Elemental ion release from four different fixed prosthodontic materials

The risk of dental restoration-related lead exposure on renal function

OBJECTIVE

To explore the relationship between oral restoration count, blood lead (PbB) level, and renal function as potential heavy metal releases, and the related toxicity of dental restorative materials.

METHODS

A total of 3682 participants from the National Health and Nutrition Examination Survey (January 2017 to March 2020) were included in this cross-sectional analysis. We utilized multivariable linear regression models to investigate the associations between the number of oral restorations and PbB levels or renal function. The mediating effect of PbB on renal function indicators was analyzed using the R mediation package.

RESULTS

Based on the indicators of 3682 participants, we found that the elderly, females, and whites were fit with more oral restoration, which was accompanied by increased PbB levels and decreased renal function. Meanwhile, oral restoration count was positively associated with PbB level (β = 0.023, 95% CI: -0.020 to 0.027), renal function-related urine albumin creatinine ratio (β = 1.541, 95% CI: 0.615-2.468), serum uric acid level (β = 0.012, 95% CI: 0.007 to 0.017), and serum creatinine level, and negatively associated with estimated glomerular filtration rate (eGFR) (β = -0.804, 95% CI: -0.880 to -0.728). Furthermore, the mediation effect test confirmed that PbB played a mediating role in the relationship between restoration count and serum uric acid or eGFR, with mediation effects accounting for 98.0% and 71.0%, respectively.

CONCLUSIONS

Oral restoration negatively affects renal function. Oral restoration-related PbB level is a potential mediating factor.

Does Simulated Porcelain Firing Influence Corrosion Properties of Casted and Sintered CoCr Alloys?

The aim of the study was to evaluate how heat processing used for dental porcelain firing influences the surface properties of sintered and casted CoCr alloy. Two CoCr alloys, Soft Metal LHK (milling in soft material and sintering) and MoguCera C (casting), were used for the study. The samples were examined using SEM-EDS before and after heat treatment. Next, corrosion examinations (E_corr, j_corr, polarization curve, E_br) were performed. Finally, the samples were evaluated under SEM. Based on the results, the following conclusions might be drawn: 1. Thermal treatment (porcelain firing) did not cause chemical impurities formation on the surface of CoCr alloy; 2. The sintered metal exhibited significantly higher corrosion resistance than the casted one due to its homogeneity of structure and chemical composition; 3. Heat treatment (porcelain firing) decreased the resistance of casted and sintered CoCr alloy to electrochemical corrosion. The reduction in corrosion resistance was significantly higher for the casted alloy than for the sintered alloy; 4. The corrosion resistance decrease might be due to an increased thickness and heterogeneity of oxide layers on the surface (especially for the casted alloy). The development of corrosion process started in the low-density areas of the oxide layers; 5. The sintered metal seems to be a favourable framework material for porcelain fused to metal crowns.

Cytotoxic evaluation of two orthodontic silver solder materials on human periodontal ligament fibroblast cells and the effects of antioxidant and antiapoptotic reagents

OBJECTIVES

To evaluate the cytotoxicity effects of two different solder materials used for orthodontic appliances on human periodontal ligament fibroblast (HPLF) cells, and to determine whether the mechanism of toxicity may involve oxidative stress and apoptosis.

MATERIALS AND METHODS

The silver solder samples (Leone and Summit) were soldered to orthodontic stainless steel bands and exposed to HPLF cells via cell culture inserts for 48 hours. Cytotoxicity effect of the soldered materials on HPLF cells was measured via tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) colorimetric assay (n = 10/sample) and morphological observation. In addition, the mechanism of cytotoxicity of the most toxic silver solder was investigated using both a caspase inhibitor Z-VAL-Ala-Asp-flu-oromethylketone (ZVAD-fmk) and the free radical scavenger Trolox (n = 8/sample). Statistical analysis was performed using one-way analysis of variance with a Bonferroni test. P < .05 was considered statistically significant.

