On the maxillary nerve

The trigeminal, the fifth cranial nerve of vertebrates, represents the rostralmost component of the nerves assigned to pharyngeal arches. It consists of the ophthalmic and maxillomandibular nerves, and in jawed vertebrates, the latter is further divided into two major branches dorsoventrally. Of these, the dorsal one is called the maxillary nerve because it predominantly innervates the upper jaw, as seen in the human anatomy. However, developmentally, the upper jaw is derived not only from the dorsal part of the mandibular arch, but also from the premandibular primordium: the medial nasal prominence rostral to the mandibular arch domain. The latter component forms the premaxillary region of the upper jaw in mammals. Thus, there is an apparent discrepancy between the morphological trigeminal innervation pattern and the developmental derivation of the gnathostome upper jaw. To reconcile this, we compared the embryonic developmental patterns of the trigeminal nerve in a variety of gnathostome species. With the exception of the diapsid species studied, we found that the maxillary nerve issues a branch (nasopalatine nerve in human) that innervates the medial nasal prominence derivatives. Because the trigeminal nerve in cyclostomes also possesses a similar branch, we conclude that the vertebrate maxillomandibular nerve primarily has had a premandibular branch as its dorsal element. The presence of this branch would thus represent the plesiomorphic condition for the gnathostomes, implying its secondary loss within some lineages. The branch for the maxillary process, more appropriately called the palatoquadrate component of the maxillary nerve (V₂), represents the apomorphic gnathostome trait that has evolved in association with the acquisition of an upper jaw. J. Morphol. 275:17–38, 2014. © 2013 Wiley Periodicals, Inc.     

Identification of maxillary factor, a maxillary process-derived chemoattractant for developing trigeminal sensory axons

Trigeminal sensory axons project to several epithelial targets, including those of the maxillary and mandibular processes. Previous studies identified a chemoattractant activity, termed Maxillary Factor, secreted by these processes, which can attract developing trigeminal axons in vitro. We report that Maxillary Factor activity is composed of two neurotrophins, neurotrophin-3 (NT-3) and Brain-Derived Neurotrophic Factor (BDNF), which are produced by both target epithelium and pathway mesenchyme and which are therefore more likely to have a trophic effect on the neurons or their axons than to provide directional information, at least at initial stages of trigeminal axon growth. Consistent with this, the initial trajectories of trigeminal sensory axons are largely or completely normal in mice deficient in both BDNF and NT-3, indicating that other cues must be sufficient for the initial stages of trigeminal axon guidance.     

Variation in maxillary sinus anatomy among platyrrhine monkeys

Variations in the maxillary sinus anatomy of extant and fossil catarrhine primates have been extensively examined using computed tomography (CT), and have potential utility for phylogenetic analyses. This approach has also been used to demonstrate its anatomical variation in eight of the 16 extant genera of platyrrhines and the absence of the sinus in Saimiri and Cacajao. We used this approach to evaluate the three-dimensional anatomy of the maxillary sinus in all extant platyrrhine genera, and here argue the phylogenic implications of this variation. This study confirms, for the most part, previous CT studies and augments them with the six genera not studied previously: Ateles, Lagothrix, Callithrix, Cebuella, Pithecia and Chiropotes. The entire maxilla is pneumatized by the sinus in the atelines, Cebus, and Callicebus, whereas the sinus pneumatizes only the medial part of the maxilla in the callitrichines and Aotus. Pithecia has a unique conformation in which the maxillary sinus and the expanded inferior meatus pneumatize the posteromedial and anterolateral parts of the entire maxilla, respectively. Chiropotes has no sinus, and the inferior meatus possibly expands into the area between the middle meatus and medial surface of the maxilla to disturb sinus formation, as in the case of its close relative Cacajao. Finally, we argue that the sinus that pneumatizes the entire maxilla is a primitive feature in extant platyrrhines and was probably shared by the last common ancestor of the anthropoids.     

