影像科学与光化学  2020, Vol. 38 Issue (1): 73-79  DOI: 10.7517/issn.1674-0475.190712   PDF    
上颌第二磨牙牙冠颊舌径、近远中径和牙面形态的CBCT研究
罗成, 杨馥榕, 雷延颖     
青海大学附属医院 口腔修复种植正畸科, 青海 西宁 810000
摘要: 本文通过三维重建上颌第二磨牙的锥形束计算机断层扫描(CBCT)图像,探讨了其牙冠颊舌径、近远中径和牙面形态与牙根及根管类型的关系。收集220例患者(共410颗)上颌第二磨牙的CBCT图像资料,在矢状面放大水平面图像至400%后观察上颌第二磨牙形态,记录牙根、根管数目及融合情况。三维重建上颌第二磨牙的CBCT图像,观察及测量牙冠部和牙面形态,分析牙冠颊舌径、近远中径和牙面形态与牙根及根管类型的关系。结果显示,200例两侧都存在上颌第二磨牙的研究对象中,88%(176/200)根管类型完全对称。410颗上颌第二磨牙中,46.83%(192/410)的第二磨牙形态为三根三根管,54.39%(223/410)有三个独立的牙根,42.20%(173/410)发生牙根融合,82.44%(338/410)为三根管。不同根管类型的上颌第二磨牙牙冠颊舌径存在差异(P < 0.05),单根管的上颌第二磨牙牙冠近远中径存在差异(P < 0.05),其余各根管类型的上颌第二磨牙牙冠近远中径无显著差异(P>0.05)。410颗上颌第二磨牙中,牙面形态分类为:斜方形64.15%(263/410)、方圆形11.95%(49/410)、圆三角形13.17%(54/410)、卵圆形10.73%(44/410)。其中,圆三角形的牙根多为单根和双根,卵圆形的多为双根,而方圆形和斜方形的则多为三根。不同牙根数目的上颌第二磨牙牙面形态存在差异(P < 0.05)。研究结果显示,上颌第二磨牙牙冠颊舌径、近远中径和牙面形态与牙根及根管类型存在一定的联系,临床中可通过三维重建上颌第二磨牙的CBCT图像,利用牙冠的解剖形态来判断上颌第二磨牙牙根及根管类型,为根管治疗提供参考。
关键词: 上颌第二磨牙    锥形束计算机断层扫描    牙冠解剖形态    根管治疗    
CBCT Study of Buccal-lingual Diameter, Proximal-distal Mid-diameter and Occlusal Surface Morphology of Maxillary Second Molar Crown
LUO Cheng, YANG Furong, LEI Yanying     
Department of Orthodontics and Prosthodontics, Qinghai University Affiliated Hospital, Xining 810000, Qinghai, P. R. China
Abstract: The relationships between crown buccal-lingual diameter, proximal-distal mid-diameter and occlusal surface morphology and root and root canal types of maxillary second molars was studied by three-dimensional reconstruction of CBCT images. The CBCT images of 220 patients (410 maxillary second molars) were collected. The morphology of maxillary second molars was observed after enlarging the horizontal images to 400% on sagittal plane, and the number of root canals and fusion were recorded. Three-dimensional reconstruction of the CBCT images of the maxillary second molars was performed to observe and measure the morphology of the crown and occlusal surface, and to analyze the relationship between the buccal and lingual diameters, distal and distal diameters of the crown and occlusal surface morphology and root and root canal types. Of 200 subjects with maxillary second molars on both sides, 88% (176/200) had completely symmetrical root canal types. Of 410 maxillary second molars, 46.83% (192/410) had three root canals, 54.39% (223/410) had three independent root canals, 42.20% (173/410) had root fusion, and 82.44% (338/410) had three root canals. The buccal and lingual diameters of the crowns of the maxillary second molars with different root canal types were different (P < 0.05). The proximal and distal diameters of the crowns of the maxillary second molars with single root canal were different (P < 0.05). There was no significant difference in the proximal and distal diameters of the crowns of the other root canal types (P>0.05). Among 410 maxillary second molars, occlusal surface morphology was classified as oblique 64.15% (263/410), square 11.95% (49/410), circular triangle 13.17% (54/410), oval 10.73% (44/410). Among them, the root of the round triangle is mostly single and double, the oval is mostly double, and the square and oblique are mostly three. The occlusal morphology of maxillary second molars with different root numbers was different (P < 0.05). In a word, the buccal and lingual diameters, distal and distal diameters and occlusal surfaces of maxillary second molars are related to root and root canal types. Three-dimensional reconstruction of CBCT images of maxillary second molars can be used to determine the root and root canal types of maxillary second molars by using the anatomical morphology of crowns, which can provide a reference for root canal therapy.
Key words: maxillary second molar    cone beam computed tomography    anatomical morphology of crown    root canal therapy    

