Bacterial translocation and microgap formation at a novel conical indexed implant abutment system for single crowns.

OBJECTIVES: A conometric concept was recently introduced in which conical implant abutments hold the matching crown copings by friction alone, eliminating the need for cement or screws. The aim of this in vitro study was to assess the presence of microgap formation and bacterial leakage at the Acuris conometric restorative interface of three different implant abutment systems. MATERIAL AND METHODS: A total of 75 Acuris samples of three implant-abutment systems (Ankylos, Astra Tech EV, Xive) were subjected to microbiological (n = 60) and scanning electron microscopic (SEM) investigation (n = 15). Bacterial migration into and out of the conical coupling system were analyzed in an anaerobic workstation for 48, 96, 144, and 192 h. Bacterial DNA quantification using qrt-PCR was performed at each time point. The precision of the conometric coupling and internal fit of cemented CAD/CAM crowns on corresponding Acuris TiN copings were determined by means of SEM. RESULTS: qrt-PCR results failed to demonstrate microbial leakage from or into the Acuris system. SEM analysis revealed minute punctate microgaps at the apical aspect of the conometric junction (2.04 to 2.64 µm), while mean cement gaps of 12 to 145 µm were observed at the crown-coping interface. CONCLUSIONS: The prosthetic morse taper connection of all systems examined does not allow bacterial passage. Marginal integrity and internal luting gap between the ceramic crown and the coping remained within the clinically acceptable limits. CLINICAL RELEVANCE: Conometrically seated single crowns provide sufficient sealing efficiency, relocating potential misfits from the crown-abutment interface to the crown-coping interface.

Impact of sterilization treatments on biodegradability and cytocompatibility of zinc-based implant materials.

Biodegradable zinc (Zn) and Zn-based alloys have been recognized as promising biomaterials for biomedical implants. Sterilization is an essential step in handling Zn-based implants before their use in clinical practice and there are various sterilization methods are available. However, how these treatments influence the Zn-based biomaterials remains unknown and is of critical relevance. In this study, three commonly-applied standard sterilization methods, namely gamma irradiation, hydrogen peroxide gas plasma and steam autoclave, were used on pure Zn and Zn3Cu (wt%) alloy. The treated Zn and ZnCu alloy were investigated to compare the different influences of sterilizations on surface characteristics, transient and long-term degradation behavior and cytotoxicity of Zn and Zn alloy. Our results indicate that autoclaving brought about apparently a formation of inhomogeneous zinc oxide film whereas the other two methods produced no apparent alterations on the material surfaces. Consequently, the samples after autoclaving showed significantly faster degradation rates and more severe localized corrosion, especially for the ZnCu alloy, owing to the incomplete covering and unstable zinc oxide layer. Moreover, the autoclave-treated Zn and ZnCu alloy exhibited apparent cytotoxic effects towards fibroblasts, which may be due to the excessive Zn ion releasing and its local concentration exceeds the cellular tolerance capacity. In contrast, gamma irradiation and hydrogen peroxide gas plasma had no apparent adverse effects on the biodegradability and cytocompatibility of Zn and ZnCu alloy. Our findings may have significant implications regarding the selection of suitable sterilization methods for Zn-based implant materials among others.

A Novel C1-Esterase Inhibitor Oxygenator Coating Prevents FXII Activation in Human Blood.

The limited hemocompatibility of currently used oxygenator membranes prevents long-term use of artificial lungs in patients with lung failure. To improve hemocompatibility, we developed a novel covalent C1-esterase inhibitor (C1-INH) coating. Besides complement inhibition, C1-INH also prevents FXII activation, a very early event of contact phase activation at the crossroads of coagulation and inflammation. Covalently coated heparin, as the current anticoagulation gold standard, served as control. Additionally, a combination of both coatings (C1-INH/heparin) was established. The coatings were tested for their hemocompatibility by dynamic incubation with freshly drawn human whole blood. The analysis of various blood and plasma parameters revealed that C1-INH-containing coatings were able to markedly reduce FXIIa activity compared to heparin coating. Combined C1-INH/heparin coatings yielded similarly low levels of thrombin-antithrombin III complex formation as heparin coating. In particular, adhesion of monocytes and platelets as well as the diminished formation of fibrin networks were observed for combined coatings. We could show for the first time that a covalent coating with complement inhibitor C1-INH was able to ameliorate hemocompatibility. Thus, the early inhibition of the coagulation cascade is likely to have far-reaching consequences for the other cross-reacting plasma protein pathways.

