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.

A review on manufacturing processes of cobalt-chromium alloy implants and its impact on corrosion resistance and biocompatibility.

Cobalt-Chromium (CoCr) alloys are currently used for various cardiovascular, orthopedic, fracture fixation, and dental implants. A variety of processes such as casting, forging, wrought processing, hot isostatic pressing, metal injection molding, milling, selective laser melting, and electron beam melting are used in the manufacture of CoCr alloy implants. The microstructure and precipitates (carbides, nitrides, carbonitrides, and intermetallic compounds) formed within the alloy are primarily determined by the type of manufacturing process employed. Although the effects of microstructure and precipitates on the physical and mechanical properties of CoCr alloys are well reviewed and documented in the literature, the effects on corrosion resistance and biocompatibility are not comprehensively reviewed. This article reviews the various processes used to manufacture CoCr alloy implants and discusses the effects of manufacturing processes on corrosion resistance and biocompatibility. This review concludes that the microstructure and precipitates formed in the alloy are unique to the manufacturing process employed and have a significant impact on the corrosion resistance and biocompatibility of CoCr alloys. Additionally, a historical and scientific overview of corrosion and biocompatibility for metallic implants is included in this review. Specifically, the failure of CoCr alloys when used in metal-on-metal bearing surfaces of total hip replacements is highlighted. It is recommended that the type of implant/application (orthopedic, dental, cardiovascular, etc.) should be the first and foremost factor to be considered when selecting biomaterials for medical device development.

Influence of the Manufacturing Trinomial (Technology, Printer, and Material) on the Marginal and Internal Discrepancies of Printed Metal Frameworks for the Fabrication of Tooth-Supported Prostheses: A Systematic Review and Meta-analysis.

PURPOSE: The purpose of this systematic review and meta-analysis was to compare the influence of fabrication method (conventional, subtractive, and additive procedures) and manufacturing trinomial (technology, printer, and material combination) on the marginal and internal fit of cobaltchromium (Co-Cr) tooth-supported frameworks. MATERIALS AND METHODS: An electronic systematic review was performed in five data bases: MEDLINE/PubMed, Embase, World of Science, Cochrane, and Scopus. Studies that reported the marginal and internal discrepancies of tooth-supported Co-Cr additive manufacturing (AM) frameworks were included. Two authors independently completed the quality assessment of the studies by applying the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies. A third examiner was consulted to resolve lack of consensus. RESULTS: A total of 31 articles were included and classified based on the evaluation method: manufacturing accuracy, the dual- or triple-scan method, stereomicroscope, optical coordinate measurement machine, microCT, profilometer, and silicone replica. Six subgroups were created: 3D Systems, Bego, Concept Laser, EOS, Kulzer, and Sisma. Due to the heterogeneity and limited data available, only the silicone replica group was considered for meta-analysis. The metaanalysis showed a mean marginal discrepancy of 91.09 µm (I2 = 95%, P < .001) in the conventional group, 77.48 µm (I2 = 99%, P < .001) in the milling group, and 82.92 µm (I2 = 98%, P < .001) in the printing group. Additionally, a mean internal discrepancy of 111.29 µm (I2 = 94%, P < .001) was obtained in the conventional casting group, 121.96 µm (I2 = 100%, P < .001) in the milling group, and 121.25 µm (I2 = 99%, P < .001) in the printing group. CONCLUSIONS: Manufacturing method and selective laser melting (SLM) metal manufacturing trinomial did not impact the marginal and internal discrepancies of Co-Cr frameworks for the fabrication of tooth-supported restorations.

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).

The Effects of Reusing Cobalt-Chromium Alloy Powder on Its Mechanical Properties and Grain Size: An In Vitro Study.

