Occlusal tactile acuity in temporomandibular disorder pain patients: A case-control study

OBJECTIVE

To compare the smallest thickness that can be perceived between occluding teeth (occlusal tactile acuity, OTA) of temporomandibular disorder pain (TMD-P) patients with that of control (CTR) individuals.

METHODS

Twenty TMD-P patients (17 women and 3 men, mean age: 31.3 ± 10.4 years) diagnosed according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) protocol and 20 age- and gender-matched controls (17 women and 3 men, mean age: 31.4 ± 10.5 years) were enrolled. The OTA was tested with 10 different thicknesses: 9 aluminium foils (8 µm-72 µm with a constant increment of 8 µm) and 1 sham test (without foil), each thickness being tested 10 times in random order (100 tests in total). The participants were instructed to close their mouth once and to report whether they felt the foil between their molar teeth. A between-group comparison (TMD-P vs CTR) was performed for each testing thickness (analysis of variance for repeated measurements, with Bonferroni multiple correction) (P < .005).

RESULTS

Significantly increased OTA was observed in the TMD-P group for the thicknesses between 8 µm and 40 µm, while no significant differences were found for the sham test and for the larger thicknesses tested (from 48 µm to 72 µm).

CONCLUSIONS

TMD-pain subjects presented an increased OTA as compared to controls.

Limited Pre-Speech Auditory Modulation in Individuals Who Stutter: Data and Hypotheses

Purpose We review and interpret our recent series of studies investigating motor-to-auditory influences during speech movement planning in fluent speakers and speakers who stutter. In those studies, we recorded auditory evoked potentials in response to probe tones presented immediately prior to speaking or at the equivalent time in no-speaking control conditions. As a measure of pre-speech auditory modulation (PSAM), we calculated changes in auditory evoked potential amplitude in the speaking conditions relative to the no-speaking conditions. Whereas adults who do not stutter consistently showed PSAM, this phenomenon was greatly reduced or absent in adults who stutter. The same between-group difference was observed in conditions where participants expected to hear their prerecorded speech played back without actively producing it, suggesting that the speakers who stutter use inefficient forward modeling processes rather than inefficient motor command generation processes. Compared with fluent participants, adults who stutter showed both less PSAM and less auditory-motor adaptation when producing speech while exposed to formant-shifted auditory feedback. Across individual participants, however, PSAM and auditory-motor adaptation did not correlate in the typically fluent group, and they were negatively correlated in the stuttering group. Interestingly, speaking with a consistent 100-ms delay added to the auditory feedback signal-normalized PSAM in speakers who stutter, and there no longer was a between-group difference in this condition. Conclusions Combining our own data with human and animal neurophysiological evidence from other laboratories, we interpret the overall findings as suggesting that (a) speech movement planning modulates auditory processing in a manner that may optimize its tuning characteristics for monitoring feedback during speech production and, (b) in conditions with typical auditory feedback, adults who stutter do not appropriately modulate the auditory system prior to speech onset. Lack of modulation of speakers who stutter may lead to maladaptive feedback-driven movement corrections that manifest themselves as repetitive movements or postural fixations.

Occlusal loading during biting from an experimental and simulation point of view

OBJECTIVES

Occlusal loading during clenching and biting is achieved by the action of the masticatory system, and forms the basis for the evaluation of the functional performance of prosthodontic and maxillofacial components. This review provides an overview of (i) current bite force measurement techniques and their limitations and (ii) the use of computational modelling to predict bite force. A brief simulation study highlighting the challenges of current computational dental models is also presented.

METHODS

Appropriate studies were used to highlight the development and current bite force measurement methodologies and state-of-the-art simulation for computing bite forces using biomechanical models.

RESULTS

While a number of strategies have been developed to measure occlusal forces in three-dimensions, the use of strain-gauges, piezo-electric sensors and pressure sheets remain the most widespread. In addition to experimental-based measurement techniques, bite force may be also estimated using computational models of the masticatory system. Simulations of different bite force models clearly show that the use of three-dimensional force measurements enriches the evaluation of masticatory functional performance.

SIGNIFICANCE

Hence, combining computational modelling with three-dimensional force measurement techniques can significantly improve the evaluation of masticatory system and the functional performance of prosthodontic components.

Reflex responses of human masseter motor units to mechanical stimulation of the teeth

Our aim was to investigate the jaw reflexes using both the probability- and the discharge rate-based analysis methods. Twelve consenting volunteer subjects participated in this study. Subjects bit gently on bite bars that carried the impression of their teeth. Surface and intramuscular electrical activity of the masseter was recorded. With the help of audio feedback from one motor unit, each subject bit to discharge the unit at a fixed rate. While the subject continuously activated the selected motor unit, 4-N stimuli were delivered to the upper right central incisor either at a rapid or a slow rate. For each trial, ≥300 stimuli were delivered, and, once a trial was completed, local anesthetic block was applied around the stimulated tooth, and the experiment was repeated. While preceding local anesthesia, the rapid-rate stimuli ("tap") induced substantial inhibitory reflex responses; during local anesthetic block, the same stimulus induced excitatory and inhibitory reflex responses. Slow-rate stimuli ("push"), on the other hand, usually generated a combination of inhibitory and excitatory responses that disappeared completely during the local anesthetic block. This study discovered that the strength of the inhibitory reflex response to a tooth-tap stimulus was much larger than previously reported. This study also found that whereas the probability-based analyses were better for illustrating the existence and latency of small earlier responses, the discharge rate-based method was better for indicating the duration of earlier responses and the existence, sign, and duration of later responses.

