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.

Influence of orthodontic appliance-derived artifacts on 3-T MRI movies.

BACKGROUND: Magnetic resonance imaging (MRI) has been used to study configurations of speech organs in the resting state. However, MRI is sensitive to metals, and numerous types of metallic appliances, most of which have a large magnetic susceptibility, are used in orthodontic treatment and may cause severe artifacts on MRI. We have developed techniques for obtaining MRI movies of the oral region, to evaluate articulatory changes, especially movement of the tongue, palate, and teeth, pre- and post-orthodontic/orthognathic treatment. We evaluated the influence of artifacts caused by orthodontic appliances, including fixed retainers, metal brackets, and wires, on measurements in 3-T MRI movies. METHODS: Sixteen healthy young adults (nine males, seven females; average age, 27 years) with normal occlusion were recruited. Four types of customized maxillary and mandibular plates were prepared by incorporating one of the following into the plate: (a) nothing, (b) a fixed canine-to-canine retainer, (c) metal brackets for the anterior and molar teeth, or (d) clear brackets for the anterior teeth and metal brackets for molars. A 3-T MRI movie, in segmented cine mode, was generated for each plate condition while participants pronounced a vowel-consonant-vowel syllable (/asa/). The size of the artifact due to the metallic brackets was measured. The face size and orthodontically important anatomical structures, such as the velum, the hard palate, and the laryngeal ventricle, were also measured. RESULTS: A large artifact was observed over the entire oral region around orthodontic appliances, altering regional visibility. The velopharyngeal height was measured as significantly longer in the presence of metal brackets. The maximum artifact size due to a metallic bracket was > 8 cm. Our results show that even if it is possible to obtain the measurements of palate length, nasion to sella, and nasion to basion in individuals wearing metal brackets for molars, the measurements might be affected due to the presence of artifacts. CONCLUSIONS: Orthodontic appliances, including metallic materials, sometimes produce significant measurement error in speech evaluation using MRI movies, which often become invisible or distorted by metallic orthodontic appliances. When the distorted image is measured, caution should be exercised, as the measurement may be affected. Based on the study, it is concluded that orthodontists should not necessarily remove all metallic appliances before MRI examination because the influence varies among the appliances and should also know that a significant measurement error in speech evaluation using MRI movie may occur by image distortion caused by metallic artifacts.

Differences in Velopharyngeal Structure during Speech among Asians Revealed by 3-Tesla Magnetic Resonance Imaging Movie Mode.

OBJECTIVE: Different bony structures can affect the function of the velopharyngeal muscles. Asian populations differ morphologically, including the morphologies of their bony structures. The purpose of this study was to compare the velopharyngeal structures during speech in two Asian populations: Japanese and Thai. METHODS: Ten healthy Japanese and Thai females (five each) were evaluated with a 3-Tesla (3 T) magnetic resonance imaging (MRI) scanner while they produced vowel-consonant-vowel syllable (/asa/). A gradient-echo sequence, fast low-angle shot with segmented cine and parallel imaging technique was used to obtain sagittal images of the velopharyngeal structures. RESULTS: MRI was carried out in real time during speech production, allowing investigations of the time-to-time changes in the velopharyngeal structures. Thai subjects had a significantly longer hard palate and produced shorter consonant than Japanese subjects. The velum of the Thai participants showed significant thickening during consonant production and their retroglossal space was significantly wider at rest, whereas the dimensional change during task performance was similar in the two populations. CONCLUSIONS: The 3 T MRI movie method can be used to investigate velopharyngeal function and diagnose velopharyngeal insufficiency. The racial differences may include differences in skeletal patterns and soft-tissue morphology that result in functional differences for the affected structures.

Use of an advanced 3-T MRI movie to investigate articulation.

OBJECTIVE: To develop a magnetic resonance imaging (MRI) movie to reveal the dynamic movement of articulators and teeth. STUDY DESIGN: Five healthy females with normal occlusion participated in this study. Various concentrations of MRI contrast media (ferric ammonium citrate [FAC]) were tested for visualization of teeth, according to facial markers and with the use of a gel. Custom-made circuitry was connected to synchronize pronunciation of fricative sounds (/asa/) with scans. Three gradient echo sequences (True fast imaging with steady state precession [true FISP], FISP, and fast low angle shot [FLASH]) with a segmented cine were tested with the use of repetition times (TRs) of 9 ms and 31.5 ms. The MRI movie images were superimposed over the boundaries of teeth. The images produced during pronunciation, using the two different TRs (9 ms and 31 ms), were compared to assess the position of the lips and the tongue. RESULTS: Images obtained using the FLASH sequence, with a TR of 9 ms or 31.5 ms, can be used for diagnostic purposes. A TR of 9 ms, with 161 continuous images acquired, produced the highest-quality images of teeth, with few artifacts present. Pronunciation of the consonant "s" was clearly discernable. CONCLUSIONS: Our 3-T MRI movie system, with a temporal resolution less than 9 ms, can provide detailed information pertaining to variations in speech or oropharyngeal function.

