Circumferential Clasp Research Articles

Retentive Forces and Deformation of Fitting Surface in RPD Clasp Made of Polyether-Ether-Ketone (PEEK).

Polyetheretherketone (PEEK) has provided the option to fabricate RPDs with aesthetics unlike metal RPDs, but little attention has been paid to its suitability, especially towards the retentive forces and deformation of the clasp. This study aimed to examine the retentive forces and the fitting surface (inner surface) deformation of clasps made from PEEK and compare it with cobalt-chromium (Co-Cr) clasp. Forty-two circumferential clasps (14 Co-Cr and 28 PEEK) were fabricated and divided into two groups with clasp undercuts (0.25 mm and 0.5 mm) with thicknesses of 1 mm and 1.5 mm. Each was examined for retentive forces after cycle test on its abutment for 360 cycles. Initial and final retentive forces were recorded. The fitting surface deformation was determined using 3-Matic research analysis software. The results revealed that highest mean initial retentive force was of Co-Cr clasps with 0.50 mm undercut 22.26 N (±10.15 N), and the lowest was the 1 mm PEEK clasps with 0.25 mm undercut 3.35 N (±0.72 N) and highest mean final retentive force was the Co-Cr clasps with 0.50 mm undercut 21.40 N (±9.66 N), and the lowest was the 1 mm PEEK clasps with 0.25 mm undercut 2.71 N (±0.47 N). PEEK clasps had a lower retentive force than Co-Cr clasps with 0.50 undercut. PEEK clasps (1.5 mm) at 0.25 mm undercut had the least deformation (35.3 µm). PEEK showed significantly less deformation (p ≤ 0.014) than Co-Cr. The deformation of PEEK clasps fitting surface was lower than Co-Cr clasps and retentive forces were close to the Co-Cr clasps, suggesting the use of PEEK as an aesthetic clasp option for RPD framework.

Designing Cast Partial Dentures in Relation to Partial Edentulism

Objective: To determine the pattern of partial edentulism and the cast removable dental prosthesis design in relation to the Classes recorded.
 Study Design: Cross-sectional study.
 Place and Duration of Study: Department of Prosthodontics, Armed Forces Institute of Dentistry (AFID), Rawalpindi Pakistan, from Apr to Sep 2021.
 Methodology: A total of 67 partially dentate male and female patients presenting to the Prosthodontics Department requiring partial cast dentures were included in the study. Visual inspection of the master casts and partial denture frameworks was carried out in the laboratory. Kennedy's Classification, modification areas, type of major connector, direct retainer, rest and use of indirect retention were recorded.
 Results: The most prevalent Class of partially dentate arch was Kennedy Class-II in maxilla 10 (45.5%) and Class-I and III in mandible 15 (33.3%) each. Major connectors most frequently encountered were anteroposterior palatal strap (59.1%) and lingual bar (57.8%). Circumferential clasp (35.8%) was the most used retainer type in Classes II and III, whereas RPI was mostly found in Classes I and II (32.1%). Occlusal rests were most commonly used (72.4%). Indirect retention was mostly used in Class-I and II denture frameworks (95.9%).
 Conclusion: The most commonly encountered partial edentulism pattern was Kennedy's Class I and II. Following basic principles of RPD design can help elevate the standards of removable denture treatment.

Evaluation of Retention Force of Polyetheretherketone (PEEK) and Cast Cobalt-Chromium Circumferential Clasps: A comparative study

