下颌第一磨牙牙体缺损修复的三维有限元力学分析

目的:对根管治疗的下颌第一恒磨牙髓室壁未破坏与部分破坏的两种最大远中牙合面牙体缺损充填,全冠与桩核全冠修复进行三维有限元应力分析,为临床修复方式的选择提供一定的理论依据。方法:通过三维激光扫描、三维造型设计技术,建立下颌第一恒磨牙髓室壁未破坏和髓室壁部分破坏的最大远中牙合面牙体缺损,银汞合金、复合树脂充填,镍铬合金全冠修复或铸造镍铬合金桩核全冠、金合金桩核全冠修复的三维有限元模型。观察4种载荷下牙本质Mohr应力分布,比较牙本质最大Mohr值。结果:在最大、垂直、斜向载荷下,两类修复牙本质最大Mohr值均明显小于牙本质拉伸极限强度。髓室壁牙体组织部分破坏的模型,在垂直、斜向载荷下,牙本质最大Mohr值为桩核全冠的小于充填全冠的,应力由充填全冠集中于冠边缘、牙颈部分散到根部。在水平载荷下,两类修复牙本质最大Mohr值均有急剧增加,接近或超过牙本质拉伸极限强度。结论:髓室壁牙体组织是否保留对修复后牙体的抗折力及修复方法的选择有重要影响。     

下颌第一磨牙任意两壁缺损不同充填材料全瓷冠修复的三维有限元应力分析

目的:应用三维有限元法对不同充填材料全瓷冠修复两壁缺损下颌第一磨牙应力分析。方法:通过CBCT扫描离体牙,Mincis三维重建,Geomagic优化处理,Ansys布尔运算建立下颌第一磨牙两壁缺损6种模型,分别使用银汞合金充填及复合树脂充填全瓷冠修复,在最大、垂直、斜向及水平4种载荷下,分别比较牙本质Mohr应力分布及牙本质最大Mohr值。结果:下颌第一磨牙牙冠缺损1/2时,不同充填材料全瓷冠修复,同一载荷下6种缺损模型的牙根应力分布无明显区别,银汞合金充填全瓷冠修复的应力集中区较复合树脂充填全瓷冠修复更偏向根方。结论:下颌第一磨牙牙冠缺损1/2时,复合树脂充填全瓷冠修复优于银汞合金充填全瓷冠修复,且缺损位置对修复效果无明显影响。     

下颌第一磨牙牙体缺损修复后静力与冲击动力的三维有限元分析

目的对下颌第一磨牙根管治疗术后远中!面牙体组织缺损复合树脂或银汞合金充填金属全冠修复模型进行静力与冲击动力的三维有限元法初步比较分析，为临床的修复设计提供理论依据。方法运用逆向工程技术法建立三维有限元模型，模拟上下颌第一磨牙牙尖交错!及尖对尖咬合状态，冲击动力选用半正弦脉冲型，冲击载荷较静载荷下的应力变化用冲击系数表示。结果在两种载荷下，复合树脂或银汞合金充填金属全冠修复的有限元模型的最大Mohr应力值均出现在金属冠上；而这两种修复方式中，牙本质的Mohr应力值差别不大，远小于牙本质拉伸极限强度；冲击系数接近于1。结论冲击载荷更符合口腔的实际情况，但适当的静载荷分析是可接受的。金属全冠修复是必要的；复合树脂或银汞合金充填金属全冠修复效果无明显差异。     

纤维桩与金属桩核修复磨牙牙体缺损的三维有限元应力分析

目的：通过对磨牙牙体破坏较大的牙体缺损，采用纤维桩与铸造镍铬合金桩核、金合金桩核修复进行三维有限元应力分析，为临床应用提供一定的理论依据。方法：运用逆向工程技术法建立上下颌第一磨牙牙尖交错胎及尖对尖咬合状态的三维有限元模型，于上颌第一磨牙牙颈部平面施加均布载荷，进行静力与冲击动力计算，观察牙本质Mohr应力值的变化。结果：静载及动载下3种桩核修复，牙本质最大Mohr值均小于牙本质拉伸极限强度；牙本质最大Mohr值均位于根分歧部位，以纤维桩修复者为小；金合金桩核对减轻牙颈部应力明显；冲击载荷较静载下的应力变化一冲击系数均接近1。结论：3种桩核修复在临床上虽均可行，但建议临床上除牙颈部的的牙体组织过于薄弱或修复牙体组织缺损时固位需要外，尽量不使用桩核；其中，以纤维桩和金合金桩核为好；在有限元应力分析中，静载的研究是可行的。     