RESULTS

Compared to the control (no treatment, cells only), both silver solders were cytotoxic (P < .001). The bands alone were significantly cytotoxic compared to the control. There was a significant difference in cytotoxicity between the stainless steel bands alone and the Summit silver solder (P < .001), but not the Leone silver solder. The Summit silver solder was more cytotoxic than the Leone silver solder (P < .05). MTT results were supported by the microscopic morphological changes of the HPLF cells. Neither ZVAD-fmk nor Trolox provided significant protection.

CONCLUSIONS

The two silver solder materials demonstrated different levels of cytotoxicity, and neither oxidative stress nor apoptosis is involved in the mechanism of cytotoxicity.

Effect of guide sleeve material, region, diameter, and number of times drills were used on the material loss from sleeves and drills used for surgical guides: An in vitro study

STATEMENT OF PROBLEM

How material loss from sleeves and drills is affected when different guide sleeve materials and different sizes of implant drills are used for different regions of surgical guides is unclear.

PURPOSE

The purpose of this in vitro study was to compare the amount of material loss from different guide sleeves (zirconia and cobalt-chromium) and drills of different diameters during osteotomy preparation in different regions.

MATERIAL AND METHODS

Three tooth-supported surgical guides with sleeve holes positioned in the first premolar and second molar sites were prepared. Guide sleeves (Ø 2.20 mm, 3.40 mm, and 4.05 mm) were milled from zirconia (n=60) and cobalt-chromium (n=60) blocks. A total of 12 titanium nitride-coated stainless steel twisted drills (n=6 per sleeve material) of different diameters (Ø 2.00, 3.20, 3.85 mm) were used with corresponding sleeves during the drilling. The weight loss from the drills and the volume loss from the guide sleeves after drilling were analyzed by using multiple linear mixed effect models (α=.05).

RESULTS

According to the 4-way ANOVA for volume loss from sleeves, no significant interaction was found among the 4 main effects (number of times a drill was used, region, diameter, and material), but interactions between the number of times a drill was used and diameter (P=.001) and between the number of times the drill was used and material were significant (P<.001). For weight loss from the drills, a significant interaction was detected between the number of times the drill was used and diameter (P=.024).

CONCLUSIONS

Less sleeve material was lost when zirconia sleeves were used. All sleeves had more material loss in the molar region than in the premolar region. The diameter had varying effects on the amount of material loss from drills and sleeves. The sleeve material and the region did not affect the material loss from drills.

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.

Effect of in vitro aging and acidic storage on color, translucency, and contrast ratio of monolithic zirconia and lithium disilicate ceramics

STATEMENT OF PROBLEM

How the translucency and color of ceramic restorations are affected by surface changes from the corrosive environment in the oral cavity and aging of materials is unclear.

PURPOSE

The purpose of this in vitro study was to compare the impact of acidic exposure and aging on the color and translucency of monolithic zirconia and lithium disilicate ceramics.

MATERIAL AND METHODS

Twenty computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic zirconia specimens and 20 pressed lithium disilicate specimens were fabricated. Half of the specimens of each group were aged in an autoclave (7.5 hours, 134 °C, 0.2 MPa), and the rest were immersed in hydrochloric acid to simulate the acidic conditions in the oral cavity from gastric reflux. The color coordinates L∗, a∗, and b∗ were measured with an ultraviolet spectrophotometer before and after aging or acidic storage. The translucency parameters and contrast ratios were calculated, and the CIEDE2000 color difference formula was used to determine color differences before and after each treatment. ANOVA and ANCOVA test models were used for data analysis (α=.05), while differences of color parameters in respect to acceptability and perceptibility thresholds were evaluated with the 1-sample t test (α=.05).

RESULTS

Lithium disilicate presented a significantly higher translucency parameter and lower contrast ratio at baseline compared with monolithic zirconia specimens (P<.001). Acidic storage significantly impacted all parameters compared with aging, especially for the lithium disilicate group. Color differences were above the acceptability ΔΕ₀₀ threshold for lithium disilicate after acidic storage (P=.001) and below for monolithic zirconia after acidic storage (P=.003).

