人類的下顎第一大恆臼齒通常只有兩個牙根，臨床上卻也發現在台灣有為數不少的病患，其下顎第一大恆臼齒具有三個牙根，亦即出現了遠心舌側牙根。此第三牙根的出現，可能增加牙髓病治療、拔牙或矯正治療的困難度，提高牙根分叉侵犯的機會，降低牙周治療的預後。有鑑於先前之文獻報告，多認為蒙古人下顎第一大恆臼齒出現第三牙根的盛行率較高。因此本篇研究藉由比較同一下顎第一大恆臼齒拍攝的放射線咬翼片及根尖片，得知根尖片在判讀第三牙根是否存在的可信度與咬翼片無異，並進一步以放射線根尖片，研究台灣人下顎第一大恆臼齒具第三牙根的盛行率。結果顯示在台灣人下顎第一大恆臼齒具第三牙根的盛行率為11.95%，約落在多數學者所研究亞洲人的盛行率範圍中；其中，男性的盛行率（12.56%）略高於女性（11.30%），但並無統計學上的差異；出現在雙側的盛行率（7.41%）較出現在單側的盛行率（4.54%）高；又單獨出現在右側者的盛行率約為單獨出現在左側者的3.1倍。本篇報告並提供給臨床牙醫師一個簡易的判讀方法，藉由放射線根尖片及早診斷下顎第一大恆臼齒是否具第三牙根，以期達到預防疾病的目的。

Background: Permanent mandibular first molar usually has two roots and two furcations. Existence of a third root, the distolingual (DL) root, may increase the difficulties of endodontic treatment, extraction procedure, orthodontic movement, as well as the likelihood of periodontal breakdown which hampers the periodontal prognosis.
Purpose: The purpose of this study was to investigate the prevalence of three-rooted permanent mandibular first molars in Taiwanese by conventional dental radiography, and to find out whether single periapical or bitewing radiograph is sufficient to serve as a diagnostic tool in detecting the presence of this extra DL root on the permanent mandibular first molar.
Methods: Six hundred thirty four permanent mandibular first molars were randomly selected for observing the difference of diagnostic accuracy between periapical and bitewing radiographic techniques. Statistical analysis was performed with McNemar’s Chi-square test (P<0.05). Paired periapical radiographs of bilateral permanent mandibular first molars from 1255 subjects were used to investigate the overall prevalence of 3-rooted occurrence as well as to compare the prevalence between female and male, bilateral and unilateral, left- and right-side occurrences. The data were analyzed by Pearson Chi-square test (p<0.05). All radiographs were examined by two periodontists. Intra- and inter-examiner reproducibility was evaluated by Kappa statistics.
Result: There was no statistically significant difference between using periapical radiography and bite-wing radiography in diagnosing the occurrence of a third root on the mandibular first molar (p>0.05). Overall prevalence of the 3-rooted permanent mandibular first molar was 11.95%; there was no statistically significant difference between males and females (12.56% v.s 11.30%)(p>0.05). Bilateral occurrence (7.41%) was higher than unilateral one (4.54%)(p<0.001) in which right-side occurrence was 3.1 fold higher than that on the left side (p<0.01).
Conclusion: This study concludes that the prevalence of 3-rooted permanent mandibular first molars is 11.95% in Taiwanese. Single periapical radiography is an efficient tool to diagnose the occurrence of a third root on a permanent mandibular first molar. Clinicians should be aware of this anatomic variation. Further investigations need to be conducted to verify the influence of this DL root on its periodontal health.

目錄
表目錄…………………………………………………………………….x
圖目錄 xii
第一章 緒論 1
第二章 文獻回顧 3
2.1 下顎第一大恆臼齒第三牙根的出現 4
2.2 下顎第一大恆臼齒第三牙根的型態特徵 6
2.3 下顎第一大恆臼齒發生三牙根的原因 8
2.4 研究下顎第一大恆臼齒盛行率的方式 10
2.5 下顎第一大恆臼齒含三牙根在不同種族的盛行率 12
第三章 目的與假說 14
第四章 材料與方法 16
4.1 比較咬翼片與根尖片判讀第三牙根之正確性是否有差異 17
4.1.1 取樣 17
4.1.2 資料搜集 17
4.1.3 統計分析 18
4.2 以根尖片檢查含三牙根之下顎第一大恆臼齒之盛行率 20
4.2.1 取樣 20
4.2.2 資料搜集 20
4.2.3 統計分析 21
第五章 結果 22
5.1 比較咬翼片與根尖片判讀第三牙根之正確性 23
5.2 下顎第一大恆臼齒含三牙根之盛行率及性別分析 24
5.3 下顎第一大恆臼齒含三牙根發生在單雙側之分析 25
5.4 下顎第一大恆臼齒含三牙根發生在單側時位於左側或右側之分析 26
第六章 討論 27
6.1 判讀下顎第一大恆臼齒具第三牙根的方法 28
6.2 三牙根之下顎第一大恆臼齒在不同性別的盛行率 33
6.3 三牙根之下顎第一大恆臼齒在單側或雙側的發生情形 34
6.4 三牙根之下顎第一大恆臼齒在單側出現時左側、右側的發生情形 36
6.5 三牙根之下顎第一大恆臼齒在診斷上的重要性 37
6.5.1 在牙周治療方面的重要性 37
6.5.2 在齒內治療方面的重要性 38
6.5.3 在矯正治療方面的重要性 40
6.5.4 在拔牙方面的重要性 41
第七章 結論 42
參考文獻 44

表目錄
表一 三牙根之下顎第一大恆臼齒的相關研究文獻 52
表二 三牙根之下顎第一大恆臼齒不同種族/人種盛行率的相關研究文獻 54
表三 三牙根之下顎第一大恆臼齒不同人種盛行率的比較的相關研究文獻 57
表四 Kappa(κ)值的評估標準 58
表五 由放射線咬翼片及根尖片檢查出的三牙根之下顎第一大恆臼齒的數量 59
表六 受檢者至少有一側具三牙根之下顎第一大恆臼齒的盛行率及性別分析 60
表七 具三牙根之下顎第一大恆臼齒的受檢者中，其發生於單側或雙側的分析 61
表八 單側出現三牙根之下顎第一大恆臼齒的受檢者中，位於右側或左側的分析 62
表九 三牙根之下顎第一大恆臼齒的男女盛行率的相關研究文獻 63
表十 三牙根之下顎第一大恆臼齒單雙側出現率的比較之相關研究文獻 64
表十一 三牙根之下顎第一大恆臼齒在單側出現時左右側盛行率的相關研究文獻 65

圖目錄
圖一 含三牙根之下顎第一大恆臼齒遠心側觀 66
圖二 含三牙根之下顎第一大恆臼齒根尖側觀 67
圖三 含三牙根之下顎第一大恆臼齒舌側觀 68
圖四 含三牙根之下顎第一大恆臼齒牙科電腦斷層片之橫切面觀 69
圖五 牙根管型態系統分類 (Classification of root canal system types) 70
圖六 符合選取標準的X光片 71
圖七 咬翼片中第三牙根與遠心頰側根齒頸部重疊的部份 72
圖八 根尖片中第三牙根與遠心頰側根齒頸部重疊的部份 73
圖九 根尖片中第三牙根與遠心頰側根齒頸部重疊的部份 74
圖十 錨定值anchorage value 75
圖十一 牙科電腦斷層片中左下第一大恆臼齒之軸向切面圖 76

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