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PubMed1994

Jaw muscle function and wishboning of the mandible during mastication in macaques and baboons.

An analysis of in vivo bone strain indicates that the mandibular symphysis of macaques experiences lateral transverse bending or "wishboning" during the power stroke of mastication, and this loading regime results in relatively intense concentrations of stress along the lingual aspect of the symphysis (Hylander 1984, 1985). It has been hypothesized that peak wishboning of the macaque mandible, which probably occurs at the very end of the power stroke, that is, after the initial occurrence of maximum intercuspation, is associated with the late peak activity of the balancing-side deep masseter muscle coupled with the rapid decline in the activity of the balancing-side medial pterygoid and superficial masseter muscles (Hylander et al., 1987). The main purpose of this study is to do a detailed analysis of the electromyographic (EMG) activity of the deep and superficial masseter and medial pterygoid muscles so as to provide a better understanding of the external forces associated with wishboning. This was done by recording and analyzing EMG activity from the superficial masseter, deep masseter, and medial pterygoid muscles in macaques and baboons. EMG activity was recorded from bipolar fine-wire electrodes, and the data were quantified and analyzed using digital techniques. The EMG data clearly support our original observation that the balancing-side posterior deep masseter exhibits peak EMG activity relatively late in the power stroke at a time when activity is rapidly decreasing in the balancing-side medial pterygoid and superficial masseter muscles. Moreover, peak activity of the balancing-side deep masseter occurs at a time when the activity of the working-side deep and superficial masseter and medial pterygoid muscles are also decreasing. Thus, these data are consistent with the hypothesis that wishboning of the mandible is influenced significantly by the late occurrence of force from the balancing-side deep masseter. The EMG data also indicate that residual force from the relaxing superficial masseter may contribute significantly to wishboning. Finally, patterns of wishboning are not fully accounted for by our EMG analysis of the deep and superficial masseter and medial pterygoid muscles. This is probably because the lateral ptergyoids, which can either counter increased wishboning or actually cause reverse wishboning, were not included in our EMG analysis. The EMG data demonstrate that jaw-closing muscle recruitment patterns for macaques and baboons differ from those of humans. Nevertheless, in spite of these differences, it appears, based on previously published EMG data, that the human symphysis may also experience wishboning.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1976

Logarithmic growth of the hominoid mandible.

The growth of the basal unit of the mandible was studied by plotting the position, relative to the median plane, of the oval, mandibular and mental foramina in immature and adult skulls of Man, chimpanzee and gorilla. In Man, the basal unit was found to grow out along a constant logarithmic spiral. In the apes, the basal unit grew along a constant logarithmic spiral, the amount of unfolding being greater in the gorilla than in the chimpanzee. It is argued that the mode of growth seen in the apes evolved, as these forms became more prognathous, because it requires less compensatory rotation of the mandible, while the mode seen in Man is probably closer to that which occurred in common ancestral form.

Adult↗

PubMed1990

Effect of occlusal functional forces on incisor socket morphology and location in the rat mandible.

The effect of functional occlusal stress on dimensional alterations of the rat incisor socket and mandible were studied from roentgenograms. In 12 rats, the lower left incisor was shortened twice weekly, whereas the lower right incisor was allowed to remain in contact with both upper incisors. Thus, the right incisors were subjected to hyperfunction, and the left ones, to hypofunction. The lower incisors of 16 rats with normal occlusal contact served as control. Following an experimental period of 3 months, the animals were killed and standardized radiographs were taken of the cleaned mandibles. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Socket area, its posterior length, posterior mandibular length, and gonial angle changed in the same direction under both hyper- and hypofunction. The anterior socket was relocated in opposite directions: under hyperfunction, it assumed a more inferior position, whereas in hypofunction, it moved superiorly. The angulation of the socket became significantly more acute under hyperfunction, whereas in hypofunction, this parameter remained unchanged. It is concluded that altered functional demands affect the morphology of the incisor socket and its location within the mandibular borders.

Animals↗

PubMed2005

Finite-element modeling of the anthropoid mandible: the effects of altered boundary conditions.

