Papers by Daniel Hellmann
Gait & Posture, 2015
Recent studies reported on the potential benefits of submaximum clenching of the jaw on human pos... more Recent studies reported on the potential benefits of submaximum clenching of the jaw on human postural control in upright unperturbed stance. However, it remained unclear whether these effects might also be observed among active controls. The purpose of the present study, therefore, was to comparatively examine the influence of concurrent muscle activation in terms of submaximum clenching of the jaw and submaximum clenching of the fists on postural stability. Posturographic analyses were conducted with 17 healthy young adults on firm and foam surfaces while either clenching the jaw (JAW) or clenching the fists (FIST), whereas habitual standing served as the control condition (CON). Both submaximum tasks were performed at 25% maximum voluntary contraction, assessed, and visualized in real time by means of electromyography. Statistical analyses revealed that center of pressure (COP) displacements were significantly reduced during JAW and FIST, but with no differences between both concurrent clenching activities. Further, a significant increase in COP displacements was observed for the foam as compared to the firm condition. The results showed that concurrent muscle activation significantly improved postural stability compared with habitual standing, and thus emphasize the beneficial effects of jaw and fist clenching for static postural control. It is suggested that concurrent activities contribute to the facilitation of human motor excitability, finally increasing the neural drive to the distal muscles. Future studies should evaluate whether elderly or patients with compromised postural control might benefit from these physiological responses, e.g., in the form of a reduced risk of falling.
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Objectives: Epidemiological surveys indicate high comorbidity of masticatory-muscle and neck-musc... more Objectives: Epidemiological surveys indicate high comorbidity of masticatory-muscle and neck-muscle pain. It is hypothesized that close functional coupling between both muscle groups may be involved in the etiology of myofascial pain conditions. So far, however, interactions between pathophysiological loading of the masticatory system and the adjacent neck muscles, in particular caused by bruxism, lack the confirmation of neuromuscular coupling of both segments at submaximum bite forces. The objective of this study was to test the hypothesis that jaw and neck muscles co-contract during clenching of the masticatory system. Methods: Bite force transducers which measured all three spatial force components were incorporated in 11 healthy subjects. The test persons developed different feedback-controlled submaximum bite forces in a variety of bite-force directions. The corresponding electrical activity (EMG) of the levator scapulae, splenius capitis, and trapezius muscles was recorded by...
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OBJECTIVES: The standard procedure for the determination of masticatory performance is the fracti... more OBJECTIVES: The standard procedure for the determination of masticatory performance is the fractionated sieving of comminuted test-food, which is time-consuming. Aim of this study was to introduce a comparable feasible and valid technique based on scanning. METHODS: Twenty-one chewing samples (Optosil) were comminuted by healthy dentate adults and analysed by a sieving and scanning method. The sieving procedure was carried out using ten sieves (5.6-4.0-2.8-2.0-1.4-1.0-0.71-0.5-0.355-0.25 mm), the retained particles per sieve were weighed. Scanning was performed with a conventional flatbed scanner (Epson Expression1600Pro, Seiko-Epson-Corporation, Japan, 1200dpi). All scanned images underwent image analysis (ImageJ1.42q, NIH, USA ), which yielded descriptive parameters such as area, best-fitting ellipse etc. for each particle. Out of the 2D-image, a volume was estimated for each particle, which was converted into a weight. In order to receive a discrete distribution of particle sizes...
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Objectives: Neuromuscular adaptations during skill acquisition have been extensively investigated... more Objectives: Neuromuscular adaptations during skill acquisition have been extensively investigated for the skeletal muscles, yet only few data are available for motor learning by the masticatory system. The objective of this study was to evaluate the long-term training effects on the masseter and temporal muscles. Methods: In 20 healthy subjects the surface electromyographic response to unilateral and bilateral maximum voluntary tooth clenching, balancing the mandible on a hydrostatic system under force-feedback-controlled conditions (coordination tasks), and unilateral chewing was investigated in an initial session then in two two follow-up sessions separated by two and ten weeks from baseline. Motor tasks were repeated three times for chewing, nine times for maximum biting and 24 times for the coordination tasks. The sequences of the various motor tasks were applied once in the first session and twice each in the second and third sessions. Results: No training effects were observed...
