Direct Retainers Research Articles

Use of the University of Barcelona gauge in the design of direct retainers

Use of the University of Barcelona gauge in the design of direct retainers

片側性遊離端義歯の直接維持装置が荷重時にかぎ歯および歯槽骨に与える影響 三次元光弾性実験による応力解析

A photoelastic stress analysis technique has been conducted for many years as a test to analyze the stress distribution of the abutments and the alveolar bone under a load. The purpose of this study was to investigate the stress distribution of the abutments and the alveolar bone produced by the direct retainers of unilateral distal-extension removable partial dentures under a static load. Three types of direct retainers (R. P. I., Akers and Double Akers) were chosen, since they were frequently used in clinical case.In the case of R. P. I., a load was transmitted vertically to the abutment and the alveolar bone. And the value of internal stress around the second premolar root apex was greatest. When Akers was applied, it forced the second premolar to lean distally. And the value of internal stress of the mesial bone near the second premolar root apex was greatest. Furthermore, when Double Akers was applied, it forced the premolars to lean distally, but a load was distributed vertically to the abutments and the alveolar bone. And the value of internal stress around the each premolar root apex was least. And the value of internal force under the denture tended to be least.

維持装置のこう腕がこう歯歯根膜に与える影響

Restoration of an edentulous space with a removable partial denture presents various problems of the design of a retainer set on a distal molar, when the molar shifts in angle or position. The two-dimensional finite element technique was used to analyze the design factors of the retainer's arm influencing the periodontium of an abutment tooth, for a direct retainer being set on a tilted molar.The results obtained are as follows:1. When only a retentive arm is used, the von Mises stress of the periodontium increases as the shifted position or angle of a retentive tooth increases.2. When both retentive and reciprocal arms are properly located, von Mises stress is less than what with the retentive arm only. It is suggested that the reciprocation is effective for the stress -relaxation of the periodontium of a abutment tooth.3. When both retentive and reciprocal arms are properly located and a retentive force is equal to a reciprocal one, the value of von Mises stress is within 0.10 kg/mm2.4. Effective design factors of a retainer's arm for the stress relaxation of the periodontium are suggested.

Prosthetic restoration of the anterior edentulous space

The dentition of partially edentulous patients with an anterior modification space may be restored in several ways. If a removable partial denture is selected as the treatment of choice, denture tooth selection, direct retainer display, and anteriorposterior rotation may be sources of concern for the patient and dentist. A way to overcome the treatment problems associated with these partially edentulous patients is use of a Hader bar and clip-retained removable partial denture with the attachment of an anterior porcelain-fused-to-metal facade. This article describes this treatment option and the technique for fabrication.

An analysis of rotational movement of asymmetrical distal-extension removable partial dentures

An axis of rotation is created through the most distally placed occlusal rests when a distal-extension removable partial denture is loaded. If the residual ridges are of unequal lengths, this axis of rotation may not be perpendicular to the residual ridges. The resultant movement of asymmetric denture bases and their effect on the tissues are discussed. Movement of I-bar retainers located on the mesiobuccal aspect of asymmetrical abutment teeth may torque the abutment teeth as the denture base moves tissueward. Use of L-shaped direct retainers on the distobuccal surveyed undercut will create a more favorable class II lever effect on the abutment tooth.

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. 1. The duplication of direct retainer function by other prosthesis components 2. 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. 3. Intimate adaptation of denture bases to the residual mucosa, with recall visits to monitor this adaptation 4. 4. Specific loading of the denture bases through selective placement of artificial teeth 5. 5. Splinting of abutment teeth

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.

Esthetic placement of bar-clasp direct retainers

A technique has been described that will allow for the esthetic placement of artificial teeth by precisely controlling the location of the approach arm of the I-bar clasp.

