Patient satisfaction with laser-sintered removable partial dentures: A crossover pilot clinical trial

Seating accuracy of removable partial denture frameworks fabricated by different digital workflows in comparison to conventional workflow

PURPOSE

To evaluate the seating accuracy of removable partial denture (RPD) frameworks fabricated by two digital workflows involving selective laser melting (SLM) in comparison to the conventional workflow.

MATERIALS AND METHODS

A Kennedy class III modification 1 partially edentulous mandibular arch was used as a master model. Three RPD framework groups were included: (1) a conventional workflow group with conventional impression and casting (CC), (2) a partial digital workflow group with conventional impression and digital fabrication (CD), and (3) a complete digital workflow group with digital impression and digital fabrication (DD). A total of 10 frameworks were produced for each group. The marginal gaps at the occlusal rests, retention arms, and reciprocating arms were measured by a traveling microscope. The data were analyzed with the one-way analysis of variance test.

RESULTS

At the framework level, the most superior fit was observed for the CD group (79.5 µm) followed by DD (85.3 µm) and CC (114.2 µm) groups. The CD and DD groups were significantly superior to CC (p < 0.001). This fit pattern was consistent for the retention and reciprocating arms, while the occlusal rest fit was similar among all the groups.

CONCLUSIONS

The SLM frameworks had a promising seating accuracy in comparison to conventional frameworks. The type of impression, conventional or digital, did not affect the accuracy of SLM frameworks. The differences observed in the present study are likely to be of minimal clinical significance.

A technical and clinical digital approach to the altered cast technique with an intraoral scanner and polyvinyl siloxane impression material

This technique digitalizes the clinical and laboratory steps of fabricating removable partial dentures (RPDs) with the altered cast technique. An intraoral scanner was used to capture the mandibular Kennedy class II partially edentulous arch. An RPD framework was fabricated digitally and then combined with a custom tray with a wax occlusal rim. A conventional polyvinyl siloxane altered cast impression was made and then digitalized both intraorally and extraorally, followed by a digital interocclusal record. The resulting scan was modified to produce an additively manufactured cast. The teeth and gingival components were then designed and fabricated with a combination of additive and subtractive manufacturing, followed by the conventional acrylic resin pour technique. The definitive prosthesis was completed with minimal conventional techniques and without the use of gypsum, prefabricated teeth, or a physical articulator. The technique reduces the number of appointments and achieves the functional extension of the prosthesis through border molding, which is not possible with intraoral scanning.

Patient-reported outcomes and framework fit accuracy of removable partial dentures fabricated using digital techniques: A systematic review and meta-analysis

PURPOSE

This review aimed to summarize the evidence on patient-reported outcomes and clinical performance of digitally fabricated removable partial dentures (RPDs) compared to traditionally fabricated dentures.

METHODS

Three databases were systematically searched (PubMed, CENTRAL, and Wiley online library) for clinical studies comparing digitally and conventionally fabricated RPDs regardless of data acquisition methods used for fabrication. The Cochrane Collaboration risk of bias assessment tool 2 and the Oxford Center for Evidence-based Medicine tool were used to assess risk of bias, and level of evidence, respectively. Descriptive narrative analysis was used to summarize data on patient-reported outcomes, as there were inadequate studies to pool data in a meta-analysis. A random-effects model was used to analyze the data of framework fit accuracy.

RESULTS

Ten randomized controlled trials were included in the systematic review, and 4 were included in the meta-analysis. Two studies showed that digitally fabricated RPDs are associated with higher patient satisfaction than conventionally fabricated RPDs (with a mean difference of 12.5 mm on a 100-satisfaction scale, p = .008). The pooled standardized mean difference for framework fit accuracy was 0.49 (p = 0.02) in favor of conventionally fabricated RPDs, which showed that conventionally fabricated RPDs have a quantitatively better fit compared to digitally fabricated RPDs. However, clinical evaluation studies showed that both frameworks have clinically acceptable fit.

CONCLUSIONS

Current evidence shows that digitally fabricated RPDs are associated with higher patient satisfaction compared to conventionally fabricated RPDs. However, the scarcity of literature here warrants the generalization of this conclusion. Both digitally and conventionally fabricated metal RPD frameworks showed acceptable fit clinically.

Adaptation of removable partial denture rest seats in prostheses made with selective laser sintering or casting techniques: A randomized clinical trial

STATEMENT OF PROBLEM

New fabrication techniques have been developed for removable partial denture (RPD) frameworks although studies validating the clinical application of these techniques are scarce.

PURPOSE

The purpose of this clinical study was to compare the adaptation of RPD framework rests made with conventional casting or computer-aided design and computer-aided manufacturing (CAD-CAM) with selective laser sintering (SLS) at the clinical evaluation and 1 year after the delivery of the prostheses.