上颌第二磨牙由于牙面窝沟形态及萌出位置靠后,导致其牙髓根尖周病变的患病率较高[1]。同时,因其解剖结构复杂、根管形态变异较多、视野狭窄等原因,也一直是临床上根管治疗的难点[2]。既往研究多采用游标卡尺测量离体牙标本的解剖外形,因临床收集完整标本的难度较大,通常其样本量较小,且拔除的患牙多为重度牙周病,导致样本产生偏倚[3]。而通过三维重建锥形束计算机断层扫描(CBCT)图像获得高质量的牙体解剖外形,可以有效解决样本量过小及偏倚等问题[4]。本研究选取于我院拍摄CBCT的220例患者(共410颗上颌第二磨牙)作为研究对象,旨在通过三维重建上颌第二磨牙的CBCT图像,探讨其牙冠颊舌径、近远中径和牙面形态与牙根及根管类型的关系,利用牙冠的解剖形态来预估牙根和根管的数目,从而为临床根管治疗提供参考意见。

1 资料与方法 1.1 临床资料

选取2017年1月~2019年4月青海大学附属医院口腔科就诊,且因诊断或者治疗需要拍摄CBCT的220例患者作为研究对象,其中男性104名、女性116名,年龄15~70岁,平均(35.4±13.7)岁。20名患者有一侧上颌第二磨牙缺失,共计410颗上颌第二磨牙。研究对象选择标准:年龄在15~70岁之间;上颌第二磨牙根尖发育完全,冠部无明显龋损或磨耗;牙齿无明显牙周病变、根尖周病变,无桩或冠部修复体,冠部无充填物。

1.2 方法 1.2.1 设备及影像学参数

意大利NewTom VGi锥形束CT,扫描参数为管电压110 kV,管电流10 mA,体素0.15 mm,视野18 cm×16 cm,扫描时间3.6~4.8 s,图像最小层厚0.3 mm。

1.2.2 测量方法

所有CBCT图像原始数据传至CBCT自带影像分析软件工作站处理。在矢状面放大水平面图像至400%后观察上颌第二磨牙形态,记录髓室底平面的根管、牙根数目及融合情况。然后三维重建上颌第二磨牙的CBCT图像,观察及测量牙冠部和牙面形态。牙冠部形态测量参照文献[5]进行,利用解剖学标志点,测量以下数据:(1)牙冠颊舌径:颊面最凸点和舌面最凸点之间的垂直距离;(2)牙冠近远中径:近中邻面与远中邻面之间的最大垂直距离(图 1)。所有指标的测量和记录均由同一名实验者完成,每个数据测量2次,计算平均值。牙面形态分类参考文献[6],使用几何图形将牙面形态分为圆三角形、卵圆形、方圆形和斜方形。

图 1 测量时各面示意图 a.测量近远中径(颊面观);b.测量颊舌径远中(邻面观)
1.3 统计学分析

采用SPSS 17.0软件进行统计学分析,对多组间定量资料行方差分析,有统计学差异再行LSD-t检验;对分类变量资料行卡方检验;以P < 0.05为差异有统计学意义。

2 结果 2.1 上颌第二磨牙根管类型与牙根数目的关系

200例两侧都具有上颌第二磨牙的研究对象中,176例双侧根管类型一致,双侧对称性为88%。410颗上颌第二磨牙中,形态以三根三根管和双根三根管居多,发生率分别为46.83%(192/410)、21.71%(89/410)。在牙根形态方面,以三个独立的牙根最为多见,发生率为54.39%(223/410),其次为融合根、独立双根和独立单根,发生率分别为42.20%(173/410)、2.44%(10/410)、0.98%(4/410)。根管数目以三根管最多,发生率为82.44%(338/410),相关数据见表 1

表 1 上颌第二磨牙不同根管类型与牙根数目的关系(n)
2.2 上颌第二磨牙牙冠颊舌径、近远中径与根管类型的关系

单因素方差LSD分析发现,不同根管类型的上颌第二磨牙牙冠颊舌径存在差异(P < 0.05),单根管的上颌第二磨牙牙冠近远中径存在差异(P < 0.05),其余各根管类型的上颌第二磨牙牙冠近远中径无显著差异(P>0.05)。见表 2

