Marginal Ridge Research Articles

Odontogenic Factors Associated with Food Impaction in Patients Attending Periodontics OPD of Universal College of Medical Sciences

Introduction: Food impaction is a common problem experienced by almost everyone during their lifetime. It is believed that the interproximal wedging of food normally occurs due to loss of integrity of the proximal contact and its location along with the contour of the marginal ridges and lack of papilla fill. The objective of the study was to assess the role of odontogenic factors for food impaction and identify the odontogenic factors most prevalent in patients attending Periodontics OPD of Universal College of Medical Sciences.
 Materials and Methods: A total of hundred subjects with natural dentition from the second molar to the second molar in both the maxillary and mandibular arches were enrolled in this cross-sectional study. Clinical parameters like pocket depth, bleeding index, and plaque index were recorded. The integrity of contact was recorded using dental floss. A study cast was fabricated for each subject. The presence of plunger cusps along with marginal ridge relationship, the position of the tooth in the arch, and contiguity of contact points were analyzed on it.
 Results: A significant association between plaque index score and food impaction was found (p=0.03). Of all the factors, loose contact showed a slightly significant positive correlation with a plaque index score (r= 0.19, p=0.05).
 Conclusions: Amongst all the odontogenic factors, loose contact is positively correlated with plaque index and food impaction is significantly associated with plaque score. The odds of food impaction were significant with the brushing technique employed and frequency of tooth brushing in the subjects.

<p><strong>A new marine epiphytic diatom species, <em>Halamphora yundangensis</em> sp. nov. (Bacillariophyceae), from Yundang Lake, Southeast coast of China</strong></p>

Halamphora yundangensis sp. nov. is described as a new species epiphytic on the green seaweed Ulva lactuca, from Yundang Lake, Fujian Province, China. Morphological details of the new species with respect to shape, size and valve ultrastructure are presented, with observations based on light microscopy (LM) and scanning electron microscopy (SEM). The main features of Halamphora yundangensis are dorsiventral, semi-lanceolate valves with convex dorsal margin and straight ventral margin, as well as valve ends distinctly protracted and capitate. Externally, a prominent marginal ridge forming the image of a broad hyaline area is present. Internally, dorsal striae are regularly biseriate, and a row of areolae lies along raphe. The new species is compared with similar species in both Amphora and Halamphora.

Ornithodoros cerradoensis n. sp. (Acari: Argasidae), a member of the Ornithodoros talaje (Guérin-Méneville, 1849) group, parasite of rodents in the Brazilian Savannah

Ornithodoros cerradoensis n. sp. is described from field-collected and laboratory reared nymphs, males, females, and larvae parasitizing the rodents Cavia aperea and Thrichomys sp. in the Brazilian Savannah. This new species is morphologically and genetically related with the Ornithodoros talaje group and can be separated from other Neotropical species using the following combination of characters: larva with 18 pairs of setae on dorsum (seven anterolateral, four central and seven posterolateral), hypostome with median dentition 2/2; adults provided with large mammillae; dorsal disks surrounded by bulked marginal ridges delimiting barely pebbled areas; three disks in the anterolateral file, and median disk not merging with the posteromedian file. Feeding assays in the laboratory demonstrated that (1) larvae of O. cerradoensis are slow-feeders (∼6 days), (2) first nymphal instar (N1) molts to second instar (N2) without feeding, and (3) N2 and third nymphal instar (N3) engorge rapidly (minutes). With the exception of Ornithodoros hasei nymphs that depict flattened bodies, O. cerradoensis N1, N2, and N3 highly resemble homologous instars of other species in O. talaje sensu lato, therefore are not suitable for morphological comparisons within the group. In addition to morphological signature of larvae and adults that separate this new species; results of cross-mating attempts between O. cerradoensis and Ornithodoros guaporensis a morphologically and phylogenetically closely related species that also parasitizes rodents in the Brazilian Savannah; a Principal Component Analysis using larval characters; and a phylogenetic analysis using mitochondrial markers, support O. cerradoensis as an independent lineage within the Ornithodorinae.

