Cobalt-chromium Removable Partial Dentures Research Articles

Dental Students' Perception and Self-Perceived Confidence Level in Key Dental Procedures for General Practice and the Impact of Competency Implementation on Their Confidence Level, Part I (Prosthodontics and Conservative Dentistry).

Evaluating the level of dental students' competence is crucial for validating their preparedness for graduation. Confidence has a significant role in achieving competence. There are limited studies that assess the level of self-perceived confidence among final-year dental students regarding their ability to conduct key dental procedures. This study aims to assess the self-perceived confidence level of final-year dental students in performing essential dental procedures across various dental disciplines and to assess the effect of implementing competencies in the curriculum on the self-perceived confidence level of students by comparing two cohorts of final-year students in two different years 2016 (Traditional Cohort) and 2019 (Competencies Cohort). An questionnaire was answered by two cohorts of final-year dental students: one group in 2016 before the implementation of the competency-based assessment system (group 1, n = 153), and the other in 2019 after the implementation of this system (group 2, n = 199), the same questionnaire was used for both cohorts. The results from the two groups were compared regarding the degree of self-perceived confidence in conducting key dental procedures. The data were analysed using SPSS statistics and Levene's Test for Equality of Variances and t-test for Equality of Means calculated. Group 1 showed a significantly higher means of self-perceived confidence levels than group 2 in the ability to conduct seven out of the 20 prosthodontics procedures studied: providing patients with Cobalt-Chromium (Co-Cr) removable partial dentures (RPD) (3.77 vs. 3.56), providing the patient with Acrylic RPD (3.70 vs. 3.23), treatment planning for partially edentulous patients (3.83 vs. 3.34), giving OHIs for denture patients (4.17 vs. 3.95), dealing with CD postinsertion complaints (3.97 vs. 3.76), giving postinsertion instructions for removable prostheses cases (4.12 vs. 3.82), and providing patients with immediate dentures (2.67 vs. 2.32). The same applies to 6 out of 16 conservative dentistry procedures: placing anterior composite (4.41 vs. 4.12), placing posterior composite (4.43 vs. 3.88), placing posterior amalgam (4.29 vs. 4.02), placing matrix band for Class II restorations (4.24 vs. 3.71), placing a prefabricated post (3.34 vs. 2.88), and placing fiber post (3.45 vs. 3.34). On the other hand, group 2 shows higher means of self-perceived confidence than group 1 in only two conservative dentistry procedures: onlay restorations (2.18 vs. 2.76) and inlay restorations (2.22 vs. 2.75). No significant differences in means of self-perceived confidence were found between the two groups in the remaining 21 procedures studied. This study has shown that final-year dental students have high self-perceived confidence levels in doing simple dental procedures yet less confidence in more complex ones. Although, students' self-perceived confidence decreases after the introduction of a competency-based assessment system. Competency implementation and execution criteria may differ between schools which may have an impact on final outcomes. Hence, there is a need for regular evaluation of competencies being assessed to maintain a curriculum that is up to date.

Physicomechanical properties of cobalt-chromium removable partial denture palatal major connectors fabricated by selective laser melting

Statement of problemAdditive manufacturing by selective laser melting (SLM) has been claimed to be less challenging than conventional casting of cobalt-chromium (Co-Cr) removable partial dentures (RPDs), providing significant improvements. However, how the physicomechanical properties of Co-Cr RPDs fabricated by SLM compare with those fabricated by conventional casting is unclear. PurposeThe purpose of this in vitro study was to evaluate the physicomechanical properties of Co-Cr RPD palatal major connectors fabricated by SLM compared with those fabricated by conventional casting. Material and methodsA master die simulating a maxillary arch of Kennedy class III modification 1 was scanned to create a virtual 3-dimensional (3D) cast. Two groups of 5 Co-Cr RPD major connectors were fabricated. In the 3D printing group, the Co-Cr major connector was virtually designed and exported for direct SLM 3D printing. For the conventional group, Co-Cr major connectors were constructed conventionally. The Co-Cr major connectors were virtually superimposed with the master die for surface adaptation analysis. Additional comparative analyses of surface roughness, relative density, microhardness, and microstructure of the 2 groups were performed. Data were analyzed by using independent t tests (α=.05). ResultsThe overall volumetric and linear discrepancies were significantly higher (P<.05) in the 3D printing group. Significant differences in the surface roughness (P<.05) and microhardness (P<.05) were observed, with the 3D printing group having higher surface roughness and microhardness than the conventional group. Unlike conventional connectors, the microstructure of 3D-printed connectors showed fine homogeneous granules. ConclusionsCompared with the conventional casting technique, SLM 3D printing enabled the fabrication of Co-Cr RPD major connectors with higher microhardness and fine homogenous microstructure. However, the surface adaptation and surface roughness of SLM 3D printing Co-Cr connectors were worse than those produced conventionally. Both techniques showed similar relative densities.

