Kazuo Shimazaki

Functional relationships between the masseter and sternocleidomastoid muscle activities during gum chewing

The purpose of this study was to investigate the functional relationship between masseter muscle (MM) and sternocleidomastoid muscle (SCM) activities and between mandibular and head movements during mastication, under experimental muscle fatigue. The sample consisted of 12 adults with individually normal occlusion. The subjects were asked to chew gum at three different times: before maximum clenching, immediately after maximum clenching, and 3 minutes after maximum clenching. At these times, we examined the activity of the MM and SCM as well as the movement of the mandible and head. The activity and movement were simultaneously measured using both electromyography and the motion capture system. The MM activity time after clenching was significantly shorter than that before clenching, whereas the SCM activity time was significantly longer after clenching. There was no significant difference in the changes of three-dimensional distance of the mandibular movement between the respective times. On the other hand, the changes in the three-dimensional distance of head movement after clenching increased when compared with before clenching. Furthermore, the difference in the time of MM and SCM activity onset and of mandibular and head movement onset after clenching was shorter than that before clenching. A functional relationship exists between the MM and SCM activities and between mandibular and head movements during mastication.

An anatomic study of the attachments on the condylar process of the mandible: muscle bundles from the temporalis.

PurposeThe aim of this study was to evaluate anatomically the relationship between bone and muscles by detailed observation of the bone shape and the structure of muscles to facilitate an understanding of the function of the muscles involved in jaw movement.Methods36 specimens of 24 Japanese cadavers were examined. The insertion areas were marked using a radiopaque marker and examined by micro-computed tomography. For morphological observation, we used 101 condylar processes. In addition, we made histological sections in some specimens to observe the detailed attachments of the muscle.ResultsBased on the micro-CT images and dissection findings, the lateral pterygoid muscle was found to be most frequently inserted into the anterior impression and attached to the medial impression of the process. According to the histological observations, the lateral pterygoid muscle mainly inserted to the condylar process. The micro-CT images indicated that the obvious bony ridge was lateral to the pterygoid fovea on the condylar process in all specimens. The midmedial muscle bundle of the temporalis was attached to the ridge. Based on the morphological observations, the ridge was situated on the lateral area of the condylar process.ConclusionsSince dysfunction of the temporomandibular joint is likely closely related to both the lateral pterygoid muscle and also the temporalis, further studies are necessary to evaluate the function of these muscles and consider jaw movement.

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.

Severe unilateral scissor bite and bimaxillary protrusion treated by horseshoe Le Fort I osteotomy combined with mid-alveolar osteotomy

This report describes an orthognathic surgical case employing horseshoe Le Fort I osteotomy (HLFO) combined with mid-alveolar osteotomy and bilateral sagittal split ramus osteotomy (BSSRO) for a patient with severe unilateral scissor bite and bimaxillary protrusion. A female patient (aged 26 years, 2 months) presented with a chief complaint of dysmasesis caused by scissor bite on the right side. The clinical examination revealed difficulty in lip closure and a convex profile. Overerupted right maxillary premolars and molars and lingual tipping of the right mandibular premolars and molars were indicated before treatment. After 3 months of presurgical orthodontic treatment, two-jaw surgery involving a combination of HLFO with mid-alveolar osteotomy and BSSRO was performed. A good interdigitation in the right side was established by superior-posterior-medial movement of the dento-alveolar segment of the maxilla. Next, both the maxilla and mandible were moved superiorly and posteriorly to correct the improper lip protrusion, thereby improving the patients profile. Our results suggest that this new orthognathic surgery technique-achieved by combining HLFO with mid-alveolar osteotomy and BSSRO-is effective for adult patients exhibiting severe unilateral scissor bite and bimaxillary protrusion.

Influence of habitual mouth breathing on taste sensation

Abstract Purpose Although habitual mouth breathing is recognized to cause various disorders of orofacial growth and function, including taste sensation, the relationship between habitual mouth breathing and taste disorders has not been investigated sufficiently. This study aimed to examine the influence of habitual mouth breathing on taste sensitivity and relevant factors such as salivation, oral moisture, and olfactory function. Materials and methods Thirty volunteers (male, 18; female, 12) aged 22–35 years participated in this study. On the basis of their responses to a questionnaire regarding habitual breathing, 15 subjects each were assigned to the mouth-breathing (MB) and control groups. Recognition thresholds for sweet, salty, sour, bitter, and umami tastes at the tip and root of the tongue were measured using the filter-paper disk method. Salivary flow and spinnbarkeit (viscosity), oral moisture, and olfactory function were also measured as factors related to taste sensitivity. Additionally, a questionnaire about dry mouth, nasal obstruction, snoring, and olfaction was implemented. Results The MB group exhibited significantly higher recognition thresholds for sweetness and sourness at the tip and for bitterness and sourness at the root of the tongue compared with the control group. However, there was no significant intergroup difference in the threshold for salty or umami taste, salivary flow or spinnbarkeit, oral moisture, or olfactory function. The MB group exhibited a significantly higher subjective feeling of dry mouth, nasal obstruction, and snoring than the control group. Conclusions Mouth breathing habit poses a risk for taste deterioration without affecting salivary secretion and olfactory function.

