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At least 1,333 records · Page 74Linked to original sources
PubMed2004

Combined finite-element and rigid-body analysis of human jaw joint dynamics.

The jaw joint plays a crucial role in human mastication. It acts as a guidance for jaw movements and as a fulcrum for force generation. The joint is subjected to loading which causes tensions and deformations in its cartilaginous structures. These are assumed to be a major determinant for development, maintenance and also degeneration of the joint. To analyze the distribution of tensions and deformations in the cartilaginous structures of the jaw joint during jaw movement, a dynamical model of the human masticatory system has been constructed. Its movements are controlled by muscle activation. The articular cartilage layers and articular disc were included as finite-element (FE) models. As this combination of rigid-body and FE modeling had not been applied to musculoskeletal systems yet, its benefits and limitations were assessed by simulating both unloaded and loaded jaw movements. It was demonstrated that joint loads increase with muscle activation, irrespective of the external loads. With increasing joint load, the size of the stressed area of the articular surfaces was enlarged, whereas the peak stresses were much less affected. The results suggest that the articular disc enables distribution of local contact stresses over a much wider area of the very incongruent articular surfaces by transforming compressive principal stress into shear stress.

Bite Force↗
PubMed2005

Mandibular stiffness in humans: numerical predictions.

The chin is a feature unique to humans. This study evaluates the effect of mandibular symphyseal design on biomechanical masticatory effectiveness as determined by structural stiffness and stress developed under flexural and torsional loading. A simple model of three symphyseal shapes (chin, flat symphysis and lingual buttress), was built to represent human, Neanderthal and higher primate symphyses and these were subjected to wishboning and torsional forces. Additionally, an anatomically detailed reconstruction was made of the CT scan of an actual human mandible, which was then also morphed into a chinless model. The results of a 3-D finite element analysis show firstly, that none of the three different symphyseal shapes is biomechanically more advantageous than the others for the given loading condition. Secondly, we show in a CT-derived model, that the presence of a chin does not confer significantly improved stiffness to torsional or flexural loading. These results indicate that the acquisition of a chin in modern humans is not related to the functional demands placed upon the mandible during mastication, but suggest that it may have developed in response to other biomechanical demands.

Animals↗
PubMed2004

Chronic neck pain and masticatory dysfunction.

Chronic nonspecific neck pain is a common problem in rheumatology and may resist conventional treatment. Pathophysiological links exist between the cervical spine and masticatory system. Occlusal disorders may cause neck pain and may respond to dental treatment. The estimated prevalence of occlusal disorders is about 45%, with half the cases being due to functional factors. Minor repeated masticatory dysfunction (MD) with craniocervical asymmetry is the most common clinical picture. The pain is usually located in the suboccipital region and refractory to conventional treatment. The time pattern may be suggestive, with nocturnal arousals or triggering by temporomandibular movements. MD should be strongly suspected in patients with at least two of the following: history of treated or untreated MD, unilateral temporomandibular joint pain and clicking, lateral deviation during mouth opening, and limitation of mouth opening (less than three fingerbreadths). Rheumatologists should consider MD among causes of neck pain, most notably in patients with abnormal craniocervical posture, signs linking the neck pain to mastication, and clinical manifestations of MD. Evidence suggesting that MD may cause neck pain has been published. However, studies are needed to determine whether treatment of MD can relieve neck pain.

Facial Muscles↗
PubMed2004

Health benefits of saliva: a review.

OBJECTIVE: The aim is to present a review of the literature on human saliva composition, flow rates and some of the health benefits of saliva, with emphasis on studies from our laboratory that have looked at effects of age and age-related diseases on saliva output and composition. DATA: Saliva influences oral health both through its non-specific physico-chemical properties, as well as through more specific effects. The proline-rich proteins, statherin and the histatins are salivary proteins that influence calcium phosphate chemistry, initial plaque formation and candida infection. Increases or decreases in mastication may affect saliva output. Our cross-sectional studies of saliva in a large population-based study cohort (N=1130) indicate that there is an age-related decline in saliva output for unstimulated whole, stimulated parotid, unstimulated submandibular/sublingual and stimulated submandibular/sublingual saliva, as well as some compositional alterations in anti-microbial and other proteins. Some of these alterations also appear to be specific for certain age-related medical conditions, such as diabetes mellitus. CONCLUSIONS: These studies and data presented confirm the importance of saliva in maintaining a healthy oral environment; the practitioner is encouraged to consider saliva output and medical conditions that may compromise it as part of routine dental treatment planning.

