Vowel sound production and its association with cephalometric characteristics in skeletal Class III subjects.

BACKGROUND: This study aimed to evaluate differences in vowel production using acoustic analysis in skeletal Class III and Class I Japanese participants and to identify the correlation between vowel sounds and cephalometric variables in skeletal Class III subjects. MATERIALS AND METHODS: Japanese males with skeletal Class III (ANB < 0°) and Class I skeletal anatomy (0.62° < ANB < 5.94°) were recruited (n = 18/group). Acoustic analysis of vowel sounds and cephalometric analysis of lateral cephalograms were performed. For sound analysis, an isolated Japanese vowel (/a/,/i/,/u/,/e/,/o/) pattern was recorded. Praat software was used to extract acoustic parameters such as fundamental frequency (F0) and the first four formants (F1, F2, F3, and F4). The formant graph area was calculated. Cephalometric values were obtained using ImageJ. Correlations between acoustic and cephalometric variables in skeletal Class III subjects were then investigated. RESULTS: Skeletal Class III subjects exhibited significantly higher/o/F2 and lower/o/F4 values. Mandibular length, SNB, and overjet of Class III subjects were moderately negatively correlated with acoustic variables. LIMITATIONS: This study did not take into account vertical skeletal patterns and tissue movements during sound production. CONCLUSION: Skeletal Class III males produced different /o/ (back and rounded vowel), possibly owing to their anatomical positions or adaptive changes. Vowel production was moderately associated with cephalometric characteristics of Class III subjects. Thus, changes in speech after orthognathic surgery may be expected. A multidisciplinary team approach that included the input of a speech pathologist would be useful.

Three-dimensional characteristics of temporomandibular joint morphology and condylar movement in patients with mandibular asymmetry.

BACKGROUND: Investigating the morphological and functional effects on mandibular asymmetry (MA) is important not only to understand the developmental process of masticatory dysfunction, but also to provide suggestions for evidence-based occlusal treatment. AIM: To evaluate three-dimensional temporomandibular joint (TMJ) morphology and its relationship to asymmetrical condylar movement in MA patients. MATERIALS AND METHODS: Fifty subjects were divided into MA and control groups (n = 25 each) according to a menton deviation of 4 mm from the mid-sagittal plane. TMJ morphology (condyle, glenoid fossa and TMJ spaces) were evaluated using a three-dimensional analysis programme. Three-dimensional condylar movements (from the sagittal and horizontal planes) were recorded and measured by computerized axiography on protrusion. Side-to-side asymmetry was measured for each parameter. The asymmetry index value was calculated to assess the correlation between TMJ morphology and condylar movement. For the statistical analysis, Wilcoxon's signed-ranked test, the Mann-Whitney U test, and Spearman's rank correlation were used. RESULTS: Glenoid fossa volume, surface area, anteroposterior length, and condylar volume were significantly smaller, and articular eminence angle, glenoid fossa, and condylar axial angle were significantly larger, on the shifted side of the MA group when compared with those on the non-shifted side and the mean values of the control group (P < 0.05). The TMJ spaces of the MA group showed no bilateral difference but were significantly narrower in the medial, superior, and anterior joint spaces when compared with the control group (P < 0.05). Condylar path length and sagittal condylar inclination were significantly asymmetrical. The asymmetry index of the condyle volume was significantly correlated with that of the condylar path length (P = 0.005). The asymmetry index of the glenoid fossa volume and the articular eminence angle were significantly correlated with that of the sagittal condylar inclination (P = 0.009 and P = 0.002, respectively), and the asymmetry index of glenoid fossa volume was significantly correlated with the bilateral transverse condylar inclination (P = 0.006 and P = 0.016, respectively). CONCLUSIONS: Morphological asymmetry of the TMJ is significantly different between the shifted and non-shifted sides and is closely related to functional asymmetry of condylar movement in MA patients. (350/350).

Correlation between the position of the glenoid fossa and condylar translational movement in skeletal Class III mandibular asymmetry patients.