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Objective: Bruxism is being considered as predisposing, initiating or perpetuating factor for tem... more Objective: Bruxism is being considered as predisposing, initiating or perpetuating factor for temporomandibular and cervical spine disorders (TMDs and CSDs). The present study aimed to test the hypothesis that jaw and neck muscles co-contract during a range of clenching activities in a static bruxism model. Method: Ten healthy subjects developed various feedback-controlled submaximum bite forces with changing bite force directions in a supine position. The electromyographic (EMG) activities of levator scapulae, trapezius, splenius capitis, semispinalis cervicis, semispinalis capitis, multifidi, supra-/infra-hyoidal, and sternocleidomastoideus muscles were recorded by intramuscular and surface electrodes. For normalization of the EMG data, maximum effort tasks of the neck muscles were conducted. A special force transducer system allowed for maximum effort EMG recordings of the neck musculature in 8 different loading directions. Result: The results confirmed the initially stated hypot...
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Objectives: Closing movements must be appropriately tailored by coordinated spatial and temporal ... more Objectives: Closing movements must be appropriately tailored by coordinated spatial and temporal muscle co-contraction to achieve the required functional task. We hypothesize that periodontal proprioception plays a crucial role for the calibration of muscle receptors, which in turn provide essential peripheral feedback for the adjustments of motor programs controlling jaw movements. The goal of the study was to test the hypothesis that compromised periodontal proprioception in the short term run does not significantly reduce the precision of jaw closing movements. Methods: Twenty healthy subjects performed controlled slow/fast jaw closing movements which were stopped by small plane front-plateaus at vertical jaw separations of 1,2,4,6,8, and 10mm, respectively, complemented by non-interrupted physiological closing movements into maximum intercuspation (IC). For each vertical increment, the spatial displacement of the incisor point and the condyles were telemetrically measured in rel...
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Objective: The functional significance of occlusal interferences has been extensively discussed. ... more Objective: The functional significance of occlusal interferences has been extensively discussed. Whereas many studies focussed on the electromyographic measurements (EMG) and 3D kinematic jaw movement records in static or dynamic conditions, there is little evidence on the impact of balance side interferences on performance parameters. The aim of this study was to integrate EMG, jaw movement and masticatory performance as target variables. Method: Twenty healthy subjects (ten female, mean age: 24.1±1.2 years) performed a standardized chewing test (Optocal cubes, 15 masticatory cycles). Three experimental conditions were investigated: chewing on (a) the natural dentition (ND), (b) splints with structured occlusal profiles simulating the subject’s natural dentition (SS), (c) splints with a balance side interference in the molar region (BS). The minced particles were analyzed by a validated scanning procedure. The size distribution of the particles was calculated using the Rosin-Rammle...
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Objective: Therapeutic effects on musculoskeletal pain are lately attributed to intramuscular reo... more Objective: Therapeutic effects on musculoskeletal pain are lately attributed to intramuscular reorganisation of motor unit (MU) activity unloading injured MUs. Oral splints might evoke similar effects. Should this be the case for masticatory muscles, the prerequisite is a local differential activation at the level of MUs. The goal of this experimental study was to investigate the influence of small changes of the vertical and horizontal jaw relation on the recruitment behaviour of masseter MUs. Method: 20 healthy subjects (10 female) were involved in the experimental study (mean age: 24.7±2.5 years). An intraoral force-measuring system enabled the subjects to perform feedback-controlled submaximum bite-force tasks in three different vertical and horizontal jaw relations, comparable with positional changes induced by oral splints. The electromyographic (EMG) activity of the right masseter was registered with intramuscular bipolar wire electrodes in three different muscle regions. The...
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Journal of oral rehabilitation, 2015
Human posture is characterised by inherent body sway which forces the sensory and motor systems t... more Human posture is characterised by inherent body sway which forces the sensory and motor systems to counter the destabilising oscillations. Although the potential of biting to increase postural stability has recently been reported, the mechanisms by which the craniomandibular system (CMS) and the motor systems for human postural control are functionally coupled are not yet fully understood. The purpose of our study was, therefore, to investigate the effect of submaximum biting on postural stability and on the kinematics of the trunk and head. Twelve healthy young adults performed force-controlled biting (FB) and non-biting (NB) during bipedal narrow stance and single-leg stance. Postural stability was quantified on the basis of centre of pressure (COP) displacements, detected by use of a force platform. Trunk and head kinematics were investigated by biomechanical motion analysis, and bite forces were measured using a hydrostatic system. The results revealed that FB significantly impr...
