Spiros Zinelis

Metallurgical and interfacial characterization of PFM Co–Cr dental alloys fabricated via casting, milling or selective laser melting

OBJECTIVES Bulk and interfacial characterization of porcelain fused to metal (PFM) Co-Cr dental alloys fabricated via conventional casting, milling and selective laser melting. METHODS Three groups of metallic specimens made of PFM Co-Cr dental alloys were prepared using casting (CST), milling (MIL) and selective laser sintering (SLM). The porosity of the groups was evaluated using X-ray scans. The microstructures of the specimens were evaluated via SEM examination, EDX and XRD analysis. Vickers hardness testing was utilized to measure the hardness of the specimens. Interfacial characterization was conducted on the porcelain-covered specimens from each group to test the elemental distribution with and without the application of INmetalbond. The elemental distribution of the probed elements was assessed using EDX line profile analysis. Hardness results were statistically analyzed using one-way ANOVA and Holm-Sidaks method (α=0.05). RESULTS X-ray radiography revealed the presence of porosity only in the CST group. Different microstructures were identified among the groups. Together with the γ phase matrix, a second phase, believed to be the Co3Mo phase, was also observed by SEM and subsequent XRD analysis. Cr7C3 and Cr23C6 carbides were also identified via XRD analysis in the CST and MIL groups. The hardness values were 320±12 HV, 297±5 HV and 371±10 HV, and statistically significant differences were evident among the groups. SIGNIFICANCE The microstructure and hardness of PFM Co-Cr dental alloys are dependent on the manufacturing technique employed. Given the differences in microstructural and hardness properties among the tested groups, further differences in their clinical behavior are anticipated.

Selective Laser Melting Technique of Co-Cr Dental Alloys: A Review of Structure and Properties and Comparative Analysis with Other Available Techniques.

PURPOSE The aim of this study was to review the effect of selective laser melting (SLM) procedure on the properties of dental structures made of Co-Cr alloys and to evaluate its quality and compare it to those produced by conventional casting and milling fabrication techniques. MATERIALS AND METHODS A computerized database search using PubMed and Scopus was conducted for peer-reviewed scientific research studies regarding the use of SLM in Co-Cr dental alloys with no restrictions for publication years. The search engines provided hundreds of results, and only 48 scientific research papers, case studies, or literature reviews were considered relevant for this review. RESULTS The innovative manufacturing concept of SLM offers many advantages compared with casting and milling fabrication techniques. SLM provides different microstructure from casting and milling with minimal internal porosity and internal fitting, marginal adaptation, and comparable bond strength to porcelain. Mechanical and electrochemical properties of SLM structures are enhanced compared to cast, while clinical longevity of single-metal ceramic crowns is comparable to Au-Pt dental alloy. CONCLUSION The SLM technique provides dental prosthetic restorations more quickly and less expensively without compromising their quality compared with restorations prepared by casting and milling techniques. CLINICAL SIGNIFICANCE The current SLM devices provide metallic restorations made of Co-Cr alloys for removable and fixed partial dentures without compromising the alloy or restoration properties at a fraction of the time and cost, showing great potential to replace the aforementioned fabrication techniques in the long term; however, further clinical studies are essential to increase the acceptance of this technology by the worldwide dental community.

Multitechnique characterization of CPTi surfaces after electro discharge machining (EDM).

ObjectivesThe aim of this study was to comparatively assess the surface roughness parameters, the hardness, and the elemental and molecular alterations induced on CPTi surfaces after conventional finishing and finishing with electro discharge machining (EDM).Materials and methodsA completed cast model of an arch that received four implants was used for the preparation of two grade II CPTi castings. One framework was conventionally finished (CF), whereas the other was subjected to EDM finishing. The surface morphology was imaged employing SEM. 3D surface parameters (Sa, Sq, Sz, Sds, Sdr, and Sci) were calculated by optical profilometry. The elemental composition of the treated surfaces was determined by energy dispersive X-ray analysis, whereas the elemental and chemical states of the outmost layer were investigated by X-ray photoelectron spectrometry. Surface hardness was also tested with a Knoop indenter. The results of surface roughness parameters, elemental analysis, and hardness were compared using unpaired t test (a = 0.05).ResultsThe EDM group demonstrated a rougher surface, with a significant uptake of C and Cu. The CF surface mainly consisted of TiO2. On EDM surface though, Ti was probed in different chemicals states (TiO2, Ti2O3, TiC and metallic Ti) and Cu was traced as Cu2O and CuO. Hardness after EDM was almost ten times higher than CF.ConclusionsEDM significantly affected surface roughness, chemical state, and hardness properties of grade II CPTi castings in comparison with CF.Clinical relevanceThe morphological and elemental alterations of EDM-treated CPTi surfaces may strongly contribute to the reduced corrosion resistance documented for this procedure. The degradation of electrochemical properties may have further biological implications through ionic release in the oral environment.