Gastric emptying rate before and after orthodontic treatment examined with the [13C] breath test: A pilot study

Introduction: Orthodontic patients with malocclusion have significantly lower masticatory and gastrointestinal digestive function than persons with normal occlusion. Although several studies have suggested that masticatory function is improved after orthodontic treatment, the relationship between such improvement and change in gastrointestinal symptoms has not been quantitatively evaluated. In this study, we aimed to investigate the change in masticatory function and the gastric emptying rate in patients with malocclusion, before and after orthodontic treatment. Methods: Seven women with malocclusion, before (pretreatment group) and after orthodontic treatment (posttreatment group), and 7 healthy dentate female volunteers (control group) underwent a 13C‐acetate breath test (13CO2) with a liquid meal and the color changeable gum test, along with completing the frequency scale for symptoms of gastroesophageal reflux and a questionnaire on food intake. Between‐group differences were evaluated. Results: The pretreatment group had significantly longer maximum 13CO2 exhalation time and lower masticatory function, quantified using a higher red‐color value on the gum test and the questionnaire on food intake, than did the posttreatment and control groups. No significant differences were identified between the posttreatment and the control groups. Conclusions: We provide evidence of improvement of masticatory function after orthodontic treatment, which was associated with a faster rate of gastric emptying.

Changes in position of the hyoid bone and the pharyngeal airway with dental arch expansion

The purpose of this study was to investigate factors that may influence the position of the tongue during speech by the use of acoustic analysis. The subjects were 21 patients diagnosed with mandibular prognathism who had undergone a sagittal split ramus osteotomy. The formants of / R / were analyzed before operation (BO), one month after operation (AO1m), and one year after operation (AO1y). To divided into 2 groups, F1/ F04 and F2/F04 of the control, and at the time of AO1y they were compared. These are the cases within the standard formants of AO1y (improved group), and cases over 1S.D. formants of AO1y (nonimproved group). The cephalometric analysis of each group was compared as well as the correlation between the formants and the cephalometric values. The results were as follows:

The effects of cognitive behavioral therapy on experimental orthodontic pain

Abstract Purpose To evaluate the effectiveness of cognitive behavioral therapy (CBT) for subjects with experimental orthodontic pain. Materials and methods Thirty-two healthy adult volunteers (mean age of 24.8 years) were recruited and randomized into two groups: CBT intervention group (CBT group; n = 16) and no intervention group (control group; n = 16). Subjects had no spaces in a row of teeth, and contact between the second bicuspid tooth and first molar tooth of upper jaw of both sides could tolerate insertion of a contact gauge (50–110 μm). Elastic separators were inserted between both sides of the second bicuspid tooth and first molar tooth of the upper jaw. CBT was conducted in the CBT group immediately and 1 day after insertion with a CBT operator, and 2–7 days after insertion by the subjects themselves. Pain evaluation was assessed using the methods of magnitude estimation and visual analog scales were carried out as rating scales. All evaluations were conducted before, immediately after, 1 day, and 7 days after insertion of the separator. Results In the standardized scores of magnitude estimates of pain, the scores of the CBT group immediately after insertion were significantly higher than those of the control group. Scores of the CBT group 1 day after insertion were significantly lower than those of the control group. Conclusion CBT was shown to be effective in the management of orthodontic pain and could merit clinical application.

Gastric emptying rate in subjects with malocclusion examined by [13C] breath test

Masticatory function is significantly lower in individuals with malocclusion than in those with normal occlusion. Although several studies suggest that masticatory function influences gastrointestinal digestive function, the relationship between malocclusion and gastrointestinal symptoms has not been studied extensively. The purpose of this study was to investigate masticatory function and gastric emptying rate in subjects with malocclusion. Eleven healthy dentate female volunteers and eleven female patients with malocclusion underwent a C-acetate breath test with a liquid meal. Maximum CO2 exhalation time (Tmax) was compared statistically between both groups. Masticatory function was assessed by color-changeable chewing gum. The CIE L*a*b color system was used for color recording. The mean Tmax of the malocclusion group was significantly longer than that of the normal occlusion group. Masticatory performance, measured by color changeable gum and questionnaires, was significantly lower in the malocclusion group than in the normal occlusion group. This study suggested that there was a close relationship between malocclusion and gastrointestinal digestive function.