Mandibular Tip Research Articles

Msx1 is essential for proper rostral tip formation of the mouse mandible

The right and left mandibular processes derived from the first branchial arch grow toward the midline and fuse to create the rostral tip region of the mandible during mandibular development. Severe and mild cases of failure in this process results in rare median cleft of the lower lip and cleft chin, respectively. The detailed molecular mechanisms of mandibular tip formation are unknown. We hypothesize that the Msx1 gene is involved in mandibular tip development, because Msx1 has a central role in other craniofacial morphogenesis processes, such as teeth and the secondary palate development. Normal Msx1 expression was observed in the rostral end of the developing mandible; however, a reduced expression of Msx1 was observed in the soft tissue of the mandibular tip than in the lower incisor bud region. The rostral tip of the right and left mandibular processes was unfused in both control and Msx1-null (Msx1−/−) mice at embryonic day (E) 12.5; however, a complete fusion of these processes was observed at E13.5 in the control. The fused processes exhibited a conical shape in the control, whereas the same region remained bifurcated in Msx1−/−. This phenotype occurred with 100% penetrance and was not restored at subsequent stages of development. Furthermore, Meckel's cartilage in addition to the outline surface soft tissues was also unfused and bifurcated in Msx1−/− from E14.5 onward. The expression of phosho-Smad1/5, which is a mediator of bone morphogenetic protein (Bmp) signaling, was downregulated in the mandibular tip of Msx1−/− at E12.5 and E13.5, probably due to the downregulated Bmp4 expression in the neighboring lower incisor bud. Cell proliferation was significantly reduced in the midline region of the mandibular tip in Msx1−/− at the same developmental stages in which downregulation of pSmad was observed. Our results indicate that Msx1 is indispensable for proper mandibular tip development.

Morphometric analysis of secondary palate development in human embryos.

Rapid shelf elevation and contact of the secondary palate and fusion reportedly occur due to a growth-related equilibrium change in the structures within the oro-nasal cavity. This study aimed to quantitatively evaluate complex three-dimensional morphological changes and their effects on rapid movements, such as shelf elevation and contact, and fusion. Morphological changes during secondary palate formation were analyzed using high-resolution digitalized imaging data (phase-contrast X-ray computed tomography and magnetic resonance images) obtained from 22 human embryonic and fetal samples. The three-dimensional images of the oro-nasal structures, including the maxilla, palate, pterygoid hamulus, tongue, Meckel's cartilage, nasal cavity, pharyngeal cavity, and nasal septum, were reconstructed manually. The palatal shelves were not elevated in all the samples at Carnegie stage (CS)21 and CS22 and in three samples at CS23. In contrast, the palatal shelves were elevated but not in contact in one sample at CS23. Further, the palatal shelves were elevated and fused in the remaining four samples at CS23 and all three samples from the early fetal period. For each sample, 70 landmarks were subjected to Procrustes and principal component (PC) analysis. PC-1 accounted for 67.4% of the extracted gross changes before and after shelf elevations. Notably, the PC-1 values of the negative and positive value groups differed significantly. The PC-2 value changed during the phases in which the change in the PC-1 value was unnaturally slow and stopped at CS22 and the first half of CS23. This period, defined as the "approach period", corresponds to the time before dynamic changes occur as the palatal shelves elevate, the tongue and mandibular tip change their position and shape, and secondary palatal shelves contact and fuse. During the "approach period", measurements of PC-2 changes showed that structures on the mandible (Meckel's cartilage and tongue) and maxilla (palate and nasal cavity) did not change positions, albeit both groups of structures appeared to be compressed anterior-posteriorly. However, during and after shelf elevation, measurements of PC-1 changes showed significant changes between maxillary and mandibular structures, particularly positioning of the shelves above the tongue and protrusion of the tongue and mandible. These results suggest an active role for Meckel's cartilage growth in repositioning the tongue to facilitate shelf elevation. The present data representing three distinct phases of secondary palate closure in humans can advance the understanding of morphological growth changes occurring before and after the horizontal positioning of palatal shelves and their fusion to close the secondary palate in humans successfully.

