Removable Partial Denture Frameworks Research Articles

A Pilot Randomized Controlled Crossover Trial Comparing Early OHRQoL Outcomes of Cobalt-Chromium Versus PEEK Removable Partial Denture Frameworks.

To investigate differences in the performance of polyether ether ketone (PEEK) frameworks vs traditional metal frameworks for removable partial dentures (RPDs) in terms of OHRQoL, patient preference, periodontal indices, and denture satistfaction. Twenty-six participants were recruited to a randomized controlled crossover trial and were provided with either PEEK or cobalt-chromium (Co-Cr) RPDs. After 4 weeks, the participants were provided with the other RPD. After both 4-week testing periods, the participants chose their preferred RPD and were followed up again at 6 months and 1 year. The primary outcome measure was effect on OHIP-20 score, which was compared among patients using repeated measures ANOVA. Secondary outcomes were participant preference compared using chi-square analysis; Plaque Index and Gingival Bleeding Index (PI and GBI, respectively) compared using repeated measures ANOVA; and McGill Denture Satisfaction Questionnaire (MDSQ) score compared between the two 4-week follow-ups using paired-samples t test. Both Co-Cr and PEEK frameworks resulted in a significant improvement in OHIP-20 score (P < .001), but the material was not a significant factor in changes over 1 year (P = .87). There were no statistically significant differences in participant preference at 1 year (P = .491), nor between RPD materials in their effect on GBI (P = .476), PI (P = .967), or MDSQ (P = .368). Both Co-Cr and PEEK RPDs improved OHRQoL to a degree greater than the minimum clinically important difference at 4 weeks, 6 months, and 1 year compared to baseline. No significant preference or improved denture satisfaction score was seen for either material. PEEK frameworks seem to be associated with similar degrees of periodontal effects as Co-Cr frameworks.

Fabrication of a removable partial denture combining conventional and digital techniques

This article describes a combined conventional and digital workflow for fabricating removable partial dentures (RPDs). After scanning the dental cast and RPD framework assembly, artificial teeth and denture base regions were designed using computer-aided design software. The artificial teeth and denture base assembly was milled as a single structure by using a wax disk and then placed on the RPD framework. The artificial teeth were additionally milled from a polymethyl methacrylate disk. Conventional procedures were followed for denture investment until the wax elimination procedure, after which the assembly was replaced with the artificial teeth in the cope of the flasks, and the denture resin material was injected to process the RPD. This technique enabled the RPD to be fabricated in the same form as the design state.

Effect of different support angles on the fitness of removable partial denture framework fabricated using selective laser melting technique

Objective: To evaluate the fitness of bilateral free-end dentition defect removable partial denture framework fabricated by selective laser melting (SLM) technique with different support angles. Methods: After the control group has been set to eliminate the system error, and according to the standard model of bilateral mandibular posterior teeth loss, eighteen titanium alloy removable partial denture frameworks fabricated by SLM technology were divided into 3 groups with support angles of 0° (horizontal group), 45°(45° group) and 90° (vertical group). Plaster cast with duplicated structure of tissue surface of the removable partial denture (RPD) framework was obtained. A three-dimensional scanner was used to scan original and duplicated plaster casts. The gaps between framework and the model in different parts were analyzed using Geomagic Qualify software to evaluate the fitness of the framework with visual method. Results: The framework fits on the plaster model completely, and its tissue surface fitted on the plaster model well. The deviation between frameworks and plaster casts was calculated as follow: the total deviations of the horizontal, 45°, and vertical group were (0.146±0.017), (0.182±0.015) and (0.185±0.022) mm respectively. The mean deviation of the horizontal group was significantly less than those of the 45° group and the vertical group (P<0.05). Moreover, there was no significant difference in the total deviation between the 45° group and the vertical group. The total deviation of occlusal rest of the horizontal group was significantly less than that of the 45° group (P<0.05). However, no significant difference was detected in the deviation of occlusal rest among the vertical group, the horizontal group, and the 45° group (P>0.05). There was no significant difference in the deviation of occlusal rest among the vertical group, the horizontal group, and the 45° group. The deviation of clasp of the horizontal group was significantly smaller than those of the 45° group and the vertical group (P<0.05). Whereas, there was no significant difference in the deviation of clasp between the 45° group and the 90° group (P>0.05). No significant difference was found in the deviation of lingual bar among the three groups (P>0.05). Conclusions: Among the three kinds of bilateral free-end dentition defect RPD framework fabricated by SLM in different support angles, horizontal printing was proved to reach the minimal deviation, even though the fitness of all three kinds of frameworks can fullfil clinical requirements according to previous studies.

