Comparative analysis of the retention force and deformation of PEEK and PEKK removable partial denture clasps with different thicknesses and undercut depths.

STATEMENT OF PROBLEM: The retentive force and deformation of milled polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) removable partial denture (RPD) frameworks are not well understood. PURPOSE: The purpose of this in vitro study was to assess the retentive force and deformation of PEEK and PEKK Akers clasps with different designs and undercut depths. MATERIAL AND METHODS: A master model containing the first and second molar abutments was used to design Akers clasps of different cross-sectional dimensions, undercut depths (0.5 and 0.75 mm), and materials. The components of the removable partial denture framework also included an occlusal rest and were manufactured using a milling machine (n=5). The fatigue resistance of the Akers clasps was measured before and after deformation regarding the retentive forces. RESULTS: The PEEK2-U50 clasp had the largest retentive force with no significant difference among all groups before and after the insertion and removal cycle. In addition, the increased cross-sectional dimensions of the design resulted in significant differences in retentive forces between the PEEK1 and PEEK2 groups and between the PEEK and PEKK materials. CONCLUSIONS: Increasing the clasp's cross-sectional dimensions significantly impacted retentive forces, especially between different PEEK groups and between PEEK and PEKK materials.

Different Undercut Depths Influence on Fatigue Behavior and Retentive Force of Removable Partial Denture Clasp Materials: A Systematic Review.

PURPOSE: To perform a systematic review that provides an overview of the current literature on fatigue behavior of removable partial denture (RPD) clasp materials based on different retentive areas. MATERIALS AND METHODS: The review followed the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Electronic searches were done via PubMed, Scopus, and OVID for studies reporting on RPD clasps and the fatigue failure of clasp materials. Inclusion criteria were English language with full text and in vitro studies only. Exclusion criteria were studies that did not assess the fatigue of RPD clasp materials. A quality assessment and selection of full-text articles were performed according to Consolidated Standards of Reporting Trials criteria. RESULTS: A total of 182 articles were initially identified and screened. After applying inclusion and exclusion criteria, 15 articles were selected for the final analysis. Seven of the included studies utilized a vertical insertion/removal testing approach. Ten studies used the constant deflection test. Three studies used untapered specimens, and 12 studies used tapered specimens. Ten studies performed post-test analysis. CONCLUSIONS: Cobalt-chromium (CoCr) is the strongest material in terms of fatigue in relation to the undercut depth and the modern, digitally manufactured RPD clasp materials also exhibit comparable fatigue behavior. Recent RPD clasp materials such as polyetheretherketone (PEEK) or laser sintered CoCr, however, require further study in terms of their fatigue behavior. In order to improve the quality of future studies, a standardized and calibrated fatigue testing method is needed with standardized specimen size and shape, which will reduce the risk of bias and enable meta-analysis for bulk comparison between studies.

Polyetheretherketone materials for removable partial denture frameworks: an integrative review.

Polyetheretherketone (PEEK) resin is a high-performance thermoplastic polymer that has been introduced as a possible candidate to replace metallic components in dental prostheses. The objective of this integrative review was to compare, through analysis of studies in the literature, the mechanical performance of removable partial denture frameworks and clasps manufactured with PEEK with the performance of cobalt-chromium (Co-Cr) frameworks and clasps. The guiding question was, "Does the use of PEEK as a substitute for Co-Cr alloys for the construction of removable partial denture frameworks result in better mechanical properties?" The PubMed/ MEDLINE, Embase, Web of Science, Scopus, and SciELO databases were searched for articles published through October 2021. The JBI Critical Appraisal Checklist for Quasi-Experimental Studies was used to assess the methodologic quality of the selected in vitro studies. A total of 208 articles were identified. After the exclusion of duplicates and articles that did not meet the inclusion criteria, 7 studies- -4 in vitro and 3 three-dimensional finite element analyses- -published between 2012 and 2021 were included in the integrative review. The appraisal checklist revealed that the reviewed studies had a low risk of bias and high methodologic quality. The results of the review showed that PEEK alloys have adequate mechanical properties for use in clasps and removable partial denture frameworks, but Co-Cr alloys exhibit better mechanical properties and are more suitable in most circumstances.

[Finite element analyses of retention of removable partial denture circumferential clasps manufactured by selective laser melting].