OBJECTIVES: Understanding the mechanism of mandibular asymmetry (MA) is important to provide suggestions for occlusal treatment and to know the developmental process of masticatory dysfunction. To investigate the morphological and functional effects on MA, we evaluated the three-dimensional position of the glenoid fossa and its relationship to asymmetrical condylar translational movement. METHODS: In this retrospective study, 50 subjects who previously underwent computed tomography for surgical purposes were divided into MA and control groups according to a menton deviation of at least 4 mm from the mid-sagittal plane. The glenoid fossae positions were evaluated using a three-dimensional analysis program. Condylar translational movements were recorded and measured by computerized axiography on protrusion. Side-to-side asymmetry was measured for each parameter. Asymmetry index value was calculated to assess the correlation between glenoid fossa position and condylar movement. Wilcoxon's signed-ranked test, Mann-Whitney U-test, and Spearman's rank correlation were used for the statistical analysis. RESULTS: In the MA group, glenoid fossa position on the shifted side was significantly inferior and posterior as compared to that on the non-shifted side and of the control group. Condylar path length and sagittal condylar inclination were significantly greater on the shifted side versus non-shifted side, while no significant difference was found in transverse condylar inclination. The asymmetry index of the anterior-posterior glenoid fossa position was significantly correlated with that of condylar path length and bilateral transverse condylar inclination. In the control group, there were no significant correlations among the morphological and functional parameters. LIMITATIONS: This study did not consider muscle activity and disc position, which may affect condylar movement. CONCLUSIONS: Functional asymmetry of condylar translational movements is closely related to asymmetry of glenoid fossa position in MA patients.

Reciprocal cortical activation patterns during incisal and molar biting correlated with bite force levels: an fMRI study.

In humans, the incisors and molars have distinct functions during mastication, analogous to the two main types of handgrip, the precision and power grips. In the present study, we investigated cortical activation and masticatory muscle activity during incisal and molar biting via simultaneous functional magnetic resonance imaging and electromyogram (EMG) recordings. We conducted recordings in 15 healthy adult participants while they performed incisal and molar biting tasks at three step-wise force levels using two custom-made splints. Regarding the results of the ROI analysis, we found a significantly stronger positive linear correlation between the blood oxygenation level dependent signal and EMG activity during molar biting than incisal biting, which was particularly prominent in the primary sensorimotor cortex and the cerebellum. We also found a significantly stronger negative linear correlation during incisal biting than molar biting, which was particularly prominent in the rostral cingulate motor area, superior frontal gyrus, and caudate nucleus. These findings indicate that molar biting enables powerful chewing: brain activity in several brain areas related to motor function was increased with increasing bite force levels, while incisal biting enables fine motor control: brain activity in several brain areas related to motor control was increased with reduced bite force levels.

New application of dynamic magnetic resonance imaging for the assessment of deglutitive tongue movement.

BACKGROUND: Deglutitive motion of the tongue may function to maintain tooth position. However, the causation between abnormal patterns of orofacial muscle function and dental malocclusion remains unclear. To clarify the pathogenic mechanism of malocclusion, it is important to determine the relative positional relationship between the tongue tip and incisor edge or the dorsal tongue and palate during deglutition. Here, we assessed the utility of 3-T segmented cine-magnetic resonance (MR) imaging, combined with static MR images for hard tissue visualization, in assessing the relationship between the tongue and the surrounding tissues during deglutitive tongue movement. METHODS: Cine-MR images were acquired from three healthy female volunteers during deglutition who had no history of swallowing disorder or other chronic illness, normal alignment and occlusion, and a skeletal class I relationship. Three cine-MR images were taken during deglutition in accordance with an auditory cue for each volunteer. During static imaging, custom-made, contrast-medium-filled clear retainers were positioned in the mouth to allow visualization of the upper and lower incisors and hard palate boundaries. Static images were superimposed onto images of the three stages in deglutitive tongue movement, which were selected from a series of cine-MR images. These superimpositions were assessed five times by tracing cephalometric parameters to examine the reproducibility of the method. RESULTS: Traces varied little across repeated measurements, and all subjects had a similar pattern of dorsal tongue movement. Tongue-to-palate contact increased slightly during the first to second stage of swallowing and abruptly increased during the second to third stage, while the tongue tip position remained constant. CONCLUSIONS: Segmented cine-MR imaging combined with static MR images is useful for assessing soft tissue motion during deglutition. This method is particularly useful in dentistry to evaluate the relationship between tongue function and maxillofacial morphology in terms of orthodontic treatment and orofacial myofunctional therapy, and for improving tongue movement during speech therapy.

