Types Of Clasps Research Articles

Comparison of cast Ti-Ni alloy clasp retention with conventional removable partial denture clasps

Statement of problem The elastic property of Ti-Ni alloy may be a desirable property for cast removable partial dentures. However, little is known about the retentive properties of cast Ti-Ni alloy clasps. Purpose This in vitro study investigated the retentive force of various types of clasps during repeated cycles of placement and removal to determine whether Ti-Ni alloy clasps maintain their initial retentive force under varied conditions, including different retentive undercut depths and clasp size (thickness and width). Material and methods The test models were developed using a mandibular dentiform with a horizontal plane of occlusion. Two complete metal abutment crowns were made for the left second molar, differing only in retentive undercut depths. A total of 98 clasps (n=7) were fabricated, including 14 wrought wire clasps and 28 clasps from each of the following alloys: Co-Cr alloy (Biosil), Type IV gold alloy (Cast-4), and Ti-Ni alloy (TN-10). Clasps were made to engage one of 2 retentive undercut depths (0.25 mm or 0.75 mm) and were made in 2 sizes (0.8 mm or 1.4 mm). Each clasp was radiographically examined for casting defects and porosity. The force (N) required to remove the clasps was measured using a universal testing machine with a crosshead speed of 10 mm/min. After measuring the retentive force, a masticatory simulator was used to cycle the clasps on and off the metal crown 500 times, simulating the insertion and removal of a removable partial denture clasp. The cycling sequence was repeated 10 times, and retention force was measured after each sequence. The internal surface of the clasp arms was examined for evidence of metal fatigue using scanning electron microscopy. Data were subjected to 2-way and 4-way analysis of variance, followed by Scheffe's multiple comparison test (α=.05). Results Co-Cr alloy and gold alloy clasps in the 0.25-mm retentive undercut groups experienced a gradual decrease in retentive force measurements ( P<.001). In contrast, the Ti-Ni alloy clasps maintained a retentive force of approximately 1.8 N and 2.6 N for the 0.8 mm and 1.4 mm clasp groups, respectively. Although Ti-Ni alloy clasps' retentive force was reduced slightly after the first cycling sequence, it was negligible compared with other clasps tested. The wrought wire clasps also retained their retentive force until the final cycling sequence. A similar trend was found in the clasp groups engaging 0.75-mm retentive undercuts. Conclusion Although the end-point retention for all the clasps was similar, there was less change in the retentive force of the cast Ti-Ni alloy clasps after repeated cycling sequences of simulated placement and removal.

Redução da força de retenção e abertura de grampos a barra em "I" de Roach e sua correlação

A pesquisa utilizando grampos a barra em "I" de Roach teve por objetivo determinar a diminuição da força de retenção após 20 mil ciclos de inserção e remoção. Também determinou-se a abertura dos grampos durante a ciclagem e a correlação com a diminuição da retenção. Usaram-se 2 ligas à base de Co-Cr (Vera PDI e Wironit) e 4 tipos de grampos (CF, curto-fino; CG, curto-grosso; LF, longo-fino; LG, longo-grosso). Ainda os corpos-de-prova foram cobertos ou não, parcialmente, com resina acrílica. Os resultados permitiram concluir que: as ligas apresentaram diminuição de retenção semelhantes; as aberturas dos grampos foram semelhantes nos diversos tipos de grampos, mas a perda de retenção menor foi para o longo-fino e maior para o curto-grosso; a cobertura parcial dos grampos com resina não influiu em sua abertura mas aumentou significantemente a perda de retenção; não foi encontrada correlação significante entre abertura e diminuição de retenção dos grampos.

