J钩高位牵引压低内收上颌切牙的三维有限元分析

目的分析J钩高位牵引时牵引钩高度变化对切牙牙周膜应力和初始位移的影响,探讨J钩牵引过程中的力学机制,为临床正畸提供客观的理论依据。方法建立上颌牙齿及矫治器的三维有限元模型;牵引钩高度分2、4、6、8、10、12 mm 6种高度;于牵引钩顶端加载与矢状面颊向30°及与牙合平面向上30°,力大小为1.5 N;描绘出上颌切牙牙周膜应力图和初始位移图。结果当牵引钩高度增加时,中切牙最大主压应力变大,牵引钩高度小于4 mm时表现为舌倾压低,牵引钩高度大于8mm时表现为唇倾压低;侧切牙最大主压应力值先变小后增大,在牵引钩高度为4 mm时最小、12 mm时最大,舌倾伸长趋势增加。结论 J钩高位牵引时随着牵引钩高度增加,中切牙从舌倾压低变为唇倾压低;侧切牙舌倾伸长趋势增加。     

J钩高位牵引压低并内收上颌前牙的三维有限元分析

目的 利用三维有限元方法探讨J钩高位牵引辅助压低并内收上颌前牙的生物力学机制,以期为临床治疗提供参考.方法 在ANSYS 14.0软件中建立包括上颌牙列、牙周膜、直丝弓矫治器及上颌骨的三维有限元模型.模拟J钩施加1.5 N力量压低内收上前牙,A组加载于侧切牙近中,B组加载于侧切牙远中.牵引方向与矢状面保持30°不变、与(牙合)平面的角度在20°～ 60°之间,每间隔5°设置1种工况,两组共18种工况.分析上前牙位移及牙周膜应力情况.结果 随着牵引角度增大,上前牙位移趋势逐渐由舌向移动为主伴压低的顺时针旋转移动,变为整体压低、内收移动,最后变为压低伴唇向倾斜的逆时针旋转移动.在侧切牙近中以35°加载或在侧切牙远中以45°加载时,上前牙出现相对均匀一致的整体压低、内收移动,整体无旋转的趋势.结论 对于唇倾度正常的上颌前牙,J钩高位牵引加载于侧切牙近中更有利于前牙的整体压低和内收,临床上应根据个体情况和治疗目标调整牵引角度.     

安氏I类错儿童上颌切牙唇腭侧齿槽厚度的CBCT研究

目的:采用CBCT影像测量安氏I类错患儿上颌前牙唇倾度及前牙唇腭侧齿槽骨的厚度,探讨上颌切牙与其支持骨的空间位置关系。方法:选取深圳市儿童医院口腔正畸科2010.1～2012.1年间就诊的正畸患儿25名,年龄11～14岁,平均12.5岁,男9例,女16例。Angle I类轻度错畸形。上前牙排列良好,无严重拥挤。所有病例均拍摄CBCT影像,在重建后的图像下进行定量测量。测定上切牙唇腭向的倾斜度,上切牙不同层面唇腭侧齿槽骨的厚度,上切牙根尖上方唇侧齿槽骨的曲度以及上切牙根尖距唇侧齿槽骨最凹点的距离。测量得到的数据采用SPSS13.0软件进行统计分析。结果:釉牙骨质界下2 mm唇侧骨板的厚度:中切牙(0.96±0.32)mm,侧切牙(0.78±0.32)mm。釉牙骨质界下2 mm腭侧骨板的厚度:中切牙(1.53±0.40)mm,侧切牙(1.12±0.48)mm。中切牙与腭平面的角度为114.59°±5.25°,侧切牙与腭平面的角度为111.75°±5.98°。切牙根尖上方唇侧齿槽骨的曲度:中切牙145.70°±11.09°,侧切牙156.92°±8.33°。切牙根尖距其上方唇侧齿槽骨最凹点的距离:中切牙(2.88±1.49)mm,侧切牙(2.69±0.99)mm。结论:上颌中切牙较侧切牙更加唇倾,切牙唇侧骨板均较薄,腭侧骨板相对较厚。切牙根尖位置更接近齿槽骨的唇侧。     