Bond strength of commercial veneering porcelain to experimental cast Ti-Cr alloy.

This study evaluated bond strengths of three commercial veneering porcelains to experimental cast titanium-chromium (Ti-Cr) alloy and commercially pure titanium (cp-Ti) via three-point bending test. After the bending test, the fractured specimens were analyzed using an electron probe microanalyzer (EPMA). The Ti-Cr specimens showed lower bond strengths than the cp-Ti specimens, irrespective of the layering porcelain material; however, all the strengths exceeded the minimum requirement of ISO 9693-1:2012 (>25 MPa). EPMA revealed that titanium and/or chromium elements were detected on the debonded porcelain surface of the Ti-Cr and cp-Ti specimens in the case of the higher bond strength. Contrastingly, the residual porcelain was retained on the metallic surface in the case of the lower bond strength. Although porcelain bonding to the titanium alloy is influenced by porcelain type, the Ti-Cr alloy could be feasible for porcelain-fused-to-metal restorations.

Correction: Li, P. et al. Mechanical Characteristics, In Vitro Degradation, Cytotoxicity, and Antibacterial Evaluation of Zn-4.0Ag Alloy as a Biodegradable Material. Int. J. Mol. Sci. 2018, 19, 755.

The authors wish to make the following corrections to this paper [...].

Response of human periosteal cells to degradation products of zinc and its alloy.

Zinc (Zn) and its alloys are proposed as promising resorbable materials for osteosynthesis implants. Detailed studies should be undertaken to clarify their properties in terms of degradability, biocompatibility and osteoinductivity. Degradation products of Zn alloys might affect directly adjacent cellular and tissue responses. Periosteal stem cells are responsible for participating in intramembranous ossification during fracture healing. The present study aims at examining possible effects emanating from Zn or Zn-4Ag (wt%) alloy degradation products on cell viability and osteogenic differentiation of a human immortalized cranial periosteal cell line (TAg cells). Therefore, a modified extraction method was used to investigate the degradation behavior of Zn and Zn-4Ag alloys under cell culture conditions. Compared with pure Zn, Zn-4Ag alloy showed almost fourfold higher degradation rates under cell culture conditions, while the associated degradation products had no adverse effects on cell viability. Osteogenic induction of TAg cells revealed that high concentration extracts significantly reduced calcium deposition of TAg cells, while low concentration extracts enhanced calcium deposition, indicating a dose-dependent effect of Zn ions. Our results give evidence that the observed cytotoxicity effects were determined by the released degradation products of Zn and Zn-4Ag alloys, rather than by degradation rates calculated by weight loss. Extracellular Zn ion concentration was found to modulate osteogenic differentiation of TAg cells. These findings provide significant implications and guidance for the development of Zn-based alloys with an optimized degradation behavior for Zn-based osteosynthesis implants.

Evaluation of a Zn-2Ag-1.8Au-0.2V Alloy for Absorbable Biocompatible Materials.

Zinc (Zn) and Zn-based alloys have been proposed as a new generation of absorbable metals mainly owing to the moderate degradation behavior of zinc between magnesium and iron. Nonetheless, mechanical strength of pure Zn is relatively poor, making it insufficient for the majority of clinical applications. In this study, a novel Zn-2Ag-1.8Au-0.2V (wt.%) alloy (Zn-Ag-Au-V) was fabricated and investigated for use as a potential absorbable biocompatible material. Microstructural characterization indicated an effective grain-refining effect on the Zn alloy after a thermomechanical treatment. Compared to pure Zn, the Zn-Ag-Au-V alloy showed significantly enhanced mechanical properties, with a yield strength of 168 MPa, an ultimate tensile strength of 233 MPa, and an elongation of 17%. Immersion test indicated that the degradation rate of the Zn-Ag-Au-V alloy in Dulbecco's phosphate buffered saline was approximately 7.34 ± 0.64 µm/year, thus being slightly lower than that of pure Zn. Biocompatibility tests with L929 and Saos-2 cells showed a moderate cytotoxicity, alloy extracts at 16.7%, and 10% concentration did not affect metabolic activity and cell proliferation. Plaque formation in vitro was reduced, the Zn-Ag-Au-V surface inhibited adhesion and biofilm formation by the early oral colonizer Streptococcus gordonii, indicating antibacterial properties of the alloy.

