Comparison of particle-size distributions determined by optical scanning and by sieving in the assessment of masticatory performance

Aim of this study was to introduce a feasible and valid technique for the assessment of masticatory performance that is comparable to the standard sieving method. Twenty-one chewing samples (Optosil) comminuted by healthy dentate adults were analysed with a sieving and scanning method. Scanning was performed using a conventional flatbed scanner (1200dpi). All scanned images underwent image analysis (ImageJ), which yielded descriptive parameters such as area, best-fitting ellipse for each particle. Of the 2D-image, a volume was estimated for each particle, which was converted into a weight. To receive a discrete distribution of particle sizes comparable to sieving, five chewing samples were used to calculate a size-dependent area-volume-conversion factor. The sieving procedure was carried out with a stack of 10 sieves, and the retained particles per sieve were weighed. The cumulated weights yielded by either method were curve-fitted with the Rosin-Rammler distribution to determine the median particle size x(50) . The Rosin-Rammler distributions for sieving and scanning resemble each other. The distributions show a high correlation (0·919-1·0, n= 21, P<0·01, Pearson's correlation coefficient). The median particle sizes vary between 3·83 and 4·77mm (mean: 4·31) for scanning and 3·53 and 4·55mm (mean: 4·21) for sieving. On average, scanning overestimates the x(50) values by 2·4%. A modified Bland-Altman plot reveals that 95% of the x(50) values fall within 10% of the average x(50) . The scanning method is a valid, simple and feasible method to determine masticatory performance.

Clinical relevance of surface EMG of the masticatory muscles. (Part 1): Resting activity, maximal and submaximal voluntary contraction, symmetry of EMG activity

Based on a comprehensive computerized literature search supplemented by a specific manual search of the literature, the present review article focuses on concrete aspects of the application of surface electromyography (EMG) for evaluation of the masticatory muscles in general and of the masseter and anterior temporal muscles in particular, and presents the current base of knowledge on the clinical relevance of surface EMG in dental applications. In the first stage of the review, publications from the year 2000 or later reporting the results of controlled clinical trials (randomized as far as available) of patients with craniomandibular or temporomandibular disorders (TMD) were analyzed. Data from the selected publications were systematically compiled and divided into subject areas as follows: Resting activity, maximal and sub-maximal voluntary contraction, symmetry of EMG activity, and fatigue effects; EMG activity during mastication, factors (including pain) that affect EMG activity, and the impact of adjusting static and dynamic occlusal relationships; Effects of occlusal splints and other occlusal treatments. Surface electromyography is in principle a suitable tool for neuromuscular function analysis in the field of dentistry. If used according to the specific recommendations and in conjunction with a thorough and conscientious clinical history and physical examination, surface EMG measurements can provide objective, documentable, valid, and reproducible data on the functional condition of the masticatory muscles of an individual patient.

Muscle and joint forces under variable equilibrium states of the mandible

It is well established that subjects without molars have reduced ability to comminute foods. However, epidemiological studies have indicated that the masticatory system is able to functionally adapt to the absence of posterior teeth. This supports the shortened dental arch concept which, as a prosthetic option, recommends no replacement of missing molars. Biomechanical modeling, however, indicates that using more anterior teeth will result in a larger temporomandibular joint load per unit of bite force. In contrast, changing bite from incisor to molar position increases the maximum possible bite force and reduces joint loads. There have been few attempts, however, to determine realistic joint loads and corresponding muscular effort during generation of occlusal forces similar to those used during chewing with intact or shortened dental arches. Therefore, joint and cumulative muscle loads generated by vertical bite forces of submaximum magnitude moving from canine to molar region, were calculated. Calculations were based on intraoral measurement of the feedback-controlled resultant bite force, simultaneous electromyograms, individual geometrical data of the skull, lines of action, and physiological cross-sectional areas of all jaw muscles. Compared to premolar and canine biting, bilateral and unilateral molar bites reduced cumulative muscle and joint loads in a range from 14% to 33% and 25% to 53%, respectively. During unilateral molar bites, the ipsilateral joints and contralateral muscles were about 20% less loaded than the opposing ones. In conclusion, unilateral or bilateral molar biting at chewing-like force ranges caused the least muscle and joint loading.

