SciCombinator

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Concept: Jaw

200

Razanandrongobe sakalavae Maganuco, Dal Sasso & Pasini, 2006 is a large predatory archosaur from the Middle Jurassic (Bathonian) of the Mahajanga Basin, NW Madagascar. It was diagnosed on the basis of teeth and a fragmentary maxilla, but its affinities were uncertain. Here we describe new cranial remains (above all, an almost complete right premaxilla and a caudally incomplete left dentary) that greatly improve our knowledge on this enigmatic species and reveal its anatomy to be crocodylomorph. The right premaxilla indicates that the rostrum was deep, wide, and not pointed; it bears five teeth that are sub-vertical and just slightly curved lingually; the mesial teeth are U-shaped in cross-section and have serrated carinae on the lingual side; the aperturae nasi osseae (external bony nares) are confluent and face rostrally; and there is no lateral groove at the premaxillomaxillary suture for reception of a hypertrophied lower caniniform tooth. The preserved portion of the left dentary has an edentulous tip and bears eight large mandibular teeth of which the mesial (1-3) are the largest, but none is a hypertrophied caniniform tooth; the mandibular (dentary) symphysis extends caudally to the level of the third tooth; the splenial is not preserved, but its sutural marks on the dentary indicate that it contributed to the mandibular symphysis for at least 20% of the symphyseal length in dorsal aspect. On the basis of this new data, some previously uncertain features of the holotype maxilla-such as the margin of the suborbital fenestra, the contact surfaces for the palatine, the ectopterygoid, and the jugal-are now apparent. Testing of the phylogenetic position of the species within Crocodylomorpha indicates that R. sakalavae is a mesoeucrocodylian. It also represents one of the earliest events of exacerbated increase in body size along the evolutionary history of the group. In addition, it is by far the oldest notosuchian. A cranial reconstruction of this gigantic predator is also attempted here. The very robust jaw bones of R. sakalavae, coupled with its peculiar dentition, strongly suggest a diet that included hard tissue such as bone and tendon.

Concepts: Left-wing politics, Mandible, Teeth, Animal anatomy, Jaw, Maxilla, Symphysis menti, Symphysis

151

Central odontogenic fibroma (COF) is a rare benign tumor that accounts for 0.1% of all odontogenic tumors. A case of COF (simple type) of the mandible in a four-year-old boy is described in this report. The patient showed asymptomatic swelling in the right inferior border of the lower jaw for one week. A panoramic radiograph showed a poorly-defined destructive unilocular radiolucent area. Cone-beam computed tomography showed expansion and perforation of the adjacent cortical bone plates. A periosteal reaction with the Codman triangle pattern was clearly visible in the buccal cortex. Since the tumor had destroyed a considerable amount of bone, surgical resection was performed. No recurrence was noted.

Concepts: Bone, Oncology, Mandible, Tomographic reconstruction, Benign tumor, Tumor, Temporomandibular joint, Jaw

126

Five striking and prey capture events of two goblin sharks were videotaped at sea for the first time, showing their extraordinary biting process. The goblin sharks swung their lower jaw downward and backward to attain a huge gape and then rapidly protruded the jaws forward a considerable distance. The jaws were projected at a maximum velocity of 3.1 m/s to 8.6-9.4% of the total length of the shark, which is by far the fastest and greatest jaw protrusion among sharks. While the jaws were being retracted, the mouth opened and closed again, which was considered a novel feeding event for sharks. Phylogenetic evidence suggested that their feeding behavior has evolved as an adaptation to food-poor deep-sea environments, possibly as a trade-off for the loss of strong swimming ability.