Biologic basis for maxillary osteotomies

Adult Rhesus monkeys were used as experimental models to investigate revascularization and bone healing in different single-stage anterior, posterior and total maxillary osteotomy techniques. Microangiographic and histologic studies demonstrated that intraosseous and intrapulpal circulation to the mobilized maxillary segments were maintained by the experimental flap designs which maintained intact soft tissue; the fragments healed by osseous union within six weeks without immobilization of the mandible. The treatment of many severe dental-facial deformities is difficult and challenging. Functional and stable occlusions with facial balance and harmony have been attained in many adult patients by maxillary osteotomy techniques. The Rhesus monkey serves as an excellent experimental model to develop new biologically sound maxillary surgical orthodontic techniques.     

Contours of maxillary molars studied in Australian aboriginals

Distances from the central pit to the perimeter of the crown of permanent upper molars were measured on standardized occlusal photographs of dental casts representing 210 male and 181 female Aboriginals from Yuendumu in the Northern Territory of Australia. In both males and females the first molar was the largest tooth but it showed least variability. Variabilities of the distances tended to be greater for radii constructed in the buccolingual direction than for the transverse mesiodistal radii. The most marked size reduction in the molar series from first to third related to the distolingual part of the crown, which was also the most variable region. Size differences between molars in the mesial contour radii were not marked. Sexual dimorphism was evident in most crown radii, being most marked for the second molar.     

The maxillary plate of Homoptera-Auchenorrhyncha

It is suggested that a sensory structure situated on the maxillary plates of Homoptera may represent a modified maxillary palp. A discussion on the origin of the maxillary plates of Hemiptera is included.     

Isometric scaling of maxillary sinus volume in hominoids

Previous hypotheses of maxillary sinus size evolution have proposed one or more changes in the volume of the structure across hominoid phylogeny. These hypotheses have been used subsequently to support the phylogenetic placement of fossil taxa relative to the living Hominoidea. The null hypothesis, that no change in sinus volume independent of size has occurred in ape evolution, is evaluated here by scaling analysis. Mixed sex samples of adult dry crania for the extant ape genera were examined by computer tomography imaging and the volume of the maxillary sinus was obtained. Sinus volume was then regressed, using both least squares and reduced major axis models, against cranial size variables.The results clearly demonstrate that the null hypothesis of no change in relative sinus volume cannot be rejected; thus, there is no support for hypotheses that maxillary sinus volume, independent of cranial size, has changed in the course of hominoid evolution. This result, in turn, has implications for the phylogenetic placement of fossil taxa and highlights the need for the careful delineation of character states in studies of hominoid systematics.     

3-D stress analysis in first maxillary premolar

The aim of this study was to investigate the stress distribution in a 3-D model of two-rooted tooth (first maxillary premolar) under two different occlusal force vectors by using finite element analysis. In the first model overall force of 200 N was divided into three vectors (cusp to fossa occlusion), and in the second model overall force was divided into 4 vectors (cusp to fossa and cusp to marginal ridge occlusion). The greatest compressive stress was found at the dentino- enamel junction in the cervical area of the both models (about -200 MPa). The greatest tensile stress was found at the vestibular aspect of buccal cusp in second model (about +3 MPa) and in the central fossa of the both models (about +28 MPa). Results indicate that in the both types of occlusal loadings the stress distribution was mainly compression and compressive forces were predominant over tensile stresses. In the second model with 4 vectors, stresses generated in the tooth structure were higher compared to the stresses generated in the first model with 3 vectors.     

