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At least 1,387 records · Page 77Linked to original sources
PubMed1999

An investigation of the stress values on a tooth restored by amalgam.

The study was carried out in two stages: (1) MOD amalgam cavities were prepared on maxillary second premolars and three strain gauges were attached to the palatal surface of each tooth. The teeth were filled using amalgam with and without base material (glass-ionomer). Stresses occurred during the hardening phase and also through mastication and were measured by strain-gauge rosettes. (2) The stresses which occurred at the same points were calculated by the finite element method and compared with the values obtained experimentally. The highest stress values were observed when no base material was used.

Bicuspid↗
PubMed1999

Does chewing performance depend upon a specific masticatory pattern?

The purpose of this article is to review the literature concerning the ideal chewing pattern for best chewing performance. We conclude that at this time there is not one ideal chewing pattern which can be used clinically or in research to assess the health of the mastication apparatus nor to predict chewing performance. It is clear that human masticatory behaviour is one of the most complex human behaviours. Chewing is under the control of the central pattern generator located in the brain stem but is influenced by dental and temporomandibular joint morphology. The most important portion of the chewing cycle is the area entering and leaving the intercuspal position where gliding contacts occur. Maximal chewing capability will likely occur when the chewing pattern follows the dental anatomy unique to the individual. The chewing cycle appears to increase the lateral component of its movement when increased chewing efficiency is required. These situations include increased hardness or the size of bolus, the position of the bolus and the results of the proceeding chewing stroke. The chewing pattern for any one cycle is influenced by a number of factors, thus it is not surprising that the question of the ideal chewing pattern remains unresolved.

Dental Occlusion↗
PubMed1999

The contribution of mechanoreceptive neurones in the gingival tissues to the masticatory-parotid salivary reflex in man.

The masticatory-parotid salivary reflex has been studied in fully dentate subjects. Salivary flow was recorded by siting a modified Lashley cup over the orifice of the parotid duct on one side of the mouth. Subjects chewed on small pieces of silicone rubber for 1-min periods which resulted in a reflex secretion of parotid saliva. The secretion was greatest when the subject chewed on the same side of the mouth (ipsilateral) as the salivary flow was recorded. Less salivary flow resulted when the subjects chewed on the opposite side of the mouth (contralateral). Selected areas of the buccal or lingual gingival tissues were then anaesthetized on the side ipsilateral to the Lashley cup. Anaesthesia of the lingual and buccal gingival tissues together resulted in a reduction of salivary flow in response to similar chewing cycles. Anaesthesia of the lingual gingival tissues alone also resulted in a reduction of salivary flow, but anaesthesia of the buccal gingival tissues alone did not. During mastication it is likely that mechanoreceptors in the gingival tissues will be stimulated which may result in salivary flow. This requires further study as other mechanoreceptive neurones are also known to be involved in the masticatory-parotid salivary reflex.

Adult↗
PubMed2000

Measuring system for lip movements using two video trackers.

Movements of soft tissues surrounding the oral cavity, especially lips and cheeks, have a strong influence on mastication and phonetics. They also influence the relationship between a denture and its oral environment. The purpose of this study was to develop a three-dimensional measuring system for soft tissue movement. This system consisted of two video trackers placed stereographically and a computer. In addition, one video tracker was connected for measuring mandibular movements. The accuracy of this system was evaluated using computerized XYZ pulse stage. The resolution of this system was 0.10 x 0.10 x 0.10 mm, when the measurement was carried out in the area of the 24.0 (X) x 20.0 (Y) x 20.0 (Z) mm with a working distance of 500 mm and a frequency of 120 Hz. In the present study, the lip movements of a dentulous subject with mandibular movements during chewing peanuts were analysed using this system. The new system demonstrated its value for analysing soft tissue movement.

Adult↗
PubMed2001

Functional-rhythmical coupling of head and mandibular movements.

It is known that small head movements accompany the movements of the jaw during mastication; however, it is unknown whether these movements occur rhythmically and synchronously. The objective of this study was to determine whether there exists a functional coupling between the head and mandibular movements. Four healthy male adults (mean age 25.5) with normal occlusion and without TMD history were selected as subjects. Using the Trimet system, we measured tridimensionally both the movement of the head and the mandible by tracking upper and lower incisal points, respectively, during tapping movements with different opening range and frequency, then analysed the vertical component of these movements. The upper incisal point moved in opposite direction to the mandible in all tapping strokes in all subjects, during opening the head moved in a cranial direction and during closing in a caudal direction; the incidence rate for this concomitant movement was 98%, implying that the head moves periodically and rhythmically, as the mandible does. The cycle time of these coincident movements showed a correlation coefficient of 0.94. Moreover, the vertical range of head movement was within 10% of the jaw's movement. From these results we concluded that, at least during teeth tapping, the head moves in rhythmical coordination with mandibular movement.

