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PubMed2003

Trabecular alveolar bone in the human mandible: a dual-energy x-ray absorptiometry study.

OBJECTIVE: The purpose of this study was to evaluate the potential use of dual energy x-ray absorptiometry for the assessment of bone mineral content and bone mineral density before implant placement. MATERIALS AND METHODS: The material examined consisted of 63 mandibular bone specimens cut from 21 fresh cadavers (11 men; 10 women). Three specimens were cut per cadaver in the incisal, premolar, and molar regions. Three regions of interest (G, R1, and R2) were delineated. The global bone specimen (G) consisted of the whole specimen (ie, both cortical and trabecular bone). R1 and R2 were delineated in the trabecular bone of the alveolar process. RESULTS: In all subjects, the combined bone mineral content of the whole mandible specimens (global bone mineral content) was significantly correlated with age. The difference between the mean bone mineral densities of the male and female mandibles was found to be significant for G (P = .009). The mean bone mineral densities of dentate and edentulous specimens were also found to be significantly different for G and R1, respectively (P = .001 and P = .02), but not for R2. A positive correlation could be detected among the mean bone mineral density of G and R1, G and R2, and R1 and R2 of (1) male and female specimens, (2) dentate and edentulous specimens, and (3) incisal, premolar, and molar specimens. CONCLUSIONS: The intra-alveolar trabecular bone of these 21 mandibles is affected by the same local and systemic influences as cortical bone, whereas the infra-alveolar trabecular bone is mostly sensitive to dental status. The cortical and trabecular bone of the 10 mandibles from women is more sensitive to systemic influences, whereas that from men is more sensitive to local influences. This is somewhat in agreement with some studies that found an association between osteoporosis and oral bone loss, which is a metric measure.

Absorptiometry, Photon↗
PubMed1999

Osteoradionecrosis of the mandible: a microradiographic study of cortical bone.

We undertook a microradiographic study in osteoradionecrotic mandibular bone to estimate the number of vascular channels in the compact bone, number of resorption areas, and number of regeneration areas. Normal mandibles had a similar number of vascular channels/vision field compared with compact bone in other parts of the body. Irradiation itself did not significantly alter this number. After osteoradionecrosis had developed in the mandible, the number of vascular channels increased (p = 0.02). Treatment with hyperbaric oxygen further increased the number of vascular channels/vision field (p < 0.003). The normal mandible had no resorptive or regenerative areas, either before or after radiotherapy. The osteoradionecrotic mandible, however, had an increased number of resorptive as well as regenerative areas/vision field. Fluorescence as an indication of incorporation of tetracycline was seen in the regenerative areas of all osteoradionecrotic specimens treated with doxycycline. The process started from the vascular channels, periosteum, and endosteum. We conclude that the compact bone of mandibular osteoradionecrosis has high metabolic activity with active resorption and regeneration of bone and the limitation of the blood supply through cortical vascular channels, seems to be only one of many important factors.

Adult↗
PubMed1998

Mandible position and head posture: electromyography of sternocleidomastoids.

A study was performed to evaluate relationships between mandible position, dynamics, muscle activity and head posture while swallowing by use of surface EMG and mandible kinesiograph on two population groups (118 pathologics and 31 controls). The study produced the following: 1. specific mandible dynamics with a very fast rising phase (0.3 sec) and longer phase of stabilization (1.5 sec); 2. more than 60% of the subjects presented deglutition at occlusion level, the others swallowing at a distance of 0.1-4.6 mm; 3. the whole muscle activity (temporals, masseters, digastrics, sternocleidomastoids) lasted 1.5 sec with no correlation of duration to age; 4. sternocleidomastoids fired at swallowing with an effort of one-half of temporals or masseters; 6. firing order presented a particular pattern: digastrics more often first, sternocleidomastoids more often last. No differences were found between the pathologics and controls. Findings suggest that the oral phase or mandible dynamic, and the stabilization phase or oropharyngeal phase of swallowing, has an individual role that is important in head postural equilibrium.

Adolescent↗
PubMed2004

A method for material parameter determination for the human mandible based on simulation and experiment.

In cranio-maxillofacial surgery planning and implant design, it is important to know the elastic response of the mandible to load forces as they occur, e.g., in biting. The goal of the present study is to provide a method for a quantitative determination of material parameters for the human jaw bone, whose values can, e.g., be used to devise a prototype plastic model for the mandible. Non-destructive load experiments are performed on a cadaveric mandible using a specially designed test bed. The identical physiological situation is simulated in a computer program. The underlying mathematical model is based on a two component, linear elastic material law. The numerical realization of the model, difficult due to the complex geometry and morphology of the mandible, is via the finite element (FE) method. Combining the validated simulation with the results of the tests, an inverse problem for the determination of Young's modulus and the Poisson ratio of both cortical and cancellous bone can then be solved.

