Thesis--Karolinska Instituet. / Extra t.p. with thesis statement inserted. Includes bibliographical references (p. 22-24).

Thesis--Karolinska Instituet. / Extra t.p. with thesis statement inserted. Includes bibliographical references (p. 22-24).

No description available.

Animal experiments indicate that the main form of feedback for jaw-closing muscles is from periodontal mechanoreceptors (PMRs). However, due primarily to limitations on methods, this is yet to be confirmed in humans. The main aim of this thesis was to investigate the reflex contribution of PMRs to the human jaws using vertical (axial) stimulation. To this end the electromyographic and bite force responses of the jaw to a number of different mechanical stimulus conditions, delivered to both the upper central incisors and the upper right first molars, were investigated. The principal hypothesis was that PMRs are responsible for the majority of the reflex responses seen in the human jaw muscles. Furthermore this reflex response is modulated by different characteristics of the stimulus such as: rate of rise, maximum force applied, the amount of constant offset force (preload), the level of muscle contraction and also the physical characteristics of the subject's jaw including: dental health and tooth spacing. These studies have contributed towards the understanding of the neuronal wiring and the receptor systems contained in the jaw. The results indicate that PMRs around the incisors are of fundamental importance for the development of reflex patterns but little if any PMR related reflexes exist around the molar teeth. The reflexes originating from the PMRs around the incisors are modulated by different mechanical characteristics of the stimulus, thus helping to explain how the jaw muscles perform numerous and complex patterns of activation which move the jaw in many different ways and develop forces that are optimum for the task at hand. / Thesis (Ph.D.)--School of Molecular & Biomedical Science, 2004.

No description available.

Background: Maximal voluntary occlusal bite force (MVOBF) is the maximal force applied by the jaw muscles in dental occlusion. MVOBF is one parameter for functional capacity of the jaw system.  Aim: To evaluate MVOBF in different positions in the bite and to evaluate possible intra-individual differences between sessions.  Methods: MVOBF was measured with an electronic bite force device, with transducers sensitive to force, in 20 healthy men (mean 24.5 years). Eligibility of participants was full dental occlusion, Angle Class I relation, no diagnosis according to Diagnostic criteria for temporomandibular disorders. The test included three repeated measurements on each site: first molar right, first molar left and central incisor, in random order, with test-retest study design. Unpaired T-test was used to test the MVOBF in different positions in the bite and paired T-test for possible intra-individual differences between sessions. A post hoc test for repeated measure one-way ANOVA was added.  Results: MVOBF in different positions in the bite was lower in the incisor area compared with the molar region (P<0.0001), but similar between right and left molar side (P=0.48 and P= 0.96, respectively). No intra-individual differences between sessions (molar right P= 0.40; molar left P= 0.81; incisor area P= 0.66). The intra-individual variability for repeated measurements showed variability for incisor area (P= 0.007), but not for molar right and left region (P=0.95 and P=0.49, respectively).  Conclusion: The results may provide reference values for MVOBF in young adult men, to be compared with men with pain or dysfunction in the jaw system.

Les mouvements masticatoires sont générés par un réseau neuronal localisé dans le tronc cérébral connu sous le nom de générateur de patron central (GPC). De plus en plus d’évidences dans la littérature associent le noyau sensoriel principal du trijumeau (NVsnpr) au cœur rythmogène du GPC masticatoire, bien qu’il soit traditionnellement considéré comme un relais sensoriel au thalamus. La présente étude amène une nouvelle preuve de connectivité fonctionnelle entre le NVsnpr et le noyau moteur du trijumeau (NVmt) contenant les motoneurones (MNs) innervant les différents muscles masticatoires. Nos résultats indiquent que les neurones projetant vers NVmt sont situés dans le ¾ dorsal du NVsnpr. La stimulation électrique dans le NVsnpr dorsal évoque des réponses synaptiques excitatrices multiphasiques dans les MNs trigéminaux tandis que l'application locale de BAPTA, connue pour induire une activité rythmique dans les neurones du NVsnpr, évoqua aussi une activité rythmique dans les MNs, supportant davantage la relation fonctionnelle entre ces deux noyaux en termes de transmission de rythme. En imagerie calcique, la stimulation électrique de NVsnpr évoquait des réponses calciques dans les MNs situées principalement dans la région dorsolatérale contenant les MNs des muscles de fermeture et révéla un patron spécifique de connectivité entre les deux noyaux. L'organisation des projections semblait dépendre de manière critique de la localisation dorso-ventrale du site de stimulation au sein du NVsnpr. La principale tendance observée concernait la région DL de NVmt recevant des inputs du NVsnpr dorsal (R1 et R2), alors que la région ventromédiane de NVmt recevait plutôt des inputs de R2 et R3, qui représentent la majeure partie de la région intermédiaire du NVsnpr. Cette étude confirme et développe les expériences antérieures en explorant la nature physiologique et la topographie fonctionnelle de la connectivité entre NVsnpr et NVmt. / Masticatory movements are generated by a brainstem neuronal network known as the central pattern generator (CPG). Increasing evidence associate the trigeminal main sensory nucleus (NVsnpr) to the rhythmogenic heart of the masticatory CPG, despite the fact that it is conventionally seen as a sensory relay to the thalamus. The present study provides new evidence of a functional connectivity between NVsnpr and the trigeminal motor nucleus (NVmt), known to contain all the motoneurons (MNs) innervating jaw muscles. Our results indicate that neurons projecting to NVmt are located in the dorsal ¾ region of NVsnpr. Electrical stimulation of the dorsal NVsnpr induced multiphasic excitatory synaptic responses in trigeminal MNs while BAPTA application, which causes NVsnpr neurons to fire rhythmically, also induced rhythmic firing in some MNs, further emphasizing the functional relationship between these two nuclei in terms of rhythm transmission. In our calcium imaging experiments, electrical stimulation of NVsnpr evoked calcium responses in MNs located mainly in the jaw-closing region of NVmt and revealed a specific pattern of connectivity between the two nuclei. The organization of the projections seemed to depend critically on the dorsoventral location of the stimulation site within NVsnpr. The dorsolateral region of NVmt received mainly inputs from the dorsal NVsnpr (R1 and R2), whereas the ventromedial region of NVmt was found to receive inputs from R2 and R3 which account for the major part of the intermediate division of the NVsnpr. This study confirms and develops earlier experiments by exploring the physiological nature and functional topography of the connectivity between NVsnpr and NVmt that was demonstrated in the past with neuroanatomical techniques.