A novel digital altered cast impression technique for fabricating a removable partial denture with a distal extension

BackgroundAlthough computer-aided design and computer-aided manufacturing has been successfully used in fabricating removable partial dentures (RPDs), making altered cast impressions is still a time-consuming and labor-intensive process for fabricating RPDs with a distal extension. An alternative digital technique has been developed to simplify this process. MethodsThe authors present a case in which they sought to improve the efficiency and simplicity in obtaining altered cast impressions by means of digital technology. Initially, a primary plaster cast was scanned as a digital cast. Based on the digital cast, a novel custom tray was designed and fabricated using a 3-dimensional printing method. With the custom tray, the novel altered cast impression was fabricated and scanned, and the final virtual altered cast was reconstructed by a stitching method. ResultsBased on the virtual altered cast, the authors designed the virtual RPD framework. Finally, the titanium alloy framework was fabricated using a 3-dimensional printing process, and the authors fit the final RPD to the patient. ConclusionsThis novel digital altered cast impression technique may eliminate interoperator variability and increase precision compared with the traditional technique. Practical ImplicationsThis technique showed the potential for reducing clinical appointments, chair time, and laboratory procedures.

In vitro evaluation of a removable partial denture framework using multi-directionally forged titanium.

PURPOSEThis study evaluated the availability of multi-directionally forged (MDF) titanium (Ti) as a component of removable partial dentures (RPDs). MDF-Ti remarkably improved the mechanical properties of RPDs due to its ultrafine-grained structure.MATERIALS AND METHODSThe wear resistance, plaque adhesion, and machinability of MDF-Ti were tested. As controls, commercially pure (CP) titanium was used for wear, plaque adhesion, and machinability tests. For wear resistance, the volume losses of the titanium teeth before and after wear tests were evaluated. Plaque adhesion was evaluated by the assay of Streptococcus mutans. In the machinability test, samples were cut and ground by a steel fissure bur and carborundum (SiC) point. An unpaired t-test was employed for the analysis of the significant differences between MDF-Ti and the control in the results for each test.RESULTSWear resistance and plaque adherence of MDF-Ti similar to those of CP-Ti (P>.05) were indicated. MDF-Ti exhibited significantly larger volume loss than CP-Ti in all conditions except 100/30,000 g/rpm in machinability tests (P<.05).CONCLUSIONAlthough the wear resistance and plaque adherence of MDF-Ti were comparable to those of controls, MDF-Ti showed better machinability than did CP-Ti. MDF-Ti could be used as a framework material for RPDs.

Internal porosities, retentive force, and survival of cobalt–chromium alloy clasps fabricated by selective laser-sintering

PurposeThe purpose of this study was to evaluate internal porosities, retentive force values and survival of cobalt–chromium (Co–Cr) alloy clasps fabricated by direct metal laser-sintering (DMLS) and compare them to conventionally cast clasps. MethodsEmbrasure clasps were digitally designed fitting teeth 35 and 36 on identical metal models (N = 32). Sixteen clasps were fabricated using DMLS (group DMLS) and another sixteen clasps were additively manufactured from wax and then cast from a Co–Cr alloy (group CAST). Internal porosities were examined using micro-focus X-ray (micro-CT) and analyzed applying Kolmogorov–Smirnov test, Mann–Whitney test, and T test (significance level: p < 0.050). A universal testing machine was used to determine the retentive force values at baseline and after 1095, 5475, 10,950 and 65,000 cycles of simulated aging. Data were analyzed employing Kolmogorov–Smirnov test, one-way ANOVA, and Scheffé’s post-hoc test (significance level: p < 0.050). Survival was estimated for 65,000 cycles of artificial aging using Kaplan–Meier analysis. ResultsMicro-CT analysis revealed a higher prevalence (p < 0.001), but a more homogeneous size and a significantly smaller mean (p = 0.009) and total volume (p < 0.001) of internal porosities for group DMLS. The groups showed mean initial retentive force values of 13.57 N (CAST) and 15.74 N (DMLS), which significantly declined over aging for group CAST (p = 0.003), but not for group DMLS (p = 0.107). Survival was considerably higher for group DMLS (93.8%) than for group CAST (43.8%) after 65,000 cycles of aging. ConclusionsClasps made by laser-sintering could be an alternative to conventional cast clasps for the fabrication of removable partial denture frameworks.