MATERIAL AND METHODS

This triple-blinded pilot study included 18 participants presenting with maxillary and/or mandibular partial edentulism, of which only 7 returned for the second measurement 1 year after prosthesis delivery. Participants were randomly assigned to 1 of 2 groups depending on whether the RPD framework was made with SLS or conventional lost-wax casting. The adaptation of the RPD at the rest seat area was evaluated by injecting a silicone material on the abutment tooth before seating. The silicone specimens were then sectioned transversely and measured with a scanning electron microscope. The statistical analysis was performed with a linear mixed-effect model with the intention to treat and with a 3-factor repeated measures ANOVA (α=.05).

RESULTS

At the metal framework evaluation (T0), the prostheses made with SLS showed a mean ±standard deviation adaptation of 398 ±45 μm, while those made with conventional casting presented a mean ±standard deviation adaptation of 176 ±41 μm (P=.009). One year after the delivery of the prostheses (T1), the adaptation of the frameworks made with conventional casting was still significantly better (88 ±6 μm versus 197 ±94 μm, P=.03).

CONCLUSIONS

Frameworks made with SLS showed worse clinical accuracy at the rest than frameworks produced with conventional casting.

Accuracy of Mandibular Removable Partial Denture Frameworks Fabricated by 3D Printing and Conventional Techniques

Herein, we used digital superimposition to evaluate the accuracy of metal frameworks for mandibular removable partial dentures fabricated using three techniques. Thirty master casts of a mandibular dentiform were categorized into three groups (n = 10) based on the framework manufacturing method: selective laser melting-based metal three-dimensional (3D) printing (SLM), digital light projection-based resin 3D printing and subsequent casting (RPC), and conventional casting (CON). The master casts were scanned twice, initially after preparation and subsequently after attaching silicone using the frameworks. These scan files were digitally superimposed to measure the silicone thickness. Statistical analysis was conducted using SPSS Statistics (Version 23.0, IBM Corp., Somers, NY, USA). One-way ANOVA and a post hoc Tukey's multiple comparison tests were performed to determine differences among the three groups (α = 0.05). The RPC group exhibited significantly higher overall and mean internal discrepancies at rest and tissue stops than the SLM and CON groups, which exhibited statistically insignificant differences. Thus, SLM fabrication resulted in comparable accuracy to that achieved by CON, whereas sequentially performing resin 3D printing and casting induced inferior accuracy. However, all frameworks across the three groups were clinically acceptable.

Fit of removable partial denture frameworks fabricated from 3D printed patterns versus the conventional method: An in vitro comparison

STATEMENT OF PROBLEM

The conventional method of fabricating removable partial denture (RPD) patterns is a time-consuming, expensive, and complex process, and the success of the treatment depends on the fit of the framework. Questions still remain as to whether the 3D-printing method is an acceptable procedure compared with the conventional method.

PURPOSE

The purpose of this in vitro study was to compare the fit of RPDs cast from 3D printed frameworks and conventionally fabricated RPDs according to the gaps between the framework and the reference model.

MATERIAL AND METHODS

A metal reference model was made from a Kennedy class III modification 1 maxillary typodont. For the conventional group (n=9), impressions were made from the metal cast. Cobalt chromium frameworks were cast with the conventional method. For the digital group (n=9), the metal cast was scanned with a laboratory scanner, and the RPD was designed in the 3Shape platform. The standard tessellation language (STL) file of the design was downloaded to a 3D printer (Hunter DLP), and 9 resin frameworks were printed. These frameworks were invested and cast in the same dental laboratory as the first group. Gap measurement was assessed vertically with a superimposition software program (Geomagic Control X), and additional measurements were assessed under rests, reciprocal arms, and a 2.2-mm box under the major connector. The independent t test was used for determining the results and statistical analysis between groups. The paired t test was used for statistical analysis within groups (α=.05 for all tests).

RESULTS

No significant differences (P>.05) were observed in the mean ±standard deviation in overall fit according to the gaps in the conventional group (103 ±18 μm) and those in the digital group (109 ±21 μm). The biggest gap (poorest fit) was observed in the 2.2-mm box under the major connector (115 ±6 μm).

CONCLUSIONS

Both conventional and 3D-printing methods showed clinically acceptable fits. Further clinical studies with a larger sample size and long-term follow-up are needed.

Dimensional stability of 3D-printed edentulous and fully dentate hollowed maxillary models over periods of time

BACKGROUND

Dental casts made utilising digital workflow are becoming more common because to their speed and cost savings. However, studies on their dimensional accuracy over time with diverse designs are missing.

OBJECTIVE

The aim of this in vitro study was to assess the dimensional stability of 3D-printed edentulous and fully dentate hollowed maxillary models with 50-micrometer resolution over 1 day, 14 days, and 28 days using surface matching software.