Investigation of zinc­copper alloys as potential materials for craniomaxillofacial osteosynthesis implants.

In this study, zinc­copper (ZnCu) alloys were investigated regarding their feasibility as absorbable metals for osteosynthesis implants, especially in the craniomaxillofacial area. Mechanical properties and in vitro corrosion behavior of as-rolled Zn-xCu (x = 1, 2 and 4 wt%) alloys were systematically evaluated and screened. The as-rolled Zn4Cu alloy had mechanical properties that were superior to the most absorbable craniomaxillofacial osteosynthesis materials recently reported. The addition of Cu to Zn showed to have no apparent effect on the corrosion rates of the samples. The rolling process on Zn and Zn1Cu resulted in more uniform corrosion than on as-cast counterparts after 28 days immersion. Furthermore, the Zn4Cu alloys exhibited no apparent cytotoxic effect towards L929, TAg or Saos-2 cells. Proliferation rates of TAg and Saos-2 cells were shown to be activated by specific Zn ion concentrations in the as-rolled Zn4Cu alloy extracts. Analysis of in vitro antibacterial properties revealed that the as-rolled Zn4Cu alloy possessed the potential to inhibit biofilm formation of mixed oral bacteria. We conclude that the as-rolled Zn4Cu alloy might be a promising material for fabrication of craniomaxillofacial osteosynthesis implants.

Selection of extraction medium influences cytotoxicity of zinc and its alloys.

Zinc (Zn) alloys have been considered as promising absorbable metals, mainly due to their moderate degradation rates ranging between magnesium alloys and iron alloys. The degradation behavior depends on the specific physiological environment. Released metallic ions and corrosion products directly influence biocompatibility. The initial contact of orthopedic implants or vascular stents after implantation will be with blood. In this study, fetal bovine serum (FBS) was used as a model system of blood components. We investigated the influence of FBS on in vitro degradation behavior and cytotoxicity of pure Zn, and Zn-4Ag and Zn-2Ag-1.8Au-0.2 V (wt%) alloys. The initial degradation rates in FBS were assessed and compared with the degradation and toxicity in four other common physiological model systems: DMEM cell culture medium ±â€¯FBS and McCoy's 5A medium ±â€¯FBS. Test samples in pure FBS showed the highest initial degradation rates, and accordingly, FBS supplemented media accelerated the degradation process as well. Moreover, an extract test according to ISO 10993-5 and -12 with L929 and Saos-2 cells was performed to investigate the role of FBS in the extraction medium. The cytotoxic effects observed in the tests were correlated with FBS-mediated Zn2+ release. These findings have significant implications regarding the selection of appropriate media for in vitro degradation and cytotoxicity evaluation of Zn and its alloys. STATEMENT OF SIGNIFICANCE: Metallic zinc and its alloys have been considered as promising biodegradable metals, mainly due to their moderate degradation rates. However, in vitro cytotoxicity tests according to the current ISO 10993 standard series are not suitable to predict biocompatibility of Zn alloys due to the inconsistent correlation between in vitro and in vitro biocompatibility. In this study, we show that the outcomes of standardized in vitro cytotoxicity tests of Zn and Zn alloys are influenced by fetal bovine serum in the extraction vehicle because FBS promotes Zn2+ release during the extraction process. The results of the study provide significant information for selection of appropriate model systems to evaluate in vitro degradation behavior and cytotoxicity.

Nine prophylactic polishing pastes: impact on discoloration, gloss, and surface properties of a CAD/CAM resin composite.

