Mesial Rest Research Articles

Evaluation of Incorporating Bracing Arm in Precision Attachment Evaluation of Incorporating Bracing Arm in Precision Attachment Unilateral Removable Partial Denture

Purpose: This Randomized Control Trial study aimed to compare between two designs of Precision Attachment Unilateral Removable Partial Denture, one conventional design and the other modified with bracing arm and mesial rest. Materials and Methods: twenty male patients having Kennedy Class II mandibular edentulous ridges received the two designs in a split mouth study for a follow-up period of eighteen months. Probing Pocket Depth around abutment was measured. A standardized radiographic technique was used to evaluate bone height changes. Results: The results showed insignificant pocket depth and bone height changes in the two groups. Conclusion: Precision Attachment Unilateral Removable Partial Denture proved to be a viable treatment therapy in treating unilateral edentulous ridges

Stress distribution and patient satisfaction in flexible and cast metal removable partial dentures: Finite element analysis and randomized pilot study

PurposeTo compare stress distribution in polyacetyl based flexible RPD (FRPD) with cast metal RPD (CRPD) by using three-dimensional finite element analysis (FEA) and patient satisfaction by using OHIP-14 questionnaire in participants with Kennedy's class I partially edentulous mandibular arch rehabilitated with CRPD and FRPD. Material and methodsFor FEA, 3D models of Kennedy's class I partially edentulous mandibular arch, CRPD in chrome-cobolt alloy, and polyacetyl based FRPD were geometrically modelled and subjected to a vertical load of 100 ​N bilaterally. The in vivo comparison of satisfaction was assessed by enrolling 22 participants with Kennedy's class I partially edentulous mandibular arch. After randomization, 11 participants were rehabilitated by CRPD (group C), and 11 participants by polyacetyl based FRPD (group F). OHIP-14 questionnaire in Hindi language was filled at 1 week and 1 year after denture insertion. ResultsVon Mises stress distribution in CRPD was maximum in mesial rest seat of the primary abutment (100 ​MPa) and minimum for edentulous ridge (7 ​MPa on bone and 6 ​MPa on mucosa). Von Mises stress distribution for polyaccetyl based FRPD was maximum in ridge (25 ​MPa) and minimum in periodontal ligament of the second premolar (3 ​MPa). Patient satisfaction in group F was significantly more than in group C at end of 1 year (P ​= ​.0158). ConclusionFRPD is useful in periodontally compromised abutment teeth and CRPD in resorbed ridge conditions. Patient satisfaction is more with polyacetyl based flexible RPD when compared with cast metal RPD at the end of 1 year.

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

The effects of loading locations and direct retainers on the movements of the abutment tooth and denture base of removable partial dentures.

The purpose of this study was to evaluate the degree and amount of movement of the abutment tooth and denture base influenced by the direct retainer of distal extension removable partial denture and the location of functional loading, then to suggest direct retainer design with minimal adverse effect and with optimum functional loading location for residual tissue. The displacement of the abutment tooth and inclination of the denture base were determined, with 30 N as work load utilizing simulation model and strain gauge system, about two types of direct retainers with mesial or distal rest and nine loading points on denture base. Displacement and inclination was determined with the one-way analysis of variance and Scheffe's multiple test was performed. The results revealed that type of direct retainer influenced on the magnitude rather than direction of the abutment tooth displacement. The distal displacement of abutment tooth was significantly less in Type M clasp (with mesial rest and connection) than in Type D clasp (with distal rest and connection) (p<0.05). The location of loading points influenced both of the magnitude and direction of the abutment tooth and denture base movement. Posterior and lingual loading resulted in significantly distal displacement of abutment tooth (p < 0.05).

Prosthetic reconstruction with an obturator using swing-lock attachment for a patient underwent maxillectomy: A clinical report.

