Cast Circumferential Clasps Research Articles

Studying the effect of the circumferential clasp arm design on stress distribution using three-dimensional finite element analysis

High stresses which result during functions in the cast clasps arms are the main causes of deformations or fractures. The purpose of the study was to evaluate the stress distribution in three-dimensional finite element analysis models of clasps and to select their preferable design.A three-dimensional finite element analysis was used for the investigations. Preformed clasp wax patterns for circumferential clasps were selected and three parameters namely length, thickness and width at the base and tip were measured to generate purposely designed experimental three-dimensional models. Generated stresses and deformatioans were calculated numerically and plotted graphically.Within the limitations of this study, the preferable cross-sectional shape of the retentive cast circumferential clasp arm was determined as half-round and the taper 0.6 mm.the ideal cross section of the retentive clasp arm was half round with 0.6mm taper diameter.

Effects of clasp retention forces and abrasion on different cast crowns

Dental alloys have different mechanical properties compared with enamel. However, few studies have been conducted to determine the effects of the retention forces of clasps when applied on different cast crowns. The purpose of this study was to evaluate the retention forces of cast circumferential clasps made of cobalt-chromium alloy on complete cast crowns made of cobalt-chromium (CC group) and gold-silver-palladium (AC group) alloys, and to observe their abrasion patterns. Two groups of specimens were fabricated (n=5) and subjected to repeated insertion-removal tests (100 to 15,000 cycles). The mean values of removal forces at 100, 400, 800, 1500, 4500, 7500, 10,000, and 15,000 cycles, and their corresponding change rates compared with the initial 100 cycles' retention were determined. The differences between the 2 groups were analyzed by 2-way repeated measures analysis of variance at 100, 7500, and 15,000 cycles. The surfaces of specimens were observed with scanning electron microscopy. There were significant differences between the CC and AC groups in retention forces (P<.05). Clasp retention showed a descending trend for cobalt-chromium alloy crowns from the initial value, which decreased by 29.9% after 15,000 insertion-removal cycles. A sharp increase in retention could be observed in the AC group, which rose by 99.7% ultimately. The worn surfaces of the gold-silver-palladium crowns showed different wear patterns compared with the cobalt-chromium alloy crowns. The results indicate that cobalt-chromium alloy crowns and gold-silver-palladium alloy crowns perform differently when cobalt-chromium alloy clasps are designed as retainers for partial removable dental prostheses. Crown designs should be changed, depending on the retainer and clasp materials for partial removable dental prostheses abutment teeth.

Esthetic Cast Direct Retainers for Distal Extension Removable Partial Dentures

Extra coronal cast direct retainers are an essential component of cast removable partial denture prosthesis. The conventional cast circumferential clasp or the bar clasp appear unaesthetic due to visible metal display when used in the smile zone. This article describes two hidden clasp designs as an alternative to the conventional extra coronal cast direct retainer assembly for the distal extension partially edentulous situation. The same is highlighted via two case reports.

In vitro investigation of the performance of different restorative materials under cast circumferential clasps for removable dental prostheses

The objective of this in vitro study was to investigate the behavior of different composite restorative materials under the load of cast circumferential clasps for removable dental prostheses (RDPs). In 60 human molars, standardized mesial-occlusal-distal cavities were prepared. The cavities were restored with the following materials: Definite, Tetric Ceram, SureFil, Heliomolar RO, Ariston pHc, and Oralloy, and provided with a rest seat. The rest seats were subjected to 5,000 cycles of thermal cycling and 1,200,000 masticatory cycles in a mastication simulator via cobalt-chromium circumferential clasps cast to standardized frameworks in a laboratory model designed to simulate the biomechanics of a free-end denture base. Fracture analysis of the restorations was performed by light microscopy. Before and after loading, material wear was measured with a 3D-laser scanner, and an analysis of the marginal quality was performed in an SEM at ×200 applying the replica technique. No significant differences in the fracture behavior among the composite materials were found; the amalgam control group showed a significantly higher fracture resistance. Regarding the wear of the materials, the composites Definite and SureFil exhibited a behavior similar to that of amalgam. The other composites demonstrated higher wear rates. The initial marginal quality was significantly worse for Ariston pHc. The marginal adaptation decreased significantly after thermal and mechanical loading for Definite and Ariston pHc. In terms of the investigated aspects of mechanical performance, the tested composites seemed to be inferior to amalgam. Further clinical studies are needed to evaluate the ability of composite restorations to provide support for RDP clasps. The use of composites as direct restoration materials should be avoided in teeth, which serve as abutments for clasp-retained RDPs.

