不同包绕度对桩冠箍效应影响的三维有限元分析

目的：研究桩冠修复中箍的不同包绕度与箍效应之间的相互关系及影响。方法：建立上颌中切牙烤瓷核桩冠三维有限元模型，模拟箍效应的4种包绕形式，通过三维有限元方法分析才本质受力情况。结果：①根管口周围余留牙本质壁完整，牙本质应力分布最好。②仅余留唇侧牙体时，须部牙本质应力水平明显升高。结论：随着箍包绕才体壁的减少，箍效应有所降低，但保留唇舌侧牙体和仅保留石侧牙体部可获得一定的箍效应。     

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。     

牙本质领对桩冠修复牙牙体应力的影响--三维有限元研究

目的：研究牙本质领对牙体应力的影响，揭示箍效应的力学本质。方法：建立上中切牙桩核修复的三维有限元模型，分析100N静载荷下，牙本质领高度由0～2mm按0．5mm递增，共5种情况下，牙体内Von Mises应力的变化和分布规律。结果：①在100N载荷下，牙体内Von Mises应力由桩末端向牙颈部方向逐渐升高，并在颊侧根颈1／3和颈缘形成两个应力高峰区。②增加牙本质领高度可以降低牙体内Von Mises应力峰值。结论：牙本质领对牙体具有一定的保护作用，临床上应尽量保留冠部牙体组织。     

纤维桩直径和深度对牙根应力分布影响的三维有限元分析

本研究通过三维有限元分析法，建立上颌中切牙经石英纤维桩修复的桩冠三维有限元模型，分析不同直径和深度的石英纤维桩对桩冠修复体牙根组织应力分布的影响。     

上颌前牙带角度桩冠的三维有限元应力分析

目的 :研究上前牙带角度桩冠修复的应力分布。方法 :通过对上前牙桩冠修复患者进行CT扫描 ,建立上前牙带角度桩冠的三维有限元模型 ,在ANSYS软件中设定各种材料参数 ,施加载荷 ,进行数据运算处理。结果 :最大应力峰值出现在唇侧颈部皮质骨区域 ,唇侧为压应力 ,腭侧为拉应力。结论 :带角度桩冠修复上前牙 ,应力主要集中在颈部皮质骨区域内 ,唇侧大于腭侧 ,并且应力随桩冠角度的增大而增大     

前牙桩冠(牙合)接触形式对剩余牙本质应力分布影响的有限元分析

目的 :研究不同牙合接触形式对前牙桩冠牙本质应力分布的影响。方法 :运用三维有限元法构建解剖标准前牙桩冠修复体模型 ,并模拟不同牙合接触形式进行加载以分析剩余牙本质应力。结果 :牙合接触形式变化时前牙桩冠牙本质相应呈现不同应力分布状态。结论 :前牙桩冠设计制作应该充分考虑牙合接触形式 ,优化牙体制备和桩的设计使修复体应力分布更为合理。     

上中切牙牙周支持组织高度降低的三维有限元分析

目的:研究牙周支持高度降低状态下施加舌向集中力时,牙周组织的应力变化、分布规律和牙的初始位移。方法:采用螺旋CT扫描、数字影像传输与转录方法,获得中切牙三维形态的原始数据。通过减少牙周支持组织的高度,产生代表6种不同牙周支持高度的三维有限元模型。结果:随着牙槽骨高度的降低,上中切牙牙周膜最大等效应力和主应力逐渐增大。最大拉应力位于舌侧根尖部,最大压应力位于舌侧牙槽嵴顶。牙周膜的应力随牙槽骨高度的降低呈非等比增加。结论:随着牙周支持组织高度的逐渐降低,牙的旋转中心向根尖移动,牙周支持组织对牙的支持能力明显减弱。在正畸治疗中,所应用的力必须成比例减小,以维持正常生理的可耐受的运动而不造成支持组织的进一步损伤。     

