Classification of Mandibular Dental Arches by Correlation and Principal Component Analyses

下顎牙弓形態的分類－主要及相關組成要素之分析

Yasutomo Iwai-Liao ； Michiko Nakatsuka ； Shun-Te Huang ； Lian Guo ； Fumiko Aikawa

《Taiwan Journal of Oral Medicine & Health Sciences》 20卷2期 (2004/10) Pp. 69-90

https://doi.org/10.7059/TJOMHS.200410.0069

摘要

本研究從396個年齡介於18至26歲的樣本中（男生257位，女生139位）選出53個（男生29位，女生24位）具有理想咬合及齒列的樣本來進行牙弓型態的評估。下顎的齒列依照傳統牙弓型態的描述標準，我們預先將之分為以下幾類：方形(square)，圓方形(round-square)，圓形(round)，圓V形(round V-shaped)。另外，在解剖位置上我們亦選擇了以下幾處做為參考點，包括：門齒切端中點(I1(下標 R)，I1(下標 L)，I2R，I2(下標 L))，犬齒尖端(C(下標 R)，C(下標 L))，小臼齒之頰側咬頭(P1(下標 R)，P1(下標 L)，P2(下標 R)，P2(下標 L))，第一及第二大臼齒之近心頰側咬頭(M1(下標 R)，M1(下標 L)，M2(下標 R)，M2(下標 L))，I1(下標 R)-I1(下標 L)連線之中點(A)，經由A並垂直M2(下標 R)-M2(下標 L)連線之交叉點B以及A-B連線與C(下標 R)-C(下標 L)連線交點E。藉由以上參考點所量得數值，我們分析以下項目：(1)量測∠R（I2(下標 R)-C(下標 R)-P1(下標 R)三點所形成之角度）＋∠L（I2(下標 L)-C(下標 L)-P1(下標 L)三點所形成之角度）來評估犬齒之前凸情形。(2)計算(A-B)/(C(下標 R)-C(下標 L))、180°-∠(C(下標 R)-A-C(下標 L))來評估前牙的曲度(curvature)。(3)計算(A-B)/(M2(下標 R)-M2(下標 L))來評估牙弓長度與寬度的比值。(4)計算(rθ5-rθ4)R＋(rθ5-rθ4)(下標 L)來評估下顎牙弓呈現圓形的程度。(5)分析牙弓兩側外型及折線P1-P2-M1-M2(ⅰ)與P1-M2(ⅱ)位置的關係，來區別type Ⅰ與type Ⅱ的圓方形(round-square)牙弓。
上述所得資料我們將之進一步標準化並統整成三個主要部分：(1)前牙的曲度。(2)牙弓外型的曲線。(3)牙弓長度與寬度的比例。結果顯示 (1) 36個下顎齒列樣本(67.9%)呈現出圓方形(round-square)的牙弓形狀，11個下顎齒列樣本(20.8%)為方形牙弓形狀，6個樣本(11.3%)則呈現出圓V形(round V-shaped)的牙弓形狀，在本實驗中並無發現呈現圓形的下顎牙弓形狀。(2)在不同的下顎牙弓中180°-∠(C(下標 R)-A-C(下標 L))、(A-E)/(C(下標 R)-C(下標 L))、(rθ5-rθ4)(下標 R)+( rθ5-rθ4)(下標 L)，此三項數值在統計上呈現出顯著之差異。(3)藉由檢測上述提及之三個主要部分，我們可以發現在圓V形(round V-shaped)、方形及圓方形(round-square)下顎牙弓中，(A-B)/(M2(下標 R)-M2(下標 L))此數值在統計上亦呈現出顯著之差異。由上可知本研究顯示出下顎的牙弓型態是由下列兩項因素所決定：一為呈現出前牙曲度(curvature)的參數－由(A-B)/(C(下標 R)-C(下標 L))、180°-∠(C(下標 R)-A-C(下標 L))、(A-E)/(C(下標 R)-C(下標 L))所組成，另一為由(rθ5-rθ4)(下標 R)＋(rθ5-rθ4)(下標 L)組成，來決定下顎牙弓圓形程度的參數。

關鍵字

人類下顎 ； 牙弓型態分析

並列摘要

To evaluate the morphology of dental arches, 53 (male: 29, female: 24) paired casts having normal dentitions and occlusion were selected from 396 (age: 18 to 26 years old; male: 257, female: 139) sets of dental study models. The mandibular dentitions were preliminarily classified as square, round-square, round and round V-shaped arches based on the conventional morphological descriptions. Midpoints of the incisor edge (I1(subscript R), I1(subscript L), I2(subscript R), &I2(subscript L)), summits of the cuspids (C(subscript R) & C(subscript L)), buccal cusps of the premolars (P1(subscript R), P1(subscript L), P2(subscript R), P2(subscript L)), mesial buccal cusps of the first and second molars (M1(subscript R), M1(subscript L), M2(subscript R), & M2(subscript L)), and the midpoint (A) of line I1(subscript R)-I1(subscript L) were designated as reference points. From A, let a vertical line intersected line M2(subscript R)-M2(subscript L) at reference point B. The line A-B intersected C(subscript R)-C(subscript L) at reference point E. We evaluated 1) the protrusion of the cuspids by ① angle I2(subscript R)-C(subscript R)-P1(subscript R) (∠R)+angle I2(subscript L) C(subscript L) P1(subscript L)(∠L); 2) the curvature of the anterior teeth by ② (A-B)/(C(subscript R)-C(subscript L)), ③ 180°-∠(C(subscript R)-A-C(subscript L)), and (A-E)/(C(subscript R)-C(subscript L)); 3) the length to width ratio of the dental arch by ⑤ (A-B)/(M2(subscript R)-M2(subscript L)); 4) the degree of roundness of the mandibular arch by estimation of ⑥ (rθ5-rθ4)R+(rθ9-rθ4)L; and 5) an item ⑦ for the differentiation of type Ⅰ and type Ⅱ round-square arches by relating the bilateral contour and position of break line P1-P2-M1-M2 (ⅰ) to line P1-M2 (ⅱ). The data of items ①, ②, ③, ④, ⑤and ⑥ were further standardized and summarized into three essential principal components: 1) the curvature of the anterior teeth, 2) the curvilinear contour of the dental arch, and 3) the length-to-width ratio of the dental arch. The results indicated that: 1) 36 cases (67.9%) of the mandibular denth ions were round-square arches which showed no prominent principal component. 11 cases (20.8%) were square arches and 6 cases (11.3%) were round V-shaped arches; no round arches was found in mandibular dentitions. 2) Statistical analysis indicated significant differences of items ③, ④ and ⑥ in various mandibular arches (Student's t-test). 3 )By examination of the three principal components, significant differences of item ⑤ between the round V-shaped arches and square and round-square mandibular arches were evident (Student's t-test). The present study elucidated that morphology of the mandibular arch was determined by a parameters representing the curvature of anterior teeth (composed of items ②, ③ and ④), and another parameter (item ⑥) representing roundness of the mandibular arch.

並列關鍵字

principal component analysis ； dental arch ； mandible ； human ； morphology