OBJECTIVE: To compare the retentions of different designs of cobalt-chromium (Co-Cr), pure titanium (CP Ti), and titanium alloy (Ti-6Al-4V) removable partial denture (RPD) circumferential clasps manufactured by selective laser melting (SLM) and to analyze the stress distribution of these clasps during the removal from abutment teeth. METHODS: Clasps with clasp arm size A (1.9 mm width/1.1 mm thickness at the body and 0.8-taper) or B (1.2 times A) and 0.25 mm or 0.50 mm undercut engagement were modeled on a prepared first premolar die, named as designs A1, A2, A3, and A4, respectively. The density and elastic modulus of SLM-built Co-Cr, CP Ti, and Ti-6Al-4V were measured and given to different groups of clasps. The density, elastic modulus, and Poisson ' s ratio of enamel were given to the die. The control group was the cast Co-Cr clasp with design A1, to which the density and elastic modulus of cast Co-Cr alloy were given. The Poisson's ratio of all metals was 0.33. The initial 5 N dislodging force was applied, and the maximum displacement of the clasp along the insertion path was computed. The load was reapplied with an increment of 5 N than in the last simulation until the clasp was completely dislodged. The retentive force range of different groups of clasps was obtained. The retentive forces of the SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with equivalent computed retentive force range to the control group were validated through the insertion/removal experiment. The von Mises stress distributions of these three groups of SLM-built clasps under 15 N loads were analyzed. RESULTS: SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with designs B1 or B2, and Co-Cr clasps with design A2 had higher retentive forces than those of the control group. SLM-built CP Ti and Ti-6Al-4V clasps with design A1 had lower retentive forces than those of the control group. SLM-built Co-Cr clasp with design A1 and SLM-built CP Ti and Ti-6Al-4V clasps with design A2 had equivalent retentive forces to those of the control group. The insertion/removal experiment showed that the measured retentive forces of these three groups of SLM-built clasps were (21.57±5.41) N, (19.75±4.47) N, and (19.32±2.04) N, respectively. No statistically significant measured retentive force difference was found among these three groups of SLM-built clasps (P>0.05). The maximum von Mises stress of these three groups of SLM-built clasps exceeded their responding yield strength except for the Ti-6Al-4V one. CONCLUSION: SLM-built Co-Cr circumferential clasps had higher retention than CP Ti and Ti-6Al-4V ones with the same clasp arm size and undercut engagement. The retention of SLM-built circumferential clasps could be adjusted by changing the undercut engagement and clasp arm size. If SLM-built circumferential clasps are used in clinical practice, the Ti-6Al-4V clasp with clasp arm size A and 0.50 mm undercut engagement is recommended considering the long-term use of RPD in the patient's mouth.

Retentive Forces of Removable Partial Denture Clasp Assemblies Made from Polyaryletherketone and Cobalt-Chromium: A Comparative Study.

PURPOSE: To compare retentive forces of removable partial denture clasps traditionally fabricated with cobalt-chromium (CoCr) material and two computer-aided design and computer-aided manufactured (CAD/CAM) thermoplastic polymers. MATERIALS AND METHODS: Forty-eight clasp assemblies (16 CoCr, 16 polyetheretherketone (PEEK) and 16 polyetherketoneketone (PEKK) thermoplastic polymer) were fabricated for 48 mandibular tooth analogs. Individual clasps were inserted and removed on the tooth analogs utilizing a chewing simulator for 15,000 cycles to simulate 10 years of use. Retentive forces were measured utilizing a mechanical load tester at baseline and intervals of 1500 cycles. Data were analyzed with one-way Analysis of Variance, Tukey post-hoc, and paired T tests. RESULTS: Mean retentive forces between all groups were significantly different (p < 0.001). Retentive forces of CoCr clasps were significantly higher than both polymers (p < 0.001). The mean retentive forces for PEEK were not significantly different from PEKK (p = 0.23). A significant increase in retentive forces was observed for all three clasps after the first period of cycling, followed by continual decrease for the remaining cycles. At the endpoint of 15,000 cycles, no clasp assemblies showed lower retentive forces than at initial baseline. CONCLUSION: Thermoplastic polymer clasps demonstrated lower retentive forces compared to CoCr clasps. All three groups displayed a similar pattern of initial increase, followed by a gradual decrease, of retentive force. Despite this observation, the clasps maintained similar or higher retentive forces than measured at baseline. This resistance to fatigue and ability to fabricate with CAD/CAM technologies provides support for clinical use of these high-performance polymer (HPP) materials.