METHODS

Scanned edentulous and fully dentate maxillary typodont models were used as references. The models were scanned by a desktop lab scanner of 15-micrometer accuracy (D900, 3Shape). Then, the files were used in designing software (Meshmixer, Autodesk) to create hollowed maxillary casts. Fifteen edentulous and 15 fully dentate (total of 30) models were printed using a DLP lab printer (Cara print 4.0, Kulzer). The 3D-printed models were scanned using the same desktop lab scanner of 15-micrometer accuracy at intervals of baseline days, 1 day, 14 days, and 28 days to assess the effect of aging (n = 120). The dimensional changes were quantified and compared using the root mean square (RMS) method, expressed in micrometres (µm). The study employed repeated measures analysis of variance (ANOVA) to assess and compare the root mean square (RMS) values across the variables. The data was analysed using SPSS (26, Chicago, Illinois, USA).

RESULTS

The RMS of the edentulous models rapidly increased from a mean value of 0.257 at the beginning of the study to 0.384 after twenty-eight days. However, the mean RMS values for the dentate models did not change much over the four intervals. It varied only from 0.355 to 0.347. The mean values for edentulous patients increased from 0.014 to 0.029 during the period from baseline to twenty-eight days. However, the mean average values decreased for the dentate models from 0.033 to 0.014 during this period. By utilizing ANOVA, mean RMS values increased insignificantly till one day but significantly to fourteen and twenty-eight days. Dentate model mean values differed insignificantly across four intervals. Repeated measures ANOVA for combined and separated data showed no significant differences across edentulous, dentate, and total models over times.

CONCLUSION

The study revealed changes in the dimensions of 3D-printed edentulous models over a span of 3 and 4 weeks. Caution should be applied when using 3D-printed dental master models for constructing definitive prostheses on edentulous models over a period of 3 to 4 weeks.

Comparison between digital superimposition and microcomputed tomography methods of fit assessment of removable partial denture frameworks

STATEMENT OF PROBLEM

The fit of removable partial denture frameworks should be assessed to optimize clinical adaptation. Potential discrepancies between framework and supporting structures are typically precisely measured with negative subtracts and high-resolution equipment. The growth of computer-aided engineering technology allows the development of new methods for the direct evaluation of discrepancies. However, how the methods compare is unclear.

PURPOSE

The purpose of this in vitro study was to compare 2 digital methods of fit assessment based on direct digital superimposition and microcomputed tomography indirect analysis.

MATERIAL AND METHODS

Twelve cobalt chromium removable partial denture frameworks were fabricated by conventional lost-wax casting or additive manufacturing techniques. The thickness of the gap between occlusal rests and respective definitive cast rest seats (n=34) was evaluated by using 2 different digital methods. Silicone elastomer impressions of the gaps were obtained, and microcomputed tomography measurements were used as controls for validation purposes. Digitization of the framework, the respective definitive cast, and the combination was followed by digital superimposition and direct measurements with the Geomagic Control X software program. Because normality and homogeneity of variance were not verified (Shapiro-Wilk and Levene tests, P<.05), the data were analyzed with Wilcoxon signed rank and Spearman correlation tests (α=.05).

RESULTS

The thicknesses measured by microcomputed tomography (median=242 μm) and digital superimposition (median=236 μm) did not reveal statistically significant differences (P=.180). A positive correlation (ρ=0.612) was detected between the 2 methods of assessing fit.

CONCLUSIONS

The frameworks presented median gap thicknesses under the limit of clinical acceptability without differences between the proposed methods. The digital superimposition method was determined to be as acceptable as the high-resolution microcomputed tomography method for assessing removable partial denture framework fit.

Clinical evaluation of removable partial dentures with digitally fabricated metal framework after 4 years of clinical service

This case report describes the clinical outcomes of three patients who received removable partial dentures with a completely digitally designed and manufactured metal framework. The initial intraoral impressions were prepared, and the resulting standard tessellation language files were sent to a dental laboratory, where the alloy framework was designed using inLab software and printed using a 3D printer or milled directly from a Co-Cr disc. The quality of fit of the framework was evaluated intraorally to confirm the laboratory design. The acrylic teeth were set, and the definitive partial dentures were delivered after the acrylic resin bases were processed. The follow-up time was 4 years. No complications or failures related to the components of the partial dentures were observed.

Accuracy of models of partially edentulous arches obtained by three-dimensional printing: An in vitro study

Aim

The aim of this study was to evaluate the accuracy of models of partially edentulous arches obtained by three-dimensional (3D) printing.

Settings and Design

This was an in vitro study.

Materials and Methods

Fifteen partially edentulous models were evaluated, using two methods of measuring dimensions: virtual, using the Standard Tessellation Language files of the models and software (control group), and physical, through printing the models and digital caliper (test group). For both methods, measurements were made regarding the dimensions of the teeth (width and length - buccal/lingual or palatal/occlusal) and distances between the teeth.

Statistical Analysis Used

For the variable of linear measurements (width and length) and distances between teeth of the same hemiarch, the Wilcoxon test was used, while for the variable between opposite hemiarches, the paired t-test was used.