OBJECTIVES: To investigate discoloration reduction and changes of surface properties of a CAD/CAM resin composite after 14 days´ storage in red wine and polishing with nine different prophylactic polishing pastes (PPPs). MATERIALS AND METHODS: Rectangular discs (N = 172) were fabricated and polished (P4000) using GC Cerasmart (GC Europe) to investigate different polishing protocols with 1-4 related descending PPPs (22 in total): Cleanic/CLE-Kerr, CleanJoy/CLJ-Voco, Clean Polish/Super Polish/SPO-Kerr, Clinpro Prophy Paste/CPP-3M, Détartrine/DET-Septodont, Nupro/NUP-Dentsply Sirona, Prophy Paste CCS/CCS-Directa, Proxyt/PXT-Ivoclar Vivadent, and Zircate/ZIR Prophy Paste-Dentsply Sirona. Surface properties (roughness values (RV)/Ra, Rz, Rv, surface free energy (SFE), surface gloss (G), and discoloration (ΔE)) were analyzed before and after storage and additional polishing. Data were examined using Kolmogorov-Smirnov test, three-way ANOVA followed by Tukey-B post hoc, Mann-Whitney U, and Kruskal-Wallis H tests (α < 0.05). RESULTS: Regarding RV, CLE, followed by CCS, and CPP showed the highest values; the lowest presented SPO and DET (p < 0.001). No impact of PPP was observed on ΔE values (p = 0.160). The lowest SFE presented DET, followed by SPO; highest showed CCS followed by NUP and CPP (p < 0.001). Within G, lowest values were observed for CLE and NUP, followed by CCS, ZIP, and CLJ (p < 0.001); the highest presented SPO (p < 0.001). Polishing showed generally a positive impact on SFE values (p < 0.001-p = 0.007), except ZIP (p = 0.322) and CLE (p = 0.083). G increased and RV decreased after polishing (p < 0.001), except SPO, with no significant change for G (p = 0.786). CONCLUSIONS: Polishing with PPPs improves the surface properties and is generally recommended. The choice of PPP has a minor role in removing discolorations. Multi-step systems should be carried out conscientiously. CLINICAL RELEVANCE: The proper selection of PPP is essential for the clinical outcome of surface properties of prosthetic restorations. Not every polishing paste leads to the same final surface quality.

Effect of slow-cooling protocol on biaxial flexural strengths of bilayered porcelain-ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks.

OBJECTIVE: The present study investigated the biaxial flexural strengths of bilayered ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks with various layering porcelains veneered using a slow-cooling protocol. METHODS: Five porcelain materials (VITA VM9, Cercon Ceram Kiss, and Vintage ZR with experimental coefficient of thermal expansions; CTEs of 8.45, 9.04, and 9.61ppm/°C) were veneered on Ce-TZP/A disks and slow-cooled after firing to fabricate bilayered specimens (core-to-porcelain thickness: 0.8mm/1.5mm). Biaxial flexural strengths of the specimens with the porcelain layer in tension were tested based on the piston-on-three-ball method (ISO 6872:2008). The data were statistically analyzed using Weibull distribution and Fisher's exact test. RESULTS: Tensile stresses were observed in the entire porcelain layer while compressive stress at the surface of the Ce-TZP/A layer shifted to tensile stress at the interface between the materials. The cases of small CTE mismatches between the materials showed high Weibull characteristic strengths at the internal and external surfaces of the specimens, except the VM9 group (CTE: 9.0-9.2ppm/°C). The maximum tensile stress was observed on the surface of the porcelain layer, where cracks originated and continuously propagated into the Ce-TZP layer. The Ce-TZP/A fractured into two pieces for large CTE mismatches between the materials, resulting in significantly lower flexural strengths than those fracturing into three pieces for small CTE mismatches. SIGNIFICANCE: Flexural strengths and fracture behaviors of bilayered porcelain-Ce-TZP/A disks were influenced by the CTE mismatches, and a small CTE mismatch between the materials was preferred when using a slow-cooling protocol.

Comparative Analysis of Mechanical Properties and Metal-Ceramic Bond Strength of Co-Cr Dental Alloy Fabricated by Different Manufacturing Processes.