Is the high-performance thermoplastic polyetheretherketone indicated as a clasp material for removable dental prostheses?

OBJECTIVES: To investigate the retention force of polyetheretherketone (PEEK) removable dental prosthesis clasps in comparison with a cobalt-chrome-molybdenum control group after storage in artificial saliva. MATERIALS AND METHODS: Clasps were milled (Dentokeep (PEEKmilled1), NT digital implant technology; breCAM BioHPP Blank (PEEKmilled2), bredent), pressed (BioHPP Granulat for 2 press (PEEKpressed), bredent), or cast (remanium GM 800+ (cobalt-chrome-molybdenum), Dentaurum); N = 60, n = 15/subgroup. Retention force was examined 50 times/specimen in a pull-off test using the universal testing machine (Zwick 1445), where pull-off force was applied with a crosshead speed of 5 mm/minute until the maximum force dropped by 10%, at different aging levels: (1) initial, after storage in artificial saliva for (2) 90 and (3) 180 days. Statistical analysis was performed using one-way ANOVA followed by post hoc Scheffé-test and mixed models (p < 0.05). RESULTS: Cobalt-chrome-molybdenum presented the highest retention force. No differences were observed between polyetheretherketone materials. Cobalt-chrome-molybdenum showed a significant decrease of its values after artificial aging, while polyetheretherketone materials presented similar results over the course of aging. Regarding a repetitive insertion and removal, even though PEEKmilled2 and cobalt-chrome-molybdenum showed an initial increase, ultimately, a decrease in retention force was observed for all tested groups. CONCLUSIONS: Although the control group showed significantly higher results, the retention force of polyetheretherketone materials indicate a potential clinical application. Neither the manufacturing process nor artificial aging showed an impact on the retention force of polyetheretherketone clasps. CLINICAL RELEVANCE: Mechanical properties of novel removable dental prosthesis clasp materials devised to meet the growing esthetic demands of patients need to be investigated to ensure a successful long-term clinical application.

Retention force of polyetheretherketone and cobalt-chrome-molybdenum removable dental prosthesis clasps after artificial aging.

OBJECTIVES: To examine the retention force of removable dental prosthesis (RDP) clasps made from polyetheretherketone (PEEK) and cobalt-chrome-molybdenum (CoCrMo, control group) after storage in water and artificial aging. MATERIALS AND METHODS: For each material, 15 Bonwill clasps with retentive buccal and reciprocal lingual arms situated between the second pre- and first molar were manufactured by milling (Dentokeep [PEEKmilled1], NT digital implant technology; breCAM BioHPP Blank [PEEKmilled2], bredent), pressing (BioHPP Granulat for 2 press [PEEKpressed], bredent), or casting (remanium GM 800+ [CoCrMo], Dentaurum); N = 60, n = 15/subgroup. A total of 50 retention force measurements were performed for each specimen per aging level (initial; after storage [30 days, 37 °C] and 10,000 thermal cycles; after storage [60 days, 37 °C] and 20,000 thermal cycles) in a pull-off test. Data were statistically analyzed using one-way ANOVA, post hoc Scheffé and mixed models (p < 0.05). RESULTS: Initial, PEEKpressed (80.2 ± 35.2) and PEEKmilled1 (98.9 ± 40.3) presented the lowest results, while PEEKmilled2 (170.2 ± 51.8) showed the highest values. After artificial aging, the highest retention force was observed for the control group (131.4 ± 56.8). The influence of artificial aging was significantly higher for PEEK-based materials. While PEEKmilled2 and PEEKpressed showed an initial decline in retention force, all other groups presented no impact or an increase in retention force over a repetitive insertion and removal of the clasps. CONCLUSIONS: Within the tested PEEK materials, PEEKmilled2 presented superior results than PEEKpressed. Although CoCrMo showed higher values after artificial aging, all materials exhibited sufficient retention to recommend usage under clinical conditions. CLINICAL RELEVANCE: As RDPs are still employed for a wide range of indications, esthetic alternatives to conventional CoCrMo clasps are sought.

A combined analog and digital workflow for retrofitting a monolithic ceramic crown to an existing removable partial denture.