Finite element stress analysis and fatigue behavior of cast circumferential clasps

Deformation and fracture of cast circumferential clasps may be a result of stresses induced during mastication. Most biomechanical clasp studies have been performed only under static conditions. There is little information regarding behavior of clasps over time. The purpose of this study was to evaluate stress distribution on cast circumferential clasps, and the displacements or deformations, depending on the load placement and range. Fatigue analysis was then conducted to evaluate the behavior of clasps over time. Static stress values and distribution induced in cast circumferential clasps were calculated and studied using 3-dimensional finite element experimental models for Co-Cr cast circumferential clasps. Average loads between 20 and 35 N were applied vertically along the clasp components to simulate static stress distribution during translation and rotation of the denture. After determination of stress concentration areas, the fatigue behavior of clasps was studied using finite element analysis during simulated cyclic masticatory loads (loads between 0 and 20 N included in 4500 masticatory cycles over 24 hours). For the translation simulation, the maximum stress was 310.27 MPa, located near the lower margin of the retentive arm, and for the rotation simulation, the maximum stress was 310.31 MPa, located near the upper margin of the same arm. Under simulated static load, the magnitude of stresses found in the clasps was under the reported yield strength (640 MPa) of the Co-Cr alloy. The maximum stresses indicated the area of highest fracture risk, but fractures occurred only under a simulated cyclic mastication load representing 5.5 years of service. Within the limitations of the simulation study, static stress analysis of cast circumferential clasps indicated the location of greatest fracture risk to be at the junction of the clasp arm with the body, for all situations. In addition, fatigue analysis estimated clasp degradation over time and the survival rate of the same clasps, which was found to be 5.5 years, on average.

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.)

エーカースクラスプアームの湾曲が剛性および応力に及ぼす影響に関する三次元有限要素解析

The effect of the variation of the curvature of the cast circumferential clasp arm on clasp stiffness and stress was evaluated using three-dimensional finite element analysis.The results were as follows:1. The curvature of the clasp arm under the condition of different lengths affected stiffness and stress.1) The clasp arm using a non-tapered pattern with a small curvature showed less stiffness and lower stress than the arm with a large curvature.2) The clasp arms using the original patterns, which were established from our previous study (taper 0.8, T/W ratio: 1/2 or 1/3), showed constant stiffness and low stress instead of change of curvature.3) The clasp arm using Rapid flex pattern with large curvature showed lower stress than the arm with a small curvature.2. The clasp arm with an adequate curvature in the condition of the same length showed low stress. This seemed to be the effect of torsion elasticity which was regarded to distribute the stress in the clasp arm.

Longitudinal study on occlusal force distribution in lower distal-extension removable partial dentures with circumferential clasps.

In this study, longitudinal changes of the occlusal force distribution ratio were examined in lower distal extension removable partial dentures with cast circumferential clasps. Occlusal force applied to the denture base and forces transmitted to the retainers were measured on several separate occasions from the insertion of new dentures to about 4 months after. Two rates of loading were chosen. One was simulated mastication (fast loading rate) and the other was 10 Ns-1 (slow loading rate). Location of the loading points were first premolar (P1), second premolar (P2) and first molar (P3) of the denture. The occlusal force distribution ratio to the retainers was calculated when a load of 20N was applied to the loading point. The results are summarized as follows: (1) The occlusal force distribution ratio at fast loading rate on P1 and P2 was changed until 1 or 1 1/2 months after the insertion of the new dentures, and then became constant. This constant value was 30% on P1, 20% on P2 and 10% on P3. (2) Slow loading rate produced a greater ratio than the fast loading rate on P2 and P3 while there were no remarkable differences in the ratio between both loading rates on P1.