Adult↗
PubMed2001

Coffee beans as a natural test food for the evaluation of the masticatory efficiency.

UNLABELLED: A lot of test foods have been used during this century to evaluate the masticatory ability of human subjects. Nevertheless, none has been universally admitted. If the test food by itself is of importance, attention should also be paid to its behaviour during the chewing test procedure. Therefore, we analysed step by step coffee beans through the processing of the chewing test and a dry sieving METHOD: The development of a compression test and a computer simulation have shown that groups of 11 coffee beans give satisfactory results and deserve to be used in mastication studies.

Coffee↗
PubMed2002

A calculation of stress distribution in metal-porcelain crowns by using three-dimensional finite element method.

The objective of this study was to calculate stress distribution in a maxillary second premolar tooth which occurred by the mastication force. The tooth model was crowned with Au-Pd alloy, Ni-Cr alloy and porcelain. A load of 450 N, at an angle of 45 degrees to the longitudinal axis was applied on the occlusal margin of the crown tooth. The tooth was assumed isotropic, homogenous, elastic and unsymmetrical. This numerical study was carried out using three-dimensional finite element models and calculation programs were prepared by the authors using FORTRAN 77. The distribution of compressive, tensile and shear stress were plotted for the dentine, dentine-metal and metal-porcelain interfaces. The highest stress values were observed when Ni-Cr alloy and porcelain was used.

Bicuspid↗
PubMed2002

Clinical relevance of a simple fragmentation model to evaluate human masticatory performance.

To explain the breakage process of food particles in human mastication, we propose a simple fragmentation model. To verify its clinical accuracy, a mechanical test with a sieving method and a natural test food (coffee) was performed on three groups of subjects. The values obtained permitted to demonstrate that the model could predict, at least qualitatively, the general trend of the experimental data, even for a very small group (two subjects). It also shows that the choice of the yielding factors used to calculate the masticatory index (MI) is relevant.

Coffee↗
PubMed2003

Validity and reliability of a newly developed method for evaluating masticatory function using discriminant analysis.

The objective of the study was to assess validity and reliability of a newly developed method for evaluating mixing ability of masticatory function. A two-coloured paraffin wax cube was used as a test food in the mixing ability test. Eleven full dentate and 33 denture wearers participated in the validity assessment. They were divided into three groups according to their dental state. Validity was assessed by the Spearman's coefficient of correlations between the mixing ability test and the sieving method used as a 'gold standard' test of the masticatory performance. The subjects were asked to masticate the test foods for 5, 7, 10, 15, 20 and 30 strokes in each test. Significant correlations (P < 0.001) were obtained in natural dentition group (r(s) = 0.66), in denture-natural dentition group (r(s) = 0.72) and in denture-denture group (r(s) = 0.56). In the reliability assessment, three full dentate subjects were asked to repeat the mixing ability test a number of times. The intraclass correlation coefficients were 0.94 in interexaminer consistency, 0.98 in intra-examiner consistency, 0.89 in test-retest consistency and 0.99 in measuring consistency. These results indicated that the mixing ability test had the validity and the reliability for evaluation of the masticatory performance.

Adult↗
PubMed2003

Functional magnetic resonance imaging of human jaw movements.

This study used functional magnetic resonance images (fMRI) to examine brain activity during clenching, gum chewing, and tapping tasks. It has been considered difficult to obtain sufficient fMRI data during jaw movement because the head motion associated with the jaw movements creates artifacts on the images. To avoid these artifacts, larger pixels were used, thus allowing some head motion of the subjects, and data from subjects where the heads were evaluated to have moved more than 0.5 mm were discarded. Further, all pixels obtained by fMRI were evaluated and pixels positively synchronized with the task, which were considered to show brain activity, were selected. Sufficient fMRI data was obtained from 30 experiments, 10 sets for each task. During the clenching and tapping tasks, the activated pixels were in the sensory, motor and pre-motor cortexes, and in the sensory and motor cortexes but not in the pre-motor cortex during the gum chewing task. There appears to be no significant differences between right- and left-hemispheres. It is conceivable that there are differences between voluntary jaw movements (clenching and tapping tasks) and mastication (gum chewing task) concerning the control of jaw movements.

Brain↗
PubMed2003

Influence of abrasion in clinical manifestation of human dental erosion.