Electromyographic activity during awake tooth grinding tasks at different jaw posture in the sagittal plane

OBJECTIVE

The goal of this study was to evaluate the electromyographic (EMG) activity of the anterior temporalis, suprahyoid, infrahyoid and trapezius muscles during tooth grinding at different jaw posture tasks.

MATERIALS AND METHODS

Participants were 30 healthy subjects with natural dentition, bilateral molar support and incisive protrusive guidance. Bipolar surface electrodes were located on the right side of the subject. EMG recordings were performed in the following tasks: (A) Eccentric grinding from intercuspal position to protrusive edge-to-edge contact position; (B) concentric grinding from protrusive edge-to-edge contact position to intercuspal position; (C) eccentric grinding from intercuspal position to the maximum voluntary retrusive position; and (D) concentric grinding from the maximum voluntary retrusive position to intercuspal position. The results were analyzed statistically by Friedman test and Wilcoxon signed rank-sum test.

RESULTS

EMG activity in the anterior temporalis and infrahyoid muscles was significantly higher during task C than the other tasks. EMG activity in the suprahyoid muscles was significantly higher during task C than task D. EMG activity in the trapezius muscle was significantly higher during task C than tasks A and B.

CONCLUSIONS

The higher EMG activity recorded in task C could become important when its frequency, duration and magnitude are enough to exceed the adaptation capability of the individual.

New approaches to dental occlusion: a literature update

Because the study of occlusion is a basic area in dentistry, its components, physiology and integration with the stomatognathic system (SS) have been the subject of interest in the scientific literature. However, the focus given to this issue has changed substantially. Currently, new approaches have been proposed in order to update concepts and to demonstrate the full integration and functionality of this system within the human body. With this approach, the authors proposed the following literature review aimed at gathering recent papers (published from 2000 to 2010) with innovative study design, methodology and/or results. The authors' intention is to show the main trends in the study of occlusion and the SS. The literature review was conducted in the PubMed database, using initially the term "dental occlusion" as a key-word. As items of interest were found, papers were grouped by categories according to their main subject matter. Forty-seven articles were selected and the main categories obtained were: 1. functional magnetic resonance imaging (fMRI); 2. brain activation; 3. masticatory/occlusal function; 4. body function and physical performance; 5. osseoperception; 6. finite element models; and 7. occlusion and pain. Observing the current literature, the authors found that recent studies present different methodologies for the study of occlusion. These studies have allowed scientists to obtain detailed information about the physiology of occlusion and the SS, as well as about its integration in the body. Research in this area should be continued in order to clarify, in detail, the role of each component of the SS and its interaction with human physiology.

Self-initiation and temporal cueing of monaural tones reduce the auditory N1 and P2

Event-related potentials (ERPs) to tones that are self-initiated are reduced in their magnitude in comparison with ERPs to tones that are externally generated. This phenomenon has been taken as evidence for an efference copy of the motor command acting to suppress the sensory response. However, self-initiation provides a strong temporal cue for the stimulus which might also contribute to the ERP suppression for self-initiated tones. The current experiment sought to investigate the suppression of monaural tones by temporal cueing and also whether the addition of self-initiation enhanced this suppression. Lastly, the experiment sought to investigate the lateralisation of the ERP suppression via presenting these monaural tones to each ear respectively. We examined source waveforms extracted from the lateralised auditory cortices and measured the modulation of the N1 and P2 components by cueing and self-initiation. Self-initiation significantly reduced the amplitude of the N1 component. Temporal cueing without self-initiation significantly reduced the P2 component. There were no significant differences in the amplitude of either the N1 or the P2 between self-initiation and temporal cuing. There was a significant lateralisation effect on the N1—it being significantly larger contralateral to the ear of stimulation. There was no interaction between lateralisation and side of the temporal cue or side of self-initiation suggesting that the effects of self-initiation and temporal cuing are equal bilaterally. We conclude that a significant proportion of ERP suppression by self-initiation is a result of inherent temporal cueing.

Measurement of dynamic bite force during mastication

Efficient mastication of different types and size of food depends on fast integration of sensory information from mechanoreceptors and central control mechanisms of jaw movements and applied bite force. The neural basis underlying mastication has been studied for decades but little progress in understanding the dynamics of bite force has been made mainly due to technical limitations of bite force recorders. The aims of this study were to develop a new intraoral bite force recorder which would allow the study of natural mastication without an increase in the occlusal vertical dimension and subsequently to analyze the relation between electromyographic (EMG) activity of jaw-closing muscles, jaw movements and bite force during mastication of five different types of food. Customized force recorders based on strain gauge sensors were fitted to the upper and lower molar teeth on the preferred chewing side in fourteen healthy and dentate subjects (21-39 years), and recordings were carried out during voluntary mastication of five different kinds of food. Intraoral force recordings were successively obtained from all subjects. anova showed that impulse of bite force as well as integrated EMG was significantly influenced by food (P<0·05), while time-related parameters were significantly affected by chewing cycles (P<0·001). This study demonstrates that intraoral force recordings are feasible and can provide new information on the dynamics of human mastication with direct implications for oral rehabilitation. We also propose that the control of bite force during mastication is achieved by anticipatory adjustment and encoding of bolus characteristics.