Anatomosurgical study of the marginal mandibular branch of the facial nerve for submandibular surgical approach

The purpose of this study was to estimate the distance from the mandibular marginal branch of the facial nerve to the inferior margin of the mandible in order to determine the best and safest location to approach the posterior mandibular region. Forty-five hemi-faces of 27 Brazilian adult cadavers were dissected and the distance between the mandibular marginal branch and the inferior margin of the mandible was measured. The number of marginal branches and anastomoses with other branches of the facial nerve was also recorded. The evaluation of the anatomic pieces showed 1 to 3 branches of the marginal mandibular branch, anastomoses with the buccal and cervical branches of the facial nerve and distances between 1.3 cm to +1.2 cm from the inferior margin of the mandible. In 57.7% of the cases, the nerve passed superiorly and along the length of the inferior margin of the mandible. Based on the findings of the present anatomosurgical study, it may be recommended an incision 3 cm below the inferior margin of the mandible associated to a careful dissection in planes and flap retraction. This is expected to reduce the risk of neuropraxia of the marginal mandibular nerve making the submandibular incision a safe approach.

Early habituation of severe blepharoptosis in marcus gunn jaw-winking syndrome

A 23-day-old neonate had severe unilateral Marcus Gunn jaw-winking syndrome (MGJWS). By 2 1/2 months of age, she controlled the ptosis with jaw positioning. Habituation of the pterygoid-levator synkinesis has not been reported this early. Surgery can be delayed until a safer time in MGJWS with severe ptosis that lacks objective signs of amblyopia.

Pre-operative radiographic evaluation of lower third molars with computed tomography

OBJECTIVES

To report radiographic findings of examinations with computed tomography (CT) of impacted lower third molars with an intimate relation to the mandibular canal and to investigate how findings of a dark band across the roots of the lower third molar on panoramic views correspond to the CT findings.

METHODS

CT images of 90 lower third molars (64 patients, mean age 34.6 years) in which plain radiography was insufficient to allow determination of the precise anatomical relations were reviewed retrospectively. Panoramic views of 88 teeth existed; these images were interpreted independent of the CT examinations with respect to presence of a dark band across the roots.

RESULTS

In 31% of the CT images, the course of the mandibular canal was buccal, in 33% lingual, in 26% inferior, and in 10% inter-radicular. The tooth was in contact with the mandibular canal in 94% and with the lingual cortex in 86%. In 23%, grooving of the root by the canal was judged to be present. In 63% of the cases where a dark band across the roots was observed on panoramic radiographs, CT revealed grooving of the root.

CONCLUSIONS

Pre-operative CT of lower third molars is motivated in selected cases when plain radiography is inconclusive. The finding of a dark band across the roots on panoramic radiographs is an indicator of grooving of the tooth by the canal and justifies a pre-operative CT examination. The absence of dark bands on panoramic views does not exclude grooving of the roots.

Rare courses of the mandibular canal in the molar regions of the human mandible: a cadaveric study

The inferior alveolar artery, vein and nerve send some branches to the molar teeth via the mandibular canal to the mental foramen. The present study attempted to define the presence and course of the mandibular canal in the mandible with the alveolar process by macroscopic cadaveric dissection and computerized tomography (CT) in order to provide information that might prevent injuries to vessels and nerves at risk during root canal treatment. We identified the position of the mandibular canal within a 30% ratio of the distance from inferior border of mandible to the apices of the root for 39 out of 131 sides (mesial root of first molar, 20%; distal root of first molar, 22.6%; mesial root of second molar, 27.8% and distal root of second molar, 47%) on panoramic X-ray observation. In one cadaver (male, 64 years old), the root apex of the second molar was in close proximity to the upper bony mandibular canal. Macroscopic dissection and computerized tomography showed that the main trunks of the inferior alveolar artery, vein, and nerve were in tight contact with the apex of the second molar. These observations of the anatomic course of the mandibular canal will be important to consider during root canal treatment of mandibular teeth.