Results

In the evaluation of the linear measurements, a significant difference was observed only when the width of the molar tooth was analyzed (P = 0.014). When the buccal length was measured, all teeth had linear measurements provided by the virtual method that was lower than the physical (P = 0.000), as well as the lingual/palatal length in incisors (P = 0.003) and molars (P = 0.009) and in total (P = 0.001). As for the analyses between teeth, no difference was identified between the measurements provided by the virtual method compared to the physical one.

Conclusions

The 3D printer used to print partially edentulous models provided linear distortions in the teeth but without changes in the distances between teeth of the same hemiarch and between teeth of opposite hemiarches.

Castability of a Ti-7.5Mo alloy for fabricating frameworks for removable partial dentures

STATEMENT OF PROBLEM

The properties of commercially pure titanium are better than those of cobalt chromium alloys in various ways. However, casting pure titanium is challenging because of its high melting point and chemical reactivity. Because of excellent mechanical strength, a titanium alloy, Ti-6Al-4V, has been commonly adopted, but the aluminum and vanadium ions released may be cytotoxic.

PURPOSE

The purpose of the present study was to evaluate a new titanium alloy, Ti-7.5Mo, developed by the National Cheng Kung University for casting removable denture frameworks. The casting success rate, porosity, and guide plane or rest fit were compared among frameworks cast with Ti-7.5Mo alloy and pure titanium for 3 types of edentulism.

MATERIAL AND METHODS

Ti-7.5Mo alloy and pure titanium were used to cast frameworks for Kennedy Class I and II and completely edentulous conditions, with 5 frameworks for each condition. Wax patterns of the frameworks were designed and fabricated by using computer-aided design and computer-aided manufacture (CAD-CAM) technology to ensure their geometrical consistency. They were then invested with aluminum oxide-based material and cast. The castings were examined with microcomputed tomography (μCT) for porosity, and fit was evaluated from the thickness of a vinyl polyether silicone material at the guide plane or the rest by using an optical microscope. The casting was determined to be successful if the frameworks were complete. The porosity and fit were statistically evaluated by using 2-way ANOVA (α=.05).

RESULTS

Using pure titanium, the casting success rate was 80%, with only 64% of the major connectors in the deficient castings being complete. The μCT images showed that the percentage of casting defects in Ti-7.5Mo castings was one-third of the pure titanium castings. Furthermore, internal voids were detected in the clasps of the pure titanium castings, while the Ti-7.5Mo castings had few defects in the minor connectors and no radiographically detectable defects in the clasps. The fit analysis demonstrated smaller gaps over both guide planes and rests in the Ti-7.5Mo castings.

CONCLUSIONS

Ti-7.5Mo alloy had better castability than pure titanium. Based on the results, Ti-7.5Mo alloy is suitable for dental casting and may provide better performance.

Influence of fabrication method on the manufacturing accuracy and internal discrepancy of removable partial dentures: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Removable partial dentures (RPDs) can be fabricated with conventional casting procedures or computer-aided design and computer-aided manufacturing (CAD-CAM) technologies; however, the manufacturing accuracy and internal discrepancy differences among these manufacturing methods remain uncertain.

PURPOSE

The purpose of this systematic review and meta-analysis was to assess the influence of the fabricating method (casting, milling, or additive manufacturing) on the accuracy and internal discrepancy of RPDs.

MATERIAL AND METHODS

An electronic search of the literature was performed in 6 databases: PubMed/Medline, Embase, Web of Science, Scopus, Cochrane, and Google Scholar. The studies that assessed the accuracy and internal discrepancy of RPDs fabricated from casting, milling, and additive manufacturing were included. Studies reporting gaps (mean) and standard deviations were included in the meta-analysis. Publication bias was identified using funnel plot asymmetry and the Egger test.

RESULTS

A total of 25 articles were included. The internal discrepancy of the additively manufactured RPDs ranged from 14.4 to 511 μm and from 7 to 419 μm in conventionally fabricated RPDs. For the milling method, 20 to 66 μm horizontal and 17 to 59 μm vertical discrepancies were reported. The Egger tests indicated no publication bias among the studies that were included in the meta-analysis. Four included studies resulted in more than the acceptable clinical gap (311 μm) for the CAD-CAM method. Independently of the manufacturing method, the greatest internal discrepancies reported were observed under the major connectors. RPDs fabricated by using CAD-CAM techniques required fewer clinical appointments, the RPD design was easier to reproduce, and laboratory time was less than with conventional procedures. However, the reviewed studies described several disadvantages, including limited RPD design programs, difficulties in defining the occlusal plane, expensive materials, and increased laboratory cost.

CONCLUSIONS

Additive and subtractive technologies provide accurate methods for RPD fabrication; however, all challenges, including limited design software programs have not yet been overcome, and casting is still needed when the framework pattern is milled or printed.