Reporte de Peridiniopsis borgei Lemmermann (Dinophyceae) en aguas continentales de Perú

We reported the presence of Peridiniopsis borgei Lemmermann in La Encantada lake (Province of Huaura) and studied the specimens using optical and scanning electron microscopical techniques. The population of P. borgei showed a variation in the number and degree of development of the marginal ridges. This is the first illustrated report of the species in Peru

Accuracy of intraoral scans in the mixed dentition: a prospective non-randomized comparative clinical trial

ObjectiveIn-vivo accuracy of intraoral scans of complete mixed dentitions of patients in active treatment have not yet been investigated. The aim was to test the hypothesis that dimensional differences between intraoral scans and conventional alginate impressions in the mixed dentition are clinically irrelevant.MethodsTrial design: Prospective non-randomized comparative clinical trial. Based on sample size calculation 44 evaluable mixed dentition jaws of patients in active orthodontic treatment were included. Each patient received an alginate impression following an intraoral scan (TRIOS® Ortho). Plaster cast was fabricated and scanned with an external scanner (ATOS-SO®). Both STL datasets were analyzed with the 3D inspection and mesh processing software GOM Inspect®. Statistical analysis comprised sample size calculation, t-test as well as nonparametric tests.ResultsThe absolute mean difference between digital plaster casts and intraoral scans is 0.022 mm ± 0.027 mm (median 0.015 mm). The obtained measurements are in the range of comparable studies on full arch permanent dentitions. Gender, the size of the jaw represented by the dentition stage and upper respectively lower jaw, as well the malocclusion have no effect on the total deviations between digital plaster casts and intraoral scans. Detectable impression errors were bubbles in fissures and marginal ridges as well as incomplete alginate flow and detachment from the tray. Detectable scanning errors were incomplete distal surface of the most distal molar.ConclusionDimensional differences between intraoral scans and conventional alginate impressions in the mixed dentition are clinically irrelevant for orthodontic purposes. In all clinical situations of active treatment in the mixed dentition, the intraoral scans are more detailed and less error-prone.

Stamp technique- A novel approach in pediatric restorative dentistry

Stamp technique is new and novel method for restoring mainly class I and sometimes class II with accurate occlusal topography with near perfection. Since proprioceptors of stomatognatic system react sensibly under pressure as such occlusal discrepancy after direct restorations, even if it is minor, leads to discomfort to the patients. Eventually patients compensate by adapting to new habitual occlusal position, which causes serious long term craniomandibular disturbances. The restoration of Class I cavities and erosively damaged teeth was the main consideration for Stamp technique but can be utilized for class II cavity restorations where marginal ridge is intact. This technique is possible in teeth where preoperative anatomy of the tooth is intact and not destructed by carious lesion. The stamp technique is perfomed in order to get a precise tooth‑like restoration with an accurate functional occlusion. This case report presents a case of stamp technique for simple class I composite restoration. The intent was to replicate occlusal anatomy by making a copy of the original unprepared tooth structure to get absolute anatomy in few minutes.

Clareamento dental interno: relato de caso

Objetivo: Relatar o caso clínico de uma paciente com escurecimento dental, o tratamento realizado e a condução do caso. Detalhamento do caso: Paciente, sexo feminino, 25 anos, compareceu a clínica odontológica, com a queixa principal “meu dente escureceu”. Na história da doença atual, a paciente relatava o escurecimento do dente 11, aproximadamente um ano após um canal endodôntico, que foi realizado devido a um trauma sofrido em um acidente cerca de dois anos atrás. No exame intra oral observou-se, escurecimento na face cervical do dente citado, as cristas marginais mantiveram-se integras e a face palatina com restauração onde foi realizado o acesso da câmara pulpar para a realização do tratamento endodôntico. Foi traçado o plano de tratamento, e foi escolhida a técnica mediata walking bleaching. Considerações finais: A técnica escolhida se deu após o diagnóstico do caso, sendo ela uma forma de clareamento endógeno e torna-se uma boa alternativa para a reversibilidade cromática, visto que é menos invasiva, conservadora, rápida, segura e de baixo custo no restabelecimento estético do dente comparada as outras técnicas de clareamento mais invasivas.