Chewing Stimulation Reduces Appetite Ratings and Attentional Bias toward Visual Food Stimuli in Healthy-Weight Individuals.

Based on the theory of incentive sensitization, the exposure to food stimuli sensitizes the brain's reward circuits and enhances attentional bias toward food. Therefore, reducing attentional bias to food could possibly be beneficial in preventing impulsive eating. The importance of chewing has been increasingly implicated as one of the methods for reducing appetite, however, no studies to investigate the effect of chewing on attentional bias to food. In this study, we investigated whether chewing stimulation (i.e., chewing tasteless gum) reduces attentional bias to food as well as an actual feeding (i.e., ingesting a standardized meal) does. We measured reaction time, gaze direction and gaze duration to assess attentional bias toward food images in pairs of food and non-food images that were presented in a visual probe task (Experiment 1, n = 21) and/or eye-tracking task (Experiment 2, n = 20). We also measured appetite ratings using visual analog scale. In addition, we conducted a control study in which the same number of participants performed the identical tasks to Experiments 1 and 2, but the participants did not perform sham feeding with gum-chewing/actual feeding between tasks and they took a rest. Two-way ANOVA revealed that after actual feeding, subjective ratings of hunger, preoccupation with food, and desire to eat significantly decreased, whereas fullness significantly increased. Sham feeding showed the same trends, but to a lesser degree. Results of the visual probe task in Experiment 1 showed that both sham feeding and actual feeding reduced reaction time bias significantly. Eye-tracking data showed that both sham and actual feeding resulted in significant reduction in gaze direction bias, indexing initial attentional orientation. Gaze duration bias was unaffected. In both control experiments, one-way ANOVAs showed no significant differences between immediately before and after the resting state for any of the appetite ratings, reaction time bias, gaze direction bias, or gaze duration bias. In conclusion, chewing stimulation reduced subjective appetite and attentional bias to food, particularly initial attentional orientation to food. These findings suggest that chewing stimulation, even without taste, odor, or ingestion, may affect reward circuits and help prevent impulsive eating.

Comparison of EMG activity and blood flow during graded exertion in the orbicularis oris muscle of adult subjects with and without lip incompetence: a cross-sectional survey.

Background/Objectives: The peri-oral muscles-including orbicularis oris-are critical in maintaining equilibrium in tooth position. Lip incompetence (LI) can thus be a factor in malocclusion. We therefore aimed to validate a technique to evaluate not only muscle activity via electromyography (EMG) but also muscle endurance and fatigue via blood flow (BF) for LI. Subjects/Methods: Subjects were classified into increased muscle tension/lip incompetent (experimental) and normal muscle tension/lip competent (control) groups. Each subject then exerted force on a custom-made traction plate connected to a tension gauge. Using laser speckle imaging and electromyographic measurements, we characterized muscle activity and corresponding BF rates in these subjects in various states of resting, loading, and recovery. Results: Results showed a significant difference between the experimental and control groups, notably in the rate of change in BF to the inferior orbicularis oris muscle under conditions of increasing load (graded exertion). Furthermore, the data suggested that the muscles in the control group undergo a more prolonged (and therefore presumably more complete) recovery than muscles in the experimental group. These factors of reduced BF and short recovery may combine to accelerate muscle fatigue and produce LI. Limitations: The sample used here was controlled for malocclusion (including open bite) to eliminate this type of confounding effect. Conclusions/Implications: From these findings, we conclude that reduced BF and inadequate recovery in the orbicularis oris muscles may be more significant than EMG activity in the assessment of LI.

