Passive fit and time efficiency for prefabricated versus conventionally constructed cobalt chromium CAD\CAM 3-unit implant supported frameworks in free end saddle models: a pilot invitro study.

BACKGROUND: The passive fit of 3-unit implant supported prefabricated metal screw-retained prosthesis before implant placement might be difficult. Hence, we aim to evaluate the passive fit and time efficiency of CAD/CAM 3-unit implant supported fixed prostheses that were constructed based on virtual versus those based on actual implant positions in Kennedy Class I models. METHODS: A sample of 5 Kennedy class I models with thin wiry ridges were restored by 20 frameworks bilaterally, 10 based on actual (group A) and 10 based on virtual (group V) implant positions. The models were imaged using cone beam computed tomography and scanned using an intraoral scanner. The STL (Standard Tessellation Language files) and the DICOM (Digital Imaging and Communications in Medicine) files were registered on a 3D planning software. A CAD/CAM surgical guide was planned, resin printed and used for installing 6 implants bilaterally. In group V, the framework was designed based on the virtual scan bodies and virtual multi-unit abutments, while in group A intra-oral scanning of the model after attaching the scan bodies was necessary. Frameworks of both groups were milled and tested for passive fit using 8 clinical tests. McNemar and Wilcoxon signed rank tests were used to study the effect of the group on passive fit and time efficiency, respectively. The significance level was set at P ≤ 0.05. RESULTS: No statistically significant difference was found between group V and group A frameworks regarding passive fit (p-value = 1, OR = 0.5) and time efficiency (P = 0.179, Effect size = 0.948). CONCLUSION: Within the limitations of this study, it can be concluded that in free end saddle cases, prefabricated CAD\CAM 3-unit implant-supported cobalt chromium screw retained prostheses can achieve an adequate passive fit. However, their fit might be negatively affected in thin ridges and they might require some adjustments.

Marginal bone loss and soft tissue health around two-implant mandibular overdenture retained with milled versus selective laser melted cobalt chromium bar: a randomized clinical trial.

BACKGROUND: To assess marginal bone loss and soft tissue health around two-implant mandibular overdenture retained with milled versus selective laser-melted cobalt chromium (Co-Cr) bars. METHOD: This research was set to be a parallel, triple-blinded, randomised controlled trial. Twenty completely edentulous patients received new conventional complete dentures according to conventional techniques. Two implants were placed at mandibular canine areas bilaterally, and patients were randomly allocated into two equal groups: the milled Co-Cr bar group and the selective laser melted (SLM) Co-Cr bar group. Marginal bone loss (MBL), modified plaque index (mPI), modified gingival index (mGI), and probing depth (PD) were evaluated at 0-month (baseline), 6-month, and 12-month follow-up visits. Repeated measures ANOVA test and Bonferroni's post-hoc test were used for parametric data as PD, while for non-parametric data as MBL, mGI, and mPI, Mann-Whitney U test and Friedman's test were used. A P-value ≤ 0.05 was set as the statistical level of significance. The study protocol was approved by the Faculty Research Ethics Committee at Minia University (636 4/10/2022). Registration for the clinical trial was made retrospectively on clinicaltrials.gov with ID NCT06401200 at 04/30/2024. RESULTS: The follow-up period (one year) was completed without a dropout. Regarding MBL, no statistically significant difference was found between the two groups throughout the study. However, the milled group showed significantly increased MBL from 0- to 6-month follow up period. In both groups, mPI increased significantly from 0- to 6-months post-loading. On the other hand, no statistically significant difference between the two groups was found regarding mPI and mGI throughout the study follow-up periods. The PD was significantly lower in the milled compared to the SLM group at the 6- and 12-month follow up period. CONCLUSION: Two-implant mandibular overdenture retained with milled or SLM Co-Cr bar can provide an acceptable treatment option for completely edentulous patients regarding marginal bone loss and soft tissue outcomes.

Shear bond strength of resin cement to a CAD/CAM millable alloy subjected to various surface treatments.