Metallic Dental Implants Wear Mechanisms, Materials, and Manufacturing Processes: A Literature Review

OBJECTIVES

From the treatment of damaged teeth to replacing missing teeth, dental biomaterials cover the scientific interest of many fields. Dental biomaterials are one of the implants whose effective life depends vastly on their material and manufacturing techniques. The purpose of this review is to summarize the important aspects for metallic dental implants from biomedical, mechanical and materials science perspectives. The review article will focus on five major aspects as mentioned below. Tooth anatomy: Maximizing the implant performance depends on proper understanding of human tooth anatomy and the failure behavior of the implants. Major parts from tooth anatomy including saliva characteristics are explored in this section. Wear mechanisms: The prominent wear mechanisms having a high impact on dental wear are abrasive, adhesive, fatigue and corrosion wear. To imitate the physiological working condition of dental implants, reports on the broad range of mastication force and various composition of artificial saliva have been included in this section, which can affect the tribo-corrosion behavior of dental implants. Dental implants classifications: The review paper includes a dedicated discussion on major dental implants types and their details for better understanding their applicability and characteristics. Implant materials: As of today, the most established dental implant materials are SS316L, cobalt chrome alloy and titanium. Detailed discussion on their material properties, microstructures, phase transformations and chemical compositions have been discussed here. Manufacturing techniques: In terms of different production methods, the lost wax casting method as traditional manufacturing is considered. Selective Laser Melting (SLM) and Directed Energy Deposition (DED) as additive manufacturing techniques (AM) have been discussed. For AM, the relationships between process-property-performance details have been explored briefly. The effectiveness of different manufacturing techniques was compared based on porosity distribution, mechanical and biomechanical properties.

SUMMARY

Despite having substantial research available on dental implants, there is a lack of systematic reviews to present a holistic viewpoint combining state-of-the-art from biomedical, mechanical, materials science and manufacturing perspectives. This review article attempts to combine a wide variety of analyzing approaches from those interdisciplinary fields to deliver deeper insights to researchers both in academia and industry to develop next-generation dental implants.

Patient-reported outcome measures of digitally versus conventionally constructed removable dentures: a systematic review protocol

OBJECTIVE

This review will evaluate patient-reported outcome measures of treatment with digitally fabricated versus conventionally manufactured removable dental prostheses in partially or completely edentate adults.

INTRODUCTION

Compared with conventionally manufactured dental prostheses, digitally fabricated prostheses may simplify and reduce the number of clinical steps and minimize errors in the production of prostheses without compromising occlusal accuracy and fit. This may, in turn, improve patient satisfaction, ability to speak, esthetics, stability, and oral health status. Determining evidence of patient-reported outcomes will assist the dental practitioner when communicating patient expectations.

INCLUSION CRITERIA

This review will consider experimental and quasi-experimental study designs, including randomized and non-randomized controlled trials, comparative clinical studies, prospective or retrospective trials, longitudinal clinical studies, clinical reports, and technique articles. The review will include patient-reported outcome measures from fully or partially edentulous adult participants who received either conventionally or digitally fabricated dental prostheses.

METHODS

The following databases will be searched for scientific, peer-reviewed literature: Academic Search Complete, CINAHL, Dentistry and Oral Sciences (all via EBSCO), MEDLINE (PubMed), ScienceDirect, and Cochrane Central Register of Controlled Trials. The search strategy will include terms relevant to the intervention, which will be adapted for each bibliographic database, in combination with database-specific filters, where available. The language restriction will be English and Dutch. All included studies will be critically appraised and data will be extracted for synthesis. If possible, a meta-analysis will be conducted. The Grading of Recommendations, Assessment, Development and Evaluation approach will be followed to evaluate the certainty of evidence.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO CRD42018094357.

Fit Accuracy of Removable Partial Denture Frameworks Fabricated with CAD/CAM, Rapid Prototyping, and Conventional Techniques: A Systematic Review

Objective

Analyzing and comparing the fit and accuracy of removable partial denture (RPDs) frameworks fabricated with CAD/CAM and rapid prototyping methods with conventional techniques.

Materials and Methods

The present systematic review was carried out according to PRISMA guidelines. The search was carried out on PubMed/MEDLINE, Cochrane collaboration, Science direct, and Scopus scientific engines using selected MeSH keywords. The articles fulfilling the predefined selection criteria based on the fit and accuracy of removable partial denture (RPD) frameworks constructed from digital workflow (CAD/CAM; rapid prototyping) and conventional techniques were included.

Results

Nine full-text articles comprising 6 in vitro and 3 in vivo studies were included in this review. The digital RPDs were fabricated in all articles by CAD/CAM selective laser sintering and selective laser melting techniques. The articles that have used CAD/CAM and rapid prototyping technique demonstrated better fit and accuracy as compared to the RPDs fabricated through conventional techniques. The least gaps between the framework and cast (41.677 ± 15.546 μm) were found in RPDs constructed through digital CAD/CAM systems.

Conclusion

A better accuracy was achieved using CAD/CAM and rapid prototyping techniques. The RPD frameworks fabricated by CAD/CAM and rapid prototyping techniques had clinically acceptable fit, superior precision, and better accuracy than conventionally fabricated RPD frameworks.