Adult↗
PubMed2006

Mandibular mechanics following osteotomy and appliance placement II: Bone strain on the body and condylar neck.

PURPOSE: The purpose of this investigation was to determine if the mechanical environment of the mandible is changed by osteotomy and fixation, as assessed by the measurement of bone strain on the condylar neck and mandibular corpus. MATERIALS AND METHODS: Immediately following unilateral mandibular osteotomy and distractor placement, strain gauges were attached directly to the corpus and condylar neck in a sample of domestic pigs. Bone strains were recorded during mastication and muscle stimulation. Comparisons of principal strain magnitudes and orientations were made between sides and between the osteotomy sample and a control database. RESULTS: The animals preferred to chew on the non-osteotomy side. Corpus strains were higher for osteotomy-side chewing but were comparable to the control database, regardless of chewing side. For the condyle, compared with the control database and the non-osteotomy side, the osteotomy side was underloaded in compression. Furthermore, the orientation of compressive strain was highly variable and more horizontally oriented than that of control and non-osteotomy condyles. Stimulation of the masseter and medial pterygoid loaded the mandible to normal levels. CONCLUSION: Masticatory behavior was altered, probably as a combined result of disruption of the occlusion, changes in muscle recruitment, and probable loss of sensory feedback. However, neither these changes nor damage to the muscles explain the decrease and reorientation of compressive strain on the condylar neck. Alternatively, the modified strain pattern could have arisen from positional instability of the proximal bone fragment.

Animals↗
PubMed2006

Long-term results of free radial forearm flap used for oral reconstruction: functional and histological evaluation.

PURPOSE: The aim of this study was to evaluate the radial forearm flap with regard to recovery of sensory function, general performance status, cutaneous blood flow and histological observations. PATIENTS AND METHODS: Thirty patients (23 male and 7 female) with oral carcinoma underwent immediate reconstruction with radial forearm flap after ablative surgery and returned for evaluation. Interviews were conducted to assess the degree of articulation and mastication. RESULTS: Sensory function tests suggested the restoration of cutaneous sensibility of the forearm flap. Histological findings indicated mucosa-like changes of flaps about 10 months after reconstruction. The clarity of conversation recovered favorably in most patients. However, the degree of recovery was generally related to the time after surgery. CONCLUSION: The radial forearm flap is a unique flap with specific characters that allowed for best available functional reconstruction of the oral cavity in terms of restoration of sensation, performance, and histological changes to adapt to the new oral environment.

Adult↗
PubMed2005

Excitatory GABAergic synaptic potentials in the mesencephalic trigeminal nucleus of adult rat in vitro.

The mesencephalic trigeminal nucleus (MesV) contains the somata of primary afferent neurons innervating masticatory muscle spindles and the periodontal membrane. MesV afferent somata are unique in receiving synaptic inputs. Intracellular recordings in coronal pontine slices from adult rats were made from MesV neurons identified by having Cs-sensitive inward rectification and pseudounipolar morphology. Stimuli near the MesV evoked either a cluster of action potentials superimposed on a postsynaptic potential (PSP) or an antidromic spike at resting membrane potential (RMP). Membrane hyperpolarization revealed that each cluster of action potentials consisted of an antidromic spike and a subsequent PSP. Evoked PSPs in slices and miniature postsynaptic currents (mPSCs) recorded using whole-cell patch in dissociated MesV neurons were resistant to glutamate antagonists and strychnine but were reversibly abolished by 40 microM bicuculline. Superfusion of 1-10 mM GABA decreased input resistance and depolarized the membrane. Reversal potentials for evoked PSPs and GABA-induced depolarizations were similar and close to that for mPSCs which matched the Cl- equilibrium potential. Thus activation of synapses on MesV somata evokes GABAergic PSPs that generate action potentials at RMP in the adult. These data also indicate that primary afferent MesV neurons can act as interneurons in the central control of mastication.

