Youichi Yamasaki

Oropharyngeal airway in children with Class III malocclusion evaluated by cone-beam computed tomography

INTRODUCTION Upper airway size is increasingly recognized as an important factor in malocclusion. However, children with Class III malocclusion are somewhat neglected compared with those with a Class II skeletal pattern. Therefore, the purpose of this study was to establish the characteristic shape of the oropharyngeal airway (OA) in children with Class III malocclusion. METHODS The sample comprised 45 children (average age, 8.6 +/- 1.0 years) divided into 2 groups: 25 with Class I and 20 with Class III malocclusions. OA size of each group was evaluated by cone-beam computed tomography. Cluster analysis, based on OA shape, redivided the subjects into wide, square, and long types. The distributions of Class I and Class III subjects were compared among the types. RESULTS The Class III group showed statistically larger OA area and width compared with the Class I group. Area was positively correlated with Class III severity. The square type included 84% of the Class I malocclusions but only 30% of the Class III malocclusions, indicating that the OA in Class III malocclusion tends to be flat. CONCLUSIONS The Class III malocclusion is associated with a large and flat OA compared with the Class I malocclusion.

Tongue posture improvement and pharyngeal airway enlargement as secondary effects of rapid maxillary expansion: A cone-beam computed tomography study

INTRODUCTION Rapid maxillary expansion (RME) is known to improve nasal airway ventilation. Recent evidence suggests that RME is an effective treatment for obstructive sleep apnea in children with maxillary constriction. However, the effect of RME on tongue posture and pharyngeal airway volume in children with nasal airway obstruction is not clear. In this study, we evaluated these effects using cone-beam computed tomography. METHODS Twenty-eight treatment subjects (mean age 9.96 ± 1.21 years) who required RME treatment had cone-beam computed tomography images taken before and after RME. Twenty control subjects (mean age 9.68 ± 1.02 years) received regular orthodontic treatment. Nasal airway ventilation was analyzed by using computational fluid dynamics, and intraoral airway (the low tongue space between tongue and palate) and pharyngeal airway volumes were measured. RESULTS Intraoral airway volume decreased significantly in the RME group from 1212.9 ± 1370.9 mm(3) before RME to 279.7 ± 472.0 mm(3) after RME. Nasal airway ventilation was significantly correlated with intraoral airway volume. The increase of pharyngeal airway volume in the control group (1226.3 ± 1782.5 mm(3)) was only 41% that of the RME group (3015.4 ± 1297.6 mm(3)). CONCLUSIONS In children with nasal obstruction, RME not only reduces nasal obstruction but also raises tongue posture and enlarges the pharyngeal airway.

Improvement of nasal airway ventilation after rapid maxillary expansion evaluated with computational fluid dynamics

INTRODUCTION Rapid maxillary expansion is known to improve nasal airway ventilation. However, it is difficult to precisely evaluate this improvement with conventional methods. The purpose of this longitudinal study was to use computational fluid dynamics to estimate the effect of rapid maxillary expansion. METHODS Twenty-three subjects (9 boys, 14 girls; mean ages, 9.74 ± 1.29 years before rapid maxillary expansion and 10.87 ± 1.18 years after rapid maxillary expansion) who required rapid maxillary expansion as part of their orthodontic treatment had cone-beam computed tomography images taken before and after rapid maxillary expansion. The computed tomography data were used to reconstruct the 3-dimensional shape of the nasal cavity. Two measures of nasal airflow function (pressure and velocity) were simulated by using computational fluid dynamics. RESULTS The pressure after rapid maxillary expansion (80.55 Pa) was significantly lower than before rapid maxillary expansion (147.70 Pa), and the velocity after rapid maxillary expansion (9.63 m/sec) was slower than before rapid maxillary expansion (13.46 m/sec). CONCLUSIONS Improvement of nasal airway ventilation by rapid maxillary expansion was detected by computational fluid dynamics.