Analytical model of I-bar clasps for removable partial dentures

OBJECTIVE

Clasps of removable partial dentures (RPDs) often suffer from fatigue stress that leads to plastic deformation, loss of retention, and RPD failure. Recently, computer-based technologies were proposed to optimize clasp geometry design. The objective of this study was to create an analytic model of I-bar clasps for computer-aided design (CAD)-RPD.

METHODS

The analytical model based on mechanical laws was established to simulate I-bar clasp retention, and optimize its design. The model considered the lengths of the vertical (L₁) and horizontal (L₂) arms of the I-bar as well as the radius (r) of its half-round cross-section. The analytical model was validated with mechanical experiments evaluating the retention of cobalt-chromium (Co-Cr) clasps in vitro and compared with finite element analysis (FEA).

RESULTS

The analytical model was in good agreement with the mechanical experiments and FEA, and showed that I-bar clasp design could provide optimal mechanical performance as long as the length of arms (L₁ and L₂) do not exceed 6 mm. Clasps with L₁ > 8 mm and L₂ > 9 mm presented stress values exceeding the fatigue limit of Co-Cr. The proposed solution was to increase the radius of I-bar to conserve the initial mechanical performance of Co-Cr.

SIGNIFICANCE

Co-Cr I-bar clasps perform best on teeth with reduced mesiodistal dimensions (canine and premolar), and their designs could be optimized to prevent stress from reaching the yield strength and the fatigue failure limit.

Prosthetic Rehabilitation of a Repaired Cleft Palate with Use of a Two-Part Hinged Magnet Retained Removable Prosthesis

The presence of a cleft lip and palate is associated with a number of complications and the oral rehabilitation for the improvement of speech, function and esthetics can involve conventional and surgical orthodontics, distraction osteogenesis, fixed and removable prosthodontics, providing obturation of open defects if required. This clinical report describes the prosthodontic management of a patient with a repaired cleft lip and palate with significant maxillary hypoplasia and primary concern of aesthetics with the use of a two-part hinged magnet retained removable prosthesis.

A systematic review of digital removable partial dentures. Part I: Clinical evidence, digital impression, and maxillomandibular relationship record

PURPOSE

This study comprehensively reviewed the current status of digital workflows in fabricating removable partial dentures (RPDs) using evidence from clinical trials and case reports.

STUDY SELECTION

We performed a systematic review of the literature on the materials and fabrication of RPDs using digital technologies published in online databases from 1980 to 2020. We selected eligible articles from the search results, retrieved information on digital RPDs from these, and conducted a qualitative analysis. We report evidence from clinical papers and case reports, digital impression-taking methods, and maxillomandibular relationship (MMR) records.

RESULTS

A case report electronically published in 2019 introduced a clasp-retained RPD fabricated via a full-digital workflow without a gypsum definitive cast. Computer-aided design and computer-aided manufacturing of double-crown-retained RPDs with nonmetal materials were described in some case reports. Intraoral scanners were used to obtain digital impressions and MMR records in the fabrication of digital RPDs, which have potential advantages for reducing the number of clinical appointments and simplifying laboratory procedures. Evidence from clinical trials is scarce; a randomized controlled trial reported higher patient satisfaction with digital clasp-retained RPDs than with conventional RPDs.

CONCLUSIONS

Full-digital RPDs can be fabricated without a gypsum definitive cast. However, the indication for full-digital RPDs is limited to cases with Kennedy Class III/IV partially edentulous arches with several missing teeth. Challenges in digital impression-taking and MMR recording remain to be solved to extend these indications. More evidence from clinical trials is required to evaluate the efficacy and usefulness of digital R PDs.

A systematic review of digital removable partial dentures. Part II: CAD/CAM framework, artificial teeth, and denture base

PURPOSE

This study comprehensively reviewed the current status of the digital workflow of removable partial dentures (RPDs) and summarized information about the fabrication methods and material properties of the dental framework, artificial teeth, and denture base.

STUDY SELECTION

We performed a systematic review of the literature published in online databases from January 1980 to April 2020 regarding RPD fabrication and materials used in the related digital technology. We selected eligible articles, retrieved information regarding digital RPDs, and conducted qualitative/quantitative analyses. In this paper, the computer-aided design/computer-aided manufacturing (CAD/CAM) framework, artificial teeth, and denture base materials are reported.

RESULTS

A variety of materials, such as cobalt-chromium alloy, titanium, zirconia, and polyether ether ketone, are used for dental CAD/CAM frameworks. The mechanical strength of the metal materials used for the CAD/CAM framework was superior to that of the cast framework. However, the fitness and surface roughness of the framework and clasp fabricated using a selective laser melting (SLM) method were not superior to those obtained via cast fabrication. Most material properties and the surface roughness of poly methyl methacrylate (PMMA) discs used for digital RPDs were superior to those of heat-cured PMMA.

