Extension Base Removable Partial Dentures Research Articles

What Occlusal Scheme Should Be Used with Removable Partial Dentures?

Multiple clinical studies have been published comparing different philosophies of complete denture occlusion and different types of denture teeth. However, it is unclear whether comparable data are available for occlusal schemes used with removable partial dentures (RPDs). Therefore, this review investigated the dental literature related to occlusal schemes for RPDs. A PubMed search of English language articles was performed using the term "removable partial denture, occlusion" with 765 results. When the term "occlusion in removable partial prosthodontics" was used there were 784 results. Seventy-four articles were identified using the different search term of "RPD, occlusion" while use of the term "occlusal scheme, with removable partial dentures" listed 18 publications. The term "removable partial denture, occlusion, literature reviews" produced 38 potential publications related to the topic. Using the term "removable partial denture occlusion systematic review" resulted in 2 citations. Using the term "RPD occlusion literature review" resulted in one foreign language manuscript whereas using the term "RPD occlusion systematic review" resulted in one article unrelated to dentistry. The term "clinical studies of RPD occlusion" produced 5 results with none related to the topic. There were 23 results using the term "clinical studies of removable partial denture occlusion" with one potentially related to RPD occlusal schemes. A review of the titles and abstracts revealed 12 articles that appeared to contain specific information about the occlusal scheme used with RPDs. Following a detailed review of those publications, only 4 contained recommendations for RPD occlusion and were included in this review. The available information regarding the recommendations for occlusal schemes in these articles was based on expert opinion. A decision was made to include a hand search of 9 textbooks containing varying amounts of information related to occlusal schemes for RPDs, but no evidence-based references related to RPD occlusal schemes were found in the textbooks. Since this entire review is based on expert opinion, no attempt was made to critique the opinions expressed by these authors but rather to present their perspectives for evaluation by readers. The occlusion developed with RPDs should be physiologically harmonious, allowing the supporting structures to remain in a good state of health with functional stress distributed among all the occluding teeth. Multiple authors indicate the occlusion in maximum intercuspation/centric occlusion should incorporate bilateral posterior contacts with no deflective occlusal contacts. When most occlusal contacts on natural teeth are missing, it has been proposed that extension base RPDs have their occlusal contacts developed in centric occlusion. Regarding eccentric occlusal relationships, a balanced occlusal scheme has been recommended by multiple authors with one author advocating use of a lingualized balanced. An anterior guided (canine-protected) occlusion has also been recommended when the canines are present and not periodontally compromised. When RPDs oppose a complete denture, several authors indicate a bilateral balanced occlusion should be used to help stabilize the complete denture.

Exerted Stresses from Loading Distal -Extension Removable Partial Denture with Different Occlusal Rest Position A Finite Element Stress Analysis Study

The treatment of distal extension base removable partial denture has long been the dilemma of many Prosthodontists, since the support for this type of restoration is based on two functionally different systems, the teeth and associated periodontal membrane and the edentulous ridges. So one of their most elusive goals were to finish the prosthesis by utilizing both systems of support without exposing the tissues to undue stresses which might lead otherwise to bone resorption. Material and method: A two-dimensional finite element analysis method was used to assess the stress distribution on supporting structure where different rest position, including mesial-occlusal rest, distal-occlusal rest, and mesio-distal occlusal rest. The X, and Y coordinate for each node of the model was transferred to the ANSYS program, a load of 10MP was used in this study, where each of the models was subjected to load distributed on the saddle area. Results: Von Mises stress values revealed that, mesial rest produces less stress concentration

RETRACTED: Muscle activity and masticatory efficiency with bilateral extension base removable partial dentures with different cusp angles

Whether masticatory efficiency and electromyographic activity are influenced by type of artificial teeth and food is unclear. The purpose of this clinical study was to evaluate the influence of extension base removable partial dentures (RPDs) with different cusp angles: anatomic (33 degrees), semianatomic (20 degrees), and nonanatomic (0 degrees) teeth on masticatory efficiency and muscle activity during the mastication of test foods with different textures. Twelve participants with RPDs were selected to perform masticatory efficiency and electromyographic tests. Surface electromyograms (EMGs) were used to record the activities of the masseter and temporalis muscles during the mastication of different types of test foods. The maximal voltage and duration were measured on the integrated EMG signal in each muscle during food mastication, and the mean reading of both sides was then recorded. Analysis of variance and the Tukey post hoc test were used to perform statistical analyses (α=.05). The masticatory efficiency of RPDs with nonanatomic teeth was significantly inferior to that of RPDs with anatomic and semianatomic teeth (P<.05). However, masticatory efficiency did not differ between anatomic and semianatomic teeth (P>.05). Also, muscle activity (according to EMG) with RPDs with NA teeth was significantly higher than that with anatomic and semianatomic teeth (P<.05). RPDs with NA teeth were associated with higher EMG muscle activity and reduced masticatory efficiency than anatomic or semianatomic teeth.