PURPOSE: To characterize material changes that may occur in virgin cobalt-chromium (Co-Cr) alloy powder when it is blended with alloy powders that have been reused multiple times. MATERIALS AND METHODS: Initially, 20 kg of virgin Co-Cr powder was loaded into a laser-sintering device. The tensile test specimens were fabricated in the first (Group 1), fourth (Group 2), seventh (Group 3), tenth (Group 4), and thirteenth (Group 5) production cycles (N = 15). Prior to fabricating the specimens, powder alloy samples were collected from the powder bed for analysis. The tensile strength, elastic modulus, and percent elongation were calculated with tensile testing. Scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS) and laser particle size distribution (LPSD) were used to analyze the alloy powder samples. The fracture surface of one tensile test specimen from each group was examined via SEM/EDS. One-way ANOVA followed by Dunnett T3 test was used for statistical analysis (α = .05). RESULTS: No difference was observed between groups in terms of tensile strength. A statistically significant difference was observed between Groups 1 and 2 in terms of percent elongation. Groups 2 and 4 were statistically significantly different in terms of both elastic modulus and percent elongation (P ≤ .05). SEM images of the powder alloy showed noticeable differences with increasing numbers of cycles. SEM images and the EDS analysis of the fractured specimens were in accordance with the strength data. CONCLUSIONS: Reusing Co-Cr alloy powder increased the particle size distribution. However, there was no correlation between increased cycle number and the mechanical properties of the powder.

Effect of laser etching on surface characteristics and porcelain bond to soft milled and direct metal laser sintered cobalt chromium alloys.

STATEMENT OF PROBLEM: The surface topography of metal substrate can affect its bond to porcelain. A neodynium-doped yttrium aluminum garnet (Nd:YAG) laser has been introduced to modify the metal surface topography and improve porcelain bond strength. However, studies on the effect of laser etching on metal to porcelain bond strength are lacking. PURPOSE: The purpose of this in vitro study was to determine the effect of Nd:YAG laser etching on the surface roughness and wettability of and the porcelain bond strength to cobalt chromium (Co-Cr) substrate fabricated by milling and direct metal laser sintering (DMLS). MATERIAL AND METHODS: Thirty-two 0.5×3×25-mm Co-Cr specimens were fabricated by milling soft Co-Cr (M group) and DMLS Co-Cr metal powder (DML group). The surface topography of representative specimens from each study group was assessed under a scanning electron microscope (SEM) and an atomic force microscope (AFM). All specimens were assessed for surface roughness using a contact profilometer, and for wettability with a contact angle goniometer. Half of the specimens of each study group (n=8) were subjected to surface laser etching by using a Nd:YAG laser. The specimens subjected to etching were assessed again for surface topography and wettability. All specimens in both study groups were veneered with porcelain. The porcelain bond strength was tested with a 3-point bend test in a universal testing machine. The results were statistically analyzed with 2-way ANOVA test followed by the post hoc Tukey test for pairwise comparisons (α=.05). RESULTS: After etching, the M group had a higher mean ±standard deviation Ra and Rz of 2.9 ±0.6 and 17.7 ±3.2 µm and significantly better wettability and bond strength of 79 ±6 and 52 ±13 MPa. In contrast, after etching, the DMLS group had a significantly lower Ra and Rz of 7.9 ±2.4 and 41.8 ±9.3 µm and significantly lower wettability and bond strength of 87 ±4 and 70 ±10 MPa. The DMLS group had a significantly higher roughness and bond strength than the M group before and after laser etching. The SEM and AFM showed different surface topography in the study groups. CONCLUSIONS: The manufacturing process of Co-Cr substrate had a significant effect on surface characteristics and porcelain bond strength. Laser etching improved the surface topography and bond strength of milled Co-Cr but not of DMLS Co-Cr.

Fabrication trueness and internal fit of different lithium disilicate ceramics according to post-milling firing and material type.

OBJECTIVES: To evaluate whether post-milling firing and material type affect the fabrication trueness and internal fit of lithium disilicate crowns. METHODS: A prefabricated cobalt chromium abutment was digitized to design a mandibular right first molar crown. This design file was used to fabricate crowns from different lithium disilicate ceramics (nano-lithium disilicate (AM), fully crystallized lithium disilicate (IN), advanced lithium disilicate (TS), and lithium disilicate (EX)) (n = 10). Crowns, the abutment, and the crowns when seated on the abutment were digitized by using an intraoral scanner. Fabrication trueness was assessed by using the root mean square method, while the internal fit was evaluated according to the triple scan method. These processes were repeated after the post-milling firing of AM, TS, and EX. Paired samples t-tests were used to analyze the effect of post-milling firing within AM, TS, and EX, while all materials were compared with 1-way analysis of variance and Tukey HSD tests (α = 0.05). RESULTS: Post-milling firing reduced the surface deviations and internal gap of AM and EX (P ≤ 0.014). AM mostly had higher deviations and internal gaps than other materials (P ≤ 0.030). CONCLUSIONS: Post-milling firing increased the trueness and internal fit of tested nano-lithium disilicate and lithium disilicate ceramics. Nano-lithium disilicate mostly had lower trueness and higher internal gap; however, the maximum meaningful differences among tested materials were small. Therefore, the adjustment duration and clinical fit of tested crowns may be similar. CLINICAL SIGNIFICANCE: Tested lithium disilicate ceramics may be suitable alternatives to one another in terms of fabrication trueness and internal fit, considering the small differences in measured deviations and internal gaps.