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.

Differential articulatory movements during Japanese /s/ and /t/ as revealed by MR image sequences with tooth visualization.

OBJECTIVE: To evaluate the spatio-temporal relationships between articulators in the anterior oral cavity, during the production of Japanese fricative and plosive articulation using our proposed method for tooth visualization in MR image sequences. DESIGN: Ten healthy adults without malocclusion participated in the study. Customized maxillary and mandibular plates with space around the central incisors that was to be filled with MR-compatible contrast medium were made. During image-acquisition by a cine magnetic resonance imaging (MRI) technique, the subjects repeated vowel-consonant-vowel syllables (/asa/ and /ata/) without wearing the plates. The subjects then wore the plates for tooth imaging. All data were acquired in the midsagittal plane. Tooth boundaries were superimposed using landmarks. Several parameters and spatio-temporal changes in the centre of gravity (CoG) of the tongue were measured. RESULTS: During /t/, the duration and amount of tongue-to-palate/incisor contact were significantly greater and the radius of the inscribed circle between the tongue-maxillary incisor-mandibular incisor was significantly shorter than those during /s/. /t/ also had a more anteriorly located CoG of the tongue than /s/ during maximum constriction. The spatio-temporal changes in the CoG of the tongue were significantly different between /asa/ and /ata/. CONCLUSIONS: We conclude that increased tongue-to-palate/incisor contact and greater anterior closure are necessary for the production of Japanese /t/ compared to /s/. With the use of this new method for tooth visualization in MR image sequences, it should be possible to evaluate the interaction of teeth and other articulators during speech.

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.

Motor coordination of articulators depends on the place of articulation.

Although the sounds/p/and/k/are both voiceless plosives, they have different places of articulation: bilabial and velar, respectively. The purpose of this study was to determine the relationship among articulators in plosives with reference to their place of articulation. Ten healthy subjects repeated bilabial and velar plosives in synchronization with magnetic resonance scanning. Each run was measured using a gradient echo sequence. Several linear and angular variables were defined to delineate the individual movements of articulators and to determine the temporal relationships among articulators. These variables showed distinctive changes depending on the place of articulation. In addition, movement of the velum was significantly correlated with that of the lips and the anterior part of the tongue in the bilabial plosive and with the posterior part of the tongue in the velar plosive. We conclude that unitary motor coordination of articulators depends on the place of articulation.

Combined fMRI and MRI movie in the evaluation of articulation in subjects with and without cleft lip and palate.

OBJECTIVE: This study was undertaken to explore the application of functional magnetic resonance imaging (fMRI) and MRI movies in the evaluation of articulatory function in subjects with and without cleft lip and palate (CLP). DESIGN: The authors examined brain activation and the dynamic movement of articulators during bilabial and velar plosives using fMRI and MRI movies. SUBJECTS: Two subjects, one with unilateral cleft lip and palate (UCLP) and one with bilateral cleft lip and palate (BCLP), and 12 non-CLP volunteers. RESULTS: Activation foci were found in the precentral gyrus, thalamus, and cerebellum in non-CLP volunteers. In comparison, similar regions were activated in the UCLP subject during both plosives, whereas the regions activated in the BCLP subject were different, particularly during the velar plosive. The dynamic movement of articulators in the UCLP subject was comparable to that in a non-CLP volunteer but different from that in the BCLP subject. CONCLUSIONS: The results suggest that these two MRI modalities may be a promising evaluation methodology for articulatory function in CLP from central and peripheral perspectives.

Changes in horizontal jaw position and intraoral pressure.

OBJECTIVE: To determine the effect of an imbalance in buccolingual pressure that may be involved in molar dental compensation in the mandible and asymmetry of the dental arch in subjects with facial asymmetry. MATERIALS AND METHODS: We performed simultaneous measurement of the buccolingual pressure on the mandibular right first molar when subjects without facial asymmetry experimentally shifted the mandible laterally. Buccolingual pressures in the rest position (RP), right-shifted position (RS), and left-shifted position (LS) were compared. Moreover, T1-weighted magnetic resonance images were obtained in RP, RS, and LS. RESULTS: Tongue pressure tended to decrease in the order LS > RP > RS, while cheek pressure tended to increase in the order LS < RP < RS. The tongue/cheek pressure ratio tended to decrease in the order LS > RP > RS. There were significant positive (in RS) and negative (in LS) correlations between displacement of the tongue and tongue pressure. CONCLUSIONS: This imbalance in buccolingual pressures in the laterally-shifted mandibular position may partly explain molar dental compensation in the mandible and asymmetry of the dental arch in subjects with facial asymmetry.

