Fit of anchors in frame prostheses

The fit of clasps was assessed in 101 removable partial dentures (RPD), including 54 free-end prostheses without any tooth bound replacements and 47 tooth bound prostheses replacing only premolars and molars. The age and the design of the RPD had a significant influence on the fit: in older and in stress broken free-end RPD's the clasps had a worse fit in terms of standing away from the abutment tooth.     

Stress distribution and abutment tooth mobility of distal-extension removable partial dentures with different retainers: an in vivo study

Three types of retainers (wrought wire clasp, Aker's cast clasp, and conical crown telescopic retainer) designed for distal-extension removable partial dentures (RPDs) were assessed in two Kennedy class I patients' mouths. The assessment, included the ratio of denture base shearing load and mobility of the terminal abutments when loaded on a free-end RPD occlusal surface. The mean values of denture base shearing ratios of wrought wire clasp, Aker's clasp and conical crown telescope were 60, 42 and 20%, respectively. The abutment mobility of the three types of retainers were all within the 'mobile ability area' except the wrought wire clasp for patient A's right side. The greatest tooth mobility was observed with the wrought wire clasps, followed by Aker's clasp and the conical crown telescopic retainer. From the analysis the following was concluded: (i) different retainers do influence the occlusal load distribution; (ii) the occlusal load distributed to the free-end saddle is closely related to the connecting rigidity of the retainer; (iii) mucosal support has an indispensable role in sharing the occlusal load with various retainers, even the rigid telescopic retainer.     

Clasp Retention: The Effects of Five Variables

An attempt was made to determine the relative retention of each of the four most commonly used clasp assemblies. They are the rest, proximal plate, 1 bar (RPI); rest, proximal plate, facial circumferential arm (RPA); modified T; and Akers (facial and lingual circumferential arms). A mandibular bilateral distal extension base removable partial denture design was selected because it is most commonly used. A test model was made by removing all mandibular molars from a Columbia Dentoform and replacing the ivorine second bicuspids with natural teeth. These, in turn, were later replaced with gold crowns that were identical in contour to the natural teeth. Eight removable partial dentures were constructed using preformed plastic lingual bars, minor connectors, denture base retention loops, and clasps. Artificial teeth and the denture bases were processed to each framework as for a clinical patient. Each removable partial denture was placed in the Instron testing machine and pulled from the test model. The investigation examined the effectiveness of each of four types of clasps in resisting displacing forces, in both vertical (occlusal) and mesio-occlusal directions. Each clasp was tested using natural teeth and gold crowns, in dry and wet environments, both with and without indirect retainers. Results indicate that, (1) The RPA clasp was the most retentive of all on natural abutments, against both directions of pull, but only slightly so over the RPI clasp with a vertical pull. (2) The Akers clasp was most retentive against a mesio-occlusal pull on the gold abutments. (3) Natural tooth structure gives slightly more frictional resistance than a gold surface. (4) The presence of artificial saliva caused little change in forces required for dislodgment. (5) The absence of indirect retainers greatly reduced the retentive properties of the RPD frameworks.     

负荷汪颌肯氏Ⅱ类可摘义齿游离端基牙牙槽骨位移的全息干涉测量

目的：比较下颌肯氏Ⅱ类可摘局部义齿的不同卡环对基牙牙槽骨产生作用的差异。方法：在离体人下颌骨上,设计制作5种直接固位体的肯氏Ⅱ类可摘局部义齿,即RPA卡环、RPI卡环、改良RPI卡环、铸造三臂卡环、颊侧锻丝固位臂卡环,用全息干涉测量技术,比较5种固位体使基牙颊舌侧牙槽骨产生位移的情况。结果：近中He支托卡环产生的位移小于过错中He支托卡环,杆型卡环产生颊侧牙槽骨位移分布均匀,圆环形卡环引起的颊侧位移信中在根尖,结论：临床修复此类牙列缺损时应尽量使用近中He支托和杆型卡环。     