Resin cements are widely used to cement dental restorations; however, limited studies are available on the bond strength of these cements to computer-aided design/computer-aided manufacturing (CAD/CAM) base metal alloys. This study compared the shear bond strength between a self-etching resin cement (Panavia F 2.0) and a millable cobalt-chromium alloy (Ceramill Sintron) following various surface treatments. A total of 40 cylindrical alloy cores (6 mm in diameter × 8 mm in height) were milled and assigned to 1 of 5 groups for different surface treatments (n = 8): control (no surface treatment); sandblasting; metal primer; sandblasting + metal primer; or acid etching. Resin cement was then used to bond cylindrical composite resin specimens to the pretreated core surfaces. The specimens underwent a 1500-cycle thermocycling procedure and shear bond strength testing. The data were analyzed using 1-way analysis of variance, and P < 0.05 was considered statistically significant. The mean (SD) shear bond strength values in the different surface treatment groups were significantly different (P < 0.05): sandblasting, 16.59 (7.10) MPa; acid etching, 15.63 (2.94) MPa; sandblasting + metal primer, 13.28 (1.27) MPa; metal primer, 8.90 (2.08) MPa; and control, 8.86 (3.57) MPa. The mean differences in shear bond strength values were significant between the sandblasting and control groups (P = 0.003) and between the acid-etching and metal primer groups (P = 0.013). Surface roughening procedures--either sandblasting or acid etching of the alloy surface--improved the shear bond strength of resin cement to milled alloy surfaces. The use of metal primer between the alloy surface and resin cement did not significantly increase the bond strength.

Surface topography changes and wear resistance of different non-metallic telescopic crown attachment materials in implant retained overdenture (prospective comparative in vitro study).

BACKGROUND: The purpose of this study was to evaluate the effect of using different types of metallic and non-metallic telescopic crown attachment materials on wear resistance and surface tomography changes in implant-retained mandibular overdentures. MATERIALS AND METHODS: Completely edentulous mandibular epoxy models were fabricated, in which two implants were placed in the canine region and retained to the implants with three different material combinations used for the construction of telescopic attachments. Thirty-three identical mandibular overdentures were fabricated using the conventional standardized technique. The study groups were divided into three categories according to the material used for the construction of the secondary copings. The primary copings in all the study groups were constructed of PEEK, while the secondary coping in group I was PEEK, group II was ZrO2 and CoCr for group III. Primary copings were cemented on a ready-made abutment. Secondary copings were placed over the primary copings in the desired path of insertion, then picked up into the intaglio surface of the overdentures. A cyclic loading machine was used to apply repeated insertion-removal cycles simulating nearly 10 years of clinical use. Stereomicroscope with a built-in camera was used to monitor the reduction in width of the primary copings to evaluate the wear resistance of each material combination. RESULTS: There was highly statistically significant difference between the study groups after the application of 1.000, 5.000 and 10.000 cycles. The highest level of wear resistance was recorded for the PEEK/PEEK combination, whereas PEEK/ZrO2 and PEEK/CoCr showed no significant differences. CONCLUSIONS: Implant retained overdenture with PEEK-PEEK telescopic crown attachment is associated with the highest wear resistance among all the study groups. PEEK-PEEK combination may be the treatment of choice for fabrication of telescopic attachment in implant retained overdenture as it provides better resistance to wear. It offers the advantages for geriatric patients as it decreases the possibility for repeated repair and replacement of attachment, increase long-term patient satisfaction and shelf life of prosthesis.

Methods of Processing Dental Chromium-Cobalt Alloys for Production of Metal Frameworks Faced with Ceramics to Obtain the Best Mechanical Properties.

BACKGROUND Modern prosthetic technologies make it possible to fabricate prosthetic restorations without material loss and to make prosthetic restorations with complex geometric shapes in a relatively simple way. One such technology is selective laser melting (SLM), or additive manufacturing of metal materials, better known as 3D printing from metal or selective laser melting, but currently the most commonly used method is casting. The present study investigated use of dental chromium-cobalt alloys for prosthetic bridges and compared methods of processing dental chromium-cobalt alloys to obtain the best mechanical properties. MATERIAL AND METHODS We used dental chromium-cobalt alloy (SCHEFTNER GMBH) for laser melting StarbondCoSEeasy Powder with grain size of 10-30 µm and StarbondCoS alloy casting, made in accordance with the European standard EN ISO 22674. SLM-made specimens and induction melted alloy castings were prepared for the study. A centrifugal casting system with induction current melting of the metal alloy was used to produce the samples. The melting and casting process is automatic and limits changes in chemical composition. RESULTS The results show that none of the samples changed their chemical composition, while the samples made by SLM had better mechanical properties. CONCLUSIONS The SLM technique makes it possible to produce restorations faster and cheaper without any loss of quality compared to restorations made with the casting technique. Casting technology reduces mechanical properties, but still provides good mechanical properties.

Polyethylene wear and cup migration of cemented total hip arthroplasty with femoral heads made of oxidized zirconium, steel, or cobalt chromium: a 10-year secondary analysis from a randomized trial using radiostereometry.