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Journal of Orofacial Pain, 2013
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Journal of Oral Rehabilitation, 2011
Alterations of body sway caused by isometric contractions of the jaw muscles have been reported p... more Alterations of body sway caused by isometric contractions of the jaw muscles have been reported previously. The objective of this study was to test if motor tasks of the masticatory system with different control demands affect body posture differently during quiet stance. Position and sway displacements of the center of foot pressure (COP) were measured for 20 healthy subjects who either kept the mandible at rest or performed unilateral and bilateral maximum voluntary teeth clenching, feedback-controlled biting tasks at submaximum bite forces, or unilateral chewing. Two weeks later the measurements were repeated. Compared with quiet stance, the COP results revealed significant changes during the feedback-controlled biting tasks. Robust sway reduction and anterior displacement of the COP were observed under these conditions. Body oscillations were not significantly affected by maximum bites or by unilateral chewing. For most of the variables investigated there were no significant differences between unilateral and bilateral biting. Robust sway reduction during feedback-controlled biting tasks in healthy subjects involved a stiffening phenomenon that was attributed to the common physiological repertoire of posture control, and might optimize the stability of posture under these conditions.
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Journal of Oral Rehabilitation, 2011
Neuromuscular adaptations during skill acquisition have been extensively investigated for skeleta... more Neuromuscular adaptations during skill acquisition have been extensively investigated for skeletal muscles. Motor rehabilitation is the main target for application of motor training. Such measures are also relevant for the musculature of the jaw, but few data are available for motor adaptation of the masticatory system. The objective of this study was to evaluate and compare long-term training effects of different motor tasks on masseter and temporal muscles. In 20 healthy subjects, the electromyographic response to unilateral and bilateral maximum voluntary tooth clenching, balancing the mandible on a hydrostatic system under force-feedback-controlled conditions, and unilateral chewing was investigated in an initial session and then in two follow-up sessions separated by 2 and 10 weeks from baseline. Motor tasks were repeated three times for chewing, nine times for maximum biting (MB) and 24 times for the coordination tasks (CT). The sequences of the various motor tasks were applied once in the first session and twice in the second and third sessions. No effects of training were observed for MB tasks except for MB in intercuspation, for which significant yet transient avoidance behaviour occurred in the second session. No significant effects were found for chewing tests. For the CT, however, a robust significant long-term training effect was detected which reduced the electric muscle activity in session 2 by approximately 20% and in session 3 by approximately 40% compared with the initial measurements. The study showed that the masticatory muscles are remarkably prone to motor adaptation if demanding CT must be accomplished.
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Journal of Oral Rehabilitation, 2012
Aim of this study was to introduce a feasible and valid technique for the assessment of masticato... more 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.
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Journal of Oral Rehabilitation, 2014
Immediate adaptation to experimental-balancing interferences is known to affect jaw kinematics an... more Immediate adaptation to experimental-balancing interferences is known to affect jaw kinematics and electromyographic activity (EMG). However, little is known about the influence on masticatory performance parameters. This study hypothesises that balancing-side interferences significantly reduce the performance of the masticatory system. Twenty-one healthy subjects (eleven female, mean age: 24.1 ± 1.2 years) chewed standardised silicone cubes performing 15 masticatory cycles on the right side under three experimental conditions: (i) natural dentition (ND), (ii) splints with structured occlusal profiles (SS) (iii) splints with balancing interferences in the left molar region (OI). The particle size distribution was determined by a validated scanning procedure and curve fitted with the Rosin-Rammler function to determine X(50)-values. The EMG of both temporalis and masseter muscles was recorded simultaneously, and the total muscle work (TMW) was calculated. A jaw-tracking device recorded the incisal movement path (IMP). The functional parameters under the experimental conditions were compared by repeated-measures analysis of variance. The findings confirm our hypothesis. The X(50)-values differed significantly (P < 0.01) between ND and OI (4.34 vs. 4.60 mm), and between SS and OI (4.34 vs. 4.60 mm), respectively. In contrast, no significant differences (P > 0.05) were observed between SS and ND. There was no significant difference in both TMW (1269.0 vs. 1284.9 vs. 1193.9 μV*s) and IMP (720.2 vs. 735.3 vs. 723.1 mm) amongst the three conditions (P > 0.05). These findings confirm the assumption that the disturbance of the habitual chewing cycles by balancing-side interferences significantly reduces the masticatory performance in the short term. Occlusal balancing-side interferences are common technical failures of dental restorations. Simulation of this condition caused deterioration of masticatory performance in healthy young adults. Further studies should be carried out, on whether the observed effect is long-term and whether masticatory performance decreases even more in patients with reduced adaptive capacity.