安氏I类错(牙合)儿童上颌切牙唇腭侧齿槽厚度的CBCT研究

目的:采用CBCT影像测量安氏I类错(牙合)患儿上颌前牙唇倾度及前牙唇腭侧齿槽骨的厚度,探讨上颌切牙与其支持骨的空间位置关系.方法:选取深圳市儿童医院口腔正畸科2010.1～2012.1年间就诊的正畸患儿25名,年龄11～14岁,平均12.5岁,男9例,女16例.Angle I类轻度错(牙合)畸形.上前牙排列良好,无严重拥挤.所有病例均拍摄CBCT影像,在重建后的图像下进行定量测量.测定上切牙唇腭向的倾斜度,上切牙不同层面唇腭侧齿槽骨的厚度,上切牙根尖上方唇侧齿槽骨的曲度以及上切牙根尖距唇侧齿槽骨最凹点的距离.测量得到的数据采用SPSS13.0软件进行统计分析.结果:釉牙骨质界下2 mm唇侧骨板的厚度:中切牙(0.96±0.32) mm,侧切牙(0.78±0.32) mm.釉牙骨质界下2 mm腭侧骨板的厚度:中切牙(1.53±0.40) mm,侧切牙(1.12±0.48) mm.中切牙与腭平面的角度为114.59°±5.25°,侧切牙与腭平面的角度为111.75°±5.98°.切牙根尖上方唇侧齿槽骨的曲度:中切牙145.70°±11.09°,侧切牙156.92°±8.33°.切牙根尖距其上方唇侧齿槽骨最凹点的距离:中切牙(2.88±1.49) mm,侧切牙(2.69±0.99) mm.结论:上颌中切牙较侧切牙更加唇倾,切牙唇侧骨板均较薄,腭侧骨板相对较厚.切牙根尖位置更接近齿槽骨的唇侧.     

无托槽隐形矫治中牙周炎患者下切牙压低的三维有限元研究

研究不同硬度及矫治位移量隐形矫治器在牙周炎患者切牙压低时的生物力学机制。方法:建立轻、中度牙周炎患者的三维有限元模型,分析415.6 MPa、528.0 MPa、816.31 MPa硬度及0.15 mm、0.2 mm隐形矫治器在切牙压低时牙齿位移趋势及牙周膜应力分布情况。结果:8组工况切牙均表现为伴唇侧倾斜的压低,隐形矫治器硬度增加,垂直向位移趋势增加,唇侧倾斜趋势减小而随着矫治位移量增加,唇侧倾斜趋势增大。牙周膜最大应力分布于牙颈部和根尖区,最小应力分布于根中部。随着硬度增加,牙周膜整体应力值增大,牙颈部应力分布更均匀而随着矫治位移量增加牙颈部应力更集中。结论:隐形矫治器硬度增大,有利于提高矫治器效能和三维向控制,矫治位移量增加不利于三维向控制。临床上建议使用中等硬度矫治器,配合较小的步距可以实现牙齿压低,维护牙周组织健康。     

摇椅形唇弓作用下下颌中切牙牙周膜应力分布的三维有限元研究

目的　通过建立下中切牙的三维有限元模型对不同深度摇椅弓作用下牙周膜应力分布情况进行定性定量研究。方法　采用有限元分析软件建立下中切牙牙周膜的三维有限元模型 ,所建模型包括783个节点、984个单元。分析其在摇椅弓作用下的应力分布规律。结果　摇椅弓作用下下切牙牙周膜在唇侧颈缘和根中部为压应力区 ,在舌侧颈 1/ 3为拉应力区 ,根尖部为压应力集中区。结论　摇椅弓作用下下切牙有压低、唇倾的趋势 ,且此趋势随摇椅弓深度的加深而愈加明显。     

