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Context dependent adaptation of biting behavior in human
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis was to study an action that humans perform regularly, namely, to hold a morsel between the teeth and split it into smaller pieces. Three different issues related to this biting behavior were addressed:  (1) the effect of redu­c­ed perio­dontal tissues on food holding and splitting behavior; (2) the behavioral conse­quences of performing different bite tasks with different functional requirements, i.e., to split a peanut half resting on a piece of chocolate or to split both the peanut and the chocolate; and (3) the reflex modulations resul­ting from such a change in the intended bite action. The main conclusions from the experi­mental studies were the following:

First, perio­dontitis, an inflam­matory disease that destroys the peri­o­dontal ligaments and the embedded perio­dontal mechanoreceptors, causes significant impairments in the masticatory abili­ty: the manipulative bite forces when holding a morsel are elevated compared to a matched control population and the bite force development prior to food split is altered. These changes are likely due to a combination of reduced sensory informa­tion from the damaged ligaments and to changes in the bite stra­tegy secon­d­ary to the unstable oral situation.

Second, people exploit the anatomy of jaw-closing muscles to regulate the amount of bite force that dissipates following a sudden unloading of the jaw. Such control is necessary because without mechanisms that quickly halt jaw-closing movements after sudden unloading, the impact forces when the teeth collide could otherwise damage both the teeth and related soft tissues. Splitting a piece of chocolate, for instance, regularly requires >100N of bite force and the jaws collide within 5 ms of a split. On the other hand, when biting through heterogeneous food, the bite force needs to be kept high until the whole morsel is split. The required regulation is achieved by differen­tial­ly engaging parts of the masseter muscles along the anteroposterior axis of the jaw to exploit differences between muscle portions in their bite force generating capa­ci­ty and muscle shortening velocity.

Finally, the reflex evoked by suddenly unloading the jaw—apparent only after the initial bite force dissipation—is modulated according to the bite intention. That is, when the intention is to bite through food items with multiple layers, the reflex response in the jaw opening muscles following a split is small, thus minimizing the bite force reduction. In contrast, when the intention is to rapidly decrease the bite force once a split has occurred, the reflex response is high. This pattern of reflex modulation is functionally beneficial when biting through heterogeneous food in a smooth manner.

The presented studies show the significance of integrating cogni­tive, physiological and anatomical aspects when attempting to understand human masticatory control.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2014. , 35 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1666
Keyword [en]
EMG, bite force, human, mastication, muscles, jaw opening reflex, motor control, reflex modulation, periodontal attachment loss, periodontitis
National Category
Physiology
Research subject
Physiology
Identifiers
URN: urn:nbn:se:umu:diva-91664ISBN: 978-91-7601-096-9 (print)OAI: oai:DiVA.org:umu-91664DiVA: diva2:737638
Public defence
2014-09-03, Biologihuset, BiA 201, Umeå Universitet, Umeå, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2011-3128
Available from: 2014-08-15 Created: 2014-08-13 Last updated: 2014-08-13Bibliographically approved
List of papers
1. Impaired masticatory behavior in subjects with reduced periodontal tissue support.
Open this publication in new window or tab >>Impaired masticatory behavior in subjects with reduced periodontal tissue support.
2006 (English)In: Journal of Periodontology, ISSN 0022-3492, Vol. 77, no 9, 1491-7 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Mechanoreceptors situated in the periodontal ligament provide detailed information about intensive and spatial aspects of tooth loads, which support the neural control of masticatory forces. We asked whether a reduced periodontal ligament due to periodontitis, and, thus, an altered mechanoreceptive innervation of the teeth, would affect masticatory behavior when subjects used incisors to hold and split food. METHODS: We tested 11 subjects with reduced periodontal tissue support that rendered 30% to 70% alveolar bone loss for at least one pair of opposing anterior incisors. Forces were recorded when subjects used their affected incisors to hold half of a peanut for approximately 4 seconds and then split it. Age- and gender-matched healthy subjects served as the control group. None of the participants showed acute oral symptoms or massive periodontal inflammation. RESULTS: The test group used greater force when holding food between the teeth (1.1+/-0.4 N [ mean+/-1 SD]) compared to the control group (0.4+/-0.2 N). Hold forces used by subjects in the test group were also more variable, both within and between trials. The increase in bite force applied to split the peanut was slower and more hesitant for subjects in the test group compared to the control group. CONCLUSIONS: Reduced periodontal tissue support accompanies impaired regulation of masticatory forces. Faulty mechanoreceptive innervation of the periodontal ligament explains the elevated hold force, whereas a change in biting strategy due to the weakened support of the teeth may account for the more defensive food-splitting behavior.