Evaluation of upper airway obstruction in Class II children with fluid-mechanical simulation

INTRODUCTION The purpose of this study was to test the null hypothesis that dolichofacial and brachyfacial children with Class II malocclusion do not differ in upper airway obstruction. Furthermore, the ability of fluid-mechanical simulation to detect airway obstruction within the limitations of simulation was examined. METHODS Forty subjects from 7 to 11 years of age with Class II malocclusion participated and were divided into 2 groups, dolichofacial and brachyfacial, based on their Frankfort mandibular plane angles. Cone-beam computed tomography images supplied the shape of the entire airway. Two measures of respiratory function, air velocity and pressure, were simulated by using 3-dimensional images of the airway. The images and simulations were compared between the 2 facial types. RESULTS The size of the upper airway did not differ statistically between facial types; however, the simulated maximal pressure and velocity of the dolichofacial type were significantly higher than those of the brachyfacial type. CONCLUSIONS Airway obstruction differs with the Frankfort mandibular plane angle, even though the depth and cross-sectional area of the airway do not. The fluid-mechanical simulation system developed in this study detected differences in airway obstruction that were not apparent from morphologic studies.

The effect of rapid maxillary expansion on pharyngeal airway pressure during inspiration evaluated using computational fluid dynamics.

INTRODUCTION Recent evidence suggests that rapid maxillary expansion (RME) is an effective treatment of obstructive sleep apnea syndrome (OSAS) in children with maxillary constriction. Nonetheless, the effect of RME on pharyngeal airway pressure during inspiration is not clear. The purpose of this retrospective study was to evaluate changes induced by the RME in ventilation conditions using computational fluid dynamics. METHODS Twenty-five subjects (14 boys, 11 girls; mean age 9.7 years) who required RME had cone-beam computed tomography (CBCT) images taken before and after the RME. The CBCT data were used to reconstruct 3-dimensional shapes of nasal and pharyngeal airways. Measurement of airflow pressure was simulated using computational fluid dynamics for calculating nasal resistance during exhalation. This value was used to assess maximal negative pressure in the pharyngeal airway during inspiration. RESULTS Nasal resistance after RME, 0.137 Pa/(cm(3)/s), was significantly lower than that before RME, 0.496 Pa/(cm(3)/s), and the maximal negative pressure in the pharyngeal airway during inspiration was smaller after RME (-48.66 Pa) than before (-124.96 Pa). CONCLUSION Pharyngeal airway pressure during inspiration is decreased with the reduction of nasal resistance by the RME. This mechanism may contribute to the alleviation of OSAS in children.

Maternal deprivation in neonatal rats alters the expression of circadian system under light-dark cycles and restricted daily feeding in adulthood.

Effects of maternal deprivation (MD) with different conditions were examined on the circadian rhythms in plasma corticosterone and locomotor activity in adult rats under ad libitum and restricted daily feeding (RF), in which rats had free access to food for 2 h for 3 weeks. Three different types of MD were performed from postnatal day 1 (P1) to day 6 (P6); MD for 12 h/day (MD12), for 3 h/day in the morning (MD3am) and in the afternoon (MD3pm). Under ad libitum feeding, corticosterone levels at 08:00 h and 24:00 h were significantly increased in MD12 rats. A similar increase was detected in MD3am rats, but not in MD3pm rats. Under the RF, corticosterone levels at 08:00 h, 24:00 h, and 04:00 h were significantly increased in MD12 rats. Similar elevations were detected in MD3am rats, but not in MD3pm rats. Furthermore, prefeeding locomotor activities under the RF increased significantly in MD12 rats. A similar increase was observed in MD3am rats, but not in MD3pm rats. Keeping ambient temperature and humidity at 37 degrees C and 70-80% during MD attenuated the effects of MD on the corticosterone rhythmicities under RF as well as ad lib feeding. It is concluded that MD in the early postnatal period influences the expressions of circadian rhythms in plasma corticosterone and locomotor activity in adult rats. Not only the length but also the time of day of MD seems to be critical for these effects. Ambient temperature and/or humidity are suggested to be one of the factors by which MD exerts its effect.

