Search

BACKGROUND: Malocclusion deformity and caries are common oral diseases in adolescents. In order to explore the correlation between malocclusion deformity and caries prevalence in adolescents, this study analyzed the influence of factors such as poor oral habits on caries in adolescents. METHODS: In this study, 1,093 adolescents aged 11 to 14 enrolled in 2–3 schools in Zhangjiakou area from September 2020 to June 2021 were selected as the research subjects. The basic data of these adolescents were collected by questionnaires. Malocclusion and caries were examined by on-site inspection. Their bad oral habits were also investigated. After data collection, the chi-square test, logistic regression, the Mann-Whitney U test, and the Kruskal-Wallis H test were used for multivariate analysis. RESULTS: The results showed that the incidence of malocclusion was 72.66% and the caries rate was 68.8% among adolescents aged 11–14 in this area. The 4 bad oral habits of biting, mandibular protrusion, lateral chewing, and mouth breathing were the influencing factors of malocclusion in adolescents. Bad oral habits, malocclusion, and frequent consumption of sugary beverages were independent risk factors for caries in adolescents, and significantly positively correlated with the caries rate. CONCLUSIONS: Malocclusion and the four bad oral habits were independent risk factors of caries in adolescents.

The hydrogen recirculating pump is the key equipment of the hydrogen recirculating system for the fuel cell vehicles. The scroll pump is one of the preferred types of hydrogen recirculating pumps because of its unique advantages of higher efficiency and lower noise. In order to provide valuable basis for improving the reliability and durability of hydrogen pumps under oil-free high-speed conditions, this paper carried out dynamics performance research based on the theoretical method. The gas force, force and torque of moving parts were calculated. Tangential gas force is about 100 N and axial gas force is about 200 N which are much smaller than the traditional scroll compressors due to lower designed pressure ratio of hydrogen pump. Due to the exist of bearing assembly tolerances of sub-crankshafts during practical operation, the actual contact forces and dynamics characteristics were further analyzed based on multibody dynamics simulation. It is found that the rotating speed and the actual assembly tolerance have significant influence on the dynamics characteristics. The radial and tangential forces can reach 3000 N at 6000 r·min−1 which is three times than the value at 3000 r·min−1. Furthermore, the service lives of bearings were analyzed. The contact force considering assembly tolerance presented the high-frequency oscillations. When the size of clearance is increasing, the oscillation frequency is reducing, but the contact force is enlarging. The radial force on a sub-crankshaft was 30 N without assembly tolerances. It increased to 150 N and 330 N, respectively, when the assembly clearances were designed separately as 2~−14 μm and −8~−24 μm, and the corresponding bearing service life decreased by 46% and 83%.