Patients who underwent resection of maxilla due to benign or malignant tumor, or accident will have defect in palatal area. They get retention, support and stability from remaining tissues which are hardly optimal. The advantage of swing-lock attachment design is having multiple contacts on labial and lingual side of the abutment teeth by retentive strut and palatal bracing component. Because the force is distributed equally to abutment teeth, abutment teeth of poor prognosis can be benefited from it. It is also more advantageous to cover soft tissue defects which are hard to reach with conventional prosthesis. A 56-year-old female patient who had undergone a maxillectomy due to malignant melanoma complaining of loose and unstable surgical obturator. Surveyed crowns were placed on #12, 26, and 27. Teeth #11, 21, 22, and 23 had lingual rest seat and #24 had mesial rest seat to improve stability and support of the obturator. This clinical report presents the prosthetic management of a patient treated with obturator on the maxilla using swing-lock attachment to the remaining teeth.

New Clasp Assembly for Distal Extension Removable Partial Dentures: The Reverse RPA Clasp.

Several clasp types are used in distal extension removable partial dentures. In some cases the terminal abutments have only distal retentive undercuts that can be occupied by bar clasps; however, bar clasps may be contraindicated with no suitable alternative. This article presents a reasonable solution by introducing a new clasp design as a modification to the well-known RPA clasp. The design includes a mesial rest, proximal plate, and buccal retentive arm arising from the rest and extending to reach the distal retentive undercut.

The RPH Clasp Assembly: A Simple Alternative to Traditional Designs

One of the popular designs for the distal extension partial removable dental prosthesis is the RPI clasp assembly. A modification of the RPI clasp assembly is introduced. It incorporates a mesial rest (R), proximal plate (P), and a horizontal retentive arm (H-RPH). This clasp assembly provides benefits of the RPI clasp and can be used in clinical situations where the RPI clasp is contraindicated.

Implants in conjunction with removable partial denture

The benefits of implant supported overdenture are readily apparent for the fully edentulous patients and have been well documented, however, there is deficiency of the studies regarding the combination of implants with removable partial dentures for partially edentulous patients. The purpose of this article is to review the literature concerning implants with removable partial dentures and evaluate the evidence for this clinical approach. Through many clinical case reports and studies we have searched from a broad variety of journals, we present the six considerations needed to contemplate respecting implants with removable partial denture in partially edentulous patients. First, the connection between abutment tooth and removable partial denture has to be rigid and the link between implant and removable partial denture should be hinged. Second, a mesial rest acts better in the point of force distribution for distal extension removable partial denture and splinting between implants is also a favorable choice. Third, T bar has an advantage for implants which are used as abutments in distal extension removable partial denture. Forth, as we all known functional impression is better way to reproduce movement for distal extension removable partial denture. Fifth, indirect retainer and guiding plane on the proximal surfaces of terminal abutment teeth are important in preventing denture base lifting. Sixth, implants in conjunction with removable partial denture is superior in the esthetic and phonetic as well as cost-effective point of view. We also suggest that which place we should install implants for force distribution and which diameter and length of implants should be used. in this review article, we recommend to locate the implant near of the abutment tooth for esthetics or near of first molar position for good stress distribution. The diameter and length of implant also influence to stress distribution. When we compare to conservative partial denture, patients go for removable partial denture using implants due to convenience, better support and retention according to several studies. But it is true that we need to study more on this subject and collect long term follow up cases before we discuss on it. So it is enough to bring this subject into the surface of prosthetic treatment by this article.

Development of in vivo measuring system of the pressure distribution under the denture base of removable partial denture

To develop a system to measure the pressure distribution under the base of a removable partial denture (RPD) and to apply it in vivo. A tactile sensor sheet with 100 sensing points and a measuring system (I-SCAN, Nitta, Osaka, Japan) were used. The sensor was calibrated before being applied in vivo. A subject with a mandibular RPD (Kennedy class II, division 1) participated in this study, and the RPD was duplicated as the experimental denture. The basal surface at distal extension was accommodated to the sensor in a manner similar to direct relining. Measurements were performed with three patterns of occlusal rest design (mesial and distal rests, mesial rest only, and without a rest) during maximal voluntary clenching (MVC) and gum chewing. The calibration measurements showed that the output value from each sensing point and total output of sensing points were positively correlated with the applied load. The pressures recorded in vivo varied depending on the locations of sensing points on the basal surface of the denture. During MVC the pressure distribution changed with the clenching level, and the highest pressure was registered near the residual ridge crest. The pressure distribution also changed according to the number of occlusal rests. The load center shifted about 2mm during MVC and about 4mm during gum chewing. The measuring system developed here enabled us to measure the pressure distribution under the denture base of RPD. The pressure distribution varied along with the design of the occlusal rest.