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Journal of Oral Rehabilitation, 2014
Localised motor-unit (MU) recruitment in the masseter was analysed in this study. We investigated... more Localised motor-unit (MU) recruitment in the masseter was analysed in this study. We investigated whether differential activation behaviour, which has already been reported for distant masseter regions, can also be detected in small muscle subvolumes at the level of single MUs. Two bipolar fine-wire electrodes and an intra-oral 3D bite-force transmitter were used to record intra-muscular electromyograms (EMG) resulting from controlled bite-forces of 10 healthy human subjects (mean age 24.1 ± 1.2 years). Two-hundred and seventeen decomposed MUs were organised into localised MU task groups with different (P < 0.001) force-direction-specific behaviour. Proportions of MUs involved in one, two, three or four examined tasks were 46%, 31%, 18% and 5%, respectively. This study provides evidence of the ability of the neuromuscular system to modify the mechanical output of small masseter subvolumes by differential control of adjacent MUs belonging to distinct task groups. Localised differential activation behaviour of the masseter may be the crucial factor enabling highly flexible and efficient adjustment of the muscle activity in response to complex local biomechanical needs, for example, continually varying bite-forces during the demanding masticatory process.
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European Journal of Oral Sciences, 2012
Bruxism may be involved in the aetiology of myofascial neck pain. The objective of this study was... more Bruxism may be involved in the aetiology of myofascial neck pain. The objective of this study was to test the hypothesis that anterior and posterior neck muscles co-contract during jaw clenching. Ten test subjects developed different feedback-controlled submaximum bite forces in a variety of bite-force directions by means of bite-force transducers. The electromyographic activity of the sternocleidomastoid and supra/infrahyoidal muscles, and of the semispinalis capitis, semispinalis cervicis, and multifidi muscles was recorded by use of surface electrodes and intramuscular wire electrodes, respectively. For normalization of electromyography data, maximum voluntary contraction tasks of the neck muscles were conducted in eight different loading directions. The results confirmed co-contraction of the neck muscles in the range of 2-14% of the maximum voluntary contraction at a bite force ranging from 50 to 300 N. Significant activity differences were observed as a result of the different force levels and force directions exerted by the jaw muscles. Long-lasting tonic activation of specific neck muscles triggered by the jaw-clenching tasks was also detected. These findings support the assumption of a relationship between jaw clenching and the activity of the neck muscles investigated. The low level of co-contraction activity, however, requires further study to elucidate possible pathophysiological interactions at the level of single motor units.
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Clinical Oral Investigations, 2013
A key aspect of complex restorative therapy is reconstruction of a new three-dimensional jaw rela... more A key aspect of complex restorative therapy is reconstruction of a new three-dimensional jaw relation. The objective of this study was to test the hypotheses that the initially recorded jaw relation would deviate substantially from the jaw position of the prosthetic reconstruction and that activity ratios of the jaw muscles would be significantly different for each of these jaw positions. In 41 healthy subjects, 41 examiners incorporated intraoral occlusal devices fabricated with all the technical details and procedures commonly used during prosthetic reconstructions. The jaw positions in centric relation with the incorporated occlusal devices were telemetrically measured in the condylar, first molar and incisal regions, relative to intercuspation. Electromyographic (EMG) activity of the temporalis and masseter muscles was recorded, and activity ratios were calculated for homonymous and heteronymous muscles. The recorded jaw relation differed significantly (p < 0.001) from the jaw position reconstructed with the intraoral occlusal devices. The initially recorded jaw relation was reproduced with the intraoral occlusal device with spatial accuracy of approximately 0.3 mm in the condylar, molar and incisal regions. The EMG ratios between centric relations and the reconstructed positions were significantly different (p < 0.05) for the temporal muscle and the temporalis/masseter ratio. The findings revealed that three-dimensional jaw-relation recording may be reproduced in a simulated prosthetic reconstruction within the accuracy reported for replicate intraoral bite recordings. Centric relation recordings may be reproduced in a prosthetic reconstruction with the spatial accuracy of 0.3 mm.
