Loss of Masticatory Function Affects Morphology of the Tooth Root in Rats

Masticatory hypofunction and soft food affect the tooth rows, occlusion, and jawbone. This study aimed to clarify the influence of tooth loss and a soft diet on morphology of the tooth root during the growth period. We divided 3-week-old Wistar rats into the following three groups: Hard diet group (rats raised on solid standard diet), Powder diet group (rats raised on powdered standard feed diet), and Extraction group (rats raised on powdered standard diet with maxillary molars extraction). Length, width, cross-sectional area, and volume of the root of the mandibular M1 and M2 were measured using micro-CT analysis. Non-decalcified thin-slice specimens of sagittal sections of the M1 were obtained at the age of 20 weeks, and the roots were observed. The root length of all roots in the Extraction group was significantly longer than that in the other groups. The root width and cross-sectional area at the apical side 1/4 of all roots in the Extraction group were significantly smaller than those in the other groups. The root volume of the M1 mesial root in the Extraction group was significantly smaller than that in the other groups. This study clarified that when masticatory stimulus in the immature teeth is reduced by the extraction of opposing teeth and a powder diet, the root length increases due to the promotion of cellular cementum addition at the apex, and the root width and cross-sectional area decrease due to the suppression of cellular cementum addition at the apical side 1/4 of the roots.

Effects of Prestressing of the Ring Gear in Interference Fit on Flexural Fatigue Strength of Tooth Root

When the gearbox body interference is connected to the ring gear, prestressing occurs in the ring gear, which has a significant impact on the strength and life of the gear. Research on the prestressing of the inner ring gear is in the preliminary stage, and the distribution rule of the prestressing and the influence of each parameter on the interference prestressing have not been derived. In this paper, based on the method of calculating the prestressing of the thick cylinder in interference fit, the ring gear is found to be equivalent to a thick cylinder, and the distribution rule of prestressing of the ring gear in the interference fit is inferred. Then, by modeling and analyzing the gearbox body and ring gear in the interference fit using ABAQUS, the distribution rule of prestressing the ring gear in the interference fit is obtained through a numerical simulation. Finally, the prestressing of the ring gear in the interference fit is measured using X-ray di raction, and the distribution rule of prestressing of the ring gear in the interference fit is obtained through analysis. Compared with the distribution rule of prestressing in theory, numerical simulation, and experiment, the theoretical distribution rule of prestressing is amended through a statistical method, and a more accurate formula of prestressing is obtained. Through the calculation of the stress and bending moment in the dangerous section of the ring gear through prestressing, the formula for checking the tooth root flexural fatigue strength in the interference fit prestressing is inferred. This research proposes a tooth root bending strength conditional formula for the inner ring gear of the interference fit, which serves as a guide for the design and production of the actual interference joint inner ring gear.

Molecular regulatory mechanism of tooth root development

The root is crucial for the physiological function of the tooth, and a healthy root allows an artificial crown to function as required clinically. Tooth crown development has been studied intensively during the last few decades, but root development remains not well understood. Here we review the root development processes, including cell fate determination, induction of odontoblast and cementoblast differentiation, interaction of root epithelium and mesenchyme, and other molecular mechanisms. This review summarizes our current understanding of the signaling cascades and mechanisms involved in root development. It also sets the stage for de novo tooth regeneration.

Fate of root shell after pontic/socket shield techniques,is it better to extract the whole tooth?

A series of changes occur in the remaining alveolar process after whole tooth extraction.The basic question is,why do the bony walls(especially the labial/buccal)get resorbed immediately after the tooth is removed?This could be because,with cementum of the concerned tooth and its periodontal ligament,the supporting bundle bone is dependent on the presence of the tooth.This loss can be compensated using numerous techniques,such as socket grafting using various biomaterials to preserve the alveolar bone and buccal grafting with guided tissue regeneration to increase the thickness of buccal bone or placement of implant immediately.However,none of these techniques prevent the modelling of the alveolar bone post-extraction.Few studies have demonstrated that preservation of the roots in the alveolar process maintains the bone volume and facilitates vertical bone growth.A histological study in animals and humans has shown that the retained root shell does not pose any interference in the osseointegration of the implant(if placed simultaneously).Although various names have been proposed to describe the concept of retaining full or part of the root to prevent the resorption of the ridge,socket-shield and pontic-shield are the two most commonly used terms worldwide.The extraction of the whole tooth might be the choice of therapy when socket-shield or pontic-shield is not possible due to anatomical variations,infections,or lack of clinical expertise.Irrespective of the size,when a whole root or a root fragment(is left in situ),it is the dentist’s ethical duty to advise/inform the patient and ensure repeated clinical and radiographic follow-up.The present study aimed to highlight the current status of these techniques,their benefits,and possible complications and address whether the paradigm of the teeth extraction methods should be altered.

