卡环固位力的循环测试与分析

目的　观察卡环在反复脱位循环过程中固位力的变化趋势 ,探讨卡环设计时适宜倒凹的选择依据 ,为义齿卡环设计获得最佳临床效果提供依据。方法　使用Chatillon测力仪 ,测试临床常用钴铬合金铸造三臂卡。在前磨牙与磨牙的 0 2 5mm、0 5 0mm、0 75mm 3个倒凹深度上 ,卡环在脱位循环中固位力的变化。结果　所得数据经SPSS10 0统计软件做相关及回归分析 ,表明卡环固位力随脱戴次数增加而减小 ,二者存在线性关系 ,且不同基牙、不同倒凹的固位力衰减率之间差异有极显著性 (P <0 0 1)。前磨牙 0 5 0mm倒凹组卡环经 4 0 0次脱位后 ,其固位力反而开始小于 0 2 5mm倒凹组卡环的固位力 ;0 75mm倒凹组卡环固位力衰减最明显 ,达 0 76 70kg。磨牙组卡环固位力衰减趋势比较相似 ,最终固位力仍以 0 75mm倒凹组者最大 ,0 2 5mm倒凹组卡环固位力最小。结论钴铬合金铸造前磨牙卡环进入倒凹深度以 0 2 5mm为宜 ;磨牙卡环弹性较大 ,因此卡环进入倒凹的深度可较前磨牙更深。     

树脂卡环固位力和形变的体外研究

目的研究树脂卡环固位力和形变的大小。方法整体铸造前磨牙和磨牙试件各40个,倒凹计测定出0.25 mm和0.50 mm的倒凹。根据基牙类型和倒凹深度,将试件分为4组：0.25 mm倒凹前磨牙组、0.50 mm倒凹前磨牙组、0.25 mm倒凹磨牙组、0.50 mm倒凹磨牙组,每组20个试件。每组试件分别制作树脂三臂卡和Co-Cr合金三臂卡各10个。将卡环戴入相应的基牙并浸泡于去离子水中,测定在0、720、1 440、2 160、2 880、3 600、4 320次连续取出和戴入循环周期时卡环的固位力,并记录0和4 320次循环周期时卡环固位臂卡环尖和抗力臂卡环尖之间的距离。结果1）树脂卡环的平均固位力为1.69 N,低于Co-Cr卡环的平均固位力5.87 N（P<0.01）。在其他因素相同的情况下,树脂卡环的固位力小于Co-Cr卡环的固位力（P<0.01）,磨牙卡环的固位力小于前磨牙卡环的固位力（P<0.01）,0.25 mm倒凹卡环的固位力小于0.50 mm倒凹卡环的固位力（P<0.01）。随着循环次数的增加,Co-Cr卡环的固位力显著降低（P<0.01）,而树脂卡环的固位力无显著变化（P＞0.05）。2）4 320次循环周期后,Co-Cr卡环的固位臂卡环尖和抗力臂卡环尖之间的距离显著增加（P<0.05）,而树脂卡环的固位臂卡环尖和抗力臂卡环尖之间的距离无显著变化（P＞0.05）。结论树脂卡环的固位力和形变均明显低于铸造卡环。     

3种钴铬钼合金美观卡环用于前磨牙的固位力分析

目的:研究3种不同设计的钴铬钼合金卡环在前磨牙的固位力变化,为临床选择适合美观要求的卡环提供依据.方法:采用EZ20万能测力仪,测定钴铬钼合金的传统三臂卡、改良RPI卡环和变异Y形卡环在上颌第二前磨牙的0.25、0.50、0.75 mm 3个倒凹深度上的固位力.采用SPSS22.0软件包对数据进行统计学分析.结果:在0.25和0.50 mm倒凹深度时,卡环固位力大小排序为传统三臂卡＞变异Y形卡环＞改良RPI卡.在0.75 mm倒凹深度,循环开始时卡环固位力大小排序与前2组相似,但在衰减后改变为变异Y形卡环＞传统三臂卡＞改良RPI卡.结论:对位于美学区域的前磨牙区,进入0.75 mm倒凹深度的变异Y形卡环即可提供足够的固位力,又位于美观固位区并靠近龈缘,临床设计义齿时可优先考虑.     