Neurosensory function of the inferior alveolar nerve after bilateral sagittal ramus osteotomy: a retrospective study of 68 patients

The aim of the present study was to report the incidence of neurosensory dysfunction in the lower lip and chin after bilateral sagittal split osteotomy at four postoperative time points, and the relation of impairment to factors connected with the operation. Sixty-eight patients who had undergone the procedure (at 136 operated sites) were reviewed, and neurosensory recovery was studied at 2, 6, 18 and finally 30 months postoperatively. A change in neurosensory recovery was seen over this period of time. Two months postoperatively, 84 sites had reduced sensitivity (62%). The incidence of disorder decreased to 52 sites (38%) at 6 months, 43 sites (32%) at 1.5 years and 32 sites (24%) at the final 2.5-year check up. The patient age at the time of surgery, the type of osteosynthesis and the perioperative position of the inferior alveolar nerve were variables that influenced the neurosensory outcome. In conclusion, this retrospective study shows that the most important factors influencing postoperative nerve function are patient age, fixation method and the perioperative position of the inferior alveolar nerve.

Sensory and motor function of teeth and dental implants: a basis for osseoperception

1. When dental implants are loaded mechanically, a sensation, often referred to as osseoperception, is evoked. The sensory signals underlying this phenomenon are qualitatively different from the signals evoked when loading a natural tooth. In contrast with osseointegrated dental implants, natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the functional properties of human periodontal mechanoreceptors will be presented, along with a discussion about their likely functional role in the control of human jaw actions. 2. Microneurographic experiments reveal that human periodontal mechanoreceptors adapt slowly to maintained tooth loads. Populations of periodontal receptors encode information about both which teeth are loaded and the direction of forces applied to individual teeth. 3. Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at surprisingly low forces (below 1 N for anterior teeth and 4 N for posterior teeth). Accordingly, periodontal receptors efficiently encode tooth load when subjects first contact, hold and gently manipulate food by the teeth. In contrast, only a minority of receptors encodes the rapid and strong increase in force generated when biting through food. 4. It is concluded that humans use periodontal afferent signals to control jaw actions associated with intra-oral manipulation of food rather than exertion of jaw power actions. Consequently, patients who lack information from periodontal receptors show an impaired fine motor control of the mandible.

The localization and anthropometry of mental foramen on late Byzantine mandibles

Comprehensive studies of the human skeletal features and variations between and within populations are beneficial both for clinical applications and determination of racial characteristics of populations. The aim of this study was to examine the location and anthropometric characteristics of the mental foramen in 36 adult male mandibles of the Late Byzantine period. The results demonstrated that the most common position of the mental foramen was in line with the longitudinal axis of the second premolar (50% right side; 47% left side) followed by a location between the first and second premolars (33% right side; 36% left side). When compared with the results of previous similar studies, the results obtained in the present study suggest that traits such as the localization of mental foramen may not only differ between populations of different geographic environment but also within the inhabitants of the same geography.

Neurosensory disturbances following bone harvesting in the symphysis: a prospective clinical study

OBJECTIVE

To analyse the occurrence and resolution of neurosensory disturbances following bone harvesting from the symphysis.

MATERIAL AND METHODS

In 30 patients, skin sensitivity of the chin/lower lip area and pulp sensitivity of all mandibular anterior teeth were assessed preoperatively, at the time of suture removal, at 6 and 12 months postoperatively. In addition, bone defect dimensions of the donor site were measured intraoperatively, and distances from defect margins to adjacent anatomical structures, such as root apices, mental foramen and inferior border of mandible, were assessed postoperatively on a panoramic radiograph.

RESULTS

Pulp sensitivity changes were found in 18.6% of adjacent teeth at the time of suture removal. At the 6-month follow-up, 8.1% of teeth, and at the 12-month re-examination, 0.6% of teeth presented with altered sensitivity. This decrease over time of the number of affected teeth per patients with sensitivity changes was significant (P=2.35e-007). Lower lip hypaesthesia was only observed in one patient postoperatively, with complete resolution at the 6-month follow-up. Radiographic measurements of distances between donor defect and adjacent anatomical structures only reached significant difference for one parameter in patients with sensitivity changes compared with patients without sensitivity changes.

CONCLUSIONS

Patients must be informed about possible transient and long-term sensitivity changes of adjacent teeth and soft tissues following bone harvesting from the chin. However, by correctly placing mucoperiosteal incisions and bone cuts, the risk of sensitivity changes can be minimized.