A clinical and laboratory workflow for fabricating and retrofitting a monolithic ceramic crown to an existing removable partial denture (RPD) is described. A conventional polyvinyl siloxane impression was made of the prepared tooth with the RPD in place. A stone cast was poured and, after die sectioning, scanned with a tabletop scanner. The ceramic crown was designed and fabricated by using a digital workflow to fit the RPD clasp assembly, providing an adequate undercut for the clasp. The crown was then delivered and the RPD evaluated for adequate fit.

Evaluation of the design-driven prediction of removable partial denture retention.

STATEMENT OF PROBLEM: Removable partial dentures (RPDs) are a cost-effective treatment designed to replace missing teeth for partially edentulous patients. However, RPDs often have insufficient retention, which results in treatment failure and patient dissatisfaction. PURPOSE: The purpose of this clinical study was to investigate the factors related to RPD retention that affect patient satisfaction, to clinically validate a newly published model for predicting RPD retention based on the number and position of missing teeth and clasps, and to identify the predictions of patient satisfaction to improve the guidelines for RPD design. MATERIAL AND METHODS: Seventy-five patients treated with 107 RPDs delivered at the McGill University Dental Clinic (Montreal, Canada) and Estaing University Hospital (Clermont-Ferrand, France) participated in this study. Data on the RPD design were collected from the clinical records, and the retention of each RPD was tested with the mathematical model designed for predicting RPD retention. Data on patient satisfaction with their RPDs were collected by using a standardized questionnaire (McGill Denture Satisfaction Instrument). Statistical analysis of factors related to RPD retention and patient satisfaction was performed by using the chi-square test and Mann-Whitney test, while the developed model for predicting RPD retention was evaluated by using sensitivity and specificity analysis. RESULTS: The average satisfaction score for all RPDs was 8.2 ±1.7 out of 10. Patients were more satisfied with RPDs in the maxillary arch, tooth-supported, or retained by ≥3 clasps than with RPDs in the mandibular arch, with distal extension bases, or retained by <3 clasps. The materials used for RPD fabrication (metal-based or acrylic resin-based), the number of missing teeth, and the presence of indirect retention were not associated with patient satisfaction. Participants were significantly more satisfied with RPD designs predicted by the developed mathematical model to have enough retention than with RPD designs predicted to have insufficient retention. The mathematical model for predicting the RPD retention showed a clinical specificity of 83% in predicting patient satisfaction. CONCLUSIONS: RPD retention predicted from the number and position of clasps and missing teeth might help to determine patient satisfaction. In addition, patient satisfaction with RPDs was influenced by the arch type, the presence of a distal extension base, and the number of clasps.

The effect of build orientation on the microstructure and properties of selective laser melting Ti-6Al-4V for removable partial denture clasps.

STATEMENT OF PROBLEM: Selective laser melting (SLM) Ti-6Al-4V has been used for removable partial dentures, but the impact of SLM Ti-6Al-4V build orientation is not evident. PURPOSE: The purpose of this in vitro study was to investigate the microstructure and properties of SLM Ti-6Al-4V clasps with different build orientations compared with cast Ti-6Al-4V clasps. MATERIAL AND METHODS: Forty-eight clasps were made from Ti-6Al-4V alloys-by SLM with 3 different build orientations (SLM0, SLM45, and SLM90) and cast (CAST) as a control. The microstructure was investigated by using a metallographic microscope and a confocal laser scanning microscope. The fit and surface roughness of the clasps were measured, and the physical properties were evaluated. In addition, the von Mises stresses in the clasps were calculated by finite element analysis. All specimens were then subjected to insertion and removal tests in artificial saliva to model 5 years of clinical use. After these tests, 3-point bend tests were used to analyze the fracture surface of the clasp arms, which were observed by using a scanning electron microscope. All data were statistically analyzed (α=.05). RESULTS: The microstructure of the Ti-6Al-4V specimens was a comixture of α+ß phases. In addition, growth directions of ß grains were approximately parallel to the build orientation, with acicular α grains present between ß grains. SLM0 and SLM45 had significantly higher roughness than SLM90. Even though the fit was inferior to that of SLM90, SLM0 and SLM45 still performed better than cast specimens (P<.05). The finite element analysis showed that the maximum von Mises stress was located on the middle part of the retainer arms and that the values of the 0.50-mm undercut clasps were much lower than the elastic limit. In addition, the decrease of retentive force in SLM90 clasps was less than that of the CAST group (P<.05). CAST clasps showed brittle fracture, whereas all SLM clasps showed ductile fracture. CONCLUSIONS: The microstructure of SLM Ti-6Al-4V affected the properties of clasps by changing the anisotropy of specimens. Among the tested groups, SLM90 clasps had the best fit, the lowest surface roughness, and the best fatigue resistance. Furthermore, SLM Ti-6Al-4V clasps could be engaged into 0.50-mm undercuts.