STRESS ANALYSIS OF REMOVABLE PARTIAL DENTURES OF DISTAL EXTENSION CASES FABRICATED OF TWO RECENT AESTHETIC CAD/CAM PROSTHETIC MATERIALS VERSUS CONVENTIONALLY MANUFACTURED METALLIC RPDs

Recently, there are different types of esthetic materials used for RPDs framework fabrication some of which are applicable for CAD/CAM system. Distal extension base removable partial dentures exhibit composite type of support, which leads to movement of the denture base under load application and transmission of high amount of stresses to the supporting structures.Aim: The current study was conducted to analyze the stress transmitted to the abutment teeth and the residual ridge by three types of RPDs of different materials; Conventionally manufactured metallic Co-Cr RPDs, and two thermoplastic RPD materials; Acetal (Polyoxymethylene; POM) and a modified PEEK (Poly-Ether-Ether-Ketone) material (BioHPP; Biocompatible high performance polymer) distal extension RPD frameworks both manufactured by computer aided design and computer aided manufacturing (CAD/CAM) system as two esthetic prosthetic materials. Methods: Strain gauge technology was used to assess micro-strains induced to the denture supporting structures for the three fabricated RPDs groups. Master casts of ten patients with mandibular bilateral distal extension (the remaining teeth extending from left 1st premolar to right 1st premolar) were used so that each cast was duplicated into 4 casts; three of these casts were used for manufacturing of acetal and BioHPP frameworks by CAD/CAM system, and conventional Co-Cr RPD frameworks. The fourth cast was duplicated to obtain acrylic cast with movable acrylic abutment teeth over which the three RPDs (two metal-free and one metallic RPDs) of each case were seated and tested. The microstrain of the supporting structures was recorded on bilateral and unilateral loading.Results: On bilateral loading: Mean value of microstrains recorded at the abutments was -63.75 and -18.75 at the ridge for Co-Cr group; For acetal group, it was -91.25 at the abutments and 18.94 at the ridge; For BioHPP group, microstrain was -106 at abutments, while it was 37.15 at the ridges. On unilateral loading: For Co-Cr group, microstrains recorded at right abutment was -52, while it was -6 at left abutment, and at right ridge it was -16.5 and -2 at left ridge; For acetal group, microstrains recorded at right abutment was -176 and -10 at left abutment, and at right ridge it was 17 and 4.5 at left ridge; For BioHPP group, microstrains recorded at right abutment was -284, while it was 10.5 at left abutment, and at right ridge it was 50.5 and 6.5 at left ridge.Conclusion: Co-Cr RPDs group showed the least stresses transmitted to the supporting tissues followed by Acetal RPDs, while BioHPP RPDs group showed the highest mean values of microstrain induced to the abutment teeth and the residual ridge.

Development of an RPD CAD system with finite element stress analysis

The structural design of removable partial dentures (RPDs) is critical for preventing distortion of the prosthesis, protecting abutment teeth and residual ridges as well as for high masticatory performance. The aim of this study was to clarify the feasibility and utility of a computer-aided designing (CAD) system with finite element analysis (FEA) for molar teeth arrangement in unilateral distal extension base RPDs. The shapes of artificial teeth and residual ridge were measured and converted into point group data. Solid models were created from surface-modelled point group data in a 3D surface CAD format. An occlusal rim was created on the residual ridge mucosa and the occlusal rim - residual ridge mucosa model with FEA function was created. Stress distribution on the residual ridge mucosa was compared by changing the loading point. The artificial teeth were then arranged in locations with the lowest amount of stress. After building an artificial teeth - saddle - residual ridge mucosa model, stress distribution in the residual ridge mucosa was re-evaluated by simulating occlusal force. On the occlusal rim - residual ridge mucosa model, stress was reduced when the loading point was located around the buccal shelf where functional cusps of artificial teeth were charted. It was confirmed that stress distribution in the residual ridge mucosa was equalized on the artificial teeth - saddle - residual ridge mucosa model. This system might be clinically useful tool for designing RPDs if FEA-guided designing of retainers and connectors can be added.