BACKGROUND AND PURPOSE: We aimed to evaluate polyethylene (PE) wear, cup migration, and clinical outcome over 10 years in total hip arthroplasties (THA) using different articulations. METHODS:  This is a secondary analysis of 150 patients randomized into 5 groups, using different articulations: Charnley/Charnley Ogee for steel and conventional polyethylene (CPE), or Spectron EF/Reflection with either CPE or highly cross linked polyethylene (XLPE) cups, paired with heads made of either cobalt-chromium (CoCr) or oxidized zirconium (OxZr). All cups were cemented. Patients underwent repeated radiostereometric analysis (RSA) measurements for up to 10 years to assess wear and migration. Clinical outcome was assessed using Harris Hip Score (HHS). RESULTS:  After 10 years, the XLPE cups demonstrated low wear rates: 0.08 mm (95% confidence interval [CI] -0.11 to 0.26 mm) with CoCr heads and 0.06 mm (CI -0.14 to 0.26 mm) with OxZr heads, with a mean difference of 0.01 mm (CI -0.26 to 0.29 mm). In contrast, CPE cups exhibited significantly more wear: 1.35 mm (CI 1.16 to 1.55 mm) with CoCr heads and 1.68 mm (CI 1.44 to 1.92 mm) with OxZr heads, with a mean difference of 0.33 mm (CI 0.02 to 0.64 mm). The Charnley/Ogee group (CPE) showed PE wear of 0.34 mm (CI 0.12 to 0.56 mm). The CPE groups with OxZr and CoCr heads had 0.67 mm (CI 0.38 to 0.96 mm) and 0.35 mm (CI 0.09 to 0.61 mm) greater proximal migration respectively than the corresponding XLPE groups. HHS was similar across all groups. CONCLUSION:  We found no significant advantage of OxZr over CoCr heads in reducing wear or migration. XLPE demonstrated a major reduction in wear as well as a reduction in cup migration compared with CPE. Charnley performed better than the other CPE cups in terms of PE wear and cup migration. No differences in clinical outcome were found.

Preliminary study of microbiologically influenced corrosion by Pseudomonas aeruginosa on high Chromium white iron.

Microbiologically Influenced Corrosion (MIC) poses a significant challenge to various industries, leading to substantial economic losses and potential safety hazards. Despite extensive research on the MIC resistance of various materials, there is a lack of studies focusing on High Chromium White Iron (HCWI) alloys, which are widely used in wear-resistant applications. This study addresses this knowledge gap by providing a comprehensive investigation of the MIC resistance of three HCWI alloys with varying chromium contents (22 wt%, 30.7 wt%, and 21 wt%) in the presence of Pseudomonas aeruginosa (P. Aeruginosa), a common bacterial species associated with MIC. The alloys were exposed to an artificial seawater medium inoculated with P.Aeruginosa for 14 days, and their corrosion behaviour was evaluated using electrochemical techniques, surface analysis, and microscopy. Electrochemical Impedance Spectroscopy (EIS) results revealed that the alloy with the highest chromium content (A2, 30.7 wt% Cr) exhibited superior MIC resistance compared to the other alloys (A1, 22 wt% Cr and M1, 21 wt% Cr). The enhanced performance of alloy A2 was attributed to the formation of a more stable and protective passive film, as well as the development of a more compact and less permeable biofilm. The EIS data, interpreted using equivalent circuit models, showed that alloy A2 had the highest charge transfer resistance and the lowest biofilm capacitance, indicating a more effective barrier against corrosive species. Bode plots further confirmed the superior corrosion resistance of alloy A2, with higher impedance values and phase angles at low frequencies compared to alloys A1 and M1. Scanning Electron Microscopy (SEM) and optical microscopy analyses corroborated these findings, showing that alloy A2 had the lowest pit density and size after 14 days of exposure. The insights gained from this study highlight the critical role of chromium content in the MIC resistance of HCWI alloys and have significant implications for the design and selection of materials for applications prone to microbial corrosion.

Comparison of misfit and roughness of CAD-CAM ZrO, selective laser sintered CoCr and preformed Ti implant abutment crowns.