选择性激光熔融与铸造钛合金卡环的模拟摘戴固位力研究

目的通过模拟患者卡环摘戴实验,研究3D打印和铸造2种不同加工工艺对钛合金卡环固位力变化的影响,为卡环的临床设计及制作提供参考。方法用计算机辅助设计(CAD)方法进行基牙、牙冠和卡环的设计。卡环设计为0.25和0.75 mm ^2种倒凹深度,其他参数相同;加工方式分3组,实验组分别用EOSINT和Concept Laser对设计好的数据进行3D打印成型,对照组为铸造工艺卡环组,合计36组。用万能力学测试仪进行模拟卡环摘戴的循环实验,总循环次数为15000次,记录初始固位力,并每1500次记录1次固位力。结果相同的加工工艺,0.75 mm倒凹深度的卡环固位力大于0.25 mm倒凹深度的卡环固位力;其他参数相同时,选择性激光熔化成型(SLM)的钛合金卡环固位力大于失蜡铸造的钛合金卡环固位力;尚不能认为EOSINT和Concept Laser这2种打印系统加工的卡环固位力存在差异。结论SLM技术成型的钛合金卡环固位力比失蜡铸造钛合金卡环固位力更高。失蜡铸造的钛合金卡环倒凹深度应该设计为0.75 mm,而使用数字化设计配合3D打印制造的钛合金卡环倒凹深度为0.25 mm就可以达到临床需求;EOSINT和Concept Laser这2种SLM系统成型的钛合金卡环固位力基本相同。     

钴铬合金铸造三臂卡环固位臂宽度设计与基牙倒凹关系的三维有限元分析

目的用三维有限元方法分析钻铬合金铸造三臂卡环固位臂在摘取时的应力分布，探讨3种宽度固位臂可放置的最大倒凹深度，为可摘局部义齿的设计和制作提供参考。方法以下颌第二磨牙为基牙，建立基牙和3种宽度固位臂的三维有限元模型，设定固位臂宽厚比为3：1，设计卡臂尖和固位臂中部进入基牙的倒凹深度不同，在固位臂中部施加动态位移载荷（以3mm／s速度，使卡环向上产生3mm的位移），计算固位臂从基牙上摘取时的接触受力。采用的统计学方法为直线相关与回归分析和两条回归直线的比较。结果固位臂的最大应力与卡臂尖进入基牙的倒凹深度呈正相关关系，与固位臂中部1／3进入基牙的倒凹深度无明显相关性。当卡臂尖进入基牙的倒凹深度相同时，随固位臂宽度的增大，固位臂最大应力的增加有统计学意义（P〈0．01）。1．8、1．6和1．4mm^3种宽度的钻铬合金固位臂可放人基牙的最大倒凹深度分别为0．25mm、0．30mm和0．35mm。结论当宽厚比一定时，固位臂越宽，卡臂尖可进入基牙的最大倒凹深度越小。为防止固位臂永久变形，应根据卡臂尖进入基牙的倒凹深度选择不同宽度的固位臂。     

影响卡环固位力的因素

卡环是目前可摘层部义齿设计中应用较为广泛的固位体。富有弹性的卡环臂伸入基牙倒凹区从而获得固位效果,而影响卡环固位力大小的因素主要有：1．摩擦系数;2．倒凹深度。3．制作卡环材料的特性;4．卡环臂的锥度、断而与长度;5．卡环进入倒凹的方向。在获得理想固位力的同时,能够尽量保护基牙的牙周组织健康,是合理设计卡环的基本原则。     