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Archives of Oral Biology, 2013
The purpose of this study was to test the hypothesis that jaw clenching induces co-contraction an... more The purpose of this study was to test the hypothesis that jaw clenching induces co-contraction and low-level long-lasting tonic activation (LLTA) of neck muscles in the supine position. Ten healthy subjects developed various feedback-controlled submaximum bite forces in different bite-force directions in supine position. The electromyographic (EMG) activity of the semispinalis capitis, semispinalis cervicis, multifidi, splenius capitis, levator scapulae, trapezius, sternocleidomastoideus, masseter and infra/supra-hyoidal muscles was recorded. For normalization of EMG data, maximum-effort tasks of the neck muscles were performed. Co-contractions of the posterior neck muscles varied between 2% and 11% of their maximum voluntary contraction. Different bite forces and bite-force directions resulted in significant (p<.05) activity differences between the co-contraction levels of the neck muscles. In addition, LLTA of specific neck muscles, provoked by the jaw clenching tasks, was observed. This study demonstrated for the first time moderate co-contractions of jaw and neck muscles in the supine position under controlled submaximum jaw clenching forces. LLTA of most neck muscles was observed, outlasting clenching episodes and indicating an additional neuromuscular interaction between the two muscle groups.
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Jaw-closing movements are basic components of physiological motor actions precisely achieving int... more Jaw-closing movements are basic components of physiological motor actions precisely achieving intercuspation without significant interference. The main purpose of this study was to test the hypothesis that, despite an imperfect intercuspal position, the precision of jaw-closing movements fluctuates within the range of physiological closing movements indispensable for meeting intercuspation without significant interference. For 35 healthy subjects, condylar and incisal point positions for fast and slow jaw-closing, interrupted at different jaw gaps by the use of frontal occlusal plateaus, were compared with uninterrupted physiological jaw closing, with identical jaw gaps, using a telemetric system for measuring jaw position. Examiner-guided centric relation served as a clinically relevant reference position. For jaw gaps ≤4 mm, no significant horizontal or vertical displacement differences were observed for the incisal or condylar points among physiological, fast, and slow jaw-closing. However, the jaw positions under these three closing conditions differed significantly from guided centric relation for nearly all experimental jaw gaps. The findings provide evidence of stringent neuromuscular control of jaw-closing movements in the vicinity of intercuspation. These results might be of clinical relevance to occlusal intervention with different objectives.
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European journal of oral sciences, Jan 8, 2015
The objective of this study was to investigate the mechanisms of physiological control of the cra... more The objective of this study was to investigate the mechanisms of physiological control of the craniomandibular system during force-controlled biting: in intercuspation, restricted by predetermined anatomic-geometrical conditions [i.e. biting in intercuspation (BIC)]; and on a hydrostatic system [i.e. auto-balanced static equilibrium of the mandible (BAL)], in which the mandible is balanced under unrestricted occlusal conditions. For 20 healthy subjects, the spatial positions of the condyles, the lower molars, and the incisal point were measured, and the electromyographic (EMG) activity of the musculus masseter and musculus temporalis anterior were recorded bilaterally, during force-controlled biting (50, 75, 100 N) on a hydrostatic device. The results were compared with those obtained during BIC. During BAL, the neuromuscular system stabilizes one condyle, so it behaves as a virtual fulcrum, and all available biomechanical degrees of freedom of the opposite side are used to achieve ...
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Papers by Daniel Hellmann