Denture Frameworks Research Articles

Ultrasonic welding of polyetheretherketone for dental applications

ObjectiveDue to its favorable properties, the high-performance polymer polyetheretherketone (PEEK) is used as a metal-free alternative for the fabrication of denture frameworks. For dental applications, PEEK is available in different colors, such as red or white, by compounding with different fillers. In order to permanently bond such different dental PEEK types together in a denture framework, ultrasonic welding could be a viable process.Therefore, the aim of this study was to determine the optimum processing welding parameters for welding different dental PEEK grades in terms of maximum weld strength. MethodsRectangular plates from three PEEK compounds were prepared according to the dimensions of a removable partial denture (RPD) of PEEK. These were combined in a way that four groups resulted, whereas the combination of pure PEEK served as control. In each group, 5 samples were ultrasonically welded at one of four welding energies using a microprocessor-controlled ultrasonic welder, where the welder was activated only once. Afterwards, the samples were subjected to tensile tests to evaluate the shear bond strength (SBS) of the joint. ResultsIncreasing the welding energy resulted in an increase in the welding time. Accordingly, the increase in the welding energy increased the surface deformation for all tested samples. The shear bond strengths ranged from 4.8 ± 0.68 MPa for samples welded with 50 Ws to 16.37 ± 1.69 MPa for samples welded with 90 Ws. Excessive weld energy of 130 Ws led to a significant decrease of SBS due to a severe indentation and perforation induced by the sonotrode. SignificanceThe SBS and topography of the welded samples were systematically studied and the optimal welding parameters were determined. This could serve as a reference and instruction for clinical applications.

Novel fully digital workflow for removable partial denture fabrication

Background: Digital dentistry technology based on computer-aided design and computer-aided manufacturing (CAD/CAM) has been widely applied in the field of prosthodontics, ranging from digital techniques for impression processes, jaw registration, artificial tooth arrangement and base design, along with base and denture fabrication. However, conventional analog workflows are still used and digital workflows have not completely replaced analog workflows. Purpose: Knowing the latest complete digi-tal workflow in the manufacture of removable partial dentures (RPD). Methods: Full-arch digital impressions of the partially edentulous jaw were made with an intraoral scanner or by conventional methods. The denture framework, artificial teeth, and denture base were designed by commercially available CAD software. Each of the denture components including connectors, clasps, and artificial teeth and the denture bases were fabricated separately by the CAM machine, and then assembled using an adhesive material. Conclusion: RPDs were successfully fabricated using a fully digital workflow and no clinical complications were reported.

PEEK Biomaterial in Long-Term Provisional Implant Restorations: A Review.

Polyetheretherketone (PEEK) has become a useful polymeric biomaterial due to its superior properties and has been increasingly used in dentistry, especially in prosthetic dentistry and dental implantology. Promising applications of PEEK in dentistry are dental implants, temporary abutment, implant-supported provisional crowns, fixed prosthesis, removable denture framework, and finger prosthesis. PEEK as a long-term provisional implant restoration has not been studied much. Hence, this review article aims to review PEEK as a long-term provisional implant restoration for applications focusing on implant dentistry. Articles published in English on PEEK biomaterial for long-term provisional implant restoration were searched in Google Scholar, ScienceDirect, PubMed/MEDLINE, and Scopus. Then, relevant articles were selected and included in this literature review. PEEK presents suitable properties for various implant components in implant dentistry, including temporary and long-term provisional restorations. The modifications of PEEK result in wider applications in clinical dentistry. The PEEK reinforced by 30–50% carbon fibers can be a suitable material for the various implant components in dentistry.

Optimization of Digital Light Processing Three-Dimensional Printing of the Removable Partial Denture Frameworks; The Role of Build Angle and Support Structure Diameter.

The optimal three-dimensional (3D) printing parameters of removable partial denture (RPD) frameworks should be studied to achieve the best accuracy, printing time, and least materials consumed. This study aimed to find the best build angle and support structures’ diameter of the 3D printed (RPD) framework. Sixty (RPD) frameworks (10 in each group) were manufactured by digital light processing (DLP) 3D printing technology at three build angles (110-D, 135-D, and 150-D) and two support structures diameters (thick, L, and thin, S). Six groups were named according to their printing setting as (110-DS, 135-DS, 150-DS, 110-DL, 135-DL, and 150-DL). Frameworks were 3D scanned and compared to the original cast surface using 3D metrology software (Geomagic Control X; 3D Systems, Rock Hill, SC). Both printing time and material consumption were also recorded. Data were tested for the significant difference by one-way analysis of variance (ANOVA) test at (α = 0.05). The correlations between outcome parameters were also calculated. The 110-DL group showed the least accuracy. Significantly, the printing time of the 150-D groups had the lowest time. Material consumption of group 110-DS presented the lowest significantly statistical value. Printing time had a linear correlation with both accuracy and material consumption. Within the study limitations, the 150-degree build angle and thin diameter support structures showed optimal accuracy and time-saving regardless of material consumption.