Examination of inter-rater and intra-rater reliability during retentive force measurement of different clasps using the developed small-sized retentive force measurement device.

BACKGROUND: The design process of a removable partial denture (RPD) consists of rests, major connectors, minor connectors, denture base, and retainer. The abutment tooth contour determines the location of the retention portion of the clasp at the retention areas. The load capacity of the clasp depends on various factors such as type, the position of a clasp, tooth position, clasp length, and pullout location. As a general rule, the amount of retention required to dislodge the RPD from the supporting structure should always be the minimum necessary to resist reasonable dislodging forces. Excessive force from the clasps may cause many problems. Although there are many reports on the retentive force of cast clasps using large devices, it has not been possible to measure it using simple devices until now. METHOD: The purpose of the present study is to develop a small-sized retentive force measurement device that can easily measure the retentive force of a clasp used for an RPD. It is to examine inter-rater and intra-rater reliability. A small-sized retentive force measurement device that can be easily measured in the laboratory has been developed. Using commercially available hard plaster cast, a skilled dental technician has made 10 types of cast clasps used in clinical practice using conventional techniques. Three assessors measured the retentive force of 10 types of cast clasps. To confirm the reliability, the intra-class correlation coefficients ICC (1,1) and ICC (1,3) of the 3 assessors were calculated, and the reliability within the assessor was examined. The inter-class correlation coefficients ICC (3,1) and ICC (3,3) were calculated, and the reliability of the assessors was examined. RESULT: The intra-class correlation coefficients of 3 assessors are as follows: assessor 1 has ICC (1,1) = 0.971, ICC (1,3) = 0.990, assessor 2 has ICC (1,1) = 0.967, ICC (1,3) = 0.989, assessor 3 has ICC (1,1) = 0.962, ICC (1,3) = 0.987. The inter-class correlation coefficients of 3 assessors are as follows: ICC (3,1) = 0.993, ICC (3,3) = 0.998. From the evaluation standard of the intraclass correlation coefficients of reliability value by ICC, it was evaluated as almost perfect and high reproducibility was confirmed. CONCLUSION: The developed small-sized retentive force measurement device has reproducibility within and between the assessors.

Determining the retention of removable partial dentures.

STATEMENT OF PROBLEM: Removable partial dentures (RPDs) provide a cost-effective treatment for millions of partially edentulous patients worldwide. However, they often fail because of loss of retention. One reason for this problem is lack of precise guidelines for designing retentive RPDs. PURPOSE: The purpose of this in vitro study was to determine the forces produced by food and clasps during mastication to develop an algorithm for predicting RPD retention and to help determine the optimal number of clasps. MATERIAL AND METHODS: The forces that food exerts on acrylic resin teeth during simulated mastication and the retention forces provided by clasps (wrought wire, circumferential, and I-bar) engaging on teeth were measured using a universal testing machine. A statistical analysis was performed with a 1-way ANOVA and repeated-measures ANOVA while the developed algorithm was evaluated by using sensitivity and specificity analysis. RESULTS: The force exerted by food mastication on each individual tooth ranged between 1.7 and 12.2 N, depending on the type of tooth, tooth anatomy, occlusion, and food. The retention force of the clasps after cyclic testing ranged between 2.9 and 14.5 N, depending on the type of tooth abutment and clasp. Using these measurements, an algorithm was developed to predict RPD retention. The algorithm was confirmed experimentally on 36 RPDs, showing a sensitivity of 96%, specificity of 100%, and an accuracy of 97%. CONCLUSIONS: The forces generated by food mastication on teeth varied according to the type of tooth, occlusion, and food. The retention force of RPD clasps varied according to the type of tooth and clasp. An algorithm for predicting RPD retention and determining the optimal number of clasps was developed and validated experimentally.