Comparative Evaluation Of Physical Properties Of Conventionally Constructed Versus CAD/CAM Milled Frameworks For Kennedy Class I Partial Dentures

Aim: The objective of this study was to compare the physical properties (retention, surface roughness, and wear) of conventionally constructed (pressed) bioHPP removable partial denture (RPD) frameworks versus computer aided designed - computer manufactured (CAD/CAM) RPD frameworks. Materials and Methods: Over standardized epoxy resin cast models, twenty frameworks were fabricated and divided equally into two groups, group A received ten conventionally fabricated (pressed) bioHPP frameworks and group B received ten CAD/CAM milled frameworks. Each framework was subjected to insertion/ removal cycles by using universal testing machine, (360, 720, 1080, 1440, 2116 cycles) representing time intervals baseline, three, six, nine- and twelve-months respectively, where retention, wear and surface roughness were measured before and after each time interval.Results: Group B(CAD/CAM) milled RPD frameworks results showed statistically significant difference with higher mean values than group A (pressed) RPD frameworks results in all measured parameters throughout all time intervals.Conclusion: Within the limitations of this study, it could be concluded that either with milled or pressed way of construction BioHPP remains a reliable material that could be used to construct a highly accurate RPD framework with acceptable physical properties.

Digital PEEK framework and patient satisfaction compared to conventional metal framework in removable partial dentures. A clinical trial

Introduction: Utilization of removable partial dentures (RPD) is inevitable in some patients that are not indicated for any other treatment option, thus patient satisfaction with this line of treatment is of great importance. However, a notable need exists to advance materials and fabrication technologies due to the undesirable health outcomes linked with current RPDs. Aim: In this study patient satisfaction with conventionally manufactured metal RPD framework, was compared with their satisfaction using digitally milled PEEK (Juvora) framework. Methods: Ten patients were selected having class I partially edentulous mandibles. A conventional metal framework RPD was constructed for each patient, then another RPD with milled PEEK framework was digitally fabricated for each one of them. Each patient had the chance to use each denture for three months, then questionnaires were filled to assess their satisfaction. Results: The questionnaires were statistically analyzed and resulted in more patients’ satisfaction with the digital PEEK framework RPD, than with conventional metallic RPD framework.Conclusion: PEEK material increases patients’ satisfaction with RPDs than the conventional metal framework material, thus decreasing patients’ complaints from removable appliances.

Accuracy of removable partial denture framework fabricated by casting with a 3D printed pattern and selective laser sintering

PurposeThe present study aimed to compare the accuracy of removable partial denture (RPD) frameworks fabricated by 3D-printed pattern casting and those fabricated by selective laser sintering (SLS). MethodsA partially edentulous mandibular model was used for the simulation model. Scanning of the model was performed using a dental scanner. The framework was designed by using CAD software. The 3D-printed resin pattern was formed using a 3D printer and casting was performed (AM-Cast framework), and a direct metal laser sintering machine was used for the framework of SLS (SLS framework). 3D scanning of fabricated two types of framework were performed, and these data were overlapped with design data. Fabrication accuracy was verified using the Mann–Whitney U test to compare the discrepancy between the AM-Cast and SLS frameworks. ResultsThe range of differences for the AM-Cast and SLS framework were −0.185±0.138 to 0.352±0.143mm and −0.166±0.009 to 0.123±0.009mm, respectively. Statistically significant differences were observed at the rests, proximal plates, connectors, and clasp arms. Regarding the rests, both lateral and medial displacement in the two types framework was observed in relation to the design data. Large lateral discrepancies of the connectors were observed at the joining area on the tooth-supported side of the lingual bar for the AM-Cast framework. Localized discrepancies were observed at the center of the lingual bar for the SLS framework. ConclusionThe accuracies of RPD frameworks fabricated by AM-Cast and SLS differ depending on the specific structural component of the RPD.