CONCLUSIONS

The use of a CAD/CAM framework and PMMA disc for digital RPDs offers numerous advantages over conventional RPDs. However, technical challenges regarding the accuracy and durability of adhesion between the framework and denture base remain to be solved. In digital fabrication, human technical factors influence the quality of the framework.

Laboratory efficiency of additive manufacturing for removable denture frameworks: A literature-based review

The purpose of this literature review was to verify the laboratory efficiency of additive manufacturing (AM) systems for removable partial denture (RPD) frameworks. All available relevant articles in English published from 1990 to 2020 were found by searching online databases and by hand research. A total of 17 articles dealt with the surface roughness, fitness accuracy, and retentive forces of AM frameworks. The surface roughness of AM was inferior to that of casting and milling. Whether conventional cast or AM RPD frameworks had superior fitness accuracy could not be clarified. As compared with casting and AM, milling enabled the fabrication of RPD clasps with comparable or better fitness accuracy. Over time, AM clasps had retentive force values of superior consistency as compared with those of conventional cast clasps. Clasps fabricated by repeated laser sintering and high-speed milling could obtain smoother surfaces and more suitable retention than those of AM clasps.

Impact of Aging on the Accuracy of 3D-Printed Dental Models: An In Vitro Investigation

The aim of this in vitro study was to analyze the impact of model aging on the accuracy of 3D-printed dental models. A maxillary full-arch reference model with prepared teeth for a three-unit fixed dental prosthesis was scanned ten times with an intraoral scanner (3Shape TRIOS Pod) and ten models were 3D printed (Straumann P-Series). All models were stored under constant conditions and digitized with a desktop scanner after 1 day; 1 week; and 2, 3, and 4 weeks. For accuracy, a best-fit algorithm was used to analyze the deviations of the abutment teeth (GFaI e.V Final Surface^®). Wilcoxon Rank Sum Tests were used for comparisons with the level of significance set at α = 0.05. Deviation analysis of the tested models showed homogenous intragroup distance calculations at each timepoint. The most accurate result was for 1 day of aging (3.3 ± 1.3 µm). A continuous decrease in accuracy was observed with each aging stage from day 1 to week 4. A time-dependent difference was statistically significant after 3 weeks (p = 0.0008) and 4 weeks (p < 0.0001). Based on these findings, dental models should not be used longer than 3 to 4 weeks after 3D printing for the fabrication of definitive prosthetic reconstructions.

A digital cast-free clinical workflow for oral rehabilitation with removable partial dentures: A dental technique

The present report describes a technique for a digital cast-free clinical workflow for the fabrication of a combined tooth-implant-supported removable partial denture. This technique comprises digital intraoral scanning, computer-aided design, and subtractive computer-aided manufacturing for the denture base, denture teeth, and crowns and additive computer-aided manufacturing for the denture framework (CAD-CAM).

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.

Fatigue properties of removable partial denture clasps fabricated by selective laser melting followed by heat treatment

The aim of the study was to investigate the effect of post-heat treatment on the microstructures and fatigue strengths of Co-Cr-Mo (CCM) clasps prepared by selective laser melting (SLM). Clasp specimens and rod-shaped specimens were fabricated by SLM using CCM powders with different angulations (0°, 45°, and 90°). Two heat treatment conditions were used: 1 and 6 h at 1150 °C in an argon atmosphere followed by cooling in a furnace. Subsequently, the fatigue strength and microstructure were investigated. The results revealed that for the control group, the mean fatigue life was different when building angulations were changed as manifested by the control-90 specimen, which exhibited the highest fatigue life, followed by control-45 and then control-0. One-hour heat treated samples showed higher fatigue strength in all axes than the 0°- and 45°-axes control samples and lower fatigue strength than the 90°-axes control samples. The survival rate after heat treatment for 1 h exhibited no significant difference in all the axes. In terms of microstructure, after heat treatment, the samples showed homogeneous equiaxed grain and randomized texture in all angulations. Therefore, using a post-heat treatment can reduce the anisotropy effect on the microstructure and fatigue strength due to homogenized microstructure.

Patient satisfaction and preference with thermoplastic resin removable partial dentures: a randomised cross-over trial

PURPOSE

This randomised cross-over trial aimed to comparatively investigate patient preference and satisfaction with thermoplastic resin removable partial dentures (TR-RPDs) and conventional metal clasp-retained removable partial dentures (MC-RPDs).

METHODS

Twenty-eight partially dentate subjects were enrolled and randomised to receive MC-RPDs followed by TR-RPDs or vice versa (n=14, each group). The subjects were asked to score overall satisfaction and denture-related parameters 3 months after delivery of each denture. Additionally, they were asked to choose their preferred denture type at the end of the trial.