Fabricating abutment crowns for existing removable partial dentures using custom resin clasp analogs

A universal approach for fabricating abutment crowns for existing removable partial dentures is described. A replica (analog) of the clasp assembly is generated and transferred to a traditional working cast, which includes the abutment die. The analog is incorporated into the working cast as a removable component to allow the formation of the crown contours. The article reviews in detail the procedures required to transfer accurately all the essential components and information from the mouth to the working cast while allowing the patient uninterrupted use of the removable partial denture. Prestabilizing the removable partial denture, creating the analog impression, avoiding errors due to soft tissue components, forming a precise analog base, selecting materials, generating a rigid resin analog, and prescribing a path of insertion and withdrawal to the analog are described. The method replicates all types of clasps and can generate all types of fixed prosthodontic retainers to function harmoniously with the existing partial denture. (J Prosthet Dent 1998;80:619-29.)

Falhas de grampos circunferenciais de próteses removíveis em função de ciclagens de flexão

A finalidade da pesquisa foi a determinação da freqüência da perda de retenção de grampos de próteses removíveis. A freqüência foi determinada após os vários períodos de ciclagem (x103: 1, 5, 15, 25). O número de freqüências foi baseado no número de "células" vazias, ou inexistentes, por fratura de grampos ou presença de retenção menor que 120 g, quando era feito ajuste. Assim, o número de "células" vazias é caracterizado pelo número de grampos que se fraturaram ou perderam retenção. As variáveis foram: 4 ligas de metais básicos; 2 tipos de grampos (padrão e extra, mais fino); dentes pré-molar e molar. Os resultados permitiram concluir que: o número de "células" vazias depende das ligas, tanto com ajuste como sem; o número de falhas sem ajuste não foi dependente do tipo de grampo, porém, com ajuste, o extra apresentou menor freqüência de falhas; a freqüência de falhas foi muito grande; e quase a metade ocorreu até 1.000 ciclos.

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 : 単独腕鉤による作業側・非作業側支台の比較

A series of laboratory tests in unilateral distal-extended removable partial dentures have been undertaken to observe and evaluate the effect of clasp assemblies and their component parts on abutment tooth movements by our department. A lot of valuable findings were obtained from these studies. However, about the behavior of abutment tooth in bilateral distal-extended ones does not make it clear in detail, although it has been reported that the abutment tooth movements were greater when the teeth were on the same side with the load applied to the denture than those measured when the tooth was on the opposite side to the application of the load. The purpose of this examination was to observe and to clarify the difference of abutment behaviors on the working side by comparison with those on the non-working side in the bilateral distal-extended partial prosthesis with four clasps : Aker's wrought wire clasp (Aw), two types of combination clasps (Ca and Ct), and Krol's RPI retainer (Rk). The direction and magnitude of abutment tooth movements in these prostheses with four clasp accemblies were measured by utilizing the same condition as Koga's ones and the equation for physical analysis of the movement of an abutment tooth itself, and t-test was used to compare the means for the four clasp designs. The obtained results were as follows : 1. The total displacement of the abutment on the working side was greater than that on the non-working side. Contrary to this, it was observed in one or two clasps that the former movements were smaller than the latter ones. 2. With regard to the effect which the food shapes would give to the abutment tooth movements, the magnitude of the movement of abutments on the working side has a tendancy to increase significantly when crushing the long type of food than when crushing the short ones, but little difference of the magnitude of the abutment movements was recognized on the non-working side. 3. In each abutment tooth with a different type of clasp, there were four mode movements : parallel movement, inclination, twist-like movement and depression. The most remarkable parallel movements on the working side were observed in the abutment tooth with Rk, and the smallest movement in one with Ct. As for the maximum of the other movements ; inclination was in the abutment tooth with Aw and was the minimum with Rk, and the maximum of the twist-like movement was in one with Rk and the minimum with Ct. Little difference in the depression, however, was detected in four type clasps used in this experiment.