负荷下颌肯氏Ⅱ类可摘义齿游离端基牙牙槽骨位移的全息干涉测量

目的:比较下颌肯氏Ⅱ类可摘局部义齿的不同卡环对基牙牙槽骨产生作用的差异。方法:在离体人下颌骨上,设计制作5种直接固位体的肯氏Ⅱ类可摘局部义齿,即RPA卡环、RPI卡环、改良RPI卡环、铸造三臂卡环、颊侧锻丝固位臂卡环。用全息干涉测量技术,比较5种固位体使基牙颊舌侧牙槽骨产生位移的情况。结果:近中支托卡环产生的位移小于远中支托卡环,杆型卡环产生颊侧牙槽骨位移分布均匀,圆环形卡环引起的颊侧位移集中在根尖。结论:临床修复此类牙列缺损时应尽量使用近中支托和杆型卡环。     

Indirect retainers in soft palate obturator design

Definitive framework design for the maxillofacial patient with complete maxillary dentition who has had a soft palate resection requires the use of direct and indirect retainers. It is possible to retain these prostheses, however, with only two posterior clasps and indirect retainers without clasps. This design offers an esthetic, retentive, and functional restoration while preserving existing structures. Four clinical applications are described.     

Esthetic designs of removable partial dentures

The increased emphasis on physical appearance in contemporary society has increased the demand for esthetic dental restorations. Although the success of implant dentistry has expanded the scope of esthetic fixed prostheses, many patients demand a removable partial denture (RPD) for health, anatomic, psychological, or financial reasons. Fabricating an esthetically pleasing RPD while avoiding the unsightly display associated with conventional clasp assemblies often presents a challenge to dentists. This article examines using lingual clasps, proximal undercuts (also known as rotational path insertion), and acetal resin clasps as simple and effective means of improving RPD esthetics.     

Influence of removable partial dentures on the formation of dental plaque on abutment teeth

PurposeThis study aimed to clarify the relation between the shape of the retainers and the plaque formation on abutment teeth to improve the denture design.MethodsThis study observed the buccal surface for the clasps and distoproximal surface for a guide plate of the mandibular first premolar which was the abutment tooth with a direct retainer of a distal extension RPD. The buccal surface was observed in 10 subjects and the distoproximal surface in 14 subjects. The latter cohort was divided into two groups (the group with an open type guide plane and a close type guide plane). All subjects provided their informed consent. The state of plaque accumulation was inspected by standardized photography and bacterial quantification and compared among the cast circumferential (CC), Ibar, wire circumferential (WC) and control (no clasps) in individuals regarding the buccal surface and between the groups with the open type and close type guide plane of the distoproximal surface.ResultsNo significant differences were observed among the CC, Ibar, WC and control (P > 0.05) regarding the buccal surface, while in regard to the distoproximal surface, the group with the open type guide plane had significantly more plaque than the group with the close type guide plane (P < 0.05).ConclusionThe plaque formation on the buccal surface is not dependent on the types of clasps. It is effective to prepare a guide plane as close to the gingival margin as possible to reduce the plaque accumulation on the distoproximal surface.     

A systematic approach for removable partial denture design

Patients' attitudes, medical, surgical and financial considerations lead to the use of a removable partial denture (RPD) as the chosen prosthetic restoration even in the "dental implant era". The aim of this article is to describe a systematic approach to RPD design, so the RPD will be a long-term solution that will not harm the remaining oral tissues. There is an unlimited RPD design options. Choosing the right one involves considering biochemical factors, aesthetics and patients' comfort. A systematic approach starts with a correct diagnosis of the remaining hard and soft tissues, followed by a careful planning of support, stability and retention in that order. Additional elements should be added only at a later stage. A systematic track starting with a preliminary design, surveying of the model and analyzing the preliminary design on that surveyed model. If needed, that track should be reversed until an acceptable design is found. Support should ideally be achieved by using metal rests on healthy tooth structure. Tooth supported RPD are the most convenient ones and have a very good long-term prognosis. Old restorations or caries might impose changes from the ideal supporting rests. When posterior teeth are missing or when the edentulous area is vast, tooth-tissue supported RPD are used. In these cases one should gain initial support from the teeth and an additional support from the soft tissues. A denture base that is similar to a full denture base that would have been prepared for a fully edentulous patient should achieve this. If the prognosis of the potential supporting teeth is poor, a tissue-tooth supported RPD is considered. In these cases, the denture base is the primary supporting element, and stress relieving clasp-assemblies such as the RPI/RPA should be considered. Stability is achieved primarily by metal contacts between teeth and the metal framework of the RPD. In fact, any embracing part of the clasp assembly and a correct denture base can contribute to the stability. The distal parts of the retentive clasps produce the active retention. Since these parts generate lateral forces on the abutment teeth, a reciprocating element should be used. True reciprocation can only be achieved if the reciprocating element touches the tooth before the retentive clasp. After designing support, stability and retention, other parts should be considered. When a distal extension RPD is considered, an indirect retainer should be incorporated into the framework in order to prevent upward rotational movement of the denture. The major connector converts forces from one side to the other. In the upper jaw, that part acts also as a supporting element in Kennedy class I and class II cases. In other cases, a minimal type of a major connector should be chosen. As for minor connectors, these should only be added if other parts--such as guiding planes--couldn't be used for the purpose of connecting functional elements to the major connector. In any case, a 5 mm distance between two adjacent minor connectors should be allowed in order to prevent food from being trapped in that space. A systematic approach starts with diagnosis of the remaining tissues and with finding the correct prosthetic solution with the patient. If a RPD is the chosen solution, start designing with analysis of support, followed by stability and only then, decide upon the necessary retentive elements. All other parts should be considered later. Such a systematic approach will ensure a long-term solution and a happy patient.     