Computed tomographic analysis of the position and course of the mandibular canal: relevance to the sagittal split ramus osteotomy

The aim of this study was to investigate the position and course of the mandibular canal through the mandibular ramus using computed tomographic (CT) imaging and to relate the findings to performing sagittal split ramus osteotomies. The mandibles of 35 patients with skeletal Class III prognathism with symmetry (12 males and 23 females) were observed on transaxial computed tomograms acquired with a slice thickness of 2 mm. The position and course of the mandibular canal from the mandibular foramen to the mandibular body at the level of the second molar were measured at four specific locations in the same plane. Among the 70 rami examined, lack of a bone marrow space on the buccal side, including a fusion type anatomy with no buccal side cortical bone of the mandibular canal, were observed at the CT location between the mandibular foramen and mandibular angle. Our results suggest that special care must be taken when sagittal splitting is performed, and the safest location for the buccal corticotomy is anterior to the mandibular angle.

The course and distribution of the inferior alveolar nerve in the edentulous mandible

The authors undertook the study to determine the pattern of intrabony distribution of the branches of the inferior alveolar nerve (IAN) in the edentulous mandible. One hundred seven human cadaveric mandibles were microdissected from their buccal aspect. In each case the height and distribution of the IAN was classified. The authors found that the IAN was located in the lower half of the mandible in 73% of males and 70% of females. The most common branching pattern observed was a single nerve trunk with a series of simple branches directed at the superior border of the mandible (59.6% males, 52% females). The second most common pattern was that of a small nerve plexus in the molar region (21.1% males, 26% females). The results showed that the pattern of distribution does not significantly differ between the sexes, between sides of the jaw, or with age.

Vertical alveolar ridge augmentation prior to inferior alveolar nerve repositioning: a patient report

This report describes treatment of a patient using vertical alveolar ridge augmentation performed prior to transposition of the inferior alveolar nerve (IAN). A preoperative computerized tomographic (CT) scan revealed 2 to 3 mm of bone above the canal in the left mandibular molar region. An autogenous bone graft harvested from the chin area was utilized along with a titanium mesh for vertical alveolar ridge augmentation in this area. CT scan after bone grafting revealed 5 mm of vertical ridge augmentation. Bone height above the IAN was 7 to 8 mm after bone grafting procedure. For IAN transposition, an osteotomy was performed to obtain a lateral access window located 4 mm below the crestal bone along the lateral side of the mandible. Two cylindric hydroxyapatite-coated implants were placed. Autogenous bone from the lateral access window that had been removed en bloc was particulated and placed around the implants. Because vertical alveolar ridge augmentation had been performed, the coronal portion of the implant was not exposed after transposition of the IAN. It is suggested that vertical ridge augmentation may be considered prior to transposition of the IAN in situations where minimal bone height exists above the IAN canal. However, long-term clinical investigations are recommended.

Interactive web-based programs to teach functional anatomy: the pterygopalatine fossa

Certain areas of the body contain structures that are difficult to envision in their proper spatial orientations and whose functions are complex and difficult to grasp. This is especially true in the head, where many structures are relatively small and inaccessible. To address this problem, we are designing Web-based programs that consist of high-resolution interactive bitmap illustrations, prepared using Adobe Photoshop, and vector-based animations, prepared via Macromedia Flash. Flash action script language is used for the animations. We have used this approach to prepare a program on the pterygopalatine fossa, an important neurovascular junction in the deep face that is especially difficult to approach by dissection and to depict in static images in an atlas. The program can be viewed online at http://cds.osr.columbia.edu/anatomy/ppfossa/. A table of contents simplifies navigation through the program and a menu enables the user to identify each of the vascular and neuronal components and either to insert or to remove each from its position in the fossa. The functional anatomy of the nerves in the fossa is animated. For example, users can activate and subsequently follow action potentials as they course along axons to their targets. This high degree of interactivity helps promote learning.