Load on Abutment Teeth and Displacement of Denture Base in Unilateral Distal-Extension Removable Dentures

Objectives: The purpose of this study was to determine the mechanically appropriate retainer design for unilateral distal-extension removable dentures.Methods: Two models were constructed, each with a different design of retainer placed on the first and second mandibular premolars. Each model was composed of bone, denture underlying mucosa, retainer and denture base. In design A, Akers clasps were set on the first and second premolars, and in design B, an occlusal rest and back-action clasp with mesial rest were set on the first and second premolars, respectively. Loading on the occlusal surface of the denture was performed in the vertical and oblique directions. Load on the abutment tooth and displacement of the denture base were determined by 3-dimensional finite element analysis.Results: Load on the abutment tooth in the vertical direction caused by vertical loading on the denture was lower in design B than in design A. No large difference in displacement of the denture base was observed between design A and B. Load on the abutment tooth both in the vertical and buccolingual direction induced by loading on the denture in the lingual and buccal directions was lower in design B than in design A. However, displacement of the denture base in the vertical and buccolingual directions induced by loading on the denture in the lingual direction was higher in design B than in design A.Conclusion: In this study, displacement of the denture base was smaller in design A than in design B, so design A would be more useful clinically than design B, but the abutment tooth would require greater support.

903 高度な顎堤吸収を持つ下顎両側性遊離端義歯・支台歯とその周辺組織のインプラント支持による荷重伝達特性(J04-1 臨床医歯学における非・低侵襲計測技術の展開(1) 歯科・整形外科における計測および生体シミュレーション,ジョイントセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The purpose of this study was to photoelastically compare the load transfer characteristics of a distal extension RPD with implant assisted support in the posterior of a mandible with an atrophic edentulous ridge. The model included the anterior teeth and the first premolars bilaterally. Threaded implants, 3.75mm diameter 7mm length, were embedded 20mm distal to the first premolars on the posterior edentulous ridges. I-bar partial dentures with mesial rests were fabricated and physiologically adjusted to the models. The implant support conditions tested were healing abutments and 3mm ball attachments. Simulated vertical and lateral occlusal loads were applied at the first molar position and the stress developed in the abutment teeth were monitored photoelastically. Posterior implants with both healing abutment and ball attachments in the posterior of a mandible tended to assist support of a distal extension RPD and produce only low level stresses in the supporting atrophic edentulous ridge.

Clinical evaluation of abutment teeth of removable partial denture by means of the Periotest method

Prosthodontics should be one of the means of establishing conditions for the maintenance of periodontal health. The forces applied to the abutment teeth and their effects are very important considerations in the design and construction of the removable partial dentures. This 6-month follow-up clinical study evaluated the degree of mobility of abutment teeth of distal extension and tooth supported removable partial dentures by using Periotest. Two types of clasp design were selected for evaluation. In cases with unilateral and bilateral distal-extension, a clasp design including a T clasp of Roach retentive arm, a rigid reciprocal arm and a mesial rest were used. For the abutments of tooth-supported removable partial dentures, a second clasp design with a cast circumferential buccal retentive arm, a rigid reciprocal clasp arm and a rest adjacent to the edentulous ridges was selected. A total of 68 abutment teeth was analysed. Periotest values were made at the time of denture placement (control) and at 1, 3 and 6 months after the denture placement. The statistical analysis was performed using Friedman test. All analysis was performed at a 0.05 level of significance. The results revelled that no significant changes in tooth mobility were observed during the 6-months follow-up (P > 0.05). In conclusion, our findings suggest that adequate oral hygiene instructions, careful prosthetic treatment planning and regular recall appointments play an important role in preventing changes in abutment tooth mobility caused by removable partial denture placement.