BACKGROUND: Marginal misfit and surface roughness of customized implant abutments is critical for restorative success. However, little is known about the comparison of misfit and surface roughness of CAD-CAM Zirconium oxide (ZrO), selective laser melting (SLM) Cobalt Chrome (CoCr) and preformed abutments. The aim of the study is to investigate the relation of misfit and micro-roughness of selective laser melting (SLM), preformed and CAD-CAM implant abutments. METHODS: Thirty internal connection, endosseous dental implants (Ø 4.0 mm x 10 mm, Dentium) were mounted in Polymethyl methacrylate vertically. Ten preformed Titanium alloy (Ti) abutments with 1 mm soft tissue height and Ø 4.5 mm were included as controls. Ten each of Y-TZP and SLM-CoCr, abutment/crowns were fabricated using CAD-CAM milling (CAD-CAM-ZrO) and SLM techniques. Surface micro-roughness (Ra) of the fabricated implant abutment/crown was evaluated with a 3D optical non-contact microscope. All implant restorations were torqued to implants (30 Ncm) using a Tohnichi BTGE digital torque gauge and were analyzed with Bruker micro-CT (Skyscan 1173) to detect micro-gaps at pre-selected points at implant abutment interface. The Ra and misfit data were compared using ANOVA, Tukey-Kramer, Kruskal-Wallis test and Pearson correlation (p < 0.05). RESULTS: Mean Ra among SLM CoCr abutments [0.88 (0.09) µm] were lower than CAD-CAM-ZrO and higher than preformed Ti abutments. Horizontal misfit among SLM-CoCr [45.43 (9.41) µm] and preformed Ti [36.87 (13.23) µm] abutments was not statistically different (p > 0.05). Misfit was significantly higher in Y-TZP samples compared to SLM-CoCr (p = 0.031) and preformed Ti abutments (p = 0.01). Preformed Ti abutments showed significantly lower misfit compared to SLM-CoCr abutments (p = 0.01). A positive linear correlation was observed between the surface roughness (Ra) and vertical misfit (r = 0.61, p < 0.05). CONCLUSION: SLM CoCr abutments showed rough surface compared to preformed Ti abutments, while horizontal misfit was comparable among SLM-CoCr and preformed abutments. Misfit was significantly greater in Y-TZP abutments, compared to SLM and preformed abutments. SLM abutment fabrication technique needs further improvement to provide better fit and surface topography.

Influence of various fabrication techniques and porcelain firing on the accuracy of metal-ceramic crowns.

BACKGROUND: The fit of a metal-ceramic restoration is essential to its long-term durability. Regarding marginal and internal fit, there is not enough information about the technologies used in the production of metal-ceramic restorations. The aim of this in vitro study is to compare, both before and after porcelain firing, the marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic restorations manufactured using casting, additive or subtractive computer-aided design, and computer-aided manufacturing techniques (CAD/CAM). METHODS: CAD/CAM were used to create 50 prepared maxillary first molar-shaped Co-Cr die models, which were randomly divided into 5 groups (n = 10). Cobalt-chrome copings were produced by casting (C), hard metal milling (HM), soft metal milling (SM), selective laser melting (SLM), and selective laser sintering (SLS) techniques. Before and after porcelain firing, discrepancies of the copings were measured using the silicone replica technique. The data obtained by measurements with a stereomicroscope at x80 magnification were analyzed statistically in the SPSS program. The ROBUST three-way analysis of variance (ANOVA) method was used to compare the discrepancy values. RESULTS: There were statistically significant differences among fabrication methods (P < .001). The HM method showed the highest discrepancy (90.1 µm), and the C (63 µm) method showed the lowest discrepancy in terms of the die model- crown fit. The C, SLS, and SM methods (63 µm; 61.6 µm; 67.7 µm) were statistically similar (P > .001). The highest discrepancy was observed on the occlusal area (87.1 µm), and the lowest discrepancy was observed on the axial area (47.7 µm) of the coping. Porcelain firing had a decrease in the discrepancy values (P = .001). CONCLUSION: All CAD/CAM techniques are appropriate for clinical use; selective laser sintering and soft milling can be the more recommended methods for the compatibility of metal-porcelain restorations, as they have lower discrepancy values than the SLM and HM methods.

Effect of disinfectants on multispecies biofilm, the physical and mechanical properties of polymethyl methacrylate, and the corrosion of cobalt chromium alloy.

STATEMENT OF PROBLEM: The optimal disinfection protocol that controls adverse effects and promotes effective antimicrobial action on removable prostheses is unclear. PURPOSE: This in vitro study investigated the effect of disinfectant solutions on the biological, physical, mechanical, and chemical properties of removable prosthesis materials. MATERIAL AND METHODS: Specimens of polymethyl methacrylate (PMMA) and cobalt chromium (Co-Cr) alloy were immersed in distilled water (PMMA) or artificial saliva (Co-Cr) as the control and in 0.25% sodium hypochlorite (NaOCl0.25%), 0.5% chloramine T (CT0.5%), and 0.15% Triclosan (TR0.15%). The antibiofilm activity was evaluated by microbial load and cell metabolisms of the mixed biofilm. Physical (color change, sorption, solubility, and surface roughness), mechanical (hardness, flexural, and impact strength), and chemical (corrosion) properties were analyzed before and after simulating a 5-year immersion. Laser confocal microscopy, scanning electron microscopy (SEM), and dispersive energy spectroscopy (EDS) complemented the analyses. The data were analyzed by using the Mann-Whitney U test, Kruskal-Wallis with Dunn posttests, 1-way ANOVA, and repeated measures ANOVA (α=.05). RESULTS: All solutions were effective against bacteria, but only NaOCl0.25% eliminated Candida spp. TR0.15%, and CT0.5% increased cell metabolisms. For interaction (time and solution), there was a reduction in PMMA hardness in the control and TR0.15%. Color, sorption, solubility, and flexural strength did not change. CT0.5% and TR0.15% were similar for impact resistance. CT0.5% caused the lowest roughness. NaOCl0.25% showed the greatest corrosive potential. Dark spots were seen under SEM in Co-Cr stored with NaOCl0.25% and TR0.15%. EDS indicated different proportions of oxygen, cobalt, chromium, and molybdenum. CONCLUSIONS: NaOCl0.25% had the best antimicrobial action. CT0.5% and TR0.15% have potential. Hardness and roughness changes were clinically acceptable, and the other properties remained unchanged. All the solutions caused color changes. NaOCl0.25% was unsatisfactory for use with Co-Cr, CT0.5% was intermediate, and TR0.15% was suitable.