Regular nicotine intake increased tooth movement velocity,osteoclastogenesis and orthodontically induced dental root resorptions in a rat model

Orthodontic forces have been reported to significantly increase nicotine-induced periodontal bone loss. At present, however, it is unknown, which further （side） effects can be expected during orthodontic treatment at a nicotine exposure corresponding to that of an average European smoker. 63 male Fischer344 rats were randomized in three consecutive experiments of 21 animals each （A/B/C） to 3 experimental groups （7 rats, 112/3）. （A） cone-beam-computed tomography （CBCT）; （B） histology/serology; （C） reverse- transcription quantitative real-time polymerase chain reaction （RT-qPCR）/cotinine serology--（1） control; （2） orthodontic tooth movement （OTM） of the first and second upper left molar （NiTi closed coil spring, 0.25 N）; （3） OTM with 1.89 mg-kg- 1 per day s.c. of L（- ）-nicotine. After 14 days of OTM, serum cotinine and IL-6 concentration as well as orthodontically induced inflammatory root resorption （OIIRR）, osteoclast activity （histology）, orthodontic tooth movement velocity （CBCT, within 14 and 28 days of OTM） and relative gene expression of known inflammatory and osteoclast markers were quantified in the dental-periodontal tissue （RT-qPCR）. Animals exposed to nicotine showed significantly heightened serum cotinine and IL-6 levels corresponding to those of regular European smokers. Both the extent of root resorption, osteoclast activity, orthodontic tooth movement and gene expression of inflammatory and osteoclast markers were significantly increased compared to controls with and without OTM under the influence of nicotine. We conclude that apart from increased periodontal bone loss, a progression of dental root resorption and accelerated orthodontic tooth movement are to be anticipated during orthodontic therapy, if nicotine consumption is present. Thus patients should be informed about these risks and the necessity of nicotine abstinence during treatment.

External Root Resorption During Standardised Orthodontic Tooth Movement In Young And Adult Rats

目的 :比较研究幼鼠和成年鼠正畸牙齿移动过程中的牙根吸收。方法 :本研究包括两组大鼠 ,其中幼鼠 30只 (年龄约 6周 ) ,成年鼠 30只 (年龄约 912个月 )。大鼠上颌牙一侧用于实验侧 ,另一侧用于对照。实验侧的三颗磨牙用结扎丝颌粘接剂固为一个整体 ,在超弹性拉簧作用下 (力值为 0 .1牛顿 )向切牙侧移动。 1,2 ,4 ,8和 12周时给予大鼠过量麻醉剂 ,材料用于组织学研究。上颌第一磨牙的近中颊侧根为根吸收研究对象。压力侧和张力侧的牙根吸收程度在显微镜下进行长度测量。实验侧与对照侧 ,压力侧与张力侧 ,幼鼠与成年鼠之间的牙根吸收程度分别以实验时间为参照 ,在统计学手段下进行了组间和组内分析和比较 ,以探讨牙齿移动时间和年龄因素对于牙根吸收的影响。结果 :实验侧的牙根吸收在幼鼠与成年鼠之间在 1,2 ,4 ,8周时均没有统计学差异。而在第 12周时 ,成年鼠实验侧牙根吸收大于幼鼠 (P <0 .0 5 )。成年鼠实验组压力侧的牙根吸收明显大于对照组压力侧 ,而在幼鼠组没有发现这一差异。两组年龄幼鼠的实验组其压力侧和张力侧的牙根吸收均高度相关。结论 :相对于对照侧 ,正畸牙齿移动并没有在幼鼠的实验侧诱发更多的牙根吸收。在成年鼠 ,长期的正畸作用力倾向于诱发更多的牙根吸收。这些研究结果表明对于正?

