Haruaki Hayasaki

Quantification of human chewing-cycle kinematics

This study introduces new methods of quantifying and evaluating the human chewing cycle. These methods were validated on a sample of 26 young adults (11 women and 15 men) between 20-35 years of age. Movements of the mandibular central incisors were recorded (100 Hz) using an optoelectric computer system while the participants chewed gum. A subsample of 10 cycles was automatically selected, based on multiple objective criteria to ensure representative cycles for each individual. Once representative cycles had been identified, multilevel statistical models were used to evaluate and describe the samples kinematic patterns. The multilevel procedures allow for missing observations, they do not assume equal intervals, and variation can be partitioned hierarchically. Two-level models showed significantly shorter cycle duration for males (835 msec) than females (973 msec). Inferior-superior (IS) cycle range was 2.6 mm larger and maximum IS velocity was 19.6 mm/sec faster in males than females. There were no significant differences in medial-lateral (ML) and anteroposterior (AP) excursive ranges or velocities. With the exception of cycle duration and ML ranges of motion, random variation was three to five times larger between individuals than between cycles. The three-level models showed that eighth-order polynomials were necessary to describe IS, AP, and ML chewing movements of the entire cycle. The models identified highly significant sex differences in cycle kinematics (excursions, velocities, accelerations, etc.) for each aspect of movement (AP, IS, and ML). It is concluded that this approach provides several important advantages over existing methods, including (a) its objectivity, (b) a more complete description of kinematic patterns, (c) a hierarchical description of variation, and (d) its ability to test hypotheses statistically.

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.

Incisor and mandibular condylar movements of young adult females during maximum protrusion and lateratrusion of the jaw

This study evaluated the correlations between condylar translation and incisor movements during maximum protrusion and lateratrusion. The sample was 27 adult females (23--35 years old), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements [linear distances (LD) and curvilinear pathways (CP)] were recorded in three dimensions for 20 s with an optoelectric (Optotrak) jaw-tracking system while each participant performed multiple maximum protrusive and lateratrusive cycles. Masticatory analysis and multilevel statistical programs computed the three-dimensional movements of the incisors and condylar hinge axis during protrusion and lateratrusion. CP of the incisor point averaged 12.0 mm (9.3 mm LD) during protrusion, 13.0 mm (11.5 mm LD) during right excursion and 12.3 mm (11.0 mm LD) during left excursion. CP of the condyles averaged 11.9--12.9 (9.2--9.5 LD) mm during protrusion. During lateratrusion the contralateral condyles moved anteroinferiorly 11.6--14.1 mm (9.5--10.2 mm LD); the ipsilateral condyles moved posterolaterally 5.8-6.8 mm (2.3--2.5 mm LD). The left condyles demonstrated more movement than the right condyles during protrusion and than the contralateral condyles during laterotrusion. Relative variation, as measured by the coefficient of variation, was greater for the movements of the ipsilateral than contralateral condyles. Incisor movements were only moderately related to condylar movements between individuals and between replicates; LDs showed stronger correlations than CPs; and correlations were stronger for lateratrusion than protrusion. While incisor and condylar movements were not affected by repeated protrusion, incisor CP (approx. 0.2 mm/cycle) and LD (approx. 0.1 mm/cycle) increased significantly with repeated excursive movements to the left and right. It was concluded that (1) incisor protrusion and lateratrusion provide moderately reliable measures of condylar translation; (2) the linear distances that the incisors move during lateratrusion provide the best measure of contralateral condylar translation; and (3) condylar movements are not affected by repeated protrusion or lateratrusion.

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.

Occlusal Contacts during lateral Excursions in Children with Primary Dentition

The presence of non-working occlusal contacts in adults is considered abnormal and may initiate parafunctional activity. Few studies have looked for non-working occlusal contacts in children with primary dentition. The purposes of this study were (1) to prove the existence of non-working-side occlusal contacts, and (2) to quantify their area during lateral excursion in children with primary dentition. To achieve this purpose, we developed a measurement system that combined a tracking system for mandibular movements with a three-dimensional digitizer for tooth shape. Ten children were selected for this study. Estimated occlusal contact area of the primary second molar on the non-working side was 0.8 mm2, in contrast to 2.0 mm2 on the working side, at 3.0 mm of movement of the lower incisor. All children examined had some occlusal contacts on the non-working side during the first part of lateral excursion.

The P561T polymorphism of the growth hormone receptor gene has an inhibitory effect on mandibular growth in young children

P561T heterozygous missense mutation in the growth hormone receptor (GHR) is a candidate genetic polymorphism (single-nucleotide polymorphism) for human mandibular growth. The purpose of this study was to assess whether this mutation affects mandibular growth during early childhood. The difference in mandibular growth between P561T heterozygous and wild-type individuals was analysed by cephalometric measurements during childhood. The subjects included 33 children with mandibular protrusion (aged 3-12 years, 16 males and 17 females) and 27 normal children (aged 3-13 years, 14 males and 13 females). Genomic DNA extracted from buccal epithelial cells was genotyped for the P561T heterozygous mutation with a molecular analysis (polymerase chain reaction--restriction fragment length polymorphism method). Two of the patients with normal occlusion and five with mandibular protrusion were heterozygous for the mutation. Chi-square analysis showed that the frequency of this mutation did not differ statistically between the normal and mandibular protrusion subjects. Multilevel model analysis of the 101 cephalograms showed that the mutation reduced the linear measurements of the mandible. These findings suggest that P561T heterozygous mutation affects mandibular growth during early childhood, and this mutation in the GHR gene is hypothesized to function as an inhibitory factor in the process of mandibular growth.

Four-dimensional analysis of stomatognathic function

Many researchers have attempted to clarify the complex relationships between stomatognathic function and craniofacial morphology. Most studies investigated the trajectories of incisal or condylar points and measured temporomandibular morphology projected onto 2-dimensional radiographic films. Although these methods provided valuable information, their diagnostic capabilities were limited. We introduce a new 4-dimensional (4D) analysis of stomatognathic function that combines the 3-dimensional (3D) computed tomography of the cranium and mandible, dental surface imaging with a noncontact 3D laser scanner, and mandibular movement data recorded with a 6 degrees of freedom jaw-movement analyzer. This method performs dynamic and precise simulations that can analyze and display condyle to fossa distances and occlusal contacts during mandibular function. These comprehensive relationships can be analyzed and displayed not only at intercuspal position, but also at any mandibular position during functional movements. We believe that our 4D analyzing system will be useful for diagnosing temporomandibular disorders of patients with jaw deformities and other malocclusions.

Improvement in Jaw Motion Following Treatment of Unilateral Crossbite in a Child with Primary Dentition: A Case Report

ABSTRACT This case report examines jaw motion during both habitual opening-closing and gum chewing in a young (3 years, 10 months) patient with unilateral crossbite at the primary dentition stage. Jaw motion was measured three times: 1. before treatment; 2. after active treatment; and 3. after retention. The abnormal habitual open-close pathway seen prior to treatment was improved after retention. Prior to treatment, movement of the affected-side condyle preceded movement of the non-affected-side condyle during opening. After retention, the movement of the condyles was better coordinated. The chopping type chewing pattern, with less lateral movement, before treatment changed to a more grinding type pattern on the affected side after activation. This study suggests that the prescribed treatment effectively improved both the patients morphology and function. However, neither the open-close pathways nor the chewing patterns were completely normal after retention. The results in this case suggest that early treatment of functional unilateral crossbite can be effective.