Effect of laser process parameters on the pores, surface roughness, and hardness of laser selective melting of dental cobalt-chrome alloys.

OBJECTIVES: To address the quality problems caused by high porosity in the preparation of dental cobalt-chrome alloy prosthetics based on selective laser melting (SLM) technology, we investigated the influence mechanism of different forming process parameters on the microstructure and properties of the materials. Moreover, the range of forming process parameters that can effectively reduce defects was precisely defined. METHODS: The effects of laser power, scanning speed, and scanning distance on the pore properties, surface roughness, and hardness of dental cobalt-chrome alloy were investigated by adjusting the printing parameters in the process of SLM. Through metallographic analysis, image analysis, and molten pool simulation, the pore formation mechanism was revealed, and the relationship between the porosity and energy density of SLM dental cobalt-chrome alloy was elucidated. RESULTS: When the linear energy density was higher than 0.18 J/mm, the porosity defect easily appeared at the bottom of the molten pool. When the laser energy density was lower than 0.13 J/mm, defects occurred in the gap of the molten pool due to insufficient melting of powder. In particular, when the linear energy density exceeded the threshold of 0.30 J/mm or was below 0.12 J/mm, the porosity increased significantly to more than 1%. In addition, we observed a negative correlation between free surface roughness and energy density and an inverse relationship between macroscopic hardness and porosity. CONCLUSIONS: On the basis of the conditions of raw materials and molding equipment used in this study, the key process parameters of SLM of molding parts with porosity lower than 1% were successfully determined. Specifically, these key parameters included the line energy density, which ranged from 0.13 J/mm to 0.30 J/mm, and the scan spacing should be strictly controlled below 90 µm.

Application of digital impression and model in removable partial dentures for Kennedy classâ andâ ¡dentition defects.

OBJECTIVES: This study aimed to evaluate the application of digital impression and resin model technology in removable partial dentures (RPD) for Kennedy classⅠandⅡdentition defects. METHODS: Patients with Kennedy classⅠorⅡdental defect were selected and grouped in accordance with the following denture production processes: digital impression/resin model/cast cobalt-chromium alloy framework group (group A), digital impression/resin model/laser printed titanium framework group (group B), alginate impression/plaster model/cast cobalt-chromium alloy framework group (group C), and alginate impression/plaster model/laser printed titanium framework group (group D), with 40 cases in each group. The final RPD was examined in place in the mouth, and the evaluation indicators included the retention force of clamp ring, the tightness of connector and base, and the accuracy of occlusion. The evaluation scores of each index were used for analysis on the Kruskal-Wallis rank-sum test. RESULTS: No statistically significant difference in the score of each index was found among the four groups in RPD. CONCLUSIONS: The cast cobalt-chromium alloy and laser-printed titanium framework RPD using digital impression and resin model can meet the clinical restoration requirements of patients with Kennedy classⅠandⅡdentition defects.

Longevity of acrylic and cobalt-chromium removable partial dentures-A ten-year retrospective survival analysis of 1246 denture-wearing patients.

OBJECTIVES: to assess the survival rates of removable partial dentures (RPDs) and identify factors impacting their longevity. METHODS: electronic health records were retrieved of patients aged ≥18 who received RPDs between 2010 - 2021 with a follow-up of ≥ three months. Data extracted included demographics, medical history, dental charting, periodontal screening and recording scores, prostheses details and related interventions, including new dentures/denture remakes, and maintenance. Multivariate Mixed-Effect Cox regression was performed to identify potential RPD survival risk factors. Reduced model selection was reached using a backward step-down by comparing the performance of these multivariable models using the ANOVA test. RESULTS: 1893 RPDs from 1246 patients were included, with a median follow-up of 21.8 months (range from 3 to 131.3 months). Three hundred and twelve patients received a maxillary RPD, 460 received a mandibular RPD, and the remaining 474 patients received both maxillary and mandibular RPDs. Metal-based RPDs had a median survival of 73 months (95%CI: 70 - 82) versus 45 months (95% CI: 37-67) for acrylic ones. Multivariable mixed effects Cox model showed that the lifespans of RPDs were longer amongst patients receiving more maintenance care within three months [Hazards Ratio (HR)=0.89 (0.83, 0.96)] and after three months [HR=0.53 (0.46, 0.61)] of denture delivery, patients wearing both maxillary and mandibular RPDs [HR=0.67 (0.52, 0.87)], and patients receiving metal-based RPDs [HR=0.31 (0.23, 0.42)]. CONCLUSIONS: Metal-based dentures, dual arch restoration, and increased maintenance positively impact the survival of RPDs. CLINICAL SIGNIFICANCE: Adapting consent and warranty practices is advised to reflect RPD performance variations.