Influence of neck rotation and neck lateroflexion on mandibular equilibrium

Neuromuscular interaction between neck and jaw muscles has been reported in several studies. However, the influence of experimentally modified posture of the neck on jaw muscle activity during isometric biting was not investigated so far. The aim of the present study was to test by the aid of simultaneous electromyographic and intraoral bite force measurements whether neck rotation and lateroflexion, in contrast to a straightforward neck position, change the isometric cocontraction patterns of masticatory muscles under identical submaximum bite forces of 50-200 N. Electric muscle activity of all masticatory muscles and changes of the reduction point (RP) of the resultant bite force vectors were examined. An anteroposterior displacement of the RPs could be observed for the rotated and lateroflexed neck position in comparison with the straightforward position. On the other hand, the results revealed no significant differences between bilateral muscle activation under the different test conditions. These findings suggest a force transmission between the neck and the masticatory system, but no essential activity changes in the masticatory muscles under short time posture modification of the neck.

Surface electromyography of the masticatory muscles for application in dental practice. Current evidence and future developments

On the basis of well-founded clinical evaluations and taking into account special methodological recommendations, surface electromyography (EMG) enables the acquisition of valid and reliable quantitative data on the functional condition of the masticatory muscles as a "neuromuscular functional analysis". On the basis of a current review of the literature, surface EMG appears to be able to deliver additional diagnostic and therapy-relevant information. Meaningful EMG data can be gained regarding resting activity, maximum muscle activation, frequency spectrum under various loading conditions, as well as bilateral symmetry of the contraction behavior of the jaw muscles. With these parameters--completed by kinematic information on movements of the mandible--it appears to be possible under clinical conditions to assess (a) the neuromuscular chewing performance after prosthetic reconstructions, (b) to record the influence of pain on the neuromuscular system, and (c) to document the individual efffect of therapeutic interventions on temporomandibular disorders.

Is there a superiority of multimodal as opposed to simple therapy in patients with temporomandibular disorders? A qualitative systematic review of the literature

BACKGROUND

Pain is the most common motivation for patients with temporomandibular disorders (TMDs) to seek care. Therapeutic options range from patient education to joint surgery.

OBJECTIVES

To conduct a systematic review of articles reporting on simple and multimodal management strategies in TMD patients. 'Simple therapy' was defined as care provided by a dentist, without using technical dental interventions, whereas 'multimodal' refers to at least two different modalities. We followed the null hypothesis of no difference between these two approaches.

MATERIAL AND METHODS

A systematic search was carried out in the following databases: Ovid Medline (1966-2006), Cochrane Library (Issue 3/2006), and Science Citation Index (1945-2006). Subsequently, the reference lists of the identified articles were searched to find additional pertinent publications. We divided the study reports according to the main presenting symptom: (1) disc displacement without reduction, with pain; (2) TMD pain, without major psychological symptoms; and (3) TMD pain, with major psychological symptoms.

RESULTS

Eleven articles representing nine different clinical studies were identified. (1) In the disc displacement group with pain, multimodal therapy was not superior to explanation and advice. (2) A combination of occlusal appliance and biofeedback-assisted relaxation/stress management was not significantly superior to either of these therapies after 6 months. Furthermore, brief information alone or combined with relaxation training or occlusal appliance, respectively, were equally efficacious at the 6-month follow-up. There was no superiority of multimodal therapy including splints as compared with simple care. A slightly better outcome was reported for a combination of education and home physical therapy regimen than for patient education alone. (3) In temporomandibular pain patients with major psychological disturbances, patients benefited more from a combined therapeutic approach compared with simple care.

CONCLUSION

Current research suggests that individuals without major psychological symptoms do not require more than simple therapy. In contrast, patients with major psychological involvement need multimodal, interdisciplinary therapeutic strategies. The clinician's acceptance of the importance of psychological factors in TMD pain forms the platform for convincingly educating patients about the need for multimodal management.