表 2 上颌第二磨牙牙冠颊舌径、近远中径与根管类型的关系(x ±s)
2.3 上颌第二磨牙牙面形态与牙根数目的关系

410颗上颌第二磨牙中,牙面形态64.15%为斜方形(263/410),35.85%(147/410)存在牙面形态变异,其中11.95%(49/410)变异为仍具有四个边的方圆形,13.17%(54/410)变异为圆三角形,10.73%(44/410)变异为卵圆形。牙面形态为圆三角形的牙根多为单根和双根,卵圆形的多为双根,而方圆形和斜方形的则多为三根。卡方检验发现,不同牙根数目的上颌第二磨牙牙面形态存在差异(P < 0.05),相关数据见表 3

表 3 上颌第二磨牙牙面形态与牙根数目的关系(n)
3 讨论

上颌第二磨牙因其牙髓及根尖周病变患病率较高、牙齿形态复杂等原因,一直是牙齿形态学研究的热点。上颌第二磨牙通常为三个牙根,即两个颊根和一个腭根,并且每个牙根内各有一个根管,但其解剖形态变异复杂,如出现牙根融合、近中颊根第二根管(MB2)等,这进一步增加了根管治疗的难度[7]。既往研究通常采用离体牙、透明牙、根管染色、X线片及CBCT等方法研究其形态特点[8],研究结果多为直观的数据统计,为临床诊疗提供了一定的理论依据。

本研究采用CBCT对上颌第二磨牙牙根数目观察,发现54.39%的第二磨牙有三个独立的牙根,这一结果与Ghoncheh等[9]报道的57.75%基本一致。近年来,研究发现上颌第二磨牙融合根的发率为10.71%~23.90%[10]。本研究中上颌第二磨牙融合根的发生率为42.20%,与Naseri等[11]报道的42.25%相近。而牙根的融合会导致合并根管、峡部、C形根管的发生率较高[12],增加了操作过程中根管清理的难度,在临床工作中应引起重视。在根管形态方面,上颌第二磨牙最常见的为三个独立的根管,其次是存在MB2,既往报道MB2的发生率为13.87%~78.9%[13]。本研究结果显示,根管数目以三根管(82.44%)发生率最高,MB2的发生率仅为9.76%,这可能与本研究计数根管数目的方法有关。本研究为了使实验数据有可比性,以髓室底平面的根管口数目为准,但牙齿内部复杂的根管构型,如Vertucci Type Ⅲ型(1-2-1)、Type Ⅴ型(1-2)、Type Ⅶ型(1-2-1-2)等均是在髓室底平面下方形成MB2[14],未纳入本研究根管数目的统计,有待改进。

受限于CBCT的辐射、费用等原因,临床根管治疗术前还多采用X线片来了解牙齿的根管形态。本研究通过观察上颌第二磨牙的CBCT图像,发现第二磨牙的根管数目与牙冠颊舌径及近远中径存在一定联系,不同根管类型的上颌第二磨牙牙冠颊舌径存在差异(P < 0.05),其中单根管的上颌第二磨牙牙冠颊舌径及近远中径均显著小于其他根管类型(P < 0.05),提示在临床操作过程中若发现牙冠部较小,应注意是否为单根管。而随着根管数目的增多,上颌第二磨牙牙冠颊舌径的值也逐渐增大,当颊舌径明显大于近远中径时,要仔细探查是否存在第四根管口。戴德华等[15]对上颌第二磨牙的解剖外形进行测量,所得颊舌径与近远中径与本研究结果的均值基本一致。

面形态变异复杂、观察记录受观察者主观影响较大,本研究虽进行了两次观察,但仍可能存在一定的误差。既往对于上颌第二磨牙牙面形态的描述多为斜方形[16]。本研究通过观察上颌第二磨牙的CBCT图像,发现第二磨牙牙面形态64.15%为斜方形,35.85%存在变异。学者们对牙面形态的研究多集中在上颌第三磨牙,Khademi等[17]报道75.45%的上颌第三磨牙牙面出现形态变异,可能与力、发育空间受限及融合根的多发等有关。本研究中,上颌第二磨牙牙面形态变异为圆三角形和卵圆形时,牙根为三根的发生率分别为12.96%和29.55%,提示在临床中若发现上颌第三磨牙牙面形态为圆三角形或卵圆形时应多考虑为单根或双根。同时与前文所述的根管类型判断方法相结合,能更好地在根管治疗术前预估牙齿的形态。

综上所述,上颌第二磨牙牙体形态变异复杂,其牙冠颊舌径、近远中径和牙面形态与牙根及根管类型存在一定的联系,临床中可通过三维重建上颌第二磨牙的CBCT图像,利用牙冠的解剖形态来判断上颌第二磨牙牙根及根管类型,为根管治疗提供参考。

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