Load transfer characteristics of unilateral distal extension removable partial dentures with polyacetal resin supporting components

To photoelastically examine load transfer by unilateral distal extension removable partial dentures with supporting and retentive components made of the lower stiffness polyacetal resins. A mandibular photoelastic model, with edentulous space distal to the right second premolar and missing the left first molar, was constructed to determine the load transmission characteristics of a unilateral distal extension base removable partial denture. Individual simulants were used for tooth structure, periodontal ligament, and alveolar bone. Three designs were fabricated: a major connector and clasps made from polyacetal resin, a metal framework as the major connector with polyacetal resin clasp and denture base, and a traditional metal framework I-bar removable partial denture. Simulated posterior bilateral and unilateral occlusal loads were applied to the removable partial dentures. Under bilateral and left side unilateral loading, the highest stress was observed adjacent to the left side posterior teeth with the polyacetal removable partial denture. The lowest stress was seen with the traditional metal framework. Unilateral loads on the right edentulous region produced similar distributed stress under the denture base with all three designs but a somewhat higher intensity with the polyacetal framework. The polyacetal resin removable partial denture concentrated the highest stresses to the abutment and the bone. The traditional metal framework I-bar removable partial denture most equitably distributed force. The hybrid design that combined a metal framework and polyacetal clasp and denture base may be a viable alternative when aesthetics are of primary concern.

Effects of the Insertion of Unilateral Extension Base Removable Partial Dentures on the Amount of an Umami Component Eluted during Mastication

Purpose: The purpose of this study was to investigate the effects of the insertion of unilateral extension base removable partial dentures (RPDs) on the elution of umami components during mastication in Kennedy Class II cases.Methods: Rishiri kelp cut into 25 mm×25 mm pieces was selected as the test food. Eight patients with unilateral molar teeth defects were instructed to masticate samples for 50 strokes each, on the edentate side with RPDs, on the edentate side without RPDs, and on the dentate side. The amount of glutamic acid extracted from the samples was determined by spectrometry; the difference between the amounts of glutamic acid in the original and chewed samples was regarded as the amount intraorally eluted. The ratios of the amounts of glutamic acid eluted intraorally to that present in the original samples were compared among the groups.Results: Bonferroni-adjusted Wilcoxon matched-pairs signed-rank tests revealed a significant difference between the ratios of the amount of glutamic acid eluted intraorally from samples chewed on the edentate side with RPDs and that from samples chewed on the edentate side without RPDs and between the ratios of the amount of glutamic acid eluted intraorally from samples chewed on the dentate side and that from samples chewed on the edentate side without RPDs (P<0.017). There was no significant difference between the ratios of the amount of glutamic acid eluted intraorally from samples chewed on the edentate side with RPDs and that from samples chewed on the dentate side (P=0.48).Conclusion: Our results suggested that the insertion of unilateral extension base RPDs were useful for the elution of umami components during mastication.

Selection of a major connector for the extension-base removable partial denture

The selection of a major connector is not a difficult procedure if the dentist considers two important factors. The first is the degree to which the removable partial denture must be supported by structures other than the natural teeth. The second is the degree of rigidity required of the major connector to adequately distribute functional stresses from one side of the arch to the other.

Ten-year evaluation of removable partial dentures: Survival rates based on retreatment, not wearing and replacement

From a group of 1480 patients, 1036 were treated with metal frame removable partial dentures (RPDs) at least 5 years before this analysis. Of those, 748 patients who wore 886 RPDs were followed up between 5 and 10 years; 288 patients dropped out. The 748 patients in the study groups were wearing 703 conventionally designed metal frame RPDs and 183 RPDs with attachments. When dropout patients and patients who remained in the study were compared, no differences were shown in the variables analyzed, which indicated that the dropouts did not bias the results. Survival rates of the RPDs were calculated by different failure criteria. Taking abutment retreatment as failure criterion, 40% of the conventional RPDs survived 5 years and more than 20% survived 10 years. In RPDs with attachments crowning abutments seemed to retard abutment retreatment. Fracture of the metal frame was found in 10% to 20% of the RPDs after 5 years and in 27% to 44% after 10 years. Extension base RPDs needed more adjustments of the denture base than did tooth-supported base RPDs. Taking replacement or not wearing the RPD as failure criteria, the survival rate was 75% after 5 years and 50% after 10 years (half-life time). The treatment approach in this study was characterized by a simple design of the RPD and regular surveillance of the patient in a recall system.

