氏 名 陳 揚佳 博士の専攻分野の名称 博 士 ( 医科学 ) 学 位 記 番 号 医工博甲 第３２３号 学 位 授 与 年 月 日 平成２７年３月１８日 学 位 授 与 の 要 件 学位規則第４条第１項該当 専 攻 名 人間環境医工学専攻（生体環境学コース）
学 位 論 文 題 名 Trajectories of the number of caries in permanent teeth and the risk factors associated with the incidence of caries in the permanent teeth of children in a rural Japanese population—from the Project Koshu birth cohort
(子どもの永久歯のむし歯本数の経年変化とむし歯の発生に対す るリスクファクターに関する研究ー甲州プロジェクトから) 論 文 審 査 委 員 委員長 教 授 上木 耕一郎 委 員 准教授 犬飼 岳史 委 員 准教授 平野 雅己
学位論文内容の要旨
（Purpose）Dental caries in permanent teeth is an important oral health problem for school age children. Investigations about caries in permanent teeth in rural areas of Japan are rare. This thesis focuses on studying the severity and incidence of caries in permanent teeth from elementary school to junior high school using an appropriate repeated-measurements method. Thus, the aims of this thesis were: 1) to compare the trajectories of the numbers of caries in permanent teeth based on sex and caries experience in deciduous teeth; 2) to examine the association between sex and caries experience in deciduous teeth and the incidence of caries in permanent teeth by using a survival analysis; and 3) to detect factors affecting the incidence of caries by using a Cox proportional hazard regression analysis.
（Methods）
The data came from Project Koshu, a prospective cohort study. Children who were born between 1995 and 2001 in Koshu City (Enzan area), Japan were included in this thesis. The participants were followed from a medical checkup at 5 years of age until the third grade of junior high school. Some subjects without maternal data were included in the trajectory study only. Annual dental caries measurement data were recorded as the numbers of decayed and filled teeth. Independent variables were obtained from a questionnaire survey at 5 years of age. Maternal data were obtained from questionnaire surveys from pregnancy and birth
registrations. Multilevel analysis was used to describe the trajectories of the number of caries in permanent teeth. Kaplan-Meier survival curve was used to estimate the incidence of caries in permanent teeth. Cox proportional hazard regression model used to establish the risk assessment model for the incidence of caries in permanent teeth.
（Results）
The prevalence of primary caries at baseline was 64% in boys and 63% in girls. The prevalence of caries in permanent teeth at 14–15 years old (the third grade of junior high school) was 56% in boys and 63% in girls; the Decayed, Filled Tooth (DFT) scores in boys and girls were 1.9 ± 2.5 and 3.0 ± 3.7, respectively. The trajectory analysis showed that the numbers of caries in the permanent teeth of girls were significantly increasing at 12–13 years old, although there was no significant difference in the trajectories of either sex before 12–13 years of age.
However, the survival analysis study did not show a difference by sex in the incidence of caries in permanent teeth. Children who were caries in deciduous teeth was found faster increasing of the number of caries in permanent teeth than children who were caries free in deciduous teeth. Meanwhile, Caries experience in deciduous teeth was found to be strongly associated with the severity and incidence of caries in permanent teeth (Hazard Ratio 1.9, 95%CI 1.5-2.4). The trajectories analysis based on caries experience in deciduous teeth and daily toothbrush frequency showed boys who were caries in deciduous teeth with high frequency of daily toothbrush shared similar trajectories with boys who were caries free in deciduous teeth with low frequency of daily toothbrush. In the final Cox proportional hazards regression model, low maternal education level (Hazard Ratio 1.3, 95%CI 1.0-1.7), smoking parents (Hazard Ratio 1.6, 95%CI 1.2-2.1), later birth order (Hazard Ratio 1.6, 95%CI 1.2-2.0) and low tooth brushing frequency (Hazard Ratio 1.4, 95%CI 1.1-1.8) were considered risk factors for the incidence of caries in permanent teeth. On the other hand, high frequency of salty snacks intake (Hazard Ratio 1.6, 95%CI 1.0-2.4) and the high frequency of snacktime (Hazard Ratio 1.4, 95%CI 1.1-1.9) was significant in the univariate Cox proportional hazards regression model only.