Cobalt-chromium (Co-Cr) alloy is a widely used base material for dental fixed prostheses. These restorations can be produced through casting technique, subtractive or additive manufacturing technologies. However, limited information is available regarding the influence of manufacturing techniques on the properties of Co-Cr alloy since most studies used different chemical compositions of Co-Cr alloy for different manufacturing methods. This study compares the mechanical properties, metal-ceramic bond strength, and microstructures of specimens produced by casting, milling, and selective laser melting (SLM) from one single Co-Cr alloy composition. The mechanical properties of the alloy were investigated by tensile and Vickers hardness tests, and metal-ceramic bond strength was determined by three-point bending. Scanning electron microscopy (SEM) with backscattered electron (BSE) images and optical microphotographs were used to analyze the surface microstructures. Compared with the casting and milling techniques, SLM Co-Cr alloy specimens indicated enhanced mechanical properties and comparable metal-ceramic bond strength. Besides, the microstructures of the SLM specimens showed finer grains with more second phase particles than the casting and milling specimens. The results of our study indicate that SLM might be superior to traditional techniques for the manufacturing of fixed dental restorations.

Biaxial flexural strength of the bilayered disk composed of ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) and veneering porcelain.

OBJECTIVE: Herein we investigated the flexural strengths of bilayered ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks using different veneering porcelains. METHODS: Commercial (VITA VM9, Cercon Ceram Kiss, and IPS e.max Ceram) and experimental porcelains (Vintage ZR with coefficient of thermal expansions: CTEs of 8.45, 9.04, and 9.61ppm/°C) with various layer thicknesses (1.0, 1.5, and 2.0mm) were applied to Ce-TZP/A disks (0.8mm thickness, n=180). Biaxial flexural tests of the specimens with the porcelain layer in tension were evaluated based on the piston-on-three-ball method (ISO 6872: 2008). The calculated strengths were statistically analyzed using the two-parameter Weibull distribution with the maximum likelihood estimation. RESULTS: Although no significant differences were observed among the experimental porcelains, most specimens with the thinner layer of commercial porcelain showed higher Weibull characteristic strengths at the external surfaces than those with the thicker layer. Irrespective of the porcelain material, the thinner porcelain layer showed significantly higher strengths at the interface between the layers. Fracture origins were always observed at the bottom surface and continuously propagated into Ce-TZP/A substrates. The maximum tensile stress was located at the interface in specimens with the 1.0mm porcelain layer, except for IPS e.max Ceram. Porcelain delamination was dominant in the case of the higher CTE value and thicker layer thickness of the porcelain. SIGNIFICANCE: The calculated biaxial flexural strengths and the stress distributions for bilayered Ce-TZP/A disks were dependent on the porcelain materials. Optimum behavior was observed for a combination of a small CTE mismatch between the materials and a low core-to-porcelain thickness ratio.

Mechanical Characteristics, In Vitro Degradation, Cytotoxicity, and Antibacterial Evaluation of Zn-4.0Ag Alloy as a Biodegradable Material.

Zn-based biodegradable metallic materials have been regarded as new potential biomaterials for use as biodegradable implants, mainly because of the ideal degradation rate compared with those of Mg-based alloys and Fe-based alloys. In this study, we developed and investigated a novel Zn-4 wt % Ag alloy as a potential biodegradable metal. A thermomechanical treatment was applied to refine the microstructure and, consequently, to improve the mechanical properties, compared to pure Zn. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the Zn-4Ag alloy are 157 MPa, 261 MPa, and 37%, respectively. The corrosion rate of Zn-4Ag calculated from released Zn ions in DMEM extracts is approximately 10.75 ± 0.16 µg cm-2 day-1, which is higher than that of pure Zn [corrected]. In vitro cytotoxicity tests showed that the Zn-4Ag alloy exhibits acceptable toxicity to L929 and Saos-2 cells, and could effectively inhibit initial bacteria adhesion. This study shows that the Zn-4Ag exhibits excellent mechanical properties, predictable degradation behavior, acceptable biocompatibility, and effective antibacterial properties, which make it a candidate biodegradable material.

Influence of a surface conditioner to pre-sintered zirconia on the biaxial flexural strength and phase transformation.