Preservation of a Split Tooth: Nonsurgical Clinical Management

A tooth is considered to be a split tooth if it contains a fracture line extending from the occlusal surface through both marginal ridges. Currently, the only treatment option for a split tooth is extraction. The present case report describes a novel therapeutic strategy for the preservation of a split tooth (first maxillary premolar) with a fracture in the mesiodistal direction. A systematic nonsurgical procedure involving visualization and slight widening of the fracture line is described. This procedure facilitates sealing of the fracture gap with a biocompatible calcium silicate cement (mineral trioxide aggregate) as well as internal composite resin stabilization and cuspal coverage restoration of the tooth. A 3-year follow-up showed a promising clinical and radiographic outcome. The concept presented here is an alternative treatment option for a split tooth, which allows preservation of the tooth rather than its extraction.

Minimally invasive proximal cavities restored with a hybrid, flowable and low-shrinking composite: effect of marginal ridge preservation on failure pattern

Objectives: The present study assessed the restorative potential of silorane, flowable or hybrid-based composite resin for the ultraconservative occlusal fossa technique. Materials and methods: Thirty-two intact human molars received in the proximal ridge a 1x2x4 mm size occlusal cavity leaving the enamel ridge intact. The bur was then tilted at 30° alongside enamel ridge to simulate a typical carious cavity. After enamel etching and application of adhesive system, cavities were filled with three composites and then, a 0.8 mm diameter hole was prepared beneath the proximal contact area to simulate an incipient enamel carious lesion. Restored molars were submitted to mechanical loading. The adhesive interfaces before and after loading were evaluated with SEM. The fracture test was performed on fatigued molars and maximum breaking loads were recorded. Results: The hybrid and silorane composites showed, after the fatigue test, higher percentages of continuous margins (81±12 and 75±17, respectively) in comparison to flowable material (53±24). Similar fracture resistance was recorded by the three composite types, but significantly lower than the fracture resistance of the non-restored group. Nevertheless, a trend to a ductile behaviour, i.e. better capacity for elastic deformation, was observed in the group restored with the hybrid composite. Conclusions: Minimally invasive occlusal restorations with marginal ridge preservation and simulated proximal decay can be efficiently restored with hybrid and low shrinking composites. The flowable composite might not be indicated in this cavity type, in view of the marginal degradation observed after the fatigue test.

Influence of cavity depth and restoration of non-carious cervical root lesions on strain distribution from various loading sites

BackgroundWe aimed to investigate the load-induced strain variation in teeth with unrestored and resin-based composite restored non-carious cervical lesions (NCCLs).MethodsTwelve extracted premolars were provided for measuring buccal-side root NCCLs. Strain gauges were fixed at four measuring sites of each tooth, two at the buccal surface and two at the lingual surface. NCCLs were prepared with occlusal margins at the cemento-enamel junction. A static 9-kg load was applied at seven occlusal loading points: buccal cusp tip (BC), inner inclination of the BC, lingual cusp tip (LC), inner inclination of the LC, center of the mesial marginal ridge or distal marginal ridge, and center of the central groove. The strain was detected at each site in teeth with NCCL depths of 0 (control), 0.5, 1.0, and 1.5 mm. Each NCCL was restored using an adhesive composite resin, and the strains were re-measured.ResultsThe strains at the NCCL occlusal and gingival margins decreased with increasing defect depths, and the effect was significant when the depth of the defect was 1.5 mm. Loading on the buccal and lingual cusps induced prominent strain variation. The strains at all depth distribution recovered to nearly intact conditions when the NCCLs were restored.ConclusionsNCCLs at 1.5 mm depth are detrimental, but they can be restored using resin composites.Clinical significanceThe existence of NCCLs should not be ignored. The depth of the NCCL may affect the progression of the lesion. Resin composite restoration is an appropriate method for preventing persistent NCCL deterioration.