Concepts: Great white shark, Ocean, Jaw, Shark, Lamniformes, Goblin shark, Mitsukurinidae, Scapanorhynchus

47

Arthodire placoderms have been proposed as the sister group of Chinese ‘maxillate’ placoderms plus all the more crownward gnathostomes. These basal groups provide key information for understanding the early evolution of jaws. Here, we test previous assumptions about placoderm jaw structure and function by using high-resolution computed tomography, digital dissection, and enlarged 3D printouts on a unique articulated 400 million-year-old buchanosteid arthrodire. The upper jaw has a double ethmoid and a palatobasal connection, but no otic connection; the dermal bone attachment for the quadrate is different to other placoderms. A separately ossified cartilage behind the mandibular joint is comparable to the interhyal of osteichthyans. Two articular facets on the braincase associated with the hyomandibular nerve foramen supported a possible epihyal element and a separate opercular cartilage. Reassembling and manipulating 3D printouts demonstrates the limits of jaw kenetics. The new evidence indicates unrecognized similarities in jaw structure between arthrodires and osteichthyans, and will help to clarify the sequence of character acquisition in the evolution of basal gnathostome groups. New details on the hyoid arch will help to reformulate characters that are key in the heated debate of placoderm monophyly or paraphyly.

Concepts: Bone, Phylogenetics, Vertebrate, Gnathostomata, Jaw, Placodermi, Arthrodira, Dunkleosteus

44

A pterosaur bone bed with at least 47 individuals (wing spans: 0.65-2.35 m) of a new species is reported from southern Brazil from an interdunal lake deposit of a Cretaceous desert, shedding new light on several biological aspects of those flying reptiles. The material represents a new pterosaur, Caiuajara dobruskii gen. et sp. nov., that is the southermost occurrence of the edentulous clade Tapejaridae (Tapejarinae, Pterodactyloidea) recovered so far. Caiuajara dobruskii differs from all other members of this clade in several cranial features, including the presence of a ventral sagittal bony expansion projected inside the nasoantorbital fenestra, which is formed by the premaxillae; and features of the lower jaw, like a marked rounded depression in the occlusal concavity of the dentary. Ontogenetic variation of Caiuajara dobruskii is mainly reflected in the size and inclination of the premaxillary crest, changing from small and inclined (∼115°) in juveniles to large and steep (∼90°) in adults. No particular ontogenetic features are observed in postcranial elements. The available information suggests that this species was gregarious, living in colonies, and most likely precocial, being able to fly at a very young age, which might have been a general trend for at least derived pterosaurs.

Concepts: Mandible, Reptile, Mammal, Cretaceous, Pterosaur, Pterodactyloidea, Tapejaridae, Jaw

37

The early tetrapod Acanthostega gunnari is an iconic fossil taxon exhibiting skeletal morphology reflecting the transition of vertebrates from water onto land. Computed tomography data of two Acanthostega skulls was segmented using visualization software to digitally separate bone from matrix and individual bones of the skull from each other. A revised description of cranial and lower jaw anatomy in this taxon based on CT data includes new details of sutural morphology, the previously undescribed quadrate and articular bones, and the mandibular symphysis. Sutural morphology is used to infer loading regime in the skull during feeding, and suggests Acanthostega used its anterior jaws to initially seize prey while smaller posterior teeth were used to restrain struggling prey during ingestion. Novel methods were used to repair and retrodeform the skull, resulting in a three-dimensional digital reconstruction that features a longer postorbital region and more strongly hooked anterior lower jaw than previous attempts while supporting the presence of a midline gap between the nasals and median rostrals.

Concepts: Bone, Skeletal system, Mandible, Skull, Tetrapod, Synapsid, Jaw, Acanthostega

27

Osteopetrosis is a rare congenital (autosomal type) disorder of the skeletal system. Several variants have been described in the literature with grossly variant prognosis and clinical behaviour. Several reports of intractable osteomyelitis of the jaw bones secondary to osteopetrosis, particularly the mandible, have been published widely. However, there is no published report of the complete mandible sequestrating de novo, in the literature. An overview of this spectrum of sclerotic bone disease, its presentation in the oro-facial region, the diagnostic challenge it poses and the management dilemma it offers to the maxillofacial surgeon is discussed and a protocol for managing this disease effectively is presented. A clinical illustration of the complexities of management of osteopetrosis-induced osteomyelitis of jaw bones is demonstrated with a very rare case in which the entire mandible had sequestrated.