Microstructural and mechanical characterization of six Co-Cr alloys made by conventional casting and selective laser melting.

STATEMENT OF PROBLEM: Three Co-Cr alloy types (Co-Cr-Mo, Co-Cr-W, and Co-Cr-Mo-W) have been commonly used in the fabrication of dental prostheses. These alloys can be manufactured using either conventional casting or selective laser melting (SLM) techniques. Nevertheless, research that directly compares these materials and/or manufacturing processes in terms of their microstructural and mechanical characteristics is sparse. PURPOSE: The purpose of this in vitro study was to conduct microstructural and mechanical analysis via X-ray interpretation, optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), image analysis, X-ray diffraction (XRD), instrumented indentation testing (IIT), and 3-point bending testing to characterize Co-Cr-Mo, Co-Cr-W, and Co-Cr-Mo-W alloys produced through conventional casting and SLM. MATERIAL AND METHODS: Six Co-Cr-based alloys were analyzed and divided into 3 types based on their elemental composition (Co-Cr-Mo, Co-Cr-W, and Co-Cr-Mo-W). Additionally, each group was categorized based on the manufacturing process used (casting or SLM). X-ray scans were used to assess porosity. The microstructures of the specimens were assessed through SEM/EDS examination and XRD analysis. IIT was used to determine the Martens hardness (HM) and elastic index (ηIT), while the elastic modulus (E) was estimated through the 3-point bending test. The mechanical properties were statistically analyzed using 2-way analysis of variance (ANOVA) and the Tukey multiple comparison post hoc test, with alloy type and manufacturing process as discriminating variables (α=.05). RESULTS: All cast groups exhibited gross porosity, while no pores or other flaws were found in the SLM groups. Based on the XRD results, the crystalline structure of all Co-Cr specimens consisted of the face-centered cubic γ phase (γ-fcc), along with the hexagonal close-packed ε phase (ε-hcp) and Cr23C6 carbide. Different microstructures were identified between the cast and SLM alloys. Significant differences were identified for the mean standard deviation HM (ranging from 2601 ±94 N/mm2 to 3633 ±61 N/mm2) and mean ±standard deviation ηIT (ranging from 16.8 ±0.3% to 20.9 ±0.3%) among alloys prepared by the same manufacturing process, while all SLM alloys had statistically higher HM and ηIT results than their cast counterparts (P<.05). No statistically significant differences were identified for the mean ±standard deviation Eb (ranging from 170 ±25 GPa to 244 ±36 GPa) among the groups prepared with the same manufacturing process (P>.05), but the SLM alloys had significantly higher results (P<.05) than the cast alloys. CONCLUSIONS: In general, the manufacturing procedure significantly affected the porosity, microstructure, and mechanical properties of the tested Co-Cr alloys. SLM decreased the internal porosity, provided a uniform microstructure, and improved the mechanical properties for all the tested alloy types.

Comparative in vitro evaluation of microgap in titanium stock versus cobalt-chrome custom abutments on a conical connection implant: Effect of crown cementation and ceramic veneering.

OBJECTIVE: To compare the implant-abutment connection microgap between computer-aided design and computer-aided manufacturing (CAD/CAM) milled or laser-sintered cobalt-chrome custom abutments with or without ceramic veneering and titanium stock abutments with or without crown cementation. MATERIAL AND METHODS: Six groups of six abutments each were prepared: (1) CAD/CAM cobalt-chrome custom abutments: milled, milled with ceramic veneering, laser-sintered, and laser-sintered with ceramic veneering (four groups: MIL, MIL-C, SIN, and SIN-C, respectively) and (2) titanium stock abutments with or without zirconia crown cementation (two groups: STK and STK-Z, respectively). Abutments were screwed to the implants by applying 30 Ncm torque. All 36 samples were sectioned along their long axes. The implant-abutment connection microgap was measured using scanning electron microscopy on the right and left sides of the connection at the upper, middle, and lower levels. Data were analyzed using the Kruskal-Wallis test (p < .05). RESULTS: Mean values (µm) of the microgap were 0.54 ± 0.44 (STK), 0.55 ± 0.48 (STK-Z), 1.53 ± 1.30 (MIL), 2.30 ± 2.2 (MIL-C), 1.53 ± 1.37 (SIN), and 1.87 ± 1.8 (SIN-C). Although significant differences were observed between the STK and STK-Z groups and the other groups (p < .05), none were observed between the milled and laser-sintered groups before or after ceramic veneering. The largest microgap was observed at the upper level in all groups. CONCLUSIONS: Titanium stock abutments provided a closer fit than cobalt-chrome custom abutments. Neither crown cementation nor ceramic veneering resulted in significant changes in the implant-abutment connection microgap.