Abutment tooth and base movement witl attachment retained removable partial dentures

Using a laboratory model for the distal extension removable partial denture situation, the effect of resilient and rigid precision attachment retainers on abutment tooth and denture base movement was studied. It was found that both abutment tooth and denture base movement was least with the rigid and semi-precision attachments used compared to the resilient attachments. Abutment tooth movement was generally towards the mesial, except for the C and L attachment which produced distal movement.     

The path of placement of a removable partial denture: a microscope based approach to survey and design

This article reviews the topic of how to identify and develop a removable partial denture (RPD) path of placement, and provides a literature review of the concept of the RPD path of placement, also known as the path of insertion. An optimal RPD path of placement, guided by mutually parallel guide planes, ensures that the RPD flanges fit intimately over edentulous ridge structures and that the framework fits intimately with guide plane surfaces, which prevents food collecting empty spaces between the intaglio surface of the framework and intraoral surfaces, and ensures that RPD clasps engage adequate numbers of tooth undercuts to ensure RPD retention. The article covers topics such as the causes of obstructions to RPD intra-oral seating, the causes of food collecting empty spaces that may exist around an RPD, and how to identify if a guide plane is parallel with the projected RPD path of placement. The article presents a method of using a surgical operating microscope, or high magnification (6-8x or greater) binocular surgical loupes telescopes, combined with co-axial illumination, to identify a preliminary path of placement for an arch. This preliminary path of placement concept may help to guide a dentist or a dental laboratory technician when surveying a master cast of the arch to develop an RPD path of placement, or in verifying that intra-oral contouring has aligned teeth surfaces optimally with the RPD path of placement. In dentistry, a well-fitting RPD reduces long-term periodontal or structural damage to abutment teeth.     

Dual Path: A Concept to Improve the Esthetic Replacement of Missing Anterior Teeth with a Removable Partial Denture

The dual path of insertion concept for removable partial denture (RPD) design may be used in esthetically demanding situations. When compared to conventional RPDs, the main advantage of this design is the minimal use of clasps. This clinical report describes the treatment of a patient with an anterior maxillary edentulous area using a dual path RPD. The diagnostic cast was surveyed to ensure the adequacy of the undercuts on the mesial surfaces of the anterior abutments, where rigid minor connectors were placed. Inverted V‐shaped canine cingulum rest seats were prepared to provide resistance to tooth movement during function. The dual path RPD concept allows excellent esthetic results, minimizes tooth preparation, and reduces the tendency toward plaque accumulation in a Kennedy class IV partially edentulous arch.     

Longitudinal study on forces transmitted from denture base to retainers of lower free-end saddle dentures with Aker''s clasps

The aim of this study was to make a longitudinal analysis of the forces transmitted from denture base to retainers of lower free-end saddle dentures with Aker's clasps using a newly developed transducer. The experimental apparatus consisted of two components, a metal framework and a denture base embedded with a force-detecting unit. This device was the transducer, which could detect changes in lateral and vertical forces transmitted from denture base to retainers at the same time. Forces were measured on several separate occasions from the insertion of new dentures to about 4 months afterwards. The result are summarized as follows: (i) the maximal mean value of vertical forces transmitted from denture base to retainers was decreased after 1 week of insertion of new dentures, then increased and reached a constant level (about 10N) 4-6 weeks after the insertion of new dentures; (ii) there were large differences in the maximal mean value of lateral forces between subjects.     

