Toothbrushing causes elemental release from dental casting alloys over extended intervals

Metal Ions Release from Welded Co-Cr Dental Alloys

Cobalt-chromium alloys (Co-Cr) are widely used in dentistry due to their excellent mechanical properties and corrosion resistance. Since prosthetic materials must be permanently stable in the oral cavity, it is very important to determine the release of ions from alloys in the oral cavity. In dentistry today, metals and alloys are mainly joined by laser and tungsten inert gas (TIG) welding. Therefore, in this work, the release of metal ions from six different Co-Cr alloys joined by these two welding methods was quantified to determine the effects of the welding method on an ion release. Static immersion tests, atomic absorption spectrometry and statistical analysis were performed for this purpose. The results showed that laser-welded alloys release a lower amount of metal ions compared to TIG-welded alloys.

The Effect of Porcelain Firing on Electrochemical Behavior of a Dental Alloy in Hydrogen Peroxide

PURPOSE

The aim of this study was to evaluate changes in electrochemical corrosion properties of porcelain firing simulated nickel-chromium dental casting alloy exposed to a 10% hydrogen peroxide bleaching agent.

MATERIALS AND METHODS

The electrochemical corrosion behavior of a Ni-Cr alloy was evaluated by cyclic polarization test in the aerated electrolyte (pH = 6.5). Test groups were produced in as-cast (group 1, control group) and simulated porcelain firing (group 2: heat-treated/mean value; group 3: heat-treated/cycle) conditions. Scanning electron microscopy (SEM) was also used to examine the alloy surfaces before and after the corrosion test.

RESULTS

The ranking of the groups with respect to Ecorr and Icorr was as follows: 1, 2, 3 and 3, 1, 2, respectively. Group 3 exhibited the greatest and group 2 displayed the least corrosion tendencies. An increase in corrosion rates was observed after heat treatment/cycle state. Post-corrosion SEM photographs were also consistent with the test results.

CONCLUSION

Within the parameters of this study, a single heat treatment is insufficient to cause upheaval in corrosion behavior of a Ni-Cr alloy subjected to 10% hydrogen peroxide.

Electrochemical corrosion and surface analyses of a ni-cr alloy in bleaching agents

PURPOSE

The aim of this study was to evaluate the corrosion behavior of a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) and 10% carbamide peroxide (CP) bleaching solutions and to determine the composition of the surface oxide layer formed on the alloy specimens.

MATERIALS AND METHODS

Ten cylindrical specimens (4 mm in diameter × 25 mm in height) were cast from a Ni-Cr alloy (Wiron 99) and divided into two groups (n = 5). A potentiodynamic polarization test was used to compare the corrosion rates of specimens in HP and CP (pH = 6.5). Before cyclic polarization tests, all alloy specimens were allowed to reach a steady open circuit potential (Ecorr ) for a period of 1 hour. Then tests were initiated at 100 mV versus standard calomel electrode (SCE) below Ecorr and scanned at a rate of 1 mV/s in the anodic direction until reaching 1000 mV over the Ecorr value. The scan then was reversed back to the Ecorr of the specimens. The open circuit potentials (Ecorr ) and the current densities (Icorr ) were determined using the anodic Tafel regions extrapolating from the curves. Differences in Ecorr and Icorr were determined using one-way ANOVA (α = 0.05). In addition, corrosion rates were calculated from these curves. Before and after polarization tests, a scanning electron microscope (SEM) examination accompanied by energy dispersive X-ray spectroscopy (EDS) was used to analyze the surface morphology. The surface characterization of the passive film formed on alloy specimens was also performed by using X-ray photoelectron spectroscopy (XPS).

RESULTS

In this study, bleaching agents had an effect on the anodic process for two groups. Although no statistical difference was identified between the groups for both corrosion parameters, results indicated that the effect of CP on the corrosion behavior was less than that of HP. These results agreed with the SEM observations. XPS data showed that oxide layers formed on all groups contained mainly Cr2 O3 , NiO, and MoO3 , and the amounts of oxides formed on CP-treated specimens were higher than HP treated ones. Also, molybdenum rates were increased with CP application compared to HP.

CONCLUSIONS

The comparison of the effects of the two bleaching agents at 10% showed that the alloy suffered less corrosion with CP than HP. This result was also confirmed by the SEM and XPS data. The presence of Mo on the oxide layer affected the oxide layer, leading to lower corrosion rates.

Influence of S. mutans on Base-metal Dental Casting Alloy Toxicity

We have highlighted that exposure of base-metal dental casting alloys to the acidogenic bacterium Streptococcus mutans significantly increases cellular toxicity following exposure to immortalized human TR146 oral keratinocytes. With Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), S. mutans-treated nickel-based (Ni-based) and cobalt-chromium-based (Co-Cr-based) dental casting alloys were shown to leach elevated levels of metal ions compared with untreated dental casting alloys. We targeted several biological parameters: cell morphology, viable cell counts, cell metabolic activity, cell toxicity, and inflammatory cytokine expression. S. mutans-treated dental casting alloys disrupted cell morphology, elicited significantly decreased viable cell counts (p < 0.0001) and cell metabolic activity (p < 0.0001), and significantly increased cell toxicity (p < 0.0001) and inflammatory cytokine expression (p < 0.0001). S. mutans-treated Ni-based dental casting alloys induced elevated levels of cellular toxicity compared with S. mutans-treated Co-Cr-based dental casting alloys. While our findings indicated that the exacerbated release of metal ions from S. mutans-treated base-metal dental casting alloys was the likely result of the pH reduction during S. mutans growth, the exact nature of mechanisms leading to accelerated dissolution of alloy-discs is not yet fully understood. Given the predominance of S. mutans oral carriage and the exacerbated cytotoxicity observed in TR146 cells following exposure to S. mutans-treated base-metal dental casting alloys, the implications for the long-term stability of base-metal dental restorations in the oral cavity are a cause for concern.