Vulnerability of the Inferior Alveolar Nerve and Mental Nerve During Genioplasty: An Anatomic Study

Microgenia or "small chin" is corrected by various techniques, such as insertion of an alloplastic implant, cartilage or bone grafting, or horizontal advancement osteotomy. Horizontal recession osteotomy is used in macrogenia. Particularly in a microgenic mandible, the mental foramen is unexpectedly nearer to the inferior border of the body. During sliding horizontal osteotomy of the mentum, the inferior alveolar nerve (IAN) and mental nerve are vulnerable to an injury. Thirty fresh hemimandibles were used for a study of the IAN. The IAN course was traced by serial sections at intervals of 5 mm. In 50 dry specimens the direction of the mandibular canal was evaluated by the photographs with a stick put into the mental foramen. The IAN in mandibular canal runs above the lower one-third of the mandibular body. The terminal mandibular canal locates at an average of 4.5 mm under the mental foramen, advances 5.0 mm anteriorly, loops, and ends at the foramen. The direction of the mandibular canal at the mental foramen was 39.4 degrees lateral, 67.2 degrees superior, and 80.2 degrees posterior. It is advisable for surgeons to keep the level of sliding osteotomy of the mentum at least 4.5 mm below the mental foramen to spare the IAN.

The influence of jaw innervation on the dental maturation pattern in the mandible

OBJECTIVES

To explore the relationship between mandibular dental maturation and the pattern of jaw innervation.

SETTING AND SAMPLE POPULATION

The sample included 365 panoramic radiographs taken in the period 1965-1969 in a Danish municipality.

DESIGN

For assessing dental maturity, the seven left mandibular teeth (M2, M1, P2, P1, C, I2, I1) were given a dental maturity score according to a method introduced by Demirjian. Spearman correlation coefficients between the maturity score of an index tooth (one of each teeth) and the maturity score of the 6 other teeth was calculated and illustrated.

RESULTS

All the correlation coefficients were larger than 0.5 indicating a rather high level of association between the development of mandibular teeth in the same individual. Thus, associations between the pattern of dental maturation and jaw innervation were not obvious.

CONCLUSION

When the correlation between the dental maturity stages was analysed, no significant relation was found between dental maturation and jaw innervation in the mandible. This is interesting considering the results presented in a recent study, which showed that the clinical observed tooth eruption was closely related to the pattern of jaw innervation. Those authors suggested that the factors influencing the eruption might be associated with jaw innervation. In our study, the stepwise dental maturation process, however, is not equally associated with jaw innervation.

Geometric morphometric analysis of allometric variation in the mandibular morphology of the hominids of Atapuerca, Sima de los Huesos site

Allometry is an important factor of morphological integration that contributes to the organization of the phenotype and its variation. Variation in the allometric shape of the mandible is particularly important in hominid evolution because the mandible carries important taxonomic traits. Some of these traits are known to covary with size, particularly the retromolar space, symphyseal curvature, and position of the mental foramen. The mandible is a well studied system in the context of the evolutionary development of complex morphological structures because it is composed of different developmental units that are integrated within a single bone. In the present study, we investigated the allometric variation of two important developmental units that are separated by the inferior nerve (a branch of CN V3). We tested the null hypothesis that there would be no difference in allometric variation between the two components. Procrustes-based geometric morphometrics of 20 two-dimensional (2D) landmarks were analyzed by multivariate regressions of shape on size in samples from 121 humans, 48 chimpanzees, and 50 gorillas (all recent specimens), eight fossil hominids from Atapuerca, Sima de los Huesos (AT-SH), and 17 Neandertals. The findings show that in all of the examined species, there was significantly greater allometric variation in the supra-nerve unit than in the infra-nerve unit. The formation of the retromolar space exhibited an allometric relationship with the supra-nerve unit in all of the species studied. The formation of the chin-like morphology is an "apodynamic" feature of the infra-nerve unit in the AT-SH hominids. The results of this study support the hypothesis that allometry contributes to the organization of variation in complex morphological structures.

Jaw-winking ptosis in a patient with Kabuki syndrome

We present a case of a child with Kabuki syndrome and jaw-winking ptosis. Kabuki syndrome is rare and consists of a constellation of findings including mental retardation, characteristic oculofacial features, and skeletal abnormalities. The association of Kabuki syndrome and jaw-winking ptosis has not been previously reported.

