Finite Element Stress Analysis of Tooth-to-Implant Fixed Partial Denture Designs

Purpose The purpose of this study was to conduct a three-dimensional finite element stress analysis to compare models representing a natural tooth and an integrated implant connected with rigid and nonrigid prostheses. Materials and Methods The mathematical models described an integrated implant connected to a second premolar tooth with a three-unit metal-ceramic fixed partial denture. In one model, the tooth and implant were rigidly connected, and in the other, a nonrigid connection was assumed. From a simulated vertical load the computer generated resultant stress contours and values (compressive and tensile) in horizontal and vertical dimensions. Results A comparison of the magnitude and pattern of stresses generated in the models shows minimal differences. Although the maximum stress values were slightly higher in some areas of the rigid prosthesis model, the differences were negligible. Conclusions Based on the similarities in both the patterns of stress contours and the stress values generated in the two models, advocating a nonrigid connection because of a biomechanical advantage may be erroneous.     

Simplifying Prosthetic Procedures while Converting an Interim Maxillary Removable Complete Denture to an Interim Implant‐Supported Fixed Complete Denture

This article describes a method of converting an interim maxillary removable complete denture to an interim implant‐supported fixed complete denture. The advantages of this method are that it provides the opportunity to evaluate the patient's function and esthetics, and helps the accurate transfer of the maxillomandibular relationship to the laboratory. Consequently, the fabrication of the definitive prostheses is accurate, and the final result is predictable.     

Retention for a Removable Partial Denture

This article addresses the complex nature of retention in a removable partial denture. Retentive features range from magnets and springs to clips, clasps, and interfacial surface tension. The retentive quality of an extracoronal clasp varies with the alloy, physical form, location on the abutment, and positional relationship to other elements. Surveying to identify both occlusogingival and mesiodistal undercuts when the path of random dislodging forces are not definitely controlled is needed for effective retention. Augmentation of ineffective retention in existing clasps should concentrate on methods of deepening the undercut or increasing the suprabulge. Tightening of clasps already in contact with a tooth frequently produces adverse changes.     

分割式和普通可摘局部义齿三维有限元模型的建立

目的 较为快捷、精确地建立部分上颌骨以及可摘局部义齿三维有限元模型.方法 应用薄层CT扫描技术和Mimics软件,Pro/Engineer软件以及ANSYS Workbench软件对49张CT断层影像进行分析处理.结果 建立了两种精确的上颌可摘局部义齿的三维有限元模型.结论 利用Pro/Engineer软件完成上颌义齿模型的制作,可减小建模难度;ANSYS Workbench软件可提高有限元分析效率,适用于口腔医师对有限元模型前期以及后期的处理.     

Using a Visible Light‐Polymerized Resin to Fabricate an Interim Partial Removable Dental Prosthesis

An interim partial removable dental prosthesis (RDP) is any dental prosthesis that replaces some teeth in a partially dentate arch designed to enhance esthetics, stabilization, and/or function for a limited period of time, after which it is to be replaced by a definitive dental prosthesis. This article describes a technique that uses a visible light‐polymerized (VLP) resin as the base material for an interim partial RDP. This technique can be easily accomplished in a dental office or laboratory and results in a predictable dental prosthesis. This technique eliminates the need for laboratory processing.     

An Interactive Multimedia Solution to Learning Removable Partial Denture Design

Surveys of the dental profession and dental laboratories show that up to 60% of cases received by laboratories have little or no input from dentists into the design of their patients' removable partial dentures (RPD). Thus, there is a clear mandate for dental schools to teach RPD design in new ways that will give their students confidence and allow their graduates to approach the task readily and easily. This computer-aided learning program addresses that need. In designing it, we have exploited the unique properties of computers as a learning tool. The program uses Quicktime VR to simulate a three-dimensional perspective of diagnostic casts. It is also possible to incorporate animated diagrams to illustrate various points. Control of timed answers promotes the use of inquiry-based learning and allows the program to be interactive and completely problem-oriented. Students can practice at their own pace, on a variety of virtual cases, and thus learn the craft behind the art of designing RPDs. With this foundation, discussions with experts in the field regarding the patients they treat in senior years and as graduates can be conducted at a higher and more productive level. Student evaluation so far has been very encouraging.     

