Brushing-induced surface roughness of nickel-, palladium-, and gold-based dental casting alloys

Improved Corrosion Resistance and Cytotoxicity of Nickel-based alloy using Novel Plasma processing technique.. [DOI: 10.21203/rs.3.rs-3200844/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Nickel-based (NiCr) alloys are mostly utilized in the dental industry because of their good corrosion resistance, ease of casting, and adequate thermal coefficient of friction with ceramic porcelain. However, leakage of toxic metal ions (Ni and Cr) due to breakage or damage of protective metal oxide layers in aggressive body fluids affects corrosion resistance, tribological properties, and cytotoxicity. These drawbacks ultimately affect the biocompatibility of NiCr alloys for medical applications. This study employs magnetron sputtering in conjunction with cathodic cage plasma nitriding (CCPN) to perform a novel duplex plasma treatment on Ni-Cr alloy. Moreover, the cathodic cage plasma-treated TiN (CCPN-TiN) samples showed further enhanced corrosion resistance and low metal ion leakage. These findings made duplex plasma treatment an efficient method for the surface modification of metallic alloys against the leaching of toxic ions in chloride-aggressive electrolytes, thus proving an excellent strategy for various biomedical applications.

The apoptotic and autophagic effects of cast Au-Pt, and differently manufactured Co-Cr and cp-Ti on three-dimensional oral mucosal model

The application of digitally manufactured dental metals has aroused the attention on their biocompatibilities. Three-dimensional oral mucosal model (3D OMM) would provide excellent assessments to the biocompatibility. In the current study, we set to measure metal ion release levels in the extracts of cast gold-platinum alloy (Au-Pt), differently manufactured cobalt-chromium alloy (Co-Cr) and commercially pure titanium (cp-Ti). We further tested two scaffold materials of 3D OMM to determine the better one for the succedent work. Lastly, we evaluated the apoptotic and autophagic effects of cast Au-Pt, and differently manufactured Co-Cr and cp-Ti on mucosal cells based on 3D OMM. We found that, in the construction of 3D OMM, Matrigel showed better performance than bovine acellular dermal matrix. Thus, Matrigel was chosen to construct the 3D OMM in the succedent studies. The results of ion release and biological assessments showed that, firstly, cast Au-Pt and cp-Ti triggered less early apoptotic cells and ion release than cast Co-Cr, implying better chemical stability and biocompatibility of them; secondly, digitally manufactured (including CAD/CAM milling and SLM) Co-Cr showed significantly lower ion release levels and lesser early apoptotic effects on 3D OMM as compared to the cast one. Although cast cp-Ti released much more ions than CAD/CAM milling one, manufacturing methods had no impact on apoptotic effect of cp-Ti. Therefore, we believe that digital methods possess same or even better chemical stability and biocompatibility than conventional casting one. Thirdly, although increased autophagic levels are observed in all test groups, so far there is no evidence that the test metals trigger different levels of autophagy as compared to each other. In addition, correlation analysis indicates that Co, W, and Mn appear to be the potential inducements for the apoptotic and autophagic effects of Co-Cr.

Tribological characteristics of dental metal biomaterials

The paper is a report of the examination of the tribological wear characteristics of certain dental metal biomaterials. In the study, tests were undertaken on the following materials: 316L steel, NiCrMo alloy, technically pure titanium (ASTM-grade 2) and Ti6Al4V ELI alloy (ASTM-grade 5). The tribological tests were performed in artificial saliva to determine the coefficient of friction and wear factor; the traces of wear were then ascertained through SEM. The significance of variations in the wear factor, was subsequently assessed by the U Mann-Whitney test. The resistance to wear in the ball-on-disc test under in vitro conditions was observed for the tested materials in the following order: NiCrMo>316L>Ti6Al4V>Ti grade 2.

Effect of casting atmosphere on the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium

STATEMENT OF PROBLEM

The marginal adaptation of prosthetic crowns is still a significant clinical problem.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium under different casting conditions.