The influence of abrasion from oral soft tissues on softened enamel lesion remineralization and erosion development was investigated. Using orange juice, softened enamel lesions were produced on 20 human premolars assigned randomly to 10 volunteers. Sections used as control and two test slabs were cut from each tooth. One of the two slabs from each tooth had an appliance built on it, which protected the lesion from abrasion. The two slabs (with/without appliance) were bonded to the palatal surfaces of upper right and left lateral incisor teeth of the participants who chewed sugar-free gum four times daily. After 28-day intra-oral exposure, mineral loss (Delta Z) and lesion depth (ld) in both control and test samples were quantified using transverse microradiography, and the data was analysed by paired t-test. Delta Z was significantly lower in lesions with appliance (protected), but higher in lesions without appliance (unprotected) when compared with control (unexposed). Similar pattern was observed with lesion depth. In unprotected slabs the lesions were abraded resulting in eroded enamel lesions. It was concluded that erosion observed clinically is the combined effect of demineralization of the tooth surface by an erosive agent and abrasion of the demineralized surface by surrounding oral soft tissues and through food mastication. Abrasion from oral soft tissues can contribute to site-specificity of dental erosion.

Adult↗
PubMed2003

Occlusal phase of gum-chewing strokes.

The occlusal phase of chewing is especially interesting because food particles are being pulverized in this phase. For efficient chewing the upper and lower teeth must come together in a congruent fashion with less variation than in other phases. To examine this expectation the chewing motions of 28 women were recorded optoelectrically, and their frontal and sagittal angles of the closing and following opening strokes were measured at 3.0 mm (3-D linear distance) of opening. Closing strokes were more stable than opening strokes. The frontal angle was correlated with the sagittal angle during closing. The opening and closing sagittal angles were moderately correlated, and the opening and closing frontal angles were negatively correlated at the intersubject level. No direct association was found between the closing strokes and following opening strokes at the intra-subject level. These results suggest that closing strokes are more stable than opening strokes, resulting in efficient mastication.

Adult↗
PubMed2003

Simple disc reshaping surgery for internal derangement of the temporomandibular joint: 5-year follow-up results.

PURPOSE: The goal of this study was to evaluate the clinical results of simple disc reshaping (SDR) surgery alone for treating dysfunctional internal derangement of the temporomandibular joint. PATIENTS AND METHODS: Eleven patients with symptomatic unilateral anterior disc displacement with disc deformation were treated using reshaping of the inferior surface of the disc without disc repositioning. This was performed as an open-joint procedure. All patients were evaluated clinically for joint pain and jaw motion 5 years after surgery. Structural changes of the joint tissues such as disc displacement and deformation were evaluated using magnetic resonance imaging. The postoperative results were compared with preoperative findings. RESULTS: Joint pain during mastication or opening was reported by all patients before surgery. In 10 of 11 patients (91%), the joint pain disappeared postoperatively. Preoperatively, all 11 patients had limitation of mouth opening: the mean opening was 24.9 mm (standard deviation [SD], 4.13 mm). Postoperatively, the mean opening increased to 43.0 mm (SD, 3.00 mm). Based on the preoperative magnetic resonance imaging, all cases were diagnosed as anterior disc displacement without reduction and with disc deformation. Five years postoperatively, the disc configuration had maintained the reshaped status with decreased thickness of the deformed disc in 5 patients, and was changed to an almost normal biconcave shape in 3 patients. In the remaining 3 patients, the disc was unchanged from its preoperative condition. The position of the disc was unchanged in 8 patients, and in 3 patients disc position improved to near normal. CONCLUSION: The 5-year follow-up results suggest that SDR is a stable and favorable surgical procedure. Successful outcomes were attained in 91% of the patients.

Adult↗
PubMed2003

A biologic model for assessment of osseous strain patterns and plating systems in the human maxilla.

PURPOSE: This study was conducted to examine a biomechanical model and to help answer fundamental questions that relate to rigid plate fixation in the maxilla. Specifically, we sought to elucidate the principal strain patterns generated in the maxilla secondary to masticatory forces as well as the amount of permanent deformational changes incurred due to these loading forces. MATERIALS AND METHODS: Cadaveric heads with the mandible removed were defleshed and placed in a 2-part testing rig to hold and position the skull for testing in a standard material testing system. Rosette strain gages were attached at predefined points on the skull, and an Instron machine was used to load the skull through the loading port on the tray. A Le Fort I osteotomy was then performed on the skull, and a Walter Lorenz Ultra-Micro plating system was applied by a surgeon to reconnect the upper jaw. A 2-mm gap was left at the line of the osteotomy, and a transducer was attached to measure closure of the gap. Again the skull was loaded with the Instron (Canton, MA) machine. RESULTS: The results indicate a linear relationship exists with both maximum (tensile) and minimum (compressive) strain patterns relative to incremental load placement on the intact maxilla. The strain patterns after the Le Fort I osteotomy and plating were different and less linear. The differential variable reluctance transducer data showed a low rate of closure or transient increase in the gap at low loads (0 to 15 kilopond [kp] range) and a steeper slope of closure during high loads (15 to 60 kp range). It is also evident that axial loading forces cause permanent deformation and failure of osseous plating systems predominantly through bending. CONCLUSIONS: This model provides a foundation of knowledge regarding biomechanical strains in the maxilla subjected to static compressive loads in the force range of mastication. In addition, it serves as a comparative reference to assess rigidity of various craniofacial plating systems and to validate proposed standardized synthetic models. With the advent of increasingly precise surgery and new plating systems, this model can be used to help guide placement and design of plating systems; thereby allowing for ideal stabilization and optimizing surgical outcome.