CONCLUSIONS

The performance of lithium disilicate was slightly inferior compared with that of monolithic zirconia specimens, as they presented significant and clinically observable differences for the translucency parameter and ΔΕ₀₀ after acidic storage and aging.

Removal of dental alloys and titanium attenuates trace metals and biological effects on liver and kidney

To determine whether the potential effects on liver and kidney caused by dental alloys could be reduced or terminated by the removal of nickel-chromium (Ni-Cr) alloy, cobalt-chromium (Co-Cr) alloy, and commercially pure titanium (CP-Ti), they were placed in the cheek pouches of Syrian hamsters according to ISO 10993-10. Then, the peak/plateau and end times of trace metals in the blood were determined with or without the removal of the dental alloys. Based on these time points, the trace metals and their effects on liver and kidney were examined. We found that trace metals released from these dental alloys and titanium were accumulated transiently in the blood, liver, and kidney but had no effect on the histopathology of the liver or kidney. Although the functions of the liver and kidney were compromised, the function of these tissues seemed to be clinically acceptable compared to those in control Syrian hamsters. In addition, the apoptotic effect on renal cells was terminated by removing the Ni-Cr and Co-Cr alloys, and that on hepatocytes was also eliminated by removing the Ni-Cr alloy. In contrast, the effect of the Co-Cr alloy on hepatocytes was temporary and recovered by itself. Taken together, Ni- and Co-based dental alloys and titanium have no effect on the histopathology or function of liver and kidney. Moreover, Ni-Cr and Co-Cr alloys induce transient trace metal accumulation and apoptotic effects in liver and kidney, which can be reduced or terminated by the removal of the alloys, while CP-Ti shows favorable biocompatibility.

Metal allergy patient treated by titanium implant denture: A case report with at least 4-year follow-up

Patch testing with metal reagents was positive on female patient with history of metal hypersensitivity after dental treatment. All of the dental restorations with metal components were removed, and subsequent oral rehabilitation utilizing dental implants and metal-free prostheses was carried out. The treatments alleviate the presenting signs and symptoms.

Assessment of exposures and potential risks to the US adult population from the leaching of elements from gold and ceramic dental restorations

Using data from the 2001 to 2004 US National Health and Nutrition Examination Survey (NHANES) on the number and placement of tooth restorations in adults, we quantified daily doses due to leaching of elements from gold (Au) alloy and ceramic restorative materials. The elements with the greatest leaching rates from these materials are often the elements of lowest proportional composition. As a result, exposure due to wear will predominate for those elements of relatively high proportional composition, while exposure due leaching may predominate for elements of relatively low proportional composition. The exposure due to leaching of silver (Ag) and palladium (Pd) from Au alloys exceeded published reference exposure levels (RELs) for these elements when multiple full surface crowns were present. Six or more molar crowns would result in exceeding the REL for Ag, whereas three or more crowns would be necessary to exceed the REL for Pd. For platinum (Pt), the majority of tooth surfaces, beyond just molar crowns, would be necessary to exceed the REL for Pd. Exposures due to leaching of elements from ceramic dental materials were less than published RELs for all components examined here, including having all restorations composed of ceramic.

Corrosion behavior of dental alloys used for retention elements in prosthodontics

The purpose of this study was to investigate the corrosion behavior of 10 different high noble gold-based dental alloys, used for prosthodontic retention elements, according to ISO 10271. Samples of 10 high-noble and noble gold-based dental alloys were subjected to: (i) static immersion tests with subsequent analysis of ion release for eight different elements using mass spectrometry; (ii) electrochemical tests, including open-circuit potential and potentiodynamic scans; and (iii) scanning electron microscopy, followed by energy-dispersive X-ray microscopy. The results were analyzed using one-way ANOVA and Sidak multiple-comparisons post-hoc test at a level of significance of α = 0.05. Significant differences were found among the 10 alloys studied for all ions (P < 0.001). The potentiodynamic analysis showed values from -82.5 to 102.8 mV for the open-circuit potential and from 566.7 to 1367.5 mV for the breakdown potential. Both the open-circuit and the breakdown potential varied considerably among these alloys. Scanning electron microscopy analysis confirmed the existence of typically small-diameter corrosion defects, whilst the energy-dispersive X-ray analysis found no significant alteration in the elemental composition of the alloys. The results of this study reveal the variability in the corrosive resistance among the materials used for retention elements in prosthodontics.