Labeled citrate metabolism in bone fractures and impaired innervation

Changes in (14)C incorporation into regenerate after bone fracture and impairment of mandibular innervation, and injection of [3-(14)C]cytrate corresponded to the stages of reparative osteogenesis: after 1 week (14)C incorporation in the cellular-fibrous callus surpassed its release, after 2 weeks the rates of (14)C incorporation and release in the chondroid callus become similar, and after 4 weeks the release of the label predominated in the primary bone callus. Denervation reduced (14)C incorporation into regenerate, which impaired bone remodeling. Citrate in the bones is characterized by high metabolic activity.

Injury to the inferior alveolar nerve during implant placement: a formula for protection of the patient and clinician

This article concerns the problem of nerve damage associated with implant placement in the posterior mandible. The causes are discussed, with particular emphasis on intrusion of the drill or implant into the nerve canal. Recommendations are made to help the practitioner avoid this too-common complication.

Intraosseous course of the inferior alveolar (dental) nerve and its relative position in the mandible

The present study was planned to evaluate the position of the mandibular foramen (MF) and the course of the inferior alveolar nerve in 12 right and 14 left cadaveric hemimandibles. The soft tissue including the muscle attachments of the mandible was cleaned and the inferior neurovascular bundle was dissected up to the MF. The distances from the MF to the angle, symphysis menti, 3rd molar, and the lower point of the mandibular notch were measured. The bone was chiseled from its lingual surface to expose the mandibular canal. The distances from the nerve to the alveolar and inferior borders were measured. The distance from the MF to different landmarks did not show any side differences except the one to the symphysis menti (P<0.05; Mann-Whitney 'U' test). Similarly the distances from the nerve to the borders also did not show any significant side differences. These data indicate that, on average, MF is located at a symmetrical point on the ramus on either side, although, not exactly at a fixed distance from any landmarks tested. Further, the canals were located either at near to the middle or below near to the base of the mandible. This study concludes that, the location of the MF varies from bone to bone despite its bilateral symmetry. Further, the canal and consequently the nerve do not maintain a constant position in the mandible.

The Position of the Inferior Alveolar Nerve at the Mandibular Angle:

Mandibular angle reduction is a popular contouring surgery in Asia. Avoidance of injury to the inferior alveolar nerve is crucial during these procedures. Anatomic data regarding the position of the nerve in the mandibular angle area are sparse. The purpose of this study was to use 3-dimensional computed tomographic data to evaluate the nerve in patients with prominent mandibular angles and to compare the nerve position with a normative group. A total of 28 female and 5 male adult patients who presented with a complaint of prominent angles or a "square-face" look, as well as 20 female and 22 male adult normal subjects were included, for a total of 150 hemimandibles for extraction of the inferior alveolar nerve. The nerve and the mandible were displayed. Point O was defined on the oblique line along the anterior cortex of ramus, where it intersected with a line extending from the alveolar arch. From the O point, linear distances were defined, including horizontal distances to the posterior cortex, oblique distances to the gonion, and the vertical distances to the inferior cortex. Mandibular width was defined as the distance between the 2 gonion points. Results demonstrated significant differences mainly in the oblique distances (ie, from the O point to the nerve [O1], from the nerve to the gonion [O2], and from the O point to the gonion [O1-O2]) in both female and male patients. The O2 distance was 23.69 mm versus 20.66 mm in women and 27.30 mm versus 23.28 mm in men (square face vs norm). The mandibular width was significantly larger in the male square-face patients, but the difference was not significant between the female groups. These results provide useful information for surgeons planning mandibular angle reduction. These findings suggest that the mandibular contouring procedure should be aimed at correcting regional osseous dysmorphology in the angle area and improving the relationship to the chin, rather than merely reducing the mandibular width.

A Comparative Study of Computed Tomography and Magnetic Resonance Imaging for the Detection of Mandibular Canals and Cross-Sectional Areas in Diagnosis prior to Dental Implant Treatment

BACKGROUND

Computed tomography (CT) is effective in the diagnosis of dental implants. However, it has the disadvantage of exposing patients to high doses of x-rays, and the mandibular canals cannot be detected by CT in some clinical cases.

PURPOSE

The purpose of this study was to examine the detectability of the anatomic morphology of the molar region in the lower jaw (where implantation is common) by CT and magnetic resonance imaging (MRI), to compare the data, and to determine the usefulness of MRI in diagnosis prior to dental implant treatments.