Aged↗
PubMed2003

Evaluation of long-term stability in second metatarsal reconstruction of the temporomandibular joint.

PURPOSE: Our goal was to evaluate long-term stability and function of 5 condyles reconstructed with vascularized second metatarsal joint grafts. MATERIALS AND METHODS: Four patients were reconstructed with 5 vascularized metatarsal grafts. These reconstructed joints were then followed for an average of 12.5 years. These patients represent the entire series and were all successfully contacted and reevaluated for this article. Measures of opening, deviation, excursion, symmetry, and clinical symptoms relating to the reconstructed joints are evaluated. RESULTS: Mean preoperative interincisal aperture was 12 mm, and postoperative aperture 48.5 mm. Three unilaterally treated patients had lateral excursion with opening. The mean deflection was 4.3 mm toward the operated side. Lateral and protrusive movements were limited in reconstructed joints, but up to 3 mm of protrusion was shown at 12.5 years. Subjectively, all patients rated their function as acceptable and were able to occlude and masticate without difficulty. Symmetry at rest was improved by surgery. CONCLUSIONS: Vascularized metatarsal joints represent a potentially suitable long-term substitute for condylar reconstruction. This limited series shows the technical viability of the procedure. A larger series may be warranted to compare this promising technique with conventional methods of temporomandibular joint reconstruction.

Adolescent↗
PubMed1999

Coexisting congenital sublingual dermoid and bronchogenic cyst.

A congenital dermoid together with a bronchogenic cyst at the base of the tongue is extremely rare. We describe a 5-year-old boy who presented with an enlarged anterior segment of mandible, slight swelling of the left submandibular region, and a large swelling of the floor of the mouth that was displacing the tongue posteriorly. Both cysts were successfully excised and the boy made an uncomplicated recovery. Occlusion and mastication returned to normal and his speech improved remarkably.

Bronchogenic Cyst↗
PubMed2002

Factors influencing the therapeutic effect of muscle afferent block for oromandibular dystonia and dyskinesia: implications for their distinct pathophysiology.

Oromandibular dystonia (OMD) is a focal dystonia manifested by involuntary masticatory and/or lingual muscle contractions. Muscle afferent block (MAB) by injecting anaesthetic and alcohol intramuscularly is recently used for the treatment of OMD. To study the factors affecting the efficacy of MAB, 44 patients with OMD were treated by local injection of lidocaine and ethanol. They were divided into four groups (spastic, rhythmic, dyskinetic, and task-specific) according to the pattern of incisal movement and involuntary contraction. We used a clinical scaling protocol in terms of four parameters (mastication, speech, pain, and discomfort) to evaluate the change of symptoms objectively. The relationship of improvement in clinical scores with various parameters was assessed statistically. The overall objective improvement was 60.2 +/- 29.5%. The scores decreased significantly (P<0.0001, paired t-test) after MAB. The maximal incisal velocity significantly correlated inversely with the clinical improvement, and MAB was particularly effective for spastic contraction. Dyskinetic and rhythmic groups showed variable and significantly less improvements than the spastic group. MAB is highly effective for OMD, but not for the patients with dyskinetic symptoms. The jaw movement pattern is an important factor for predicting the outcome. The difference in the response to MAB in OMD and oral and/or orofacial dyskinesia suggests the distinct pathophysiology between the two.

Adolescent↗
PubMed2000

Development of a static simulator of the mandible.

Our aim was to build and assess a static mandibular simulator capable of reproducing various masticatory exercises as closely as possible to physiological situations. Unlike existing devices that reproduce a small number of exercises and of muscular bundles, our simulator is able to reproduce all types of effort in the sagittal plane and integrates eleven muscular groups considered by the majority of authors as being the most important in mastication. The value of our simulator arises from its ability to replicate the external forces (including muscular traction, intra-articular reaction and resultant forces applied to the mandible) as determined in vivo during previous studies. The importance of such a versatile simulator, in addition to enabling study of the mechanical behaviour of the mandible, is that it greatly enhances evaluation of a possible mathematical model by means of finite element analysis. Stages of the development and evaluation of this device are described.

Computer Simulation↗