摘取方式对铸造三臂卡环固位臂应力影响的三维有限元研究

目的 用三维有限元方法分析钴铬合金和金合金铸造三臂卡环固位臂在不同摘取方式时的应力分布,探讨可摘局部义齿的适宜摘取方式,为临床指导患者摘取义齿提供参考.方法 以下颌第二前磨牙为基牙,建立基牙和三种宽度固位臂的三维有限元模型,设计卡臂尖和固位臂中部进入基牙的倒凹深度不同,分别在固位臂的中部和起始部施加速度为3mm/s的动态位移载荷,使卡环向上产生3mm的位移,计算不同方式摘取时固位臂的接触受力.结果 用推拉基托方式摘取义齿时,三种宽度的钴铬合金和金合金铸造卡环固位臂的最大应力与卡臂尖进入基牙的倒凹深度均呈正相关关系;同种材料的卡环固位臂,当卡臂尖进入基牙的倒凹深度相同时,随着固位臂宽度的增大,最大应力增加,差异有统计学意义;相同宽度、不同材料卡环固位臂,随卡臂尖进入基牙倒凹深度的增大,最大应力增加,差异有统计学意义.用推拉卡环方式摘取义齿时,相关的结果与用推拉基托方式摘取义齿时类似.对于同种材料、同一宽度的固位臂,随着卡臂尖进入基牙倒凹深度的增大,推拉卡环摘取义齿时固位臂的最大应力比推拉基托时增加得快,最大应力拟合直线的斜率大,且两条拟合直线有交点.结论 钴铬合金铸造三臂卡环的可摘局部义齿,适宜用推拉卡环方式摘取.金合金铸造三臂卡环的可摘局部义齿,当卡臂尖进入基牙的倒凹深度较浅时,适宜用推拉卡环的方式摘取;当卡臂尖进入基牙的倒凹深度较深时,适宜用推拉基托的方式摘取.     

钴铬合金与金合金铸造三臂卡环的三维有限元对比分析

目的 对比分析两种材料铸造卡环在义齿摘取时的应力，为临床设计提供参考。方法建立前磨牙和不同形态的卡环固位臂的三维有限元模型，施加动态位移栽荷，计算卡环与基牙的接触受力情况。结果所得数据经SPSS10．0统计软件和数理统计方法分析表明：当宽度一定时，随着卡臂尖倒凹深度的增大，钴铬合金铸造卡环固位臂的峰值应力与金合金卡环相比增加得快；金合金铸造卡环在前磨牙上所能放置的最大倒凹深度比钴铬合金卡环大。结论在设计和制作铸造卡环时，选择钴铬合金卡环进入基牙的倒凹深度较金合金卡环要更加慎重。当基牙的倒凹深度较大时，建议设计金合金卡环，以防卡环在使用中发生永久变形。     

树脂卡环与Co-Cr卡环的脱位力及体外循环疲劳测试

目的:比较树脂卡环与Co-Cr卡环在循环疲劳测试中的脱位力及其衰减趋势。方法:制作树脂和Co-Cr卡环,在基牙0.25mm和0.50mm两种倒凹深度下,利用多功能生物力学测定仪进行循环疲劳测试,对比其脱位力大小及衰减情况,同时测试各卡环的形变距离。结果:卡环在循环疲劳测试后其脱位力都不同程度的下降,脱位力下降最明显的是Co-Cr卡环0.50mm倒凹组,达6.937N,最小的是树脂卡环0.25mm倒凹组,为0.050N;循环测试前后2种倒凹深度下Co-Cr卡环组脱位力差异显著,树脂卡环组脱位力差异无统计学意义;Co-Cr卡环组的形变距离大于树脂卡环组。结论:树脂卡环固位力较Co-Cr卡环小,但衰减缓慢、形变小。     