Assessment of exposures and potential risks to the US adult population from wear (attrition and abrasion) of gold and ceramic dental restorations

Little has been published on the chemical exposures and risks of dental restorative materials other than from dental amalgam and composite resins. Here we provide the first exposure and risk assessment for gold (Au) alloy and ceramic restorative materials. Based on the 2001-2004 US National Health and Nutrition Examination Survey (NHANES), we assessed the exposure of US adults to the components of Au alloy and ceramic dental restorations owing to dental material wear. Silver (Ag) is the most problematic component of Au alloy restorations, owing to a combination of toxicity and proportional composition. It was estimated that adults could possess an average of four tooth surfaces restored with Au alloy before exceeding, on average, the reference exposure level (REL) for Ag. Lithium (Li) is the most problematic component of dental ceramics. It was estimated that adults could possess an average of 15 tooth surfaces restored with ceramics before exceeding the REL for Li. Relative risks of chemical exposures from dental materials decrease in the following order: Amalgam>Au alloys>ceramics>composite resins.

In vivo determination of aluminum, cobalt, chromium, copper, nickel, titanium and vanadium in oral mucosa cells from orthodontic patients with mini-implants by Inductively coupled plasma-mass spectrometry (ICP-MS)

Miniscrews are used as orthodontic anchorage devices in the dentistry clinical practice but the in vivo metallic release from these structures has been not previously investigated. The aim of this study was to determine the content of Al, Co, Cr, Cu, Ni, Ti and V in oral mucosa cells of control subjects, patients under orthodontic treatment and with both, orthodontic treatment and miniscrew, in order to know the contribution of these mini-implants to the total metallic content. ICP-MS measurements revealed the following ascending order: Cr<Ni<Ti<Cu<Al, and Co and V were practically undetected. Significant differences in comparison to the control group were found for Cu in the orthodontic group, and for Ni in both, orthodontic and orthodontic+miniscrew groups. Potential correlations among metallic elements and with some clinical factors were also explored. These findings suggest that miniscrews do not increase significantly the metal release.

In vitro element release and biological aspects of base-metal alloys for metal-ceramic applications

Objective: The aims of this study were to investigate the release of element from, and the biological response in vitro to, cobalt–chromium alloys and other base–metal alloys used for the fabrication of metal-ceramic restorations.

Material and methods: Eighteen different alloys were investigated. Nine cobalt–chromium alloys, three nickel–chromium alloys, two cobalt–chromium–iron alloys, one palladium–silver alloy, one high-noble gold alloy, titanium grade II and one type III copper–aluminium alloy. Pure copper served as positive control. The specimens were prepared according to the ISO standards for biological and corrosion testing. Passive leaching of elements was measured by using Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) after incubation in cell culture media, MEM, for 3 days. Corrosion testing was carried out in 0.9% sodium chloride (NaCl) and 1% lactic acid for 7 days, and the element release was measured by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES). The biological response from the extract solutions was measured though MTT cytotoxicity testing and the Hen's egg test-chorio-allantoic membrane (HET-CAM) technique for irritationt.

Results: The corrosion test showed similar element release from base-metal alloys compared to noble alloys such as gold. Apart from the high-copper alloy, all alloys expressed low element release in the immersion test, no cytotoxic effect in the MTT test, and were rated non-irritant in the HET-CAM test.

Conclusions: Minimal biological response was observed for all the alloys tested, with the exception of the high-copper alloy.