In patients with temporomandibular disorders, do particular interventions influence oral health-related quality of life? A qualitative systematic review of the literature

OBJECTIVES

The use of patient-based outcomes to measure therapeutic effectiveness is increasing, because a growing number of clinical scientists are attempting to evaluate the impact of therapy on the recipient. There are indications that patients suffering from temporomandibular disorders (TMDs) may also show a reduced oral health-related quality of life (OHQoL). It was the purpose of this paper to answer the question as to whether therapeutic interventions in TMD patients have a positive effect on their OHQoL.

MATERIAL AND METHODS

A systematic electronic search (Ovid Medline 1966-2006; Science Citation Index 1945-2006) of the literature was carried out to identify pertinent articles of randomized and non-randomized clinical trials. Reports on retrospective and prospective studies that specifically focused on OHQoL changes in TMD patients as a consequence of therapeutic interventions were included. The reference lists of the identified articles were screened to find additional pertinent publications.

RESULTS

The investigation yielded seven relevant contributions from Medline. A quantitative analysis of the seven identified articles was not possible. There was considerable heterogeneity among the investigations with regard to study design, patient characteristics, and provided therapy. Three of the identified articles reported about prospective controlled studies, of which one was an RCT. Four additional investigations were retrospective. According to the results of the only RCT, a 6-week course of the non-selective cyclooxygenase (COX) inhibitor naproxen may lead to slightly better OHQoL in patients with temporomandibular joint (TMJ) arthralgia than the selective COX-2 inhibitor celecoxib. The two other articles reporting of a controlled study showed that selective serotonine uptake inhibitors accompanied by psychological therapy improved OHQoL in individuals with TMJ arthralgia. In contrast, TMJ surgery did not improve OHQoL.

CONCLUSION

It appears that all therapeutic interventions reported in the identified publications led to at least some improvement of OHQoL. The only exception were patients with multiple TMJ surgeries.

Therapie bei Schmerzen der Kaumuskulatur

Myalgias of the masticatory muscles are the most frequent noninfectious complaints in the orofacial region. After summarizing the current knowledge on the physiology, etiology, pathophysiology, diagnosis, and differential diagnosis of masticatory muscle pain, we specifically focus on management recommendations. Results of an extensive literature search show that for the majority of patients pain reduction or pain relief can be achieved with noninvasive reversible methods. Longitudinal short- and long-term studies have revealed that different therapeutic measures are similarly effective. In patients with chronic masticatory myalgias associated with psychosocial impairment, however, additional involvement of a psychotherapist is crucial.

Therapie bei Arthralgie der Kiefergelenke

Arthralgias of the temporomandibular joint occur rarely in their isolated form, in contrast to myalgias of the jaw muscles. Most often, arthralgias are combined with myofascial pain. Here we define relevant terms (arthralgia, arthropathy, arthritis, osteoarthritis/osteoarthrosis), describe special diagnostic aspects and provide diagnosis-related specifications. We then present current information on the clinical management of temporomandibular joint pain. A systematic literature search revealed that pain reduction or pain relief can be achieved with non-invasive reversible methods for the majority of patients. Results from short and long-term longitudinal studies show that different therapeutic methods are similarly effective. For the management of chronic forms with extensive psychosocial impairment a multidisciplinary approach is essential.

Aktualisierung der Empfehlungen zur standardisierten Diagnostik und Klassifikation von Kaumuskel- und Kiefergelenkschmerzen

BACKGROUND

In 2000, the interdisciplinary Working Group of Orofacial Pain within the German Chapter of the IASP (German Association for the Study of Pain) published recommendations for the standardized evaluation and diagnostic classification of patients with painful masticatory muscles and/or temporomandibular joints. The purpose of the present study was to critically review and update these recommendations.

RESULTS

Appraisal of the relevant literature published after the release of the recommendations (up to December 2005) shows that the two-axis approach for the assessment of the somatic and psychosocial parameters of the orofacial pain experience has found wide support. Single aspects of the recommendations have been substantiated by additional scientific evidence.

CONCLUSIONS

The recommendations reflect the current state of pain medicine. Therefore, they should be considered among practitioners who diagnose and manage patients suffering from temporomandibular disorders.

[Pain drawings of patients with orofacial pain. Comparison of acceptance and gain of information]

AIM OF THE STUDY

The aim of this prospective multicentric study was to compare two different types of pain drawings in terms of acceptance and gain of information in patients with orofacial pain.