An in vitro study of dentin exposure during resin-bonded fixed partial denture preparation

Objectives The aim of this in vitro study was to investigate whether dentin is exposed during tooth preparation for resin-bonded fixed partial dentures and, if so, to quantify the amount of dentin exposure. Method and materials Twenty extracted premolars were prepared in the following manner: The palatolingual and proximal axial surfaces were reduced by 0.50 mm. Mesial and distal grooves, 1.00 mm in depth, and mesial and distal occlusal rest seats, measuring 2.00 mm buccolingually × 1.50 mm mesiodistally × 1.00 mm deep, were prepared. The specimens were stained with a modified van Gieson's stain to identify dentin exposure, mounted on a jig to allow standardization, and photographed after 30-degree rotation to create a panoramic image of each tooth. The image was modified and analyzed to measure the percentage of the preparation area that exhibited dentin exposure. Results Dentin exposure was noted in all specimens. The mean area of dentin exposure was 11.06 mm 2 (16.15% of the preparation area). The minimum and maximum areas of dentin exposure were 4.07 mm 2 (7.03%) and 19.73 mm 2 (27.28%), respectively. Conclusion Dentin is exposed during resin-bonded fixed partial denture preparation if current tooth preparation guidelines are followed, despite the commonly made recommendation that the preparation remain within enamel. The region of the grooves consistently exhibited exposed dentin; exposure at the cervical margin was variable. — Reprinted with permission of Quintessence Publishing.

The mandibular first premolar as an abutment for distal-extension removable partial dentures: a modified clasp assembly design

Sound mandibular first premolars can be used as sole abutments for bilateral distal-extension removable partial dentures, if the denture is designed to minimise the torque applied to the abutment teeth. A simplified modification of the conventional torque-releasing clasp-assembly designs is suggested for these teeth. This modification entails a mesial rest on each abutment tooth connected to the distal proximal plate via a lingual bracing arm. A circumferential clasp arm is optional for buccal retention of the removable partial denture. As with conventional designs, the metal framework is designed to permit some rotational tissueward movement of the distal extension bases, yet not compromise the retention and stability of the prosthesis.

レストの設定位置および形態が支台歯の挙動に及ぼす影響 : Kennedy II 級義歯模型における中間欠損側負荷時の作業側・非作業側支台の挙動分析

The purpose of this laboratory study was to examine seven types of rests to determine through the abutment tooth movements which type transmits forces to abutment teeth in the most favorable manner. An acrylic resin/ silicone rubber simulation model of a Kennedy class II modified 1 mandibular arch with missing teeth (right second premolar and first molars, and left first and second molars) which permitted tooth movement and ridge displacement was constructed. The behaviors of abutment teeth were measured by using digital laser displacement sensors and the measured values were reciprocally compared through the statistical analysis. The results obtained were as follows : 1) On comparing the occlusal mesial rest (design 2) and the mesiodistal rest extended to the mesial tooth (design 3) with the most basic occlusal distal rest (design 1, control), the design 2 had a tendency to be smaller, and the design 3 the smallest in inclination of the abutment tooth. Also, in twist-like movement, the designs 2 and 3 were significantly smaller (99.9 per cent confidence level) than the design 1. 2) On comparing design 4 for which the rest of design 1 was extended to mesial fossa and design 5 for which the rest of design 1 was extended to the mesial margine with the design 1, the designs 4 and 5 were significantly smaller than the design 1 in inclination and twist-like movement of the abutment tooth (p<0.001). However, an analysis of variance (95 per cent confidence level) showed no significant difference in movement between the design 4 and the design 5. 3) On comparing design 6 for which the rest of design 1 was moved to near the cervical portion with the design 1, inclination and twist-like movement of the abutment tooth with the former were significantly smaller than those with the latter (p<0.001). 4) On comparing design 7, the onlay type of rest, with design 1 in inclination and twist-like movement of the abutment tooth, the former showed significantly smaller values than the former (p<0.001). 5) On comparing with design 1, the others showed no significant difference in depression of the abutment tooth, but significantly smaller values in parallel movement (p<0.001). 6) Displacement of the abutment tooth (〓) on the non-working side was smaller than that the on the working side (〓) in all designs. On the basis of the foregoing findings, this study comfirmed that displacing the occlusal distal rest which is the typical type to occlusal mesial portion, and extending it to the mesial direction, and lowering it to near the cervical portion enabled a great reduction in inclination and twist-like movement which are said be most hazardous to the abutment tooth.