Action Potentials↗
PubMed2006

Concomitant chemo-radio-immunotherapy has a lethal therapeutic effect on tongue carcinomas independent of the clinical stage and histological characteristics of the tumor.

We examined the effect of concomitant chemo-radio-immunotherapy on 80 patients with tongue carcinoma. Disappearance of the tumor without recurrence was observed in 21 patients (38.9%) in intravenous infusion chemotherapy group (A) and in 20 patients (76.9%) in intra-arterial infusion chemotherapy group (B) (P<0.005). A total of 41 patients (51.3%) were free from the tumor after the combined therapy. Along with the good therapeutic effect, oral function was preserved with minimal impairment of speech and mastication. Tumor stage, the mode of tumor cell invasion and tumor cell differentiation were not correlated with the therapeutic effect. In addition, the expression of p53, p21(Cip1/WAF1) and proliferating cell nuclear antigen did not differ between the patients with lethal and non-lethal effects. The 5-year-survival rate was 56.8% in Group A, 76.9% in Group B and 59.6% overall. Thus, combined chemo-radio-immunotherapy, especially intra-arterial infusion, may bring a universal therapeutic effect in tongue carcinoma regardless of the tumor stage and the expression of cell phase-regulating proteins.

Aged↗
PubMed2006

Oral behavior from food intake until terminal swallow.

We analyzed oral behavior from food intake until terminal swallow for mastication and swallowing under a freely eating condition with a natural food. Measurements, including movement of the mandible and tongue, the size of the gape, different sequences involved in the oral aspect of the swallowing action, and bolus size and movement were carried out in five "freely eating subjects" using videofluorography. During food intake, the tongue moved forwards and backwards to introduce food into the mouth, to compress the food against the hard palate, and to transport food to the occlusal surface of the molar teeth. Most of the food was swallowed in the first swallow, and any residual food was aggregated by the tongue into a bolus and then swallowed in the last swallow. These findings suggest that 1) tongue manipulation plays an important role in recognizing and evaluating the volume of bite taken, 2) the intra-oral compression of food has a role in the recognition of food texture, 3) stage I transport is closely bound to the texture recognition process, 4) humans need at least two swallows, even with one bite of food, when ingesting food freely, and 5) the duration time of the oral stage of swallowing may depend on the bolus volume and be longer for smaller volumes unlike those measured under the command swallow.

Adult↗
PubMed2006

Masticatory and swallowing threshold performances with conventional and implant-supported prostheses after mandibular fibula free-flap reconstruction.

STATEMENT OF PROBLEM: Significant strides in microvascular surgical techniques allow predictable restoration of bony and soft tissue orofacial defects. In combination with prosthetic rehabilitation, varying degrees of improvement in esthetics, speech intelligibility, and swallowing have been noted; however, the relative impact of conventional and implant-supported prostheses on restoration of masticatory function are not known. PURPOSE: The purpose of this study was to determine whether conventional or implant-supported dental prostheses and current surgical reconstructive procedures restore patients' masticatory function to presurgical levels. MATERIAL AND METHODS: Of the 46 subjects enrolled in this study, 23 (7 edentulous and 16 partially dentate) completed conventional prosthesis (CP) treatment and masticatory evaluation, and of these, 15 (3 edentulous and 12 partially dentate) completed treatment and evaluation with an implant-supported prosthesis (IP). Standardized masticatory performance tests with peanuts and carrots as the test food were made on the defect and nondefect sides. Tests of swallowing threshold performance were made with carrots as the test food. Statistical analysis included repeated-measures analysis of variance (ANOVA) with post hoc Tukey HSD tests (alpha=.05). RESULTS: Masticatory function at entry was markedly compromised. Further performance declines were noted following surgery (PS) on both the defect and nondefect sides. Restoration with CP and IP produced improvements (significant for defect side only, P<.05) in performance over the PS interval and were not significantly different from performances at entry prior to surgery. In addition, the performance on the defect side with the IP was significantly greater than the performance with the CP (P<.001). CONCLUSION: Impairment in masticatory ability remains following free-flap reconstruction prior to prosthetic rehabilitation. Both CP and IP may provide improved masticatory ability, permitting patients to regain the functional level they possessed prior to surgical intervention. The IP may contribute to greater support and stability of the prosthesis, resulting in increased use for mastication and superior performance on the defect side compared to the CP.