Accuracy of digital predictions with CAD/CAM labial and lingual appliances: A retrospective cohort study

Purpose: To compare the treatment efficacy and efficiency of the two CAD/CAM customized bracket systems Incognito (lingual) and Insignia (labial) for differences in: 1) ABO Cast and Radiograph Evaluation system scores, 2) efficiency as assessed by three clinical measures of efficiency, and 3) final treatment outcome and the virtual set up. Materials & Methods: Consecutive patients treated with Insignia (n = 21) and Incognito (n = 16) treatment systems had STL Images evaluated at pretreatment, post treatment and virtual set-up (predicted outcome); predicted and post treatment STL images were superimposed upon each other and differences were recorded. Results: Incognito patients had fewer emergency appointments. ABO scores were also better for Incognito in 4 of the 8 categories and in total score; a “pass” total score of <27 was achieved in 87.5% on Incognito cases versus 42.9% of Insignia cases. Predicted versus actual outcomes assessment showed the following: right-left symmetry for incognito (95.2%) and Insignia (75.0%), more efficacious linear tooth movements of <0.5 mm for Incognito (78.6% vs 57.1%), more efficacious angular tooth movements of <2.0° for Insignia (21.4% vs 7.1%). Incognito was more effective with linear predicted versus actual outcomes and more efficaciousness especially in remaining within clinical significance guidelines. Incognito out performed Insignia in the maxilla, especially by staying within the clinical significant guidelines, and Incognito also out performed Insignia in the mandible, except for mandibular tip discrepancies. Conclusions: Based upon the conditions of the present study, the Incognito treatment system was more efficacious than Insignia when the two treatment systems were critically compared.

Gene expression changes in the tyrosine metabolic pathway regulate caste-specific cuticular pigmentation of termites

In social insects, all castes have characteristic phenotypes suitable for their own tasks and to engage in social behavior. The acquisition of caste-specific phenotypes was a key event in the course of social insect evolution. However, understanding of the genetic basis and the developmental mechanisms that produce these phenotypes is still very limited. In particular, termites normally possess more than two castes with specific phenotypes (i.e. workers, soldiers, and reproductives), but proximate developmental mechanisms are far from being fully understood. In this study, we focused on the pigmentation of the cuticle as a model trait for caste-specific phenotypes, during the molts of each caste; workers, soldiers, presoldiers (intermediate stage of soldiers), and alates (primary reproductives) in Zootermopsis nevadensis. Expression patterns of cuticular tanning genes (members of the tyrosine metabolic pathway) were different among each molt, and high expression levels of several “key genes” were observed during each caste differentiation. For the differentiation of castes with well-tanned cuticles (i.e. soldiers and alates), all focal genes except DDC in the former were highly expressed. On the other hand, high expression levels of yellow and aaNAT were observed during worker and presoldier molts, respectively, but most other genes in the pathway were expressed at low levels. RNA interference (RNAi) of these key genes affected caste-specific cuticular pigmentation, leading to soldiers with yellowish-white heads and pigmented mandibular tips, presoldiers with partly pigmented head cuticles, and alates with the yellow head capsules. These results suggest that the pigmentation of caste-specific cuticles is achieved by the regulation of gene expression in the tyrosine metabolic pathway.

A comparison of external and internal maxilla and mandible morphology of water bugs (Hemiptera: Heteroptera: Nepomorpha)

This paper describes the file of the mandible, the apices of the maxillae, the rupturing device on the maxillae, and the internal structures of the mouthparts in sixty representatives of the nepomorphan families (Heteroptera), using scanning electron microscopy. Eight morphologically distinct types of files are identified on the mandibular tip, as well as six distinct types of the maxillary endings, and three distinct types of rupturing devices of the maxillae. The features of the internal maxillary and mandibular structures share a common connection model, differing only by virtue of specific appendages in different subfamilies. The water bugs morphological ground plan is represented by a mandibular file identically serrated, asymmetrical apices of maxillae (left maxilla tapers with lobe + right maxilla tapers and straight), rupturing device evidently exposed ventrally and inner structures: the maxillae are extended dorso-laterally, forming a wide lobe; symmetrical processes connect with the mandibles. The main patterns (belostomatid and nepid) together with two more specialized patterns (gelastocorids, corixids, micronectids, and diaprepocorids) and (ochterid, aphelocheirid, naucorid, notonectid, pleid and helotrephid) are reported. Diversity of the elements (maxillae and mandibles) are analyzed from a phylogenetic signals and nutrition perspective. Finally, further lines of study are suggested for future work on the phylogeny of the group based on the studied characters.

Depredation Investigation: Using Canine Spread to Identify the Predator Species

When livestock are killed by predators, circumstantial evidence is often the only information available to determine wh ich predator species made the kill. Evidence can consist of rake marks, scat, hair, attack points, tracks, sightings, and canine punctures. Canine punctures in particular can be informative because they offer the most direct evidence of attack, particularly if they are linked to tissue hemorrhaging. When investigating canine punctures, a common technique to identify the predator species is to measure the canine cusp spread for maxillary and mandibular tips as measured from the maxillary to maxillary tip or mandibular to mandibular tip. The assumption is that different predator species will have different and distinct canine spread. Surprisingly, little has been published on canine spread and comparing different carnivore species, leaving wildlife managers unable to reliably use this technique for predator identification. During 2008, we started a project to assess the width of canine spread in carnivores. The majority of information gathered to date shows a narrow range of measurements for coyotes and broad variation in feral/free ranging dogs that can overlap coyote measurements. The information provided on scientifically measured canine spread will assist the wildlife damage manager in determining the actual predatory species, especially when used with additional evidence gathered on site.

