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The purpose of this study was to evaluate the relationship between craniofacial morphology and the fatigability of the masseter muscle during isometric contraction. Data were obtained from 23 healthy Japanese males (25.7 ± 3.8 years). EMG signals were taken from bilateral masseter muscles. The subjects were instructed to perform maximal clenching for 10 s. The analyses were conducted using 2–4 s sampling (T1) and 8–10 s sampling (T2) of 10 s sampling. The integrated EMG (IEMG) and the median frequency of the power spectrum for EMG (MF) were determined for each sampling. The fatigability index (FI) was determined by calculating the ratio of (T1–T2) to T1 for the MF. Lateral cephalograms were taken to evaluate the craniofacial morphology. Thirteen angular and 10 ratio variables were constructed for the craniofacial measurements. Paired t-tests were used to determine the mean differences for each EMG measurement between T1 and T2. Pearson's correlation coefficients were calculated to determine the correlation between the cephalometric parameters and the FI values. Both the IEMG and the MF for EMG significantly decreased from T1 to T2. The FI values were positively correlated with Y-axis, palatal plane angle, occlusal plane angle, anterior facial height and molar height and also negatively correlated with anterior lower facial height and maxillary anterior tooth height. These results suggested that the fatigability in the masseter muscle might therefore be associated with the craniofacial morphology.

In order to evaluate the effectiveness of daily mastication for occlusal stability, the relationship between the subjective masticatory feeling and electromyogram (EMG) activity was examined. Seventeen female volunteers aged 20.5 ± 1.0 years and nine test foodstuffs were selected. Five kinds of food texture, i.e., hardness, cohesiveness, springiness, gumminess, and chewiness, were measured and calculated in each test foodstuff. Electromyograms were measured while subjects ate to evaluate masticatory muscle activity during chewing the foodstuffs up to swallowing. Correlations between the mechanical property of the foodstuffs and the EMG parameters were examined. For each of the five properties, subjects were divided into those having high (top 8) or low (low 8) correlations between the score for subjective feeling of toughness and the food property. Significant positive correlations were found between masticatory muscle activity or the total mastication time and the score for subjective feeling of toughness. The top 8 group in “hardness” had significantly longer chewing cycle times, and the top 8 group in “cohesiveness” had significantly higher total masticatory muscle activity and longer total mastication time. There are different features of EMG parameters between the top 8 in “hardness” and “cohesiveness”. These findings suggest that the subjective feeling of toughness influences effective daily mastication, and that recognition of the subjective feeling of toughness would be useful in masticatory training for occlusal stability.

This case report presents a case that underwent orthognathic treatment with intra-oral vertical ramus osteotomy (IVRO). The patient was a 19-year-old female with mandibular protrusion and severe maxillary anterior crowding. The overbite was +0.5 mm and the overjet −1.5 mm. She had orofacial pain and tenderness of the temporomandibular joints (TMJ) and surrounding muscles. The pre-surgical orthodontic treatment included the extraction of the maxillary right lateral incisor, maxillary right second premolar, maxillary left canine, mandibular left second molar and mandibular right second premolar. After 18 months of pre-surgical orthodontic treatment, the left and right sides of the mandible were set back 8 and 6 mm, respectively, via IVRO to improve mandibular protrusion. The total treatment period was 26 months. The patient showed the backward reaction of the mandible, which occurred after release of the maxillo-mandibular fixation. The usage of the Class II elastics during the post-surgical phase to maintain the overjet made the inclination of the maxillary incisors more lingual.

This case report presents a case that underwent orthognathic treatment with anterior segmental osteotomies on both jaws. The patient was a 26-year-old female with maxillary protrusion, lip incompetence with an everted vermilion border. The overbite was +1.0 mm, overjet +1.0 mm. The pre-surgical orthodontic treatment included the extraction of the four first premolars and a multi-bracket treatment was started. After 12 months of pre-surgical orthodontic treatment, both the anterior maxillary and the anterior mandibular segments were retracted surgically by 5.5 mm. The total treatment period was 18 months. An anterior segmental osteotomy can induce the remarkable structural changes for bimaxillary lip protrusion patients.

This article presents an orthognathic treatment case after severe apical root resorption of maxillary anterior teeth using anterior segmental osteotomy. This case involved a 20-year-old female with the chief complaint of maxillary protruding and irregularly aligned mandibular anterior teeth. Her medical history showed no allergies or medical problems. The overbite was +3.0 mm, and the overjet +3.0 mm. After extraction of the four first premolars, a multi-bracket treatment was started. A severe root resorption of the maxillary anterior teeth was found 12 months after active treatment. The maxillary anterior segmental osteotomy was chosen as the compensatory treatment. The total treatment period was 2 years and 7 months. The post-retention panoramic radiograph showed no developmental root resorption.

This case report describes the orthodontic treatment done to an 11-year-old female patient having Apert syndrome, a genetic disorder manifested by craniofacial and limb anomalies. The orthodontic treatment was accompanied with distraction osteogenesis for forward advancement of the correction of midfacial hypoplasia. After the active treatment, a better facial profile and occlusion were achieved. The occlusion remained stable during the 2 years and 8 months follow-up.