牙体缺损类型与纤维桩位置对桩核冠修复上颌前磨牙抗折性能的影响

纳入120颗离体上颌前磨牙分成5组(每组24颗),制备360°牙本质肩领(A组)、颊侧180°牙本质肩领(B组)、腭侧180°牙本质肩领(C组)、远中180°牙本质肩领(D组)、近中180°牙本质肩领(E组),分别用树脂核+全冠修复、颊侧根管纤维桩+树脂核+全冠修复、腭侧根管纤维桩+树脂核+全冠修复、颊、腭侧根管纤维桩+树脂核+全冠修复。结果显示:A组样本牙的抗折破坏载荷值高于B、C、D、E组(P<0.05),颊侧根管置入纤维桩抗折强度高于腭侧(P<0.05)。提示360°完整牙本质肩领能提供最佳的抗折强度,牙本质肩领不完整时,推荐置入颊侧根管纤维桩修复。

齿廓修形在降低齿轮箱啮合噪声中的应用

本研究旨在解决齿轮箱在啮合过程中由负载齿轮产生的啸叫问题。为解决这个问题,利用牛顿运动定律,建立一个齿轮副啮合的一维振动模型。在不改变齿轮基本参数的前提下,分别对齿轮齿顶和齿根进行修形。通过对比多种不同齿廓修形量的方案,计算齿廓修形量对齿轮强度及性能参数的影响,并根据齿廓修形量、修形长度和齿形公差绘制齿轮齿形检测的“K”形图。通过齿轮箱台架试验评估所提出的解决方案的有效性,证明齿轮啮合噪声的显著降低,从根源上改善齿轮啸叫现象。研究结果表明,齿廓修形是降低齿轮箱中齿轮啮合噪声的有效方法。

裂纹故障下细高齿齿轮齿根动应变研究

为探究裂纹故障对细高齿齿轮齿根动应变的影响规律,采用集中质量法建立齿轮系统动力学模型,将故障下的时变啮合刚度作为输入,对系统动力学方程进行求解得到不同裂纹深度下的齿轮副动态啮合力。利用有限元法建立含裂纹故障齿轮结构动力学分析模型,结合轮齿承载接触分析确定裂纹故障下的齿间载荷分配关系,采用瞬态分析得到齿根应变时域历程,并对不同裂纹深度下的齿根动应变进行分析。仿真结果表明,当从动轮发生裂纹故障后,其齿根动应变故障特征主要表现为啮合区内齿根应变数值的变化,主动轮齿根动应变故障特征主要表现为齿根应变时域历程中出现周期性冲击及幅值衰减,在1.5 mm裂纹深度下主动轮齿根应变峰值因子相对变化量达到12.72%。

特立帕肽对骨质疏松大鼠正畸牙移动中牙根吸收影响的mirco-CT研究

目的:使用mirco-CT探究特立帕肽对骨质疏松大鼠正畸牙移动过程中牙根吸收的影响。方法:将72只8周龄的雌性Wistar大鼠均分为去势组、特立帕肽组和对照组,对去势组及特立帕肽组行去卵巢手术并对对照组行假手术处理。12周后,对大鼠左上第一磨牙施加50 g牙移动力;每日给予特立帕肽组大鼠特立帕肽溶液皮下注射,去势组及对照组给予等量的PBS溶液。牙移动第0、7、14、21天处死大鼠、取材并行micro-CT扫描分析。结果:各组从7 d起可开始观察到牙根吸收陷窝,且陷窝体积随时间延长逐渐增大。去势组大鼠的牙根吸收与对照组相比较为严重,特立帕肽治疗可以显著降低骨质疏松大鼠牙移动21 d时的牙根吸收。结论:骨质疏松状态可加重大鼠牙移动过程中的牙根吸收,间歇性应用特立帕肽可以减少骨质疏松大鼠正畸牙移动中的牙根吸收。