CLINICAL EVALUATION OF REMOVABLE PARTIAL DENTURE CONSTRUCTED FROM 3D PRINTED RESIN PATTERN DESIGNED USING CAD CAM TECHNOLOGY

INTRODUCTION: Computer-assisted design, computer-assisted manufacture (CAD/CAM) can be successfully applied to the fabrication of removable partial denture (RPD) alloy frameworks and replace laboratory crafting techniques. The CAD/CAM techniques have been widely used for a long time to manufacture dental prostheses. Computer-aided technologies allow more precise and systematic modeling, and could therefore reduce the burdensome steps of both chair-side and laboratory work, saving vital time.OBJECTIVES: This study was aimed to compare between the accuracy of chrome-cobalt removable partial denture frameworks designed and fabricated using CAD/CAM technique with that fabricated using conventional techniqueMATERIALS AND METHODS: Seven maxillary bilateral partially edentulous patients having Class III modification 1 Kennedy classification were selected from those attended to the prosthodontic department, Faculty of Dentistry, Alexandria University. For each patient, two different cobalt chromium removable partial frameworks were constructed; the first one was fabricated using CAD CAM technique (group A)and the other framework was fabricated using conventional manufacturing technique(group B) and were compared through evaluation of: (1) Guiding plane/plate relation. (2) Accuracy of fit of occlusal rests and major connector.RESULTS: all removable partial dentures fabricated by CAD/CAM technology showed increased improvement of accurate adaptation of the palatal strap major connector, guiding plane\plate relation and fit of occlusal rest, also it was less time consuming and economic need compared to conventional technique.CONCLUSIONS: The use of CAD/CAM technology for fabrication of removable partial denture frameworks should be widely applied because of its favorable clinical accuracy.KEYWORDS: Removable partial denture, CAD/CAM, Guiding planes, Chrome-Cobalt powder, Occlusal rests adaptation.

Virtual Evaluation of the Accuracy of Fit and Trueness in Maxillary Poly(etheretherketone) Removable Partial Denture Frameworks Fabricated by Direct and Indirect CAD/CAM Techniques.

To compare the accuracy of fit and trueness of maxillary poly(etheretherketone) (PEEK) removable partial denture (RPD) frameworks fabricated by direct and indirect computer-aided design/computer-aided manufacturing (CAD/CAM) techniques. A definitive maxillary class I master epoxy model was duplicated to create a stone cast. The cast was scanned, and an RPD was designed. Standard tessellation language (STL) data were used to fabricate 20 identical RPD frameworks using two CAD/CAM techniques: direct milling of PEEK and indirect additive manufacturing (resin printing combined with PEEK thermopressing using the lost-wax technique). All the frameworks for each technique (n = 10) and the reference cast were scanned. To assess the accuracy of fit, a color map was constructed using metrology software, and the misfit (distance between each framework and the reference cast) was measured at 25 standardized points. To assess the overall trueness, each framework STL file was superimposed over the original design's STL file, and the average deviation was recorded in microns. Data were statistically analyzed using t-test. Color mapping showed distinct pressure areas in the anterior and posterior straps of the major connector in the indirect technique, while a more uniform distribution of the color map was observed in the direct technique. A significant difference was found between the two techniques regarding the overall accuracy of fit. Compared with the indirect technique, the milled frameworks showed significantly better overall trueness (p < 0.001). Although a significant difference in the overall fit accuracy was noted between both techniques, the fit was an acceptable clinical fit. The fabrication method affects the fit in the anterior and posterior strap areas. The frameworks of the direct technique revealed better overall trueness values compared with the indirect technique.

Evaluation of removable partial denture frameworks fabricated using 3 different techniques

Statement of problemRapid advancements in computer-aided design and computer-aided manufacturing (CAD-CAM) have opened new pathways in the fabrication of removable partial dentures (RPDs) through additive and subtractive processes. Questions remain whether the digital pathway is an acceptable one compared with conventional analog or combined analog and digital pathways. PurposeThe purpose of this clinical study was to determine the quality of RPD frameworks fabricated using 3 different fabrication methods: analog, combined analog-digital, and digital. Material and methodsThree RPD frameworks were fabricated for each of the 9 participants using each of the 3 techniques. Of the 9 participants enrolled, 4 were of Kennedy class I, 3 were of Kennedy class II, and 2 were of Kennedy class III. The first technique was completely analog: a physical impression was made using polyvinyl siloxane, stone casts were made, a survey was performed, and a laboratory technician waxed and cast the RPD framework. The combined analog-digital workflow had the analog steps, but the stone cast was scanned with a laboratory scanner to generate a digital cast. The 3Shape CAD software was then used to design a digital RPD, which was fabricated from a cobalt-chroumum alloy by selective laser melting. The third technique was completely digital: an intraoral digital scanner was used to make a definitive scan, which was sent to the 3Shape software for digitally designing the RPD framework and subsequent selective laser melting for fabrication. For all frameworks in the same participant, the same design was used for consistency. The evaluation consisted of a yes/no survey with 7 framework-related parameters and was completed by 5 clinicians. For statistics, an overall P value was calculated using a chi-squared test to determine any difference among the groups (α=.05). ResultsSeven of the 9 participants received the framework fabricated using the digital pathway as their definitive prosthesis. The completely digital method was significantly better than the traditional method of analog fabrication (P<.001). Intraoral scanning was also significantly better than the combined method of fabrication (P<.001). The completely analog method was better than the combined method of framework fabrication (P=.008). ConclusionsWithin the limitations of this clinical study, it was concluded that the combined analog-digital pathway of RPD fabrication was the least clinically acceptable one as determined by 5 calibrated clinicians using a yes/no questionnaire, whereas the completely digital method of fabrication was found to be the best.