Tectono-sedimentary evolution and petroleum systems of the Mundaú subbasin: A new deep-water exploration frontier in equatorial Brazil

The Brazilian equatorial margin (BEM) evolved in response to transform motion between Brazil and Africa. In 2012, Petrobras drilled the Pecem well in the Mundau subbasin (Ceara Basin) of the BEM to record the first deep-water oil discovery in the region. This work investigates the deep-water evolution of the Mundau subbasin focusing on its structural and sedimentary evolution, and characterizes the petroleum systems in this new exploration frontier. For such purposes, poststack seismic reflection, borehole, and geochemical data were used. Three tectono-stratigraphic sequences representing synrift (Mundau Formation), transitional (Paracuru Formation), and drift strata (Ubarana Formation) were divided into seven seismic units. Different tectonic domains were interpreted: proximal, distal, and Romanche Fracture Zone. Typical structures of transform margins, such as marginal ridges and marginal plateaus, were not identified in the Mundau subbasin. Instead, the subbasin was predominantly deformed by transtensional movements. The Mundau and Paracuru Formations are mature within the oil window, whereas the Ubarana Formation is immature. Main reservoir intervals consist of approximately 1-m (∼3.28-ft)-thick intercalations of sandstone between shales, siltstones, and marls. The seal rocks comprise shales in the Ubarana Formation, whereas the hydrocarbon trap is related to an unconformity and a normal fault. This work concludes that the Paracuru Formation is the main source and reservoir in the deep-water Mundau subbasin, effectively comprising a Paracuru–Paracuru petroleum system. The results have significant implications for petroleum exploration in the BEM by proposing a developed transitional petroleum system in the distal parts of northeastern Brazil.

Evidence for Late Quaternary Deformation Along Crowleys Ridge, New Madrid Seismic Zone

AbstractThe New Madrid seismic zone has been the source of multiple major (M ~7.0–7.5) earthquakes in the past 2 ka, yet the surface expression of recent deformation remains ambiguous. Crowleys Ridge, a linear ridge trending north‐south for 300+ km through the Mississippi Embayment, has been interpreted as either a fault‐bounded uplift or a nontectonic erosional remnant. New and previously published seismic reflection and shallow resistivity data show discontinuities at the ridge margins in Plio‐Pleistocene strata, yet the timing of most recent faulting and the lateral extent of these faults remain unknown. To assess Pleistocene‐to‐recent tectonic activity of Crowleys Ridge, we perform landscape‐scale geomorphic analyses, such as relief, slope, hypsometry, and drainage basin shape, on a 10‐m digital elevation model (DEM). North‐to‐south variations in geomorphic indices indicate Pleistocene‐to‐recent tectonic uplift of the southern ridge. Moreover, mapping on a <1‐m lidar‐derived DEM reveals scarps on late Pleistocene geomorphic surfaces. The scarps are primarily located along the southern ridge, trend parallel to the ridge margin discontinuously for 0.1–1 km, and vertically offset <56 ka surfaces 0.4 m with up to 6 m of tilting. These landscape‐scale patterns and scarps, integrated with discontinuities in the seismic reflection and resistivity data, provide evidence of low‐rate (<0.2 mm/year) late Quaternary tectonic activity along the southern segment of Crowleys Ridge. The interpretations agree with recent tectonic models suggesting southern Crowleys Ridge is a compressional step over in a right‐lateral fault system within the Reelfoot Rift.

Stability of occlusal outcome during long-term retention: the time-dependent variation of the American Board of Orthodontics index.

The aim of this retrospective cohort study was to assess long-term occlusal changes at debond and a median of 8 years afterwards (in retention) with the American Board of Orthodontics (ABO) objective grading system and identify risk factors. Fifty patients (median age: 14.3 years at debond; 60% female) treated with fixed appliances (25 with and 25 without premolar extractions) were included. The occlusal outcome was assessed with the ABO tool and analyzed statistically at 5%. Extraction treatment was associated with better occlusal outcome than non-extraction treatment (34.2 versus 40.9 points; P = 0.009). In retention, ABO scores improved by 7.4 points, while patients with worse debond finishing improved more afterwards (P = 0.001). Alignment/rotations deteriorated in 58% of the cases and occlusal relationships in 38% of the cases. Marginal ridges improved more for extraction than non-extraction patients (28% versus 0%; P = 0.001). Occlusal relationships improved more for cases that 'passed' the ABO requirements at debond than failed cases (64% versus 28%; P = 0.02). Furthermore, patients with worse debond ABO scores were more likely to deteriorate at alignment/rotations in retention. Finally, the proportion of cases passing the ABO requirements improved considerably between debond (28%) and in retention (54%) as half (47%) of the cases that had failed the ABO requirements at debond passed them in retention. Considerable long-term occlusal changes are seen post-debond, which mostly favour improved settling. Extraction treatment and higher finishing quality at debond significantly influenced the chance for improvement. However, setting a cut-off score to denote treatment excellence showed considerable instability through time.