Porcelain-Fused-to-Metal Pontics for Improved Removable Partial Denture Esthetics

A removable partial denture fabrication technique that uses custom-constructed porcelain fused-to-metal (PFM) pontics is described. PFM pontics enhance the dentist's shade matching effort in esthetically demanding situations.     

两种游离端半精密附着体可摘局部义齿的应力分析

目的:研究双侧游离缺失活动义齿使用两种不同类型的半精密附着体固位时周围支持骨的表面应力。方法:采用电阻应变测量法在人体下颌骨标本上测量以冠内栓道式及冠外垂直杆式半精密附着体固位的双侧游离缺失活动)固定联合修复体的表面应力值并做统计分析。结果:冠内附着体在基牙周围牙槽骨上产生的总体应力较大,而冠外附着体在缺牙区牙槽嵴和近缺隙侧基牙远中颈部牙槽嵴上产生的应力较大。结论:冠内附着体适用于远中基牙牙周条件良好的情况,而冠外附着体则适用于缺牙区牙槽嵴条件良好、远中基牙条件相对欠佳的情况。     

Removable Partial Denture Education in U.S. Dental Schools

PURPOSE: A survey of U.S. dental schools was conducted in 2001 to determine the curricular structure, techniques, and materials used in predoctoral clinical removable partial denture (RPD) programs. MATERIALS AND METHODS: The questionnaire was mailed to the chairperson of the prosthodontic/restorative departments of 54 U.S. dental schools. Of these, 44 schools returned the completed survey, resulting in a response rate of 82%. RESULTS: Results from this survey show that a large majority of schools are using similar materials in clinical RPDs; for instance, using modeling compound for border molding final impression trays (61%) and using a semi-adjustable articulator for mounting preliminary casts (90%) and final casts (98%). In addition, a large majority of schools are using similar techniques in clinical RPDs, such as border molding the edentulous areas of the final impression tray (80%) and using the altered cast impression technique (59%). A set post-insertion protocol is present for patients who receive partial dentures in the majority of the schools (93%). Only 25% of schools reported incorporating new educational materials such as the use of Portrait artificial teeth at the predoctoral level. Eighteen percent of schools are allowing students to graduate without a set number of RPD clinical requirements as has been traditionally the case. CONCLUSIONS: Predoctoral clinical RPD programs vary from school to school, yet a large percentage of schools agree on many topics.     

Restoration of the Occlusal Vertical Dimension with an Overlay Removable Partial Denture: A Clinical Report

The process of tooth loss throughout life associated with severe occlusal wear may pose a challenge in the rehabilitation of partially edentulous arches. In these cases, many therapeutic procedures are necessary because each tooth must be restored to obtain the correct anatomical contour and recover the occlusal vertical dimension (OVD). A removable partial denture (RPD) with occlusal/incisal coverage, also known as an overlay RPD, is an alternative treatment option with fewer interventions, and, consequently, lower cost. This clinical report reviews the principles involved in the clinical indication for an overlay RPD, as well as the necessary planning and execution, to discuss the feasibility and clinical effectiveness of this treatment, identifying the indications, advantages, and disadvantages of this procedure through the presentation of a clinical case. The overlay RPD can be an alternative treatment for special situations involving partially edentulous arches in patients who need reestablishment of the OVD and/or realignment of the occlusal plane, and it can be used as a temporary or definitive treatment. The main advantages of this type of treatment are its simplicity, reversibility, and relatively low cost; however, further studies are needed to ensure the efficacy of this treatment option.     