Does the choice of the measuring technique affect the comparison of fit between zirconia and cobalt-chromium prostheses?

AIMS: The objectives of the study were to compare the adaptation of presintered zirconia and cobalt- chromium prostheses using microcomputed tomography (µCT), scanning electron microscopy (SEM), and stereomicroscope (SM). MATERIALS AND METHODS: Twenty-four fixed dental prostheses (FDPs) were fabricated on metal abutments, duplicated from maxillary first premolar and first molar prepared on a typodont model. Teeth were reduced to obtain chamfer of 1.2 mm and reduction occlusaly of 2 mm occlusal. Scanning of the abutments was done with random assignment to two groups receiving the FDPs made from soft-milled Co-Cr (n = 12) and zirconia (n = 12). Marginal and internal gaps were assessed using three evaluation techniques (X-ray microcomputer tomography, SEM, and stereomicroscopy). STATISTICAL ANALYSIS USED: Comparison of the results was made using Levene and analysis of variance tests (α =0.05). RESULTS: Irrespective of the material tested, statistical differences were found between the measuring techniques (P = 0.001 overall); the obtained mean gaps were for CT scan (92.60 ± 13.31), for SEM (101.92 ± 23.03), and for SM (113.44 ± 14.68): the multiple comparisons between techniques found a significant difference between CT and SM (P < 0.001), and SEM and SM (P = 0.025). When materials were compared within each measuring technique, Co-Cr showed lower values compared to zirconia in SEM (P < 0.001) and Stereo (P = 0.049); similar results were found in CT. CONCLUSIONS: Results values differed with the chosen measuring technique. Co-Cr prostheses had a better fit than zirconia prostheses in SEM and Stereo. µCT showed comparable results to SEM, smaller than SM results.

Retention and fatigue performance of modified polyetheretherketone clasps for removable prosthesis.

PURPOSE: Polyetheretherketone (PEEK) is considered as an alternative to metal material for removable partial denture (RPD). However, the retentive force is not strong as a metal RPD. This study investigated the retention and fatigue performance of PEEK clasps with different proportions of clasp arm engaging the undercut to verify a new strategy to improve their clinical performance. METHODS: Three groups (n = 10/group) of PEEK clasps with their terminal 1/3, 2/3 and the whole of retentive arms engaging the undercut were fabricated along with a group (n = 10) of conventional cobalt-chrome (CoCr) clasps as control group. Retentive forces were measured by universal testing machine initially and at an interval of 1500 cycles for a total of 15,000 fatigue cycles. The fatigue cycles were conducted by repeated insertion and removal of the clasp using fatigue testing machine. Each clasp was scanned by Trios3 scanner before and after fatigue test to obtain digital models. The deformation of the clasp was evaluated by root mean square (RMS) through aligning the two models in Geomagic wrap (2021). Scanning electron microscopy (SEM) and finite element analysis were carried out to observe the abrasion and the von Mises stress of the clasp arm. Kruskal-Wallis H test was used to compare the retentive forces and the RMSs of the studied groups followed by Bonferroni multiple comparisons. RESULTS: The whole of PEEK clasp arm engaging the undercut provided higher mean retentive forces (7.99 ± 2.02 N) than other PEEK clasp groups (P < 0.001) and was closer to CoCr clasps (11.88 ± 2.05 N). The RMSs of PEEK clasps were lower than CoCr clasps (P < 0.05) while the differences among PEEK clasps were of no statistical significance (P > 0.05). SEM showed that evidences of surface abrasion were observed on the section that engaged the undercut for all groups of clasps. The stress concentration mainly occurred on the initial part of the retentive arm. The maximum von Mises stress of each group was below the compressive strength of PEEK. CONCLUSIONS: Proportions of PEEK clasp arm engaging the undercut positively influenced the retentive force and the fatigue resistance of PEEK clasps was superior than CoCr clasps. It is a feasible method to improve the retention of PEEK clasps by increasing the proportion of clasp arm engaging the undercut. Clinical trials are needed to further verify this innovation.