The teaching of removable partial dentures in dental schools in Oceania

ObjectivesTo examine the current arrangements and trends in the teaching of removable partial dentures (RPDs) in dental schools in Oceania. MethodsA validated and trialled 30-item electronic survey was sent via e-mail to 12 dental schools in Oceania that offered undergraduate dentistry. The survey explored various aspects of the teaching of RPDs in preclinical and clinical courses including: educational content and process, staff members involved, facilities and techniques utilized, clinical requirements, coursework evaluation and perceived challenges to RPD teaching. ResultsThe response rate of the survey was 75 % (n = 9). All respondent schools taught a preclinical course in RPD design and production, with the majority (67 %) starting the clinical provision of RPD patients in Year 3. The mean duration of the course was 63 h for hands-on activities and 23 h for didactic teaching. The courses were mainly taught by senior lecturers. On average, students made four units of acrylic RPD and two cobalt-chromium RPDs during the course. All respondent schools taught prescription writing for RPD. The majority of schools (n = 8) stated that they had an adequate patient pool for students to treat. Lack of adequately trained staff for teaching and pressure on teaching time from other sources were the most commonly reported challenges. ConclusionThe structure and content of RPD courses in dental schools of Oceania provide an adequate level of competence on the subject, and is broadly similar to other parts of the world. Plans should be in place to maintain and improve the quality of educational programmes to keep pace with growing student numbers and the rapidly evolving profession. Clinical significanceWith increasing numbers of patients presenting to general dental practitioners requiring complex RPDs, it is paramount that undergraduate training programs produce graduates with the competencies necessary to care for such patients to a high standard.

Quality of communicating design features for cobalt chromium removable partial dentures in Riyadh, Saudi Arabia

This survey aimed to investigate quality of communicating design features for the construction of cobalt chromium removable partial dentures (RPDs) among dentists in Riyadh, Saudi Arabia. A survey of nine commercial dental laboratories located in Riyadh was carried out. In each visit, master casts for cobalt chromium RPDs and dentists' prescriptions were examined. A quality score for the provided instructions was developed and ranged from 0 to 4. A zero score means that no instructions were sent from the dentist for the design of the RPD. A score of 4 means that instructions were provided for the design of four main elements of the RPD, i.e., shape of major connector, type of direct retainers, position of direct retainers, position of dental rests. 162 dentists' prescriptions for RPDs and related casts were assessed. The majority of RPD cases were designed by the dental technician alone (64.2%). Shape of the major connector was the most frequent element in dentists' prescriptions (35.8%). The mean quality score of dentists' instructions was 0.96 (sd=1.54). 18% of the provided instructions achieved quality score equal to 4. Prescriptions for Kennedy Class III cases achieved significantly higher mean quality score compared to Kennedy Class II cases (p<0.05). 16.7% of the evaluated casts had clearly defined rest seat preparation. The results of this survey indicate inadequate quality of communicating the design features of cobalt chromium RPDs among practicing dentists in Riyadh, Saudi Arabia. The reliance on the dental technician to design the cast RPDs seems to be high.

The Perceptions of Dentists Working in Saudi Arabia of the Utility of Different Restoration Options for a Shortened Dental Arch in Patients of Different Ages.