部分床義歯装着後のこう歯動揺度の短期的な変化

The purpose of this study was to clarify the change of abutment teeth mobility by insertion of partial dentures for a short period.Twenty patients who received partial dentures at the Dental Clinic of Niigata University School of Dentistry, between August and November 1994, were selected.To evaluate changes in tooth mobility, the Periotest (PT) value of 49 abutment teeth within 3 months after initial insertion were measured and the following factors were analyzed.1. change in PT value of all abutment teeth2. change in PT value of upper abutment teeth3. change in PT value of lower abutment teeth4. the relationship between the type of edentulous space, the type of clasp and the amount of PT value changeThe results were as follows:1. PT value of all abutment teeth decreased after insertion of the dentures.2. PT value of upper abutment teeth showed no significant change within 3 months after initial insertion of the dentures.3. PT value of lower abutment teeth decreased from 2 weeks after insertion, and these decreases were clearly detected in free-end dentures.4. PT value of lower abutment teeth of free-end dentures decreased irrespective of the type of the clasp.

Measurement (in vitro) of the amount of force required to dislodge specific clasps from different depths of undercut

A fundamental principle in clasp selection for a specific abutment is the reduction of the transmission of excessive forces to that abutment. The flexibility of a clasp was believed to directly affect the reduction of such forces. This study compares the average measurements of forces required to dislodge two kinds of circumferential clasps in different amounts of undercuts: one with a half-round retentive arm and the other with a round retentive arm under tensile load. Three commonly used undercuts were created on six cast crowns, premolars, and molars. Each clasp was exposed to adequate tensile load until dislodgment occurred. The test was run six times for the same clasp. The means of tensile load required to dislodge each of the different clasps were compared statistically. However, no significant difference was detected for the main effects of the three variables studied: tooth type, undercut, and amount and clasp type. Findings indicated the possible use of cast round clasps where advantages of clinical fit and reduction of transmitted forces to the abutments can be gained.

Cmentarzysko ludności kultury wielbarskiej z okresu rzymskiego w Brusach, stan. 11, gm. loco, woj. bydgoskie

In 1982 and 1986 year’s in Brusy, Jagiellońska st. 11 during earthwork was founding urn graves. The savework delived the next urn gravers. The most interesting graves aro no 3 with 2 bronze fibulas with silver plates A. V 130 and bronze buckle with semicircular frame ad grave no 5 with bronze filbula A. VI 168, fragment of second fibula the same type, silver clasp type В by J. Kmieciński and clay whorl. This equipment is dated on the turn of early and late Roman Period (phase B2/C1 ).

Textbook of dental pharmacology and therapeutics

A reciprocating abrasion testing machine was used to measure the mutual abrasion of light-cured composites and clasps in vitro. Composite specimens were produced by packing the material into hemispherical wells in a polytetrafluoroethylene block, light-curing for 20 seconds and conditioning in distilled water for one week. The composites tested included ultrafine, hybrid and conventional types. Nine clasp types were studied including cast and wrought, round and half-round, cobalt-chromium, stainless steel and gold. The tests were carried out at 37 °C. The vertical overlap (undercut) of composite and clasp was set at 0.25mm. Ten specimens were subjected to 14,500 traverses in each test Abrasion of composite was measured as weight loss and reduction in thickness of the specimens, while abrasion of clasps was measured as weight loss. Abrasion of the composites was greatest for the conventional type and least for the ultrafines, but in all cases the changes were small and unlikely to impair the clinical performance of clasps during several years' usage. The abrasion of the clasps by conventional composite was considerable and would be expected to cause a significant reduction in retention clinically.