床下粘膜の負担圧に関する基礎的研究 下がく両側遊離端局部床義歯における直接維持装置およびレストの影響について

The present study concerns the effect of differences in the type of direct retainers and in the arrangement of rests on the distribution of pressures under dentures. A model with both mandibular molars missing (Kennedy classification of partial dentures-Class I) was prepared. Then two types of direct retainers, one using the Krol type R.P.I.clasp and the other using the Kratochvil type R.P.I.clasp, were selected.Then three types of rests were prepared.Then the pressures under dentures were measured and the conclusions presented below were obtained.1.Between the direct retainer and rest, the direct retainer tended to exert greater effect on the pressures under dentures.2.Between direct retainers, the Krol type R.P.I.clasp tended to show greater pressures than the Kratochvil type R.P.I.clasp.3.In the effect of differences in the rest arrangement, the smaller the number of rest, the greater the effect on the pressures.4.In case of the fabrication of partial dentures against the mandibular bilateral distal extention case, the combination of the use of the direct retainer as the Kratochvil R.P.I.clasp and arrangement of the rests on the mesial side of the occlusal table of the second premolars on both sides and on the mesial and distal side of theocclusal table of the first premolars on both sides was suggested to be clinically the best design from the viewpoints such as distribution and uniformity of the pressures under dentures.

Rotational path removable partial denture design

A detailed description of a rotational path of insertion design for removable partial dentures has been presented. By minimizing the use of conventional clasps, this technique offers some advantages. Rotational path designs may minimize adverse periodontal response to a removable partial denture by reducing plaque accumulation and may be applied in esthetically demanding situations. The design concept involves the use of rigid retentive components that gain access to undercut areas through a rotational path of insertion. These rigid components satisfy the basic requirements of conventional direct retainer design.

A study of the flexibility of wrought wire clasps

T he 18-gauge platinum-gold-palladium (PGP) wrought wire clasp arm is often used as a direct retainer for distal-extension removable partial dentures instead of a cast chromium-cobalt clasp arm, when the retentive undercut is on the mesial-buccal part of the abutment tooth. The wrought wire clasp arm can flex in any direction so that stresses caused by movement of the removable partial denture are dissipated. This helps to protect the abutment tooth from harmful forces. The 18-gauge PGP clasp wire has a fusing temperature sufficiently high that it can be safely cast against by gold and some chromium-cobalt alloys and soldered without changing its physical properties. An 18-gauge clasp wire is thick enough to resist breakage and allow tapering for additional flexibility.’ However, clinical observations of some wrought wire clasps on removable partial dentures constructed at the School of Dentistry, University of Washington, have indicated that these clasps may be less flexible than expected. Several reports in the dental literature have documented similar findings.

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 rests 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).

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.

An analysis of stress distribution in the free-end saddles on the mandibular model.

This experiment was designed to investigate and evaluate the characteristic behavior of mandibular free-end saddle removable partial denture using various retainers. The abutment tooth displacement and saddle movement were measured while a known vertical force was applied on the saddle. Fifteen different types of free-end saddle dentures were tested, using four various types of prefabricated attachments. Strain-measuring devices were used to measure the extent of abutment tooth displacement and saddle movement. The findings were as follows: 1) The force transmitted to the abutment tooth and the residual ridge were affected by (a) the selection of direct retainers, (b) splinting of abutment teeth, and use of indirect retainers, and (c) the variation in size and shape of the occlusal table on the saddle. 2) The influences by direct retainers a) With use of a resilient joint, the stress was heavily loaded on the residual ridge directly under the direction of force. b) With the joint incorporating the vertical rock-preventing device, a heavy proportion of lateral force was transmitted to the abutment tooth. 3) Both the lateral stress on the abutment tooth and movement of the saddle were reduced more effectively by use of indirect retainers than by splinting of abutment teeth. 4) By reduction of the occlusal area in bucco-lingual dimension, the denture saddle was better stabilized and the lateral stress on the abutment tooth was reduced effectively.

Design of a direct retainer for removable partial dentures

The direct retainer described in this technique is utilized on abutment teeth with a minimum of desirable undercut. Only the arms of the retainer should contact the tooth. All other parts are relieved.