Akers Clasp Research Articles

Comparison between Acetal Resin and Cobalt-chromium Removable Partial Denture Clasps: Effect on Abutment Teeth Supporting Structures

ABSTRACTStatement of problemAcetal resin has been introduced as an esthetic partial denture clasp material. However, the effects of these clasps on the abutment teeth supporting structures were not clear.PurposeTo evaluate the effects of acetal resin clasps on the abutment teeth supporting structures as compared to cobalt-chromium clasps.Materials and methodsTwenty patients, 12 males and 8 females, with Kennedy class III modification I partially edentulous maxilla and dentulous mandibles were selected for this study. Patients were divided into two equal groups; group 1 received maxillary cobalt-chromium partial denture frameworks with acetal resin Akers clasps. Group 2 received maxillary partial denture with cobalt-chromium frameworks and Akers cobalt-chromium clasps. Crevicular fluid, epithelial attachment loss, and bone height and density of the abutment teeth were evaluated at partial denture insertion and after 6 and 12 months. Paired t-test was used at p ≤ 0.05 to assess the changes in the above parameters in each group. Student t-test was used to compare between the two groups.ResultsCrevicular fluid measurements were significantly higher in the first group than that in the second group. There were no differences in epithelial attachment loss between the two groups. There were significantly higher reductions in the bone height and in the bone density in the second group than that in the first group.ConclusionAcetal resin clasps were superior to cobalt-chromium clasps as produced fewer reductions in bone height and in bone density around the abutment teeth inspite of produced increase in the crevicular fluid.Clinical implicationsSince there were lesser reductions in bone height and in bone density around acetal resin clasp abutments, it could be used successfully to retain partial dentures. However, meticulous oral hygiene and proper insertion and removal of partial denture with acetal resin clasps were required to decrease gingival inflammation and crevicular fluid amount.

Retainer design for unilateral extension base partial removable dental prosthesis by three-dimensional finite element analysis

The purpose of this study was to evaluate the effect of differences in the retainer design on load on abutment teeth and displacement of the denture base in mandibular unilateral extension base partial removable dental prosthesis to determine the optimum design for a mechanically appropriate retainer. Three models were used. Each incorporating a removable denture with different designs of retainer positioned. In design A, Akers clasps were positioned over the first and second premolars. In design B, embrasure clasp was positioned over the first and second premolars. In design C, rest and back-action clasps were positioned over the first and second premolars, respectively. Loading on the occlusal surface of the dentures was performed in the vertical, oblique lingual and buccal directions. Load on the abutment teeth and displacement of the denture base were determined by the three-dimensional finite element method analysis. Vertical and buccolingual load on the abutment teeth by lingual and buccal direction loading on the denture were smaller in designs B and C than in design A. However, the superioinferior and buccolingual displacement of the denture base by buccal direction loading on the denture were largest in design A. Superioinferior and buccolingual displacement of the denture base by the lingual direction loading on the denture were largest in design C. Under the conditions set in this study, the stability of design A was greater than that of design B or C, but load on the abutment teeth was larger.

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.

ガイドプレーンの設定条件がエーカースクラスプ装着時の支台歯変位に及ぼす影響

Three types of guide plane were compared to clarify the effect of guide plane setting conditions on abutment displacement which arises when an Akers clasp is inserted. An experimental model with an artificial periodontal membrane made of hydrophilic vinyl polysiloxane impression material was created. Abutments given a guide plane with only a clasp body (G1), a guide plane whose span extended as far as the reciprocal clasp arm shoulder region diametrically opposite the retention area (G2), and a guide plane for the entire reciprocal clasp arm region (G3) were created, and an Akers clasp was made for each abutment. The amount of abutment displacement and the degree of rotation that arose in the abutment when the Akers clasp was inserted were detected with three laser displacement sensors for comparison. The amount of abutment displacement that arose when the clasp was inserted was higher with G1 than with G2 and G3 in the lingual and distal directions, and no difference was seen between G2 and G3. It was lower with G1 than with G2 and G3 in the buccal direction, and no difference was seen between G2 and G3. It was high with G1 in the mesial direction, and the abutment rotation was high, whereas they were low in the case of G3. A difference was seen between each condition. Differences in guide plane setting conditions affected the abutment displacement that arose when an Akers clasp was inserted, suggesting that a difference in reciprocal action is seen depending on the setting conditions of the guide plane.