義歯構造の相違がねじり強度に及ぼす影響

We have developed structural designs of three dimensional framework from a usual metal plate.The framework consisting of double structure was representative of the structural designs, with the intention of improved mechanical strength and durability.The purpose of this study was to investigate the effect of different structural designs on torsion strength by statical bending test, and to compare torsion stiffness of extension base removable partial denture by loading test on the simulation model.The results obtained were as follows:1. Torsion strength of the double structure was approximately 10 times that of skeleton types, and torsion stiffness was about 3 times.2. When torsion moment was applied, principal strain of the skeleton types increased remarkably, but the double structure did not show significant change.3. Distal displacement of the double structure increased approximately 20 μm by changing the loading point, but skeleton types increased 80-100 μm.

義歯の構造設計に関する実験的研究

Today the removable partial dentures are used as permanent prosthetic devices. Thus, their designs must be considered the prevention of breakage or deformation. A metal plate denture consisting of double structure has been designed with the intention of improved mechanical strength and durability. Principal investigations of this study were to introduce structural design techniques and apply them to denture design, to analyze the double structure using the finite element method, to judge reliability using a statical bending test, to compare the breaking strength of each structure, and to measure movement during function of mandibular extension base removable partial dentures on the simulation model. The summary of results is shown below: 1. Calculated values and experimental values were a fairly good approximation. 2. The reinforcement and Lightweight method of double structure was made evident. 3. Regarding the packing resins, METADENT was slightly superior in mechanical strength to ACRON. 4. Maximum stiffness of the double structure was approximately 7-10 times that of skeleton types, and breaking strength was about 9 times. 5. Tensile strain generated at the double structure was statistical less than for skeleton types. 6. When loads of 10 kg applied, the difference of distal displacement between double structure and skeleton types was between 70-80 microns. 7. The stiffness of the skeleton types decreased remarkably by shortening the denture flanges, but the double structure did not show significant change.

Enhanced retention for the distal extension-base removable partial denture using a heat-cured resilient soft liner

Replacement of the conventional heat-cured acrylic resin with a soft durable liner in the retromylohyoid eminence areas allows the patient to manipulate the distal extension-base mandibular RPD into place without traumatizing the soft tissue. With maximum coverage of the edentulous ridges, the semiflexible flange minimizes food entrapment and improves the retention and stability of the RPD. The procedure can be accomplished during the initial processing of the RPD or when relining the prosthesis. We have also used the technique for overdentures and for improving retention in the maxillary anterior extension-base RPD where anterior clasping was not esthetic or was insufficient.

The measurement of forces transmitted to abutment teeth of removable partial dentures

Despite the limited number of patients in the study, the following conclusions may be made regarding the magnitude and direction of forces transmitted to abutment teeth of extension-base removable partial dentures. 1. A technique was presented for using strain gauges to determine the magnitude and direction of forces transmitted to abutment teeth of removable partial dentures. 2. There are variations in force magnitude with a patient and between patients from chewing cycle to chewing cycle. 3. The transmitted forces vary when different removable partial denture designs are used. 4. Improving adaptation of the extension bases to the residual ridge is an excellent means for providing maximum support, increasing patient comfort, and decreasing forces to abutment teeth. 5. Extension bases apply mesially directed forces to abutment teeth during mastication. 6. Further research is needed to elucidate the effects of the various philosophies of removable partial denture design.

A combination impression and occlusal registration technique for extension-base removable partial dentures

The ultimate goal of a prosthodontic service is the placement and maintenance of prostheses which are in biologic and functional harmony with the supporting tissues and remaining teeth. The combination impression and occlusal registration technique minimizes clinical and technical procedures which might introduce errors. If accurately managed, this technique will provide optimum occlusion and mucosal support for extension-base removable partial dentures.