OBJECTIVES: To assess the influence of a surface conditioner applied to pre-sintered yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) on the biaxial flexural strength and phase transformation. METHODS: Conditioner-coated specimens (12mm diameter×0.8mm thickness) were prepared by application of a slurry conditioner using a brush on pre-sintered Y-TZP discs, followed by sandblasting with 50-µm Al2O3 after sintering (C-SB) or no further treatment (C-NT). The remaining conditioner-free specimens were subjected to sandblasting before sintering (NC-SB) or were maintained without treatment (NC-NT). Surface roughness measurements and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (SEM-EDX) were performed for surface characterizations. The phase transformation of Y-TZP was identified by X-ray diffraction (XRD), and the biaxial flexural strength was measured using the piston-on-three-ball test according to ISO 6872:2015. The data were analyzed using nonparametric Kruskal-Wallis tests and Weibull distributions with the maximum likelihood estimation. RESULTS: Sandblasting resulted in significantly rougher surfaces, irrespective of conditioner application. Conditioner layers were observed on surfaces in the C-NT and C-SB specimens. Monoclinic contents were present in a very small amount in the C-SB specimens. Both median biaxial flexural and characteristic strengths of all specimens exceeded ISO 6872:2015 requirements (Class 5: >800MPa), except the NC-SB specimens which showed significantly the lowest strength (p<0.001). Although no statistical difference was observed in Weibull modulus among the specimens (p=0.598), the NC-SB specimens showed the highest. SIGNIFICANCE: Surface conditioner application does not affect the biaxial flexural strength and phase stability of Y-TZP and can be considered practical for clinical use.

Influence of a bonding agent on the bond strength between a dental Co-Cr alloy and nine different veneering porcelains.

Adequate bonding between dental veneering porcelains and non-precious metal alloys is a main factor for the long-term functionality of porcelain fused to metal restorations. Although a huge number of veneering porcelains are on the market, only few studies have reported about the role of bonding agents for the bond strength at their respective interface to cobalt-chromium (Co-Cr). The aim of this study was to compare the influence of a metal-ceramic bonding agent for Co-Cr alloys on the bond strength of metal-ceramic systems. The bond strength test was done according to ISO 9693 with additional detection of the first acoustic crack initiated signal while testing. The bonding agent had only minor effects on the bond strength of the different Co-Cr/ceramic systems. Only three of the nine studied systems showed statistically significant differences (p<0.05) upon applying the bonding agent. Scanning electron microscopy (SEM) showed cracks predominantly caused by adhesive failure. Based on this study, Co-Cr alloys veneered with porcelains with and without a bonding agent exceeded the minimum bond strength of 25 MPa required according to ISO 9693. However, if bond strength values based on acoustic signals were calculated, values below the threshold of 25 MPa could be observed. Such findings are important for failures caused by the occurrence of early cracks.

Influence of Different Framework Designs on the Fracture Properties of Ceria-Stabilized Tetragonal Zirconia/Alumina-Based All-Ceramic Crowns.

The aim of this study was to evaluate the fracture load and failure mode of all-ceramic crowns with different ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/A) framework designs. Four frameworks (anatomical shape: AS, with a buccal or lingual supporting structure: BS and LS, or buccal and lingual supporting structures: BLS) were fabricated. All frameworks were veneered with porcelain to fabricate all-ceramic crowns followed by cementation to tooth analogs. The fracture load of each crown either without or with pre-loading (1.2 million cycles, 49 N) was measured. The failure mode was classified into partial or complete fracture. Differences were tested for significance (p < 0.05) by a two-way Analysis of Variance (ANOVA), followed by Tukey's test and by Fisher's exact test, respectively. Without pre-loading, supporting structures did not influence the fracture load or failure mode. Partial fractures were the most common failure mode. Pre-loading promoted the severity of the failure mode, although the fracture load among the framework designs was not influenced. In the AS group, prefailures were observed during pre-loading, and complete fractures were significantly increased after pre-loading. In contrast, the failure mode of the BLS group remained unchanged, showing only partial fracture even after pre-loading. This Ce-TZP/A framework design, comprised of an anatomical shape with additional buccal and lingual structures, has the potential to reduce the chipping of the veneering porcelain.

Influence of Pre-Sintered Zirconia Surface Conditioning on Shear Bond Strength to Resin Cement.