钴铬合金、纯钛和Vitallium卡环3年使用期间的固位力变化

目的 体外模拟卡环3年使用期,比较钴铬合金、纯钛和Vitallium 3种材料之间卡环固位力的差异,为可摘局部义齿设计和材料的选择提供参考。方法 利用QT800-2型球墨铸铁制作15颗金属基牙。利用钴铬合金、纯钛和Vitallium 3种材料各铸造5个卡环,卡环进入基牙的倒凹深度为0.25 mm。对每个卡环进行5000次循环测试,相当于临床使用3 a。在循环测试过程中,对卡环进行11次固位力测试,采用SPSS13.0软件包对测试结果进行统计学分析。循环测试前,利用X线无损探伤技术对卡环可能存在的铸造缺陷进行检测。循环测试前后,利用扫描电镜对卡环内表面的微观形貌进行观察和分析。结果 3种卡环的固位力均随着循环次数的增加而减少;在循环测试前或测试后,3者之间相比均为Vitallium>钴铬合金>纯钛,且两两之间差异显著（P=0.000）。X线无损探伤发现,3种材料卡环的铸造缺陷多见于连接体的远心端。扫描电镜下,3种材料卡环内表面在循环测试前均未发现气孔和裂纹;循环测试后,均在卡臂尖内表面发现磨痕,但均未见裂纹产生。结论 在0.25 mm的倒凹深度,5000次循环测试前后,与钴铬合金和纯钛卡环相比,Vitallium卡环均具有最佳的固位力。钴铬合金和Vitallium卡环在0.25 mm倒凹深度可以长期保持理想的固位力。卡环在循环测试过程中的磨损,可能是固位力变化的原因之一。     

Comparison of cast Ti-Ni alloy clasp retention with conventional removable partial denture clasps

STATEMENT OF PROBLEM: The elastic property of Ti-Ni alloy may be a desirable property for cast removable partial dentures. However, little is known about the retentive properties of cast Ti-Ni alloy clasps. PURPOSE: This in vitro study investigated the retentive force of various types of clasps during repeated cycles of placement and removal to determine whether Ti-Ni alloy clasps maintain their initial retentive force under varied conditions, including different retentive undercut depths and clasp size (thickness and width). MATERIAL AND METHODS: The test models were developed using a mandibular dentiform with a horizontal plane of occlusion. Two complete metal abutment crowns were made for the left second molar, differing only in retentive undercut depths. A total of 98 clasps (n=7) were fabricated, including 14 wrought wire clasps and 28 clasps from each of the following alloys: Co-Cr alloy (Biosil), Type IV gold alloy (Cast-4), and Ti-Ni alloy (TN-10). Clasps were made to engage one of 2 retentive undercut depths (0.25 mm or 0.75 mm) and were made in 2 sizes (0.8 mm or 1.4 mm). Each clasp was radiographically examined for casting defects and porosity. The force (N) required to remove the clasps was measured using a universal testing machine with a crosshead speed of 10 mm/min. After measuring the retentive force, a masticatory simulator was used to cycle the clasps on and off the metal crown 500 times, simulating the insertion and removal of a removable partial denture clasp. The cycling sequence was repeated 10 times, and retention force was measured after each sequence. The internal surface of the clasp arms was examined for evidence of metal fatigue using scanning electron microscopy. Data were subjected to 2-way and 4-way analysis of variance, followed by Scheffe's multiple comparison test (alpha=.05). RESULTS: Co-Cr alloy and gold alloy clasps in the 0.25-mm retentive undercut groups experienced a gradual decrease in retentive force measurements (P<.001). In contrast, the Ti-Ni alloy clasps maintained a retentive force of approximately 1.8 N and 2.6 N for the 0.8 mm and 1.4 mm clasp groups, respectively. Although Ti-Ni alloy clasps' retentive force was reduced slightly after the first cycling sequence, it was negligible compared with other clasps tested. The wrought wire clasps also retained their retentive force until the final cycling sequence. A similar trend was found in the clasp groups engaging 0.75-mm retentive undercuts. CONCLUSION: Although the end-point retention for all the clasps was similar, there was less change in the retentive force of the cast Ti-Ni alloy clasps after repeated cycling sequences of simulated placement and removal.     