In vitro cytotoxicity of metallic ions released from dental alloys

The cytotoxicity of a dental alloy depends on, but is not limited to, the extent of its corrosion behavior. Individual ions may have effects on cell viability that are different from metals interacting within the alloy structure. We aimed to investigate the cytotoxicity of individual metal ions in concentrations similar to those reported to be released from Pd-based dental alloys on mouse fibroblast cells. Metal salts were used to prepare seven solutions (concentration range 100 ppm-1 ppb) of the transition metals, such as Ni(II), Pd(II), Cu(II), and Ag(I), and the metals, such as Ga(III), In(III), and Sn(II). Cytotoxicity on mouse fibroblasts L929 was evaluated using the MTT assay. Ni, Cu, and Ag are cytotoxic at 10 ppm, Pd and Ga at 100 ppm. Sn and In were not able to induce cytotoxicity at the tested concentrations. Transition metals were able to induce cytotoxic effects in concentrations similar to those reported to be released from Pd-based dental alloys. Ni, Cu, and Ag were the most cytotoxic followed by Pd and Ga; Sn and In were not cytotoxic. Cytotoxic reactions might be considered in the etiopathogenesis of clinically observed local adverse reactions.

Electrochemical and surface analyses of nanostructured Ti-24Nb-4Zr-8Sn alloys in simulated body solution

The use of nanostructuring to improve the stability of passive thin films on biomaterials can enhance their effectiveness in corrosion resistance and reduce the release of ions. The thickness of the ultrathin films that cover Ti and Ti alloys (only several nanometers) has prevented researchers from establishing systematic methods for their characterization. This study employed a multifunctional biomedical titanium alloy Ti-24Nb-4Zr-8Sn (wt.%) as a model material. Coarse-grained (CG) and nanostructured (NS) alloys were analyzed in 0.9% NaCl solution at 37°C. To reveal the details of the passive film, a method of sample preparation producing a passive layer suitable for transmission electron microscope analysis was developed. Electrochemical corrosion behavior was evaluated by potentiodynamic polarization tests and Mott-Schottky measurements. Surface depth chemical profile and morphology evolution were performed by X-ray photoelectron spectroscopy and in situ atomic force microscopy, respectively. A mechanism was proposed on the basis of the point defect model to compare the corrosion resistance of the passive film on NS and CG alloys. Results showed that the protective amorphous film on NS alloy is thicker, denser and more homogeneous with fewer defects than that on CG alloy. The film on NS alloy contains more oxygen and corrosion-resistant elements (Ti and Nb), as well as their suboxides, compared with the film on CG alloy. These characteristics can be attributed to the rapid, uniform growth of the passive film facilitated by nanostructuring.

Corrosive and cytotoxic properties of compact specimens and microparticles of Ni-Cr dental alloy

PURPOSE

Nickel-chromium (Ni-Cr) dental alloys have been widely used in prosthodontic practice, but there is a permanent concern about their biocompatibility due to the release of metal ions. This is especially important when Ni-Cr metal microparticles are incorporated into gingival tissue during prosthodontic procedures. Therefore, the aim of this study was to examine and compare the corrosion and cytotoxic properties of compact specimens and microparticles of Ni-Cr dental alloy.

MATERIALS AND METHODS

Ni-Cr alloy, Remanium CSe bars (4 mm diameter), were made by the standard casting method and then cut into 0.5-mm-thick disks. Metal particles were obtained by scraping the bars using a diamond instrument for crown preparation. The microstructure was observed by an optical microscope. Quantitative determination and morphological and dimensional characterization of metal particles were carried out by a scanning electron microscope and Leica Application Suite software for image analysis. Corrosion was studied by conditioning the alloy specimens in the RPMI 1640 medium, containing 10% fetal calf serum in an incubator with 5% CO2 for 72 hours at 37°C. Inductively coupled plasma-optical emission spectrometry was used to assess metal ion release. The cytotoxity of conditioning medium (CM) was investigated on L929 cells using an MTT test. One-way ANOVA was used for statistical analysis.

RESULTS

After casting, the microstructure of the Remanium CSe compact specimen composed of Ni, Cr, Mo, Si, Fe, Al, and Co had a typical dendritic structure. Alloy microparticles had an irregular shape with a wide size range: from less than 1 μm to more than 100 μm. The release of metal ions, especially Ni and Mo from microparticles, was significantly higher, compared to the compact alloy specimen. The CM prepared from compact alloy was not cytotoxic at any tested dilutions, whereas CM from alloy microparticles showed dose-dependent cytotoxicity (90% CM and 45% CM versus control; p < 0.005).