Strength of Polyether Ether Ketone Composite as a Major Connector Material for Removable Partial Dentures

PEEK composite was tested mechanically as a maxillary removable partial denture (RPD) framework material instead of cast cobalt chromium alloy. Methods: Partial edentulous upper jaw cast was scanned using structured-light 3D scanner, palatal strap (PS) designs for RPD were designed by a designing dental laboratory software. CAD/CAM machine fabricated PSs patterns using their designs’ STL software files. PSs were made from poly-ether-ether ketone (PEEK) reinforced by ceramic fillers using thermal injection press technique and Co-Cr alloy using centrifugal casting, each material group was subdivided into two subgroups according to storage conditions (stored and non-stored subgroups), storage took place in deionized water for about 180 days at 37.5 ± 2 o C. All specimens were subjected to fracture resistance test using universal testing machine then maximum compression load (MCL) result values were subjected to statistical analysis. PEEK composite specimens were scanned by field emission microscope (FEM) and energy dispersive spectroscopy. Storage water of PEEK composite was analyzed using atomic absorption spectroscopy (AAS). Results: In either stored or non-stored subgroups of PEEK composite straps they showed significant lower mean MCL values than corresponding alloy subgroups (p=0.0001). FEM scanning showed fillers agglomerations in non-stored PEEK composite and their nearly absence from stored PEEK composite specimens. AAS detected Al element in PEEK composite storage water. Conclusion: Mechanically thermally injected ceramic reinforced PEEK composite could not replace cast Co-Cr alloy as PSs material for maxillary RPD. Biocompatibility concerns raised in this study due to suspected Al leaching and ceramic fillers dissolution from PEEK composite matrix.

Comparative clinical evaluation of removable partial denture frameworks fabricated traditionally or with selective laser melting: A randomized controlled trial

Statement of problemThe clinical efficacy of selective laser melting (SLM) for fabricating removable partial dentures (RPDs) is not well established. PurposeThe purpose of this clinical study was to compare the performance of SLM-fabricated frameworks with that of those fabricated via traditional lost wax casting. Material and methodsA double-blind, randomized, crossover design was used to compare cobalt chromium partial denture frameworks (n=29) fabricated by using SLM or traditional methods. The time taken for adjustments and the clinical fit and stability of the adjusted frameworks were appraised. The accuracy of the frameworks was assessed by measuring the space between the occlusal rest seat and the corresponding rest seat. Statistical comparisons between the 2 frameworks were carried out by using a linear mixed-effect model for repeated measurements (α=.05). ResultsFrameworks fabricated by using both SLM and traditional techniques had an acceptable fit based on subjective clinical evaluation. The overall mean ±standard deviation space between the occlusal rest and rest seat for SLM frameworks (273.7 ±44.5 μm) was comparable with that of traditional frameworks (242.2 ±44.5 μm). The clinical fit adjustment time, 7.76 ±6.43 minutes for SLM and 5.49 ±6.39 minutes for traditionally fabricated frameworks, was statistically similar (P=.067). ConclusionsDentures fabricated via SLM and traditional techniques had comparable accuracy of fit and clinical fitting time.

Mechanical and surface properties of Co–Cr alloy produced by additive manufacturing for removable partial denture frameworks