This study analyzed the shear bond strength (SBS) of resin composite on zirconia surface to which a specific conditioner was applied before sintering. After sintering of either conditioner-coated or uncoated specimens, both groups were divided into three subgroups by their respective surface modifications (n = 10 per group): no further treatment; etched with hydrofluoric acid; and sandblasted with 50 µm Al2O3 particles. Surfaces were characterized by measuring different surface roughness parameters (e.g., Ra and Rmax) and water contact angles. Half of the specimens underwent thermocycling (10,000 cycles, 5-55 °C) after self-adhesive resin cement build-up. The SBSs were measured using a universal testing machine, and the failure modes were analyzed by microscopy. Data were analyzed by nonparametric and parametric tests followed by post-hoc comparisons (α = 0.05). Conditioner-coated specimens increased both surface roughness and hydrophilicity (p < 0.01). In the non-thermocycled condition, sandblasted surfaces showed higher SBSs than other modifications, irrespective of conditioner application (p < 0.05). Adhesive fractures were commonly observed in the specimens. Thermocycling favored debonding and decreased SBSs. However, conditioner-coated specimens upon sandblasting showed the highest SBS (p < 0.05) and mixed fractures were partially observed. The combination of conditioner application before sintering and sandblasting after sintering showed the highest shear bond strength and indicated improvements concerning the failure mode.

Influence of the Conditioning Method for Pre-Sintered Zirconia on the Shear Bond Strength of Bilayered Porcelain/Zirconia.

This study evaluated the bond strength of veneering porcelain with an experimental conditioner-coated zirconia. Pre-sintered Y-TZP specimens (n = 44) were divided in two groups based on conditioning type. After sintering, all sample surfaces were sandblasted and layered with veneering porcelain. Additionally, half of the specimens in each group underwent thermal cycling (10,000 cycles, 5-55 °C), and all shear bond strengths were measured. After testing, the failure mode of each fractured specimen was determined. Differences were tested by parametric and Fisher's exact tests (α = 0.05). The differences in bond strength were not statistically significant. Adhesive fractures were dominantly observed for the non-thermal cycled specimens. After thermal cycling, the conditioner-coated group showed cohesive and mixed fractures (p = 0.0021), whereas the uncoated group showed more adhesive fractures (p = 0.0021). Conditioning of the pre-sintered Y-TZP did not change the shear bond strength of the veneering porcelain, but did improve the failure mode after thermal cycling.

UV-A and UV-C light induced hydrophilization of dental implants.

OBJECTIVES: Wettability is increasingly considered to be an important factor determining biological responses to implant materials. In this context, the purpose of this study was to compare the dynamic wettability of dental implants made from different bulk materials and modified by different surface modifications, and to analyze the respective changes of wettability upon irradiating these implants by UV-A or UV-C light. METHODS: Four original screw-type implants were investigated: One grit-blasted/acid-etched and one anodically oxidized titanium, one zirconia and one polyetheretherketone implant. Additionally, experimental, screwless, machined titanium cylinders were included in the study. Part of that cylinders and of blasted/etched implants were further modified by a magnetron-sputtered photocatalytic anatase thin film. Scanning electron microscopy was used to investigate the surface micro- and nanostructures. Samples were treated by UV-A (382nm, 25mWcm(-2)) and UV-C (260nm, 15mWcm(-2)) for entire 40min, respectively, and their wettability was quantified by dynamic contact angle (CA) analysis from multi-loop Wilhelmy experiments. RESULTS: All implants are characterized by submicron- and nanosized surface features. Unexposed implants were hydrophobic (CA>90°). Upon UV-A, solely the implants with anatase coating became superhydrophilic (CA<5°). Upon UV-C, the blasted/etched implants turned superhydrophilic, the anodized titanium and the zirconia implants were considerably (CA=34° and 27°, respectively) and the PEEK implants slightly (CA=79°) hydrophilized. SIGNIFICANCE: The wettability of implant surfaces can be improved by UV irradiation. The efficiency of UV-A and UV-C irradiation to lower the CA by photocatalysis or photolysis, however, is strongly dependent on the specific material and surface. Thus, attempts to photofunctionalize these surfaces by irradiation is expected to result in a different pattern of bioresponses.