Bone Transplantation↗
PubMed1984

Implications of the failure rates of bonded brackets and eyelets: a clinical study.

A clinical study of the rate of failure of bonded brackets and eyelets on primary molars was undertaken. Two groups of patients (one bonded contralaterally and the other at random) were studied for 12 to 17 months. The data support the hypothesis that one major cause of bond failure is the force of occlusion during mastication. On the basis of this finding, several clinical applications are suggested. These include rotation of second premolars, closure of extraction spaces, and the management of limited treatment of lower incisors in the presence of deep, traumatic overbite.

Bite Force↗
PubMed2001

The effect of food consistency and dehydration on reflex parotid and submandibular salivary secretion in conscious rats.

Changes in salivary secretion with different consistency of diet and dehydration were studied in male Wistar rats under unrestricted conditions. To measure the salivary secretion, a stop-flow method was used. There was little unstimulated salivary secretion from the parotid and submandibular glands, but eating solid, powdered, and liquid diets induced parotid and submandibular saliva. There was no significant change in the volume and flow rate of saliva in bilateral parotid glands during the eating of solid diets. The solid and powdered diets induced significantly more salivary secretion from the parotid gland than did the liquid. The salivary flow rate with solid diets was significantly greater from the parotid gland than from the submandibular. On the other hand, the salivary flow rate with the liquid diet was significantly smaller from the parotid gland than from the submandibular. Appreciable amounts of submandibular saliva, but little parotid saliva were secreted during grooming. Clearly, parotid and submandibular saliva have different roles in the rat. When injected intraperitoneally with 1.5 M NaCl solution or water-deprived for 24 h, rats took longer to eat the solid diets, and had increased salivary volume and decreased flow rate from the parotid gland. These results indicate that the moisture content of the diet and the dryness of the mouth alters the volume of parotid saliva secreted in rats and show that parotid saliva plays an important part in mastication and swallowing.

Animals↗
PubMed2002

The induction of c-fos mRNA expression by mechanical stress in human periodontal ligament cells.

The periodontal ligament is subjected to mechanical loading during occlusion and mastication. Although internuclear transcription factors are associated with the regulatory pathway that converts these extracellular mechanical stimuli into a cellular response, there are no reports on these in human periodontal ligament fibroblasts. In this study, the amounts of c-fos mRNA in human periodontal ligament fibroblasts were investigated shortly after subjecting them to a cyclic tension force in vitro. The mRNA of alkaline phosphatase and the matrix proteins type I collagen, type III collagen, matrix Gla-protein, osteonectin, osteopontin, and osteocalcin were also examined. A significant, rapid, transient increase in c-fos mRNA was detected, which peaked 30 min after the application of mechanical force. However, there was no significant change in the mRNA for alkaline phosphatase or the matrix proteins. These results provide evidence that periodontal ligament fibroblasts and c-fos may play a critical part in the response of periodontal tissue to mechanical stimulation.

1-Carboxyglutamic Acid↗
PubMed1997

Characterization of brux-like movements in the laboratory rat by optoelectronic mandibular tracking and electromyographic techniques.