不同部位种植体支抗前牵引上颌的三维有限元分析

目的采用三维有限元方法分析不同部位的种植体支抗前牵引对上颌复合体的影响,为种植体支抗前牵引治疗骨性Ⅲ类错牙合提供客观的理论依据。方法运用已建立的上颌复合体和种植体的三维有限元模型,在上颌骨唇颊侧三个不同部位(上颌中切牙与侧切牙牙根间;尖牙与第一双尖牙牙根间;第二双尖牙与第一磨牙牙根间)植入种植体,模拟临床在种植体上加载前牵引力,不同部位和不同角度之间两两组合共形成12种工况,分析比较不同工况下上颌复合体发生的应力分布以及旋转、移位变化。结果不同部位不同角度的前牵引力对上颌复合体的影响表现为:①牵引力向前下与眶耳平面呈30°方向时,随着种植体部位的逐渐后移,除颧额缝处应力逐渐减小外,其余各骨缝处应力逐渐增大。当种植体位于第二双尖牙与第一磨牙牙根间时,上颌复合体各相关骨缝主应力值最接近。②牵引力向前下40°方向时,蝶颌缝变化较大。当种植体位于中切牙与侧切牙牙根间和尖牙与第一双尖牙牙根间时此处受到的是压应力;而当种植体位于第二双尖牙与第一磨牙牙根间前牵引时则变为拉应力。③牵引力向前下50°和60°方向时,鼻颌缝处应力在三个不同部位种植体牵引时虽发生较大变化,但均为拉应力。蝶颌缝处应力均为压应力。结论根据应力分析,随着种植体植入部位的逐渐后移,上颌复合体逆时针旋转趋势逐渐增大:①牵引角度30°,种植体位于第二双尖牙与第一磨牙牙根间时,上颌复合体可能发生近似整体前移;当种植体位于中切牙与侧切牙牙根间、尖牙与第一双尖牙牙根间时,上颌复合体均可能发生顺时针旋转。②牵引角度40°,种植体位于第二双尖牙与第一磨牙牙根间时,上颌复合体可能发生逆时针旋转,其余两部位前牵引时上颌复合体均可能发生顺时针的旋转;③牵引角度大于50°,三个不同种植体部位前牵引均可能导致上颌复合体顺时针旋转。     

打开咬合时下颌中切牙及牙周膜应力分布的有限元研究

目的对下颌中切牙及其牙周膜在打开咬合时所产生的力学系统进行有限元分析,了解打开咬合时下颌中切牙及牙周膜应力分布的情况。方法建立下颌牙列各牙齿、牙槽骨及切牙牙周膜的三维有限元模型。然后,进一步模拟临床,在中切牙处加载15 g 垂直向下的力,求得牙齿以及牙周膜的应力分布情况。结果牙根表面最大应力值分布复杂,在根尖处可见应力集中区,应力集中区集中在颈缘处,向根方应力值逐渐变小,表现为典型的弯曲变形应力分布特征。舌侧、近中面主应力值相对较小,最大应力值在远唇轴角处。牙槽嵴顶部的应力值最大值达20.5×10~5g/mm~2。结论 1)本研究建立的下颌牙列的三维有限元模型,可以适用于临床上打开咬合等矫治技术的研究。2)矫治力作用下下颌中切牙牙周膜上应力从颈缘到根尖逐渐减小,但在牙槽嵴顶部应力峰值明显增大。     

差动直丝弓矫治技术打开咬合过程中不同磨牙后倾弯曲度对下颌前牙及牙周膜应力分布的影响

目的：研究在差动直丝弓矫治技术打开咬合过程中,不同下颌磨牙后倾弯角度对下颌前牙应力分布及位移趋势的影响。方法利用志愿者锥体束CT,建立下颌牙列和差动直丝弓矫治器的三维有限元模型,模拟下颌30°、35°、40°和45°四种后倾弯,对模型加载进行有限元分析。结果下颌前牙牙根和牙周膜所受应力均随后倾弯度数增大而增大,当后倾弯角度大于40°时应力出现减小,其应力分布符合非控制性倾斜移动的特点。下颌前牙的初始位移趋势随后倾弯的增大而增大,当大于40°时初始位移趋势开始减小。下颌尖牙在颊舌向上表现为冠颊倾,下颌切牙冠唇倾,在垂直向上表现为先尖牙再切牙的顺序压低,在近远中向均表现为冠近中移动趋势。结论在差动直丝弓打开咬合阶段,通过调整磨牙后倾曲的角度可获得下颌前牙段适宜的压入以及匹配的上下颌牙弓宽度。     