A randomized clinical trial of two basic removable partial denture designs. Part II: Comparisons of masticatory scores

Statement of problem. There is no known data on the functional efficacy of different removable partial denture designs. Purpose. This randomized clinical trial compared the masticatory performance of two commonly used designs in 118 patients who needed a unilateral or bilateral mandibular partial denture. Material and methods. One half of the patients received a partial denture with distal occlusal rests and cast circumferential clasps and the other half a partial denture with mesial rests and I-bar cast clasps. The left side, right side, and swallowing threshold masticatory tests were made with peanuts and carrots before treatment and 16 weeks after the prosthesis insertion (baseline) and thereafter at 6, 18, 36, and 60 months. Results. Masticatory scores at entry were higher in the circumferential design group, but the only significant ( p < 0.05) difference was found in the right side carrot performance. Both groups realized significant improvements ( p < 0.001) in all performance scores with partial dentures. Mean improvements of 24.7 with peanuts and 35.8 with carrots in the right side performance scores and 19.0 in the swallowing threshold score with peanuts in the bar design group were significantly higher ( p = 0.017) than the respective mean improvements of 15.9, 21.4, and 5.6 in the circumferential design group. However, no significant differences were found between the two groups for any of the 10 performance scores at baseline. Conclusions. Despite some performance differences at entry, the mean performance scores for the two groups became similar at baseline and at subsequent intervals. (J Prosthet Dent 1997;78:15-21.)

有限要素法による遊離端義歯の力学的研究 第２報 レストの設定位置と顎堤粘膜の被圧変位性の違いによる応力分布への影響

The purpose of this study is to investigate the denture design and displaceability of residual ridge mucosa and its relation to the load distribution on the remaining oral structures. In this study, the effects of the location of rest and displaceability of the mucosa were demonstrated utilizing the two-dimensional non-linear analysis reported on Part 1. The results were as follows. 1. Mesial rest could be simulated on the finite element model using pin element. 2. Removable partial denture with mesial rest distributed more stress on the mesial abutment teeth than that with distal rest. 3. Lesser displaceability of residual ridge mucosa resulted in a decrease of stress concentration around the most distal abutment and the uniform stress distribution on residual ridge was increased. 4. In the simulated condition where an increased pressure was applied on the mucosa, the behavior of the saddle on the mucosa with large displaceability could be similar to that of the mucosa with small displaceability. The results of this study suggested that mesial rest on the most distal abutment and pressure impression was desirable in removable partial denture with distal-extension.

間接維持装置が義歯床と鈎歯の変位に与える影響 ＩＩ Ｃｒｏｓｓ Ａｒｃｈ Ｓｔａｂｉｌｉｚａｔｉｏｎのための間接維持装置の形態，配置について

The purpose of this experimental study is to investigate and evaluate characteristic movements of the denture bases and the abutment teeth, when the forms and locations of the indirect retainers used for the cross arch stabilization are altered. The results are as follows: 1. Under the vertical forces, the increases of abutment tooth excursion and denture base movement are observed, when the fulcrum line crosses the "loading axis" at nearly right angle. 2. When the vertical forces are applied, the displacements of abutment tooth and denture base with two indirect retainers are more reduction than that with one. 3. The distances between two indirect retainers used for cross arch stabilization increase, the less displacements of abutment tooth and denture base are. 4. When the partial denture has only one indirect retainer used for the cross arch stabilization, it is important that the positive rest is located on the anterior tooth and the indirect retainer is placed on as distal tooth as possible. 5. If the occlusal forces are supported by the residual ridge, it may be better designs that the positive rest is located on the anterior tooth and the Akers clasp with mesial rest or the double Akers clasp is located on the premolars.

The effects on function of distal-extension removable partial dentures as determined by occlusal rest position

The mesial rest may be an excellent method of reducing unfavorable occlusal forces acting on the abutment tooth. However, when anatomic conditions and therapeutic necessity require alternatives, the distal rest may be used. The use of the distal rest demands that additional procedures be used to reduce the occlusal trauma to the abutment tooth.

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.