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PubMed1996

[Fractures of the atrophic mandible--a challenge for therapy].

Because treatment of fractures of the atrophic mandible still today presents significant difficulties and treatment modalities remain controversial, 87 of these consecutive fractures which were treated by an uniform method as compression osteosynthesis were evaluated. A new classification of the degree of atrophy which considers the special interest of fracture treatment is introduced. It is based on a metrical measurement of the height of the mandible in the fracture area. Mandibles of 16 to 20 mm height are classified as class I atrophy, those of 11 to 15 mm as class II atrophy, and those with a height of 10 mm or less as extremely atrophic mandibles or class III atrophy. This simple and reliable classification could also be used in future investigations on the results of different treatment modalities in atrophic mandibles. In our series of 87 fractures of the atrophic mandible which were treated by compression osteosynthesis 97% resulted in a solid osseous union without the need of a second surgical intervention. Three major complications occurred: 1 osteomyelitis and 2 non-unions (the latter in one patient with a double fracture of a class III atrophy mandible). To the best of our knowledge this series is the largest of fractures of truly atrophic mandibles treated by one uniform method. Compared to other treatment modalities compression osteosynthesis produced acceptable results and is recommended as the treatment of choice in fractures of the atrophic mandible.

Alveolar Bone Loss↗
PubMed2002

Sexual dimorphism in the Atapuerca-SH hominids: the evidence from the mandibles.

The pattern of sexual dimorphism in 15 mandibles from the Atapuerca-SH Middle Pleistocene site, attributed to Homo heidelbergensis, is explored. Two modern human samples of known sex are used as a baseline for establishing sexing criteria. The mandible was divided for analysis into seven study regions and differential expression of sexual dimorphism in these regions is analysed. A total of 40 continuous and 32 discrete variables were scored on the mandibles. The means method given in Regh & Leigh (Am. J. phys. Anthrop.110, 95-104, 1999) was followed for evaluating the potential of correct sex attribution for each variable. On average, the mandibles from the Atapuerca-SH site present a degree of sexual dimorphism about eight points higher than in H. sapiens samples. However, mandibular anatomy of the European Middle Pleistocene hominid records sexual dimorphism differentially. Different areas of the Atapuerca-SH mandibles exhibit quite distinct degrees of sexual dimorphism. For instance, variables of the alveolar arcade present very low or practically no sexual dimorphism. Variables related to overall size of the mandible and symphysis region present a medium degree of sex differences. Finally, ramus height, and gonion and coronoid process present a high degree of sexual dimorphism (indexes of sexual dimorphism are all above 130%). Whether this marked sexual dimorphism in specific anatomical systems affects sexual differences in body size is not completely clear and further studies are needed. Sexual differences detected in the mandible of modern humans have at least two components: differences related to musculo-skeletal development and differences related to a different growth trajectory in males and females (relative development of some of the basal border features). The Atapuerca-SH mandibles display little variation in the basal border, however. The limited variation of this mandibular region may indicate that the pattern of sexual variation in H. heidelbergensis is different enough to that of H. sapiens to caution against simple extrapolation of criteria from one pattern to the other.

Animals↗
PubMed1997

Mandible muscle fibers in ants: fast or powerful?

Ants use their mandibles for catching prey, cracking seeds, cutting leaves, or for the construction of nests and the tender care of brood. The functional morphology of the mandibles reflect the species' adaptations to particular foraging habits and social life. The versatility and specialization of the mandibles depend directly on the design and physiology of the mandible closer muscles and their component fibers. A comparative video analysis of the closing movements of ant mandibles revealed that the maximal velocity varies considerably among species. The speed is correlated with the morphology of the mandible closer muscle, the largest muscle in ants. It is composed of two morphologically very distinct fiber types: long fibers with short sarcomeres (sarcomere length approximately 2 microM) showing all the structural attributes of fast muscle fibers, and shorter fibers with longer sarcomeres (sarcomere length approximately 5 microM) exhibiting the characteristics of slow and powerful fibers. Ants with fast-moving mandibles have a very high proportion of fast closer fibers, whereas the muscles of ants that cannot perform fast mandible movements have only a few or no fast fibers at all. Fast fibers always attach directly to the solid apodeme, while slow fibers often attach to thin apodeme threads. We suppose that the latter kind of fiber attachment is disadvantageous for fast contracting fibers but helps the ants to make better use of the space in the head capsule.