This study aimed to assess dentists' views of the utility of an unrestored shortened dental arch (SDA) compared to the utility of various prosthetic treatment options. A total of 142 dentists working at four sites in Riyadh, Saudi Arabia, were interviewed and presented with 18 scenarios for patients of different ages with SDAs that lost molar teeth. Participants were asked to indicate on a standardized visual analog scale (VAS) how they would value the health of the patient's mouth if the SDAs were left unrestored or restored with five prosthetic dental restorations. With a utility value of 0.0 representing the worst possible health state for a mouth and 1.0 representing the best, dentists' mean utility value for unrestored SDAs was 0.43 (standard deviation [SD] = 0.28). For implant-supported fixed dental prostheses (ISFDPs), cobalt-chromium removable partial dentures (RPDs), acrylic RPDs, cantilever conventional fixed dental prostheses (CFDPs), and cantilever resin-bonded fixed dental prostheses (RBFDPs), the mean utility values were 0.64 (SD = 0.27), 0.54 (SD = 0.20), 0.48 (SD = 0.20), 0.42 (SD = 0.28), and 0.39 (SD = 0.27), respectively. Neither patient age nor dentists' clinical experience had an impact on dentists' perceptions of the utility of unrestored SDAs and outcomes of this treatment concept (P > .01). Restoration of SDAs by ISFDPs received the highest utility value among the surveyed group of dentists. Although the assigned value for unrestored SDAs was low, this value was comparable to the value of SDAs that were restored by acrylic RPDs or cantilever FDPs of either type.

A study of dentists' preferences for the restoration of shortened dental arches with partial dentures.

Objective:This study aimed to use a utility method in order to assess dentists’ preferences for the restoration of shortened dental arches (SDAs) with partial dentures. Also, the impact of patient age and length of the SDA on dentists’ preferences for the partial dentures was investigated.Materials and Methods:Totally, 104 subjects holding a basic degree in dentistry and working as staff members in a private dental college in Saudi Arabia were interviewed and presented with 12 scenarios for patients of different ages and mandibular SDAs of varying length. Participants were asked to indicate on a standardized visual analog scale how they would value the health of the patient's mouth if the mandibular SDAs were restored with cobalt-chromium removable partial dentures (RPDs).Results:With a utility value of 0.0 representing the worst possible health state for a mouth and 1.0 representing the best, dentists’ average utility value of the RPD for the SDAs was 0.49 (sd= 0.15). Mean utility scores of the RPDs across the 12 SDA scenarios ranged between 0.35 and 0.61. RPDs that restored the extremely SDAs attracted the highest utility values and dentists’ utility of the RPD significantly increased with the increase in the number of missing posterior teeth. No significant differences in dentists’ mean utility values for the RPD were identified among SDA scenarios for patients of different ages.Conclusion:Restoration of the mandibular SDAs by RPDs is not a highly preferred treatment option among the surveyed group of dentists. Length of the SDA affects dentists’ preferences for the RPD, but patient age does not.

The impact of rehabilitation using removable partial dentures and functionally orientated treatment on oral health-related quality of life: A randomised controlled clinical trial

ObjectivesThis study aimed to compare two different tooth replacement strategies for partially dentate older patients; namely functionally orientated treatment according to the principles of the shortened dental arch (SDA) and conventional treatment using removable partial dentures (RPDs) using a randomised controlled clinical trial. The primary outcome measure for this study was impact on oral health-related quality of life (OHRQoL) measured using the short form of the oral health impact profile (OHIP-14). MethodsPatients aged 65 years and older were randomly allocated to two different treatment groups: the RPD group and the SDA group. For the RPD group each patient was restored to complete arches with cobalt–chromium RPDs used to replace missing teeth. For the SDA group, patients were restored to a premolar occlusion of 10 occluding pairs of natural and replacement teeth using resin bonded bridgework (RBB). OHRQoL was measured using the OHIP-14 questionnaire administered at baseline, 1 month, 6 months and 12 months after treatment intervention. ResultsIn total, 89 patients completed the RCT: 44 from the RPD group and 45 from the SDA group. Analysis using a mixed model of covariance (ANCOVA) illustrated that treatment according to the SDA concept resulted in significantly better mean OHIP-14 scores compared with RPD treatment (p<0.05). This result was replicated in both treatment centres used in the study. ConclusionsIn terms of impact on OHRQoL, treatment based on the SDA concept achieved significantly better results than that based on RPDs 12 months after treatment intervention (trial registration no. ISRCTN26302774). Clinical significanceFunctionally orientated treatment delivery resulted in significantly better outcomes compared to removable dentures in terms of impact on OHRQoL.