MATERIAL AND METHODS

Four casting conditions were selected: flame-torch, induction/argon, induction/vacuum, and induction/air; and 2 alloys were used, Ni-Cr-Be and Ni-Cr. For each group, 10 metal specimens were prepared. Silicone indirect impressions and analysis of the degree of rounding were used to evaluate the marginal deficiencies of metal copings, and a standardized device for the setting pressure associated with optical microscopy was used to analyze the marginal misfit. Results were evaluated with 2-way ANOVA (α=.05), followed by the Tukey honest significant difference post hoc test, and the Pearson correlation test (α=.05).

RESULTS

Alloy (P<.001) and casting technique (P<.001) were shown to affect marginal deficiencies. The Ni-Cr cast using the torch technique showed the highest marginal deficiency, and the Ni-Cr-Be cast in a controlled argon atmosphere showed the lowest (P<.001). Alloy (P=.472) and casting techniques (P=.206) did not affect the marginal misfit, but significant differences were found in the interaction (P=.001); the lowest misfit was achieved using the Ni-Cr-Be, and the highest misfit occurred with the molten Ni-Cr, using the cast torch technique. No correlation was found between deficiency and marginal misfit (r=.04, P=.69).

CONCLUSIONS

The interactions demonstrated that the alloy containing beryllium that was cast in an argon atmosphere led to reduced marginal deficiency. Improved marginal adaptation can be achieved for the same alloy by using the torch technique.

Effect of toothbrushing on shade and surface roughness of extrinsically stained pressable ceramics

STATEMENT OF PROBLEM

The effect of toothbrushing on extrinsically stained pressable ceramic materials is unknown.

PURPOSE

The purpose of this in vitro study was to investigate the effects of toothbrushing on the shade and surface roughness of extrinsically stained, pressable ceramics.

MATERIAL AND METHODS

Two materials, leucite-based (IPS Empress Esthetic [EE]; Ivoclar Vivadent AG) and lithium disilicate-based ceramic (IPS e.max Press [EP]; Ivoclar Vivadent AG), were studied. For each material, 24 disk-shaped specimens, 10 mm (diameter)×3 mm (height) were fabricated. Three different methods (n=8) of applying extrinsic stains were performed on each material: glazed only (G, control group); stained then glazed (SG); and stained and glazed together (T). The specimens were brushed with a multistation brushing machine under a load of 1.96 N at a rate of 90 strokes per minute with a soft and straight toothbrush (Oral-B #35) and a 1:1 toothpaste and distilled water slurry. Shade and roughness were measured at baseline and at 72, 144, 216, and 288 hours, which is equivalent to 3, 6, 9, and 12 years of simulated toothbrushing for 2 minutes twice a day. A repeated measures ANOVA with staining technique as a fixed factor was used to evaluate shade and roughness (α=.05).

RESULTS

For EE groups, no significant change was found after 12 years of simulated toothbrushing regarding shade and surface roughness, irrespective of staining techniques (P>.05). However, EP groups demonstrated a significant shade change and an increase in surface roughness after 12 years of simulated toothbrushing. Shade change was found to depend on the method of applying stain. For the EP-SG technique, a significant shade change was observed only at the 9- to 12-year interval (P=.047). However, the EP-T technique demonstrated a significant difference in shade between baseline and 3 years (P=.005) and in the 6- to 9-year interval (P=.005). Surface roughness was only significantly affected at baseline and 3 years for the EP-T group (P=.005).

CONCLUSIONS

For the shade and surface roughness of the EE groups, no statistically significant difference was found after 12 years of toothbrushing, irrespective of the staining technique. The shade and surface roughness of the EP groups were significantly statistically affected by toothbrushing time; only shade changes were found to depend on technique.

Evaluation and comparison of the marginal adaptation of two different substructure materials

PURPOSE

In this study, we aimed to evaluate the amount of marginal gap with two different substructure materials using identical margin preparations.

MATERIALS AND METHODS

Twenty stainless steel models with a chamfer were prepared with a CNC device. Marginal gap measurements of the galvano copings on these stainless steel models and Co-Cr copings obtained by a laser-sintering method were made with a stereomicroscope device before and after the cementation process and surface properties were evaluated by scanning electron microscopy (SEM). A dependent t-test was used to compare the mean of the two groups for normally distributed data, and two-way variance analysis was used for more than two data sets. Pearson's correlation analysis was also performed to assess relationships between variables.