Statement of problemConventional analog methods have been replaced with digital methods for removable partial denture (RPD) frameworks. However, limited information is available regarding the build direction of RPD frameworks and its effect on properties. PurposeThe purpose of this in vitro study was to evaluate the mechanical and surface properties of the cobalt chromium (Co–Cr) alloy produced at different build angles by the laser powder bed fusion additive manufacturing (AM) technology used for RPD framework fabrication. Material and methodsPlate-shaped Co–Cr specimens (n=6) were produced by the AM technology and divided into 3 groups depending on the build angle (0, 45, or 90 degrees). The elastic modulus and fracture properties were evaluated by flexural testing. Additionally, 15 disks were printed by using the same parameters of the plates (n=5) to analyze the surface hardness with microhardness testing, and surface properties were determined by surface free energy by using the contact angle and surface roughness measured by using a profilometer. Twelve Co–Cr cylindrical specimens were produced by using the same parameters (n=4), and their microstructure was examined by using an optical microscope. One-way ANOVA was used to evaluate the overall effects of the interaction between groups, and the Tukey test was applied when the interaction was statistically significant (α=.05). ResultsThe flexural strength showed a statistically significant difference (P<.05), with the peak value exhibited by the 0-degree group. A statistical difference was also observed between the angulation and modulus of elasticity; however, the highest value was exhibited by the 45-degree group. For the fracture topography, all groups observed a dimple-like fracture, although the 45-degree group showed wider cleavage planes of fractures than other angulations. For microhardness, the 0- and 45-degree groups exhibited a statistical difference in relation to the 90-degree group (P<.05). For surface properties, no statistically significant difference (P>.05) was found in any of the evaluated parameters. Dependence on the build angles was evidenced by the molten pool boundaries during observation of the microstructure. ConclusionsThe build angle influenced the flexural strength and microhardness of the Co–Cr alloy produced by AM; however, it does not affect surface free energy and surface roughness.

Acurácia da moldagem digital em prótese parcial removível – revisão sistemática

Objective: The objective is to verify the accuracy of digital impression in removable partial dentures through a systematic literature review. Methodology: Search for articles took place in the BVS, PubMed, Cochrane Library and Science Direct, published in Portuguese and English, between 2016 and 2021. The search strategy used was ((“digital impression” and “ partially edentulous” OR “removable partial denture” ) OR (“removable partial denture frameworks”) OR (“CAD-CAM” AND “ACCURACY”)). The inclusion criteria in this review were studies with research articles in Vivo, in Vitro or in Silico, systematic review on digital impression in removable partial dentures. Exclusion criteria were studies on the digital flow in the construction of the structure in PPR, research on accuracy of digital impression in total dentures, implants and fixed dentures, narrative reviews of literature, clinical case, opinion articles. The complete data of the selected texts were extracted by the reviewers. Techniques were presented regarding the steps of making. Results: Three articles were selected for review. The digital impression with intraoral scanners showed higher veracity but lower accuracy compared to conventional impression. The all-digital method produced structures with a significantly better clinical fit than the conventional method and the analog-digital method. Conclusion: The present review observed that the results are conflicting regarding the precision and adjustments of the structure to the dental arch. The results found do not respond to the proposed objective and the guiding question, due to the great variability of analyzes in the selected articles, the supporting evidence is limited.

Influence of Digital Technologies and Framework Design on the Load to Fracture of Co-Cr Posterior Fixed Partial Denture Frameworks.

To compare the load to fracture of cobalt-chromium (Co-Cr) 3-unit posterior fixed partial denture (FPD) frameworks manufactured by conventional and digital techniques and to evaluate the influence of the framework design on the fracture load. Eighty 3-unit Co-Cr posterior FPD frameworks were fabricated with two designs: intermediate pontic (n = 40) and cantilever (n = 40). Each design was randomly divided into four groups (n = 10): casting, direct metal laser sintering, soft metal milling, and hard metal milling. After thermal cycling, all specimens were subjected to a 3-point bending test until fracture. Data were statistically analyzed using one-way ANOVA, Welch and Brown-Forsythe test, Ryan-Einot-Gabriel-Welsch F and Tamhane T2 post hoc test, Student's t test, and Weibull statistics (α = 0.05). Significant differences (p < 0.001; F = 39.59) were found among intermediate pontic frameworks (except between laser sintering and hard metal milling), and cantilevered frameworks (F = 36.75) (except between laser sintering and hard metal milling, and casting and soft metal milling). The cantilever groups showed load to fracture values significantly lower than those of the intermediate pontic (p < 0.001; F = 28.29). The Weibull statistics corroborated the results. Hard metal milling and laser sintered frameworks exhibited the highest load to fracture values. However, all tested frameworks demonstrated clinically acceptable load to fracture values. The framework design directly affected the fracture load, with drastically lower values in cantilevered frameworks.

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

Statement of problemThe 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. PurposeThe 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 methodsTi-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). ResultsUsing 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. ConclusionsTi-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.

Retention Assessment of High Performance Poly-etheretherketone Removable Partial Denture Frameworks Constructed by Various Techniques (in vitro Study).