Does the Build Orientation Parameter Affect the Fit of Fixed Partial Dentures Fabricated by Additive Manufacturing?

PURPOSE: This in vitro study evaluated the adaptation of cobalt-chromium (Co-Cr) fixed dental prostheses (FDPs) fabricated by selective laser melting (SLM) with different build angles. MATERIALS AND METHODS: Maxillary right first premolars and first molars from a typodont were prepared with 1-mm chamfer, 2-mm occlusal reduction, and total taper of 8 degrees to receive three-unit FDPs. After framework design, data were sent to a laser machine, and 30 specimens were fabricated from Co-Cr metal powder by SLM. Specimens were assigned to three groups (n = 10 per group) with different build angles of 0 (A0), 30 (A30), and 45 (A45) degrees. Marginal and internal fit were evaluated. Results were compared among build orientation groups and abutments. Data were analyzed using the Levene test, t test, and analysis of variance (α = .05). RESULTS: A statistical difference was found between different angle groups (P = .015). At the abutment level, a significant difference was found in the gap values between build orientation groups for the molars (P = .048). Group A0 reported the smallest mean discrepancy values, and group A45 the highest. Statistical differences were found between group A45 and groups A0 (P < .001) and A30 (P < .024). CONCLUSIONS: The fit of printed metal FDPs was affected by the build orientation but remained clinically acceptable.

The impact of femoral head size on the wear evolution at contacting surfaces of total hip prostheses: A finite element analysis.

Total Hip Arthroplasty has been a revolutionary technique in restoring mobility to patients with damaged hip joints. The introduction of modular components of the hip prosthesis allowed for bespoke solutions based on the requirements of the patient. The femoral stem is designed with a conical trunnion to allow for assembly of different femoral head sizes based on surgical requirements. The femoral head diameters for a metal-on-polyethylene hip prosthesis have typically ranged between 22 mm and 36 mm and are typically manufactured using Cobalt-Chromium alloy. A smaller femoral head diameter is associated with lower wear of the polyethylene, however, there is a higher risk of dislocation. In this study, a finite element model of a standard commercial hip arthroplasty prosthesis was modelled with femoral head diameters ranging from 22 mm to 36 mm to investigate the wear evolution and material loss at both contacting surfaces (acetabular cup and femoral stem trunnion). The finite element model, coupled with a validated in-house wear algorithm modelled a human walking for 10 million steps. The results have shown that as the femoral head size increased, the amount of wear on all contacting surfaces increased. As the femoral head diameter increased from 22 mm to 36 mm, the highly cross-linked polyethylene (XLPE) volumetric wear increased by 61% from 98.6 mm3 to 159.5 mm3 while the femoral head taper surface volumetric wear increased by 21% from 4.18 mm3 to 4.95 mm3. This study has provided an insight into the amount of increased wear as the femoral head size increased which can highlight the life span of these prostheses in the human body.

The Effect of Different Ageing Protocols on the Shear Bond Strength of the Ceromer Indirect Composite on Two Different Substructure Materials.

BACKROUND: The evolution of restorative materials in prosthodontics has led to the emergence of indirect composite resins, including ceromers, as alternatives to traditional metal-ceramic restorations. However, research gaps exist regarding the impact of ageing protocols on the bond strength of ceromer composites to different metal substructures, necessitating further investigation in this area. AIM: This study aimed to determine the effect of five different ageing protocols on the shear bond strength (SBS) of ceromer indirect composites on two different substructures. METHODS: In this in vitro study, 120 metallic discs (10 × 2 mm) were cast from cobalt-chromium (Co-Cr) alloy (n = 60) and spark erosion treated from grade V titanium (n = 60). Each sample was sandblasted. The M.L. primer (Shofu, Germany) and layers of opaque were applied to the surface following the manufacturer's instructions. A special jig (6 × 2 mm) was placed on each disc. The ceromer was condensed in it and light-cured separately for 90 s. Following polishing, specimens were separated into five ageing groups: distilled water (as a control), thermal cycling, tea, coffee, and gastric acid immersion. All samples were placed in 37°C incubation for 28 days for distilled water, coffee, and tea, and 7 days for gastric acid immersion and thermal cycling for 5000 cycles (5-55°C). A universal test machine was used to measure the SBS. The samples were evaluated for failure modes using stereomicroscopy. Data were analyzed using one-way analysis of variance (ANOVA) (P < 0.05). RESULTS: According to one-way ANOVA, the mean SBS (MPa) between the two groups was compared in each ageing protocol, and there were no significant differences between the Co-Cr-C and Ti-C groups (P > 0.05). The most frequent mode of failure in all groups was mixed. CONCLUSIONS: Applying the ageing protocols, the type of substructure material had no significant effect on the SBS of the ceromer indirect composite except for tea immersion.