We introduce a new four-dimensional (4D) visualizing system of stomatognathic function that combines an individual's 3D head model, reconstructed from cephalograms, and mandibular movement data recorded with a six degrees-of-freedom jaw movement analyzer. The individual's head model was constructed by transforming a standard head model according to the 3D coordinate values calculated from the individual's cephalograms. The accuracy of the 3D reconstructed head model was determined. The error averaged 1.02%, with a range of 0.39–1.58%, and the accuracy was sufficient for clinical use. This method performs dynamic and precise simulation of mandibular movement. We believe that our system will be useful for evaluating the functional background of patients with malocclusions and maxillofacial deformities.

The purpose of this study was to assess the range of the top three most-favored facial profiles for each sex from a series of varying lower facial vertical proportion, and to evaluate clinically acceptable facial profiles for Japanese adults. Silhouettes of average male and female profiles were constructed from the profiles of 30 Japanese males and females with normal occlusions. Lower facial vertical proportions were increased or decreased by intervals of 5% of Sn–Me′ for each sex from the average profile. Forty-one orthodontists and 50 dental students were asked to select the 3 most-favored, well-balanced profiles for each sex. They were also asked to indicate whether they would seek surgical orthodontic treatment for each of the shorter or longer lower facial profiles if those images represented their own profile. For male profiles, both the orthodontists and dental students chose the average profile as the most-favored. For female profiles, the dental students chose a slightly shorter lower facial as the most-favored profile while the orthodontists chose the average profile. The dental students chose shorter lower facial profiles as more acceptable than longer lower facial profiles for females (p

The purposes of this study were to evaluate the upper and lower lip changes after orthodontic treatment of bimaxillary protrusion in adult Japanese. We also intended to predict the upper and lower lip positions from the changes of the maxillary and mandibular incisor positions in both the horizontal and vertical planes. Pre-treatment and post-treatment cephalograms of 38 patients (6 males and 32 females, aged 24.2 ± 2.9 and 22.8 ± 4.1 years, respectively) who had four first premolars extracted, were taken with lips in their voluntary relaxed position, traced and compared between them. Stepwise multiple regression analysis revealed that a 1 mm retraction and a 1 mm intrusion of the maxillary incisor cervical point would produce a 0.22 mm retraction of the upper lip, a 1 mm retraction of the mandibular incisor tip would produce 0.76 mm retraction of the lower lip, and a 1 mm mandibular incisor tip retraction would produce a 0.50 mm retraction of Stomion. Moreover, a 1 mm maxillary incisor tip intrusion would produce a 0.56 mm upward movement of the upper lip and a 1.00 mm upward movement of the lower lip. The predictability of this study may be beneficial for orthodontists in planning and discussing treatment plans and options with patients.

The temporomandibular joint (TMJ) is the principal adaptive center for determining the intermaxillary relationship in all three planes of space. The joint diseases, such as TMJ osteoarthritis/osteoarthrosis (OA) might associate with dentofacial morphologic changes. The purpose of this study was to investigate the relationship between TMJ OA and dentofacial morphology in Japanese females and compare findings to a normal control group. The subjects consisted of 24 Japanese females with TMJ OA (aged 22.5 ± 4.4 years) and a control group of 24 asymptomatic Japanese females (aged 23.6 ± 1.3 years). Linear and angular cephalometric measurements were noted to evaluate the skeletal, dental and soft tissue relationships of the two groups. Unpaired t -tests were used to compare the mean differences of each cephalometric measurement between the TMJ OA and the control group. The subjects with TMJ OA had a more significant posteriorly rotated mandible as well as a smaller mandible compared with the subjects in the control group. They also had more protrusive lower incisors, upper lips and lower lips. These results suggest that there might exist association between TMJ OA and dentofacial morphology in Japanese females.

The purpose of this study was to examine the validation of mechanomyogram (MMG) for assessing the masseter muscle fatigue. Data were obtained from 16 healthy Japanese males (aged 25.6 ± 2.3 years). The measuring device for the MMG consisted of an amorphous sensor and a small magnet. The bite-force, the MMG, and the electromyogram (EMG) signals were recorded simultaneously. The subjects were instructed to perform 0%, 5%, 10%, and 20% maximal voluntary contraction (MVC) for 20 s as the pre-fatigue trials. A recovery period of 5 min was allowed after each pre-fatigue trial. As the fatigue task, the subjects were instructed to sustain 40% level of MVC until they feel intolerable discomfort. The subjects were asked to perform 0%, 5%, 10%, and 20% MVC for 20 s as the post-fatigue trials. No recovery period was allowed after each post-fatigue trial. The mean values of the average rectified value for EMG of the post-fatigue trials were significantly higher than those of the pre-fatigue trials at 10% (p < 0.05) and 20% MVC (p < 0.05). The mean values of the electromechanical efficiencies of the post-fatigue trials were significantly lower than those of the pre-fatigue trials at 10% (p < 0.01) and 20% MVC (p < 0.05). These findings suggest that the MMG analysis combined with the EMG may be a more useful method for evaluating the masseter muscle status.