齿根裂纹扩展对轮齿时变啮合刚度变化关系的分析

针对齿根裂纹扩展与时变啮合刚度的理论值与实际值偏差较大的问题,该文基于能量法对传统的时变啮合刚度模型进行优化,以获得理论时变啮合刚度的变化规律与实际情况接近。在传统理论时变啮合刚度理论模型的基础上,考虑轮齿的Hertz接触刚度、径向压缩刚度、轮齿的弯曲刚度和轮齿的剪切刚度,以及轮体的柔性变形量等因素,对传统的理论刚度模型进行改进。再采用能量法计算,验证改进的理论模型对健康轮齿、齿根裂纹扩展程度和裂纹扩展角度这3种不同状态下,获得轮齿时变啮合刚度的变化规律。研究结果表明,经改进后的理论刚度模型,计算得出时变啮合刚度变化规律的一致性较好。并且,得出时变啮合刚度值的大小,随着齿根裂纹故障严重程度的增大而减小,随着齿根裂纹扩展角度增大而增大。

Root ZX根尖定位仪准确性的体外实验研究

目的:分析影响Root ZX根尖定位仪测量牙齿操作长度准确性的因素。方法:选择根尖孔发育完成的单根管离体牙40个,在生理盐水琼脂模型上,分别在根管内灌注25g/L次氯酸钠液、生理盐水、170g/LEDTA、30mL/L过氧化氢液和蒸馏水,在根管干燥条件下,用Root ZX测量牙齿操作长度,分析根管内容物对Root ZX测量值的影响。另外,选择根尖缩窄大小各异的牙齿23个,用Root ZX测量根管长度,计算探测锉尖离根尖孔的距离,分析该距离与根尖缩窄大小的相关关系。结果:以距根尖孔0～1mm为标准,RootZX的准确率为97.5%。同一根管内不同内容物时,Root ZX测量值间的差异无统计学意义(P>0.05),探测锉尖离根尖孔的距离与根尖缩窄的大小呈正相关(r=0.8584)。结论:RootZX测量牙齿操作长度的准确性不受根管内容物的影响;根尖缩窄大小是影响Root ZX准确性的决定因素,电测长与根尖缩窄大小呈负相关。

重载齿轮箱提高抗冲击载荷方法

主要探讨如何在有限的空间内提高重载齿轮箱的传动性能,延长齿轮箱的服役寿命。在不改变啮合齿轮副的传动特性情况下,经过齿根喷丸强化增加齿根许用弯曲应力值,通过改变齿轮副顶隙系数的情况下,降低齿轮弯曲应力值这两种方法提高齿轮抗冲击强度23%左右,极大提高重载齿轮箱齿轮副抗冲击载荷能力。

3D打印个性化正畸装置对单根牙垂直移动的三维有限元分析

背景:基于牙齿垂直移动原理,通过数字化设计结合3D打印制作个性化正畸装置,可使个性化正畸装置与单个切牙形成支抗系统。借助微种植体绝对支抗作用可对单根牙在三维方向上进行精准控制。目的:基于生物力学原理设计了牙位11、12、21、22压低移动与伸长移动的个性化正畸装置,通过三维有限元法分析个性化正畸装置的安全性与其对牙齿的移动作用。方法:应用Mimics、Geomagic Wrap、SolidWorks和Ansys Workbench软件分别建立了上颌前牙区(牙位11、12、21、22)牙槽骨-牙周膜-上颌切牙-个性化悬臂微种植体-连接板-个性化托槽的三维有限元模型,每个牙位分别设置个性化压低移动与伸长移动正畸装置,加载300 g拉力或推力,分析个性化正畸装置各部件应力水平,计算牙齿位移与牙周膜应力分布情况。结果与结论:①个性化压低移动正畸装置受到的最大等效应力为162.90 MPa,个性化伸长移动正畸装置受到的最大等效应力239.57 MPa,二者的最大等效应力均位于个性化托槽加力附件的垂直部分,个性化正畸装置各部件所受等效应力均在屈服强度内,均具有良好的安全性;②在个性化正畸装置作用下,牙齿初始位移呈现整体压低或伸长移动的趋势,垂直方向上的位移远远超过在水平方向和矢状方向上的位移;牙周膜根尖或颈部位置出现等效应力峰值,在根尖区牙周膜出现等效应力集中区域;③结果显示,个性化正畸装置可以使牙位11、12、21、22近似达到压低移动或伸长移动的目的,初步证实了个性化垂直移动正畸装置的有效性。

