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.     

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。     

Repair with a surveyed cast clasp while patient retains the partial denture

A technique is described that allows a removable partial denture with a broken clasp or a removable partial denture in which an abutment has been extracted to be restored by the reattachment of a new cast clasp component or a complete surveyed clasp assembly. The technique is applicable to most clasp designs and can include attachment to the acrylic denture base or the metal major connector. The technique is distinguished from other repair techniques by (1) providing a cast clasp replacement, (2) allowing the patient to retain the prosthesis during the repair, (3) generating a precisely formed surveyed clasp assembly by the laboratory, and (4) including an efficient transfer mechanism for the precision clasp created in the laboratory to be attached to the removable partial denture in the dental office. A two-step impression procedure is used to ensure proper relation of the partial denture to the abutments. (J Prosthet Dent 1997;77:624-9.)     

Fitness and retentive force of cobalt-chromium alloy clasps fabricated with repeated laser sintering and milling

Purpose

With computer-aided design and computer-aided manufacturing (CAD/CAM), the study was conducted to create a removable partial denture (RPD) framework using repeated laser sintering rather than milling and casting techniques. This study experimentally evaluated the CAM clasp and compared it to a conventional cast clasp.

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.     

Accurate procedure for transferring a cast replacement clasp arm to a removable partial denture

This article describes a simple, quick and accurate procedure to replace a broken bar-type clasp with a new clasp arm. This procedure involves a resin matrix that transfers a new clasp arm from a working cast to a removable partial denture. This simple procedure enables quick and precise replacement of a broken clasp arm.     

Influence of polishing on cast clasp properties

During the polishing of clasps, two possible changes that could affect their properties are thinning of the clasp and work hardening of the alloy. Two distinctly different clasp pattern forms were selected and 20 samples of each were cast. They were then divided into two groups, polished and unpolished, in an effort to determine the total influence of the polishing procedure on clasp behavior. The results indicate that polishing produces a slightly more flexible clasp. Any influence resulting from possible work hardening is offset by the reduction of clasp thickness. Effects of width/thickness ratios and magnitude of deflections on finishing and polishing techniques may also alter clasp flexibility in the polished clasp.     

卡环作用于烤瓷冠的固位力衰减及冠磨损研究

目的研究钴铬合金、纯钛卡环在烤瓷冠的最大脱位力变化趋势和实验前后烤瓷冠表面特定区域的磨损。方法制作模拟下颌第一磨牙外形的镍铬烤瓷冠,其上制作钴铬合金卡环和纯钛卡环。卡环就位后采用万能力学测试仪进行1500次反复摘戴实验,每摘戴20次后测试一次峰值,比较卡环与烤瓷冠脱位力的衰减情况并采用回归拟合的方法进行统计。扫描电子显微镜观察,比较实验前后烤瓷冠定点区域的磨损情况。结果纯钛卡环固位力在520次循环内呈线性衰减。其后趋于稳定,均值9．00N。钴铬合金卡环固位力没有衰减,均值9．36N。二者差别有统计学意义。纯钛卡环在烤瓷冠表面造成的磨损比钴铬合金卡环组轻。结论综合考虑固位力衰减和冠表面磨损情况,烤瓷冠表面适宜采用纯钛卡环。     

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。     

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.     

Photoelastic analysis and comparison of force-transmission characteristics of intracoronal attachments with clasp distal-extension removable partial dentures

This investigation photoelastically compared the load-transfer characteristics of various bilateral distal-extension removable partial denture designs embodying intracoronal attachments and clasp assemblies. Six distal-extension designs that included the RPI clasp assembly, cast circumferential clasp, P.D. locking semiprecision, Thompson dowel nonlocking semiprecision, and McCollum and Stern G/L precision attachments were tested. Each prosthesis was subjected to various simulated occlusal loads. Evaluation of the load-transfer characteristics of the various designs was based on comparison of the recorded isochromatic fringe distributions. The RPI clasp assembly generated the most uniform stresses. In general, the four intracoronal retainer frameworks produced higher stresses than did the two clasp frameworks. The highest stresses were developed by the Stern G/L precision attachment.     

A measurement of clasp forces on teeth

A method that measures the force which clasps transmit to abutment teeth was developed and a comparative study was made between the effectiveness of a wrought wire clasp and that of a cast bar clasp. A transducer, using a resistance strain gauge, measured the flexure of clasps and the forces exerted by the clasps on abutment teeth. The cast bar clasps were more flexible than the wrought wire clasps of equal length. All of the clasps tested exerted forces against the teeth when the removable partial denture bases were at rest. The wrought wire clasps flexed a greater distance and exerted more force against the abutment teeth when the casting was seated and removed from the model. The forces exerted by the clasps when the casting bases were moved were different from each other and yet followed a pattern. The force increased for both types of clasps as the bases were depressed; however, the wrought wire clasp exerted more force than the cast bar clasps.     