A stereotactic device for rabbits based on mandibular and cranial landmarks

The authors have developed a stereotactic device for use in rabbits that uses the plane at the base of the mandible combined with cranial sutures as an anatomical reference. The device was developed for a study designed to evaluate catheters for infection prophylaxis, and this required the implantation of silicone catheters along a reproducible trajectory through the lateral ventricle. Cadaver and atlas studies demonstrated consistent spatial relationships between intracranial structures and the surface plane on which the animals were resting during the surgery. This plane is formed by the 2 mandibular angles and the mandibular tip. The authors developed a stainless steel stereotactic device that uses this mandibular plane as well as the coronal and sagittal sutures as spatial references. Operations were performed in 60 animals using the stereotactic device, and postmortem dissections of the animals' brains demonstrated 78.6% accuracy of the trajectory within a tolerance of deviation of 5 degrees , and 94.6% accuracy within a tolerance of 10 degrees . The accuracy of the trajectory of the last 18 consecutively operated animals was constantly within a tolerance of 5 degrees . The device can be autoclaved and, since it is relatively simple and inexpensive to build, the authors manufactured 3 identical frames and used them alternately to operate under sterile conditions. The fast and pain-free head fixation minimized anesthesia-related risks. The authors' experiences suggest that the device is suitable for ventricular punctures and, dependant on the individual requirements of accuracy, other procedures that require "approximate" stereotactic guidance especially when a series of animals need to undergo operations quickly.

External morphology of antennal and rostral sensillae in four hemipteran insects and their possible role in host plant selection

The sensory receptors on the antennal flagellar segments and on the rostral tip of four adult hemipteran insects were identified and compared using scanning electron microscopy in order to better understand the role of sensillae in the process of host plant selection and the structural adaptations of feeding organs for phytophagy. The species studied are Riptortus pedestris Fabricius (Alydidae), Elasmolomus sordidus (Fabricius) (Lygaeidae), Cyclopelta siccifolia Westwood (Pentatomidae) and Chrysocoris purpurea (Westwood) (Pentatomidae). Differences in the distribution and arrangement of sensory receptors in the hemipteran families were noted, especially in the shape of the antennal apices, which are of taxonomical significance. A large array of trichoid basiconic and coeloconic sensillae is distributed on the antennal surface. Distal antennal segments have more sensillae and more types of sensillae than the proximal segments, indicating their prominent role in host plant surface exploration. There is only a slight variation in the shape of the stylets owing to the similarity in feeding habits. The mandibular tips are straight and sharp and do not contain any hooks or barbs as in carnivorous species.

The phylogeny of varanoid lizards and the affinities of snakes

Evidence that platynotan squamates (living varanoid lizards, snakes and their fossil relatives) are monophyletic is presented. Evolutionary relationships within this group are then ascertained through a cladistic analysis of 144 osteological characters. Mosasauroids (aigialosaurs and mosasaurs), a group of large marine lizards, are identified as the nearest relatives of snakes, thus resolving the long-standing problem of snake affinities. The mosasauroid–snake clade (Pythonomorpha) is corroborated by 40 derived characters, including recumbent replacement teeth, thecodonty, four or fewer premaxillary teeth, supratemporal–prootic contact, free mandibular tips, crista circumfenestralis, straight vertical splenio-angular joint, loss of posterior ramus of the coronoid, reduced basipterygoid processes, reduced interpterygoid vacuity, zygosphene–zygantral articulations, and absence of epiphyses on the axial skeleton and skull. After mosasauroids, the next closest relatives of snakes are varanids (Varanus,SaniwaandSaniwides) and lanthanotids (LanthanotusandCherminotus). Derived features uniting varanids and lanthanotids include nine cervical vertebrae and three or fewer pairs of sternal ribs. The varanid–lanthanotid–pythonomorph clade, here termed Thecoglossa, is supported by features such as the anteriorly positioned basal tubera, and the loss of the second epibranchial. Successive outgroups to thecoglossans areTelmasaurus, an unresolved polytomy (Estesia, Gobidermatidae and Helodermatidae),ParavaranusandProplatynota. The ‘necrosaurs’ are demonstrated to be an artificial (polyphyletic) assemblage of primitive platynotans that are not particularly closely related to each other. Snakes are presumed to have evolved from small, limbless, burrowing lizards and the inability of previous analyses to resolve the affinities of snakes has been attributed to extensive convergence among the numerous lineages of such lizards. The present study contradicts this claim, demonstrating that the problem is due instead to omission of critical fossil taxa. No modern phylogenetic analysis of squamate relationships has simultaneously includedbothmosasauroids and snakes: previous studies have therefore failed to identify the mosasauroid–snake association and the suite of derived characters supporting it. Mosasauroids are large aquatic animals with well-developed appendages, and none of the derived characters uniting mosasauroids and snakes is obviously correlated with miniaturization, limb reduction or fossoriality. Recognition that mosasauroids, followed by varanids and lanthanotids, are the nearest relatives of snakes will also facilitate studies of relationships within snakes, which until now have been hampered by uncertainty over the most appropriate (closely–related) lizard outgroups.