RESULTS

According to the results obtained, the marginal gap in the galvano copings before cementation was measured as, on average, 24.47 ± 5.82 µm before and 35.11 ± 6.52 µm after cementation; in the laser-sintered Co-Cr structure, it was, on average, 60.45 ± 8.87 µm before and 69.33 ± 9.03 µm after cementation. A highly significant difference (P<.001) was found in marginal gap measurements of galvano copings and a significant difference (P<.05) was found in marginal gap measurements of the laser-sintered Co-Cr copings. According to the SEM examination, surface properties of laser sintered Co-Cr copings showed rougher structure than galvano copings. The galvano copings showed a very smooth surface.

CONCLUSION

Marginal gaps values of both groups before and after cementation were within the clinically acceptable level. The smallest marginal gaps occurred with the use of galvano copings.

Nickel alloys in the oral environment

The use of nickel casting alloys for long-term restorations in dentistry has long been controversial. A 'tug-of-war' between economic, engineering and biological considerations is central to this controversy; nickel-casting alloys have low costs and favorable physical properties, but are corrosion-prone in the oral environment. Clinicians and researchers have questioned the safety of nickel-containing dental alloys because several nickel compounds are known to cause adverse biological effects in vivo and in vitro in contexts outside of dentistry. The debate revolves around the extent to which corrosion products from oral restorations cause intraoral or systemic biological problems. Current evidence suggests that nickel alloys may be used successfully and safely in dentistry if clinical risks are taken into account. However, these alloys may cause significant clinical problems, primarily allergenic and inflammatory, if the risks are ignored.

Retrieval analysis of different orthodontic brackets: the applicability of electron microprobe techniques for determining material heterogeneities and corrosive potential

Objective

The objective of this study was to investigate the applicability of micro-analytical methods with high spatial resolution to the characterization of the composition and corrosion behavior of two bracket systems.

Material and methods

The surfaces of six nickel-free brackets and six nickel-containing brackets were examined for signs of corrosion and qualitative surface analysis using an electron probe microanalyzer (EPMA), prior to bonding to patient's tooth surfaces and four months after clinical use. The surfaces were characterized qualitatively by secondary electron (SE) images and back scattered electron (BSE) images in both compositional and topographical mode. Qualitative and quantitative wavelength-dispersive analyses were performed for different elements, and by utilizing qualitative analysis the relative concentration of selected elements was mapped two-dimensionally. The absolute concentration of the elements was determined in specially prepared brackets by quantitative analysis using pure element standards for calibration and calculating correction-factors (ZAF).

Results

Clear differences were observed between the different bracket types. The nickel-containing stainless steel brackets consist of two separate pieces joined by a brazing alloy. Compositional analysis revealed two different alloy compositions, and reaction zones on both sides of the brazing alloy. The nickel-free bracket was a single piece with only slight variation in element concentration, but had a significantly rougher surface. After clinical use, no corrosive phenomena were detectable with the methods applied. Traces of intraoral wear at the contact areas between the bracket slot and the arch wire were verified.

Conclusion

Electron probe microanalysis is a valuable tool for the characterization of element distribution and quantitative analysis for corrosion studies.

Comparison of the cytogenotoxicity induced by five different dental alloys using four in vitro assays

The purpose of present investigation was to compare the cyto-genotoxicity induced by five dental alloys in vitro. The cyto-genotoxicity induced by five dental alloy extracts on human B lymphoblast cells was assessed with neutral red uptake (NRU) , CCK-8, comet and micronucleus (CBMN) assays in vitro, respectively. The results of in vitro comet and CBMN assays indicated that DNA damage (% tail DNA) and micronucleus frequencies (MNFs) in all exposure groups did not significantly increase, as compared with the control group. However, the results of NRU and CCK-8 assays demonstrated that there were to some extent differences in the cytotoxicity among 5 dental alloy extracts in vitro. The cytotoxicity may be relevant to the Ni and Be ions released in the alloy extract.