Ex vivo investigation on internal tunnel approach/internal resin infiltration and external nanosilver-modified resin infiltration of proximal caries exceeding into dentin.

This ex vivo proof-of-concept study aimed to investigate the effect of nanosilver particles (AgNP) added to a conventional infiltrant resin (Icon) on external penetration into natural proximal enamel caries exceeding into dentin after internal tunnel preparation and internal infiltration. Carious lesions (ICDAS codes 2/3) of extracted human (pre-)molars revealing proximal caries radiographically exceeding into dentin (E2/D1 lesions) were preselected. Then, 48 of those specimens showing demineralized areas transcending the enamel-dentin border as assessed by means of near-infrared light transillumination (DIAGNOcam) were deproteinized (NaOCl, 5%). Using an internal tunnel approach, occlusal cavities central to the marginal ridge were prepared. Excavation of carious dentin, total etch procedure (H3PO4, 40%), and internal resin infiltration (FITC-labeled) followed, along with final restorations (flowable composite resin). Outer lesion surfaces were etched (HCl, 15%) prior to external infiltration (RITC-labeled). Group 1 (control; n = 24) used non-modified infiltrant, while an infiltrant/AgNP mixture (20 nm; 5.5 wt%) was used with experimental Group 2 (n = 24). Non-infiltrated pores of cut lesions were stained (Berberine), and specimens were analyzed using confocal laser scanning microscopy. Compared to the non-filled infiltrant, incorporation of AgNP had no effect on the resin's external penetration. Between the groups, no significant differences regarding internal or external infiltration could be detected, and non-infiltrated lesion areas did not differ significantly (p>0.109; t-test). The internal tunnel preparation in combination with both an internal resin infiltration and an additional external infiltration approach using a nanosilver-modified infiltrant resin leads to increased infiltrated lesion areas, thus occluding and adhesively stabilizing the porous volume of the demineralized enamel. While exerting antimicrobial effects by the nanosilver particles, this approach should have the potential as a viable treatment alternative for proximal lesions extending into dentin, thus avoiding the sacrifice of sound enamel, postponing the frequently inevitable restoration/re-restoration cycle of conventional proximal caries treatment, and improving dental health.

Palatogingival groove and root canal instrumentation

To evaluate the morphology and impact of root canal preparation in maxillary incisors with palatogingival grooves (PGG). Twenty extracted human maxillary incisors with PGG were subjected to macroscopic analysis and scanning electron microscopy analysis (SEM). The following characteristics of the PGG were evaluated: depth, point of origin in the cingulum, extension and position on the lingual surface. Furthermore, the presence of calculus, communications between the root canal system and the PGG, and root resorptions were investigated. The root canals were subsequently instrumented with K-files of three consecutive sizes. The teeth were sectioned, and the axial plane of each tooth section was imaged using SEM before and after instrumentation. The distance between the root canal walls and the PGG was calculated according to the location. Additionally, the distance between canal walls and cementum was measured at three different sites, to verify if instrumentation influenced dentine removal on a specific wall in teeth with PGG. Statistical analysis was performed using the Mann-Whitney or Student's t-test (P<0.05). Macroscopic analysis revealed that a deep groove was most frequently observed (75%), followed by a depression/shallow groove (25%) (P<0.05). PGG typically originated in the distal margin ridge of the cingulum (65%) (P<0.05), extending only to the middle (45%) or up to the apical (50%) third of the root (P<0.05). Additionally, PGGs were typically located on the distal aspect of the lingual surface (70%) (P<0.05). Calculus was concentrated on the surface of the crown and cementum-enamel junction (P<0.05). Communication between the root canal and PGG was present in 35% of teeth, and root resorptions were noted in 50% of teeth. The distance between the external root surface and the pulp cavity was significantly narrower after instrumentation (P<0.05); however, root canal preparation did not influence dentine removal on the specific wall associated with the groove(P>0.05). Palatogingival grooves were characteristically deep and originated from the distal margin of the cingulum. Although it has been associated with a thinner root wall, root canal preparation did not influence the thickness of the specific wall in the maxillary incisors with PGG.

