SciCombinator

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Concept: Symphysis menti

198

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

7

The presence of a prominent chin in modern humans has been viewed by some researchers as an architectural adaptation to buttress the anterior corpus from bending stresses during mastication. In contrast, ontogenetic studies of mandibular symphyseal form suggest that a prominent chin results from the complex spatial interaction between the symphysis and surrounding soft tissue and skeletal anatomy during development. While variation in chin prominence is clearly influenced by differential growth and spatial constraints, it is unclear to what degree these developmental dynamics influence the mechanical properties of the symphysis. That is, do ontogenetic changes in symphyseal shape result in increased symphyseal bending resistance? We examined ontogenetic changes in the mechanical properties and shape of the symphysis using subjects from a longitudinal cephalometric growth study with ages ranging from 3 to 20+ years. We first examined whether ontogenetic changes in symphyseal shape were correlated with symphyseal vertical bending and wishboning resistance using multivariate regression. Secondly, we examined ontogenetic scaling of bending resistance relative to bending moment arm lengths. An ontogenetic increase in chin prominence was associated with decreased vertical bending resistance, while wishboning resistance was uncorrelated with ontogenetic development of the chin. Relative to bending moment arm lengths, vertical bending resistance scaled with significant negative allometry whereas wishboning resistance scaled isometrically. These results suggest a complex interaction between symphyseal ontogeny and bending resistance, and indicate that ontogenetic increases in chin projection do not provide greater bending resistance to the mandibular symphysis.

Concepts: Developmental biology, Torque, Force, Biomechanics, Allometry, Symphysis menti, Ontogeny, Symphysis

0

Chin ptosis is described as a descent of the soft tissue from the symphyseal region to a position under the lower contour of the mandible. Given its multifactorial causes, treatment must be determined on a patient-by-patient basis. While augmentation of the submental crease is a versatile option for the correction of chin ptosis, this only corrects the soft tissue component. A technical modification to treat dynamic chin ptosis, associated with bone reduction in the mandibular symphysis, is presented here.

Concepts: Mandible, Tissues, Orthopedic surgery, Symphysis menti, Symphysis

0

Distraction of the mandibular symphysis, initially described by Guerrero, is often indicated in instances of osseous deficiency in the anterior mandible with associated tooth-jaw discrepancy. The authors describe a technique, combined with orthodontic treatment, which offers a safe and reliable alternative to avulsions and coronoplasty. Three operative techniques are outlined in detail.

Concepts: Mandible, Creativity techniques, Orthodontics, Symphysis menti, Symphysis

0

Autogenous bone is commonly used in pre-implant bone reconstructions. Five harvesting sites are frequently used: mandibular symphysis and ramus, iliac crest, calvaria and tibia. One of the deciding criterions among these sites is the donor site morbidity. The purpose of our work was to analyze the intra- and postoperative complications that may occur on the different donor sites.

Concepts: Symphysis menti

0

In Pierre Robin sequence, a retracted tongue due to micrognathia is thought to physically obstruct palatal shelf elevation and thereby cause cleft palate. However, micrognathia is not always associated with palatal clefting. Here, by using the Bmp7-null mouse model presenting with cleft palate and severe micrognathia, we provide the first causative mechanism linking the two. In wild-type embryos, the genioglossus muscle, which mediates tongue protrusion, originates from the rostral process of Meckel’s cartilage and later from the mandibular symphysis, with 2 tendons positive for Scleraxis messenger RNA. In E13.5 Bmp7-null embryos, a rostral process failed to form, and a mandibular symphysis was absent at E17.5. Consequently, the genioglossus muscle fibers were diverted toward the lingual surface of Meckel’s cartilage and mandibles, where they attached in an aponeurosis that ectopically expressed Scleraxis. The deflection of genioglossus fibers from the anterior-posterior toward the medial-lateral axis alters their direction of contraction and necessarily compromises tongue protrusion. Since this muscle abnormality precedes palatal shelf elevation, it is likely to contribute to clefting. In contrast, embryos with a cranial mesenchyme-specific deletion of Bmp7 (Bmp7:Wnt1-Cre) exhibited some degree of micrognathia but no cleft palate. In these embryos, a rostral process was present, indicating that mesenchyme-derived Bmp7 is dispensable for its formation. Moreover, the genioglossus appeared normal in Bmp7:Wnt1-Cre embryos, further supporting a role of aberrant tongue muscle attachment in palatal clefting. We thus propose that in Pierre Robin sequence, palatal shelf elevation is not impaired simply by physical obstruction by the tongue but by a specific developmental defect that leads to functional changes in tongue movements.

Concepts: Mandible, Tendon, Tongue, Pierre Robin syndrome, Lingual nerve, Symphysis menti, Genioglossus, Lingual artery

0

We compared resorbable plates with titanium plates for treatment of combined mandibular angle and symphyseal fractures.

Concepts: Mandible, Symphysis menti, Symphysis

0

The aim of this study was to use mechanical and photoelastic tests to compare the performance of cannulated screws with other fixation methods in mandibular symphysis fractures.

Concepts: Mandible, Symphysis menti, Symphysis

0

A solitary bone cyst is a non-neoplastic osseous lesion comprising 1% of all the cysts affecting the jaws. They are generally asymptomatic, usually detected incidentally during routine radiological assessment and are less common in the mandibular anterior region. This article presents a well-documented case involving a solitary bone cyst affecting the mandibular symphysis in a 12-year-old boy with no history of previous trauma. Simple curettage of the bone cavity resulted in the resolution of the lesion with progressive osseous regeneration. No evidence of recurrence was noted 2 years after the treatment.

Concepts: Osteoporosis, Bone, Mandible, English-language films, Cyst, Jaw, Symphysis menti

0

This study was performed to obtain a quantitative evaluation of the cortical and cancellous bone graft harvestable from the mental and canine regions, and to evaluate the cortical vestibular thickness.

Concepts: Skeletal system, Osseous tissue, Cortical bone, Bone grafting, Cancellous bone, Trabecula, Symphysis menti, Symphysis