Mechanisms of tongue protraction and narial closure in the marine toad Bufo marinus.

Electromyography, kinematic analysis, muscle stimulation and denervation techniques were used to investigate the muscular mechanisms of narial closure during breathing and of tongue protraction during prey capture in the marine toad Bufo marinus. Toads were video-taped during breathing and feeding under a variety of conditions: before surgery, after unilateral or bilateral denervation of the M. submentalis, and after unilateral or bilateral denervation of the Mm. genioglossus basalis and medialis. Deeply anesthetized toads were video-taped during stimulation of several cranial muscles, and electromyograms were recorded from the M. submentalis during feeding before and after its denervation. Bufo marinus differs from many other anurans in having a relatively long tongue that experiences large accelerations (> 31 g) during protraction. Tongue protraction occurs in two phases: an early phase during which the lingual tip moves upward and forward relative to the mandibular tip as the tongue shortens, and a later phase during which the lingual tip moves downward and forward relative to the mandibular tip as the tongue elongates under its own momentum. Relative to an external reference, the lingual tip follows a straight trajectory from mouth to prey, which depends critically upon precise coordination of tongue and jaw movements. The M. submentalis is necessary for normal tongue protraction during feeding. In contrast, the Mm. genioglossus basalis and medialis are necessary for forward movement of the tongue pad over the symphysis. In B. marinus, a simple anatomical change (elongation of the tongue) has functional consequences (inertial elongation) that profoundly affect the mechanisms of neuromuscular control. Though seldom studied, it seems likely that morphological evolution has had a profound influence on mechanisms of motor control in animals generally.

Feeding behaviour in Cylindrophis and its bearing on the evolution of alethinophidian snakes

Cylindrophis ruffus ingests prey using two distinct mechanisms. During initial phases of prey transport, lateral movements of the rear of the braincase combine with small unilateral movements of the toothed bones of each side; prey is usually constricted during this phase to permit the snake to push its head over the prey. Once transport has carried the leading part of the prey into the anterior oesophagus, Cylindrophis begins to use bilaterally synchronized movements of the jaw apparatus combined with low‐amplitude, short wave‐length flexions of the anterior vertebral column. Transport of prey is many times faster during the bilateral phase than during the unilateral phase.Radiographic and cinematographic evidence indicates that the mandibular tips of Cylindrophis do not separate more than 1.5–2.0 times the resting distance between the dentary tips. Although this limits potential gape size, the intramandibular joint is highly mobile, allowing the mandibles to conform to a variety of prey shapes. Manipulations of anaesthetized and fresh, dead specimens revealed that the palatomaxillary arches are tightly attached to the ventral bones of the snout, movements of each arch being reflected in equivalent movements of the ipsilateral elements of the snout. Cylindrophis represents a functional stage intermediate between most lizards with limited palatomaxillary kinesis and advanced snakes with considerable palatomaxillary mobility. Contrary to previous hypotheses, however, upper jaw liberation in Cylindrophis is due to liberation of the ventral snout, not to reduction of attachments to the braincase and snout. This suggests that the nose played a crucial role in the evolution of the feeding apparatus in alethinophidian snakes.

The mandibular forces and pressures of some predacious Coleoptera

The forces and pressures exerted at the tips of the mandibles have been examined in 12 species of Carabidae and one species of Staphylinidae. A × 3 range of mandibular tip forces and a × 2 range of pressures were present in the group of species studied. There was no correlation between the mandibular force or pressure and the size of the beetle except for the mandibular forces in the 5 species of Pterostichini. It is suggested that mandibular forces would vary with size in geometrically similar species, but that these predacious species require similar pressures to penetrate the cuticles of their prey.