Characteristics of movement of the lips, tongue and velum during a bilabial plosive: a noninvasive study using a magnetic resonance imaging movie.

OBJECTIVE: To obtain dynamic images of articulators using a magnetic resonance imaging (MRI) movie and to clarify the relationships among the articulators. MATERIALS AND METHODS: The subjects consisted of 10 volunteers. Custom-made circuitry was connected to an MRI apparatus to enable an external trigger pulse to control the timing of the scanning sequence and to provide an auditory cue for synchronization of the subject's utterance. The subject repeated a bilabial plosive, and the run was measured using a gradient echo sequence with a repetition time of 30 ms. Several variables were defined to delineate the individual movements of articulators and to determine the temporal relationships among them. RESULTS: It was found that (1) the change in these variables showed distinctive waveforms; (2) mean values of the standard deviations for these variables were relatively small; and (3) the movement of the velum was significantly correlated with those of the lips and the anterior part of the tongue, but not with the posterior part of the tongue. CONCLUSIONS: These results suggest that (1) articulatory movements were clearly recorded using an MRI movie, and (2) there seems to be a central mechanism for controlling articulators, and the level of coupling may be associated with the place of articulation.

Mandibular distraction osteogenesis in a skeletal Class II patient with obstructive sleep apnea.

We report the orthodontic treatment of a 31-year-old man with severe skeletal Class II malocclusion and documented obstructive sleep apnea (OSA). He had a retrognathic profile with an overbite of 4 mm and an overjet of 14 mm. Mandibular distraction osteogenesis was performed to lengthen the small, retruded mandible by 18 mm and improve the symptoms of OSA. Orthodontic treatment after the mandibular distraction osteogenesis procedure lasted 3 years 1 month. An acceptable occlusion was obtained, and the patient's OSA was significantly alleviated. Although the patient was satisfied with the treatment, condylar resorption was observed. The relevance of condylar resorption with reference to a comprehensive evaluation of the treatment outcome is discussed.

Distinctive cortical articulatory representation in cleft lip and palate: a preliminary functional magnetic resonance imaging study.

OBJECTIVE: To investigate cortical representation of articulation of the bilabial plosive in patients with cleft lip and palate. DESIGN: We examined cortical representation for /pa/-articulation in cleft lip and palate patients using blood oxygenation level-dependent functional magnetic resonance imaging. SUBJECTS: Data from four postsurgical adult cleft lip and palate patients were compared with those from six healthy volunteers. RESULTS: Activation foci were found in the bilateral primary sensorimotor cortex in all cleft lip and palate patients, as in the controls. The sensorimotor cortex ipsilateral to the side of cleft lip and palate showed greater activation in unilateral cleft lip and palate patients, whereas the sensorimotor cortex contralateral to the side on which cheiloplasty had been performed earlier showed greater activation in a bilateral cleft lip and palate patient. CONCLUSIONS: The results suggest that there may be an ipsilateral dominance in cortical representation during bilabial articulation to the side of the cleft in the upper lip.

Effects of mandibular advancement on brain activation during inspiratory loading in healthy subjects: a functional magnetic resonance imaging study.

Oral appliances have been a popular treatment option for subjects with obstructive sleep apnea. However, little information is available on how brain activation induced by respiratory challenge is modulated by mandibular advancement with these appliances. We hypothesized that the brain activation caused by respiratory stress may be alleviated by mandibular advancement. Respiratory stress was induced in 12 healthy subjects by resistive inspiratory loading. The effects of mandibular advancement during resistive inspiratory loading were assessed subjectively by using a visual analog scale. These effects were also evaluated objectively by using blood oxygenation level-dependent functional magnetic resonance imaging. The score for the visual analog scale significantly decreased with mandibular advancement. Cortical deactivation, in association with mandibular advancement, was localized to several specific regions, including the left cingulate gyrus and the bilateral prefrontal cortexes. These regions are known to be involved in respiratory control. Our results suggest that mandibular advancement with an oral appliance appears to be useful for reducing respiratory stress, based on both subjective and neuronal criteria.

Radiopacity of experimental composite resins containing radiopaque materials.

This study aimed to investigate the relationship between the radiopacity of an experimental light-cured composite resin and the amount and type of its radiopaque material: Ti, SrCO3, ZrO2, BaSO4, or Bi2O3. Radiopacity of each material was evaluated in terms of aluminum equivalent thickness using an aluminum step wedge. Then, the half-value layer thickness of the experimental composite resin, which had an aluminium equivalent thickness of 1 mm, was evaluated. It was found that the effects of elemental composition were not identical when evaluated in terms of aluminum equivalent thickness and by half-value layer. Nevertheless, both measurement methods indicated that radiopacity increased with increase in radiopaque material content as well as increase in atomic number of the element.