MRI susceptibility artefacts caused by orthodontic wire.

OBJECTIVES: To evaluate magnetic susceptibility artefacts produced by orthodontic wires on MRI and the influence of wire properties and MRI image sequences on the magnitude of the artefact. METHODS: Arch form orthodontic wires [four stainless steels (SS), one cobalt chromium (CC) alloy, 13 titanium (Ti) alloys] were embedded in a polyester phantom, and scanned using a 1.5-T superconducting magnet scanner with an eight-channel phased-array coil. All wires were scanned with T1-weighted spin echo (SE) and gradient echo (GRE) sequences according to the American Society for Testing and Materials (ASTM) F2119-07 standard. The phantom also scanned other eight sequences. Artefacts were measured using the ASTM F2119-07 definition and OsiriX software. Artefact volume was analysed according to metal composition, wire length, number of wires, wire thickness, and imaging sequence as factors. RESULTS: With SE/GRE, black/white artefacts volumes from all SS wires were significantly larger than those produced by CC and Ti wires (P < .01). With the GRE, the black artefacts volume was the highest with the SS wires. With the SE, the black artefacts volume was small, whereas white artefacts were noticeable. The cranio-caudal extent of the artefacts was significantly longer with SS wires (P < .01). Although a direct relationship of wire length, number of wires, and wire thickness with artefact volume was noted, these factors did not influence artefact extension in the cranio-caudal direction. CONCLUSIONS: Ferromagnetic/paramagnetic orthodontic wires create artefacts due to local alteration of magnetic field homogeneity. The SS-type wires produced the largest artefacts followed by CC and Ti.

An in vitro evaluation of bond strength and failure behavior between 3D-printed cobalt-chromium alloy and different types of denture base resins.

OBJECTIVES: This study aimed to evaluate the shear bond strength and failure behavior between cobalt-chromium (Co-Cr) alloy and different types of denture base resins (DBRs) over time. METHODS: Seventy-two disk-shaped specimens (8 mm in diameter and 2 mm in thickness) were manufactured using a selective laser melting technology-based metal 3D printer. Three types of DBRs were used: heat-cure (HEA group), cold-cure (COL group), and 3D-printable (TDP group) DBRs (n = 12 per group). Each DBR specimen was fabricated as a 5 mm × 5 mm × 5 mm cube model. The specimens of the TDP group were manufactured using a digital light processing technology-based 3D printer. Half of the DBRs were stored in distilled water at 37 °C for 24 h, whereas the remaining half underwent thermocycling for 10,000 cycles. Shear bond strength was measured using a universal testing machine; failure modes were observed, and metal surfaces were evaluated using energy dispersive spectrometry. RESULTS: The shear bond strength did not differ between the DBR types within the non-thermocycled groups. Contrarily, the TDP group exhibited inferior strength compared to the HEA group (P = 0.008) after thermocycling. All three types of DBRs exhibited a significant decrease in the shear bond strength and an increased tendency toward adhesive failure after thermocycling. CONCLUSIONS: The bond strength between 3D-printable DBRs and Co-Cr alloy was comparable to that of heat-and cold-cure DBRs before thermocycling. However, it exhibited a considerable weakening in comparison to heat-cure DBRs after simulated short-term use. CLINICAL SIGNIFICANCE: The application of 3D-printable DBR in metal framework-incorporated removable partial dentures may be feasible during the early phase of the treatment. However, its application is currently limited because the bond strength between the 3D-printable DBR and metal may weaken after short-term use. Further studies on methods to increase the bond strength between these heterogeneous materials are required.

Finite Element Analysis: Connector Designs and Pontic Stress Distribution of Fixed Partial Denture Implant-Supported Metal Framework.