An analysis of mesial rest-I-bar clasp designs

The mesial rest-I-bar concept is the most important contribution to clasp partial denture design in the last 30 to 40 years. When used with discernment in situations where it is not contraindicated, it constitutes an excellent design for extension-base removable partial dentures. It has become the design of choice for an increasing number of dentists. Use of the three elements that make up the clasp assembly does not necessarily insure that the clasp will function as intended. There are situations for which it should not be used. Unless adequately adjusted after framework construction as well as during the maintenance program, the beneficial effects may be more imaginary than actual. Strict adherence to the mesial position for the rest is not rational for tooth-supported dentures and may be questioned for some extension-base prostheses (Fig. 17). I-bars have several advantages as direct retainers. However, no single type of retainer is applicable for all retentive situations, and other types should be selected where conditions are unfavorable for I-bar use. A framework which permits a slight amount of movement toward the edentulous residual ridge is an important consideration in design of extension-base removable partial dentures, particularly for those of the mandibular arch. However, compromise of this principle is sometimes necessary to satisfy other design requirements. Design of the framework is only one of the factors that contribute to a successful removable partial denture. Of at least equal importance is the adequacy of support provided by the denture base and the nature of the occlusion. If meticulous attention is directed to these two factors, the forces transmitted to the teeth through the framework can be kept to a minimum and within physiologic tolerance. Conversely, neglect of these considerations may cause a framework of any design to become destructive.

The efficiency of an indirect retainer

1 wo reports of recent prosthodontic research have dealt specifically with indirect retainers, but only in a general way. I, 2 Several other articles have mentioned indirect retainers as they relate to the design of an entire prosthesis”-“’ or their relative effect on abutment tooth movement.“-‘* Most reports4-1f1 that mention indirect retainers cite one or more of the following general principles: ( 1) They are needed in extension-base removable partial dentures; (2) they should be located as far from the primary fulcrum line as possible; (3) they should be placed on a positive rest seat, especially if on an anterior tooth; (4) they help in resisting rotational movement of the denture base away from the ridge and lateral movement of the restoration; and (5) they can take the form of an auxiliary occlusal rest, cingulum rest, embrasure hook, secondary Kennedy bar, or linguoplate. Few, if any, of the reported functions of indirect retainers have been studied, nor has their efficiency-particularly as it relates to resting on anterior teeth. The purpose of this study was twofold : ( 1) t o investigate the efficiency of indirect retainer design as it relates to anterior teeth and (2) to determine if the type of direct retainer design has any effect on the efficiency of indirect retainers.

RPI (Rest, Proximal Plate, I Bar) Clasp Retainer and Its Modifications

A clasp design that can be employed for abutment teeth on extension base removable partial dentures has been presented. The clasp referred to as an RPI clasp retainer minimizes tooth coverage and reduces stress on the abutment tooth. This same design may also be used to advantage on all toothborne removable partial dentures.

Selection of a major connector for the extension-base removable partial denture

Selection of a major connector for the extension-base removable partial denture

Clasp design for extension-base removable partial dentures

A clasp design that can be employed for abutment teeth on extension-base removable partial dentures has been presented. The clasp, referred to as an R.P.I. clasp, minimizes tooth coverage and reduces stress on the abutment tooth.

Occlusal requirements for removable partial dentures

This article discusses a philosophy of occlusion, its mechanism, and its effects in removable partial denture construction. It suggests that: 1. The support for an extension base removable partial denture must be distributed between both the residual ridge and the remaining teeth so that neither is individually overloaded. 2. Many factors must be considered to keep the occlusal work load transmitted to the alveolar bone within minimal limits so that it does not exceed the tissue tolerance of the host. The occlusion is one of the most important of these. 3. Different occlusal requirements exist in different removable partial denture situations. Balanced occlusion is required against dentures, and centric occlusal contact only is required when sufficient natural teeth remain to supply occlusal guidance through the full range of mandibular movement. 4. The potential to destroy alveolar support by exceeding the host's tissue tolerance appears to be greatest when a mandibular extension base removable partial denture opposes a maxillary complete denture, because the settling of the maxillary denture creates destructive occlusal forces. 5. Opposing natural teeth should be made to harmonize with the patient's mandibular movements before constructing removable partial dentures. 6. Different occlusal situations require the use of different materials in the occlusal surfaces of the teeth. 7. An extension base removable partial denture should not move under any bruxing occlusal load that the patient is capable of applying.