不同粘接剂对后牙分裂桩冠修复应力分布影响的有限元分析

目的 建立下颌第一磨牙残根分裂桩冠修复的三维有限元模型,分析不同粘接剂粘接时残根应力分布特点,从而得到在不同情况下与分裂桩冠修复相匹配的最佳粘接剂。方法 选取健康的下颌第一磨牙离体牙,沿釉牙骨质界将冠部去除,对处理后的残根进行CT扫描。将CT影像导入逆向工程软件,重建下颌后牙残根的三维有限元模型;制作与残根相匹配的纯钛分裂桩冠修复体,同样进行CT扫描,在MIMICS中重建出修复体的模型,并进行装配,对比分析不同粘接系统在垂直载荷及侧向载荷下对根管内部及残根断面应力的分布特点。结果 建立了下颌第一磨牙残根的三维有限元模型及分裂桩冠有限元模型,并进行匹配安装。随着粘接剂弹性模量的增加,根管内的最大应力也在增加,磷酸锌的弹性模量最大,根管内承受的应力最大;Superbond C&B的弹性模量最小,根管内承受的应力最小,且侧向载荷的应力要远大于垂直载荷。在垂直载荷下,对于不同粘接剂,施加在残根断面的载荷比较平均。在侧向载荷下最大应力要远大于垂直工况。使用磷酸锌粘接剂时残根断面的应力最小,使用SuperbondC&B时残根断面应力最大。结论 在分裂桩冠修复后牙残根时,不同的粘接剂对牙体组织的应力保护作用有很大区别。当根管口处牙体组织较为薄弱时,为避免其发生劈裂,建议采用弹性模量较大的粘接剂,如磷酸锌;当根管口处牙体组织抗力形较好而牙根较细或根管壁薄弱时,建议采用弹性模量较小的粘接剂,如Superbond C&B。     

不同牙槽骨高度下桩核修复后牙本质应力分析

目的应用有限元方法观察不同牙槽骨高度下桩核修复后牙本质内的应力分布情况。方法建立上颌中切牙桩核修复的三维有限元模型,并按照牙槽骨高度降低1/4、1/3和1/2建立修改模型,对模型斜向加载,计算牙体各部位最大应力。结果随着牙槽骨高度的降低,牙本质内部最大应力明显增高,牙体与桩交界部位的最大应力变化呈相同趋势,且愈靠近牙根表面应力值愈高,在4个模型中最大应力都位于牙根上1/3,在牙齿唇侧颈部有明显的应力集中。结论牙槽骨高度的变化显著影响桩核修复后牙齿内的应力变化,两者间呈反比例关系。     

纤维桩外形和深度对牙根应力分布影响的三维有限元分析

目的 :应用三维有限元法研究石英纤维桩的不同外形和深度对上颌中切牙桩冠修复后牙根应力分布的影响。方法 :建立上颌中切牙桩冠修复三维有限元模型 ,模拟牙槽骨、牙周膜、牙本质、石英纤维桩、牙胶尖、复合树脂核、金属底层冠、烤瓷层等结构 ,应用PATRAN三维有限元分析软件分析石英纤维桩的外形、深度对牙根牙本质应力分布的影响 ,静态加载 10 0N ,与牙长轴成 5 0°角。结果 :石英纤维桩对牙根部应力分布的总体趋势影响不大 ;ENDODONTIC石英纤维桩在根颈 1/ 3应力高于PROSTHETIC石英纤维桩 ,而根尖 1/ 3处两种桩的应力分布无明显区别 ;ENDODONTIC石英纤维桩的深度对应力分布有一定影响 ,而PROSTHETIC石英纤维桩的深度对应力分布基本无影响。结论 :石英纤维桩不能防止根颈部折裂 ,但可降低根中、根尖部的折裂 ;石英纤维桩的外形、深度对应力分布有一定的影响 ,临床医师应根据具体情况选择     

Bone structure effect on root resorption

Authors – Otis LL, Hong JSH, Tuncay OC Objectives – To explore if alveolar bone shape and density might promote external apical root resorption. Setting and Sample Population – Panoramic radiographs of 700 patients who had orthodontic treatment at Temple University were reviewed and 22 patients with radiographic evidence of root resorption on the lower incisors were selected for the study. Exclusion criteria included a history of systemic diseases, craniofacial abnormalities, tooth injury, endodontically treated teeth, and impacted teeth. Methods – Pre‐treatment (T1) and post‐treatment (T2) cephalometric radiographs were converted into digital format and enhanced to reduce contrast variability and improve edge definition. Tooth length, root length, root area, alveolar area around the root including cortical area, area of medullary bone, and area of the symphysis were measured using an interactive software algorithm. A region of interest within the symphysis was also defined and trabecular space area and fractal dimension calculated as an estimate of bone density. Results – Root area and tooth length were correlated negatively with changes in root area, tooth area, and root length. Larger teeth demonstrated a greater amount of root resorption. Dentoalveolar complex dimensions remained relatively unchanged during tooth movement. The amount of alveolar bone around the root, thickness of cortical bone, density of the trabecular network, and fractal dimension showed no significant correlation with the extent of the external apical root resorption. Conclusions – The results of this study suggest that the density and morphology of the dentoalveolar complex are not significant factors in the etiology of external apical root resorption.     