Ethics in the provision of removable partial dentures

Aim: To investigate the construction of cobalt-chromium removable partial dentures by commercial private dental laboratories. Methods: Ninety master casts for fabrication of cobalt-chromium removable partial dentures were obtained from three commercial laboratories randomly selected. Casts were assessed for dental arch treated, Kennedy classification, cast surveying, denture design information provided by the dentist, and mouth preparation (rest seat, guiding plane and retentive area). Dental technicians answered a questionnaire regarding qualification of assisted dentists, monthly number of framework castings, and use of dental surveyor. Mouth preparation was compared among laboratories using Kruskal-Wallis test (α=0.05). Results: The percentage of Kennedy class I was 16%, class II 19%, class III 56%, and class IV 9%. The majority of master cats (51%) examined was sent to dental laboratories without any design information and did not comply with ethical guidelines in the provision of RPD. Approximately half of the casts were considered “inappropriate” for guiding planes and retentive areas. One of the laboratories presented all casts “inappropriate” for rest seat distribution (p<0.001). Conclusions: Mouth preparation frequently failed for guiding planes, retentive areas and distribution of rest seats. It is necessary to provide students with adequate clinical experience at the dental school environment, which will actually be carried into the practice of dentistry

Partial edentulism and removable partial denture design in a dental school population: a survey in Greece

To investigate the pattern of partial edentulism and the most frequent designs of cobalt-chromium removable partial dentures (RPDs), constructed at the Dental School of Athens, Greece. Five hundred and fifty-three patients, between 42 and 81 years old, mostly males, treated by undergraduate dental students, were included. The survey was based on visual evaluation of master casts and work authorisation to dental technicians. Aspects examined were: Kennedy Classification, modification areas, major connectors, clasping, placement of rest seats and indirect retention. Kennedy Class I was the most common encountered in the maxilla (50.5%) and in the mandible (70%). The most frequent major connectors were the lingual bar (92.6%) and the U-shaped palatal strap (54%). The most common clasp was the Roach (69.2%) in Class I and Class II. In Class III and IV, the most common was the occlusally approaching clasp (55% and 70%). The most frequent location of the rest was mesial of abutment teeth. On the average, 39.5% of Class I RPDs and 58.6% of Class II RPDs had indirect retainers. A combination of the two major philosophies of RPD design (biomechanical and hygienic) was evident in the RPDs examined in our study.

Designing cobalt chromium removable partial dentures for patients with shortened dental arches - a pilot survey

The aim of this survey was to investigate the quality of prescription for the fabrication of cobalt chromium removable partial dentures (RPDs) that are used to extend the shortened dental arches (SDAs). A survey of four commercial dental laboratories located in northern England was conducted. The target of this survey was cobalt chromium RPDs that were requested to restore SDAs comprising the anterior teeth and 2-4 premolars. Dentists' prescriptions were scrutinised, and a special data collection form was completed accordingly. A total of 94 dentists' prescriptions and associated SDA casts were examined. Almost all the requested cobalt chromium RPDs were clasp-retained RPDs (97%). Scrutinising the 91 prescriptions for clasp-retained cobalt chromium RPDs showed that dentists' prescriptions did not have any instructions about the design of the partial denture in a considerable proportion of the cases (32%). Teeth to be clasped were identified clearly in 45% of the prescriptions. A majority of the dentists (64%) failed to provide any instructions about the design of the rests to be placed on the most posterior premolar abutment teeth. A considerable proportion of the dentists delegated the task of selecting the type of the major connector to the dental technician (41%). Only 21 (23%) of the examined casts had clearly defined rest seat preparation. The outcome of this pilot survey shows inadequate quality of prescription in designing RPDs for patients with SDAs. This finding has an ethical and clinical bearing and does not fit with current legal guidelines relevant to designing RPDs.