Long-term stability of retreated defective restorations in patients with vertical food impaction.

Background:Vertical food impaction (VFI) is a common complaint among patients receiving interproximal restorations. However, there is a gap in the literature regarding outcomes of treating defective restorations with VFI. This study sought to determine 10-year stability of retreated defective restorations in patients diagnosed with VFI.Materials and Methods:A total of 150 teeth (75 pair), in 38 patients comprised our study population. All the participants had been diagnosed with VFI due to faulty restorations and treated by means of redoing the restoration to build a stable contact in at least one restored tooth. The criteria for building an optimum dental contact were defined. Demographic characteristics, date and frequency of redoing the restoration, type and material of restoration, number of restored surfaces, occlusal intercuspal relationship, missing adjacent and/or opposing teeth, cemento enamel junction to alveolar crest distance, recurrence of VFI symptoms, recurrent caries, and periapical pathology as well as periodontal variables were recorded.Results:Kaplan–Meier estimator revealed that the mean ± standard deviation of 1, 3, 5, and 10-year stability of reconstructed contacts was 89/2% ± 3/6%, 79/2% ± 5%, 70/7% ± 0/06%, and 66/3% ± 7/1%, respectively. The overall cumulative stability rate was 74/4%. Further analysis predicted that over a 12-year period, restored contacts were stable for 8.86 ± 0.6 years. Cox regression model indicated that having cusp to marginal ridge occlusal relationship (95% confidence interval [CI] for hazard risk (HR) = 1/1–13/9, HR = 3/93), and being over 40 years of age (95% CI for HR = 0/88–17/66, HR = 3/95) were major determinants of contact stability.Conclusions:Long-term stability of retreated and restructured tooth contacts with a history of VFI was 66%–89% in this specific sample.

An emended description of the freshwater araphid genus Ambistria: a rare diatom from North American Eocene localities

In 1968, Lohman and Andrews described the freshwater araphid diatom genus Ambistria from the Wagon Bed Formation, a Late Eocene deposit in Wyoming, U.S.A. The genus was distinguished from other genera on the basis of the distinctive shape of the valve coupled with short striae restricted to the valve margins, the latter resulting in a wide hyaline axial region. These authors further described two species of Ambistria based on differences in size and the presence/absence of randomly spaced isolated pores in the hyaline axial region. Further details could not be discerned from the specimens illustrated, and the genus has not been reported since the original description. Numerous specimens of Ambistria were uncovered from the Giraffe Pipe locality, an Early Eocene deposit located in the Northwest Territories, Canada, near the Arctic Circle. Examination of these specimens with light and scanning electron microscopy revealed an additional suite of characters, which have now been used to emend and expand the original generic description. These features include the presence of marginal ridges, a unique mechanism used to link frustules together into chains, areolae with reniform-shaped volae, and laterally opening girdle bands. Ambistria belongs in the class Fragilariophyceae Round, and is best placed within the order Fragilariales (Silva) emended Round. Additional characters that could be used to delineate between species include shape of the central region, length to width ratio, and possibly the number of girdle bands. The recent discovery of Ambistria in the Giraffe Pipe locality extends the range of this extinct diatom to the Early Eocene.