羟基磷灰石生物陶瓷填充骨缺损对根尖切除术疗效影响的回顾分析

目的 回顾性分析实施根尖切除术的患牙是否应用羟基磷灰石生物陶瓷填充骨缺损区对临床疗效的影响。方法 对2018—2020年在我科进行根尖切除术的病例进行回顾性分析,按照接受根尖切除术患者的年龄、性别、患牙牙位、根尖周病变范围、临床病因类型分组,通过术前和术后6个月回访的临床症状转归以及影像学检查,对比术中采用羟基磷灰石生物陶瓷充填骨缺损+口腔修复膜覆盖和骨缺损区单纯覆盖口腔修复膜两种方法的临床成功率。结果 经纳入和排除标准,共筛选有效回访病例57例（男23例,女34例）,共计88颗患牙,治疗成功率为97.7%;根据统计分析结果,患者性别、年龄、牙位、根尖周阴影大小以及临床病因类型对根尖切除术疗效无统计学影响（P>0.05）,但是否使用羟基磷灰石生物陶瓷充填骨缺损区对疗效有显著性影响（P＜0.01）,且使用羟基磷灰石生物陶瓷与其他因素间不存在交互作用（P>0.05）。结论 对于根尖病变范围小于7 mm的病例,骨缺损区单纯覆盖口腔修复膜即能够达到较满意的治疗效果;对于病变大于7 mm的患牙,应使用生物陶瓷充填骨缺损区。     

应用Coben分析法评价前方牵引治疗上颌发育不足的临床疗效

目的 应用Coben分析法评价前方牵引治疗上颌发育不足的临床疗效,阐明Coben分析法在骨性安氏Ⅲ类错牙合畸形致病机制的诊断及矫治计划制定中的优势。方法 对120例处在生长发育期的由上颌发育不足所致的骨性安氏Ⅲ类错患者行上颌前方牵引治疗,分别对上颌前方牵引矫治前、后的头颅定位侧位片采用Coben分析法和北医大分析法进行头影测量分析。结果 上颌前方牵引后,Coben分析法测量结果中,面中1/3深度增加且Ptm-A段的变化有统计学差异,面下1/3深度减小,颜面高度增加（P<0.001）;北医大分析法测量结果中,SNA、ANB、U1/NA、U1/SN、MP/SN、Y轴角显著增加（P<0.001）,SNB、U1/L1显著减小（P<0.001）,L1/MP减小（P<0.05）。结论 上颌前方牵引疗法对以Coben分析法中Ptm-A段过小为主要机制的生长发育期骨性安氏Ⅲ类错畸形有显著疗效;Coben分析法是一种比较直观、容易理解的头影测量分析方法,在错畸形尤其是骨性安氏Ⅲ类错的诊断中具有临床意义。     

Short-term anti-plaque effect of two chlorhexidine varnishes

BACKGROUND: Chlorhexidine (CHX) varnishes have been mainly used for the prevention of caries in high-risk populations. Reports regarding their anti-plaque effect on a clinical level are limited to non-existing as opposed to their microbiological impact on plaque formation. AIM: The aim of this preliminary investigation was to evaluate the anti-plaque effect of two CHX varnishes applied on sound enamel in relation to a positive control, a negative control and to one another. METHODS: Sixteen healthy subjects volunteered for this randomized-controlled, single-blind, four-treatment-four-period crossover-designed clinical trial. A 3-day plaque re-growth model was used to determine de novo plaque accumulation following CHX rinsing, Cervitec application, EC40 application and no therapy. The amount of plaque was measured using the Quigley and Hein plaque index and "automatic image analysis" (AIA). RESULTS AND CONCLUSIONS: Varnish treatment resulted in significantly higher plaque levels than CHX rinsing irrespective of the varnish that was used (p< or =0.002), implying that the latter is likely to remain the gold standard as an anti-plaque agent. However, highly significant differences were also found in favour of both varnish systems when compared with no therapy (p<0.001), which indicates that varnish treatment is an effective means of inhibiting plaque formation in a short time span. Cervitec exhibited slightly, yet significantly, higher plaque levels in comparison with EC40 as determined by AIA (p=0.006). Large-scale trials with a longer observation period are necessary to substantiate these results.     