Customizable Nichrome Wire Heaters for Molecular Diagnostic Applications.

Accurate sample heating is vital for nucleic acid extraction and amplification, requiring a sophisticated thermal cycling process in nucleic acid detection. Traditional molecular detection systems with heating capability are bulky, expensive, and primarily designed for lab settings. Consequently, their use is limited where lab systems are unavailable. This study introduces a technique for performing the heating process required in molecular diagnostics applicable for point-of-care testing (POCT), by presenting a method for crafting customized heaters using freely patterned nichrome (NiCr) wire. This technique, fabricating heaters by arranging protrusions on a carbon black-polydimethylsiloxane (PDMS) cast and patterning NiCr wire, utilizes cost-effective materials and is not constrained by shape, thereby enabling customized fabrication in both two-dimensional (2D) and three-dimensional (3D). To illustrate its versatility and practicality, a 2D heater with three temperature zones was developed for a portable device capable of automatic thermocycling for polymerase chain reaction (PCR) to detect Escherichia coli (E. coli) O157:H7 pathogen DNA. Furthermore, the detection of the same pathogen was demonstrated using a customized 3D heater surrounding a microtube for loop-mediated isothermal amplification (LAMP). Successful DNA amplification using the proposed heater suggests that the heating technique introduced in this study can be effectively applied to POCT.

Long-term polyethylene wear rates and clinical outcomes of oxidized zirconium femoral heads on highly cross-linked polyethylene in total hip arthroplasty.

Aims: Oxidized zirconium (OxZi) and highly cross-linked polyethylene (HXLPE) were developed to minimize wear and risk of osteolysis in total hip arthroplasty (THA). However, retrieval studies have shown that scratched femoral heads may lead to runaway wear, and few reports of long-term results have been published. The purpose of this investigation is to report minimum ten-year wear rates and clinical outcomes of THA with OxZi femoral heads on HXLPE, and to compare them with a retrospective control group of cobalt chrome (CoCr) or ceramic heads on HXLPE. Methods: From 2003 to 2006, 108 THAs were performed on 96 patients using an OxZi head with a HXLPE liner with minimum ten-year follow-up. Harris Hip Scores (HHS) were collected preoperatively and at the most recent follow-up (mean 13.3 years). Linear and volumetric liner wear was measured on radiographs of 85 hips with a minimum ten-year follow-up (mean 14.5 years). This was compared to a retrospective control group of 45 THAs using ceramic or CoCr heads from October 1999 to February 2005, with a minimum of ten years' follow-up. Results: Average HHS improved from 50.8 to 91.9 and 51.0 to 89.8 in the OxZi group and control group, respectively (p = 0.644), with no osteolysis in either group. Linear and volumetric wear rates in the OxZi group averaged 0.03 mm/year and 3.46 mm3/year, respectively. There was no statistically significant difference in HHS scores, nor in linear or volumetric wear rate between the groups, and no revision for any indication. Conclusion: The radiological and clinical outcomes, and survivorship of THA with OxZi femoral heads and HXLPE liners, were excellent, and comparable to CoCr or ceramic heads at minimum ten-year follow-up. Wear rates are below what would be expected for development of osteolysis. OxZi-HXLPE is a durable bearing couple with excellent long-term outcomes.

Analysis of subgingival microbiota and IL-1ß, TNF-α and CX3CL1 levels in gingival crevicular fluid of fixed dental prostheses.