In vitro calcium release from four calcium hydroxide liners

The use of metal clasps on anterior teeth may cause esthetic problems. Recently, acetal resins have been used as an alternative tooth-colored denture clasp material to improve esthetics. However, there are few studies to support acetal resin use.The purpose of this in vitro study was to compare the retentive force and deformation of acetal resin and cobalt-chromium clasps after 36 months of simulated clinical use.Forty clasps each of acetal resin (1.2 or 2.0 mm thick) and cobalt-chromium (Dentorium)(1.2 mm thick) were fabricated using half-round standard prefabricated clasp patterns. The groups were further subdivided (n = 10) into the type of tooth (premolar or molar metal model) and undercut (0.25 mm or 0.50 mm). The retentive force of the clasps was measured in distilled water by a specially designed insertion-removal testing apparatus with intervals corresponding to 0, 6, 12, 18, 24, 30, and 36 months of simulated clinical use of a removable partial denture. The distance between the clasp tips (mm) was measured with a microscope before and after the insertion-removal testing procedure. Comparison of the mean values of the retentive force (gram force) of the clasps and the distance (mm) between the clasp tips was conducted with 3-way analysis of variance and a Least Significant Difference (LSD) multiple range test (α=.05).The mean values of tensile load required to dislodge acetal resin clasps with 1.2-mm thickness (111.6 g or 0.11 N) and with 2.0-mm thickness (178.4 g or 1.75 N) was significantly lower than that to dislodge Co-Cr clasps (694.1 g or 6.81 N) (P<.001). The retentive force needed to dislodge all 3 types of clasps was significantly lower for the molar than premolar models and also lower for the models with 0.25-mm undercuts than for those with 0.50-mm undercuts (P<.001). After 36 months of simulated clinical use, there was evidence of deformation in the cobalt-chromium clasps but no deformation noted for the acetal resin clasps. The retentive force of cobalt-chromium clasps (297.4 g or 2.91 N) after deformation remained significantly higher (P<.001) than the retentive force of acetal resin clasps that were 1.2 mm (110.7 g or 1.08 N) and 2.0 mm thick (177.5 g or 1.74 N), respectively.Within the limitations of this study, the results suggest that both thicknesses of acetal resin clasps evaluated required less force for insertion and removal than Co-Cr clasps over a simulated 36-month period.

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.

Veterans Administration Cooperative Dental Implant Study — Comparisons between fixed partial dentures supported by blade-vent implants and removable partial dentures. Part I: Methodology and comparisons between treatment groups at baseline

This study was conducted to determine whether fixed partial dentures supported by dental implants provide an acceptable alternative to conventional removable partial dentures in patients with Kennedy class I or class II edentulous conditions. The acceptability of the new treatment will be based on success rates, impact on the health of the remaining dentition, masticatory performance, patient satisfaction, and maintenance care and cost. The study was planned also to provide comparisons between two designs commonly used by dentists for fabricating removable partial dentures. The designs differed only in terms of the type of the retainer (clasp type) and tooth support (rest location). A total of 272 patients with Kennedy class I and class II edentulous conditions were assigned on a random basis to one of the treatment groups, 134 to receive a removable partial denture and 138 a fixed partial denture supported by a blade-vent implant. All of the patients were medically screened and met prespecified criteria for oral hygiene, bone support for abutment teeth, and size of the residual ridge. Thirty-four patients were eliminated from the study before completion of their treatment. An additional six patients with early implant failures were reentered in the study and followed up as a separate group. The remaining 232 patients received comprehensive dental care, including removable partial dentures for 118 and fixed partial dentures for 114 patients. A series of examinations, radiographs, masticatory performance tests, patient satisfaction, food selection questionnaires, and dietary history were completed before initiation of the treatment, 16 weeks after the insertion of an RPD or an implant, and thereafter at 6-, 18-, 36-, and 60-month intervals. In addition, patients were seen at 6-month intervals for a recall dental examination, oral prophylaxis, plaque instructions, radiographic survey of the implant, and any needed dental treatment. The randomization stratification approach produced two treatment groups with comparable age, number of remaining maxillary and mandibular teeth, type of opposing dentition, and percent of patients with Kennedy class I and class II edentulous conditions. The mean scores of bone support, tooth mobility, and sulcular depths of abutment teeth were also similar. Significant but comparable improvements in oral hygiene and sulcular depth occurred in the two groups after treatment. The periodontal health scores at the 16-week interval serve as the baseline to measure subsequent changes in periodontal health. This prospective longitudinal study with prespecified criteria for implant and removable partial denture failure should provide reliable estimates of failure rates, number and types of complications, maintenance care needs, and total costs for the two treatment modalities and the two RPD designs.