Algorithms↗
PubMed2006

Consideration of anisotropic elasticity minimizes volumetric rather than shear deformation in human mandible.

This article is focused on the role of anisotropic elasticity in the simulation of the load distribution in a human mandible, due to a lateral bite on the leftmost premolar. Based on experimental evidence, orthotropy of the elastic properties of the bone tissue has been adopted. The trajectories of anisotropic elasticity are reconstructed from (i) the organ's geometry and (ii) from coherent structures which can be recognized from the spatial distribution of the grey values coming from computer tomography (CT). A sensitivity analysis comprising various three-dimensional (3D) finite element (FE) simulations reveals the relevance of elastic anisotropy for the load carrying behavior of a human mandible: comparison of the load distributions in isotropic and anisotropic simulations indicates that anisotropy seems to "spare" the mandible from loading. Moreover, a maximum degree of anisotropy leads to kind of load minimization of the mandible, expressed by a minimum of different norms of local volumetric strain, evaluated throughout the organ. The observed optimization with respect to volumetric rather than shear strain seems to confirm the frequently emphazised role of volumetric-strain-induced fluid flow for the stimulation of cellular activity.

Anisotropy↗
PubMed2001

Cortical bone mineral density in asymmetrical mandibles: a three-dimensional quantitative computed tomography study.

The three-dimensional distribution (3D) of the highest mineralized cortical bone was evaluated in 32 subjects between the ages of 8 and 30 years with asymmetrical mandibles using quantitative computed tomography (QCT). The geometrical distribution of the highest mineralized areas (> 1250 mg/cm3) representative of mandibular cortical bone was determined by 3D reconstruction of the images. The length of the mandible on each side was determined by defining a new linear measurement from the centre of the 3D reconstructed condyle to the midline of the symphysis as identified from a submental view. The cross-sectional areas of the masseter and medial pterygoid muscles were assessed from bilateral axial views through the middle of the muscles parallel to the Frankfort-Horizontal plane. Comparison between the lengths of the two mandibular sides (right-left = mm) indicated a range of asymmetries with an equal number of subjects with the left and right mandible longer. Comparison of the area of highest mineralized cortical bone between the right and left sides (R/L) to the ratio of the mandibular length (R/L) showed a high correlation coefficient (r = 0.629) suggesting that the shortest mandibular side had more highly mineralized bone. A comparison of the area of highest mineralized cortical bone between the right and left sides (R/L) to the ratio of cross-sectional areas of the muscles showed the highest correlation coefficient (r = 0.724) with the ipsilateral masseter muscle. These findings indicate that asymmetrical mandibles are associated with asymmetrical distributions of the highest mineralized cortical bone and that this is age dependent.

Adolescent↗
PubMed2001

Genetic architecture of mandible shape in mice: effects of quantitative trait loci analyzed by geometric morphometrics.

This study introduces a new multivariate approach for analyzing the effects of quantitative trait loci (QTL) on shape and demonstrates this method for the mouse mandible. We quantified size and shape with the methods of geometric morphometrics, based on Procrustes superimposition of five morphological landmarks recorded on each mandible. Interval mapping for F(2) mice originating from an intercross of the LG/J and SM/J inbred strains revealed 12 QTL for size, 25 QTL for shape, and 5 QTL for left-right asymmetry. Multivariate ordination of QTL effects by principal component analysis identified two recurrent features of shape variation, which involved the positions of the coronoid and angular processes relative to each other and to the rest of the mandible. These patterns are reminiscent of the knockout phenotypes of a number of genes involved in mandible development, although only a few of these are possible candidates for QTL in our study. The variation of shape effects among the QTL showed no evidence of clustering into distinct groups, as would be expected from theories of morphological integration. Further, for most QTL, additive and dominance effects on shape were markedly different, implying overdominance for specific features of shape. We conclude that geometric morphometrics offers a promising new approach to address problems at the interface of evolutionary and developmental genetics.

Animals↗
PubMed2006

Morphologic analyses of mandible and upper airway soft tissue by MRI of patients with obstructive sleep apnea hypopnea syndrome.