MTA根尖屏障术治疗根尖敞开恒牙的疗效评价

目的研究无机三氧化物聚合物(MTA)根尖屏障术用于根尖敞开恒牙中的价值。方法选择我院2021年1月-2023年2月纳入的根尖敞开恒牙患者80例,按随机列表法进行分组,各组40例,研究组采取MTA根尖屏障术,对照组选择热牙胶充填技术,比较各组总有效率、咬合力、美学评分(PSE)评分、牙痛情况和满意度。结果研究组总有效率90.00%高出对照组72.50%(P<0.05)。2组治疗前各指标均无区别(P>0.05),治疗后研究组咬合力和PSE评分均高出对照组(P<0.05)。研究组牙痛发生率7.50%低于对照组的25.00%(P<0.05)。研究组满意度95.00%较对照组80.00%更高(P<0.05)。结论MTA根尖屏障术的效果更为理想,促进咬合力改善,并提高软组织的美观度,牙痛发生率少,患者满意度高,值得推广。

锥形束CT观察下颌第二恒磨牙牙根及根管形态的研究

目的:探讨锥形束CT(CBCT)观察下颌第二恒磨牙牙根及根管形态的临床应用.方法:选取2018年8月至2021年8月珠江路康美口腔门诊部收治的263例患者为研究对象.对其均采取口腔颌面CBCT进行下颌第二恒磨牙进行扫描,并进行三维重建及测量,记录牙根、根管数目及牙根、根管形态,并进行分类描述.结果:对263例患者526颗下颌第二恒磨牙的口腔颌面CBCT检查结果显示,双根、C形融合根、锥形融合根、三根、单根的发生率分别为53.99%(284/526)、38.97%(205/526)、4.56%(24/526)、1.52%(8/526)、0.95%(5/26).双根及C形融合根是本组患者的主要的牙根形式.双根型的284个下颌第二恒磨牙中,Ⅳ型双根的发生率为78.52%(223/284),远高于其他类型根管;远中根Ⅰ型单根管发生率为92.25%(262/284),明显高于其他根管构型;差异均有统计学意义(P<0.05).本组263例患者526颗下颌第二恒磨牙中,近中根双根管口发生率及双根尖孔发生率分别为88.73%(252/284)和79.23%(225/284),均显著高于远中根双根管口发生率及双根尖孔发生率的7.04%(20/284)和4.58%(13/284),差异均有统计学意义(P<0.05).本组患者205颗C形融合根下颌第二恒磨牙中,C3型根管发生率明显高于其他根管构型,C2型根管发生率最低,差异有统计学意义(P<0.05).结论:采用CBCT扫描观察患者下颌第二恒磨牙牙根及根管形态具有明显优势,下颌第二恒磨牙牙根及根管形态复杂多样,其中以双牙根及C形融合根居多,双牙根中近、远中根的牙根形态分布明显不同,C形融合根根管的发生以C3型居多.

不同类型的辅弓在正畸前牙压低中的应用与研究进展

前牙深覆[牙合]是临床中常见的疑难错[牙合]畸形,常伴随有不同程度的关节、牙周及美观等问题。压低辅弓是目前临床中治疗前牙深覆[牙合]的主要方式之一。压低辅弓种类繁多,不同辅弓在适应证、疗效、不良反应、弓丝弯制及生物力学等方面存在差异。在临床实践中,正畸医生应根据目标位及患者牙槽骨情况选择合适的辅弓类型,并适时调整压低力的大小和方向,以达到最佳的效果。本文就不同类型的压低辅弓的应用和研究进展作一综述,以期为临床研究的开展及临床实践提供一定的参考。