Statement of the Problem: Poly-etheretherketone is a novel material used in the construction of the removable partial dentures frameworks instead of the metal frameworks. This material can be fabricated by various techniques. Most common methods are the injection molding or Computer Aided Design/Computer Aiding Manufacturing (CAD/CAM) milling techniques. The fabrication technique may affect the adaptation of the frameworks by influencing the retention.Purpose: To assess the effect of the processing techniques of high performance Poly-etheretherketone either by injection molding (pressing) or CAD/CAM milling techniques on removable partial denture frameworks retention for rehabilitation of upper class I Kennedy classification.Materials and Method: This in vitro study was performed on one epoxy resin model representing the partially edentulous maxillary arch with natural teeth extending from first premolar to first premolar. First premolars and canines were reduced to receive porcelain fused to metal crowns with 0.50mm mesio-buccal retentive undercuts, distal guiding planes and mesial occlusal rest seat on first premolars and cingulum rest seat on canines. Considering the construction technique of frameworks, twenty samples were divided into two groups. In the group I, ten frameworks were fabricated by injection molding, and in the group II, ten frameworks were fabricated by CAD/CAM. The removal and insertion was carried out at 120, 720 and 1440 cycles for both groups, respectively. The retention values were measured by using Universal Testing Machine before cycling and after each interval.Results: Independent t-test showed significant difference on retention at different simulation cycles between groups. Group II exhibited significantly less retention than group I (p< 0.001), while comparing the retention at different cycles within each group by paired sample t-test exhibited significant decrease of retention till the end of the cycling (p< 0.001).Conclusion: From the retention point of view, high performance poly-etheretherketone frameworks fabricated by injection molding technique provided a promising method over CAD/CAM technique milling method.

Strength and flexibility of lithium disilicate bonded to polyetherketoneketone

Statement of problemPolyetherketoneketone (PEKK) is a high-performance polymer gaining popularity in dentistry for the fabrication of crowns, fixed partial dentures, removable partial denture frameworks, and frameworks for implant-supported fixed complete dentures. Despite a lack of performance data, lithium disilicate crowns have been bonded to retentive elements in PEKK frameworks. PurposeThe purpose of this in vitro study was to compare the bond strengths and flexibility of lithium disilicate to PEKK or zirconia. Material and methodsForty-five PEKK, 15 zirconia, and 60 lithium disilicate beam-shaped specimens (12.5×2×2 mm) were fabricated. The ends of the PEKK beams were subjected to 3 different surface treatments before the application and light polymerization of a primer: 50-μm aluminum oxide airborne-particle abrasion, nonthermal air plasma, and argon-oxygen plasma. The zirconia specimen bonding surfaces were prepared with 50-μm aluminum oxide airborne-particle abrasion and the application of primer. Lithium disilicate specimens were etched with 4.5% hydrofluoric acid, and primer was applied. The lithium disilicate specimens were luted with an adhesive resin cement to the PEKK and zirconia specimens by using light-activated and chemically activated polymerization. Fifteen monolithic specimens of PEKK, lithium disilicate, and zirconia (25×2×2 mm) were also fabricated. All specimens were incubated overnight in 100% humidity before testing. Bonded and monolithic specimens were loaded in a universal testing machine, and 4-point bend tests were conducted until failure (n=15). The flexural modulus and strength were calculated and statistically analyzed with 1-way analysis of variance and Student-Newman-Keuls post hoc tests (α=.05). ResultsAll bonded specimens failed at the adhesive interface. The zirconia-lithium disilicate bond strength was approximately twice that of the strongest group of PEKK (airborne-particle abrasion group) bonded to lithium disilicate (42 ±12 MPa and 24 ±13 MPa, respectively) and was approximately 9 times more rigid (71 ±19 GPa and 8 ±2 GPa, respectively). Monolithic PEKK fractured at 238 ±22 MPa, monolithic zirconia at 771 ±128 MPa, and monolithic lithium disilicate at 173 ±26 MPa. Monolithic PEKK was approximately 30 times more flexible than monolithic zirconia (6 ±1 GPa and 178 ±16 GPa, respectively). All values were statistically significantly different (P<.05), except for the bond strength between lithium disilicate and PEKK treated with airborne-particle abrasion and nonthermal air plasma and the flexural moduli of PEKK to lithium disilicate. ConclusionsBond strength between PEKK and lithium disilicate was significantly weaker than that between zirconia and lithium disilicate. Monolithic PEKK was significantly more flexible than monolithic zirconia.