Aims: The aim of this in-vitro study was to compare the retention force of Polyetheretherketone (PEEK) and Cobalt-Chromium (Co-Cr) clasps by mechanical cycling test simulating ten years of use. Materials and Methods: 72 clasps samples were fabricated on a standardized e-max upper right first premolar, it is divided into 24 Co-Cr clasps, and 48 PEEK clasps which were subdivided into 24 clasps (2.4mm width), and 24 clasps (3.00mm width).Each group was further subdivided (n=8 clasps) into amounts of abutment undercut 0.25mm, 0.50, and 0.75mm undercuts. Mechanical cycling of each clasp was performed for 15000 times on its specific abutment crown. The retention force of each clasp in newton was measured every 1500 cycles by applying a tensile force using a universal tensile machine. Results: The retention force of Co-Cr clasps was higher significantly than the PEEK clasps retention force for the three undercuts. Deeper undercut showed a significantly higher retention force for both materials. All subgroups (except 0.75mm Co-Cr group) exhibit an increase in retention force after first 1500 cycles followed by gradual decrease till the end of 15000 cycles. Conclusions: The retention force of PEEK clasps with both widths along 15000 cycles of insertion/removal were lower than Co-Cr clasps but still sufficient for clinical use at 050, and 0.75mm undercut but not enough at 0.25mm undercut.

Retentive Properties of Circumferential Clasps Manufactured by Lost-Wax Method and Additive and Subtractive Manufac-turing Techniques

Retentive Properties of Circumferential Clasps Manufactured by Lost-Wax Method and Additive and Subtractive Manufac-turing Techniques

Confecção de prótese buco-maxilo para pacientes com maxilectomia parcial.

Os defeitos da maxilectomia podem resultar em comunicação oroantral que causa dificuldade na mastigação e deglutição, fala prejudicada e desfiguração facial. O protesista desempenha um papel importante na reabilitação de tais defeitos com a confecção de próteses buco-maxilares. Este artigo descreve um relatório clínico da fabricação de uma prótese definitiva com uma estrutura de metal fundido usando método de processamento único para um defeito maxilar adquirido. Um desenho tripodal foi selecionado para este caso. Os grampos foram colocados nos pré-molares e molares dos dois quadrantes da maxila. Palato completo com o conector principal projetado para garantir a distribuição máxima da carga funcional para o tecido. O retentor indireto foi planejado no primeiro pré-molar direito. A retenção direta foi fornecida pelo fecho em barra I, colocado no primeiro pré-molar esquerdo, fecho circunferencial no primeiro pré-molar direito e fecho de abrasão entre o primeiro e o segundo molares direitos. Assim, essa prótese definitiva reabilitou o paciente, proporcionando melhor eficiência mastigatória, melhorando a clareza da fala e a qualidade de vida do paciente.

Effect of different materials and undercut on the removal force and stress distribution in circumferential clasps during direct retainer action in removable partial dentures

ObjectivesThis study aimed to evaluate the effect of different materials and undercut on the removal force and stress distribution in the supporting tooth and in the circumferential clasp used in removable partial prosthesis. MethodsUpper molars prepared for Akers circumferential clasp with retention and opposing arm were modeled, scanned, elaborated with CAD software and the geometries imported in FEA and analyzed. Six different materials were selected for the clasp (Polyamide, Polyoxymethylene, Polyetheretherketone - PEEK, Gold alloy, Titanium and CoCr) and 3 different undercuts (0.25, 0.50 and 0.75mm), totaling 18 groups. ResultsThe clasps presented greater stress in their structure and potentially greater damage to the dental enamel when made with rigid materials and with more undercut; however, they presented greater ability to remain in position. SignificancePolyamide with a higher undercut is an esthetic alternative to rigid metallic clasps. It showed promising behavior because it strongly reduces the damage to the enamel, and even with an undercut of 0.75, the retention is lower than for CoCr with a 0.25 undercut, and this retention might still be sufficient. Polyoxymethylene and Polyetheretherketone (PEEK) are not suitable materials for the clasps, because the maximum stress occurring during removal with higher undercuts is higher than the material strength.