Animals↗
PubMed2003

Quality assessment of the cortical bone of the human mandible.

This study is the first to investigate simultaneously both the regional and the directional variations in mechanical properties and computed tomography (CT) numbers of the fresh mandible bone and to explore the correlation between the two sets of data with a view to provide a noninvasive method for determining the bone quality for designers of dental implants. Using a three-point bending test the regional variation of Young's modulus of bone in the human mandible was determined from five fresh specimens from donors representative of patients in need of dental implants in that some of the mandibles were fully dentulate, some partly so, and some fully edentulate. While a pattern of the modulus distribution was evident in the mandibles we tested, these mandibles did have, as a result of their respective states, their own peculiarities. We determined also the directional variations of the modulus for the mandible, which are due to the anisotropic nature of bone. The modulus values obtained in our study were much lower than those listed in the only other published study, which was conducted on dry mandibles. These differences in the modulus data from the two studies were attributed partly to the differences in condition of the bone and differences in the dimensions of specimens tested in the two studies. Because the values of the modulus obtained in this study are lower than those previously published, they would be safer as a basis for implant designs. A weak correlation was found between the modulus values and the CT number of the mandible. This would not be sufficient for accurate predictions of the bone properties from CT scans. The development of a noninvasive method for determining the bone quality in various patients thus remains a challenge for researchers.

Aged↗
PubMed1999

Differences in static cortical bone remodeling parameters in human mandible and iliac crest.

Knowledge of the baseline turnover characteristics, and of possible general and local factors influencing alveolar bone responses, is particularly important in the planning of oral rehabilitation. The conventional tool used to obtain information on bone turnover is the iliac crest biopsy, but it is not clear whether it mirrors the situation involving the jaws. The aim of this study was to compare static bone remodeling parameters in the mandible and in the iliac crest to obtain baseline values for the mandible and to test the hypothesis of site specificity of bone remodeling. Bone specimens were obtained from 50 subjects (mean age 64 +/- 17) at autopsy. Three sites were sampled: iliac crest; jaw angle; and foramen mentalis area. In addition, occlusal status was recorded. On undecalcified thin sections, cortical porosity (Ct.Po), eroded sites (ESi), formative sites (FSi), osteonal diameter (On.Dm), Haversian canal diameter (H.Ca.Dm), and wall width (W.Wi) were measured. Ct.Po in the jaw angle and in the foramen mentalis area was lower (48% and 50%, respectively) than in the iliac crest, as was ESi and FSi (80% in the jaw angle and 74% in the foramen mentalis area). In the foramen mentalis area, Ct.Po was greater in subjects with occlusion. On.Dm, H.Ca.Dm, and W.Wi were significantly larger and mutually correlated within the mandible, whereas no correlation was found between mandibular sites and iliac crest. Static cortical bone remodeling parameters are different in the mandible and the iliac crest, thus confirming the hypothesis of site specificity of bone remodeling. Within the mandible, the parameters were correlated, whereas there was no correlation between the mandible and the iliac crest. This could be ascribed to the different functional demands to the mandible and the iliac crest, which was also reflected in the observed influence of functional occlusion on bone remodeling in the mandible. It can thus be concluded that bone reaction to dental intervention is more dependent on the local environment than on general bone turnover as reflected by the iliac crest.

Analysis of Variance↗
PubMed1993

Biomechanical changes of the mandible from orthopaedic chin cup force studied in a three-dimensional finite element model.

Biomechanical changes of the mandible from orthopaedic chin cup forces were investigated by means of finite element analysis. A three-dimensional model of the mandible including the temporomandibular joint was developed for stress analysis in the mandible. A chin cup force of 400 gf was applied at pogonion on the mandible in the direction toward the condyle. From the stress analyses, it was revealed that (1) uniform tensile stresses were produced at the outer borders of the mandible, (2) compressive stresses were induced in the centre of the mandible, (3) compressive stresses were generated widely on the surface of the condyle, and (4) stresses on the condyle were smaller in magnitude than those in the mandibular corpus. These results coincide with morphological changes of the mandible revealed in previous studies and, thus, indicate an association of stresses with remodelling of the mandible from chin cup therapy applied to adolescent patients with mandibular prognathism.