Association between 3-dimensional mandibular morphology and condylar movement in subjects with mandibular asymmetry.

INTRODUCTION: The purpose of this study was to evaluate the hypothesis that 3-dimensional mandibular morphology is correlated with condylar movement in patients with mandibular asymmetry. METHODS: Subjects were classified into 2 groups (n = 25 each): mandibular asymmetry with a menton deviation greater than 4 mm and no mandibular asymmetry with a menton deviation less than 4 mm. Linear and volumetric measurements of 3-dimensional mandibular morphology were recorded using computed tomography. Mandibular functional movement was recorded by computerized axiography (CADIAX; Gamma Dental, Klosterneuburg, Austria), and condylar path length, sagittal condylar inclination, and transverse condylar inclination on protrusion were measured. We calculated side-to-side asymmetry (shifted side vs nonshifted side) in mandibular morphology and assessed condylar movement by using an asymmetry ratio (nonshifted side/shifted side). RESULTS: Significant differences in mandibular morphology and condylar movement were found between the 2 groups. In the group with menton deviation greater than 4 mm, significant correlations were found between the asymmetry ratio of mandibular morphology and condylar movement: ie, condylar path length and transverse condylar inclination. No significant correlations were found between any of these measurements in the group with menton deviation less than 4 mm. CONCLUSIONS: In support of our hypothesis, the results suggested that 3-dimensional mandibular morphologic asymmetry is associated with condylar movement in subjects with mandibular asymmetry.

Evaluation of blood flow and electromyographic activity in the perioral muscles.

BACKGROUND/OBJECTIVES: Although the electromyographic (EMG) activity of the perioral muscles, including the orbicularis oris and mentalis muscles, has been described in individuals with lip incompetence during lip sealing, blood flow through these muscles remains to be elucidated. The purpose of this study was to examine the blood flow associated with EMG activity in the perioral muscles using laser speckle imaging in individuals with lip incompetence. SUBJECTS/METHODS: Blood flow and EMG activity of the superior and inferior orbicularis oris and mentalis muscles were measured with the lips in contact (C condition) and apart (O condition) in lip incompetence (experimental) and control subjects (n = 15 in each group; mean age: 29.5 years). The change ratios of blood flow and EMG activity in the C condition versus O condition (C/O ratios) were calculated and plotted in a scattergram. The Mann-Whitney U-test, Wilcoxon signed-rank test, discriminant analysis using the Mahalanobis generalized distance, and Spearman correlation were used for statistical analysis. RESULTS: In the experimental group, blood flow and EMG activity in all muscles were significantly greater in the C condition than in the O condition. The plots of C/O ratios in the experimental group showed a distinct and wide distribution and were significantly different than those in the control group. In both groups, a significant positive correlation was observed between blood flow and EMG activity in the mentalis muscle. CONCLUSIONS/IMPLICATIONS: The present findings suggest that observing blood flow in the mentalis muscle is an effective and easily performed method of evaluating lip incompetence.

Comparison of the mandibular hinge axis in adult patients with facial asymmetry with and without posterior unilateral crossbite.