Elemental ion release from four different fixed prosthodontic materials

OBJECTIVE

Elemental release is important because it plays a significant role in material biocompatibility. The aim of this study was to investigate the release of metal ions from four fixed prosthodontic materials.

METHODS

Specimens were prepared using the conventional lost wax technique for gold and nickel-chromium (Ni-Cr) alloys, and by cutting blocks and bar for CAD-CAM ceramic and stainless-steel (St-St) alloy, respectively. All specimens were polished (600grit SiC paper), and ultrasonically cleaned with ethanol for 5min. After they were immersed in 0.9% sodium chloride (NaCl) and 1% lactic acid, and were kept at 37 degrees C for 7 days, the elemental release (mug/cm(2)) from each material was analyzed by using inductively coupled plasma mass spectroscopy. The rate (n=5) was statistically analyzed by ANOVA/Tukey test (p<0.05). Two immersion blank solutions were used as a negative control group.

RESULTS

Higher elemental release (mean+/-S.D.) of all elements from all materials was evident into the lactic acid solution except for Ag. In the gold alloy, there was significant difference (p<0.05) between Zn and other released elements in the NaCl solution, and it also revealed significant difference between Pd or Ag and Cu which detection value was more than Zn (but no statistical difference) into lactic acid solution. The Ni was significantly more released from Ni-Cr alloy than the other elements into both NaCl and lactic acid solutions. The same was observed for Fe released from St-St alloy. There was more significant release of K than Al from CAD-CAM ceramic in only NaCl solution.

SIGNIFICANCE

Transient exposure of tested materials to an acidic environment is likely to significantly increase the elemental release from them. The significant higher release of Ni from Ni-Cr alloy, and Zn, Cu from gold alloy was evident.

Dental casting alloys behaviour during power toothbrushing with toothpastes with various abrasivities. Part I: wear behavior

The purpose of this study was to evaluate the long term effect of abrasivity of toothpastes normally used over the surface and mechanical properties of dental casting alloys. Three dental casting alloys (Ni-Cr, Co-Cr, c.p. Ti) and one ceramic were chosen. Four specimens of each material were immersed in artificial saliva, brushed without or with one of four toothpastes of different Relative Dentine Abrasivity (RDA 50, 52, 80, and 114). An electric toothbrush with a load of 250 g was used for 420 min. Mass loss was determined by difference in weight, microhardness and surface roughness were also measured. Two-way ANOVA and non-parametric tests were used to detect significant differences. Titanium specimens (478 microg/cm(2)) exhibited the most mass loss, whereas ceramic (282 microg/cm(2)) and Co-Cr (262 microg/cm(2)) exhibited the least. However, ceramic demonstrated the most volume loss (0.239 mm(3)). The abrasivity effect of the toothpaste correlated with the RDA values. Slight variations in microhardness were observed after toothbrushing and depended on the material but not on the toothpaste used. Material surfaces were slightly smoothed by toothbrushing but no significant differences were detected. Dental casting alloys and ceramic are susceptible to abrasion by brushing with an electric toothbrush depending on the RDA value of the toothpaste. Variations in microhardness and surface roughness were not clinically relevant.

In vivo study of metal content of oral mucosa cells in patients with and without fixed orthodontic appliances

OBJECTIVE

To compare the concentration of nickel, chromium and cobalt in oral mucosa cells of patients with and without fixed orthodontic appliances.

MATERIALS AND METHODS

A total of 60 patients were included in this study. The control group consisted of 30 patients without any type of fixed orthodontic appliances or metal restoration in the mouth (20 females and 10 males from 16 to 20 years with a mean age of 18 years). The test group consisted of 30 patients who had fixed orthodontic appliance in their upper and lower arches (20 females and 10 male from 16 to 20 years with a mean age of 18.2 years). The metal content determinations were carried out using atomic absorption spectrophotometry with a graphite furnace.

RESULTS

According to spectrophotometric analysis, no significant differences in chromium (p = 0.09) and cobalt (p = 0.10) content of oral mucosa cells were found between the test and control samples. The nickel content in mucosa samples was significantly higher (p = 0.003) in orthodontic patients compared with the controls. The mean levels of nickel in control and orthodontic patient group were 12.26 and 21.74 ng / ml, respectively.

CONCLUSION

Our findings indicate that there was no difference in the concentration of chromium and cobalt in oral mucosa cells of patients with or without fixed appliances. However, a significantly higher concentration of nickel can be found in oral mucosa cells of patients wearing fixed orthodontic appliances. Continued follow-up is needed to determine the long-term significance of nickel release.

The safety of nickel containing dental alloys

Nickel is a constituent of many dental alloys. This paper reviews mainly papers published after 1985 with regards to biological reactions to nickel in dentistry. Nickel is an allergen, but there is no evidence that individual patients are at a significant risk of developing sensitivity solely due to contact with nickel-containing dental appliances and restorations. Hypersensitivity reactions to nickel are only likely to occur with prior sensitization from non-dental contacts and even these are rare. Clinical evidence has been presented to show that small doses of nickel, e.g. from dental appliances, may induce tolerance to this allergen. The papers reviewed report low rates of release of nickel from dental alloys. Some nickel compounds, which are mildly cytotoxic, have been implicated as carcinogens by inhalation in industrial settings, but these compounds are not present in dentistry-related operations, including dental technology procedures. Nickel-containing alloys and compounds have not been associated with increased cancer risk by oral or dermal routes of exposure. It is concluded that, subject to use according to established techniques, nickel-containing dental alloys do not pose a risk to patients or members of the dental team.