Evaluation of Different Removable Denture Materials in Kennedy Class I Partially Edentulous Situation Mostafa Abosrie(1), Maged El saadawy (2) and Mohamed Aboshama(3) Codex

BACKGROUND: Although Cast Chromium Cobalt alloy has been the material of choice for fabricating Removable Partial Dentures (RPDs) but it has certain drawbacks. New material like the flexible Nylon based Super Polyamide has been introduced to overcome these drawbacks. The present study compared the above two materials for three clinical parameters. MATERIALS AND METHODS: The study was carried out on 15 patients, the selected cases were Kennedy Class I, with missing teeth first, second and third molars in each distal extension side. These fifteen patients received three RPDs; each one was used for six months. Three types of RPDs were made from different base materials; cobalt chromium alloy and thermoplastic denture base materials, (Group A): RPDs made of cast Cr-Co alloy incorporating RPI clasping system with denture base made of heat cured acrylic resin. (Group B): RPDs made of flexible nylon based super polyamide resin incorporating flexible circumferential clasps and denture bases made of flexible nylon, with metal occlusal rests. (Group C): RPDs made of flexible nylon based super polyamide resin. After insertion of each denture, their Clinical performances were evaluated periodically for six months for the following parameters (Gingival index, plaque index and pocket depth). RESULTS: Statistically significant results were obtained in favor of flexible RPDs, in the parameters of (Gingival index, plaque index and pocket depth).Both groups B and C showed less similar values for (Gingival index, plaque index and pocket depth). during usage’ with the incidence being slightly higher for patients wearing the cast RPDs (Group A). CONCLUSION: Based on the favorable results of this study, it can be summarized that the flexible RPDs is a viable alternative to cast RPDs in Kennedy class I partially edentulous situation in the short term.

An analytical model to design circumferential clasps for laser-sintered removable partial dentures

ObjectiveClasps of removable partial dentures (RPDs) often suffer from plastic deformation and failure by fatigue; a common complication of RPDs. A new technology for processing metal frameworks for dental prostheses based on laser-sintering, which allows for precise fabrication of clasp geometry, has been recently developed. This study sought to propose a novel method for designing circumferential clasps for laser-sintered RPDs to avoid plastic deformation or fatigue failure. MethodsAn analytical model for designing clasps with semicircular cross-sections was derived based on mechanics. The Euler–Bernoulli elastic curved beam theory and Castigliano’s energy method were used to relate the stress and undercut with the clasp length, cross-sectional radius, alloy properties, tooth type, and retention force. Finite element analysis (FEA) was conducted on a case study and the resultant tensile stress and undercut were compared with the analytical model predictions. Pull-out experiments were conducted on laser-sintered cobalt–chromium (Co–Cr) dental prostheses to validate the analytical model results. ResultsThe proposed circumferential clasp design model yields results in good agreement with FEA and experiments. The results indicate that Co–Cr circumferential clasps in molars that are 13mm long engaging undercuts of 0.25mm should have a cross-section radius of 1.2mm to provide a retention of 10N and to avoid plastic deformation or fatigue failure. However, shorter circumferential clasps such as those in premolars present high stresses and cannot avoid plastic deformation or fatigue failure. SignificanceLaser-sintered Co–Cr circumferential clasps in molars are safe, whereas they are susceptible to failure in premolars.

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.

A 30-Year Follow-Up of Partial Removable Dental Prostheses in a University Dental School Setting.

To describe the pattern of partial removable dental prosthesis (PRDP) designs over a 30-year period in a cohort of patients from the Université de Montréal, Faculty of Dentistry and to examine the effect of this design in PRDP complaints and the required treatment in a subsample of the patients' cohort. In this retrospective descriptive study, 1380 PRDP laboratory prescriptions (1980-2009) and 131 PRDP clinical complaint forms (2006-2008) from the archives of the undergraduate prosthodontics clinic of Université de Montréal were selected. Data on type of PRDPs, design, PRDP-related complaints, and the need for treatment were collected. Descriptive statistics and bivariate statistical analyses were conducted. U-shaped (54%) and lingual plate (94%) were the most common major connectors used in the maxillary and mandibular arch, respectively. In 95% of laboratory prescriptions, circumferential clasp was the design for the retainers. Fracture of PRDP components was the most common (41%) complaint. Most of the complaints (68%) were made by PRDP wearers having natural teeth in the opposing arch. There was a significant relationship between fracture of PRDP components and having opposing natural teeth (p = 0.002). Seventy-three percent of PRDP-related complaints were manageable only by minor treatments such as repair, readjustments, and oral hygiene instructions. Changes in the design of PRDPs were noticeable at the Université de Montréal since 1980, but there has been little change in the last 20 years. Biomechanical concepts and optimum hygiene were the basic elements in the design of RDPs in this university-based dental school setting. The majority of the complaints were treated by minor treatments.