Modified Equipoise Clasp: An Esthetic Option for Removable Dental Prostheses.

The objective of this clinical report is to describe a fabrication technique for a modified Equipoise clasp-retained removable dental prosthesis as an alternative esthetic clasp option when abutment teeth are visible during smiling or speaking. The use of surveyed crowns on abutment teeth with mesial reciprocating grooves, milled lingual ledges, and distobuccal undercuts facilitates the use of a modified Equipoise clasp, providing a viable treatment option in esthetically demanding cases.

Effect of cyclic bend loading on a cobalt-chromium clasp fabricated by direct metal laser sintering.

STATEMENT OF PROBLEM: Limited information is available regarding the mechanical properties of a partial removable dental prosthesis clasp fabricated by direct metal laser sintering (DMLS). PURPOSE: The purpose of this in vitro study was to measure the mechanical properties of cast clasps, DMLS clasps, and annealed DMLS clasps and to determine the correlation between cyclic bend loading, annealing, and mechanical properties. MATERIAL AND METHODS: Sixty half round clasp specimens were fabricated, with a length of 20 mm and a diameter of 1.5 mm at 10 mm from the tip. The specimens were divided into 6 groups (n=10). Twenty specimens were fabricated by casting (CS, CSAC), and 40 specimens were fabricated by DMLS (DS, DSAC, ADS, ADSAC). Of the DMLS specimens, 20 underwent annealing (ADS, ADSAC). Equivalent to 5 years of clinical use, 0.25 mm of bending was applied to group CSAC, DSAC, and ADSAC 14 600 times. After cyclic bending loads, a cantilever bend test was conducted on all groups, and the loads were measured. To compare the load values, 1-way ANOVA and the Tukey HSD test were performed and statistical significance among the groups was evaluated (α=.05). Scanning electron microscopy and energy-dispersive spectroscopy analyses were also used for surface morphology evaluation and element analysis. RESULTS: Bending loads of the DMLS specimens were significantly lower than those of the cast specimens (P<.05). The influence of cyclic bending loads was significant for cast specimens (P<.05), but not for DMLS specimens (P>.05), in terms of variation of loads. Annealed DMLS specimens had significantly higher bending loads than DMLS specimens (P<.05). CONCLUSIONS: The DMLS specimens had lower load values at 0.25 mm bending than cast specimens. The DMLS specimens were less influenced by cyclic bending loads than the cast specimens. Annealing increased load values of the DMLS specimens at 0.25 mm bending.

Fabrication of a nonmetal clasp denture supported by an intraoral scanner and CAD-CAM.

This clinical report describes the management of a patient who had a metal allergy and had difficulty sitting in a dental chair for an extended period. The presented treatment used an intraoral scanner and computer-aided design and computer-aided manufacturing (CAD-CAM) to fabricate a nonmetal clasp denture. The described procedure may reduce patient discomfort and chair-time.

Oral health-related quality of life in patients with non-metal clasp dentures: a randomised cross-over trial.

We investigated the efficacy of non-metal clasp dentures (NMCDs) with regard to the oral health-related quality of life (OHRQoL) and compare the findings with those for conventional metal clasp-retained dentures (MCDs). This single-centre, randomised controlled, two-phase, open label, cross-over trial included 28 partially dentate individuals. The patients were randomised to receive MCDs followed by NMCDs, or the opposite sequence (n = 14 in each group); each denture was worn for 3 months. OHRQoL was evaluated using the Oral Health Impact Profile-Japanese version (OHIP-J) at entry (T-entry; before treatment with the first denture) and at 3 months after treatment with each denture (T3). An examiner evaluated denture stability, oral appearance and surface roughness before denture delivery (T0) and at T3 and denture hygiene at T3. A total of 24 patients completed the trial. There were no complications related to the dentures, abutment teeth or denture-bearing mucosa during the follow-up periods for both dentures. The mean OHIP summary score was lower for NMCDs than for MCDs, and the difference (9 points) was greater than the minimal important difference (6 points), indicating the difference was clinically relevant. The effect size was medium (0·70). Statistical analyses with linear mixed models found a significant effect of the denture type on the OHIP summary score and scores for the Oro-facial appearance, Oro-facial pain and Psychological impact domains (NMCD < MCD; P < 0·05). The results of our study suggest that NMCDs allow for better OHRQoL compared with MCDs.