Long-term skeletal stability after maxillary advancement with distraction osteogenesis using a rigid external distraction device in cleft maxillary deformities

Rigid external distraction is a highly effective technique for correction of maxillary hypoplasia in patients with orofacial clefts. The clinical results after correction of sagittal maxillary deformities in both the adult and pediatric age groups have been stable. The purpose of this retrospective longitudinal cephalometric study was to review the long-term stability of the repositioned maxilla in cleft patients who underwent maxillary advancement with rigid external distraction. Between April 1, 1995, and April 1, 1999, 17 consecutive patients with cleft maxillary hypoplasia underwent maxillary advancement using rigid external distraction. There were 13 male patients and four female patients, with ages ranging from 5.2 to 23.6 years (mean, 12.6 years). After a modified complete high Le Fort I osteotomy and a latency period of 3 to 5 days, patients underwent maxillary advancement with rigid external distraction until proper facial convexity and dental overjet and overbite were obtained. After active distraction, a 3- to 4-week period of rigid retention was undertaken; this was followed by removable elastic retention for 6 to 8 weeks using, during sleep time, an orthodontic protraction face mask. Cephalometric radiographs were obtained preoperatively, after distraction, at 1 year after distraction, and 2 or more years after distraction. The mean follow-up was 3.3 years (minimum, 2.1 years; maximum, 5.3 years). The following measurements were obtained in each cephalogram: three linear horizontal and two linear vertical maxillary measurements, two angular craniomaxillary measurements, and one craniomandibular measurement. Differences between the preoperative and postoperative cephalometric values were analyzed by paired t tests (p < 0.05). The cephalometric analysis demonstrated postoperatively significant advancement of the maxilla. In addition, the mandibular plane angle opened 1.2 degrees after surgery. After the 1- to 3-year follow-up period, the maxilla was stable in the sagittal plane. Minimal anteroposterior growth was observed in the maxilla compared with that exhibited in the anterior cranial base. However, there was significant vertical maxillary growth over the 3-year observation period. The mandibular plane angle tended to decrease during the follow-up period. The cephalometric data from this study support the clinical impression of maxillary stability after maxillary advancement with rigid external distraction in cleft patients. This effective and stable technique is now considered for all pediatric patients with severe cleft maxillary hypoplasia and for adolescent and adult patients with moderate to severe deformities.     

Shape components of the maxillary molars in Australian aboriginals

Principal components analysis was used to quantify the variability in crown outlines of maxillary molars in Australian Aboriginals. The outlines were measured by 36 radii from the central pit to the crown periphery. The first component, responsible for over half of the total variance, was concerned with general crown size. Four remaining components were retained to indicate sources of variability resulting from contrasting degrees of development or reduction of different crown components. Shape changes from the first to third molars were identified with components representing overall size reduction, diminution of the hypocone, and metacone elements and mesiodistal compression. An anteroposterior gradient along the molar series in average scores and variances for all components resulted from the progressive reduction of distal crown elements, increasing mesiodistal compression, and greater morphological variation.     

Sexual dimorphism of cusp dimensions in human maxillary molars

Cusp dimensions of human maxillary molars were compared between males and females to determine whether the later-developed, distal cusps displayed greater sexual dimorphism than the earlier-developed, mesial cusps, and whether the later-forming second molar displayed greater sexual dimorphism than the first molar. First and second permanent molar crowns (M1 and M2) were measured indirectly, using dental casts obtained from 117 Japanese (65 males and 52 females). Measurements included maximum mesiodistal and buccolingual crown diameters and the diameters of the four main cusps: the paracone, protocone, metacone, and hypocone. Mean values of crown dimensions were larger in males than in females for both M1 and M2, but the sexual difference in protocone diameter of M1 was not significant. The protocone in M1 showed the least amount of sexual dimorphism, followed by the metacone, hypocone, and paracone, while in M2, the percentage sexual dimorphism corresponded to the order of cusp formation: paracone, protocone, metacone, and hypocone. With the exception of the paracone diameter, M2 showed greater sexual dimorphism than M1. Sexual dimorphism was not always greater in the later-developed, distal cusps of M1 or M2, but the protocone, the most important cusp in terms of occlusal function, displayed the least dimorphism in M1.     

The identification of isolated maxillary molars

A method of identifying isolated first and second maxillary molars based upon the relative degree of root trifurcation is presented. The derived discriminant function is successful in correctly identifying more than 95% of the cases studied.