Pregled retencijskih elemenata mobilnih djelomičnih proteza ovisno o vrsti bezubosti i zubima nosačima u komercijalnim laboratorijima u Ateni

The aim of this survey was to record removable partial denture (RPD) retentive elements and abutment teeth in partially edentulous patients, identified in commercial laboratories in Athens, Greece.628 master casts with the corresponding cast metal frameworks used in the construction of RPDs were evaluated. Casts were photographed to identify the number and position of existing teeth, the partial edentulism class and the retentive elements. Prevalence tables and the x(2) test were used for the statistical analysis of the collected data (α=.05).There were 276 maxillary (43.9%) and 352 (56.1%) mandibular casts. Maxillary edentulism entailed almost a total absence of right third molars in 96.7% and left third molars 96.0% of casts, with lower rates for the first and second molars. Edentulism in the posterior mandible presented a similar pattern. The most profound findings concerning retentive elements were: 91.9% of the retainers used were clasps and the remaining 8.1% were attachments. Of the clasps used, 48.9% were of the Roach Τ type, a finding more common in Kennedy Class I as compared to other Kennedy Classes (p<0.01). The circumferential clasps accounted for 19.3% of the total clasps used, and it was less frequently presented (8.8%) in Kennedy I Classes (p<0.01).Roach clasps were used in the majority of cases whereas RPI clasps and attachments were rarely used.

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.

Prevalence of removable partial dentures users treated at the Aracatuba Dental School – UNESP

The aim of this study was to evaluate the frequency of removable partial dentures (RPD) at the Aracatuba Dental School. The study was conducted by analysing 412 clinical history of patients attended at the RPD clinics in the period from 2000 to 2007. 412 charts were analysed: 148 (35.9%) men and 264 (64.1%) women. The mean age was 53.8 years (men) and 52.4 years (women). A total of 556 dentures were made; of these, 233 (41.90%) were maxillary and 323 (58.09%) were mandibular dentures. The most frequent Kennedy classification found was Class III (maxilla) and Class I (mandible). In the maxilla, 55% (126) of the major connectors were of the anterior-posterior palatal bar, while in the mandible, 64% (202) were the lingual bar. As regards the claps, 401 were circumferential and 318 were bar claps. The mean age of the patients was 52.9 years with higher prevalence of female patients; the most frequent Kennedy's classification was Class I in mandible and Class III in maxilla; the most common major connector was anterior-posterior palatal bar for maxilla and lingual bar for mandible; the circumferential clasps were the most common retainer used in both jaws.

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.

Effect of acetyl resin retentive arms on the retentive force of circumferential clasps: An in vitro study