Finite-element modeling provides a full-field method for describing the stress environment of the skull. The utility of finite-element models, however, remains uncertain given our ignorance of whether such models validly portray states of stress and strain. For example, the effects of boundary conditions that are chosen to represent the mechanical environment in vivo are largely unknown. We conducted an in vitro strain gauge experiment on a fresh, fully dentate adult mandible of Macaca fascicularis to model a simplified loading regime by finite-element analysis for purposes of model validation. Under various conditions of material and structural complexity, we constructed dentate and edentulous models to measure the effects of changing boundary conditions (force orientation and nodal constraints) on strain values predicted at the gauge location. Our results offer a prospective assessment of the difficulties encountered when attempting to validate finite-element models from in vivo strain data. Small errors in the direction of load application produce significant changes in predicted strains. An isotropic model, although convenient, shows poor agreement with experimental strains, while a heterogeneous orthotropic model predicts strains that are more congruent with these data. Most significantly, we find that an edentulous model performs better than a dentate one in recreating the experimental strains. While this result is undoubtedly tied to our failure to model the periodontal ligament, we interpret the finding to mean that in the absence of occlusal loads, teeth within alveoli do not contribute significantly to the structural stiffness of the mandible.

Animals↗

PubMed2004

Primary intraosseous (central) salivary gland neoplasms in jaw bones: report of a mucoepidermoid carcinoma of the mandible diagnosed by fine-needle aspiration cytology.

A case of intraosseous (central) mucoepidermoid carcinoma of the mandible diagnosed by fine-needle aspiration (FNA) cytology, with the diagnosis confirmed by surgical resection of the tumor is presented. Mucoepidermoid carcinoma is the most common histotype of malignant and benign salivary gland tumors, which occasionally arise within the facial bones of mandible and maxilla, besides their ordinary derivation from the major and minor salivary glands of the head and neck regions. This case is unusual in that although tumors of the jaws abound, only rare reports of intraosseous salivary gland-type lesions sampled by FNA exist. The current concepts exploring the intraosseous derivation of salivary gland tumors are presented and certain points on FNA technic for adequate sampling of such lesions are related.

Biopsy, Fine-Needle↗

PubMedDate not supplied

Vascular basis of lateral osteotomy of the mandible.

The sources of periosteal blood supply to the mandible have been investigated by dissection, histology, and injection studies. The facial artery has been identified as a major extraosseous source of blood supply to the body. The study confirms the importance of preserving the soft tissue attachments on the buccal aspect and lower border of the mandible during lateral mandibular osteotomy.

Adult↗

PubMedDate not supplied

Immediate reconstruction of the mandible using a vascularized segment of radius.

Resection of a segment of mandible, particularly when associated with malignant disease, carries a high morbidity and mortality. Traditional methods of autogenous bone grafting have proved unreliable in immediate reconstruction of such mandibular defects because of the variability of the recipient bed. These unfavorable conditions for bone graft survival can be largely overcome using vascularized bone and vascularized soft tissue reconstruction. The radial forearm free flap has proved a versatile and useful method in intraoral reconstruction and can be used together with a segment of radius as a composite flap. The technique of raising a segment of vascularized radius is described and its use in immediate reconstruction of the mandible at the time of resection illustrated in a series of 14 consecutive cases. There was one microvascular failure in this series and one postoperative death. The remaining 12 cases have had a successful outcome and show clinical union in the follow-up period varying from 11-36 months. There is evidence indicating that the bone maintains its viability even in the presence of preoperative or early postoperative radiotherapy.

Adult↗

PubMedDate not supplied

Reactive changes in the mandible in the presence of squamous cell carcinoma.

A series of 80 mandibles, which were removed as part of composite resections for primary intraoral squamous cell carcinoma, was examined. Of these, 58 were nonirradiated and 22 were previously irradiated. Several changes were observed in the nonirradiated mandible in response to invading tumor. Deposition of new bone was obvious on the periosteal and endosteal surfaces. Osteoclastic resorption of bone was prominent and there was replacement of hemopoietic marrow by fibrous tissue. By contrast, it was found in the irradiated specimens that osteoblastic activity was absent but that osteoclastic activity persisted. The hemopoietic marrow was replaced by fibrous tissue. The lack of osteoblastic activity was interpreted as being due to irradiation. The extent of these changes and their relationship to the invading tumor have implications for both surgeon and pathologist.

Carcinoma, Squamous Cell↗

PubMed1994

Effect of essential fatty acid deficiency on the fatty acid composition and arachidonic acid levels in rat maxillae and mandibles.