ワイヤーエーカース鉤の舌面形態の違いが犬歯支台の挙動に及ぼす影響

On a case of distal extension removable partial prostheses with only six frontal teeth remaining, the wrought wire Akers clasp system has been usually used in expectation of the stress breaking action of flexible compornents because of an unfavorable prognosis. No plactical availability of this system, however, has been confirmed in vivo and in vitro too. The measurement device in six degree of freedom was utilized for revealing the effect of five types' lingual compornents of wrought wire Akers clasp system on the canine abutment movement, especially tipping movement. From this in vitro study the following conclusions could be drawn : 1) On comparing the tipping movement of each design with the design 1 as the control, no significant difference was found between any two designs regarding inclination of the abutment tooth. 2) The tipping direction of designs 2 and 4 with an ordinary lingual rest was mostly towards labial direction, but the inclination of designs 3 and 5 without an ordinary lingual rest, and design 1 considered as a specific type without an ordinary lingual rest and a reciprocal compornent such as a hook also was all towards lingual direction. 3) No significant difference was also recognized between the magnitude of inclination of the abutment tooth in crushing short type test food and that of the abutment tooth in crushing long type test food, although the latter inclination tended to be greater than the former one. 4) In comparing the magnitude of inclination of the working side abutment with that of the balancing side abutment tooth the former had a tendency to be greater excepting that of design 1, but there was no significant difference between the magnitude of inclination of either side. 5) Significant difference of ninety nine per cent confidence levels was recognized between tipping magnitude in unilateral loading and one in bilateral loading, and the latter was larger than the former. On the basis of the foregoing findings, the lingual compornent shapes of the wrought wire clasp systems has influence upon the canine abutment movement but the influence was found to be very small, especially on the magnitude of inclination. However, on tipping direction of the abutment tooth, the indicatioin was that it was influenced considerably in the same manner as that of cast Akers clasp systems.

水平荷重時においてクラスプ形態が支台歯の負担圧分散と義歯床の変位に与える影響

The purpose of this study was to investigate the effect of the modification of clasp assemblies under horizontal load. The simulated mandibular model with unilateral free end was fabricated for this study. The eleven types of removable partial dentures (RPDs) using different retainers respectively were constructed. These retainers were a cone-telescopic crown, Akers clasp, double Akers clasp, RPI clasp (Kratochvil type) and seven modified clasps made from the first three clasps to which an enlarged bracing arm, a positive rest with hook and a distal rest with a guide plate were added. Horizontal loads were applied, and the stress on abutment teeth and the displacement of denture base were measured.The results were as follows:1. Under horizontal loads, the partial denture retained by cone-telescopic crowns had the least displacement of denture base.2. The RPDs with Akers clasps, double Akers clasps and RPI clasps generated large displacement of the denture base.3. The stress characteristics on abutment teeth and displacement of denture base of the RPDs with modified clasps were similar to those of cone-telescopic crowns with enlarged lingual bracing arms, especially.

部分床義歯の支台装置 維持装置（クラスプ）の選択基準

Two keys for clinically success of the removable partial denture have been recognized. One isinhibition of inflammation of periodontal tissue (biologically based). The other is proper broad forcedistribution. The retainer is generally accepted as having rigid connection. The selection and design of claspbring achievement of the rigid connection. The clasp has the functions of support, bracing, retention andreciprocation. When these well-balanced functions are performed effectively, stabilization of the removablepartial denture is acquired.As for the four clasps (Akers clasp, double clasp, combination clasp and RPI retainer), which are oftenapplied clinically, each of the functions was assessed from the standpoint of rigid connection and my thoughtson selecting clasps are presented.

クラスプ義歯における支台歯と顎堤の荷重分散に関する実験的研究 コーヌステレスコープ義歯との比較

The purpose of this study was to investigate the effects of various retainer designs on the characteristics of stress distribution and vertical dislodgment of the denture base. A mandible simulation model of unilateral distal-extension missing teeth (three teeth from the second premolar to the second molar) was used in this study. A conical crown, Akers clasp, and double Akers clasp were used as retainers.The results were as follows:1. The conical crown retained denture produced significantly less stress distribution and vertical dislodgment of the denture base than the two clasp designs.2. The conical crown retained denture produced the most intense stress on the apical and distal surfaces of the most distal abutment, while the double Akers clasp design produced the least stress.3. The Akers clasp design produced less load distribution of the denture base and greater vertical stress of the abutment tooth than the double Akers clasp design.4. The bilateral denture design produced less load distribution of the denture base and greater vertical stress of the abutment tooth.5. On condition of the bilateral denture design including clasps with a proximal plate, stress and load distribution were similar to those of the conical crown retained denture.