A simplified procedure for survey and design of diagnostic casts

The procedure described for survey and design of diagnostic casts is applicable to either dental arch. It is presented in a sequential manner, is not complex, and will produce uniformly acceptable results. The following steps should be followed: (1) locate a path by tilting the cast; (2) mark the survey lines and tripod the cast; (3) outline the rest and guide planes; (4) draw minor connectors; (5) draw major connectors; (6) draw retention mesh for acrylic resin; (7) draw acrylic resin base extension; and (8) draw direct retainers (clasps).     

Failure of maxillary canine retainers for fixed prostheses

A statistical survey of fixed prostheses with failed retainers, combined with information on the arch distribution of abutment teeth, supports the clinical impression that retainers on maxillary canines have a disproportionately high failure rate. The probable contributing factors are the form of the canine clinical crown, the distribution of occlusal force, and the paths of abutment tooth displacement. These factors are discussed and clinical techniques for countering their adverse effects are described.     

Retention magnets in guiding plates of distal-extension removable partial dentures

This investigation studied vertically placed magnets that act simultaneously as guiding plates and retentive devices. The retention of vertically placed magnets was less than that of horizontally or obliquely placed magnets, but comparable to that of I-bar retainers. Load-induced stresses were lower, transmitted more axially to the abutments and were generally more equitably distributed than stresses produced by magnets in other orientations to the abutment tooth. The force distribution characteristics were less stressful than those of a comparable RPD with distal guiding plates, mesial rests, and I-bar retainers. Although the investigators were initially concerned about the relative capabilities of the vertically placed magnets, in vitro and in vivo studies demonstrated that retention was as good if not better than that of conventional clasp designs.     

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.     

In vitro investigation of the wear of resin composite materials and cast direct retainers during removable partial denture placement and removal.

The purpose of this study was to determine whether wear of two resin composite materials and contacting I-bar clasp tips would occur within a simulated RPD placement and removal period of 2 years. The data were compared to enamel with contacting I-bars. Cast I-bar clasps were passed over each specimen in the resin composite and tooth experimental groups (n = 10). Computer digitized image analysis of SEM photomicrographs of the specimens provided data for analysis of wear. Results indicated a statistical difference in the amount of mean wear between the two resin composites and between the I-bar groups. The results from this study suggest that the selection of a resin composite for use as a RPD retentive undercut must be carefully undertaken to avoid excessive wear and loss of retention.     

Effect of direct retainer and major connector designs on RPD and abutment tooth movement dynamics

Designs of removable partial dentures are suggested to affect the mobility of abutment teeth and removable partial denture (RPD) during oral functions. This study aimed to examine the effect of direct retainer and major connector designs on RPD dynamics under simulated loading. Six different Kennedy class II maxillary RPDs were fabricated on a maxillary model. These dentures involved 3 different direct retainers (wrought-wire clasp, RPA clasp, and conical crown telescopic retainer) and 2 different major connectors (Co-Cr major connector and heat-cured acrylic resin with a metal strengthener). Using an experimental model with simulated periodontal ligaments and mucosa that were fabricated using silicone impression material, three-dimensional displacements of the RPDs were measured under a simulated 30-N loading with a displacement transducer type M-3. Significant effects of "direct retainer design" on bucco-palatal displacements and "major connector" on mesio-distal displacements were revealed by 2 x 3 two-way analysis of variance of abutment teeth movements (P < 0.001 and P = 0.002, respectively). Additionally, analysis of variance of RPD displacements revealed significant effects of "direct retainer design" on corono-apical displacements and "major connector" on mesio-distal displacements (P = 0.001 and P = 0.028, respectively). Rigid direct retainers and rigid major connectors decrease the movements of both abutment tooth and RPD.     

Accuracy of CAD-CAM-fabricated removable partial dentures

Statement of problem

The conventional fabrication of removable partial dentures (RPDs) is a complex, error-prone, time-consuming, and expensive process. The use of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques, especially rapid prototyping, promises a more effective method for fabricating RPD frameworks.