BACKGROUND/OBJECTIVES: Although it has been suggested that adult patients with facial asymmetry with posterior unilateral crossbite (PUXB) may have a more tilted mandibular hinge axis (MHA) than those without PUXB, whether craniofacial morphology is associated with the MHA remains unclear. The purpose of this study was to compare the craniofacial morphology and MHA in adult subjects with post-growth facial asymmetry with and without PUXB. SUBJECTS/METHODS: Thirty pre-orthodontic patients (PUXB and non-PUXB groups, n = 15 each, 9 females and 6 males, mean age: 23.2 years) participated in the study. The MHA was measured by computerized axiography and duplicated on posteroanterior and submentovertex cephalometric radiographs. Morphological asymmetry was evaluated for both skeletal and dental components and positional deviation of the mandible by cephalometric analysis. The Mann-Whitney U-test and Spearman's correlation coefficient by rank were used for statistical analysis. The level of statistical significance was set at P < 0.05. RESULTS: Significant differences in both skeletal and dental components were found between the PUXB and non-PUXB groups. In both the frontal and horizontal dimensions, the inclination of the MHA towards the mandibular shifted side was greater in the PUXB group than in the non-PUXB group. CONCLUSIONS/IMPLICATIONS: The present findings suggest that facially asymmetric adult subjects with malocclusions associated with PUXB exhibit not only mandibular asymmetry but also remodelling of the condylar head and glenoid fossa that accompanies the three-dimensional shifting of the MHA.

Cervical characteristics of Noonan syndrome.

BACKGROUND/OBJECTIVES A short neck and low posterior hairline are characteristics of Noonan syndrome (NS) and are hallmarks of basilar invagination/impression. However, it is seldom that NS has been directly linked with this symptom. Thus, this study aimed to investigate basilar impression in NS subjects compared with control subjects and individuals exhibiting Turner Syndrome (TS). SUBJECTS/METHODS The degree of basilar impression and vertical positional differences of the third and fourth cervical vertebrae and hyoid bone in NS (n = 9, mean age: 12.1 years), TS (n = 9, mean age: 12.1 years), and control subjects (n = 9, mean age: 12.0 years) were investigated using lateral cephalometric radiographs. Differences between the three groups were compared using the Steel-Dwass test. Vertical positional differences in the anatomical structures within each group were compared using the Wilcoxon signed-rank test accompanied by a Bonferroni-Holm correction. RESULTS The distance by which the odontoid tip extended past McGregor's line in subjects with NS was significantly greater compared with TS and control subjects. The third and fourth cervical vertebrae were positioned significantly superiorly in subjects with NS compared with TS and control subjects and, in NS, were also significantly superior to the hyoid bone. There was no difference in the position of the hyoid bone itself between the groups. CONCLUSION/IMPLICATION These results suggest that basilar impression may be a frequently found symptom of NS.

Effects of cortical activations on enhancement of handgrip force during teeth clenching: an fMRI study.

We assessed the effect of teeth clenching on handgrip force behaviorally, and investigated cortical activity during the occurrence of facilitatory effects using functional magnetic resonance imaging (fMRI). Twenty-three participants were assessed as to whether they had habitual teeth clenching during maximal voluntary contraction (MVC) exertion, and 21 of them were identified to have such a habit. For those participants, behavioral testing showed that MVC with clenching was greater compared with without clenching (approximately 108% greater on average). Next, cortical activity was measured under gripping with clenching (GwC), gripping without clenching (GwoC), and teeth clenching (C) conditions. We found that the activity of the hand region in primary motor cortex (M1), cingulate motor area/supplementary motor area (CMA/SMA) and anterior cerebellum (AC) was greater in contrast of GwC vs. (GwoC+C). Furthermore, significant correlation was observed between the increasing ratio of the handgrip force and the % signal change in the hand region of M1 and AC, but not in CMA/SMA. These results suggest that the activation in the hand region of M1 and AC may facilitate the spinal motoneurons, and the activation in the hand region in M1 by clenching may be due to a signal from CMA/SMA.

Association between intraoral pressure and molar position and inclination in subjects with facial asymmetry.