无托槽隐形矫治器配合微种植钉远移磨牙的三维有限元研究

目的 应用三维有限元模型研究无托槽隐形矫治器配合不同植入位置微种植钉远移磨牙时的初始上颌前牙位移及尖牙区应力分布情况。方法 选取于2021-02-16在大连市口腔医院正畸科就诊的需采用无托槽隐形矫治器行远移磨牙非减数正畸治疗的1例女性患者作为建模对象。构建三维有限元模型,模拟微种植钉位于第二前磨牙与第一磨牙之间、第一磨牙与第二磨牙之间,分别距离牙槽嵴顶4、6、8、10 mm的8种工况,并在微种植钉与尖牙唇面的舌侧扣之间加载1.47 N正畸力。分析加力1 s后8种工况的上颌前牙位移及尖牙牙周膜应力分布情况。结果 8种工况中,上颌中切牙均呈现牙冠唇向、牙根腭向的位移趋势;上颌中切牙牙冠唇向位移量随微种植钉高度的增加而减小,且微种植钉位于相对近中（上颌第二前磨牙与第一磨牙之间）时产生的位移量更小。8种工况中,上颌尖牙均呈现牙冠唇向、牙根腭向的位移趋势,且牙冠呈现唇倾趋势;上颌尖牙牙周膜最小主应力绝对值随微种植钉高度的增加而增大,且微种植钉位于相对近中时产生的最小主应力更大。结论 无托槽隐形矫治器配合微种植钉远移上颌磨牙时,配合本实验8种工况中相对近中的更高位微种植钉利于切牙转矩控制,配合相对...     

Effect of the inclination of a maxillary central incisor on periodontal stress

Abstract Objective: To determine the effect of labiolingual inclination of a maxillary central incisor on the magnitude and distribution of stresses within the periodontal space. Materials and Methods: Five three-dimensional finite element models of a right maxillary central incisor were created with 0°, 10°, 20°, 30°, and 40° inclination. Each incisor model was subjected to a 1?N lingual-directed force and 6-12?N·mm countertipping moment on the labial surface. The stress level within the periodontal ligament was calculated in terms of maximum principal stresses. Results: With increased inclination, compressive stresses tended to increase whereas tensile stresses tended to decrease. The location where compressive stress was prevalent changed from the midroot area to the apical area on the lingual side, while the area where tensile stresses were predominant changed from the midroot area to the cervical area on the labial side. Conclusion: There are more compressive stresses concentrated at the apex of incisors with a high degree of inclination than in incisors that are more upright. This may be associated with the higher clinical incidence of apical root resorption found in inclined maxillary central incisors.     

不同牵引部位对上颌埋伏中切牙牙周应力分布的影响

目的:基于对上颌唇向倒置埋伏中切牙的三维有限元模型施加不同部位的牵引力,分析比较不同工况下牙周膜的应力分布,从而为临床进行上颌埋伏中切牙助萌治疗提供参考。方法:选取1名上颌中切牙唇向倒置埋伏阻生患者的锥体束CT(CBCT)原始数据,建立统一坐标系下上颌埋伏中切牙及其支持组织的三维有限元模型。在牙冠舌面切1/3、中1/3、颈1/3的中心分别施加在矢状方向上垂直于牙体长轴的30 g、60 g、90 g的牵引力,分析比较不同工况下牙周膜的应力分布情况。结果:不同牵引部位下,埋伏牙牙周应力分布特点类似。同一力值牵引,牵引部位越靠近牙颈部,牙周膜的应力越小;同一牵引部位,牵引力越大,牙周应力越大。结论:牵引部位应尽量位于切端,牵引力不宜超过60 g。     

Effect of the inclination of a maxillary central incisor on periodontal stress: Finite element analysis