Surface and cross-sectional characterization of titanium-nitride coated nickel–titanium endodontic files

Background/purpose Although the effect of experimental surface modifications on various properties (e.g., fatigue, wear) on coated files have been tested in the past, there is no report for the coating quality of commercially available TiN coated files. The aim of this study was to characterize the surface and cross section of TiN coated endodontic files. Materials and methods TiN coated nickel–titanium endodontic files (EasyShape) were surface and cross-sectionally analyzed via scanning electron microscopy backscattered electron imaging and energy-dispersive X-ray spectroscopy analysis in spot, area, and line scan modes. Results Surface imaging revealed parallel oblong regions with higher mean atomic contrast, a finding attributed to increased Ni content. Cross-sectional analysis showed that the coating’s average total thickness was 0.31 μm and consisted of a thin layered film. Energy-dispersive X-ray spectroscopy analysis revealed the presence of Ti, Ni, N, and O in the coating, whereas only Ni and Ti were identified in the bulk of the file. Ti and O showed their peak compositions at the bulk/coating and coating/surface interfaces, respectively, whereas N displayed a rather constant content within the coated region. The N and O contents started increasing inner to the coating/bulk interface, denoting possible diffusion of both elements to the subcoating region. Conclusion Surface and bulk characterization showed no uncoated areas of the files tested. Apart from Ti, Ni, and N, oxygen was also identified within the coating region.

Assessment of fatigue parameters of dental resin composites using dynamic fatigue testing

The fatigue parameters of dental resin composites Ceram-X Mono, Clearfil Majesty and Saremco Els were studied. The dynamic fatigue method was used to obtain the crack growth exponent n and a material constant dependent on the test environment and initial material strength, σfo, through linear regression analysis. Clearfil Majesty showed a lower n than Ceram-X Mono and Saremco Els, but the highest σfo. Fractographic analysis revealed that the fracture origin was located on or near the surface opposite to loading. Fatigue parameters obtained from dynamic testing provide significant information about the mechanical degradation rate of the materials.

Does long-term intraoral service affect the mechanical properties and elemental composition of multistranded wires of lingual fixed retainers?

Purpose The aim of this study was to evaluate the elemental and mechanical alterations of stainless steel (SS) multistranded orthodontic wires used in fixed retention after intraoral ageing. Materials and Methods Two types of 0.022-inch, seven-stranded wires, Lingual Retainer Wire (LRW) and Tru-Chrome (TCH), from the same manufacturer (Rocky Mountain Orthodontics, Denver, Colo, USA) were tested. Thirty-three samples from LRW group and thirty-seven from TCH were collected, whereas three unused wires from each package were used as controls. The median ageing time for LRW was 7.4 years and 8.4 for TCH. All samples were subjected to scanning electron microscope/X-ray energy dispersive spectroscopy analysis. Three spectra were taken from the surface of each wire and then all samples were used for the assessment of Martens hardness, indentation modulus (EIT), and elastic index (ηIT) with the instrumented indentation testing method (IIT). The intraoral ageing time was statistically compared between the two groups by Mann-Whitney rank sum test and the compositional and mechanical properties were compared by unpaired t-test. The Spearman correlation between elemental content and ageing time was carried out for all elements (a = 0.05). Results No significant differences were found for both the elemental content and for the mechanical properties between the wires tested. Spearman analysis revealed no correlation between elemental content and intraoral time while two groups share statistically equal intraoral ageing times (P > 0.05). Conclusions Both wires seemed to maintain their mechanical and elemental integrity within a period of 14-year intraoral exposure, whereas no measurable ionic release could be identified.