High-resolution optoelectronic mandibular tracking and fine-wire electromyographic (EMG) data from the anterior temporalis muscles of laboratory rats (Rattus norvegicus) were collected during mastication (chewing) and bruxing/thegosis (grinding sharpening of teeth) in order to test for task-related activity patterns of the anterior temporalis. Analyses of the collected data revealed that masticatory and bruxing/thegosis cycles displayed significantly different patterns of movement trajectories, displacement, duration, velocity, and acceleration in all three spatial dimensions (frontal vertical, frontal horizontal and sagittal horizontal). Activity patterns in the anterior temporalis during masticatory and bruxing/thegosis behaviours were also significantly different from each other. High-resolution analyses revealed that the masticatory cycle had both opening-burst and closing-burst phasic patterns of anterior temporalis activity while the bruxing/thegosis cycle displayed only opening-burst phasic patterns. The opening- and closing-burst attributes of anterior temporalis phasic activity patterns in relation to physiological centric occlusion also revealed significant differences between masticatory and bruxing/thegosis behaviours. These data demonstrate that the anterior temporalis muscle of the laboratory rat does indeed display task-related activity patterns depending upon the manifested oral behaviour. The task-related shifts of EMG patterns in the anterior temporalis between masticatory bruxing/thegosis behaviours in the same animal suggests a complex neurophysiological substrate that coordinates the three-dimensional expression of phasic activity patterns in the muscle. The radically different nature of masticatory and bruxing/thegosis cycles and their associated EMG patterns in the anterior temporalis suggest the possible existence of a bruxing/thegosis pattern generator in addition to the masticatory one. Careful, high-resolution analyses of these rat behaviours by combined optoelectronic/EMG techniques suggest that the rat model for human bruxism may prove useful in future studies.

Animals↗
PubMed1995

Masseter muscle activity in denture wearers with superior and poor masticatory performance.

A cross-sectional study tested the hypothesis that denture wearers with superior and poor chewing ability use similar masseter muscle effort and biting forces during mastication. Masticatory performance tests on the preferred chewing side and swallowing threshold tests were conducted with peanuts and carrots in 70 denture wearers, 35 with superior (SP) (mean 46.3%) and 35 with poor (PP) (mean 30.7%) masticatory performance. Right and left masseter muscle electromyographic (EMG) activity was recorded during the masticatory tests and peak bite force during chewing was estimated from the bite force--EMG ratios on guided maximal biting trials. Bite force under maximal pressure did not differ significantly between the two groups. Neither the total mean EMG activity of the preferred and nonpreferred side masseter muscles nor the mean peak biting forces exerted by the two groups differed significantly (p > 0.05). This was true when denture wearers restricted chewing to their preferred side for a given number of strokes or chewed the test food freely until ready to swallow. The only significant differences (p < 0.05) were evident in the ratios of the preferred to nonpreferred side masseter EMG activity during chewing. The ratios were 1.2 for peanuts and 1.3 for carrots in the SP group compared to 1.8 for both foods in the PP group. Similar patterns of bilateral activity in the SP group and unilateral activity in the PP group were evident for the swallowing threshold tests. The results indicated that application of more equivalent force by the right and left masseter muscles during unilateral chewing is consistent with improved chewing ability in denture wearers.

Adult↗
PubMed1975

The function of the disc of the temporomandibular joint.

A study of the structure of the discs of the temporomandibular joints of three mammals showed marked differences among them. Since the animals selected had different basic patterns of mastication, it may be that each disc has become modified to different functions in different mammals.

Animals↗
PubMed1978

Clinical comparison of masticatory performance and electromyographic activity of patients with complete dentures, overdentures, and natural teeth.

In this study, which is the first of its kind, it has been shown that overdenture patients, when compared to complete denture patients, while chewing a test food for a constant number of strokes, expended an equivalent amount of muscle effort, chewed more slowly and efficiently, and evidenced significantly better masticatory performance by producing an increased volume of fine test food particles. These findings provide a sound justification for the extra effort required to retain some natural teeth to provide overdenture services to patients. The fact that patients can masticate food more efficiently with overdentures than with complete dentures justifies the increased cost and time involved in their construction. The longitudinal effects that overdentures have on the basic physiopathologic processed involved in the progression of ridge resorption and the advantages of maintaining periodontal proprioception also should be studied.

Adult↗