Objective:To determine the effect of labiolingual inclination of a maxillary central incisor on the magnitude and distribution of stresses within the periodontal space.Materials and Methods:Five three-dimensional finite element models of a right maxillary central incisor were created with 0°, 10°, 20°, 30°, and 40° inclination. Each incisor model was subjected to a 1 N lingual-directed force and 6–12 N·mm countertipping moment on the labial surface. The stress level within the periodontal ligament was calculated in terms of maximum principal stresses.Results:With increased inclination, compressive stresses tended to increase whereas tensile stresses tended to decrease. The location where compressive stress was prevalent changed from the midroot area to the apical area on the lingual side, while the area where tensile stresses were predominant changed from the midroot area to the cervical area on the labial side.Conclusion:There are more compressive stresses concentrated at the apex of incisors with a high degree of inclination than in incisors that are more upright. This may be associated with the higher clinical incidence of apical root resorption found in inclined maxillary central incisors.     

上颌唇向倒置埋伏中切牙牙周应力分布的有限元研究

目的 建立上颌唇向倒置埋伏中切牙及其支持组织的三维模型,分析其在不同工况下的牙周应力分布,为治疗上颌埋伏中切牙提供参考。方法 利用锥形束CT（CBCT）原始数据,结合Mimics 10.01和Ansys 14.0 软件建立上颌唇向倒置埋伏中切牙及其牙周组织的有限元模型。在埋伏牙切端沿其长轴垂直方向,分别加载20、30、40、50、60、70 g集中力,并测定不同工况下牙周膜Von Mises应力分布。结果 牙周膜应力随牵引力的增加而增大,30 g力时最大Von Mises应力值为24 919.0 Pa,在牙周膜的最适应力范围内且接近其最大值。结论 矫治初期,上颌唇向倒置埋伏中切牙的适宜牵引力较小,约为30 g。     

微钛板辅助上颌前方牵引支抗稳定性的三维有限元分析

目的　为临床不同方向下进行前方牵引时,不同形态微钛板的选用提供参考。方法　构建6种改良型微钛板及上颌骨的三维有限元模型。对该模型牵引位点施加大小为4.9N/侧,方向为与上颌平面夹角为0°-50°向前下的力,分析各工况下微钛板所受应力及其固位螺钉所受拉力和应力。结果 1.不同微钛板均可固定于上颌骨颧牙槽嵴处且无受力过大或应力中断现象。2.固位螺钉受力具有差异性。角度为0°时,Y3型微钛板固位螺钉受力离散程度较小为3.899,10°-40°时,L3型微钛板固位螺钉受力离散程度较小为4.544、4.170、3.820、3.547,50°时,L2型微钛板固位螺钉受力离散程度较小为2.687。结论　微钛板辅助上颌骨发育不足患者在不同方向下进行前方牵引时,应考虑选用不同形态：牵引方向与平面夹角为0°时,选用Y3型微钛板;夹角为10°-40°时,选用L3型微钛板;夹角为50°时,选用L2型微钛板。     

台阶式垂直闭合曲内收上颌切牙的三维有限元分析

目的 研究台阶式垂直闭合曲在三维空间内对上颌切牙位置的控制作用.方法 选择一名正常 志愿者,对其上颌牙列和牙槽骨进行三维螺旋CT扫描,只对上颌右侧中、侧切牙及牙槽骨进行建模和数据计算,利用Ansys软件生成右侧弓丝-托槽-上颌切牙段及牙周支持组织的三维有限元模型,最后根据镜像对称原理建立弓丝-托槽-上颌切牙段及牙周支持组织的三维有限元模型.模拟台阶式垂直闭合曲在临床上的使用情况加力,分析上颌切牙的位移趋势以及牙周支持组织中的应力分布规律.结果 台阶式垂直闭合曲作用下,上颌中切牙舌向、唇向最大位移分别为5.29×10-2和0.71×10-2 mm;龈向、向最大位移分别为10.47×10-3和10.20×10-3 mm;近中、远中最大位移分别为10.26×10-3和1.63×10-3 mm;侧切牙舌向、唇向最大位移分别为3.31×10-2和0.41×10-2 mm;龈向、向最大位移分别为10.52×10-3 和5.10×10-3 mm;近中、远中最大位移分别为6.29×10-3 和4.64×10-3 mm;二者均表现为舌向、龈向的近似整体移动趋势.中切牙牙齿、牙周膜、牙槽骨的最大应力值分别为31.35、2.52、4.64 MPa;侧切牙牙齿、牙周膜、牙槽骨的最大应力值分别为19.59、1.28、4.12 MPa;二者的应力分布规律相似,牙周膜对应力起缓冲作用.结论 台阶式垂直闭合曲在上颌切牙内收阶段可控制其在三维方向上的位置,对抗"钟摆效应",对临床实践具有一定参考意义.