封闭介质对种植义齿应力分布的影响

目的:分析封闭介质的弹性模量以及粘结厚度对种植义齿应力分布的影响.方法:建立4个不同的模型,分别采用磷酸锌水门汀和玻璃离子水门汀作为封闭介质,且封闭介质的厚度分别为 25 μm 和 100 μm,利用三维有限元方法对每个模型中种植体表面的应力分布进行分析.结果:封闭介质的厚度对种植体表面的应力分布影响很小,封闭介质的弹性模量对种植体表面的应力分布影响更小.结论:封闭介质不能充当种植义齿的应力减振器.     

An experimental study of the esthetic effect of facial profiles

In this study good-looking male and female as well as ugly facial profiles were shaped by 104 lay persons using an especially constructed device according to specific instructions. These profiles were photographed and subsequently evaluated using a series of parameters from soft tissue profile analyses. Although some significant mean value differences were found between the good-looking and ugly profile variants, they were not substantial. In contrast, markedly significant differences were revealed between the variances of all variables. In some instances the variance of the ugly profiles was more than 3 to 4 times higher than that of the good-looking profiles. These findings were convicingly confirmed when statistical distribution of the data was established and compared. This implies that perception of beauty is associated with regularity of facial features and is conveyed by measurement values which are located close to the mean. Ugliness is associated with extreme deviations from the latter in either direction. Apart from the facial proportions, the degree of convexity or concavity of facial profile and their sequence seem to be important for the esthetic effects. Male profiles in contrast to female profiles exhibited more conspicuous facial features such as pronounced convexity and concavity.     

种植义齿缓冲单元材料特性对缓冲效果的影响

目的：探究动态载荷作用下种植义齿缓冲单元不同的材料特性对应力吸收效果的影响。方法：在传统种植体与基台之间设计硅橡胶缓冲单元,利用abaqus有限元分析软件建立三维有限元模型,分别赋予缓冲单元材料不同弹性模量值,分析比较动态载荷作用下种植体-骨界面的应力分布。结果：缓冲材料弹性模量不同,种植体-骨界面的应力分布不同,弹性模量值在10~23MPa范围内时缓冲效果较好。结论：带有缓冲单元的新型种植体系统可减小皮质骨内的应力峰值,并且材料的弹性模量对缓冲效果有影响,在一定范围内,材料的弹性模量越小,缓冲效果越好。     

微型种植体长度对骨界面应力分布的影响

目的 探讨微型种植体长度对骨组织内应力分布的影响.方法建立直径1.6mm,长度分别为6、8、10、12 mm的种植体-下颌骨三维有限元模型,垂直植入种植体,给以1.96 N的水平向前及前上方向的载荷,记录并分析不同情况下的应力分布.结果 种植体水平向前载荷的应力峰值范围为3.500～3.765 MPa,位移峰值范围为1...     

Long-term effect of xylitol chewing gum on dental caries

About 85% (n = 269) of the subjects who participated in the Ylivieska follow-up studies on the effect of xylitol chewing gum on dental caries during 1982-84 or 1982-85 were re-examined in 1987 for the analysis of possible long-term preventive effects. Further caries reduction was found 2 or 3 yr after the discontinuation of the use of xylitol. The effect was especially marked in girls; the reduction in caries increment in the post-use years was 60% for the 2-yr users, suggesting that more pronounced caries reduction was associated with the most regular use of xylitol. In teeth erupting during the first year of the use of xylitol gum the long-term preventive effect was greater than in other teeth. Several explanations are suggested: lasting effect of the microbiological changes in the mouth, bacterial colonization on newly erupted teeth by organisms other than S. mutans, and/or thorough maturation of the teeth under favorable physico-chemical circumstances. The results suggest that the value of xylitol in caries prevention depends on the timing of the treatment in relation to the development of the dentition.