Adaptation of removable partial denture frameworks fabricated by selective laser melting

Statement of problemSelective laser melting (SLM) is a novel 3-dimensional (3D) printing technology that can directly form the metal frameworks of removable partial dentures. The adaptation of SLM frameworks has not been thoroughly evaluated. PurposeThe purpose of this in vitro study was to evaluate the tissue surface adaptation of removable partial denture frameworks fabricated by an SLM technique. Material and methodsFour types of maxillary partial edentulous resin models were custom made: bilateral second premolars and molars missing, bilateral premolars and first molars missing, all teeth missing except 2 canines, and 2 central incisors missing. According to these dentition-defect patterns, 4 types (I, II, III, and IV) of virtual removable partial denture frameworks were designed, and an SLM printer was used for 3D printing using cobalt-chromium (Co-Cr) alloys (repeated 3 times). As a control, refractory casts duplicated from the resin models were used to fabricate denture frameworks by the lost-wax casting technique. Average gaps and maximum gaps between frameworks and models were measured using the silicone impression material. Two-way ANOVA was used to determine the influence of production methods and design types on the gaps (α=.05). ResultsThe 2-way ANOVA showed that average gaps were significantly influenced by the production methods and design types, as well as their interactions (P<.001). With design Types I and II, the average gaps of the SLM-printed frameworks were larger than those of the cast ones (P<.001). However, no such differences were found for design Type III, P=.325, or IV, P=.862. ConclusionsSLM-printed frameworks achieved an acceptable adaptation. However, among frameworks with a large span and relatively more retainers and clasps, the adaptation of those made by the precision casting technique was slightly better than that of those printed by the SLM technique.

Clinical and Laboratory Evaluation of the Fit Accuracy of Metal Frameworks of Removable Partial Denture Fabricated from Two Different Pattern Materials

Objective: The purpose behind this conducted study was clinical and laboratory assessments of the fit accuracies of cobaltchromium frameworks for removable partial dentures fabricated by traditional lost wax technique (TT), and the Light Cure Modeling Material Technique (LCMT). Materials and Methods: Sixteen healthy male Kennedy class I patients were selected from the specialty clinics in the Faculty of Dentistry, Taif University. The patients were divided into two Groups eight patients each; Group I: their metallic framework was constructed from the traditional lost wax patterns technique (TT), Group II: their metallic framework was fabricated by Light Cure Modeling Material Technique (LCMT). Conventional clinical and laboratory steps for construction of metallic partial denture were followed. The frameworks resulted from the two pattern materials were tested clinically and laboratory for fit accuracies and the results were statistically analyzed using the two-tailed t-tests. Results: Clinical results show an appropriate thickness of the impression materials and improved fit accuracy of the Light cure group in comparison to the traditional wax pattern group. Laboratory findings also showed that the Light cure group has significantly smaller mean gap values than the traditional wax pattern group. Conclusions: The fit accuracies of cobalt-chromium frameworks of removable partial denture fabricated from LCMT are better than that fabricated from TT.