MATERIALS AND METHODS

Eleven female subjects (average age, 59 years) who had partially edentulous mandibles (total of 19 sites) were included in the study. CT and MRI were performed with the same subjects, and the degrees of identification of the mandibular canal in the first and second molar regions were compared. Dimensional accuracy in the second molar region was also compared.

RESULTS

With CT, the canals of the first molar regions were not identified in 11 of 19 sites; however, MRI identified the canals in all 19 sites. Using the kappa index, we found that the inter- and intraobserver identification reliabilities (0.84 and 0.87, respectively) were excellent, especially for MRI. Dimensional positioning of the canal in the second molar region was almost the same with MRI as with CT.

CONCLUSIONS

MRI is an alternative method in diagnosis prior to dental implant treatment in the mandibular molar region.

Intrabony course of the inferior alveolar nerve in the edentulous mandible

The purpose of this study was to investigate the vertical positioning and intrabony branching patterns of the inferior alveolar nerve (IAN) in 39 edentulous human cadaveric mandibles by buccal microdissection. Dissected mandibles were classified on the basis of the height of the IAN within the body of the mandible and the branching pattern of the IAN. The IAN was located in the superior part of the body of the mandible in 30.7% (12/39) of cases, all of which showed a small posterior molar plexus of branches. In 69.2% (27/39) of cases the IAN was half-way or closer to the inferior border of the mandible. Of these latter cases, 41% demonstrated a small, posterior molar plexus of branches, 37% showed posterior and anterior plexuses, and 22% showed either no branches or a single trunk with a small number of single branches directed at the superior border of the mandible. These findings were rendered in 3D computer format for instructional purposes.

Autonomic neural signals in bone: Physiological implications for mandible and dental growth

Signals derived from the autonomic nervous system exert potent effects on osteoclast and osteoblast function. A ubiquitous sympathetic and sensory innervation of all periosteal surfaces exists and its disruption affects bone remodeling. Several neuropeptides, neurohormones and neurotransmitters and their receptors are detectable in bone. Bone mineral content decreased in sympathetically denervated mandibular bone. When a mechanical stress was superimposed on mandibular bone by cutting out the lower incisors, an increase in bone density ensued providing the sympathetic innervation was intact. A lower eruption rate of sympathetically denervated incisors at the impeded eruption side, and a higher eruption rate of denervated incisors at the unimpeded side were also observed. A normal sympathetic neural activity appears to be a pre-requisite for maintaining a minimal normal unimpeded incisor eruption and for keeping the unimpeded eruption to attain abnormally high velocities under conditions of stimulated incisor growth. These and other results suggest that the sympathetic nervous system plays an important role in mandibular bone metabolism.

High-resolution dental magnetic resonance imaging of inferior alveolar nerve responses to the extraction of third molars

The objective of this study was to assess whether signal changes can be detected in the neurovascular bundle of the mandibular canal after the extraction of a third molar. We retrospectively analyzed MRI scans of 30 test subjects with healthy mandibles and 41 patients who had had a wisdom tooth extracted. Signal intensities were measured at particular sites in the neurovascular bundle, which were defined as regions of interest (ROI) in the sagittal T1-weighted images before and after intravenous administration of a paramagnetic contrast agent. On the basis of the signal intensity increases that were measured after contrast agent administration, we compared the signal increases obtained for the patients who had received surgical treatment with the results obtained for the population of test subjects with unremarkable mandibles ( t-test, P<0.05). Compared with the healthy test subjects, patients who had received surgical treatment showed significantly higher signal intensity increases at two measurement sites, i.e., the second molar and the second premolar ( P<0.05). We found no significant differences when the measurements were performed at the first molar ( P=0.06), the third molar ( P=0.47) and in the area of the ascending mandibular ramus ( P=0.79). Compared with a population of healthy test subjects, patients who had their third molars surgically removed show higher signal intensity increases in the neurovascular bundle after intravenous contrast agent administration. The underlying cause may be the higher blood flow in the arteries and veins and the perineural plexus, which may give evidence of the pathophysiological mechanism of nerve damage in the narrow canal as a result of osteotomy.