Evaluation of a Computer-Aided Learning Program in Removable Partial Denture Framework Designing

Assessment of a computer-assisted learning (CAL) program dealing with designing removable partial dentures was performed as both formative and summative evaluation. Formative evaluation was obtained through open-ended questions in a written questionnaire administered to 60 junior students from two Australian Dental Schools and through observation of four groups of these students as they worked through the program. Formative evaluation, fundamental to completion of the program, led to several changes and additions. Observation of the students using the program during its final stages of development was one of the most informative and helpful parts of the evaluation. It allowed nuances of expression and body language to be noted that would not have been apparent in written or numerical data. Summative evaluation was obtained through structured questions in the questionnaire and through a post-CAL test under examination conditions. Summative assessment showed that students could attain a desired standard of knowledge if a lecture series was replaced by the CAL program; that the program was user-friendly, even for students with little or no computer experience; and that most students considered it to be a useful learning resource. More than half the students were concerned about using CAL to replace human instruction. It is significant that students were particularly impressed by aspects of the program that could not be duplicated by a book; the interactive nature of the learning process and the ability to rotate the diagnostic casts. This highlights the need for CAL programs to use the full potential of computer capability, rather than merely replicate a textbook on a screen.     

Turning Points in Removable Partial Denture Philosophy

This article discusses key turning points in removable partial denture (RPD) philosophy. Early advancements tended to focus upon improving the technical quality of the prosthesis itself. The beginning of the 20th century brought significant public pressure upon the dental profession due to consequences associated with poor quality fixed prostheses. The result was dramatic improvement and heavy demand for RPDs. Technical and efficiency issues conspired to temper this enthusiasm, eventually resulting in reduced respect for RPDs. By highlighting key writings and technical issues during these periods of change it is hoped the reader will gain a more precise understanding of the current status of RPD philosophy.     

Transition from Failing Dentition to Full‐Arch Fixed Implant‐Supported Prosthesis with a Staged Approach Using Removable Partial Dentures: A Case Series

The present retrospective case series is aimed at evaluating a staged approach using a removable partial denture (RPD) as an interim prosthesis in treatment to correct a failing dentition until such time as a full‐arch fixed implant‐supported prosthesis may be inserted. Eight patients, who had undergone maxillary full‐arch rehabilitation with dental implants due to poor prognosis of their dentitions, were analyzed. All treatment included initial periodontal therapy and a strategic order of extraction of hopeless teeth. An RPD supported by selected teeth rehabilitated the compromised arch during implant osseointegration. These remaining teeth were extracted prior to definitive prosthesis delivery. Advantages and drawbacks of this technique were also recorded for the cases presented. Among the advantages provided by the staged approach are simplicity of fabrication, low cost, and ease of insertion. Additionally, RPD tooth support prevented contact between the interim prosthesis and healing abutments, promoting implant osseointegration. The main drawbacks were interference with speech and limited esthetic results. Implant survival rate was 100% within a follow‐up of at least 1 year. The use of RPDs as interim prostheses allowed for the accomplishment of the analyzed rehabilitation treatments. It is a simple treatment alternative for patients with a low smile line.     

Influence of Cusp Inclination on Stress Distribution in Implant‐Supported Prostheses. A Three‐Dimensional Finite Element Analysis

Purpose: The aim of this study was to assess the influence of cusp inclination on stress distribution in implant‐supported prostheses by 3D finite element method. Materials and Methods: Three‐dimensional models were created to simulate a mandibular bone section with an implant (3.75 mm diameter × 10 mm length) and crown by means of a 3D scanner and 3D CAD software. A screw‐retained single crown was simulated using three cusp inclinations (10°, 20°, 30°). The 3D models (model 10d, model 20d, and model 30d) were transferred to the finite element program NeiNastran 9.0 to generate a mesh and perform the stress analysis. An oblique load of 200 N was applied on the internal vestibular face of the metal ceramic crown. Results: The results were visualized by means of von Mises stress maps. Maximum stress concentration was located at the point of application. The implant showed higher stress values in model 30d (160.68 MPa). Cortical bone showed higher stress values in model 10d (28.23 MPa). Conclusion: Stresses on the implant and implant/abutment interface increased with increasing cusp inclination, and stresses on the cortical bone decreased with increasing cusp inclination.     