Endostructural morphology in hominoid mandibular third premolars: Discrete traits at the enamel-dentine junction

The mandibular third premolar (P3) exhibits substantial differences in size and shape among hominoid taxa, and displays a number of discrete traits that have proven to be useful in studies of hominin taxonomy and phylogeny. Discrete traits at the enamel-dentine junction (EDJ) can be accurately assessed on moderately worn specimens, and often appear sharper than at the outer-enamel surface (OES). Here we use microtomography to image the P3 EDJ of a broad sample of extant apes, extinct hominins and modern humans (n = 100). We present typologies for three important premolar discrete traits at the EDJ (transverse crest, marginal ridge and buccal grooves), and score trait frequencies within our sample. We find that the transverse crest is variable in extant apes, while the majority of hominins display a transverse crest which runs directly between the two major premolar cusps. Some Neanderthals display a unique form in which the transverse crest fails to reach the protoconid. We find that mesial marginal ridge discontinuity is common in Australopithecus anamensis and Australopithecus afarensis while continuous marginal ridges largely characterize Australopithecus africanus and Paranthropus. Interrupted mesial and distal marginal ridges are again seen in Homo sapiens and Neanderthals. Premolar buccal grooves, previously identified at the OES as important for hominin systematics, are again found to show a number of taxon-specific patterns at the EDJ, including a clear difference between Australopithecus and Paranthropus specimens. However, their appearance may be dependent on the morphology of other parts of the crown such as the protoconid crest, and the presence of accessory dentine horns. Finally, we discuss rare variations in the form of dentine horns that underlie premolar cusps, and their potential homology to similar morphologies in other tooth positions.

Endostructural morphology in hominoid mandibular third premolars: Geometric morphometric analysis of dentine crown shape

In apes, the mandibular third premolar (P3) is adapted for a role in honing the large upper canine. The role of honing was lost early in hominin evolution, releasing the tooth from this functional constraint and allowing it to respond to subsequent changes in masticatory demands. This led to substantial morphological changes, and as such the P3 has featured prominently in systematic analyses of the hominin clade. The application of microtomography has also demonstrated that examination of the enamel-dentine junction (EDJ) increases the taxonomic value of variations in crown morphology. Here we use geometric morphometric techniques to analyze the shape of the P3 EDJ in a broad sample of fossil hominins, modern humans, and extant apes (n = 111). We test the utility of P3 EDJ shape for distinguishing among hominoids, address the affinities of a number of hominin specimens of uncertain taxonomic attribution, and characterize the changes in P3 EDJ morphology across our sample, with particular reference to features relating to canine honing and premolar ‘molarization’. We find that the morphology of the P3 EDJ is useful in taxonomic identification of individual specimens, with a classification accuracy of up to 88%. The P3 EDJ of canine-honing apes displays a tall protoconid, little metaconid development, and an asymmetrical crown shape. Plio-Pleistocene hominin taxa display derived masticatory adaptations at the EDJ, such as the molarized premolars of Australopithecus africanus and Paranthropus, which have well-developed marginal ridges, an enlarged talonid, and a large metaconid. Modern humans and Neanderthals display a tall dentine body and reduced metaconid development, a morphology shared with premolars from Mauer and the Cave of Hearths. Homo naledi displays a P3 EDJ morphology that is unique among our sample; it is quite unlike Middle Pleistocene and recent Homo samples and most closely resembles Australopithecus, Paranthropus and early Homo specimens.

A new species of Achnanthes (Bacillariophyceae) from a freshwater habitat in a karst landform from south‐central China

SUMMARY Achnanthes maolanensis nov. sp. is a large diatom collected from subaerial, freshwater habitats in karst landforms in central‐south China. Living cells have two chloroplasts. Valves of this new species are panduriform in outline, slightly constricted in the middle part of the margins, with uniseriate areolae; the raphe is filiform, and there is a linear, thickened stauros in the central area of the RV. On the ARV, there is no central area, and as well there are no terminal orbiculi, marginal ridge, or terminal spine externally. The axial area (rapheless sternum) is located down the center, not offset from the center as in many other species of the genus and is narrow and almost straight. This suite of characters makes the new species easy to distinguish from other species in the genus. Its presence adds further documentation of the unique and diverse freshwater diatom flora from karst habitats in this region of China.