Although it has been suggested that an imbalance in buccolingual pressure may play a role in dental compensation of the molars and asymmetry in the mandibular dental arch in subjects with facial asymmetry, it is still unclear whether buccolingual pressure is associated with this phenomenon. Thus, the purpose of this study was to test the null hypothesis that there are no differences in cheek and tongue pressure between the shifted and non-shifted sides in 12 (8 females and 4 males, mean age: 24.9 years) subjects with facial asymmetry defined as 4 mm or more deviation of the midline in the mandibular incisors. The resting buccolingual pressure on the bilateral mandibular first molars was measured simultaneously using four miniature pressure sensors. Moreover, a postero-anterior (PA) cephalogram was used to determine the buccolingual positions and the inclination of the mandibular first molars. Wilcoxon t-, Kruskal-Wallis H-, and Mann-Whitney U-tests and Spearman correlation coefficient by rank were used for statistical analysis. Significance was set at P < 0.05. Cheek pressure was significantly greater on the shifted than that on the non-shifted side, while tongue pressure on the shifted side was significantly less than that on the non-shifted side. On the other hand, tongue/cheek pressure ratio on the shifted side was significantly less than that on the non-shifted side. There were significant differences between the shifted and non-shifted sides in the buccolingual positions and inclination of the mandibular first molars. Regardless of the side, there were significant negative correlations between the buccolingual position of the mandibular first molars and cheek pressure and significant positive correlations between the buccolingual position of the mandibular first molars and tongue/cheek pressure ratio. There were also significant negative correlations between tongue/cheek pressure ratio and inclination of the mandibular first molars on both the shifted and the non-shifted sides. Thus, the present findings reject the null hypothesis. The imbalance in buccolingual pressure in subjects with facial asymmetry appears to be related to dental compensation of the molars and mandibular asymmetry.

Preferred chewing side-dependent two-point discrimination and cortical activation pattern of tactile tongue sensation.

Although tactile feedback from the tongue should contribute to habitual chewing, it is unclear how the sensation of the tongue and its projection to the central nervous system differ with regard to the preferred chewing side (PCS). The purpose of this study was to investigate (1) whether the sensory threshold of the tongue differed according to the side and (2) whether the pattern of hemispheric cortical activation by tactile tongue stimulation differed, with special attention to the PCS. Twelve healthy adults participated in the study. The PCS was determined with a mandibular kinesiograph. In the behavioral study, the mean thresholds for two-point discrimination (TPD) in the anterior, canine and posterior regions on both sides of the tongue, and those between PCS and non-PCS in each region were statistically compared. In the functional magnetic resonance imaging study, tactile stimulation was delivered to either side of the tongue with acrylic balls via a mandibular splint. The runs were measured with a T2*-weighted gradient echo-type echo planar imaging sequence in a 1.5T scanner. Activated voxel numbers in the bilateral primary somatosensory cortex (S1) were statistically compared. The threshold of TPD increased in the order of the anterior, canine and posterior regions. Moreover, this threshold was significantly smaller on the PCS than on the non-PCS in both the canine and posterior regions. Moreover, the number of activated voxels in S1 contralateral to the PCS was significantly greater than that in S1 contralateral to the non-PCS. The present study shows that the PCS is associated with asymmetric tactile sensation and cortical activation of the tongue. The sensory acuity of the tongue on the PCS may play an important role in functional coupling between the jaw and tongue to maximize the efficiency of chewing.

The representation of the human oral area in the somatosensory cortex: a functional MRI study.

The tactile sensation of the teeth is involved in various oral functions, such as mastication and speech. Using functional magnetic resonance imaging, we investigated the cortical sensory representation of the oral area, including the teeth. First, we identified the somatotopic representation of the lips, teeth and tongue in the postcentral gyrus (GpoC). Tactile stimuli were applied to the lower lip, tongue and teeth. The foci activated by each stimulus were characterized by the center of gravity (COG) of activated areas. Secondly, we examined the rostro-caudal changes in the somatotopic organization in the GPoC in terms of the overlap between each sensory representation. In the rostral portion of the GPoC, the COG of the representation of teeth was located significantly superior to that of the tongue and inferior to that of the lip, consistent with the classical 'sensory homunculus' proposed by Penfield; however, this somatotopic representation became unclear in the middle and caudal portions of the GPoC. The overlap between each representation in the middle and caudal portions of the GPoC was significantly greater than that in the rostral portion of the GPoC. These findings support the theory that the input from oral structures converges hierarchically across the primary somatosensory cortex.