Effect of friction coefficient on Akers clasp retention

Statement of problem. Retentive force control of clasp retainers is one of the most essential factors for the successful function of removable partial dentures. However, it is not yet known how the friction coefficients differ among restored abutments and clasp materials, and how the friction coefficients affect the retention of clasps. Purpose. The purposes of this study were to clarify the friction coefficients among restored abutments and clasp materials and to estimate the effect of friction coefficients on the retention of clasps. Material and methods. The coefficients of static friction between three clasp materials (type IV gold, high Pd, and cobalt-chromium [Co-Cr] alloys) of two surface treatments (polished and sandblasted) and four abutment materials (human enamel, porcelain, type IV gold, and high Pd alloys) were evaluated under three conditions (dry, wet with water, and wet with saliva), and theoretically, the effect of the friction coefficients on clasp retention was estimated. Results. The friction coefficients under various conditions ranged from 0.08 (polished Co-Cr clasp on type IV abutment in dry condition) to 0.37 (sandblasted Co-Cr clasp on high Pd abutment in dry condition). The theoretical estimation clarified that the retentive force of the clasp was linear to the friction coefficient. Conclusion. The retentive force increased linearly with increasing friction coefficient between abutment material and clasp material according to the newly developed formula. This study suggested that clasp designs should be changed depending on abutment materials.(J Prosthet Dent 1997;78:22-7.)

両側性遊離端症例において維持装置のデザインの違いが支台歯の挙動に及ぼす影響 : コーヌス冠と鉤による作業側・非作業側支台の比較

By observing the movements of abutment teeth with Akers clasp, back-action clasp, single and continuous Konus-type attachments in Kennedy class I case with loss of the first and second molars, which occures more often in the clinically, evaluated the design advantages and the drawbacks in relative sense with the judgment standard of the anatomy characteristics periodontal ligament from the movements of abutment teeth. The displacements of abutment teeth were measured using six displacement sensors for three axes when two types of test food particle (short and long food particles) were crashed, and analised the valid differences with t-test. The results obtained from the simulation model were summarized as follow. There were four types of movements -parralel movements, inclinations, twist-like movements and depressions- on the abutment teeth in this situation. 1. Parallel movements : There was almost no displacement for buccolingual, the clasp group showed the distal and Konus-type group showed the mesial large movement. 2. Inclinations a) In different from the parallel movement, the buccolingual displacements were mainly occured rather than the distal movement, inclinated to the lingual direction with slightly tilted distal. b) The difference of the magnitude of inclination was recognized almost none at the non-working side, but the inclination of the clasp group at the working side was significantly greater than that of the Konus-type, and the magnitude of inclination of the abutment tooth (5^^-) had a tendency to be greater than that of 4^^- in design K1. 3. Twist-like movements : In either the clasp design, twist-like movements were very little, but the twist-like movement barely recognized was observed at the working side of the clasp design B and the non-working side of K1. 4. Depressions a) In vertical displacements, both side abutments did not moved to up ward, but only to down ward. b) There was very small difference among each design, however, the maximum accelerated occasion, the working side support showed the larger depression in the order of K2, clasp B, A, and K1, although was slight. c) Overall, the depression rate of the non-working side support was some one-third to a half of the working side support. 5. Mechanical properties of each design : With the maximum load of the 7 kilograms, the design showed the largest inclination inside the working side support was B, followed by A, and clasp group, and those showed the larger movement than Konus-type gourps of K1 and K2. As you can see above, when the designs used in this experimentation are used in the bilateral, the danger of the distal inclination as mentioned before is very slim. Therefore, the need of the stress breaking system is very small.