The mutual abrasion of light-cured composites and clasps: an in vitro study

A reciprocating abrasion testing machine was used to measure the mutual abrasion of light-cured composites and clasps in vitro. Composite specimens were produced by packing the material into hemispherical wells in a polytetrafluoroethylene block, light-curing for 20 seconds and conditioning in distilled water for one week. The composites tested included ultrafine, hybrid and conventional types. Nine clasp types were studied including cast and wrought, round and half-round, cobalt-chromium, stainless steel and gold. The tests were carried out at 37 °C. The vertical overlap (undercut) of composite and clasp was set at 0.25mm. Ten specimens were subjected to 14,500 traverses in each test Abrasion of composite was measured as weight loss and reduction in thickness of the specimens, while abrasion of clasps was measured as weight loss. Abrasion of the composites was greatest for the conventional type and least for the ultrafines, but in all cases the changes were small and unlikely to impair the clinical performance of clasps during several years' usage. The abrasion of the clasps by conventional composite was considerable and would be expected to cause a significant reduction in retention clinically.

An investigation of the effectiveness of indirect retainers

A mandibular bilateral distal-extension base removable partial denture was lifted from a model under standardized conditions. The amount of denture base displacement under various loads and the forces of removal were measured electronically. The framework was constructed to allow repeated changes in the type of clasp, location of indirect retainer, and position of the rest seat on the terminal abutment tooth. The usefulness of an indirect retainer in preventing occlusal displacement of the denture base appears to be limited. The type of clasp had the greatest influence on the amount of denture base movement. Proximal surface guiding planes were also found to be important in preventing lifting of the denture base. Use of mesial instead of distal rests on the terminal abutment teeth did not decrease indirect retention.

A measurement of clasp forces on teeth

A method that measures the force which clasps transmit to abutment teeth was developed and a comparative study was made between the effectiveness of a wrought wire clasp and that of a cast bar clasp. A transducer, using a resistance strain gauge, measured the flexure of clasps and the forces exerted by the clasps on abutment teeth. The cast bar clasps were more flexible than the wrought wire clasps of equal length. All of the clasps tested exerted forces against the teeth when the removable partial denture bases were at rest. The wrought wire clasps flexed a greater distance and exerted more force against the abutment teeth when the casting was seated and removed from the model. The forces exerted by the clasps when the casting bases were moved were different from each other and yet followed a pattern. The force increased for both types of clasps as the bases were depressed; however, the wrought wire clasp exerted more force than the cast bar clasps. The forces measured could be significant when the direction and the result of the forces were examined. The wrought wire clasps may tilt the abutment tooth distolingually and the cast bar clasp may force the tooth mesiolingually. The results of this study question some of the empirical theories used today to substantiate extension partial denture clasp designs. It appears that the theoretical and the practical do not always agree; therefore, the theoretical should be tested further.

A Study of Partial Denture Clasping

The most controversial and seemingly contradictory phase of partial denture design is that of the clasp component. Many clasp types have been presented to the profession, each being claimed by its originator to be the solution of all clasp­ ing problems and difficulties. A study of the rationale and method of design of each clasp type reveals a startling dis­ agreement. One might easily conclude that there is an irreconcilable and un­ scientific basis for the design of partial denture clasps. However, by analyzing all available clasp types from an unprejudiced point of view, and eliminating all preconceived conclusions, a common basis for clasp design can be found. Basic fundamentals applying to all clasps may be formulated and any specific clasp type may be rated on its ability to carry out these concepts. To illustrate the fundamentals of clasp design, the circumferential clasp will be used as an example. I t is the type of clasp most frequently encountered in partial denture construction, and is the basis for all types of clasp design.