卡环弹性形变限度的测试与临床意义

目的：探讨三种常用金属卡环弹性形变与卡环进入倒凹量的关系。方法：使用作者与有关人员自行设计的卡环张开位移钳，电子万能材料测试仪测试三种金属卡环弹性形变。结果：不锈钢丝卡环弹性最高，１８－８铬镍合金铸造卡环弹性较差，钴铬合金铸造卡环弹性最小。结论：不锈钢丝磨牙卡环进入倒凹量可大于０．５ｍｍ，双尖牙环进入倒凹量０．５ｍｍ，铸造合金磨牙卡环进入倒凹量应小于０．５ｍｍ，铸造合金双尖牙卡环进入倒凹量应小于０．２５ｍｍ。     

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 effect of single plane curvature on half-round cast clasps

The quality of retention produced by a half-round cast clasp is affected by its curvature in the plane of its flat side. Uncurved clasps and those that curve 90 degrees, 180 degrees, and 270 degrees become progressively stiffer. Conversely, as the radius of the curvature increases, so does the flexibility of the clasp.     

Aulen树脂卡环与Co—Cr卡环循环疲劳及对牙面磨损的研究

目的：比较Aulen树脂卡环与Co—Cr卡环在离体牙上循环疲劳测试中的脱位力衰减趋势,观察其对离体牙的磨损。方法：制作Aulen树脂卡环和Co—Cr卡环,利用多功能生物力学测定仪进行循环疲劳测试,对比其脱位力衰减情况,扫描电镜观察实验前后离体牙的磨损情况;结果：卡环在循环疲劳测试后其脱位力均不同程度下降,Aulen树脂卡环的摩擦区域无明显划痕,Co—Cr卡环的摩擦区域形成明显的划痕,破坏了原来平滑的表面。结论：Aulen树脂卡环固位力较Co—Cr卡环小,但衰减缓慢,Aulen树脂卡环对牙面的磨损程度小于Co—Cr卡环。     

Finite element analysis of the effect of vertical curvature on half-oval cast clasps

High stresses in half-oval cast clasps are the main causes of deformation or fracture. A vertical curvature in clasps is said to be effective in reducing stress. However, such claims lack scientific basis. The purpose of the present study was to evaluate stress and stiffness in a three-dimensional (3D) finite element analysis (FEA) model of clasps with different vertical curvatures, cross-sectional forms and tapers, and to clarify the effect of vertical curvature on the half-oval cast clasp. Circumferential clasp arms for the mandibular second premolar were analysed by 3D FEA. The clasp arms were approximated by curved cantilever beams with a half-oval cross-section around a cylinder. The radius of curvature was set at 4 mm and the angle subtended by the clasp arm was 120 degrees. The clasp tip was set at a point 2 mm lower than the base. In the 'No-taper' half-oval clasp arm, stress increased and stiffness decreased with the increase in vertical curvature. In the shape of a preformed wax pattern (thickness/width = 0.80, tip/base = 0.70), stress and stiffness decreased slightly. In an 'Original' form (thickness/width = 0.33, tip/base = 0.80), vertical curvature had a very slight effect on stress and stiffness, and stress was the lowest. These findings suggest the superiority of the 'Original' form, with less stress and no effect of vertical curvature.     

改良冷弯卡环与铸造支架联合应用修复牙列缺损的疗效观察

目的观察改良冷弯卡环联合铸造支架可摘局部义齿修复的临床效果。方法使用成品不锈钢圆丝锻制,配合扁丝弯制钳弯制成半圆形卡环臂、圆形卡环肩部及连接体、扁圆过度卡环体的改良冷弯卡环,与钴铬铸造支托、基托联合应用修复牙列缺损。并对90件改良冷弯卡环联合铸造支架可摘局部义齿戴入后追踪观察2年,了解义齿使用情况和基牙健康状况,并将其与钴铬合金支架义齿、传统冷弯卡环塑料基托义齿的修复效果对比。结果 2年后改良冷弯卡环联合铸造支架义齿基牙状况良好,不良症状明显低于其他两组义齿。结论改良冷弯卡环联合铸造支架可摘局部义齿具有良好的功能,可以获得良好的修复效果。     

Fitness accuracy and retentive forces of additive manufactured titanium clasp

PurposeLaboratory and clinical assessment of cast titanium dentures were reported, little is known about additive manufacturing (AM) frameworks. This study evaluated in vitro AM titanium alloy clasps for clinical use.MethodsAfter scanning the stainless steel dies to simulate the first molar, an Akers clasp was designed by CAD. AM clasp specimens were manufactured using laser sintering and AM machines from CP titanium grade 2 (CPTi), Ti-6Al-4V (Ti64), and Ti-6Al-7Nb (Ti67) powders. As controls, cast titanium clasps were conventionally made with same three titanium alloys. After nondestructive inspection and surface element analysis, surface roughness, fitness accuracy, initial retentive forces, and changes in retentive forces were measured.ResultsAlthough few porosities and little contamination of AM clasps were confirmed, the AM clasp arm and tip indicated slightly worse fitness accuracy as compared to cast clasps. The initial retentive forces of all titanium clasps showed appropriate retentive forces within the acceptable ranges, AM clasps tended to have lower decreases in retentive forces with up to 10,000 insertion/removal cycles as compared to those of the cast clasps.ConclusionsAM titanium clasps would be acceptable for clinical use similar to that of cast titanium clasps.     

Use of an adams clasp for a cast unilateral removable partial denture

A unilateral complete dentition with tight intercuspal contacts complicates the design of the interocclusal retentive elements of a cast removable partial denture. Use of an Adams clasp, which is connected to a predesigned retentive mesh in the metal framework, is suggested as a conservative and economical treatment option in this situation. Guidelines for minimizing the risk of breakage of the Adams clasp are presented.