Adolescent↗
PubMed1999

The mechanical behaviour of human mandibles studied by electronic speckle pattern interferometry.

An understanding of the mechanical behaviour of the human mandible during mastication may be useful in several specific medical fields that examine the maxillofacial area. In this research, the Electronic Speckle Pattern Interferometry Optical Technique was applied to study a dry mandible under external stress. Two images of the mandible, i.e. an image of the relaxed mandible and another of the mandible under stress, were processed using this technique and provided information concerning the most stressed areas of the bone. The advantage of interferometric analysis is that it can be carried out in real time on a mandible to which progressively greater stress has been applied. This research may be of value in maxillofacial surgery, for example, in the diagnosis and treatment of fractured mandibles, and in oral surgery and orthodontics, where it can provide information concerning stress dispersion when an osteointegrated implant or orthodontic appliance is placed in the mouth. One of the most important conclusions to be drawn from the experiments of tension, compression, and in- and out-of-plane deformations is that the capability of the mandible to bend is superior to its capability to stretch. Several quantitative results support this conclusion.

Female↗
PubMed2003

Relationship between the craniofacial complex and size of the resorbed mandible in complete denture wearers.

A cephalometric study was conducted on 34 complete denture wearers to examine the relationship between the area of the mandible and the skeletal facial form, the area of the mandible and the gonial angle, and the area of the mandible and the length of the mandible. No significant correlation was found between the area of the mandible and the skeletal facial types or the gonial angle. A statistically significant correlation (P < 0.0028) was found between the length of the mandible and the area of the mandible. Residual resorption of the mandible appears to be independent of skeletal facial form and the gonial angle.

Aged↗
PubMed2006

Sex determination using nonmetric characteristics of the mandible in Koreans.

The mandible is the largest and hardest facial bone and retains its shape better than other bones in the forensic and physical anthropologic field. The mandible can be used to distinguish among ethnic groups and between sexes. We examined the morphological characteristics of the mandibles of 102 Koreans of either sex. Of 13 nonmetric items of the mandible, the characteristic that best allowed the sexes to be distinguished was the contour of the lower border of the mandible: rocker-shaped mandibles predominated in males (68.1%), whereas most females (84.6%) exhibited a straight mandible. In addition, the mental region was shaped differently between the sexes: the shape of the chin in most males was generally bilobate or square (91.7%), whereas the chin in females was either square (45.5%) or pointed (54.5%). In this study, the positive predict values of male and female were 92.5% and 73.7%, respectively. Therefore, the nonmetric method used to analyze the mandible in this study can be used for sex discrimination.

Adolescent↗
PubMed2001

Lingual vascular canals of the mandible: evaluation with dental CT.

PURPOSE: To evaluate whether dental computed tomography (CT) can depict the frequency, diameter, position, and direction of vessels entering the mandible through lingual bone canals. MATERIALS AND METHODS: Thirty-two consecutive patients underwent preimplantation CT of the lower jaw and examination for the presence, number, location, diameter, and direction of lingual canals entering the mandible. In addition, three cadaver mandibles were investigated with dental CT and subsequently dissected to confirm the CT findings. RESULTS: All patients demonstrated at least one lingual vascular canal, and 20 (63%) had multiple (two to five) canals. The typical lingual canal locations were the midline of the mandible and the premolar region. The mean diameter of the lingual canals was 0.7 mm +/- 0.3 (SD) (range, 0.4--1.5 mm) in the midline and 0.6 mm +/- 0.2 (range, 0.3--1.2 mm) in both premolar regions of the mandible. Examination results in the three cadaver mandibles confirmed the CT findings in those mandibles. CONCLUSION: Dental CT can depict the occurrence, position, and size of the lingual vascular canals of the mandible. Radiologists should be aware of this anatomic feature and its possible implications.

