RPA clasp design for distal-extension removable partial dentures

The RPA design has been discussed as an alternative to the RPI design. With its mesial rest and special retentive arm design, it gives essentially the same kind of tooth release that the RPI clasp provides. In addition, there are some advantages over the RPI design. The circumferential-type retentive arm is easier to grasp for removal of the prosthesis. The clasp is simple in design with few variations among patients and thus can be easily and consistently fabricated by dental laboratories. But most important, the circumferential retentive arm avoids the tissue problems around abutment teeth and allows the RPA clasp to be used in many situations where the RPI clasp is contraindicated.     

Magnetizable abutment crowns for distal-extension removable partial dentures

A study of the retention and load-distributing characteristics of bilateral distal-extension dentures with magnetizable abutment crowns revealed the following findings: Comparable retention was obtained with the horizontal and oblique pedestals. Decreased retention was noted when there was space between the magnet and pedestal. The retention values were substantially higher than reported values for the I-bar retainer. For the space and no-space situations, the horizontal pedestal design provided better stress results than the oblique design. Better stress-distributing properties for horizontal and oblique pedestals were obtained with the presence of a space between the magnets and pedestals. Of all the designs tested, the horizontal pedestal with a space demonstrated the best load-transmission characteristics.     

A modified direct retainer design for distal-extension removable partial dentures

The rationale for designing a direct retainer for a distal-extension removable partial denture is described. The advantages of an L-bar clasp arm over the I-bar clasp arm are discussed. The retentive surface of an abutment tooth is divided into three zones according to the clasp tip movement and the importance of placing the retentive tip in the zone of vertical movement is emphasized.     

Direct retainers for distal-extension removable partial dentures

Clinical observations at the University of Washington indicated that the wrought wire clasp assembly, the I-bar clasp assembly, and the L-bar clasp assembly yield similar results. A periodic recall system for patients with removable partial dentures has been in effect since 1976. Several thousand observations have been made by the faculty, and no special trend of problems has been noted that would cause one clasp assembly to be favored over another. These three types of clasp assemblies work satisfactorily when properly chosen and carefully applied.     

RLS--the lingually retained clasp assembly for distal extension removable partial dentures

The design of clasp for a distal extension removable partial denture that helps preserve both the abutment teeth and the tissues of the edentulous ridge is described. The clasp assembly takes advantage of surveyed lingual undercuts to provide support, retention, and stability. It consists of a mesio-occlusal rest, a distolingual L-bar direct retainer that is located on the abutment tooth adjacent to the residual ridge, and a distobuccal stabilizer (RLS).     

Semiprecision rest system for distal-extension removable partial dentures

The history of the nonlocking type of intracoronal semiprecision rest has been traced from its origins with Neurohr in 1930, up to its present use as the Thompson dowel rest. The advantages of the use of this deep rest design and the clasp arm design for primary retention have been discussed. The Blatterfein modification of the lingual clasp arm has been introduced to overcome the problems of breakage and lack of stabilization which are present with the Thompson, Van Dam, and Wands designs.     

Influence of clasp design of distal extension removable partial dentures on the periodontium of the abutment teeth

Three removable partial denture designs were investigated to determine the effect of minor connector configuration on the periodontal health of abutment teeth. Twenty-five patients wore three different removable partial dentures for 19 weeks each. The first removable partial denture placed a tilting force on the abutment teeth; the second was stress-releasing; and the third collected the least amount of plaque. Plaque accumulation, the condition of the periodontium, migration of the abutment teeth, deformation of the clasp arms, retention of the prosthesis, and patient preferences were assessed. The results demonstrated that the partial denture retentive design did not affect plaque formation. The prosthesis designed to place a tilting force on the abutment teeth appeared to cause the least mobility and migration of the abutments and had the greatest acceptance by the patients.     

A two-stage impression technique for distal-extension removable partial dentures

Partially edentulous mouths with distal-extension ridges present the challenge of correctly registering two tissues as dissimilar as teeth and edentulous ridges. A technique is described that makes it possible to make impressions with a combination of different impression materials within the same tray and have a firm support that assures even distribution of the impression material and faithfulness of reproduction.     

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

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

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.     

The effect of various clasping systems on the mobility of abutment teeth for distal-extension removable partial dentures.

Three clasping systems were placed in five patients, and measurements of abutment tooth mobility were made. These data were compared to previously established baselines and statistically analyzed. The findings of the study are: 1. There was no difference in abutment tooth mobility during the 4-week test period with each of the three clasping systems. The important factor may have been the fit of the distal-extension denture base over the residual ridge, which provides the stability to prevent increases in abutment mobility. 2. Any mobility increases were in a buccal direction only, or toward the flexible retentive clasp arm. There was never any change in lingual mobility. 3. All five patients chose the I-bar retainer as the design of choice due to its increased resistance to dislodgment. Periodic recall of distal-extension removable partial denture patients is mandatory to ensure proper stress distribution and prevent increases in abutment tooth mobility.     

Motion vector analysis of an abutment for a distal-extension removable partial denture: A pilot study

An investigation was conducted on the effect of various rest-clasp designs on abutment tooth movement when a testing prosthesis was subjected to vertical loading of the bilateral distal-extension base. The results did not reveal statistically significant differences among the rest-clasp designs tested. Variations in rest placement and/or clasp design had an effect on the magnitude and direction of force transmission to, and resultant movement of, the abutment tooth.Less force to the abutment tooth was recorded when a mesial rest was used with the rest-clasp designs as compared to a distal rest. Force transmission to the abutment was found to be greater when the vertical load was applied to the denture base on the same side than when applied to the opposite side of the denture base.     

Factors that augment the role of direct retainers in mandibular distal-extension removable partial dentures

Several features of RPD design that augment direct retainer design were identified. They are as follows: 1. The duplication of direct retainer function by other prosthesis components 2. Physiologic adjustment of the framework to assure contacts with abutment teeth that are consistent with the design and intended functions of the components and that transfer stress in a manner those teeth are designed to accept 3. Intimate adaptation of denture bases to the residual mucosa, with recall visits to monitor this adaptation 4. Specific loading of the denture bases through selective placement of artificial teeth 5. Splinting of abutment teeth     

Attitudes toward abutment preparation for removable partial dentures

A questionnaire was sent to 58 dental schools to determine what type of abutment preparation is being used in conjunction with removable partial dentures. Responses from 43 schools indicate that enamel modification and cast restorations are still the primary type of abutment preparations. Amalgam alloys are widely used, and composite and acid-etched retained restorations are also being used.