and 7 months, with an average weekly exposure of 40 hours (8h/day, 5 days/week with the weekends in silence). The remaining 9 animals were kept in silence. The areas of the three main cusps of the molars were measured under light microscopy.Statistical analysis used: A two-way ANOVA model was applied at significance level of 5%.Results: The average area of the molar cusps was significantly different between exposed and non-exposed animals. The most remarkable differences occurred between month 1 and 4. The total crown loss from month 1 to month 7 was 17.3% in the control group, and 46.5% in the exposed group, and the differences between these variations were significant (p<0.001).Conclusions: Our data suggest that industrial noise is an important factor in the pathogenesis of tooth wear.

Additional postcranial elements of Teilhardina belgica: the oldest European primate.

Teilhardina belgica is one of the earliest fossil primates ever recovered and the oldest fossil primate from Europe. As such, this taxon has often been hypothesized as a basal tarsiiform on the basis of its primitive dental formula with four premolars and a simplified molar cusp pattern. Until recently [see Rose et al.: Am J Phys Anthropol 146 (2011) 281-305; Gebo et al.: J Hum Evol 63 (2012) 205-218], little was known concerning its postcranial anatomy with the exception of its well-known tarsals. In this article, we describe additional postcranial elements for T. belgica and compare these with other tarsiiforms and with primitive adapiforms. The forelimb of T. belgica indicates an arboreal primate with prominent forearm musculature, good elbow rotational mobility, and a horizontal, rather than a vertical body posture. The lateral hand positions imply grasps adaptive for relatively large diameter supports given its small body size. The hand is long with very long fingers, especially the middle phalanges. The hindlimb indicates foot inversion capabilities, frequent leaping, arboreal quadrupedalism, climbing, and grasping. The long and well-muscled hallux can be coupled with long lateral phalanges to reconstruct a foot with long grasping digits. Our phyletic analysis indicates that we can identify several postcranial characteristics shared in common for stem primates as well as note several derived postcranial characters for Tarsiiformes.

Spalacotheriid ‘symmetrodonts’ from the Early Cretaceous of Spain

ABSTRACTSpalacotheriids, basal trechnotheres with an acutely angled, reversed-triangle pattern of major molar cusps, are relatively rare pan-Laurasian mammals that ranged through much of the Cretaceous but are generally not well represented in the fossil record. Herein we describe newly collected specimens from the Molino Alto 1 locality, Teruel Province, Spain, and review previously described materials from the nearby locality of Galve; the sites lie in the same horizon in the upper El Castellar Formation and are of early Barremian age. On this basis, we recognize and name Aliaga molinensis, gen. et sp. nov., and provisionally place in the same genus a previously described species, cf. Aliaga henkeli, comb. nov., which appears to be the largest known spalacotheriid. The two species are characterized by a distinctive, multicuspate cingulid on lower cheek teeth. Based on acuteness of molar cusp triangulation and other features (e.g., planar molar shearing surfaces, elongation and cusp pattern of penultimate premolar, reduction of last molar, simplification of upper molar crown pattern), the species are referred to the Spalacolestinae. This subfamily is most diverse in North America, where it ranged from Albian–Campanian, but first appears in the Barremian of Western Europe, supporting the hypothesis that the group had a Eurasian origin and later dispersed to North America.

Occlusal disharmony accelerates the initiation of atherosclerosis in apoE knockout rats.

BackgroundPsychosocial stress is one of the risk factors for atherosclerosis. As occlusal disharmony induces psychological stress, we hypothesized that psychological stress by occlusal disharmony accelerates atherosclerosis. The aim of this study was to investigate the effects of occlusal disharmony on the initiation of atherosclerosis in apolipoprotein E (apoE) knockout rats.MethodsFourteen male apoE-knockout rats (age; 8 weeks) (Sprague–Dawley strain background) were divided into two groups of seven rats: the occlusal disharmony group and the no treatment (control) group. In the occlusal disharmony group, the maxillary molar cusps were cut off for the 8-week experimental period.ResultsIn the occlusal disharmony group, the percentages of the area of total aortic lumen occupied by plaques and lipid were significantly higher than those in the control group (p < 0.05, t-test). The occlusal disharmony group also showed significantly higher serum levels of very low-density lipoprotein-cholesterol (VLDL) and low-density lipoprotein-cholesterol (LDL), plasma levels of corticosterone (1.9, 1.3 and 1.3 times, respectively), higher aortic protein expression levels of vascular cell adhesion molecule-1 (VCAM1) and intercellular adhesion molecule-1 (ICAM1) (1.5 and 1.4 times, respectively), and higher aortic gene expression of levels of VCAM1 and Toll-like receptor 4 (TLR4) (1.9 and 4.3 times, respectively), as compared to the control group (p < 0.05). However, there were no significant differences in serum levels of oxidized LDL, reactive oxygen metabolites and C-reactive protein between the two groups.ConclusionIn apoE knockout rats, occlusal disharmony may induce VCAM1, ICAM1 and TLR4 expression and accelerate the initiation of atherosclerosis.