PurposeTo compare and to evaluate the stability of the retentive force of cobalt–chromium (Co–Cr) circumferential clasps (control) to those with an acetyl resin retentive arm. MethodsSixteen specimens with a couple of circumferential clasps were made using Co–Cr over a metal model providing 0.25mm undercuts. Eight specimens were fabricated without the anterior retentive arm, which was made later using acetyl resin (Dental D). Insertion and removal simulation test was performed through 7250 cycles. The retentive force was recorded in Newtons (N) for periods corresponding to 0, 1, 2, 3, 4, and 5 years. The data were subjected to ANOVA and Tukey test to compare periods and to Student's t test to compare groups (α=0.05). ResultsMean (SD) is presented for Co–Cr and resin groups, respectively: 8.09(3.05) and 2.79(1.57) in period 0; 10.48(4.25) and 3.32(1.92) in 1 year; 10.09(4.15) and 3.47(1.81) in 2 years; 9.87(4.30) and 3.46(1.87) in 3 years; 9.46(3.93) and 3.27(1.59) in 4 years; 9.63(3.79) and 3.41(1.59) in 5 years. There were significant differences for Co–Cr between periods of 0 and 1 (p<0.001), 0 and 2 (p<0.01) and 0 and 3 (p<0.05). In the resin group, no significant differences were found between periods (p>0.05). Comparisons between the groups showed statistical differences for all tested periods: 0 (p=0.0012), 1 (p=0.0013), 2 (p=0.0019), 3 (p=0.0031), 4 (p=0.0027) and 5 years (p=0.0014). ConclusionsAcetyl resin retentive arms, even if only in the anterior clasps, can significantly reduce the retentive force, but this force remained stable after 5 years of simulated use.

Optimum design for glass fiber-reinforced composite clasps using nonlinear finite element analysis

The purpose of this study was to design an optimum glass fiber-reinforced composite (FRC) clasp. Three-dimensional finite element models were constructed of FRC circumferential clasp arms and an abutment tooth. The basic clasp arm was half-oval, without a taper, 2.60 mm wide and 1.30 mm thick. Four modified clasp arms were prepared by changing the width or thickness of the basic clasp (width/thickness: 2.60 mm/0.65 mm, 2.60 mm/1.95 mm, 1.30 mm/1.30 mm, and 3.90 mm/1.30 mm). Forced displacements of 5 mm in the removal direction were applied to the nodes at the base of the clasp arm. The retentive forces and maximum tensile stresses of the five FRC clasp arms ranged from 1.00-16.30 N and from 58.9-151 MPa, respectively. Results showed that an optimum FRC clasp was a circumferential clasp with 2.60 mm width and 1.30 mm thickness, which had sufficient retentive force and low risk of tensile failure.

Retention Strength of Cobalt-Chromium vs Nickel-Chromium Titanium vs CP Titanium in a Cast Framework Association of Removable Partial Overdenture

There is little information considering the framework association between cast clasps and attachments. The aim of this study was to evaluate the retention strength of frameworks match circumferential clasps and extra resilient attachment cast in three different alloys (cobalt-chromium, nickel-chromium titanium and commercially pure titanium), using two undercut (0.25 and 0.75 mm) and considering different period of time (0, 1/2, 1, 2, 3, 4 and 5 years). Using two metallic matrices, representing a partially edentulous mandibular right hemiarch with the first molar crown, canine root and without premolars, 60 frameworks were fabricated. Three groups (n = 20) of each metal were cast and each group was divided into two subgroups (n = 10), corresponding the molar undercut of 0.25 mm and 0.75 mm. The nylon male was positioned at the matrix and attached to the acrylic resin of the prosthetic base. The samples were subjected to an insertion and removal test under artificial saliva environment. The data were analyzed and compared with ANOVAs and Tukey's test at 95% of probability. The groups cast in cobaltchromium and nickel-chromium-titanium had the highest mean retention strength (5.58 N and 6.36 N respectively) without significant difference between them, but statistically different from the group cast in commercially pure titanium, which had the lowest mean retention strength in all the periods (3.46 N). The association frameworks using nickel-chromium- titanium and cobalt-chromium could be used with 0.25 mm and 0.75 mm of undercut, but the titanium samples seems to decrease the retention strength, mainly in the 0.75 mm undercut. The circumferential clasps cast in commercially pure titanium used in 0.75 mm undercuts have a potential risk of fractures, especially after the 2nd year of use. This in vitro study showed that the framework association between cast clasp and an extra resilient attachment are suitable to the three metals evaluated, but strongly suggest extra care with commercially pure titanium in undercut of 0.75 mm. Frameworks fabricated in Cp Ti tend to decrease in retentive strength over time and have a potential risk of fracture in less than 0.75 mm of undercut.