The fatty acid composition of total lipids and total phospholipids of maxillae and mandibles of rats fed an essential fatty acid-deficient (EFAD), marginally FAD (MEFAD), and a control diet was determined. Patterns typical of an EFA deficiency such as a decrease in the levels of linoleic acid and archidonic acid along with concomitant increase in the levels of palmitoleic acid, oleic acid, and 5,8,11-eicosatrienoic acid were observed in the EFAD groups. Concentrations of arachidonic acid were significantly lower in total lipids of mandibles and maxillae of rats in the EFAD, but not in the MEFAD rats, than those of the controls.

Animals↗

PubMed1987

Anterior displacement of the mandible for better exposure of the distal segment of the extracranial carotid artery.

Anterior displacement of the mandible (ADM) was performed in 34 patients undergoing surgery for malformations or atheromatous lesions of the distal segment of the extracranial internal carotid artery (ICA). This procedure greatly facilitates surgical access to the upper cervical region and has several advantages over mandibulotomy-mandibulectomy, namely: A shorter operating time, sparing of the inferior alveolar nerve and of the mandibular branch of cranial nerve VII, with no need for post-operative immobilization of the mandible. ADM permits the correction of ICA lesions extending as far as the first cervical vertebra. For lesions extending into the carotid canal ADM needs to be supplemented by various other procedures via the base of the skull.

Carotid Artery, External↗

PubMed1984

A physicomathematical approach to the structure of the mandible.

Classical methods of anatomical study and experimentation have reached an endpoint with respect to the advancement of our knowledge of certain aspects of bone, i.e. its mechanical properties, investigation of the constraints acting on bone and the organization of bone allowing resistance to such mechanical stress. Indeed, current knowledge is rather limited regarding bone as a material. Furthermore, bone from the cadaver cannot be considered a reliable source of study material since its physicochemical composition and mechanical properties are highly different from those of living bone. The types of experimentation used to date, although allowing to study the phenomena occurring on the surface of the bone, do not allow to evaluate those that occur within the bone without modification of its mechanical features. Finally, the number and complexity of the parameters to be taken into account in this respect largely supersede the possibilities of classical study techniques. Accordingly, new types of methodology are required to evaluate the many parameters involved, to perform the corresponding computations and resolve the great number of unknown variables. Such methodology must allow experimentation to be performed without modifying the object of study and to determine the phenomena occurring within the bone itself, i.e. the mandible. A method of computer assisted simulation of a physicomathematical model was used to analyse the structural properties of the mandible.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗

PubMed2000

Advancement of the mandible facilitates nasal breathing in human subjects sedated with midazolam.

PURPOSE: To determine how anterior advancement of the mandible (ADM) affects spontaneous breathing through the nasal route in healthy human volunteers sedated with intravenous midazolam. METHODS: In four subjects who exhibited nasal breathing during midazolam sedation (intravenous dose: 0.09+/-0.02 mg x kg(-1), mean +/- SD), we measured respiratory rate (RR), peak nasal inspiratory airflow rate (V(nIpeak)) peak nasal expiratory airflow rate (V(nEpeak), duty ratio (Ti/Ttot) and nasal resistance (Rn) before and after ADM. Nasal resistance was calculated by dividing the difference between nasal mask and oropharyngeal pressure by airflow rate at peak nasal inspiratory airflow. RESULTS: The RR, V(nIpeak), and V(nEpeak) increased following ADM (P<0.001, respectively). On the contrary, Ti/Ttot decreased after ADM (P<0.001). Consequently, ADM decreased Rn from 30.4+/-40.8 to 5.0+/-5.6 (cm H2O x l(-1) x sec(-1)) (mean +/- SD) (P<0.001). In these four subjects, no respiratory airflow was observed through the oral route before and after ADM. CONCLUSION: Advancement of the mandible decreases nasal resistance, thereby facilitating spontaneous breathing through the nasal route in normal humans sedated with midazolam.

Adult↗

PubMed1999

One-step resection and reconstruction of the mandible using computer-aided techniques--experimental and clinical results.

In patients with advanced oral cancer, a resection of the mandible continuity is often indicated. This new method presented here uses computer-aided design and manufacturing (CAD/CAM) for preoperative fabrication of individual mandibular prostheses and their corresponding resection templates in a direct fashion without the need for additional physical models. In this experimental application, a segment of a dried mandible was resected and replaced by a titanium prosthesis prefabricated by CAD/CAM. It was the aim of this investigation to verify the processing chain and its precision, i.e., the fit of an individual implant, such as this. Although this new technique offers fascinating opportunities, possible clinical drawbacks have to be taken into account.