Abstract：

Objective To investigate the displacement and stress distribution of upper incisors in three-dimensional(3D) space controlled by step-shaped vertical closing loop. Methods The maxillary teeth and alveolar bone of a volunteer with normal occlusion were scanned with 3D spiral CT. Modeling and calculation were only carried out on right upper central incisor, lateral incisor and their alveolar bone in order to simplify the procedures. A 3D finite element model of archwire-brackets-upper incisors and periodontal tissues was developed using Ansys finite element package. Finally, a 3D finite element model of archwire-brackets-upper incisors and periodontal tissues was established based on mirror symmetry principle. The displacement of maxillary incisors and stress distribution in periodontal tissues were analyzed. ResultsWhen step-shaped vertical closing loop was simply drew back 1 mm, the maximum displacement of upper central incisor in labial and lingual direction were 5.29×10-2 and 0.71×10-2 mm; 10.47×10-3 and 10.20×10-3 mm in gingival and occlusal direction, 10.26×10-3 and 1.63×10-3 mm in medial and distal direction; the maximum displacement of upper lateral incisor in labial and lingual direction were 3.31×10-2 and 0.41×10-2 mm, 10.52×10-3 and 5.10×10-3 mm in gingival and occlusal direction, 6.29×10-3 and 4.64×10-3 mm in medial and distal direction, the displacement trend of them were moving lingually and gingivally similar to bodily movement. The stress peach of upper central incisor, periodontal ligament and alveolar bone were 31.35, 2.52 and 4.64 MPa, the stress peach of upper lateral incisor, periodontal ligament and alveolar bone were 19.59, 1.28 and 4.12 Mpa, the stress distribution of them were similar and the periodontal ligament buffered the stress imposed on the tooth. Conclusions The position of upper incisors in 3D space could be controlled by step-shaped vertical closing loop and the pendulum effect could be confronted.     

Secondary trauma from occlusion: three-dimensional analysis using the finite element method.

Clinical effects of forces applied by dental occlusion on the periodontium have been evaluated for decades. Historically, trauma from occlusion has been considered as a major etiologic factor of inflammatory periodontal diseases, while some researchers have interpreted it to be of less importance or without any detectable importance in periodontics. In this study, five three-dimensional models of a maxillary central incisor were created using ANSYS 5.40. The only difference in each model was the height of the alveolar bone that showed from normal height (13 mm of alveolar bone height) to 8 mm of alveolar bone loss (5 mm of alveolar bone height). Five-point forces of 0.3 N summing up to 1.5 N were applied in a parallel line, 1 mm apical to the incisal edge on the palatal side in a palatolabial direction. The maximum (S1) and minimum (S3) principal stresses in the nodes of the labial side of the periodontal ligament (apical to the alveolar crest) were assessed. Analysis was done using the finite element method. An increase of S1 (up to 16 times in the cervical and 11.25 times in the apical area) and S3 (up to 17.13 times in the cervical and 9.9 times in the apical area) in comparison to the normal model was shown. The highest stress levels were traced in the subcervical area, except for the last model (8 mm of the alveolar bone loss). According to the results of this study, 2.5 mm of alveolar bone loss can be considered as a limit beyond which stress alterations were accelerated. Based on the FEM analysis, alveolar bone loss increases stress (S1 and S3) produced in the PDL, in spite of applying the same force vector.     