PATIENTS AND METHODS

A total of 204 patients from 9 centers, who visited their dentist or physician for orofacial pain, received two different diagrams for pain drawings in random order. One was the original pain diagram of the Deutsche Schmerzfragebogen (German Pain Questionnaire, diagram A), and the other diagram had been developed to achieve a symmetrical representation of the body and to allow computer-assisted analysis (diagram B). This diagram was larger and contained a drawing of the head. The patients' answers were analyzed for the preference between diagrams, the number and distribution of pain areas, and the concordance between the diagrams. The results were correlated with the patients' data.

RESULTS

Data from 183 patients could be analyzed: 100 of 183 patients preferred diagram B and 57 of 183 preferred diagram A, independent of gender, age, or duration of disease. Most patients reported pain in more than one area; in only 43 of 183 patients was the pain limited to the face and head. The number and distribution of pain areas were not different between the two pain diagrams.

CONCLUSIONS

Detailed head and body diagrams can be used in the diagnostic evaluation of patients with orofacial pain without fear of placing excessive demands on the patients and are useful for detecting comorbidities.

Heterogeneous activation of the medial pterygoid muscle during simulated clenching

The aim of this study was to investigate whether the medial pterygoid muscle shows differential activation under experimental conditions simulating force generation during jaw clenching. To answer this question, the electromyographic activity of the right medial pterygoid was recorded with two intramuscular electrodes placed in an anterior and posterior muscle region, respectively. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with strain gauges. The activity distribution in the muscle was recorded in a central mandibular position during generation of eight different force vectors at a constant amount of force (F=150 N). The investigated muscle regions showed different amounts of EMG activity. The relative intensity of the activation in the two regions changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for various motor tasks. The results indicate a heterogeneous activation of the medial pterygoid muscle under test conditions simulating force generation during clenching. This muscle behaviour might offer an explanatory model for the therapeutic effects of oral splints.

Activity patterns of the masticatory muscles during feedback-controlled simulated clenching activities

In 10 normal subjects, the electromyographic (EMG) activities of the masseter, anterior and posterior temporalis, medial pterygoid, inferior lateral pterygoid, as well as the anterior digastric, were bilaterally recorded during clenching with various resulting force vectors. The intraoral force transfer was achieved with a three-component force transducer. The direction and magnitude of the force vectors were controlled by visual feedback. The goal of the study was to investigate how various clenching directions at constant magnitude of force influence the EMG activity in the masticatory muscles during gradual increase of the horizontal force component. Depending on the force direction and the individual muscle, an increase or decrease of activity was observed during clenching with increasing horizontal force components at constant magnitude of force. The inferior lateral pterygoid exhibited the highest activation (about 80% of maximal voluntary clenching) of all masticatory muscles. The medial pterygoid showed the greatest range of variation in activation behavior, and it was the most active muscle in relation to all clenching directions. In conclusion, the results show that with growing horizontal force components at constant magnitude of force, all muscles demonstrated an increase or decrease of activity in several clenching directions.

Differential activity patterns in the masseter muscle under simulated clenching and grinding forces

The aim of this study was to investigate (i) whether the masseter muscle shows differential activation under experimental conditions which simulate force generation during clenching and grinding activities; and (ii) whether there are (a) preferentially active muscle regions or (b) force directions which show enhanced muscle activation. To answer these questions, the electromyographic (EMG) activity of the right masseter muscle was recorded with five intramuscular electrodes placed in two deep muscle areas and in three surface regions. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with three strain gauges (SG). The activity distribution in the muscle was recorded in four different mandibular positions (central, left, right, anterior). In each position, maximum voluntary contraction (MVC) was exerted in vertical, posterior, anterior, medial and lateral directions. The investigated muscle regions showed different amount of EMG activity. The relative intensity of the activation, with respect to other regions, changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for the various motor tasks. The resultant force vectors demonstrated similar amounts in all horizontal bite directions. Protrusive force directions revealed the highest relative activation of the masseter muscle. The posterior deep muscle region seemed to be the most active compartment during the different motor tasks. The results indicate a heterogeneous activation of the masseter muscle under test conditions simulating force generation during clenching and grinding. Protrusively directed bite forces were accompanied by the highest activation in the muscle, with the posterior deep region as the most active area.