The Fit Accuracy of Removable Partial Denture Metal Frameworks Using Conventional and 3D Printed Techniques: An In Vitro Study

To evaluate the accuracy of removable partial denture (RPD) metal frameworks fabricated by the conventional lost-wax (CLW) technique and those made by the selective laser melting (SLM). A dentoform of a mandibular Kennedy class III, modification 1 dental arch were surveyed, and rest seats were prepared on the abutment teeth. The dentoform was then duplicated into a metal die which was used as a reference model. Thirty RPD metal frameworks were fabricated by two techniques; fifteen for each technique. Polyvinyl siloxane (PVS) impression material was painted on the intaglio surface of the rests of each framework which is then seated on the reference die. PVS specimens that represent the gap under the rest were measured in four zones: buccal, lingual, marginal and central by a single examiner using a digital microscope at 50x in micrometers. Comparison between the two techniques for each abutment tooth revealed that the CLW technique had better fit in one tooth, while the SLM technique showed a better fit in two teeth. Regarding the edentulous span length within the SLM technique, the long edentulous span had a significantly better fit. When comparing the four measured rest zones, it was found that in the CLW technique group, the marginal zone had the highest fit accuracy while the lingual zone showed the lowest fit accuracy. In the SLM group, the central zone had the best fit and the buccal zone had the worst fit. RPD frameworks fabricated using the SLM technique showed better fit accuracy than those made by the CLW technique, however, the difference was not statistically significant. SLM is a promising technique for the fabrication of RPD frameworks in routine clinical practice.

Alloys Used in Fixed Prosthodontics: An Overview

Various types of metals have been used in dentistry, since ages. The properties, manufacturing process, reaction within the oral cavity are to be studied by the clinician to decide a treatment for the patient. Alloys are made of two or more metals. The basis of mixing two metals is to obtain a product that has improved properties, ideal for utilization. Alloys are used as filling materials like amalgam. They are used for all-metal fixed partial denture casting; metal sub-structure for ceramic-veneered fixed partial denture casting;removable partial denture framework casting; in implant body, fixture, component fabrication by manufacturer. The most commonly used alloy now is cobalt-chromium-nickel alloy. This article is a short overview about some commonly used alloys and their applications such as silver-palladium, cobalt-chromium, cobalt-chromium nickel and also titanium alloys. These are a few among the various alloys formulated. A thorough knowledge about these materials and their properties are necessary by the clinician to obtain a desired outcome. This article shall also highlight the new trends being observed in alloy selection.

Assessment of the influence of selected electrolytic polishing process parameters on the surface roughness of casts made of the CoCrMo alloy.

To fabricate some prosthetic restorations, such as metal alloy frameworks for removable partial dentures (RPDs), casting techniques must be used. The penultimate stage of the cast finishing procedure is electropolishing. The aim of the study was to assess the influence of selected electrolytic polishing process parameters on the resulting surface smoothness of the cobalt-chromium-molybdenum (CoCrMo) alloy. The CoCrMo alloy, 3 experimental and 2 name-brand electrolytes, were used in the study. A total of 25 samples, 63 mm × 10 mm × 1 mm in size, were cast using the Nautilus® equipment. The cast samples were shaped using metal cutters and carborundum stones and separators, and were sandblasted. The prepared samples were placed in an electrolysis cell as an anode. For each sample, measurements were made by changing the potential of the electrode by 0.2 V in the range from 1.2 V to 7.0 V. The surface of the samples was analyzed using a profilometer. An optical microscope and a scanning electron microscope (SEM) were used to examine the structure of the surface. An analysis of the obtained results showed no statistically significant differences between the BEGO Wirolyt® electrolytic polishing liquid (WB) and experimental electrolytes K15, K8 and K13, all of which were significantly better than the Dentaurum Electrolyt® polishing solution (ED). The microscope images indicated differences in the surface structure of the samples; in the SEM images, inclusions were also visible. The experimental electrolytes did not differ in quality from one of the name-brand electrolytes and were even better than the other one. The obtained surface roughness values (Ra) did not differ significantly from those achieved by other researchers.

An In Vitro Investigation of Accuracy and Fit of Conventional and CAD/CAM Removable Partial Denture Frameworks.

