Ryosuke Hayashi

Relationship between masticatory function, dental arch width, and bucco-lingual inclination of the first molars

Abstract The aim of this study was to clarify the influence of masticatory function on dental arch forms. We evaluated the relationship between the masticatory movement path and occlusal force (as masticatory function) and the dental arch width and first molar bucco-lingual inclination. The subjects were 60 healthy adult females (mean 23.4 years; S.D. 1.6 years) without previous orthodontic treatment or functional abnormalities in the temporomandibular joint. Furthermore, the subjects were divided into a wide group (W-group) and a narrow group (N-group) based on mean maxillary inter-molar width in Japanese females. The masticatory path was recorded using gnathohexagraph system. Maximum occlusal force was measured using a simple type occlusal force meter. And subjects’ arch width and bucco-lingual inclination of the first molars was measured. W-group showed larger arch width and the first molar was more upright on the buccal side compared with N-group. Furthermore, the lateral component of masticatory movement and maximum occlusal force was large in W-group compared with N-group. In the group which strong occlusal force and grinding type mastication had wide arch width and the mandibular first molars upright on the buccal side.

Three-dimensional changes of the dental arch form and the inclination of the first molars: Comparison between crowding-improvement and crowding-aggravation groups

Abstract The aim of this study was to understand the differences in the growth of the dentition between persons with normal occlusion and crowding. Two groups of subjects, one with crowding-improvement group (Im-group) and the other with crowding-aggravation group (Ag-group) were analyzed longitudinally. Im-group consisted of 26 maxillary arches (14 boys and 12 girls) and 30 mandibular arches (11 boys and 19 girls), and the Ag-group consisted of 22 maxillary arches (10 boys and 12 girls) and 24 mandibular arches (12 boys and 12 girls). Dental casts were scanned with a contact-type 3D scanner. Arch form and inclination of the first molars were measured at 7 and 12 years. Our materials at the age of 7 years showed no significant differences in the arch form and inclination of the first molars between the two groups. In the Im-group, regarding changes in the amount of the dental arch form during the observation period, the maxillary arch width increased with an average of 5.0° first molar distal rotation, and the mandibular arch width increased with an average of 9.4° first molar buccal upright. As a result, maxillary and mandibular arch widths were large in the Im-group compared with the Ag-group at 12 years. Therefore, a characteristic of the difference between both groups was three-dimensional changes of the inclination of the first molars.

A discussion of masticatory force mechanics on the median palatine suture of children: Analysis involving a 3-dimensional finite element technique

A statistical analysis covering the past 10 years was carried out using new outpatients since 2001 in the Clinic of Orthodontics of Meikai University Hospital. The materials used in this study were obtained from 2739 patients who sought orthodontic treatment in our clinic. We recorded the monthly number of patients, genders, and chronological and dental ages at the initial visit, along with their addresses, patient referrals, chief complaints, public insurance coverage, and types of malocclusion. Female patients exceeded male patients by 1.9-fold. The most common average age range of the patients’ initial visits were 19–29 years, followed by 7–9 and 10–12. The rate of adult patients was 37.0%, and the most common Hellman’s dental age was IV A. A total of 77.4% of patients lived in an area of less than 20 km, and the largest number lived in Sakado city, where our hospital is located. We found that 66.4% of patients were referred from other hospitals and clinics. Most of these patients were referred from general private dental clinics (47.0%)or other clinics in our hospital (41.5%). The most common chief complaint was crowding, followed by mandibular protrusion and/or crossbite and maxillary protrusion. The rate of public insurance coverage was 20.3%, and patients with jaw deformities totaled 13.1%. Angle Classes I, II, and III were 29.2%, 42.2%, and 27.8%, respectively, showing that Class II patients totaled the highest rate. All these findings demonstrate how our clinics are based on the community’s dental health. An increased number of adult patients indicated the variety of patient characteristics.

Growth change of dental arch form in mixed dentition

To examine the potential dynamic influence of right and left imbalanced occlusal force on the cranial and facial bones, we prepared a 3-dimensional finite element model with a total of 126,534 nodes and 623,852 elements, which comprised 4 aspects including individual cranial sutures, facial bones, and cranial bones excluding mandibular bones, teeth, and periodontal ligament, according to cranial CT images taken from an adult dried skull. By using this model, we then performed 3-dimensional finite element analysis under the following 2 loading conditions: normal occlusion with right and left equality; and unilateral crossbite where the right side was normal but the left side showed crossbite, that is, where right and left imbalanced occlusal force was evident. In the normal occlusion model, a right and left symmetric stress distribution was observed around the key ridge surroundings as well as in the region covering the maxillary frontal aspect to the buccal bone. In the unilateral crossbite model as well, stress distribution was observed in both right-and left-sided key ridge surroundings as well as in the region toward the maxillary frontal aspect. When the right and left aspects were compared, however, the stress distribution was considerably biased, showing a different pattern of distribution. DOI: 10.1016/j.odw.2010.11.004

Prediction of dental crowding of permanent dentition from mixed dentition using personal longitudinal dental casts

To examine the potential dynamic influence of right and left imbalanced occlusal force on the cranial and facial bones, we prepared a 3-dimensional finite element model with a total of 126,534 nodes and 623,852 elements, which comprised 4 aspects including individual cranial sutures, facial bones, and cranial bones excluding mandibular bones, teeth, and periodontal ligament, according to cranial CT images taken from an adult dried skull. By using this model, we then performed 3-dimensional finite element analysis under the following 2 loading conditions: normal occlusion with right and left equality; and unilateral crossbite where the right side was normal but the left side showed crossbite, that is, where right and left imbalanced occlusal force was evident. In the normal occlusion model, a right and left symmetric stress distribution was observed around the key ridge surroundings as well as in the region covering the maxillary frontal aspect to the buccal bone. In the unilateral crossbite model as well, stress distribution was observed in both right-and left-sided key ridge surroundings as well as in the region toward the maxillary frontal aspect. When the right and left aspects were compared, however, the stress distribution was considerably biased, showing a different pattern of distribution. DOI: 10.1016/j.odw.2010.11.004