Effect of dynamic loading on fracture resistance of gradient zirconia fixed partial denture frameworks

Statement of problemThe new strength-gradient zirconia composed of 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 5-mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) has been claimed to have superior mechanical properties. However, data on the fracture resistance of 3-unit gradient 5Y-TZP and 3Y-TZP fixed partial denture frameworks are lacking. PurposeThe purpose of this in vitro study was to evaluate the effect of dynamic loading on the fracture resistance of gradient zirconia fixed partial denture frameworks. Material and methodsTwo standardized stainless-steel master dies were designed to simulate a mandibular left second premolar and second molar prepared to receive zirconia frameworks. The frameworks were designed with a 0.6-mm uniform wall thickness. The mesiodistal width of the connectors was 3 ±0.02 mm, and the occlusogingival height was 3 ±0.02 mm. Forty zirconia frameworks were fabricated and divided into 2 groups according to the tested materials (n=20): 3Y-TZP and gradient 5Y-TZP and 3Y-TZP. The frameworks were cemented onto their corresponding dies with a conventional glass ionomer cement. Half of the cemented frameworks in each group underwent 600 000 cycles of dynamic loading in a mastication simulator (n=10). The other half was fractured without dynamic loading (n=10). Fracture resistance measurements (N) for each framework were recorded by using a universal testing machine at a crosshead speed of 1 mm/min. A fractured framework from each group was examined by using a scanning electron microscope (SEM) at ×100 magnification. The data obtained were statistically analyzed by using 2-way ANOVA, the pairwise Tukey honestly significant difference (HSD), and simple main effect tests to detect the difference between group mean values (α=.05). ResultsThe mean ±standard deviation of fracture load value before dynamic loading was 1919 ±193 N for the 3Y-TZP group and 908 ±99 N for the gradient 5Y-TZP and 3Y-TZP group. In addition, the mean fracture load value after dynamic loading was 1418 ±163 N for the 3Y-TZP group and 716 ±85 N for the gradient 5Y-TZP and 3Y-TZP group. The interaction between the effects of the zirconia material and dynamic loading on the fracture resistance was statistically significant (P=.002). The 3Y-TZP group had a statistically significant, higher fracture load mean value the gradient 5Y-TZP and 3Y-TZP group before and after dynamic loading (P<.001). ConclusionsThe fracture resistance of 3Y-TZP frameworks was significantly higher than that of gradient 5Y-TZP and 3Y-TZP frameworks before and after dynamic loading. Dynamic loading significantly reduced the fracture resistance of 3Y-TZP and gradient 5Y-TZP and 3Y-TZP frameworks.

The Digitalisation in Cobalt-Chromium Framework Fabrication. Surface Roughness Analysis: A Pilot Study

Selective laser melting (SLM) is a new technique in fabricating cobalt-chromium denture framework. However, the surface properties of cobalt-chromium denture framework fabricated using the aforementioned technique have not been widely investigated. The aim of this paper was to investigate the surface roughness of cobalt-chromium alloy in removable partial denture fabricated with SLM technique. Cobalt-chromium denture frameworks were fabricated with two techniques (n = 10); the conventional lost-wax casting (conventional group) and SLM techniques (SLM group). Specimens from the conventional group were subjected to the standard cobalt-chromium denture polishing protocols. No treatment was employed for specimens from the SLM group. All specimens were subjected to surface roughness measurement on polished and fitting surfaces using non-contact optical three-dimensional metrology and surface roughness analysis machine (Infinite Focus Real 3D Alicona). Statistical analysis showed no significant difference in surface roughness between the specimens from conventional and SLM groups (p &gt; 0.05). There was no statistically significant difference in surface roughness between the polished and fitting surfaces of SLM specimens (p &gt; 0.05). Surface roughness quality of the cobalt-chromium denture framework fabricated with the SLM technique is comparable to that fabricated with the conventional lost-wax casting technique. The surface roughness of SLM fabricated cobalt-chromium denture frameworks carries the same surface roughness quality between the polished and fitting surfaces.

Evaluation of the Fit Accuracy of Removable Partial Denture Frameworks Fabricated Using Three Different Techniques: An In Vitro Study

Evaluation of the Fit Accuracy of Removable Partial Denture Frameworks Fabricated Using Three Different Techniques: An In Vitro Study

Evaluation of the Fit Accuracy of Removable Partial Denture Frameworks Fabricated Using Three Different Techniques: An In Vitro Study

Evaluation of the Fit Accuracy of Removable Partial Denture Frameworks Fabricated Using Three Different Techniques: An In Vitro Study

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.