Maternal deprivation in the early versus late postnatal period differentially affects growth and stress-induced corticosterone responses in adolescent rats.

Periodic maternal deprivation (MD) in the early postnatal period leads to permanently altered responsibility of the hypothalamus-pituitary-adrenocortical (HPA) axis to various types of stress. However, no reports appear to have described the effect of periodic MD under different conditions on growth of the developing rat and responsibility of the HPA axis to immobilization stress in adolescent rats. Furthermore, although body weight changes are known to affect stress responsibility, their relationship under periodic MD is not clear. The present study therefore used 4 different types of periodic MD: for 12 h/day from postnatal day (P)1 to P6 (12E group); for 3 h/day from P1 to P6 (3E group); for 12 h/day from P16 to P21 (12L group); and for 3 h/day from P16 to P21 (3L group). Mean body weights were less in the 3E and 12E groups than in the control group until at least 9 weeks old, although body weight gain in the 3L and 12L groups was only transiently affected. Stress-induced corticosterone levels in the 3E and 12E groups did not return to basal levels until at least 330 min after the termination of stress, while temporal variations of stress-induced corticosterone levels did not differ significantly between the 3L, 12L and control groups. Periodic MD in the first postnatal week affected growth of developing rats and responsibility of the HPA axis to immobilization stress in adolescent rats, and the extent of this modification was larger with MD for 12 h/day than with MD for 3 h/day. Conversely, periodic MD from P16 to P21 had little effect. Periodic MD in the postnatal period induces long-term effects on growth and stress responsibility of the HPA axis. Furthermore, a critical age of the pup at the time of MD exists as well as a critical length of MD for inducing these effects.

A Cross-Sectional Study of Developing Resting Masseter Activity in Different Angle Classifications in Adolescence

Abstract The purpose of this study was to determine whether the development of masseter muscle activity at mandibular rest position is characteristic for different angle classifications. The sample consisted of 64 boys and 108 girls, aged ten to 18. Electromyographic (EMG) activity from the right and left masseter muscles was recorded using an EMG scanner. First or second order polynomials were used to separately model the age-related changes in resting muscle activity of each gender and Angle’s classification. The EMG activity of Class I boys and girls were expressed in positive second order polynomials. The EMG activities of Class II and Class III subjects were expressed in first order polynomials, and the EMG levels in Class III subjects were lower than in Class II subjects. These results indicated that development of resting activity levels might distinguish and characterize the anteroposterior mandibular position relative to craniofacial region.

Jaw motion during gum-chewing in children with primary dentition.

Abstract This study was undertaken to characterize jaw motion during mastication in children with primary dentition and to compare jaw motion with that in adults. The means and the variances of the traditional parameters for the chewing cycle, i.e., duration, excursive ranges and 3-D distances of travel at the lower incisor, molars and condyles were analyzed and compared in 23 children and 25 female adults. The duration of opening in children was significantly shorter than that of adults. Significant differences between children and adults were observed in lateral and vertical excursion of the incisor, lateral excursion at the molars, and vertical excursion at the condyles. Many of these measurements had larger between-subject and between-cycle variances in children than adults, suggesting that chewing motion in children has not yet matured. The results of this study indicate that chewing motion in children is different from that of adults.

Normalization of Masticatory Function of a Scissors-Bite Child with Primary Dentition: A Case Report

Abstract Normalization of mandibular function in children is important for normal orofacial development because their function is not still matured. This case report examined jaw movement during chewing in a young patient with unilateral scissors-bite. He could hardly chew on the affected side, preferring to chew only on the unaffected side, and his minimum opening position was initially unstable, i.e., he had two positions before active treatment. Retention did not stabilize his minimal opening position and his dual-bite was not corrected. His minimal opening position was stabilized after equipping his upper canines with a resin cap. Although orthodontic treatment morphologically improved the patient’s malocclusion, his function did not improve. Normal jaw movement on both sides was achieved after interfering with his old chewing pattern. Because normalization is needed for acquisition of normal function in children, long-term observations of their growth and functional changes are necessary after orthodontic treatment.