复合树脂充填不同角度楔形缺损效果的三维有限元分析

目的:研究复合树脂对下颌第一前磨牙4种角度楔形缺损的修复效果。方法:在前期建立的深1 mm,夹角分别为30°、60°、90°、120°的下颌第一前磨牙颊颈部楔形缺损有限元模型上,通过赋予牙本质参数和复合树脂参数,获得模拟复合树脂充填修复模型、模拟完整牙体实验模型和未修复的楔形缺损模型,分别经100 N轴向加载后,利用三维有限元分析法进行应力分析。结果:由牙本质充填模拟的完整牙体其应力分布状况与复合树脂充填体相似,均为近中侧高于远中侧,各种角度楔缺的Von Mises应力集中点均位于修复体外表面近中侧边缘;复合树脂修复体部分的Von Mises应力最大值低于模拟牙本质修复体。30°楔缺时树脂修复模型在平面O上承受较大应力的范围略大于完整牙体;在60°楔缺时树脂修复模型在平面O上承受较大应力的范围略小于完整牙体;在90°和120°楔缺时树脂修复模型在平面O上承受较大应力的范围明显小于完整牙体。30°、60°、90°、和120°4种楔形缺损角度情况下,树脂修复组和完整牙体组在直线L上的Von Mises应力分布接近(P>0.05),均明显小于未充填的楔缺模型(P<0.05)。结论:复合树脂充填对于4种夹角角度的楔形缺损均具有保护作用,可使患牙内部的应力分布情况恢复正常,更好的阻断了牙体内部的应力集中现象。     

磨牙牙体缺损桩核冠与全冠修复的应力对比研究

目的对比分析磨牙牙体大面积缺损桩核冠和全冠修复后,存留牙体组织的应力状况,为磨牙牙体缺损的修复设计提供参考。方法分别建立上下颌磨牙大面积缺损桩核冠修复和牙体充填后全冠修复2种修复方式的三维有限元分析模型,模拟牙齿在咀嚼过程的受力情况,计算分析上述2种修复状况下,存留牙体组织的应力分布状况。结果磨牙桩核冠修复后应力集中区在根管口和牙颈部;全冠修复后,应力集中在牙颈部,全冠修复后牙颈部的最大应力小于桩核冠修复后根管口的最大应力。结论磨牙大面积缺损修复时,若牙体预备后存留壁厚度不小于1.5mm,全冠修复较桩核冠修复更有利于利用牙齿固有结构保存存留牙体组织的抗力性。     

两种桩核冠修复下颌前磨牙的抗折力研究

目的研究两种桩核修复不同牙本质领圈的下颌前磨牙的抗折性能,为临床应用提供实验依据。方法选取离体下颌恒前磨牙48颗,随机分为6组,A组~F组,每组8颗。所有牙经根管治疗后齐釉牙本质界上2 mm截冠。A、B组保留2 mm完整的牙本质壁;C、D组保留舌侧一半牙本质壁;E、F组则保留颊侧一半牙本质壁。然后A、C、E组行铸造桩核冠修复,B、D、F组行金属螺纹桩树脂核全冠修复。在万能测试机上进行加载,记录断裂时的最大载荷。结果各组平均最大载荷值大小趋势为A>B>C>E>D>F。A、B组之间比较P>0.05。C、E组之间比较P>0.05;D、F组之间比较P>0.05。C、D组之间比较P<0.05,E、F组之间比较P<0.05。试件折裂形式大部分为斜向根折,有利于再修复的折裂只出现在螺纹桩树脂核组中。结论根管治疗后的下颌前磨牙保留2 mm的完整牙本质领圈,桩核材料性能对牙体抗折力没有显著影响;同种桩核冠修复牙体,缺损范围对牙体的平均抗折力无明显影响;不完整领圈组铸造桩核冠修复后牙体的平均抗折力大于金属螺纹桩树脂核全冠组,以接近牙本质弹性模量的的复合树脂做核材料有利于保护牙根。     

存留壁和髓室底厚度对磨牙桩冠修复的应力分析

目的:研究不同牙体存留壁厚度及髓室底厚度的磨牙桩冠修复后,存留牙体组织的应力大小及分布状况,为临床牙体大面积缺损的桩冠修复提供理论依据。方法:对不同牙体存留壁和髓室底厚度进行量化分级,分别建立上下颌第一磨牙牙体缺损的量化分级三维有限元模型。其中牙体预备后存留壁厚度分别设定为1mm、1.5mm及2mm;髓室底厚度分别设定为0.5mm、1mm及2mm。计算分析三种牙体缺损状况时存留牙体组织的应力及分布状况。结果:存留壁的应力值是随着存留壁厚度的增加而减小;髓室底的应力值是随着髓室底厚度的增加而增大。结论:牙体预备后的存留壁厚度不小于1mm时,桩冠修复后牙体组织的应力值均小于牙本质的抗力强度。髓室底的薄厚对桩冠修复后髓室底的抗折强度无不利影响。     

