Dentition and feeding in Placodontia: tooth replacement in Henodus chelyops

Background Placodontia is a Triassic sauropterygian reptile group characterized by flat and enlarged crushing teeth adapted to a durophagous diet. The enigmatic placodont Henodus chelyops has numerous autapomorphic character states, including extreme tooth count reduction to only a single pair of palatine and dentary crushing teeth. This renders the species unusual among placodonts and challenges identification of its phylogenetic position. Results The skulls of two Henodus chelyops specimens were visualized with synchrotron tomography to investigate the complete anatomy of their functional and replacement crushing dentition in 3D. All teeth of both specimens were segmented, measured, and statistically compared to reveal that H. chelyops teeth are much smaller than the posterior palatine teeth of other cyamodontoid placodonts with the exception of Parahenodus atancensis from the Iberian Peninsula. The replacement teeth of this species are quite similar in size and morphology to the functional teeth. Conclusion As other placodonts, Henodus chelyops exhibits vertical tooth replacement. This suggests that vertical tooth replacement arose relatively early in placodont phylogeny. Analysis of dental morphology in H. chelyops revealed a concave shape of the occlusal surface and the notable absence of a central cusp. This dental morphology could have reduced dental wear and protected against failure. Hence, the concave teeth of H. chelyops appear to be adapted to process small invertebrate items, such as branchiopod crustaceans. Small gastropods were encountered in the matrix close to both studied skulls.

Bilateral Accessory Central Cusp on Permanent Mandibular Second Molars: An Unusual Occurrence

Anomaly like central cusp is accessory cusp which is similar to Dens Evaginatus (DE) in premolars. Such accessory occlusal/central cusps are rarely being reported in mandibular molars. The presence of these structures can be a cause of concern when they interfere with occlusion, get fractured or pulp is exposed. This report presents an unusual case of 21-year-old male patient with bilateral accessory cusp in permanent mandibular second molars, the left with Occlusal central cusp (7-cusp anatomy) and the right with a prominent expression of tuberculum sextum (5-cusp anatomy). The patient reported with sensitivity on lower left second molar. Radiograph did not reveal any pulpal extension in both the teeth. Buccal caries on left second molar was restored with composite resin and the accessory cusp was incrementally grinded. The patient reported on follow-up visit after 6 months and was asymptomatic. Early identification of supernumery occlusal central cusp and proper treatment can avoid pulpal complications.

Tometes camunani (Characiformes: Serrasalmidae), a new species of phytophagous fish from the Guiana Shield, rio Trombetas basin, Brazil

A new species of Serrasalmidae, Tometes camunani, is described from the upper drainages of the rio Trombetas basin, Pará State, Brazil. The new species is distinguished from its congeners by having neurocranium with a slight concavity at the level of the frontal bone (vs. concavity absent, dorsal profile of neurocranium straight). It can be further distinguished from its congeners by having teeth with central cusp taller and acute (vs. central cusp shorter and with rounded edge in T. trilobatus), a terminal mouth (vs. upturned mouth in T. lebaili), and 12-26 prepelvic spines (vs. 0-9 in T. makue). The new species is strictly rheophilic like other species of Tometes, and occurs exclusively in the rapids of shield rivers, complex and fragile biotopes that are threatened by anthropogenic activities. An identification key to the species of the Myleus group is provided

Reiterative pattern of sonic hedgehog expression in the catshark dentition reveals a phylogenetic template for jawed vertebrates

For a dentition representing the most basal extant gnathostomes, that of the shark can provide us with key insights into the evolution of vertebrate dentitions. To detail the pattern of odontogenesis, we have profiled the expression of sonic hedgehog , a key regulator of tooth induction. We find in the catshark ( Scyliorhinus canicula ) that intense shh expression first occurs in a bilaterally symmetrical pattern restricted to broad regions in each half of the dentition in the embryo jaw. As in the mouse, there follows a changing temporal pattern of shh spatial restriction corresponding to epithelial bands of left and right dental fields, but also a subfield for symphyseal teeth. Then, intense shh expression is restricted to loci coincident with a temporal series of teeth in iterative jaw positions. The developmental expression of shh reveals previously undetected timing within epithelial stages of tooth formation. Each locus at alternate, even then odd, jaw positions establishes precise sequential timing for successive replacement within each tooth family. Shh appears first in the central cusp, iteratively along the jaw, then reiteratively within each tooth for secondary cusps. This progressive, sequential restriction of shh is shared by toothed gnathostomes and conserved through 500 million years of evolution.

Early detection of dens evaginatus appearing on the premolars and clinical management: histological study

A review of the methods for the prevention of central cusp fracture is presented, with a case of central cusp protection of a premolar by self-curing acrylic resin by early detection. The anomalous tooth was extracted for histological observation. Closure of the pulpal horn, could be accomplished by early detection and adequate treatment for the central cusp fracture of premolars. In this case, if the gradual attrition of a central cusp were not possible, a protecting the cusp using a self-curing acrylic resin would be an effective form of treatment.