Tooth preparation for rest seats for cobalt-chromium removable partial dentures completed by general dental practitioners

The aim of this project was to examine tooth preparations made by general dental practitioners (GDPs) for occlusal and cingulum rest seats for cobalt-chromium removable partial dentures (RPDs). Master casts and prescribed denture designs for cobalt-chromium RPDs produced by a commercial dental laboratory from impressions made by 45 GDPs across Wales were evaluated over a period of 5 months. Rest seats and associated interocclusal clearances were assessed using pre-determined criteria. A total of 68 casts were examined. Of these, 33 did not have rest seats included in their prescription. Of the remaining 35 casts, 81 rests had been prescribed of which only 24 (30%) had signs of tooth preparations for these rest seats. Using pre-determined criteria, 60% of rest seats were under-prepared in the mesio-distal plane and 30% were over-prepared in the bucco-lingual plane. In 17 cases where natural teeth opposed the rest seat, the mean interocclusal clearance was 1·5 mm (range 0·6-3·5 mm) with 6 of the 17 rests (35%) being less than the recommended thickness. In total, 18 of the 24 rests prepared did not meet the criteria, and 11 of the 21 rests prescribed had no obvious preparation and insufficient occlusal clearance. Where prescribed, the majority of rests did not meet the identified criteria. The rest seat preparations varied greatly in all planes including the interocclusal clearance. Further emphasis should be given to aspects of denture design in undergraduate and continuing education programmes for dentists.

Quality of communication and master impressions for the fabrication of cobalt chromium removable partial dentures in general dental practice in England, Ireland and Wales in 2009

The aim of this study was to investigate the quality of communication and master impressions for the fabrication of cobalt chromium removable partial dentures (RPDs) in general dental practice in England, Ireland and Wales in 2009. Two hundred and ten questionnaires were distributed to 21 laboratories throughout England, Ireland and Wales. Information was collected regarding the quality of written communication and selection of master impression techniques for cobalt chromium partial dentures in general dental practice. One hundred and forty-four questionnaires were returned (response rate = 68%). Alginate was the most popular impression material being used in 58% of cases (n = 84), while plastic stock trays were the most popular impression tray, being used in 31% of cases (n = 44). Twenty-four per cent (n = 35) of impressions were not adequately disinfected. Opposing casts were provided in 81% of cases (n = 116). Written instructions were described as being 'clear' in 31% of cases (n = 44). In 54% of cases (n = 76), the technician was asked to design the RPD. Based on the findings of this study, written communication for cobalt chromium RPDs by general dental practitioners is inadequate. This finding is in breach of relevant contemporary legal and ethical guidance. There are also concerns in relation to the fabrication process for this form of prosthesis, particularly, in relation to consideration of occlusal schemes.

Retention force of T-bar clasps for titanium and cobalt-chromium removable partial dentures

The objective of this study was to evaluate the retention force of T-bar clasps made from commercially pure titanium (CP Ti) and cobalt-chromium (Co-Cr) alloy by the insertion/removal test simulating 5 years use. Thirty-six frameworks were cast from CP Ti (n=18) and Co-Cr alloy (n=18) with identical prefabricated patterns on refractory casts from a distal extension mandibular hemi-arch segment. The castings were made on a vacuum-pressure machine, under vacuum and argon atmosphere. Each group was subdivided in three, corresponding to 0.25 mm, 0.50 mm and 0.75 mm undercuts, respectively. No polishing procedures were performed to ensure uniformity. The specimens were subjected to an insertion/removal test and data was analyzed statistically to compare CP Ti and Co-Cr alloy in the same undercut (Student's t-test for independent samples) and each material in different undercuts (one-way ANOVA) (p=0.05). Comparisons between materials revealed significant differences (p=0.017) only for the 0.50-mm undercut. No significant differences (p>0.05) were found when comparing the same material for the undercuts. It may be concluded that for different undercuts, both Co-Cr alloy and CP Ti had no significant differences for T-bar clasps; CP Ti showed the lowest retention force values when compared to Co-Cr alloy in each undercut, but with significant difference only for the 0.50-mm undercut; and both materials maintained the retentive capacity during the simulation test.