Biomechanical Evaluation of Tooth‐ and Implant‐Supported Fixed Dental Prostheses with Various Nonrigid Connector Positions: A Finite Element Analysis

Purpose: In the tooth‐ and implant‐supported fixed dental prosthesis (FDP), rigid and nonrigid connector (NRC) designs have been preferred by clinicians for many years. The aim of this study was to analyze the stress distribution on the connecting areas of the superstructure and supporting structure of the tooth‐ and implant‐supported FDP designs under both static vertical and oblique occlusal loads. Materials and Methods: Four 2D finite element analysis (FEA) models were prepared presuming that the first and second molars were missing, and that the implant (3.80‐mm diameter × 13‐mm length) was placed in the second molar NRC design and patrix‐matrix position supported by teeth/implants. Nonlinear contact elements were used to simulate a realistic interface fixation within the implant system and the sliding function of the NRC. Supporting periodontal ligament and alveolar bone (cortical and trabecular) were also modeled. Linear static analysis was performed on the prepared 2D solid models with a total masticatory force of 250 N (50 N for premolar, 100 N for first molar, 100 N for second molar), 0° (at a right angle) and 30° to the long axis of the supports. The maximum equivalent Von Mises (VM_Max) was analyzed around the supporting teeth/implant and connector areas on tooth‐ and implant‐supported FDP. Results: The simulated results indicated that the highest level of VM_Max (400.377 MPa) was observed on the NRC with the matrix positioned on the implant site of tooth‐ and implant‐supported FDP under vertical occlusal load. The highest level of VM_Max (392.8 MPa) under oblique occlusal load was also observed on the same model; however, the lowest VM_Max value around implants was observed with the NRC when the patrix was positioned on the implant site of the FDP. Under vertical occlusal loads, in designs where the NRC was placed on the implant site, the stress formed around the implant decreased when compared to the designs where the NRCs were positioned on the tooth site. Conclusions: The efficiency of the NRC exhibited varying behavior depending on the direction of the load applied. The use of the patrix part of the NRC on the implant site may be more efficient in reducing the stress formation around the implant.     

Mandibular Kennedy Class I implant‐tooth‐borne removable partial denture: a systematic review

Summary The purpose of this systematic review is to evaluate the use of implant‐tooth‐borne removable partial dentures in prosthetic rehabilitation of Kennedy Class I partially edentulous arches. A comprehensive search was performed in MEDLINE, EMBASE, Cochrane Oral Health Group’s Trials Register, Cochrane Central Register of Controlled Trials, UK National Research Register, Australian New Zealand Clinical Trials Registry (ANZCTR), conference proceedings and abstracts up to 25 August 2009. Searching the reference list of the selected articles and hand searching of several journals were also performed. A total of nine studies were included. Of these, two were randomized, three were retrospective and four were case reports. All but two had a low reporting quality (level IV on a four‐level hierarchy of evidence). Nevertheless, the improvement in function, aesthetics and stability has been demonstrated in all studies with minimal prosthetic care. Within the limitations of this study, implant‐assisted/supported removable partial denture may provide a simple, economical and less invasive treatment modality. The predictability of such approach in the management of bilateral distal‐extension situation is, however, still questionable. A higher quality of published studies namely with a focus on long‐term randomized clinical trials are needed.     

模型置换印模技术修复下颌游离端牙列缺损的临床研究

目的：探讨模型置换印模技术对双侧下颌游离端缺牙患者的修复效果。方法：在解剖式印模上常规制作铸造支架,在铸造支架上制作自凝暂时基板,经口内肌功能修整并制取咬合记录后于口内取功能性印模。经模型置换后常规完成义齿。结果：90.2%的患者用模型置换印模技术制作的义齿疗效良好。结论：模型置换印模作为游离端可摘部分义齿的重要功能印模方法,可以有效改善义齿修复质量。