Adolescent↗
PubMed2000

[The effects of local stress on bone mass of mandibles in ovariectomized rats].

OBJECTIVE: To observe the relationship between the change of stress environment of mandibles and their bone mass in normal and ovariectomized(OVX) rats. METHODS: The high and low stress environment models of mandibles were established by unilateral maxillary molars extraction. The masticatory sides of the mandibles were regarded as the high stress sides and the non-masticatory sides were regarded as the low stress sides. Ovariectomized rats were utilized as postmenopausal osteoporosis models and Sham-ovariectomized(Sham-OVX) rats as control group. According to these ideas, 48 female rats were divided into 4 groups: 1) OVX + extraction group; 2) OVX + non-extraction group; 3) Sham-OVX + extraction group; 4) Sham-OVX + non-extraction group. The bone mineral densities (BMD) of all mandibles were measured by single-photon absorptiometry bilaterally 1.5 months and 3 months after extraction. RESULTS: The mandibles of ovariectomized rats had lower BMD than those of normal rats(P < 0.05). To normal rats, the BMD of mandibles in low stress sides were lower than the high stress sides 3 months after extraction(P < 0.05), but the BMD of the two sides were not significantly different to those of the non-extraction control ones(P > 0.05). To ovariectomized rats, the BMD of mandibles low stress sides were much lower than the high stress sides(P < 0.01). The BMD of mandibles in low stress sides were much lower than non-extraction ones of OVX group after 3 months(P < 0.05). The BMD of the high stress sides were much higher than those of the non-extraction control ones of OVX group(P < 0.05), but they were still lower than those of the non-extraction control ones of Sham-OVX group(P < 0.05). CONCLUSION: The results indicate that the masticatory functions(the high stress environment) tend to conserve the mandibular bone mass in patients with systemic osteopenia such as postmenopausal osteoporosis and the masticatory deficiency (the low stress environment) tends to aggravate mandibular bone loss induced by systemic osteopenia. The masticatory functions should be rehabilitated for these patients as early as possible.

Animals↗
PubMed2006

[Study of biomechanical effects on the reconstruction of mandible defect with autogenous bone grafts].

The biomechanical effects of the reconstructed mandible with autogenous bone grafts were analyzed and evaluated, under simulated mechanical environment of occlusion. Based on anatomical feature of the human skeleton, muscle system and the clinical B, BS"S" and RB"S"defect patterns, the modularized model of mandible and the three finite element models of the fibula grafts and iliac crest grafts reconstruction mandible were made. The stress state calculations under bite force were also processed. The findings are as follows: Along the right connection area to left connection area (corresponding to far-end of the molar teeth alveolar ridge and the chin section respectively), the stress state on the various grafted bone all changes from compression stress to tensile stress. There is obvious change on the stress distribution between the fibula type reconstruction mandible and normal one. The stress on the grafted bone which is mainly made up of cortical bone is approximately 5 times higher than that of normal, which indicates the obvious stress shielding effect; the stress distribution of the iliac crest type reconstruction mandible is close to the normal mandible, the iliac crest used is mainly made up of cancellous. Therefore, the mechanical properties of the reconstructed mandible with iliac crest are more similar to normal mandible, which is beneficial to wound healing and further functional reconstruction.

Bone Transplantation↗
PubMed1998

Position of the mental foramen in adult black Zimbabwean mandibles: a clinical anatomical study.