（Discussion）
The severity of caries in permanent teeth in girls seemed to be more serious than in boys in the young adolescent stage. However, the incidence of caries in permanent teeth was not different between girls and boys. It was demonstrated that caries experience in deciduous teeth is a strong risk factor for the severity and the incidence of future caries in permanent teeth. High tooth brushing frequency in young childhood was an effective interventional behavior to prevent caries in permanent teeth, especially for boys who were caries in deciduous teeth. Low maternal education level, smoking parents and later birth order were relating to higher incidence of caries in permanent teeth, it suggested environmental factors were important for the incidence of caries in permanent teeth. Dietary relating factors are also considered as risk factors for future caries incidence in permanent teeth, although they lost significant in final multivariate model.
Since dental caries is a multifatorial disease, it is difficult to explore the mechanism of the progression of dental caries in permanent teeth. However, the results of this thesis might be valuable to program the prevention of dental caries in permanent teeth for children in Japanese rural area. In detail, in order to delay caries of permanent teeth developing, girls should have dental caries treated as early as possible. Both boys and girls should be educated to establish healthy oral habits and rational consumption of snacks in early childhood. Not only children, but also parents and other family members should establish a health environment for the prevention of dental caries of children. (4567)
Key word: school age children, permanent teeth, dental caries, risk factor, sex, caries experience, toothbrush, maternal education level, smoking status of parents, birth order, snacks
論文審査結果の要旨
１． 学位論文研究テーマの学術的意義。 本研究は、出生コホート研究のデータつまり妊娠期から乳幼児健診、学校検診データを 縦断的に調査したものである。6 歳から 14 歳までの永久歯のう蝕本数の経年的変化を複数 時点の繰り返しデータ解析を行っている。う蝕に関して、甲州市という限られた地方都市 で 1363 人の大規模な縦断研究はほかに例を見ず、非常に客観的で精密な統計学的解析を行 っている点で、学術的にも非常に貴重かつ重要なものである。さらに本データ解析結果を 広く公表すすることで、母親に対し出産する段階から子供のう蝕予防に有益な情報として 活用できる。 ２． 学位論文及び研究の争点，問題点，疑問点，新しい視点等。 本研究は統計結果をどう捉えるかということに尽きる。マルチレベル解析によって様々 な要因との関連性が抽出され、う蝕発生の要因と思われる妊娠期から中学３年時までの生 活習慣までも詳細に検討されている点が、斬新であり興味深い。女児と男児の永久歯う蝕 の有意差はないものの、女児の方が若年時でより深刻であると述べられているが、各年齢 区分での男児と女児の永久歯総数の差つまり性差による歯牙萌出の差が関連していると考 察している。健診などで行われる DF 歯数あるいは DMF 歯数では現存歯数を把握でないため、 各個人の歯総数は不明である。つまり各個人あるいは性別での歯牙年齢と実際の体格、成 長度の関連性が検討できればよりよい結果が導き出せると思われる。 しかし、出生コホート研究のう蝕に関する調査データ自体が大きな制限を受けているも のであり、ここから抽出できる最大限の解析を行い、十分に価値ある結果が示されている と思われる。 また、乳歯のう蝕経験、親の低学歴、喫煙、出生順位、歯ブラシ回数の少なさおよびス ナック菓子の摂取回数が永久歯う蝕発生に大きく関与していることが客観的に指摘できた 点は非常に重要であり、う蝕予防の根本的対策を考える上で親への教育が重要であるとの 認識を根拠をもって示せたものと思われる。３． 実験及びデータの信頼性。 データ採取時の制限はあるものの大規模な出生コホート研究のデータを用いた高度な統 計解析であり、信頼性は高いと思われる。 ４． 学位論文の改善点、等々。 論文は統計解析データを基によく熟考されており、大きな改善点はないと思われる。学位 論文として提出された英語論文の邦題および抄録において、「むし歯」とあるが「う蝕」の 方が好ましいと思われる。