Prosthetic biomaterials can affect the composition of the subgingival microbiota and consequently the production of proinflammatory cytokines, causing damage to the periodontium. A total of 40 patients were divided into two groups: 20 with monolithic zirconia (MZ) prostheses and 20 with porcelain fused to metal (PFM) with nickel-chromium (Ni-Cr) alloy prostheses. Subgingival plaque and gingival crevicular fluid samples were taken. The Checkerboard technique for DNA-DNA hybridization and the enzyme-linked immunosorbent assay technique were performed. Teeth with MZ presented a lower percentage of bleeding on probing and tooth mobility compared to teeth with PFM with Ni-Cr alloy. Prosthodontic teeth harbored higher total levels of the 18 bacterial species than non-prosthodontic teeth. There was a higher prevalence of S. gordonii and V. parvula species in PFM with Ni-Cr alloy compared to MZ. There was an increase in IL-1ß, TNF-α and CX3CL1 levels in PFM with Ni-Cr alloy compared to MZ. MZ is a candidate biomaterial with fewer negative effects on the periodontium, allowing for longer prostheses longevity in the mouth.

[Mitigating metal artifacts from cobalt-chromium alloy crowns in cone-beam CT images through deep learning techniques].

Objective: To develop and evaluate metal artifact removal systems (MARS) based on deep learning to assess their effectiveness in removing artifacts caused by different thicknesses of metals in cone-beam CT (CBCT) images. Methods: A full-mouth standard model (60 mm×75 mm×110 mm) was three-dimensional (3D) printed using photosensitive resin. The model included a removable and replaceable target tooth position where cobalt-chromium alloy crowns with varying thicknesses were inserted to generate matched CBCT images. The artifacts resulting from cobalt-chromium alloys with different thicknesses were evaluated using the structural similarity index measure (SSIM) and peak signal-to-noise ratio (PSNR). CNN-MARS and U-net-MARS were developed using a convolutional neural network and U-net architecture, respectively. The effectiveness of both MARSs were assessed through visualization and by measuring SSIM and PSNR values. The SSIM and PSNR values were statistically analyzed using one-way analysis of variance (α=0.05). Results: Significant differences were observed in the range of artifacts produced by different thicknesses of cobalt-chromium alloys (all P<0.05), with 1 mm resulting in the least artifacts. The SSIM values for specimens with thicknesses of 1.0, 1.5, and 2.0 mm were 0.916±0.019, 0.873±0.010, and 0.833±0.010, respectively (F=447.89, P<0.001). The corresponding PSNR values were 20.834±1.176, 17.002±0.427, and 14.673±0.429, respectively (F=796.51, P<0.001). After applying CNN-MARS and U-net-MARS to artifact removal, the SSIM and PSNR values significantly increased for images with the same thickness of metal (both P<0.05). When using the CNN-MARS for artifact removal, the SSIM values for 1.0, 1.5 and 2.0 mm were 0.938±0.023, 0.930±0.029, and 0.928±0.020 (F=2.22, P=0.112), while the PSNR values were 30.938±1.495, 30.578±2.154 and 30.553±2.355 (F=0.54, P=0.585). When using the U-net-MARS for artifact removal, the SSIM values for 1.0, 1.5 and 2.0 mm were 0.930±0.024, 0.932±0.017 and 0.930±0.012 (F=0.24, P=0.788), and the PSNR values were 30.291±0.934, 30.351±1.002 and 30.271±1.143 (F=0.07, P=0.929). No significant differences were found in SSIM and PSNR values after artifact removal using CNN-MARS and U-net-MARS for different thicknesses of cobalt-chromium alloys (all P>0.05). Visualization demonstrated a high degree of similarity between the images before and after artifact removal using both MARS. However, CNN-MARS displayed clearer metal edges and preserved more tissue details when compared with U-net-MARS. Conclusions: Both the CNN-MARS and U-net-MARS models developed in this study effectively remove the metal artifacts and enhance the image quality. CNN-MARS exhibited an advantage in restoring tissue structure information around the artifacts compared to U-net-MARS.

Efficient removal and transformation of Cr(VI) from alkaline wastewater to form a ferrochromium spinel multiphase via a modified ferrite process.