This virtual study was designed to evaluate the stress-deformation of a metal fixed partial dentures (FPDs) pontic under different loads using two different connectors. The STL file was generated for a RPD of two implant-supported restorations. The Co-Cr metal substructure was designed with two types of connector design. The pontic is connected to implant-supported crowns with square and round shape connectors. This study was designed for a cementless-retained implant-supported FPD. Finite element modeling (FEM) is used to assess the stress and deformation of the pontic within a metal substructure as the FEM might provide virtual values that could have laboratory and clinical relevance. The Co-Cr alloy mechanical properties like the Poisson ratio and modulus of elasticity were based on the parameters of the three-dimensional structure additive method. Nonparametric analyses (Mann-Whitney U test) was used. The use of square or round connectors often resulted in non-significant changes in stress, and deformation under either three or each loaded point on the occlusal surface of a pontic (P > 0.05). However, the deformation revealed distinct variations between loads of the three points compared to each loaded point (P ≤ 0.05). According to this study data, the pontic occlusal surface appears to be the same in stress and deformation under different loads depending on whether square or round connectors are used. While at the same connector designs, the pontic occlusal surface deformed significantly at three loaded points than it did at each point.

An Aspirin-Free Strategy for Immediate Treatment Following Complex Percutaneous Coronary Intervention.

BACKGROUND: There was no study evaluating the effects of an aspirin-free strategy in patients undergoing complex percutaneous coronary intervention (PCI). OBJECTIVES: The authors aimed to evaluate the efficacy and safety of an aspirin-free strategy in patients undergoing complex PCI. METHODS: We conducted the prespecified subgroup analysis based on complex PCI in the STOPDAPT-3 (ShorT and OPtimal duration of Dual AntiPlatelet Therapy after everolimus-eluting cobalt-chromium stent-3), which randomly compared low-dose prasugrel (3.75 mg/d) monotherapy to dual antiplatelet therapy (DAPT) with low-dose prasugrel and aspirin in patients with acute coronary syndrome or high bleeding risk. Complex PCI was defined as any of the following 6 criteria: 3 vessels treated, ≥3 stents implanted, ≥3 lesions treated, bifurcation with 2 stents implanted, total stent length >60 mm, or a target of chronic total occlusion. The coprimary endpoints were major bleeding events (Bleeding Academic Research Consortium 3 or 5) and cardiovascular events (a composite of cardiovascular death, myocardial infarction, definite stent thrombosis, or ischemic stroke) at 1 month. RESULTS: Of the 5,966 study patients, there were 1,230 patients (20.6%) with complex PCI. Regardless of complex PCI, the effects of no aspirin relative to DAPT were not significant for the coprimary bleeding (complex PCI: 5.30% vs 3.70%; HR: 1.44; 95% CI: 0.84-2.47; P = 0.18 and noncomplex PCI: 4.26% vs 4.97%; HR: 0.85; 95% CI: 0.65-1.11; P = 0.24; P for interaction = 0.08) and cardiovascular (complex PCI: 5.78% vs 5.93%; HR: 0.98; 95% CI: 0.62-1.55; P = 0.92 and noncomplex PCI: 3.70% vs 3.10%; HR: 1.20; 95% CI: 0.88-1.63; P = 0.25; P for interaction = 0.48) endpoints without significant interactions. CONCLUSIONS: The effects of the aspirin-free strategy relative to standard DAPT for the cardiovascular and major bleeding events were not different regardless of complex PCI. (ShorT and OPtimal duration of Dual AntiPlatelet Therapy after everolimus-eluting cobalt-chromium stent-3 [STOPDAPT-3]; NCT04609111).

Failure Following Revision Total Hip Arthroplasty After Cobalt-Chrome Femoral Heads are Placed on a Retained Femoral Stem.

BACKGROUND: Failure due to trunnionosis with adverse local tissue reaction (ALTR) has been reported with cobalt-chrome (CoCr) heads in total hip arthroplasty (THA); however, there are limited data on the use of these heads in the revision setting. The purpose of this study was to analyze the outcomes of patients who underwent revision THA with a retained femoral component and received a CoCr femoral head on a used trunnion. METHODS: In this retrospective review, we identified all patients who underwent revision THA with a retained femoral component and received a CoCr femoral head between February 2006 and March 2014. Demographic factors, implant details, and postoperative complications, including the need for repeat revisions, were recorded. In total, 107 patients were included (mean age 67 years, 74.0% women). Of the 107 patients, 24 (22.4%) required repeat revisions. RESULTS: Patients who required repeat revision were younger than those who did not (mean age: 62.9 versus 69, P = .03). The most common indications for repeat revision were instability (8 of 24, 33.3%), ALTR (5 of 24, 20.8%), and infection (4 of 18, 16.7%). Evidence of ALTR or metallosis was identified at the time of reoperation in 10 of the 24 patients who underwent re-revision (41.7%). CONCLUSIONS: The placement of a new CoCr femoral head on a used trunnion during revision THA with a retained femoral component carries a significant risk of complication (22.4%) and should be avoided when possible.