[Chronic temporomandibular disorders]

According to the 3rd German Oral Health Study (1999), the prevalence of painful temporomandibular disorders (TMDs) is about 5%. Although limited information about the magnitude of utilization of health care services and expenses for health care in temporomandibular pain patients is available, the financial burden of affected individuals may be considerable. The etiology and pathophysiology of chronic TMDs is still obscure. However, certain (patho)physiological mechanisms may be associated with the genesis and perpetuation of these musculoskeletal facial pains (e. g. disturbances in central nervous system processing; psychosocial factors; hormonal influences). Strong scientific evidence from the dental/medical literature is currently available for the following forms of TMD treatment and management: occlusal appliances (stabilization appliance), clonazepam, diazepam, meprobamate, EMG biofeedback, multimodal approaches (somatic and psychological pain management).

FE-simulation of bone modeling around an implant in the mandible in two-stage versus one-stage implantation

On the basis of a FE-model for bone modeling which takes into account bone apposition and resorption as well as revascularization, the ossification process of the repair zone around a dental implant in the mandible is studied for two alternatives. The conventional two-stage implantation method consists of a healing phase (no direct loading of the implant) and a functional phase (direct loading). In the recently applied one-stage method the healing phase is omitted (early loading). The presented simulations show that both processes finally lead to the same degree of ossification of the repair zone. However, the relative displacements and rotations of the implant are considerably larger in the one-stage process and might therefore possibly lead to a violation of the bond between implant and bone.

[Jaw muscle pain--its neurobiological basis]

The masticatory muscles show morphologic, histochemical, electrophysical, and functional features that differ from the other muscles of the body. At least two kinds of masticatory muscle pain should be distinguished: A local pain associated with peripheral mechanical overuse, and a pain associated with changes in the central nociceptive system. Biomechanical factors appear to be important for the first type of muscle pain. Since the typical reaction of a painful muscle consists of inhibition of its activity, traditional concepts that postulate the maintenance of the pain by chronic overuse of the whole muscle are not supported by the current literature. Instead, differential overuse of discrete intramuscular regions appear to provide a more plausible explanation. On the other hand, the possible relationships between functional and structural neuroplastic changes and the second form of chronic muscle pain (e.g., fibromyalgia) still remain speculative.

Antero-posterior activity changes in the superficial masseter muscle after exposure to experimental pain

The aim of this randomized, controlled, double-blind study was to examine how the activation pattern of the masseter muscle changes during natural function when experimental pain is induced in a discrete anterior area of the muscle. In 20 subjects, three bipolar surface electrodes and three intramuscular fine-wire electrodes (antero-posterior mapping) were simultaneously attached above and in the right masseter muscle to record the electromyographic (EMG) activity during unilateral chewing before and after infusion of a 0.9% isotonic and 5% hypertonic saline bolus in the anterior area of the muscle. The activity of the contralateral masseter muscle was registered by surface electrodes. In addition, the development of pain intensity was quantitatively measured with a numerical rating scale (NRS). While both saline concentrations caused pain, the hypertonic solution evoked stronger pain. The experiments also provided evidence of a significant although differential activity reduction of the ipsilateral masseter muscle in the antero-posterior direction. The activity reduction decreased with increasing distance from the location of the infusion. The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.

Feedback control during mastication of solid food textures--a clinical-experimental study

STATEMENT OF PROBLEM

On the basis of animal experiments, it has been hypothesized that the dynamics of food reduction are controlled by peripheral receptors. Studies on this subject in human beings are rare.

PURPOSE

This study investigated the influence of periodontal and joint proprioceptors on mastication in human beings.

MATERIAL AND METHODS

Both jaw joints and the chewing-side teeth were consecutively anesthetized in a 6-person panel by chewing wine gum. The effects on the kinematics, chewing force, and electromyographic activity were measured.

RESULTS

The results substantiate a positive feedback of periodontal receptors for chewing force control. A substantial influence of joint receptors on movement control could not be found.

CONCLUSION

Despite the absence of proprioception in both jaw joints and the periodontal receptors in the chewing side, the characteristics of the measured kinematic and dynamic values remained essentially unchanged.