両側性遊離端症例において維持装置のデザインの違いが支台歯の挙動に及ぼす影響 : 連結腕鉤による作業側非作業側支台の比較

In order to find out the most desirable removable partial prosthesis, a series of experiments have been conducted in our department. As one of the experiment programs, we observed and evaluated the reactions of the abutment with three clasp assemblies, a double Aker's (design D), an extended arm (design E), and a combination consisting of two retentive T-bar and two reciprocal cast Akers clasps (design T), on the simulation model of Kennedy I with loss of lower first and second molars. We used digital type of laser displacement sensors to analysing the abutment teeth when crushing the test food of two types, short and long. The obtained results were as follows : 1. In all designs, four types of displacement, parallel movement, inclination, twist-like movement, and vertical movement (depression) were recognized during crushing the test food. 2. Parallel movement 1) Both abutment teeth on the working side showed parallel movement toward the mesiolingual direction, and those on the non-working side toward the mesiobuccal direction in most cases. 2) In general, the mesial abutment tooth (4^^-) moved with less magnitude than the distal abutment (5^^-) on the working side and on the non-working side too, but in design D alone there was more magnitude in the abutment 4^^- in comparison with that of 5^^- when crushing the long type of test food under 5 kg or 7 kg load. 3) In the distal abutment (5^^-), parallel movement of the working side abutments was always greater than that of the ones on the non-working side. 3. Inclination 1) The working side abutments showed very small inclination distolingually and the non-working side ones distobuccally when crushing the test food. 2) In design D, greater inclination of the working side abutment (4^^-) was observed than that of the same side abutment (5^^-). 4. Twist-like movement 1) The twist-like movements of abutment teeth were very small in all designs. 2) In design D, the direction of twist-like movement was opposite between the abutment tooth (5^^-) and the abutment (4^^-), and the movement of 4^^- was greater than that of 5^^-. 5. Depression 1) The working side abutments showed greater depression from one and a half to twice that of the non-working side ones. 2) Noticable depression was observed in 4^^- of the design D as compared with that in 5^^- when crushing the long type of test food. 3) The depression of the working side abutments increased as the load increased and increased more in the case of crushing the long type of test food. 4) Even distribution of occlusal force to the either abutment teeth by secondary splinting was not recognized. 6. Other results 1) The behavior of the abutments was affected by the test food shape. 2) It was suggested that inclination could be restricted when greater parallel movement was given to the abutments in the designs used in this expeiment. Above mentioned results showed that design D resulted in unexpected larger stresses on the mesial one than on the distal abutment tooth when crushing the test food. Design D proved to be the design for which abutment tooth movement could not be predicted.

義歯の構造が負担圧配分に及ぼす影響に関する実験的研究 支台装置が異なる場合

Removable partial dentures should be designed to ensure efficient distribution of masticatory loads over the abutment teeth and alveolar ridge. The relationship between the denture stiffness and the various clasp designs on the pressure distribution to a single abutment tooth and the alveolar ridge was investigated in this study.The results were as follows:1. Regardless of the retainer designs, the pressure on the alveolar ridge was less when using a double structure than a skeleton type, and the pressure on the abutment tooth in the vertical direction was greater when supported by a double structure than a skeleton type.2. When a Konus telescope was applied as a retainer the pressure on the abutment tooth in the vertical direction was greater than an Akers or an RPI clasp.3. When an RPI clasp was applied as a retainer the amount of pressure on the alveolar ridge was maximum.4. The pressure on the abutment tooth in the lateral direction showed a greater tendency when an Akers clasp was applied.5. The displacement and strain of the denture were the least when a double structure design was applied.6. When a double structure design with Konus telescope was applied, the displacement of the denture was the least.

部分床義歯離脱時における維持歯の負荷に関する研究

During function, every R.P.D. shows denture movement that is converted into stress to the abutments. Our two investigations revealed that guide surfaces on the retainers was effective in reducing the stress. In R.P.D. treatment, many different designs of clasp systems have been used with less consideration of this guiding function. In this study, four types of clasps, Aker's clasp, Krol R.P.D., Kratochvil R.P.D. and the Crown Ledge preparation, having different guide surfaces were examined to measure the mobility of abutments under the pull out force. Metal frame dentures were provided in order to measure these movement with electronic sensor. Each retainer had interchangeable feature to facilitate the investigation. The following results were obtained, 1. Aker's clasp showed small amplitude with high frequency during removal periods. 2. Both R.P.I. clasps give only small vibration when the path of removal is adjusted. To get this direction is difficult. 3. Guide surface of Crown Ledge clasp. is effective in reducing the mobility of abutment tooth. 4. The guiding surface therapy has an effect in reducing the abutment vibration.