CONCLUSION

Ni-Cr microparticles showed less corrosion resistance and lower biocompatibility than compact alloy. This could affect health on long-term exposure, especially in sensitized individuals.

Urinary levels of nickel and chromium associated with dental restoration by nickel-chromium based alloys

This paper aims to investigate if the dental restoration of nickel–chromium based alloy (Ni–Cr) leads to the enhanced excretions of Ni and Cr in urine. Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni–Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination. Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry. Compared to the control group, the urinary level of Ni was significantly higher in the patient group of <1 month of the restoration duration, among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain. Urinary levels of Cr were significantly higher in the three patient groups of <1, 1 to <3 and 3 to <6 months, especially in those with a higher metal crown exposure index. Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups. Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration. Potential short- and long-term effects of Ni–Cr alloy restoration need to be investigated.

The effect of repeated porcelain firings on corrosion resistance of different dental alloys

PURPOSE

The aim of this study was to evaluate the effects of repeated porcelain firing process on the corrosion rates of the dental alloys.

MATERIALS AND METHODS

Cr-Co, Cr-Ni and Pd-Ag alloys were used for this study. Each metal supported porcelain consisted of 30 specimens of 10 for 7, 9 and 11 firing each. Disc-shaped specimens 10 mm diameter and 3 mm thickness were formed by melting alloys with a propane-oxygen flame and casted with a centrifuge casting machine and then with the porcelain veneer fired onto the metal alloys. Corrosion tests were performed in quintuplicate for each alloy (after repeated porcelain firing) in Fusayama artificial saliva solution (pH = 5) in a low thermal-expansion borosilicate glass cell. Tamhane and Sheffe test was used to compare corrosion differences in the results after repeated firings and among 7, 9 and 11 firing for each alloy. The probability level for statistical significance was set at α=0.05.

RESULTS

The corrosion resistance was higher (30 mV), in case of 7 times firing (Commercial). On the other hand, it was lower in case of 11 times firing (5 mV) (P<.05).

CONCLUSION

Repeated firings decreased corrosion resistance of Pd-Ag, Cr-Co and Cr-Ni alloys. The Pd-Ag alloy exhibited little corrosion in in vitro tests. The Cr-Ni alloy exhibited higher corrosion resistance than Cr-Co alloys in in vitro tests.

Base-metal dental casting alloy biocompatibility assessment using a human-derived three-dimensional oral mucosal model

Nickel-chromium (Ni-Cr) alloys used in fixed prosthodontics have been associated with type IV Ni-induced hypersensitivity. We hypothesised that the full-thickness human-derived oral mucosa model employed for biocompatibility testing of base-metal dental alloys would provide insights into the mechanisms of Ni-induced toxicity. Primary oral keratinocytes and gingival fibroblasts were seeded onto Alloderm™ and maintained until full thickness was achieved prior to Ni-Cr and cobalt-chromium (Co-Cr) alloy disc exposure (2-72 h). Biocompatibility assessment involved histological analyses with cell viability measurements, oxidative stress responses, inflammatory cytokine expression and cellular toxicity analyses. Inductively coupled plasma mass spectrometry analysis determined elemental ion release levels. We detected adverse morphology with significant reductions in cell viability, significant increases in oxidative stress, inflammatory cytokine expression and cellular toxicity for the Ni-Cr alloy-treated oral mucosal models compared with untreated oral mucosal models, and adverse effects were increased for the Ni-Cr alloy that leached the most Ni. Co-Cr demonstrated significantly enhanced biocompatibility compared with Ni-Cr alloy-treated oral mucosal models. The human-derived full-thickness oral mucosal model discriminated between dental alloys and provided insights into the mechanisms of Ni-induced toxicity, highlighting potential clinical relevance.