Analysis of stress in the periodontium of the maxillary first molar with a three-dimensional finite element model.

The aim of this study was to simulate the stress response in the periodontium of the maxillary first molar to different moment to force ratios, and to determine the moment to force ratio for translational movement of the tooth by means of the finite element method. The three-dimensional finite element model of the maxillary first molar consisted of 3097 nodes and 2521 isoparametric eight-node solid elements. The model was designed to dissect the periodontal ligament, root, and alveolar bone separately. The results demonstrate the sensitivity of the periodontium to load changes. The stress pattern in the periodontal ligament for a distalizing force without counterbalancing moments showed high concentration at the cervical level of the distobuccal root due to tipping and rotation of the tooth. After various counterrotation as well as countertipping moments were applied, an even distribution of low compression on the distal side of the periodontal ligament was obtained at a countertipping moment to force ratio of 9:1 and a counterrotation moment to force ratio of 5:1. This lower and uniform stress in the periodontal ligament implies that a translational tooth movement may be achieved. Furthermore, high stress concentration was observed on the root surface at the furcation level in contrast with anterior teeth reported to display high concentration at the apex. This result may suggest that the root morphology of the maxillary first molar makes it less susceptible to apical root resorption relative to anterior teeth during tooth movement. The stress patterns in the periodontal ligament corresponded with the load types; those on the root appeared to be highly affected by bending and the high stiffness of the root.     

Stress Distribution on Trephine-Resected Root-end in Targeted Endodontic Microsurgery: A Finite Element Analysis

IntroductionThis study aimed to determine if stress distribution from occlusal loads after targeted endodontic microsurgery (TEMS) differed for trephine-resected flat and curved root-ends, with and without bone graft.MethodsFinite element analysis models were constructed from cone-beam computed tomography data of a TEMS-treated maxillary central incisor. Models included flat and curved resected root-ends, with and without apical bone graft, and normal or root canal filled controls. In centric occlusion, axial force was directed on mesial and distal lingual marginal ridges at 120° angle. For lateral excursion, additional mesiodistal forces were applied from centric occlusion. For edge biting, axial force was directed on the incisal edge. Under occlusal loads, stress distribution patterns on tooth and root-end circumference were analyzed.ResultsIn normal and root filled controls, occlusal stress was distributed on labial and palatal root surfaces, concentrated in the labial cervical area, and maximized at the apex. For resected root-ends, occlusal loads concentrated stress on the labial cervical area. With bone graft, maximum stress concentration shifted to the apex, which implied stress relief and dispersion from the cervical root area. Stress patterns on the root-end were more widely spread in models with apical bone graft, whereas curved root-end showed stress concentrating arc especially when without apical bone support. The mean stress values on root-end circumference were significantly higher in curved than flat root-end (P < .05), especially with apical bone support (P < .05).ConclusionsOcclusal stress patterns on a maxillary central incisor were markedly affected by root-end resection configuration and apical bone support. Trephine-resected curved root-end had stress pattern concentrated on its circumference. Curved and flat root-ends had labial cervical stress that was relieved by bone graft. TEMS resected root-ends should be flattened and bone grafted to disperse stress from occlusal loads.     

Stresses induced by edgewise appliances in the periodontal ligament--a finite element study.

The quantification of stress in the periodontal ligament is an important concept, as stress in this tissue is transmitted to the alveolus, with subsequent bone remodelling and tooth movement. A number of clinical studies have suggested figures for such an optimal stress range. This study makes use of a finite element technique to determine the stress induced in the periodontal ligament in three dimensions when a maxillary canine tooth is subjected to an orthodontic force similar to that produced by an edgewise appliance. The maximum stress induced at the cervical margin of the periodontal ligament was 0.072 N/mm2, while the maximum stress induced at the level of the apical foramen was 0.0038 N/mm2. These results are discussed in the light of known clinical experience and compared with the stresses produced in the periodontal ligament by other orthodontic forces. The findings would suggest that even with 'perfect' edgewise mechanics it would be difficult to obtain canine movement by pure translation or 'bodily movement.'