Cyclic fatigue properties of cobalt-chromium alloy clasps for partial removable dental prostheses

Cast cobalt-chromium (Co-Cr) alloy clasps have been widely used for prosthodontic treatment, but long-term retentiveness of these clasps is not clear. The purpose of this study was to investigate the residual retentive force of 3 types of cast Co-Cr alloy clasps in relation to their proportional limits. Thirty half-round straight clasps and 30 circumferential clasp assemblies were made from 3 Co-Cr alloys (Hardalloy, Regalloy, and Vera PDN) (n=10). All of the straight clasps were subjected to a compression-deformation test to obtain data for displacement/load at the proportional limit. Two undercut depths (0.25 mm and 0.50 mm, n=5) were included in a cyclic fatigue test. Each circumferential clasp assembly was subjected to an insertion/removal test on a metal abutment tooth for 7200 cycles to simulate 5 years of clinical use. The residual retentive force was measured after 360 cycles; thus, the retentive force of each clasp was recorded 21 times throughout the test. The data were subjected to repeated-measures ANOVA (α=.05) to compare the retentive force of each group of clasps for different periods of fatigue testing. The ANOVA. The Student t test (α=.05) was used for analysis of clasps fabricated with the same alloy but with different undercuts. A linear correlation analysis (α=.05) was used to test the correlation between retentive forces and cycling sequences. The mean values of displacement at the proportional limit for the 3 Co-Cr alloys varied from 0.30 mm to 0.36 mm. The mean retentive forces of each alloy group decreased dramatically after the first cycling phase (P<.05). Thereafter, the decrease was more gradual but was still significantly different compared to the original retentive forces (P<.05). Compared to clasps in the 0.25-mm undercut group, those in the 0.50-mm undercut group exhibited greater mean retentive forces before the cyclic fatigue test (P<.05), as well as a greater decrease in the retentive force at the end of the test (P<.05). A negative correlation was found between the retentive force of cast Co-Cr alloy clasps and the logarithm of cycling sequences. After a test simulating 5 years of service, cast Co-Cr alloy clasps exhibited a residual retentive force to satisfy the requirements for clinical use.

Comparative study of two commercially pure titanium casting methods

The interest in using titanium to fabricate removable partial denture (RPD) frameworks has increased, but there are few studies evaluating the effects of casting methods on clasp behavior.ObjectiveThis study compared the occurrence of porosities and the retentive force of commercially pure titanium (CP Ti) and cobalt-chromium (Co-Cr) removable partial denture circumferential clasps cast by induction/centrifugation and plasma/vacuum-pressure.Material and Methods72 frameworks were cast from CP Ti (n=36) and Co-Cr alloy (n=36; control group). For each material, 18 frameworks were casted by electromagnetic induction and injected by centrifugation, whereas the other 18 were casted by plasma and injected by vacuum-pressure. For each casting method, three subgroups (n=6) were formed: 0.25 mm, 0.50 mm, and 0.75 mm undercuts. The specimens were radiographed and subjected to an insertion/removal test simulating 5 years of framework use. Data were analyzed by ANOVA and Tukey's to compare materials and cast methods (α=0.05).ResultsThree of 18 specimens of the induction/centrifugation group and 9 of 18 specimens of plasma/vacuum-pressure cast presented porosities, but only 1 and 7 specimens, respectively, were rejected for simulation test. For Co-Cr alloy, no defects were found. Comparing the casting methods, statistically significant differences (p<0.05) were observed only for the Co-Cr alloy with 0.25 mm and 0.50 mm undercuts. Significant differences were found for the 0.25 mm and 0.75 mm undercuts dependent on the material used. For the 0.50 mm undercut, significant differences were found when the materials were induction casted.ConclusionAlthough both casting methods produced satisfactory CP Ti RPD frameworks, the occurrence of porosities was greater in the plasma/vacuum-pressure than in the induction/centrifugation method, the latter resulting in higher clasp rigidity, generating higher retention force values.