OBJECTIVE: To provide some anatomical information on the shape, size, and position of the mental foramen among Black Zimbabweans that could be used as reference material by dental and other health practitioners during clinical practice in Zimbabwe. DESIGN: Cross sectional anatomical study. SETTING: Department of Anatomy, Faculty of Medicine, University of Zimbabwe, Mount Pleasant, Harare, Zimbabwe. SUBJECTS: 32 mandibles derived from adult Black Zimbabweans. MAIN OUTCOME MEASURES: The shape of the mental foramen, its relation to the lower teeth and its position in relation to the mandibular symphysis, the posterior border of the ramus of the mandible, the lower border of the mandible, and the alveolar margin. RESULTS: The shape of the mental foramen was round in 14 out of 32 mandibles (43.8%) and was oval in the remaining 18 (56.3%). The percentage of occurrence of the mental foramen was highest below the lower second premolar tooth on the right side (position 4) and posterior to it on the left side (position 5). In the vertical plane, the mental foramen lay slightly below the midpoint of the distance between the lower border of the mandible and the alveolar margin (44.1% and 45.5% for the right and left sides respectively). In the horizontal plane, it lay approximately one quarter (27.3% for the right and 27.4% for the left sides) of the distance from the mandibular symphysis to the posterior border of the ramus of the mandible. CONCLUSION: The percentage distribution of the mental foremen in relation to the lower teeth in the adult Black Zimbabwean mandible was at variance with that of other population groups. However, the quantitative position of the mental foremen was bilaterally symmetrical in the adult Black Zimbabwean mandible. The latter observation is of clinical significance to dental and other health practitioners in Zimbabwe with regards to the achievement of effective mental nerve block anaesthesia and the prevention of damage to the mental nerve during surgical procedures on the lower jaw.

Adult↗
PubMed1998

Jaws that snap: control of mandible movements in the ant Mystrium.

Ants of the genus Mystrium employ a peculiar snap-jaw mechanism in which the closed mandibles cross over to deliver a stunning blow to an adversary within about 0.5 ms. The mandible snapping is preceded by antennation and antennal withdrawal. The strike is initiated by contact of the adversary with mechanosensory hairs at the side of the mandible, and is powered by large yet slow closer muscles whose energy is stored by a catapult mechanism. Recording of closer muscle activity indicates that the mandibles are not triggered by any fast muscle. Instead, we suppose that activity differences between the left and right mandible muscles imbalance a pivot at the mandible tip and release the strike. The likelihood for the strike to occur can be modulated by an alarm pheromone. The presence of specialized sensilla and of a complex muscle receptor organ shows that the mandibles are also adapted to functions other than snapping and suggests that the force of the mandible can be finely adjusted for other tasks.

Journal Article↗
PubMed1996

Results of treatment of fractures of the atrophic edentulous mandible by compression plating: a retrospective evaluation of 84 consecutive cases.

PURPOSE: This article introduces a simple and reproducible classification of the degree of atrophy in fractures of the atrophic edentulous mandible, and evaluates the results of treatment in 84 consecutive fractures based on this classification. MATERIAL AND METHODS: Eight-four fractures of the edentulous mandible, with a height at the fracture site of < or = 20 mm, were included. Using the ratio of actual plate width to plate width on the postoperative radiograph, the actual height of the mandible at the fracture site was calculated. Twenty-five fractures (30%) were in the Class I atrophy group (height at the fracture site 16 to 20 mm), 33 fractures (39%) occurred in Class II atrophic mandibles (height 11 to 15 mm), and 26 fractures (31%) were seen in extremely atrophic Class III mandibles (height < or = 10 mm). The treatment was performed by compression plating without any postoperative MMF. Primary bone grafting was used in six cases (7%) because a partial bone defect was present at the fracture site. RESULTS: In 81 (96.5%) of the 84 fractures an uncomplicated, solid, bony union was achieved. Three major complications occurred: one osteomyelitis and two nonunions. The two nonunions occurred in bilateral fracture of an extremely atrophied mandible (Class III atrophy). Minor soft tissue infections, without interference with fracture healing, were observed in six cases (7%). CONCLUSIONS: Because there is an obvious relation between the height of the mandible and the incidence of complications in fracture healing, a special classification of the degree of atrophy is needed. In fractures of the extremely atrophic mandible (Class III atrophy) periosteal degloving should be avoided and supraperiosteal placement of plates is recommended. Compression osteosynthesis has proved to be a successful method, with minimal impairment of the patient and a low frequency of serious complications.

Adult↗
PubMed2003

Malignant tumors of the mandible and maxilla.