Why do dentists struggle with removable partial denture design? An assessment of financial and educational issues

Published studies in the international dental literature illustrate that the quality of prescription and fabrication of cobalt-chromium removable partial dentures (CCRPDs) by general dental practitioners frequently fail to comply with ethical and legal requirements. The reasons cited for this in the past have broadly related to either financial or educational issues. The aim of this investigation is to determine the effect of financial and educational factors on the quality of CCRPD design and fabrication by general dental practitioners. This investigation was completed in two parts. (1) A pre-piloted pro-forma was distributed to a number of dental laboratories throughout the UK and Ireland. These sought information relating to the quality of written instructions for CCRPDs received by these laboratories, and details of the remunerative scheme under which they were being provided. Three categories of remunerative scheme were considered, private CCRPDs in Ireland, private CCRPDs in the UK, and CCRPDs being provided by salaried NHS practitioners. (2) A pre-piloted questionnaire was distributed to vocational dental practitioners in the UK and Ireland. This sought information relating to their attitudes, opinions, and educational and clinical experiences of CCRPD design and fabrication. (1) Three hundred completed pro-formas were returned from dental laboratories, 100 of which related to each of the three remunerative schemes. Poor or no written instructions were provided in 47% (n = 47) of CCRPD cases funded privately in the UK, 46% (n = 46) of CCRPD cases funded privately in Ireland, and 50% (n = 50) of CCRPDs being provided by salaried NHS practitioners. (2) One hundred and seven completed questionnaires were returned from vocational trainees. Vocational dental practitioners had completed fewer CCRPDs during VT than in dental school (dental school: median = 4, inter-quartile range = 3 to 5; VT: median = 2, inter-quartile range = 1 to 4). One-fifth of respondents (n = 22) had not completed any CCRPDs during VT. Nine per cent of VT practices (n = 10) had a surveyor on their premises. Only 15% (n = 16) of respondents felt the time they had spent in VT had increased their confidence in the design of CCRPDs. Financial factors did not have as significant an effect on the quality of prescription and fabrication of CCRPDs as did educational factors. Serious deficiencies in the teaching of CCRPDs during vocational training were identified.

Struggling with denture design

Enables readers to: Aim Published studies in the international dental literature demonstrate that the quality of prescription and fabrication of cobalt-chromium removable partial dentures (CCRPDs) by general dental practitioners frequently fail to comply with ethical and legal requirements. The reasons cited for this in the past have broadly related to either financial or educational matters. The aim of this investigation is to determine the effect of financial and educational factors on the quality of CCRPD design and fabrication by general dental practitioners. Materials and methods This investigation was completed in two parts. (1) A pre-piloted pro-forma was distributed to a number of dental laboratories throughout the UK and Ireland. These sought information relating to the quality of written instructions for CCRPDs received by these laboratories, and details of the remunerative scheme under which they were being provided. Three categories of remunerative scheme were considered, private CCRPDs in Ireland, private CCRPDs in the UK, and CCRPDs being provided by salaried NHS practitioners. (2) A pre-piloted questionnaire was distributed to vocational dental practitioners in the UK and Ireland. This sought information relating to their attitudes, opinions, and educational and clinical experiences of CCRPD design and fabrication. Results (1) Three hundred completed pro-formas were returned from dental laboratories, 100 of which related to each of the three remunerative schemes. Poor or no written instructions were provided in 47% (n = 47) of CCRPD cases funded privately in Ireland, 46% (n = 46) of CCRPD cases funded privately in the UK, and 50% (n = 50) of CCRPDs being provided by salaried NHS practitioners. (2) One hundred and seven completed questionnaires were returned from vocational trainees. Vocational dental practitioners had completed fewer CCRPDs during VT than in dental school (dental school: median = 4, inter-quartile range = 3 to 5; VT: median = 2, inter-quartile range = 1 to 4). One-fifth of respondents (n = 22) had not completed any CCRPDs during VT. Nine per cent of VT practices (n = 10) had a surveyor on their premises. Only 15% (n = 16) of respondents felt the time they had spent in VT had increased their confidence in the design of CCRPDs. Conclusion Financial factors did not have as significant an effect on the quality of prescription and fabrication of CCRPDs as did educational factors. Serious deficiencies in the teaching of CCRPDs during vocational training were identified.