STUDY OBJECTIVES: To evaluate the morphological features of the mandible and the volume of the upper airway soft tissues in determining the anatomical risk factors for the upper airway in Japanese male patients with obstructive sleep apnea hypopnea syndrome (OSAHS). METHODS: Five morphological parameters of the mandible at the mandibular base plane and three volumetric parameters of the upper airway soft tissue were analyzed using three-dimensional (3D) magnetic resonance imaging software in 31 OSAHS and 20 controls. RESULTS: There were no significant differences between the two groups in mandibular internal width (the distance between the internal right and left gonia [IRG and ILG]) and mandibular bony thickness. However, the patients with OSAHS had a significantly wider mandibular divergence (the angle between the spina mentalis (SM)- IRG line and SM- ILG line), a smaller mandibular internal length (the perpendicular distance from SM to the RG- LG line), and a smaller area than the normal subjects at the mandibular base plane. There were no significant differences in these morphological parameters for the mandible between obese and nonobese OSAHS patients. The volumes of the tongue, soft palate, and lateral pharyngeal walls were not significantly different between the OSAHS and the control groups. CONCLUSIONS: Japanese male OSAHS patients had specific anatomical features in the bottom part of the mandible; however, obesity seemed to be a less significant risk factor. Investigators and clinicians must realize that ethnicity may modify the effects of obesity and abnormal craniofacial anatomy as risk factors for the pathogenesis of OSAHS.

Asian People↗
PubMed2002

Unique rodent model of distraction osteogenesis of the mandible.

Despite the increasing use of distraction osteogenesis (DO) of the mandible, the molecular mechanisms regulating new bone formation during DO remain poorly understood. The purposes of this study were (1) to establish a unique rodent model of DO capable of outlining parameters for new bone formation at the distraction site and (2) to determine a critical-size defect to differentiate osteogenesis resulting from distraction from conventional fracture healing at the osteotomy site. Adult Sprague-Dawley rats were fitted successfully with this newly developed distraction device. Analyses demonstrated that the device could distract the rat mandible reliably to 5.1 mm with complete union. Acute intersegmental gaps of 2 mm resulted in complete bony union in a manner consistent with fracture healing, whereas 3-mm acute gaps resulted in varying degrees of bony union. Acute intersegmental gaps of 5.1 mm invariably resulted in fibrous nonunion. In summary, the authors have developed a rodent model of DO of the mandible. Their distraction protocols resulted successfully in advancement to 5.1 mm with bony consolidation. Notable fracture healing occurred at immediate intersegmental spaces as large as 3 mm. A gap of 5.1 mm was sufficient to act as a critical-size defect, resulting consistently in fibrous nonunion. These findings validate the effectiveness of this distraction device and establish the critical-size defect of a rat mandible at more than 3 mm. This novel model of DO provides an effective method of examining fundamental mechanisms responsible for new bone formation in the craniofacial skeleton.

Animals↗
PubMed2003

Distraction osteogenesis of the mandible with an internal bioresorbable device.

Lengthening of the mandible by distraction osteogenesis has been shown to be an effective treatment of hypoplastic mandibles. Use of an internal technique with a bioresorbable distraction device is presented. Mandibular lengthening was performed in seven patients aged 3.2 to 7 years. Six of the patients were diagnosed with craniofacial microsomia, anthe buccal aspect of the mandible, and distraction was started on the second postoperative day at the rate of d one was diagnosed with Nager syndrome. An internal bioresorbable device was placed along 1 mm/d and continued for 17 to 20 days. The distractor screw was maintained for retention for an additional 6 weeks and was then removed. All the patients showed clinical improvement. The postdistraction craniofacial computed tomography scans demonstrated elongation of the mandible with increase in the bony mass. The complications included device failure in one patient. The advantage of this method compared with the internal metal device is that it does not necessitate an additional procedure for device removal.

Absorbable Implants↗
PubMed2005

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.

Aged↗
PubMed1996

The multipoint contact plate in fracture treatment of the atrophied mandible: animal study and clinical application.

Rapid consolidation of osseous fractures requires stable immobilization of the fragments. In the atrophied mandible, the nutrient supply should be ensured by protecting the periosseous soft tissue, i.e., the periosteum. In the conventional placement of osteosynthesis plates, however, the subimplant nutrition is restricted because of the high surface pressure between the osteosynthesis plate and bone. In order to improve the subimplant nutrient supply, we designed a new osteosynthesis plate with a "knobbed" underside enabling multipoint contact. Histomorphologic comparative studies were conducted on 16 Göttingen minipigs with an average weight of 47.5 +/- 8 kg. In each minipig, one side of the mandible was fractured and one side was left intact. One side of each mandible was plated with a six-hole dynamic multipoint contact plate and the other side with a conventional plate. The plates were applied, either epiosseous or epiperiosteal, with bicortical screws under defined torque. The results demonstrate the advantages of multipoint contact plates over the conventional ones and create the clinical basis for a "bio-logical" plate design that allows callus to grow between the knobs and therefore provide adequate nutritional and vascular supply. The plate's knobbed profile also promotes extraosseous venous drainage without impeding intraosseous fluid flow. This plate is the logical choice for rapid fracture consolidation in the high-grade atrophied mandible.