維持歯と維持装置の連結強度 第１報 各種クラスプの連結強度について

The prerequisite to enhance the function of the free-end saddle R. P. D. is to diminish the denture dynamics in mastication. The authors have already reported the evaluating methods of the denture dynamics in the free-end R. P. D.'s with various retainers.In the previous reports, the denture dynamics were mainly affected by the retainers used; the more rigidity the retainers were connected to the abutment teeth, the less the denture dynamics were obtained. What is the key to diminish the denture dynamics? and what is the main characteristics of the cone-crown-telescope, which was revealed to have the least dynamics among the various retainers?So, we have conducted a study on the connecting rigidity which may seem to be the main characteristics of the cone-crown-telescope on the bench model assembly.Following results were obtained:1. The greatest value of the connecting rigidity was obtained in the cone-crown-telescope, then followed the R. P. P. I., the R. P. I. by Kratochvil, the R. P. I. by Krol, to the R.P.I. and the Aker's clasp without the guiding function in sequence.2. It was clearly indicated that the guiding surface/guiding plate parallelism between the abutment teeth and the retainers played the most important role in obtaining the connecting rigidity in the clasp designed R. P. D.'s.3. An ordinary refractory model method for obtaining the guiding/surface guiding plate function revealed to fail the genuine connecting rigidity matching for the one in the conecrown-telescope.

Analysis of abutment tooth movement utilizing mandibular kinesiography (MKG). Part 2. Effects of clasp design in unilateral free-end denture.

The three-dimensional dynamic movement of the abutment tooth was successfully analyzed on a simulation model utilizing the mandibular kinesiography. When the unilateral free-end denture retained by the RPA, RPI or Aker's clasp was subjected to various directions of loads, the abutment tooth was inclined mainly by the sliding displacement of the denture over the alveolar ridge and the lever action around the denture. The Aker's clasp assembly induced the largest tooth movement. The RPA clasp generally exhibited similar tendencies to the Aker's clasp, showing a larger tooth inclination in the disto-buccal direction. The RPI clasp seemed to be preferable for protecting the periodontal tissues from damage associated with unfavorable tooth movements since it induced less distal tooth inclination.

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.

A study of clasp force on abutment tooth under loading

The functional behavior of removable partial denture is destined to be transmitted directly to the abutment tooth as a stress via clasp because of most of its retention being dependent upon the clasp retainer. Therefore, the influence of the clasp on the behavior of the abutment tooth is supposed to be more important according to its designs.Thus, using a bend strain measuring system according to 2 gauge Active-Active method developed previously by the Author and 4 kinds of clasp with a high applicability to cases of distal extention, the Author examined, on experimental models, possible difference horizontal stress on the abutment tooth according clasp designs.The results are as follows:1. Both clasp of Supra-bulge type with distal rest and Infra-bulge type with mesial rest exerted respectively to make the abutment tooth incline distolingually.2. It was showed that the horizontal stress put on the abutment tooth reduced Aker's clasp, Wire combination clasp, Kratochvil I-bar clasp and Krol I-bar clasp in turn, and for the Infra-bulge type clasp was smaller than for Supra-bulge type clasp.

Development of a computer system for determining retentive force of cast clasps

The purpose of this study is to develop a rational fabricating system for determining retentive force of cast clasps. The radius of curvature of a circumferential clasp arm is considered to be one of the important factors affecting dynamical properties of cast clasps. In this study, a device for determining the radius of curvature and a computer system for Akers clasps and I-bar clasps were developed.It was suggested to be very significant in partial denture designing, that the retentive force and the bending rigidity required according to various conditions around abutment teeth can be easily obtained by using a personal computer, and that the proper part of a commercially available clasp pattern required to fabricate cast clasps providing rational retentive forces can be determined in this system.

Effect of clasp design upon retention of removable partial dentures

A model was constructed to represent an ideal removable partial denture situation with a standardized undercut. Nine chrome-cobalt alloy test frameworks, each representing a different clasp design, were fabricated according to the manufacturer's directions. The amount of force required to dislodge each framework from the model was recorded. The frameworks showed the following decreasing order of resistance to vertical displacement from an 0.02″ undercut: (1) “U” infrabulge clasp, (2) ring clasp, (3) Akers clasp, (4) Akers clasp with a wrought gold wire retentive arm, (5) “I” infrabulge clasp, (6) “I” infrabulge clasp with a wrought gold wire retentive arm, (7) Ney No. 2 clasp, (8) “T” infrabulge clasp, and (9) back action clasp.