Fractographic analysis of two fractured removable partial denture metal frameworks

This study aimed to analyze two cases of fracture of the metal framework of Co-Cr-based removable partial dentures, using fractography to identify a true cause of these failures. The first case concerned the coupling between the smaller and larger connectors; the patient brought his fractured removable partial dentures to the clinic. The second case referred to a larger connector; structure of the patient fractured during the test. For failure analysis, images of two fractured metal frameworks were taken by scanning electron microscopy to identify the origin of the fracture and to determine the mechanisms involved in the process. Subsequently, energy dispersive X-ray spectroscopy was used for elemental chemical mapping of the fracture interface. The fractography indicated material fatigue as a possible cause in the first case and an error in the casting process in the second. The energy dispersive X-ray spectroscopy test, performed in the specimen of case B, showed predominant and characteristic peaks for Co and Cr, with a higher concentration of chromium. The fractures identified were associated with inclusions and with material fatigue and a number important characteristics were evidenced by the technique.

ПЕРСПЕКТИВЫ ИЗГОТОВЛЕНИЯ КАРКАСОВ МЕТАЛЛОКЕРАМИЧЕСКИХ КОНСТРУКЦИЙ ЗУБНЫХ ПРОТЕЗОВ МЕТОДОМ СЕЛЕКТИВНОГО ЛАЗЕРНОГО СПЕКАНИЯ

The article presents the results of evaluating the prototyping of metal-ceramic structures made by casting and selective laser sintering. To achieve this goal, 27 patients with fabricated metal-ceramic crowns and bridgeworks were examined. Two study groups were created. The first group included 14 patients for whom dental prosthesis frameworks were made by casting. The second group consisted of 13 people, for whom the frames of dentures were made by the method of selective laser sintering. The analysis of clinical effectiveness was carried out according to the following criteria: 1- precision of the felling of prosthesis frame to solid tissues of abutment teeth; 2- the condition of the marginal periodontium; 3- the integrity of the ceramic cladding. The results of the study showed that the precision to solid tooth tissues of metal-ceramic dental prostheses made by laser selective sintering is higher than of frames made by casting. In accordance to the second criteria the best results were also shown by the participants of the second group. No chipping of the ceramic veneer from the metal-ceramic denture frameworks made by laser selective sintering was found. Thus, dentures which frameworks are made by the method of selective laser sintering are characterized by a higher objective assessment of their precision to the solid tissues of the abutment teeth. Lesions of the marginal periodontium both inflammatory and dystrophic were less in the participants of the second group. The frequency of defects in the coating of metal-ceramic dentures was significantly lower in the case of fabrication frameworks by laser selective sintering.

Process parameter optimization for removable partial denture frameworks manufactured by selective laser melting

Statement of problemSelective laser melting (SLM), an additive manufacturing technology, is expected to replace the traditional lost-wax casting process used in producing removable partial denture (RPD) frameworks. However, studies comparing the accuracy of RPD frameworks and the effects of process parameters are lacking. PurposeThe purpose of this in vitro study was to optimize SLM process parameters and use a quantitative analysis method to improve the accuracy of 3D-printed RPD frameworks. Material and methodsThe orientation and support structure of Kennedy Class II RPDs were designed in various ways by using 2 different software programs, CAMbridge and Magics. The optimum melt-pool parameters, including laser power, scan speed, hatch distance, and layer thickness, were determined empirically before manufacturing 12 RPD frameworks with 4 different process designs by using SLM (n=3). The accuracy of the RPD frameworks was determined by 3D scanning and comparing the 3D scan data with the original standard tessellation language (STL) RPD design with the best-fit algorithm of the Geomagic software program. ResultsOptimum melt-pool parameters were found with the function of density, surface roughness, and productivity (P=180 W, v=1200 mm/s, h=60 μm, t=30 μm). RPD frameworks fabricated by the optimized process parameters (167 ±105 μm) showed significantly better (P<.05) mean ±standard deviation accuracy than the 3 other groups of RPD frameworks manufactured by using the nonoptimized process parameters (180 ±121 μm to 222 ±136 μm). The best accuracy was found with the transverse orientation and interconnected support structure. ConclusionsWith the optimized design of process parameters, clinically acceptable RPD frameworks were produced. The accuracy of RPD frameworks fabricated by using SLM varied according to the design of the process parameters, indicating that SLM technology can replace the traditional lost-wax casting process.