Identifiers
urn:nbn:se:umu:diva-22651 (URN)10.1902/jop.2006.050355 (DOI)16945024 (PubMedID)
Available from: 2009-05-14 Created: 2009-05-14 Last updated: 2014-08-13
2. Task-dependent control of the jaw during food splitting in humans
Open this publication in new window or tab >>Task-dependent control of the jaw during food splitting in humans
2014 (English)In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 111, 2614-2623 p.Article in journal (Refereed) Published
Abstract [en]

Although splitting of food items between the incisors often requires high bite forces, rarely do the teeth harmfully collide when the jaw quickly closes after split. Previous studies indicate that the force-velocity relationship of the jaw closing muscles principally explains the prompt dissipation of jaw closing force. Here, we asked whether people could regulate the dissipation of jaw closing force during food splitting. We hypothesized that such regulation might be implemented via differential recruitment of masseter muscle portions situated along the anteroposterior axis because these portions will experience a different shortening velocity during jaw closure. Study participants performed two different tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split trials) and, in the other, to split both the peanut and the chocolate in one action (double-split trials). In double-split trials following the peanut split, the intensity of the tooth impact on the chocolate piece was on average 2.5 times greater than in single-split trials, indicating a substantially greater loss of jaw closing force in the single-split trials. We conclude that control of jaw closing force dissipation following food splitting depends on task demands. Consistent with our hypothesis, converging neurophysiological and morphometric data indicated that this control involved a differential activation of the jaw closing masseter muscle along the anteroposterior axis. These latter findings suggest that the regulation of jaw closing force after sudden unloading of the jaw exploits masseter muscle compartmentalization.

Place, publisher, year, edition, pages
The American Physiological Society, 2014
Keyword
EMG, bite force, human, mastication, muscles
National Category
Physiology Neurosciences
Research subject
Physiology
Identifiers
urn:nbn:se:umu:diva-91661 (URN)10.1152/jn.00797.2013 (DOI)000339171700020 ()
Funder
Swedish Research Council, 2011-3128
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2017-12-05Bibliographically approved
3. Biting intentions modulate digastric reflex responses to sudden unloading of the jaw
Open this publication in new window or tab >>Biting intentions modulate digastric reflex responses to sudden unloading of the jaw
2014 (English)In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 112, no 5, 1067-1073 p.Article in journal (Refereed) Published
Abstract [en]

Reflex responses in jaw opening muscles can be evoked when a brittle object cracks between the teeth and suddenly unloads the jaw. We hypothesized that this reflex response is flexible and, as such, is modulated according to the instructed goal of biting through an object. Study participants performed two different biting tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split task) and, in the other task, they were asked to split both the peanut and the chocolate in one action (double-split task). In both tasks, the peanut split evoked a jaw opening muscle response, quantified from EMG recordings of the digastric muscle in a window 20-60 ms following peanut split. Consistent with our hypothesis, we found that the jaw opening muscle response in the single-split trials was about twice the size of the jaw opening muscle response in the double-split trials. A linear model that predicted the jaw opening muscle response on a single trial basis indicated that task settings played a significant role in this modulation but also that the pre-split digastric muscle activity contributed to the modulation. These findings demonstrate that, like reflex responses to mechanical perturbations in limb muscles, reflex responses in jaw muscles not only show gain-scaling but also are modulated by subject intent.

Keyword
EMG, jaw-opening reflex, motor control, reflex modulation, trigeminal
National Category
Physiology
Identifiers
urn:nbn:se:umu:diva-89697 (URN)10.1152/jn.00133.2014 (DOI)000341687200005 ()24899675 (PubMedID)
Available from: 2014-06-10 Created: 2014-06-10 Last updated: 2017-12-05Bibliographically approved

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