Comparison of the retentive characteristics of cobalt-chromium and commercially pure titanium clasps using a novel method

This study aimed to compare the retentive forces of cast cobalt-chromium (Co-Cr) and commercially pure titanium (cpTi) clasps. A clasp assembly comprising a pair of symmetrical clasps was made to fit the opposite halves of a hardened stainless-steel sphere. This twin clasp was designed to counterbalance the tipping forces when the clasp assembly was drawn from the sphere. A total of 120 clasp assemblies were fabricated in cast Co-Cr and cpTi and placed at undercut depths of 0.25 mm, 0.50 mm, and 0.75 mm (n = 20 for each). For Co-Cr clasps, the retentive forces at these undercuts depths were 2.34 +/- 0.23 N, 4.65 +/- 0.35 N, and 7.56 +/- 0.50 N, respectively. The corresponding retentive forces for cpTi clasps were 1.24 +/- 0.13 N, 2.34 +/- 0.23 N, and 3.70 +/- 0.27 N. The retentive force of cpTi clasps was approximately half that of Co-Cr clasps for the same undercut depth.     

The flexibility of titanium clasps compared with cobalt-chromium clasps.

Retention of a partial denture depends on the amount of undercut engaged on an abutment tooth and the flexibility of the clasp. Flexibility is influenced by clasp length and the denture base material. Titanium clasps are purported to have greater flexibility than cobalt-chromium cast clasps which should enable them to engage deeper undercuts or be used where shorter clasp arms are needed such as on premolar teeth. This study investigated the flexibility of cast titanium clasps with three commonly used cobalt-chromium clasps through comparative measurements of their tip deflections and yield strengths. The results showed that the titanium clasps were significantly (P < 0.05) more flexible than the cobalt-chromium clasps. However, all four materials were found to be flexible enough to engage an undercut of 0.25 mm without exceeding their yield strengths.     

Effect of different materials and undercut on the removal force and stress distribution in circumferential clasps during direct retainer action in removable partial dentures

ObjectivesThis study aimed to evaluate the effect of different materials and undercut on the removal force and stress distribution in the supporting tooth and in the circumferential clasp used in removable partial prosthesis.MethodsUpper molars prepared for Akers circumferential clasp with retention and opposing arm were modeled, scanned, elaborated with CAD software and the geometries imported in FEA and analyzed. Six different materials were selected for the clasp (Polyamide, Polyoxymethylene, Polyetheretherketone - PEEK, Gold alloy, Titanium and CoCr) and 3 different undercuts (0.25, 0.50 and 0.75 mm), totaling 18 groups.ResultsThe clasps presented greater stress in their structure and potentially greater damage to the dental enamel when made with rigid materials and with more undercut; however, they presented greater ability to remain in position.SignificancePolyamide with a higher undercut is an esthetic alternative to rigid metallic clasps. It showed promising behavior because it strongly reduces the damage to the enamel, and even with an undercut of 0.75, the retention is lower than for CoCr with a 0.25 undercut, and this retention might still be sufficient. Polyoxymethylene and Polyetheretherketone (PEEK) are not suitable materials for the clasps, because the maximum stress occurring during removal with higher undercuts is higher than the material strength.     

Guidelines for the choice of circumferential wrought wire and cast clasp arms for removable partial dentures

PurposeThe aim of this study was to establish guidelines for the selection of cast and wrought-wire clasps for removable partial dentures (RPDs) that would be appropriate for clinically encountered undercuts and facial curvatures.MethodsRandomly selected discarded casts were collected and 30 premolars and 30 molars were surveyed, sectioned to a line representing the clasp and scanned using a flatbed scanner. The average clasp curvature and length for each group was determined and a three-dimensional model printed, to which wrought wire clasps of 0.9- and 1.0-mm diameter were adapted. Standard wax clasp patterns were adapted and cast in a stellite alloy. Each clasp was deformed beyond its proportional limit; and the forces exerted at that limit and at deflections of 0.25 mm, 0.5 mm, and 0.75 mm were measured, and a safety limit was calculated that would ensure elastic deformation at the required undercuts.ResultsA table was produced with guidelines for those clasps that would provide the highest retentive force within the proposed safety limit. The highest forces were provided by cast clasps in a 0.25-mm undercut. Wrought round wire of 1-mm diameter provided the next highest retentive forces, in a 0.25-mm undercut for premolar clasps arms and 0.5-mm for molar clasps.ConclusionsThe results provide valid guidelines for the use of combinations of clasp material and undercut that would exert the maximum retentive force without deformation for both short (premolar) as well as long (molar) clasps, for wrought and cast clasps.