Multitechnique characterization of conventional and experimental Ag-based brazing alloys for orthodontic applications

OBJECTIVES To characterize the microstructure, mechanical properties, ionic release and tarnish resistance of conventional and experimental Ag-based soldering alloys for orthodontic applications. METHODS Disk shaped specimens were prepared from four commercial Ag based soldering alloys [Dentaurum Universal Silver Solder (DEN), Orthodontic Solders (LEO), Ortho Dental Universal Solder (NOB), and Silver Solder (ORT)] and four experimental alloys Ag12Ga, Ag10Ga5Sn, Ag20In and Ag7Sn. The elemental composition and microstructure was determined by SEM/EDX and XRD analysis, while the mechanical properties were determined by Instrumented Indentation Testing. Ionic release of Ag, Cu, Zn, Ga, In and Sn was determined by ICP-EAS in 0.9% NaCl and Ringers solutions after 28, 49 and 70 days. Tarnish resistance was also tested and colorimetry was applied to quantify the differences in color (DE) before and after immersion in testing media. DSC was used to determine the melting range of the experimental alloys. Mechanical properties, ionic release and DE were statistically compared by ANOVA and Holm-Sidak multiple comparison test (a=0.05). RESULTS All commercially alloys belong to the Ag-Zn-Cu ternary system and consist a Ag rich face centered cubic (FCC) and Cu (FCC) phase. The former is the predominant phase also in experimental alloys. Conventional alloys demonstrated higherhardness, less ductility and lower melting rangers compared to experimental alloys. Immersion testing revealed the release of Cu and Zn ions from the commercially alloys and Ga ions from AgGa and AgGaSn while no ionic release was identified for AgIn and AgSn. All alloys failed tarnish testing according to ISO 10271 showing DE values much higher than the clinical acceptable limit (3.7). SIGNIFICANCE The conventional Ag based soldering alloys showed substantial differences in their microstructure, mechanical properties and ionic release, and thus different clinical performance is anticipated. Ga, Sn and In might be employed as alloying addition to modify the properties of Ag brazing alloys.

Structure/property relationships in orthodontic polymers

Polymers are characterized by a mixture of the directional, localized covalent, and ionic modes of interatomic bonding, in contrast to metals that have nondirectional and nonlocalized interatomic bonding. While strong primary bonding exists along the carbon-carbon backbone of organic polymer chains, much weaker secondary bonding exists between adjacent non-crosslinked chains. Combining these modes of bonding with the myriad of different polymer structures, along with the absence of a long-range three-dimensional repeating pattern for the atomic/molecular arrangement, polymers are generally noncrystalline materials with much different mechanical properties from metals. (Special processing techniques can yield polymeric materials with substantial crystalline structures.) This chapter focuses on how the mechanical properties of polymers are related to the general aspects of their structure, without examining the individual monomeric structural units. The reader should review textbooks on polymeric materials and dental materials for details about these structures.

The effect of rheumatoid arthritis and functional loading on the structure of the mandibular condyle in a transgenic mouse model: An FTIR study.

OBJECTIVE The objective of the present study was to investigate the effect of rheumatoid arthritis and functional loading through diet modification on the biochemical properties of the mandibular condyle in a transgenic mouse model and compare with healthy littermates. DESIGN Twenty three, 4-week old hybrid male mice were used. Eleven were of transgenic line hTNF 197 (Tg 197 - with rheumatoid arthritis - RA) and 12 healthy littermates, both from mixed background CBAxC57BL/6. Four groups of mice were formed. Group 1 [n =5, RA-hard] included transgenic mice and received ordinary (hard) diet; group 2 [n=6, RA-soft] included transgenic line and received soft diet; group 3 [n=6, control-hard] were healthy littermates receiving ordinary (hard) diet and group 4 [n=6, control-soft] were healthy littermates with soft diet. Experimental period was 28 days. Following sacrifice, the mandibular condyles were subjected to micro-attenuated reflection Fourier transform infrared spectroscopy (micro-ATR FTIR) to reveal collagen/proteoglycan conformation of the condylar cartilage, while resin-embedded and metallographically polished specimens were evaluated through reflection FTIR microscopy to identify mineralization status of the corresponding condylar bone. RESULTS The multivariable analysis revealed significantly lower a-helix to amide I percentage area ratio for the transgenic animals after adjusting for diet (β=-4.29, 95% CIs: -8.52, -0.06; p=0.04). Mineral phase indices did not differ significantly between RA and control groups regardless the type of diet. CONCLUSIONS Internal derangement of the anatomical structure with denaturation in the collagen structural components of the mandibular condyles of the RA animals was found, while no association with functional loading through diet modification was recorded.

Applications of Current Technologies for Nondestructive Testing of Dental Biomaterials

Youssef S. Al Jabbari1,2,* and Spiros Zinelis3,4 1Director, Dental Biomaterials Research and Development Chair, School of Dentistry, King Saud University, Riyadh, 2Prosthetic Dental Sciences Department, School of Dentistry, King Saud University, Riyadh, 3Department of Biomaterials, School of Dentistry, University of Athens, Athens 4Dental Biomaterials Research and Development Chair, School of Dentistry, King Saud University, Riyadh 1,2,4Saudi Arabia 3Greece