New Clasp Assembly for Distal Extension Removable Partial Dentures: The Reverse RPA Clasp.

Several clasp types are used in distal extension removable partial dentures. In some cases the terminal abutments have only distal retentive undercuts that can be occupied by bar clasps; however, bar clasps may be contraindicated with no suitable alternative. This article presents a reasonable solution by introducing a new clasp design as a modification to the well-known RPA clasp. The design includes a mesial rest, proximal plate, and buccal retentive arm arising from the rest and extending to reach the distal retentive undercut.

In vitro Assessment of Clasps of Cobalt-Chromium and Nickel-titanium Alloys in Removable Prosthesis.

BACKGROUND: It has been since a long time that the use of base-metal alloys has significantly increased in the area of prosthetic science. One of the factors contributing for the increasing use of base-metal alloys is the increasing and high cost factor of noble metals. Although numerous materials have been tried since the recent past, Cobalt-Chromium (CoCr) alloys still form the most commonly used ones because of the numerous advantages they offer. Titanium alloys are also significantly being used in this field because of their high resistance strength and high corrosion resistance. Therefore, we aimed to evaluate the flexure strength and fatigue resistance of clasps made up of CoCr alloys and Nickel-titanium (NiTi) alloys. MATERIALS AND METHODS: We evaluated the retentive forces of CoCr and NiTi clasps two different sizes engaging retentive undercuts of different depths (0.25 and 0.50 mm). Mandibluar second premolar was prepared to frame the prosthesis for missing mandibular first and second molar. A total of 50 clasps were included in the study out of which 30 were NiTi clasps and 30 CoCr clasps. We evaluated the loading of the force at the rate of half Newton(N)/second at the central part of the specimen until fracturing of the specimen occurred and finally measurement of the modulus of elasticity was also done. Statistical analysis was carried out; unpaired "t" test was used for evaluating the level of significance. RESULTS: The mean load needed for CoCr clasps was 0.7450 and for NiTi clasp was 0.6140 Kgf for producing a deflection of 0.25 mm. As far as flexibility is concerned, more value was seen in NiTi group than CoCr group. For deflecting the clasp up to 0.50 mm, the mean load needed for CoCr clasps was 1.4102 and for NiTi clasp was 0.8260 Kgf. The results were statistically significant. While measuring the flexibility, more value (p < 0.05) was seen in NiTi group than in CoCr group. NiTi alloy clasps had mean flexural strength of 1640 MPa and modulus of elasticity of 32 GPa. CONCLUSION: For producing deflection of 0.25 and 0.50 mm, the mean loading force was higher for NiTi alloys. Although being increasingly used these days, NiTi alloys have limited use as compared with CoCr alloys due to high cost of titanium and certain other limitations.

Impact of periodontal maintenance on tooth survival in patients with removable partial dentures.

AIM: Removable partial dentures (RPDs) may have a negative impact on oral health and have the potential to cause further tooth loss, especially of abutment teeth. However, no evidence indicates the effective interval of regular periodontal maintenance after RPD provision. This practice-based cohort study aimed to examine the impact of regular periodontal maintenance visits on survival of RPD abutment teeth. MATERIALS AND METHODS: One hundred and ninety-two patients had been previously provided with 304 new clasp-retained RPDs at Osaka University Dental Hospital, Japan. Using the Kaplan-Meier method and log-rank test, 1094 abutments were analysed to illustrate survival curves and to compare each curve. According to the frequency of periodontal maintenance, study samples were divided into three groups; every 3-6 months (3-6M) group, 1-year (1Y) group and no-maintenance (NM) group. RESULTS: Seven-year cumulative survival rates were 83.7% (3-6M), 75.5% (1Y) and 71.9% (NM) respectively. Survival of abutment teeth in the 3-6M group was significantly better than both 1Y (p = 0.005) and NM (p < 0.001) groups. CONCLUSION: These longitudinal clinical data indicates that periodontal maintenance at least once in 6 months had the most favourable outcome. Frequent periodontal maintenance after RPD provision could be effective in preventing further tooth loss.

Fabricating an immediate denture for a medically compromised elderly patient.

Fabricating an immediate denture (ID) in the conventional manner may be complicated and difficult. An alternative technique is described for the fabrication of an ID that eliminates the need for an interim prosthesis and reduces treatment time.