Incidence of various classes of removable partial dentures

The purpose of a classification for removable partial dentures (RPDs) is to simplify identification and enhance its teaching. A classification also allows a longitudinal comparison of various classes of RPDs to determine whether the teaching of RPD design is consistent with the relative frequencies of RPD use. This study surveyed the types of removable partial dentures being fabricated in a regional dental laboratory and compared these findings with data from previous studies. Results indicate that mandibular RPDs are more common than maxillary RPDs and the class I mandibular RPD is the most common type of RPD for either dental arch. A palatal strap was the most frequently used maxillary major connector and a lingual bar was used three times more often than a lingual plate in the mandibular arch. Cast circumferential clasps were used twice as often as RPI clasp designs. The percentage of Kennedy class I RPDs was 40%, class II 33%, class III 18%, and class IV 9%. Comparisons with a previous study indicate the percentage of Kennedy class II has increased, whereas class I, class III and class IV RPDs have not changed significantly. Findings of the study indicate that the frequency of use of the various types of RPDs has changed in the past 30 years.

Stereophotogrammetric analysis of abutment tooth movement in distal-extension removable partial dentures with intracoronal attachments and clasps

This study applied the three-dimensional measurement technique of stereophotogrammetry to measure abutment tooth movement under occlusal loading as a function of intracoronal attachment and clasp design. Six distal-extension removable partial denture designs were studied: (1) RPI-mesial occlusal rest, proximal plate, buccal I-bar; (2) cast circumferential clasp; (3) P.D. locking semiprecision attachment; (4) Thompson dowel nonlocking semiprecision attachment; (5) McCollum precision attachment; and (6) Stern G/L precision attachment. The movement in microns was determined by computer analysis. The Thompson dowel semiprecision attachment generated the most abutment movement in a gingival direction. The clasp-retained designs generally had less total movement than the attachment designs. Clasps and attachments for the abutment teeth adjacent to the distalextension bases generally moved more than the abutment teeth.

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.

A photoelastic study of stress induced by framework design in a maxillary resection

Support of a framework and obturator in a patient with an acquired maxillary defect is diminished by the removal of a portion of the palate and alveolar bone. The intent of this study was to investigate, by three-dimensional photoelastic analysis, the stress transmission that occurs with four commonly used retentive systems. The individual designs were facial cast circumferential retention with palatal plating, swing-lock design with palatal plating, facial cast circumferential retention and palatal cast circumferential clasp reciprocation, and facial cast circumferential reciprocation with palatal I-bar retention. Stresses were observed and compared on the palate and around the teeth of the four models.

A comparison of the flexibility of wrought wire and cast circumferential clasps

M any dentists use wrought wire clasps instead of cast circumferential clasps on abutment teeth for distalextension removable partial dentures. The flexibility of the wrought wire clasp is believed to reduce transmission of excessive force to the abutment tooth.’ Recent investigations have compared the flexibility of various wrought wires and nickel-chrome-cobalt alloys commonly used for clasp construction. Morris et al.’ developed a stiffness index by testing clasps with a stress-relaxation cycling instrument. The index allows the stiffness of clasps to be compared regardless of dimension, form, or material. Brudvik and Morris3 tested six wrought wires including two different alloys and several gauges. Stress-relaxation cycling was used to determine the stiffness of the specimens. In a later study, Morris et aL4 found that the stiffness of cast circumferential clasps was greatly influenced by the width/thickness ratio of the clasp. A study by Frank and Nicholls5 ranked 16 precious and nonprecious wrought wires according to their flexibility. Each clasp sample was displaced one time until the proportional limit was exceeded. Twentygauge wires were found to be twice as flexible as l&gauge wires. Flexibility values also diKered due to the various alloys used in manufacturing the wires. Several wrought wires were tested independently by both the stress-relaxation cycling and the singledisplacement methods. Although the values for stiffness and flexibility cannot be compared directly, each method resulted in the same ranking of the clasp samples. The purpose of this study was to compare the flexibility of several forms of cast nickel-chrome and cobalt-chrome clasps with that of wrought wire clasps. Round and half-round forms were selected. The single-

Clasp partial dentures

In most instances, the clasp partial den­ ture is the restoration of choice in oc­ clusal reconstruction. The slight denture movement allowed by passive clasps avoids overworking of abutment teeth and tends to stimulate and preserve ridges. The controlled, permitted move­ ment of a removable partial denture dur­ ing the chewing cycle distributes the masticatory loads to teeth and other sup­ porting tissues without trauma to any specific region. The bar clasp is much to be preferred to the cast circumferential clasp from the standpoint of the patient’s welfare.