Comparative study of circumferential clasp retention force for titanium and cobalt-chromium removable partial dentures

Statement of Problem. The interest in using titanium to fabricate removable partial denture (RPD) frameworks has increased, but there are few studies to support its use. Purpose. The objective of this study was to compare circumferential RPD clasps made of commercially pure titanium and identical clasps made of 2 different cobalt (Co)-chromium (Cr) alloys by testing insertion/removal and radiographically inspecting the casts for defects. Material and Methods. On refractory casts that represent a partially edentulous mandibular right hemi-arch segment, 36 frameworks were cast from commercially pure titanium (n = 12) and 2 Co-Cr alloys (n = 12 each) with identical prefabricated patterns and the manufacturer-designated investment and casting technique. Each group was divided into 2 subgroups, corresponding to.25-mm and.50-mm undercuts, respectively. No polishing procedures were performed to ensure uniformity. Only nodules and burs were carefully removed with tungsten burs under magnification when necessary. The specimens were radiographed and subjected to an insertion/removal test simulating 5 years of framework use. The data were subjected to analysis of variance and the Tukey complementary test (P<.01) to compare the retentive forces of RPDs made with the different materials. The Student t test (P<.01) was used to compare the retentive forces of RPDs fabricated with the same alloy with different undercuts. Results. A total of 20% of the titanium specimens demonstrated porosity, showing casting difficulties, and any defect detected on the clasps determined the sample replacement. For Co-Cr alloys, casting difficulties were not found. The data were subjected to analysis of variance and the Tukey complementary test to compare materials for the same undercut. For the.25-mm undercut, no significant difference was found between Magnum and Rematitan alloys; they were both different from the Remanium alloy (P<.01). For the.50-mm undercut, no significant difference was found between Co-Cr alloys; they were both different from Rematitan alloy (P<.01). The Student t test used to compare the same alloys with different undercuts showed no significant difference between Remanium with.25-mm and.50-mm undercuts. For Magnum and Rematitan alloys, there was a significant difference between different undercuts (P=.01). Conclusion. Within the limitations of this simulation study, the results suggest that commercially pure titanium clasps maintained retention over a simulated 5-year period, with lower retention force than identical Co-Cr clasps. (J Prosthet Dent 2002;88:290-6.)

Usage and status of cobalt-chromium removable partial dentures 5-6 years after placement.

The aim of this study was to describe the usage of cobalt-chromium (Co-Cr) removable partial dentures (RPDs) by patients 5-6 years after denture insertion and to find out the factors that affected their denture usage. A random sample of patients provided with Co-Cr RPDs from a dental teaching hospital in Hong Kong was selected. Patients were interviewed using a structured questionnaire concerning their assessment and use of the dentures. Those who had been constantly wearing their original RPDs were examined by one calibrated examiner under optimal clinical conditions. The response rate of the patients who could be contacted was 98%. The results from 189 patient interviews showed that usage of the RPDs declined with time and that half of the dentures had been discarded or replaced 5-6 years after insertion. These discarded RPDs had been in use for an average of 19.5 months. The main reason given by the patients for not using the RPDs was general dissatisfaction with the dentures in various combinations of comfort, fit and chewing ability and, less importantly, with food trapping and appearance. No statistically significant association between denture usage and their respective Kennedy classification was found. The status of the Co-Cr RPDs that had been constantly used for 5-6 years was generally good. The majority of these RPDs demonstrated fair to good cleanliness, stability and retention and had no defect of any sort.