Dynamic analysis of articulatory movement using magnetic resonance imaging movies: methods and implications in cleft lip and palate.

OBJECTIVES: To visualize articulatory movement using a magnetic resonance imaging (MRI) movie of a subject with cleft lip and palate (clp) and to demonstrate the usefulness of this method for studying oropharyngeal function. MATERIAL AND METHODS: Dynamic changes in oropharyngeal structures were assessed with an MRI movie of a man with cleft lip and palate and in a normal adult male volunteer during the articulation of /pa/, /ta/, and /ka/. RESULTS AND CONCLUSIONS: Different movement patterns were observed during articulation in the subject with CLP compared with the normal volunteer. Posterosuperior movement of the tongue and the anterior movement of the posterior pharyngeal wall were clearly visualized in the subject with CLP. Thus, MRI movies appear to be a promising tool for evaluating speech function in patients with CLP because of their noninvasive and nonradiation nature.

[Changes in shape of upper airway during titrated mandibular advancement: a magnetic resonance imaging study].

OBJECTIVE: To examine adaptive changes in the shape of the upper airway during titrated mandibular advancement. Furthermore, to understand the mechanism of mandible-adjustable therapy to improve the ventilation. METHODS: Fourteen non-apnea participated in the study. A custom-made oral device was used to keep the mandible in titrated advancement at 0% (F0), 50% (F50), 75% (F75), 100% (F100) of the maximum advancement. Magnetic resonance imaging was used to investigate the difference in the shape of upper-airway in these 4 positions. Changes in the anteroposterior direction (AP), lateral direction (Lat) and its ratio (AP/Lat) were calculated, which were transformed into the percentage of the original ones. RESULTS: The dose-dependent decrease of AP/Lat was found when the mandible was advanced (P = 0.0001). Lateral change rate in percentage increased by degrees (P = 0.0023), while the increase of anteroposterior change rate in percentage showed no statistical significance. CONCLUSION: The shape of upper airway tended to be less round. The enlargement of upper airway during titrated mandibular advancement was mainly the result of enlargement in lateral direction.

Comparison of fMRI data analysis by SPM99 on different operating systems.

The hardware chosen for fMRI data analysis may depend on the platform already present in the laboratory or the supporting software. In this study, we ran SPM99 software on multiple platforms to examine whether we could analyze fMRI data by SPM99, and to compare their differences and limitations in processing fMRI data, which can be attributed to hardware capabilities. Six normal right-handed volunteers participated in a study of hand-grasping to obtain fMRI data. Each subject performed a run that consisted of 98 images. The run was measured using a gradient echo-type echo planar imaging sequence on a 1.5T apparatus with a head coil. We used several personal computer (PC), Unix and Linux machines to analyze the fMRI data. There were no differences in the results obtained on several PC, Unix and Linux machines. The only limitations in processing large amounts of the fMRI data were found using PC machines. This suggests that the results obtained with different machines were not affected by differences in hardware components, such as the CPU, memory and hard drive. Rather, it is likely that the limitations in analyzing a huge amount of the fMRI data were due to differences in the operating system (OS).

Effect of titrated mandibular advancement and jaw opening on the upper airway in nonapneic men: a magnetic resonance imaging and cephalometric study.

The aim of this study was to examine adaptive changes in the cross-sectional area of the upper airway during mandibular advancement and jaw opening and to explore whether these changes are directly related to morphologic features of the mandible. Fourteen nonapneic men participated in this study. A custom-made oral device was used to keep the mandible at 0% (F(0)V(0)), 50% (F(50)V(0)), 75% (F(75)V(0)), or 100% (F(100)V(0)) of maximum advancement, and at 50% (F(75)V(50)), 75% (F(75)V(75)), or 100% (F(75)V(100)) of maximum gape at F(75)V(0). Magnetic resonance imaging was used to investigate differences in the upper-airway cross-sectional area in these 7 positions. To eliminate excessive individual variation, changes in the mean (mean%) and minimum (min%) cross-sectional area of the upper airway were calculated as percentages of those at F(0)V(0). Cephalograms were taken to analyze morphologic features of the mandible. A dose-dependent change was seen when the mandible was advanced. The min% in F(100)V(0) was significantly greater than those in F(50)V(0) and F(75)V(0). The change in the upper airway size varied between subjects during jaw opening. At F(75)V(0), the min% of the whole upper airway was significantly associated with morphologic features of the mandible, such as the mandibular plane angle and lengths of the mandibular body and ramus.