To evaluate the overall accuracy and fit of conventional versus computer-aided design/computer-aided manufactured (CAD/CAM) removable partial denture (RPD) frameworks based on standard tessellation language (STL) data analysis, and to evaluate the accuracy and fit of each component of the RPD framework. A maxillary metal framework was designed for a Kennedy class III Modification I arch. The master model was scanned and used to compare the fit and accuracy of RPD frameworks. Forty impressions (conventional and digital) of the master cast were made and divided into 4 groups based on fabrication method: group I, lost-wax technique (conventional technique), group II, CAD-printing, group III, CAD-printing from stone cast, and group IV, lost-wax technique from resin-printed model. RPD frameworks were fabricated in cobalt-chromium alloy. All frameworks were scanned, and the gap distance between the framework and scanned master model was measured at 8 locations. Color mapping was conducted using comprehensive metrology software. Data were statistically analyzed using the Kruskall-Wallis test, followed by the Bonferroni method for pairwise comparisons (α = 0.05). Color mapping revealed distinct discrepancies in major connectors among the groups. When compared to 3D-printed frameworks, conventional cast frameworks fabricated using dental stone or printed resin models revealed significantly better fit (p < 0.05) particularly in the major connectors and guide plates. The biggest gap (0.33mm ± 0.20 mm) was observed with the anterior strap of the major connector with the printed frameworks (groups II and III). The method of fabrication did not affect the adaptation of the rests or reciprocation plates. Although both conventional and 3D-printing methods of framework fabrication revealed clinically acceptable adaptation, the conventional cast RPD groups revealed better overall fit and accuracy.

Effect of two heat treatments on mechanical properties of selective-laser-melted Co-Cr metal-ceramic alloys for application in thin removable partial dentures

Statement of problemHeat treatment has been used to reduce the residual stress of alloys fabricated by selective laser melting (SLM) to avoid deformation. Co-Cr metal-ceramic alloys are used to fabricate metal-ceramic restorations and removable partial dentures (RPDs) on the same substrate by SLM. A heat treatment that enables the fabrication of metal-ceramic restorations and RPDs with excellent mechanical properties should be evaluated. PurposeThe purpose of this in vitro study was to determine the effects of 2 heat treatments on the mechanical properties of SLM Co-Cr metal-ceramic alloys intended for the fabrication of thin RPDs. Material and methodsTensile bars were manufactured using cast metal-ceramics (C-MC group), RPD alloys (C-RPD group), and SLM Co-Cr metal-ceramic alloys. The SLM specimens were subjected to 2 different heat treatments, L1 at 880°C and L2 at 1100°C, and were further divided into subgroups (L1-MC, L1-RPD, L2-MC, and L2-RPD). Thirty-six tensile specimens were prepared in C-RPD, L1-RPD, and L2-RPD (simulated partial denture alloys for clinical use) and in C-MC, L1-MC, and L2-MC (simulated metal-ceramic alloys); 18 metal-ceramic bond strength specimens were prepared in C-MC, L1-MC, and L2-MC groups (n=6). The tensile test and 3-point bend test were conducted using a universal testing machine. The fracture surfaces of the L2-RPD tensile bar were examined using a scanning electron microscope. The Student t test (α=.05) was used for statistical analysis. ResultsNo significant differences were observed between the bond strengths of L1-MC and C-MC (P=.74) or between those of L2-MC and C-MC (P=.124). The 0.2% yield strength (σ0.2) and elongation of all SLM specimens exceeded the minimum requirements required for the fabrication of thin RPDs as prescribed in ISO 22674:2016. The σ0.2 value of L1-MC and L2-MC was significantly higher than that of C-MC. Significant differences in σ0.2 values were found among the 3 RPD groups, L1-RPD>L2-RPD>C-RPD. For the elongation, significant differences were found among the 3 groups, L2-RPD>C-RPD>L1-RPD. The fracture surface of L2-RPD showed clear submicroscale dimples with fusion defects. ConclusionsWhen Co-Cr metal copings and RPD frameworks were fabricated on the same substrate simultaneously using SLM, heat treatment at 1100°C was found more suitable than at 880°C to release residual stress, considering the toughness required for dental prostheses.

Binder jetting of a complex-shaped metal partial denture framework

Additive manufacturing provides new chances in the manufacturing of highly complex, mass-customized structures with negligible wastes. Binder jetting holds distinctive promise among additive manufacturing technologies due to its fast, low-cost manufacturing; stress-free structures with complex internal and external geometries; and the isotropic properties of the final printed parts. An ExOne binder jet 3D printer is used to produce frameworks for removable partial dentures from metallic powder. Initially, an existing framework is scanned using micro-computed tomography and then the obtained model is printed. Consolidation of the printed parts is achieved with the relative density higher than 99% density with controlled shrinkage. Presented results demonstrate that binder jetting may be used to produce mechanically sound complex-shaped structures as shown here on a denture metal framework model.