Concepts: Bone, Skeletal system, Surgery, Intramembranous ossification, American College of Surgeons, Human skeleton, Skeleton, Jaw

26

Abstract Aim: To accurately portray the risk management of a patient presenting with mandibular osteonecrosis following bisphosphonate exposure and immediate loading of dental implant treatment. This case report describes a 58-year-old African American female having experienced previous success of implant osseointegration in the maxilla, sought similar mandibular treatment four years later and had been taking bisphosphonate for a total 5 years. All existing mandibular teeth were extracted and 6 Brånemark System implants were placed and immediately loaded without complication. Two weeks postoperative, a slower rate of healing was noticed. Over a period of six weeks, the patient’s condition worsened. An extraoral fistula exuded from a lesion on the left inferior border of the mandible. The patient was diagnosed with bisphosphonate-induced osteonecrosis of the jaw (BONJ) and discontinued bisphosphonate medication indefinitely. The patient was treated for BONJ and four of the six implants which were encapsulated in tissue were removed. She ceased the oral Fosamax therapy for two and a half years following the BONJ, and had morning-fasting serum C-terminal telopeptide (CTX) test of 457 pg/ml* which showed her bone turnover rate had returned to normal levels. Four new Brånemark System implants were placed in the mandible and were immediately loaded. Four months later, a screw-retained implant-supported final prosthesis was delivered. The patient has been followed for 5 years from the time of retreatment of mandibular arch and 11 years from time of implant placement in the maxillary arch. All postoperative evaluations have been uneventful. This case report demonstrated how management of BONJ can lead to successful retreatment with implants after a drug holiday, and how being cognizant to the length of time of Fosamax therapy can help clinicians avoid BONJ complications.

Concepts: Bone, Mandible, Implants, Prosthetics, Dental implant, Osseointegration, Jaw, Maxilla

23

Dermoid cysts are unusual neoplasms and can occur in every part of the human body. They represent only 6.9% of all dermoid cysts in the head and neck region; in the oral cavity, the incidence is low, approximately 1.6% of all dermoid cysts. Our aim is to present an unusual case of a large sublingual dermoid cyst with mandibular prognathism caused by cyst growth. We reported a case of a large sublingual dermoid cyst in an 8-year-old female patient. A bibliographic research from 1937 to 2013 is reviewed and we found only three cases of mandibular deformity, of which only one was a dermoid cyst of the floor of the mouth. Removal of dermoid cysts of the floor of the mouth should be completed as early as detected, especially in newborns and infants when osseous growth abnormalities could result if removal is delayed.

Concepts: Head and neck anatomy, Oncology, Human body, Cyst, Dermoid cyst, Pilonidal cyst, Tongue, Jaw

20

The gnathostome (jawed vertebrate) crown group comprises two extant clades with contrasting character complements. Notably, Chondrichthyes (cartilaginous fish) lack the large dermal bones that characterize Osteichthyes (bony fish and tetrapods). The polarities of these differences, and the morphology of the last common ancestor of crown gnathostomes, are the subject of continuing debate. Here we describe a three-dimensionally preserved 419-million-year-old placoderm fish from the Silurian of China that represents the first stem gnathostome with dermal marginal jaw bones (premaxilla, maxilla and dentary), features previously restricted to Osteichthyes. A phylogenetic analysis places the new form near the top of the gnathostome stem group but does not fully resolve its relationships to other placoderms. The analysis also assigns all acanthodians to the chondrichthyan stem group. These results suggest that the last common ancestor of Chondrichthyes and Osteichthyes had a macromeric dermal skeleton, and provide a new framework for studying crown gnathostome divergence.

Concepts: Fish, Vertebrate, Chordate, Gnathostomata, Jaw, Placodermi, Chondrichthyes, Teleostomi