Chromium-containing wastewater causes serious environmental pollution due to the harmfulness of Cr(VI). The ferrite process is typically used to treat chromium-containing wastewater and recycle the valuable chromium metal. However, the current ferrite process is unable to fully transform Cr(VI) into chromium ferrite under mild reaction conditions. This paper proposes a novel ferrite process to treat chromium-containing wastewater and recover valuable chromium metal. The process combines FeSO4 reduction and hydrothermal treatment to remove Cr(VI) and form chromium ferrite composites. The Cr(VI) concentration in the wastewater was reduced from 1040 mg L-1 to 0.035 mg L-1, and the Cr(VI) leaching toxicity of the precipitate was 0.21 mg L-1 under optimal hydrothermal conditions. The precipitate consisted of micron-sized ferrochromium spinel multiphase with polyhedral structure. The mechanism of Cr(VI) removal involved three steps: 1) partial oxidation of FeSO4 to Fe(III) hydroxide and oxy-hydroxide; 2) reduction of Cr(VI) by FeSO4 to Cr(III) and Fe(III) precipitates; 3) transformation and growth of the precipitates into chromium ferrite composites. This process meets the release standards of industrial wastewater and hazardous waste and can improve the efficiency of the ferrite process for toxic heavy metal removal.

Biomechanical Analysis of One-Piece Postand- Core: High-Performance Polymers vs Conventional Materials.

PURPOSE: To evaluate the stress distribution along a premolar's root dentin, its post, and its post-luting agent when materials with different elastic moduli are used to fabricate one-piece post-and-cores in two different designs. MATERIALS AND METHODS: Two 3D virtual models (for cylindrical and conical post designs) of a mandibular premolar restored with one-piece post-and-core restorations were obtained using a software. A total of eight post-and-core materials were tested: polyetheretherketone (PEEK), polyetherketoneketone (PEKK), glass fiber-reinforced polyetheretherketone (GFR-PEEK), carbon fiber-reinforced polyetheretherketone (CFR-PEEK), gold-palladium alloy (Au-Pd), titanium (Ti), zirconia (Zi), and chromium-nickel (Cr-Ni). Maximum principals stress (MPS) in the post, post-luting agent, and root dentin were determined. A load of 150 N was applied to the buccal cusp in the linguo-labial direction at an angle of 45 degrees oblique to the longitudinal axis of the crown. RESULTS: The highest MPS value in post structure was observed with Cr-Ni material for both post designs. Similarly, the highest MPS value in the post-luting agent was observed for Cr-Ni, the material with the highest elastic modulus. However, in the root dentin, the highest value was observed in PEEK, the material with the lowest elastic modulus. CONCLUSIONS: Post material and design influenced the stress concentration in the post, post-luting agent, and root dentin. The stress at the root dentin was slightly higher for polymeric materials. Cylindrical post design revealed lower stresses than conical post design at root dentin for all post-and-core materials tested.

Wear at the implant-framework interface between titanium implant platform and the additively manufactured titanium and cobalt-chromium frameworks.

PURPOSE: To measure the wear at the implant interface between the Grade 4 titanium (Ti) of the implant and frameworks fabricated using two additively manufactured alloys (Ti alloy and cobalt-chromium [Co-Cr]) pre- and post-artificial aging. MATERIAL AND METHODS: Three-unit frameworks supported by two implants were additively manufactured (Atlantis; Dentsply Sirona) using Ti and Co-Cr dental alloys. Two implants (OsseoSpeed EV, Astra Tech; Dentsply Sirona) were torqued on each non-engaging framework. The assembled implant-frameworks were secured into polyurethane foam blocks. Groups were created based on the material and surface assessed: framework (Ti-framework and Co-Cr-framework groups) and implant (Ti-implant group). Two subgroups were created depending on the location: premolar (PM) and molar (M). Computed tomography images were obtained pre- (as manufactured) and post-simulated mastication procedures. The pre- and post-simulated mastication files of each specimen were aligned using the best-fit algorithm using a metrology program. Wear was measured by calculating the volumetric discrepancies at the implant interface on 64 measurement points per area analyzed. Three-way ANOVA and Tukey tests were used to analyze the data (α = 0.05). RESULTS: The mean volumetric discrepancy values ranged from 0.8 to 3.1 µm among all the subgroups tested. The group (framework vs. implant) (p < 0.001) and tooth location (p < 0.001) were significant factors of the mean volumetric discrepancy values obtained. The framework group presented with significantly lower volumetric discrepancy mean values (1 µm) compared with the implant group (3 µm), whereas the premolar area obtained significantly lower mean volumetric discrepancy values (1.9 µm) compared with the molar location (2.3 µm). CONCLUSIONS: Volumetric discrepancies were found at the implant-framework interface tested between the pre- and post-artificial aging measurements ranging from 1 to 3 µm after 1,200,000 cyclic loading that simulated approximately 12 months of function.