Aged↗
PubMed2000

Effect of distraction rate on biomechanical, mineralization, and histologic properties of an ovine mandible model.

Craniofacial microsomia is a common congenital malformation. Ilizarov's method of distraction osteogenesis applied to the mandible has yielded promising results both experimentally and clinically. Because the technique is used predominantly in a pediatric population, length of treatment and compliance may be problematic. To date, the limits of distraction rate in the craniofacial skeleton have not been defined. This study was designed to investigate the effects of distraction rate, in a large animal model, on the mineralization, biomechanical, and histologic properties of lengthened mandibles. Clinically faster distraction rates would decrease the overall treatment time. Twenty-four animals were divided into four groups, with varying rates of distraction (1, 2, 3, and 4 mm/day). A uniaxial distractor at the angle of the mandible was used. The mandibles were lengthened to 24 mm and fixed for a period of 5 weeks, when the animals were killed. The specimens were analyzed with respect to mineralization using dual energy x-ray absorptiometry, biomechanical strength, through a modified three-point bending test, and histologic properties with hematoxylin and eosin stains. Biomechanical, mineralization, and histologic analyses of the samples indicated that group 1 (1 mm/day) samples were significantly superior (p<0.05) to those of group 4 (4 mm/day). Although bone formation was achieved in all groups, group 1 (1 mm/day) demonstrated the strongest biomechanical and histologic properties. Bone mineral density obtained using dual energy x-ray absorptiometry may be clinically useful as a reliable, noninvasive, and relatively cheap predictor for removal time of the fixator.

Animals↗
PubMed2006

Osteonecrosis of the mandible or maxilla associated with the use of new generation bisphosphonates.

OBJECTIVE: The use of bisphosphonates is well established for the treatment of patients with metastatic bone disease, osteoporosis, and Paget's disease. Osteonecrosis of the mandible or maxilla associated with the use of bisphosphonates is a newly described entity never before discussed in the otolaryngology literature. In this paper, we review a series of patients diagnosed with osteonecrosis, all treated with new generation bisphosphonates. Our objective is to inform and educate others, particularly otolaryngologists/head and neck surgeons, about this drug induced entity, a condition that should be recognized early to avoid potential devastating consequences. STUDY DESIGN: Retrospective chart review of a series of patients from a tertiary referral center. METHODS: Pathology reports of specimens submitted from either the mandible or maxilla were reviewed from the previous 12 months. Any patient diagnosed with osteonecrosis without evidence of metastatic disease at that site was included; those with a previous history of radiation therapy were excluded. Each patient's medical history and profile were reviewed. RESULTS: Twenty-three patients were identified with osteonecrosis of the mandible or maxilla. All of these were associated with the use of new generation bisphosphonates: zolendronate (Zometa, Novartis), pamidronate (Aredia, Novartis), and alendronate (Fosamax, Merck). Eighteen patients with known bone metastases had been treated with the intravenous form, whereas five patients with either osteoporosis or Paget's disease were using oral therapy. Patients typically presented with a nonhealing lesion, often times the result of previous dental intervention. Although the majority of these patients were treated with conservative surgical debridement, we present a case requiring a near total maxillectomy. CONCLUSIONS: Drug induced osteonecrosis of the mandible or maxilla has been recently recognized as a sequelae of treatment with the new generation of bisphosphonates. Most patients can be treated with conservative surgical debridement and cessation of bisphosphonate therapy, whereas a few may require radical surgical intervention. Other recommendations include regimented prophylactic care with an assessment of dental status before the administration of bisphosphonates, avoidance of dental procedures, and close monitoring of oral hygiene.

Biopsy, Needle↗
PubMed2005

The pediatric mandible: I. A primer on growth and development.

LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. Describe embryonic and fetal mandibular development. 2. Summarize the aggregate changes in mandibular form from birth to puberty. 3. Describe the eruption and maturation of the deciduous and permanent mandibular dentition. BACKGROUND: In this, the first of two articles addressing the surgical management of pediatric mandibular fractures, the authors provide a detailed discussion of mandibular development and anatomy during the fetal period, infancy, and childhood. METHODS: A review of the pertinent literature was performed. The changing structure of the developing mandible is discussed, with particular attention to surgically relevant anatomical structures. RESULTS: Throughout development, key anatomical structures with relevance to surgical therapy change markedly in position. The mandible undergoes significant change in its bony structure and the composition of its surrounding soft tissues. The mandible's bony structure becomes more robust, with an increasingly acute gonial angle and enlargement of the ramus and body. Furthermore, the mandible provides the bony structure from which tooth buds erupt as the deciduous and permanent dentition--a process that generates significant growth of the alveolar process. As a consequence, the distance between the developing dentition and the inferior mandibular border increases. While the canal of the inferior alveolar nerve undergoes significant superior displacement, the mental foramen becomes positioned more posteriorly over time. In addition, the ligamentous and muscular attachments that surround the temporomandibular joint become increasingly robust. Throughout childhood and adolescence, the blood supply of the mandibular body changes little, with the buccal periosteal plexus and inferior dental artery making significant contributions. CONCLUSIONS: Mandibular growth provides the basis for normal occlusal relations and the generation of increasingly large masticatory force. Although the exact mechanisms of bone remodeling during mandibular development remain unclear, the process likely receives contributions from primary growth centers and the response to local alterations in biomechanical force produced by surrounding soft-tissue structures. A working knowledge of the changing mandibular anatomy is a prerequisite for effective clinical management of traumatic injury.

Bone Remodeling↗
PubMed2007

Sagittal split ramus osteotomy with mandible reduction.

BACKGROUND: The sagittal split ramus osteotomy is a well-established procedure, and many authors have attempted various modifications of the surgical technique. Nowadays, it is widely acknowledged that people in Korea, Japan, and China prefer an oval face, the lower part of which is slender. Therefore, among facial contouring procedures, the mandible reduction procedure is the most popular procedure in these countries. It is quite difficult for patients to undergo two different procedures on almost the same region separately. METHODS: For patients who underwent sagittal split ramus osteotomy on their mandible for various reasons, the authors performed mandible reduction at the same time if necessary. In the event that two procedures are performed simultaneously, the risk would be higher regarding postoperative stability, but there was no significant problem in achieving stable occlusion after surgery through a rigid fixation technique and 2 weeks of rigid intermaxillary fixation. RESULTS: The authors attained satisfactory aesthetic results and good postoperative stability by performing sagittal split ramus osteotomy and mandible reduction at the same time. CONCLUSION: This procedure is thought to be useful for patients who are to undergo sagittal split ramus osteotomy for various reasons and want to have a slender lower face.

Adult↗
PubMed2001

Quantitative genetics of geometric shape in the mouse mandible.

We combine the methods of geometric morphometrics and multivariate quantitative genetics to study the patterns of phenotypic and genetic variation of mandible shape in random-bred mice. The data are the positions of 11 landmarks on the mandibles of 1,241 mice from a parent-offspring breeding design. We use Procrustes superimposition to extract shape variation and restricted maximum likelihood to estimate the additive genetic and environmental components of variance and covariance. Matrix permutation tests showed that the genetic and phenotypic as well as the genetic and environmental covariance matrices were similar, but not identical. Likewise, principal component analyses revealed correspondence in the patterns of phenotypic and genetic variation. Patterns revealed in these analyses also showed similarities to features previously found in the effects of quantitative trait loci and in the phenotypes generated in gene knockout experiments. We used the multivariate version of the breeders' equation to explore the potential for short-term response to selection on shape. In general, the correlated response is substantial and regularly exceeds the direct response: Selection applied locally to one landmark usually produces a response in other parts of the mandible as well. Moreover, even selection for shifts of the same landmark in different directions can yield dramatically different responses. These results demonstrate the role of the geometry and anatomical structure of the mandible, which are key determinants of the patterns of the genetic and phenotypic covariance matrices, in molding the potential for adaptive evolution.

Animals↗
PubMed1993

A comparison of three finite element models of an edentulous mandible provided with implants.

The stress distribution in an edentulous mandible provided with two implants in the interforaminal region was calculated by means of three different finite element models. The implants were connected with a bar or remained solitary. The first model was a three-dimensional representation of the entire mandible, the second model of the interforaminal region of this same mandible, whilst the third model was a two-dimensional representation of the interforaminal region. The differences in stress distribution around the connected implants and the solitary implants between these three models were analysed. It can be concluded that for a parameter study the stress distribution around the dental implants following from a three-dimensional finite element model of only the interforaminal region of an edentulous mandible can be used. For such studies therefore, benefit can be gained from the advantages of reduced modelling and calculation time.

Bite Force↗