磨牙严重缺损的修复

对牙体严重缺损的磨牙,可采用多种方法修复,如牙本质固位钉或根管桩加银汞或复合树脂修复体;冠桩一体铸造修复体;桩核全冠修复体等。应根据剩余牙体组织的具体情况和患者的要求等确定修复方法,常可取得良好的修复效果。     

不同修复方法对深型楔状缺损牙应力分布影响研究

目的    应用三维有限元法分析不同修复方法对深型楔状缺损牙应力分布的影响。方法    选择上海市口腔病防治院门诊患者因正畸拔除的下颌第一前磨牙1颗作为研究样本,通过Micro-CT扫描并联合应用4种软件模拟重建下颌第一前磨牙深型楔状缺损模型,模型分别用复合树脂和瓷嵌体两种材料修复,洞形制备分为有倒凹和无倒凹两种方法。加载200 N垂直载荷后应用有限元分析软件进行应力分析。结果    牙颈部楔状缺损修复后其颈部牙体组织等效应力显著降低,其中采用全瓷嵌体修复缺损的模型颈部牙体组织等效应力降低最多。各模型修复体位移和颊尖位移均无明显差异。Ⅲ度楔状缺损各修复模型中,单纯采用树脂修复模型的修复体等效应力和最大应力均低于其他两种模型。Ⅳ度楔状缺损各修复模型中,采用全瓷嵌体修复模型的修复体等效应力和最大应力均显著低于其他两种模型,采用树脂修复的两个模型其修复体等效应力之间无明显差异。结论　修复治疗可缓解楔状缺损牙缺损区的牙体硬组织应力集中。Ⅲ度楔状缺损可采用树脂修复;Ⅳ度楔状缺损推荐优先选择全瓷嵌体修复,树脂修复则建议增加固位倒凹。     

A comparison of the mechanical behavior of posterior teeth with amalgam and composite MOD restorations

OBJECTIVE: To compare the mechanical behavior, and infer differences in fracture resistance, of mandibular molars with amalgam and composite MOD restorations to that of an unrestored molar. METHOD: Finite element models were developed for an unrestored molar and molars with MOD amalgam and composite restorations. The location and magnitude of maximum principal stress resulting from simultaneous mechanical and thermal loads were determined for each molar using a series of designed experiments. An analysis of variance was conducted with the components of stress to distinguish the relative influence of oral parameters and restoration on the stress distribution in each molar. RESULTS: The maximum principal stress in the unrestored molar was the largest of all three molars examined and occurred within the dentin along the pulpal wall. Maximum principal stresses in the molars with amalgam and composite restorations both occurred along the cavosurface margin. Maximum principal stresses in the molar with amalgam restoration occurred at the pulpal floor and lingual wall junction and resulted from large occlusal loads. Although occlusal loading had minimal effects on the stress distribution within the molar with composite restoration, low oral temperatures were responsible for the maximum principal stresses, which were found at the lingual margin and occlusal surface junction. CONCLUSION: There was no significant difference in the magnitude of maximum stress that occurred in the molars with amalgam and light curing composite restorations. However, the location and orientation of maximum stress in the restored molars were largely dependent on the restorative material. Although clinical studies report that tooth fracture occurs predominately to restored molars, the unrestored molar experienced the highest stress in this investigation. Therefore, the reduction in fracture resistance of restored posterior teeth appears to result from changes in the location of maximum stress resulting from mastication and temperature changes.     

Fracture resistance of amalgam coronal-radicular restorations

The effect of pulp chamber depth and extension into the root canal space on fracture resistance was examined on endodontically treated teeth with coronal-radicular amalgam restorations. Six groups of 10 mandibular molars were mounted in acrylic resin, and crowns were ground apically until the wall height of the pulp chamber was 2, 4, or 6 mm. Three millimeters of gutta-percha was removed from the three canals of one-half the teeth and amalgam was condensed into the canal space to a height 7.5 mm above the cementoenamel junction (CEJ). The remaining teeth had amalgam condensed from the floor of the chamber to 7.5 mm above the CEJ. The amalgam restorations were loaded with an Instron instrument (Instron Corp., Canton, Mass.) until failure. Amalgam extension into the root canal space contributed minimally to the fracture resistance of the amalgam coronal-radicular restoration with four or more millimeters of chamber wall. If less than 4 mm of chamber wall height remained, however, the fracture load was substantially increased. Amalgam extension into the root canal space should be confined to teeth with limited remaining pulp chambers.     