Malignant tumors of the mandible and maxilla are grouped into primary tumors that originate within the mandible and secondary lesions, predominantly oral cancers and metastatic lesions, that involve the mandible secondarily. The most common malignant tumors of the mandible represent SCCs of the oral cavity, notably carcinoma of the floor of the mouth and gingiva that invade the mandible secondarily. Metastatic disease, most commonly from the breast and lung, are not an uncommon malignant lesion in the mandible and may be the first manifestation of a malignant lesion outside the head and neck. The osteogenic sarcoma is the most common sarcomatous lesion in the mandible and is suggested when a bone-forming matrix with sclerosis is found within the tumor on CT images. Some benign lesions may mimic a malignant tumor on imaging studies. In such cases, a biopsy is indicated to establish the diagnosis by histopathologic means. CT is indicated for assessment of bone destruction in the mandible before surgery or radiation therapy. MR imaging is the optimal modality for the assessment of marrow involvement and evaluation of the extraosseous soft tissue component. Finally, conventional films, frequently a Panorex view, are the initial radiographic examinations in suspected lesions.

Diagnosis, Differential↗
PubMed2004

The limits of elaboration: curved allometries reveal the constraints on mandible size in stag beetles.

Many studies have demonstrated the adaptive advantage of elaborate secondary sexual traits, but few if any have shown compelling evidence for the limits to the elaboration of these traits that must exist. We describe such evidence in the exaggerated mandibles of stag beetles. In 1932, Huxley showed that the slope of the allometric relationship between mandible length and body size in some stag beetles declines in the largest males. We show that this curvature is most pronounced in species with relatively long mandibles, consistent with the hypothesis that the decrease in slope is caused by the increasing costs of large mandibles, which ultimately limit their size. Increasing depletion of resources in the prepupa and pupa by the rapidly growing mandibles is the most likely way in which these costs are manifested. The curved allometries have two components: intraspecific mandible allometry is steepest among small males of the species with the longest mandibles, but shallowest among the largest males of those same species. These patterns suggest that selection continues to favour positive allometry in species that invest relatively more in weaponry despite the limits to mandible exaggeration being reached in the largest males.

Animal Structures↗
PubMed2004

Fibula free flap for mandible reconstruction.

OBJECTIVES: Microvascular mandibular reconstruction should be considered the procedure of choice for bone replacement in radiated tissue beds, orocutaneous fistulae with segmental bone loss, osteoradionecrotic mandibles, and for immediate composite tissue reconstruction. The free vascularized fibula has significant potential for the reconstruction of the mandible. We evaluated our clinical experience in 21 cases of mandible reconstruction with fibular flaps. PATIENTS AND METHODS: Between 1997 and 2002, we performed 7 free osseous fibula flaps and 14 osteocutaneous fibula flaps for a total of 21 mandible reconstructions in 21 patients (8 females, 13 males; mean age 41 years; range 22-58 years). Indications for mandibular resection were squamous cell carcinoma of the floor of the mouth, tongue, oropharynx, and/or alveolar ridge in 13 cases, ameloblastoma of the mandible in 4 cases, leiomyosarcoma of the mandible in 2 cases, and chondrosarcoma of the mandible in one case. There was a traumatic loss in one case. Of 21 patients, 17 were reconstructed primarily, and 4 patients had secondary reconstruction. RESULTS: All flaps, except one, survived and their viability was confirmed by scintigraphy when available. The skin defect in this patient was repaired by local lip flap which needed commissurotomy later, but the patient refused bone reconstruction. In two cases, because of long-lasting orocutaneous fistula and saliva drainage without flap loss, we used a pectoralis major pedicled flap as a secondary procedure. In three cases, donor side skin healing problems were managed well by secondary intention or split-thickness regrafting. Two patients had temporary foot drop which recovered in an average of three months. Simple problems with wound healing such as dehiscence and delayed healing developed in five patients, which usually required only local antiseptic treatment. After the operation, patients began oral feeding and walking with crutches in the third week, adjuvant radiotherapy began in the 6th week, and walking without crutches in the eighth week. CONCLUSION: Fibular bone allows to plan osteotomies in relation to the orientation of the bone and its vascular pedicle. Thick cortical bone readily accepts plates and screws for a secure interosseous fixation and osteointegrated implants may be placed in this bone safely. Among other alternatives like scapular and crista ilaca flaps, fibular flap has many advantages for mandible reconstruction and represents the first choice for the head and neck surgeon.

Adult↗