Bone Screws↗

PubMed1999

[Skull and mandible. On Joseph Beuys' "ancient sled." Medical art history observation].

Few people are aware that Joseph Beuys (1921-1986), one of the most important artists at the end of the twentieth century, studied various aspects of the human skull. Beuys used teeth (especially molars), antlers, and horns as organically differentiated formations of solid substances of the viscerocranium, associating them in a very visual way with the "streaming circulation" principle. In addition, in his early drawings, in particular, Beuys replaced the lower jaw with a sledge. The artist has thus created interesting and strange constructions concerned with the structure of the jaw and the craniovertebral transition. Certain characteristic structural elements of sledges show a remarkable formal analogy to the ramus of mandible. The base of the body of mandible becomes a sliding surface, the iron runners of the sledge. Replacing the lower jaw with a sledge raises questions concerning movement and the effect of energy on the skull and on the earth. The artist's understanding of anatomy goes for beyond than that of normal medicine. It is formed by his thinking, his energy plan, and by his own theory of metamorphosis. With his skull and Urschlitten motif, Beuys makes us aware of the transitory layers of consciousness between life and death. "Head" and "sledge" are early forms of sculptural thinking in the work of Joseph Beuys.

Germany↗

PubMed2002

Tooth hardness increases with zinc-content in mandibles of young adult leaf-cutter ants.

A wide variety of arthropods and members of other phyla have elevated concentrations of Zn, Mn, other heavy metals and halogens in their jaws, leg claws, and other "tools" for interacting with the environment. While measured Zn concentrations reach 25% of dry mass in scorpion stings, concentrations are often lower than this and the enriched structures are not heavily biomineralized like vertebrate teeth and the radula of mollusks. For this reason, the degree to which the inorganic components of these structures modify their mechanical properties is in question. Here we address this problem by measuring hardness during the development of Zn accumulations in ant mandibles. We found that Zn is incorporated into the mandibular teeth of leaf-cutter ants during early adult life, reaching concentrations of about 16% of dry mass. We show that the hardness of the mandibular teeth increases nearly three-fold as the adults age and that hardness correlates with Zn content ( r=0.91). We suggest that young adults rarely cut leaves partly because their mandibles are not yet rich in Zn. Zinc enrichment (along with enrichment by other heavy metals and halogens) may play an unrecognized role in the behavioral ecology and evolution of a wide variety of invertebrates.

Animals↗

PubMed1996

CT findings in osteoradionecrosis of the mandible.

CT scans of ten patients in whom the diagnosis of mandibular osteoradionecrosis was proven pathologically or by clinical follow-up were reviewed. All ten patients had bony abnormalities (cortical interruptions and loss of spongiosa trabeculation) on the symptomatic side. These were predominantly seen in the body of the mandible (premolar and molar region, eight patients), in some of these cases extending into the retromolar triangle (two patients) or mandibular angle (two patients). In the remaining two patients the abnormalities were in the ramus and angle. The two patients treated with iridium implantation showed localized lingual-sided cortical destruction. Three patients had a pathological fracture. The cortical destruction was buccal-sided in two and both buccal- and lingual-sided in three of the other five patients. Contralateral bony abnormalities were present in four patients. Soft tissue thickening on the symptomatic side was seen in nine patients. As the bony abnormalities in mandibular osteoradionecrosis are often associated with a soft tissue mass, CT differentiation from tumor recurrence can be difficult. The association with cortical defects distant from the position of the original tumor (buccal surface or opposite side of mandible) should evoke the possibility of mandibular osteoradionecrosis.

Adult↗

PubMed1996

Malignant fibrous histiocytoma of the mandible.

We report a case of MFH of the mandible in a 16-year-old girl. The mandible is a rare location of MFH of bone, with only 21 cases described in the literature. Clinical, pathologic, and radiologic features are discussed, with special emphasis on the unusual pathologic and radiographic features.

Adolescent↗

PubMedDate not supplied

Misconceptions about mandible reduction procedures.

Mandible reduction procedures are currently very popular in Asian countries. But many misconceptions or differences in concepts about these procedures still exist, mainly because of preconceived ideas and restriction in communication. The author reviewed articles and found some misconceptions about these procedures. Also, the author added some opinions regarding new ideas about these procedures (i.e., minimal incision technique and botulinum toxin), as well as logical backgrounds of associated concepts. The intraoral approach is the safest and most effective procedure. The sagittal split ostectomy is the most important procedure for mandible reduction.

Asian People↗