RESULTS

Of the 28 subjects, 24 (86%; mean age, 67.3 years) completed the trial. The overall satisfaction scores and ratings for oral appearance with TR-RPDs were significantly higher than those with MC-RPDs (P<0.05). Moreover, 75% (18/24) and 83% (20/24) of the subjects reported greater overall satisfaction and better oral appearance with TR-RPDs than with MC-RPDs (P<0.001, both). Scores for mucosal pain and food impaction were significantly better with TR-RPDs than with MC-RPDs (P<0.05). Relative to MC-RPDs, TR-RPDs provided slightly better oral comfort and speech, although the differences were not statistically significant (P>0.05). Scores for chewing ability, denture stability, and ease of denture cleaning were almost identical for both types of dentures.

CONCLUSIONS

These results suggest that TR-RPDs hold an advantage over MC-RPDs in terms of oral appearance and can offer greater satisfaction than MC-RPDs in partially dentate arches with at least an occluding pair in the posterior region.

CLINICAL TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN000007310).

Obturator fabrication incorporating computer-aided design and 3-dimensional printing technology: A clinical report

This article reports an approach to fabricating a maxillary obturator using the computer-aided design and computer-aided manufacturing (CAD-CAM) process. The maxillary definitive cast and the trial tooth arrangement were separately scanned and superimposed. The virtual cast created from the scan data was surveyed, and the framework was designed using specific software. The definitive cobalt-chromium framework was fabricated by using 3-dimensional (3D) selective laser sintering (SLS) technology. After framework trial placement, the definitive obturator prosthesis was processed using conventional heat-polymerizing resin with the lost-wax processing technique. Using CAD technology and 3D metal printing resulted in improved fit, function, and esthetics for the definitive obturator prosthesis.

Fabricating a reduction guide for parallel guiding planes with computer-aided design and computer-aided manufacturing technology

Preparing appropriate guiding planes is essential for the success of a removable partial denture. Owing to the difficulty of determining the location and dimension of proximal reduction, establishing optimal guiding planes may challenge even skilled clinicians. This article introduces a digital workflow for fabricating a reduction guide to establish parallel guiding planes.

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

PURPOSE

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.

MATERIALS AND METHODS

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).

RESULTS

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 (0.33 mm ± 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.

CONCLUSIONS

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.

Influence of novel implant selective laser melting framework design on mechanical durability of acrylic veneer

BACKGROUND

A novel implant framework design is proposed to improve the mechanical durability of acrylic veneer.

PURPOSES

Comparing the mechanical durability of acrylic veneer on implant frameworks fabricated from selective laser melting (SLM) with novel design against conventional computer numeric controlled (CNC) milled frameworks.

MATERIALS AND METHODS

Implant titanium frameworks with distal cantilever were fabricated by SLM (n = 10) and CNC milling (n = 10). The CNC frameworks had multiple vertical pins, while the SLM frameworks had 3D metal networks of horizontal beams connected by vertical struts. All the frameworks were veneered with acrylic teeth and resin material and were subjected to a static load-to-failure test at the cantilever region. The load-to-failure readings and the pattern of prosthesis damage were recorded for each prosthesis.

RESULTS

The CNC and SLM prostheses failed at statistically similar loads. The acrylic veneer around the CNC frameworks tend to initially crack around the distal implant followed by acrylic chipping. Six SLM prostheses failed at the framework connector on the mesial implant by separation of the screw seat. After reloading these prostheses, they failed by acrylic veneer chipping. The SLM prostheses had significantly less incidence of acrylic flexure and severity of acrylic veneer chipping than CNC prostheses.

CONCLUSIONS

The SLM framework with novel design is efficient in reinforcing acrylic veneering. However, the SLM frameworks appeared weak in thin sections, such as the screw seat.

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

OBJECTIVE

Clasps of removable partial dentures (RPDs) often suffer from plastic deformation and failure by fatigue; a common complication of RPDs. A new technology for processing metal frameworks for dental prostheses based on laser-sintering, which allows for precise fabrication of clasp geometry, has been recently developed. This study sought to propose a novel method for designing circumferential clasps for laser-sintered RPDs to avoid plastic deformation or fatigue failure.

METHODS

An analytical model for designing clasps with semicircular cross-sections was derived based on mechanics. The Euler-Bernoulli elastic curved beam theory and Castigliano's energy method were used to relate the stress and undercut with the clasp length, cross-sectional radius, alloy properties, tooth type, and retention force. Finite element analysis (FEA) was conducted on a case study and the resultant tensile stress and undercut were compared with the analytical model predictions. Pull-out experiments were conducted on laser-sintered cobalt-chromium (Co-Cr) dental prostheses to validate the analytical model results.

RESULTS

The proposed circumferential clasp design model yields results in good agreement with FEA and experiments. The results indicate that Co-Cr circumferential clasps in molars that are 13mm long engaging undercuts of 0.25mm should have a cross-section radius of 1.2mm to provide a retention of 10N and to avoid plastic deformation or fatigue failure. However, shorter circumferential clasps such as those in premolars present high stresses and cannot avoid plastic deformation or fatigue failure.

SIGNIFICANCE

Laser-sintered Co-Cr circumferential clasps in molars are safe, whereas they are susceptible to failure in premolars.