基于数值仿真的电动汽车高速齿轮轮辐结构优化设计

随着电动汽车对电驱动系统噪声、振动与声振粗糙度(Noise·Vibration·Harshness,NVH)性能的要求越来越高,对电驱动传动系统齿轮设计提出了更高的要求。基于数值仿真的方法对电驱动传动系统平行轴式减速器大齿轮轮辐结构进行了优化设计。从齿轮模态、齿根应力、传动误差和制造误差敏感性4个方面分析对比了简单板式、圆减重孔板式、长减重孔板式、加强筋板式和交错板式5种大齿轮轮辐结构设计。结果表明,交错板式轮辐结构在齿轮模态、齿根应力、传动误差和制造误差敏感性4个方面都具有优势,尤其在齿轮模态频率方面,相比其他4种方案有显著提升。采用所提方法优化设计的交错板式轮辐结构,在同等质量条件下相比常见的圆减重孔板式结构,齿轮1阶模态频率提高72%,传动误差降低18%,可有效避免大齿轮共振引起的高速齿轮啸叫问题。

热牙胶充填法与冷侧方加压法在牙隐裂伴牙髓病变根管治疗中的应用效果对比

目的:对比热牙胶充填法与冷侧方加压法在牙隐裂伴牙髓病变根管治疗中的应用效果。方法:选取2019年1月—2023年12月靖江市人民医院收治的牙隐裂伴牙髓病变患者80例为研究对象,采用随机数字表法分为对照组和研究组,各40例。两组均实施根管治疗,对照组采用冷侧方加压法进行根管充填,研究组采用热牙胶充填法进行根管充填。比较两组治疗总有效率、治疗满意度、咀嚼功能、牙周状况、生活质量。结果:研究组治疗总有效率高于对照组,差异有统计学意义(P=0.034);研究组治疗满意度高于对照组,差异有统计学意义(P=0.034);治疗后,两组咀嚼效率和咀嚼测试吸光度值高于治疗前,研究组高于对照组,差异有统计学意义(P<0.05);治疗后,两组菌斑指数、软垢指数、牙龈出血指数、牙周探诊深度低于治疗前,研究组低于对照组,差异有统计学意义(P<0.05);治疗后,两组世界卫生组织生活质量测定简表评分高于治疗前,研究组高于对照组,差异有统计学意义(P<0.05)。结论:在牙隐裂伴牙髓病变患者根管治疗中,应用热牙胶充填法进行根管充填的效果优于冷侧方加压法,有助于改善患者的咀嚼功能和牙周状况,提高生活质量及满意度。

体外评价新型根尖倒充填材料iRoot的生物学性能

目的:体外评价新型根尖倒充填材料iRoot BP plus和iRoot FS的生物学性能。方法:(1)将牙根预备成长3 mm、根管直径1 mm的试样,分别于根管内填充iRoot BP plus、iRoot FS和三氧化矿物凝聚体(mineral trioxide aggregate,MTA)。将制备好的试样置于模拟体液(simulated body fluid,SBF)中,用扫描电子显微镜观察暴露的材料表面矿物沉积情况,并通过X射线能谱对其表面形成的晶体进行元素分析,测定SBF的p H值随时间的变化。(2)将iRoot BP plus、iRoot FS和MTA制备成直径8 mm、高度2 mm的圆柱,制备DMEM浸提液,通过MTT实验观察材料对MG63细胞增殖活性的影响,并通过实时荧光定量PCR和碱性磷酸酶(alkaline phosphatase,ALP)染色分析材料对ALP基因及蛋白表达的影响。结果:(1)在SBF中浸泡24 h时,iRoot BP plus、iRoot FS和MTA表面均已有矿物沉积,14 d后有大量矿物沉积,钙∶磷比值分别为1.43、1.39和1.51;(2)iRoot BP plus、iRoot FS和MTA均可使SBF的p H升高,3周时分别为8.09±0.07、7.91±0.06和8.11±0.06;(3)以体积比为1∶5和1∶10稀释的iRoot BP plus、iRoot FS和MTA浸提液对MG63细胞的增殖无明显促进或抑制作用;(4)iRoot BP plus、iRoot FS和MTA组对MG63细胞ALP基因的表达均具有促进作用,ALP染色各组未见明显差异。结论:iRoot在模拟体液中可诱导矿物质沉积,促进MG63细胞的分化和矿化,具有良好的生物活性和促成骨作用。