Morphological and Geographic Definitions of the Sulawesian Shrew RatsEchiothrix leucura and E. centrosa(Muridae, Murinae), and Description of a New Species of Sucking Louse (Phthiraptera: Anoplura)

Among the 15 known genera of murine rodents endemic to the island of Sulawesi, is the shrew rat genus Echiothrix. Physically large (length of head and body = 182–235 mm; weight = 215–310 g) with a bicolored tail typically longer than head and body (100%–135% of head and body length), elongate hind feet (48–55 mm), large ears (31–35 mm), long and thin muzzle, spinous fur, and tiny molars relative to size of skull (length of molar row = 12%–13% of occipitonasal length), Echiothrix was named and described in 1867 and through the years has been treated as monotypic or containing up to three species. Results from analyses of morphometric traits derived primarily from cranial and dental measurements document the presence of two species. Echiothrix leucura (Gray, 1867) is restricted to the northern peninsular mainland east of the Gorontalo region (00°31′ N, 123° 03′ E). This distribution is concordant with that of four other murids endemic to the northeastern tip of the northern peninsula: Bunomys fratrorum, Taeromys taerae, Rattus xanthurus, and R. marmosurus. Echiothrix centrosa Miller and Hollister, 1921 (Echiothix brevicula Miller and Hollister, 1921, is a synonym), is documented by specimens from the northern peninsula west of the Gorontalo region and in the central portion of the island; 19 other murine species are also known only from the core of Sulawesi. Whether the range of E. centrosa extends to the eastern, southeastern, and southwestern peninsulas is at present unknown. Echiothrix leucura has a more elongate skull compared with E. centrosa (greater lengths of skull, rostrum, diastema, and bony palate), a wider interorbital region, larger braincase, narrower bony palate and mesopterygoid fossa, shorter incisive foramina, and appreciably larger molars; the two species also differ in frequencies of particular molar cusps and cusplets. Both species of Echiothrix are nocturnal, terrestrial, and occupy habitats in tropical lowland evergreen rain forest. Natural history observations made in the field for Echiothrix centrosa show it to be primarily vermivorous; other natural history observations derived from field work in central Sulawesi are provided. One aspect of that natural history is the ectoparasitic load borne by E. centrosa. This shrew rat is host to at least four species of ticks (Haemaphysalis kadarsani, Haemaphysalis hystricis, Haemaphysalis sp. and Amblyomma sp.), a tiny fur mite (Listrophoroides echiothrix), mesostigmatid mites belonging to the genus Laelaps, currently undetermined chiggers, a flea (Farhangia quattuordecimdentata), and a new species of sucking louse described herein as Polyplax beaucournui. This louse has tibiotarsal claws adapted for grasping slender soft hairs in the pelage and not the wide host spines; female lice also attach their eggs only to these slender hairs. The closest relative of Echiothrix is probably Paucidentomys vermidax, another Sulawesian endemic shrew rat that is also vermivorous but lacks molars and has been collected only in montane forests. The present report documents morphological and distributional limits of species in Echiothrix, places one of those species in an ecological and parasitological landscape, and generally contributes to knowledge covering endemic murid species diversity and identifying unique zoogeographical areas on Sulawesi.

Australohyaena antiqua (Mammalia, Metatheria, Sparassodonta), a large predator from the Late Oligocene of Patagonia

An almost complete skull of Australohyaena antiqua (Ameghino), from the Late Oligocene (Deseadan SALMA) of Cabeza Blanca, Chubut Province, Argentina is described and analysed. For more than a century, this species was represented by isolated teeth. The genus Australohyaena gen. nov. is proposed based on a phylogenetic reconstruction that demonstrates that A. antiqua is a Borhyaenidae (Mammalia, Sparassodonta), grouped with Arctodictis and Borhyaena, but not with Pharsophorus lacerans, the genus to which antiqua was formerly assigned. A. antiqua is recognized by several features on the skull, dentary and dentition. In addition, a short snout, large canines, deep jaw, reduced protocone and talonid determine A. antiqua as hypercarnivorous. A vaulted skull, well-developed temporal fossa and little difference on the jaw depth at p3 and m4, are suggestive of bone-cracker specializations. A. antiqua is within the largest Deseadan sparassodonts with a body mass of about 70 kg. Homoplasies are detected within borhyaenoids on lower molar cusps. The metaconid is lost within Sparassodonta, although Pharsophorus and borhyaenids retained the metaconid on m2–m4 or m2–m3.http://zoobank.org/urn:lsid:zoobank.org:pub:EDB0575A-C1D9-4C17-B6EB-3D761D1D7DB3