上颌第一前磨牙MOD洞形设计对全瓷嵌体修复影响的三维有限元分析

目的 建立全瓷嵌体修复上颌第一前磨牙近中-（牙合）面-远中（MOD）洞形的三维有限元模型，通过改变洞形的设计，观察应力分布的改变。方法 建立三维有限元模型，设定两个变量分别为髓壁距龈壁的距离（H），龈壁的宽度（G）；在Ansys11.0中依照变量进行模型修改，（牙合）面加载力大小为200N，记录应力数据并分析应力分布。结果 牙体预备MOD洞能够影响牙体全瓷嵌体修复后的应力分布。在龈壁宽度不变的情况下，牙釉质的Von mises应力值随着髓壁的高度增加而减小。近中牙颈部嵌体边缘线处的牙釉质应力分布较为集中。在髓壁距龈壁的距离保持不变的条件下，随着龈壁宽度的增加，牙本质的Vonmises应力值和最大主应力σ₁都明显增大。结论 全瓷嵌体修复后增加了牙体的应力值，而牙体MOD洞形预备影响了全瓷嵌体修复的应力分布。髓壁高度的变化是牙釉质应力改变的重要参变量，应力值随髓壁高度的增加而减小；龈壁宽度的变化是牙本质应力改变的重要参变量，应力值随龈壁宽度的增加而增大。牙颈部近中嵌体边缘线处的牙釉质易发生折裂。     

Clinical evaluation of a composite resin system with a dentin bonding agent for restoration of permanent posterior teeth: a 3-year study.

This study evaluated the clinical performance of a visible light-cured small particle bimodally filled hybrid condensable composite resin system that included a dentin bonding agent compared with an amalgam alloy in class II restorations of permanent teeth. A total of 108 restorations were placed in 34 patients. Fifty-three composite resin and 55 amalgam restorations were inserted. Each restoration was evaluated immediately after placement and then on an annual basis for a 3-year period using the Public Health Service (PHS) criteria. In addition, the Moffa-Lugassy scale was used to measure the loss of material on the occlusal surface of these materials. One hundred percent of the resin and amalgam restorations were evaluated, measured, and reasons for replacement were recorded over the 3-year period. There was no significant difference (p greater than 0.05) in the clinical performance of the composite resin and the amalgam when evaluated by the PHS criteria. Analyses of wear at each of the three annual recall periods did not reveal any significant difference (p greater than 0.05) between the two restorative materials when measured by the Moffa-Lugassy scale.     

Modification of the resistance form of amalgam coronal-radicular restorations

Three groups of 10 extracted endodontically treated mandibular molars were mounted in acrylic resin. The occlusal surface was reduced until a 4 mm pulp chamber height remained. A peripheral shelf 2 mm deep and 1.4 mm wide was placed on one group, while four TMS Minim pins were placed 45 degrees to the long axis of the tooth into the facial and lingual walls of the second group. The final group served as the control and had no further treatment. All teeth were then restored with amalgam. An Instron testing machine was used to apply a controlled force to the beveled amalgam at a crosshead speed of 2 mm/min until fracture occurred. A peripheral shelf did not improve the fracture resistance of the coronal-radicular restorations tested. The specimens with semihorizontal pins were significantly stronger than specimens from the other groups. Placement of pins into the pulp chamber is recommended when adequate dentin remains.     

Occlusal stress distribution and remaining crack propagation of a cracked tooth treated with different materials and designs: 3D finite element analysis

ObjectiveHere we used 3D finite element analysis (FEA) to analyze and directly compare stress distribution and crack propagation in identical cracked tooth models after treatment with various materials and designs.MethodsA 3D model of a cracked tooth was generated. We then applied eight restoration models, comprising combinations of three kinds of restoration designs (inlay, onlay, and crown) and four types of restoration materials (direct composite resin, indirect composite resin, ceramic, and gold). A 1000-N occlusal load was applied on the three reference points of the ball-shaped part in the direction of the longitudinal axis, causing crack line separation in the buccolingual direction. Stress distribution was analyzed on the occlusal surface, bottom level of the restoration, and mesiodistal longitudinal section. The stress on the lower margin of the crack surface was measured at 15 points on each model.ResultsCeramic inlay and onlay showed stress concentration at the restoration bottom, and low stress on the lower margin of the crack surface. Direct and indirect resin restorations exhibited low stress on the restoration bottom, and high stress on the proximal end of the lower margin of the crack surface. With a resin-unfilled gold crown, stress was concentrated on the crown bottom and the lower margin of the crack surface. Direct resin filling inside the gold crown yielded significantly decreased stress on both areas.SignificanceOur results suggest that inlay and onlay ceramic restorations, and gold crown with resin filling inside, are advantageous methods for preventing further crack propagation.