Estimating long-term survival of densely sintered alumina crowns: a cohort study over 10 years

STATEMENT OF PROBLEM

Alumina-core crowns have become a standard treatment option in contemporary dental practice. The short-term survival of alumina crowns has been well documented. However, there is still a paucity of long-term survival data.

PURPOSE

The purpose of this prospective cohort study was to estimate long-term survival of alumina crowns in anterior and posterior areas over an observation period of up to 10 years.

MATERIAL AND METHODS

Between 1997 and 2005, 155 alumina crowns were placed in 50 subjects. Clinical and technical parameters were assessed at baseline. In 2005 and 2008, the crowns were clinically assessed using modified U.S. Public Health Service (USPHS) guidelines. Treatment failure was defined as crown or tooth loss and separated into technical or biological failures. Survival probabilities were estimated using the Kaplan-Meier method.

RESULTS

In 2008, 29 subjects with 112 alumina crowns, including 86 (77%) posterior and 26 (23%) anterior crowns, were available for clinical assessment. The average observation period for these subjects was 7.8 years, with a range from 3 to 10.7 years. In total, 3 technical and 8 biological failures were observed. The estimated survival probability considering technical failures only was 95% (95% Confidence Interval (CI), 89% to 100%). The estimated overall survival probability after 10 years was 84% (95% CI, 74% to 95%). There was no significant difference in treatment failures in posterior as compared to anterior crowns (all failures: P=.713; technical failures: P=.352).

CONCLUSIONS

The results suggest that the expected 10-year survival rate of alumina crowns due to technical failures is 95% (95% CI, 89% to 100%).

Development of a discriminatory biocompatibility testing model for non-precious dental casting alloys

OBJECTIVES

To develop an enhanced, reproducible and discriminatory biocompatibility testing model for non-precious dental casting alloys, prepared to a clinically relevant surface finishing condition, using TR146 oral keratinocyte cells.

METHODS

Comparative biocompatibility was determined following direct and indirect exposure of TR146 cells to two nickel-chromium (Ni-Cr) and a cobalt-chromium (Co-Cr) alloy-discs. The surface roughness of the discs was determined using a contact stylus profilometer and the elemental ion release by inductively coupled plasma mass spectrometry (ICP-MS). Subsequent biocompatibility analysis included cell morphology, cell density measurements with Trypan blue exclusion assay, inflammatory cytokine expression with ELISAs, cellular metabolic activity using XTT and cellular toxicity using lactate dehydrogenase (LDH) release assay.

RESULTS

TR146 cell morphology was altered following direct and indirect exposure to the Ni-Cr alloys but not the Co-Cr alloy. Significant reductions (all P<0.001) in viable cell density measurements, cellular metabolic activity, significant increases inflammatory cytokine expression and cellular toxicity were observed when TR146 cells were exposed to the Ni-Cr alloys. Significant decreases in cell density measurements, cellular metabolic activity, significant increases inflammatory cytokine expression and cellular toxicity for the Ni-Cr d.Sign(®)15 alloy compared with d.Sign(®)10 alloy were identifiable (all P<0.001). Cellular toxicity was attributed to nickel ion release levels in solution detected by ICP-MS analysis.

DISCUSSION

Nickel ions from the Ni-Cr alloys permeated the epithelial cells and activated a proinflammatory response, namely IL-1a, IL-8 and PGE2 expression. Further evidence of nickel ioninduced cell death was supported by the decreased biocompatibility of the highest nickel ion releasing alloy (d.Sign(®)15 compared with d.Sign(®)10) and the increased biocompatibility of the Co-Cr (d.Sign(®)30) alloy where nickel ions were absent.

Biocompatibility of orthodontic bands following exposure to dental plaque

OBJECTIVE

The aim of this study was to assess the biocompatibility of orthodontic bands following exposure to the human oral environment.

METHODS

Cell adherence and cell morphology of gingival fibroblasts grown on 32 orthodontic bands were tested. The bands were in place intraorally for 6 to 37 months.

RESULTS

We observed cell adherence in 76% of the previously plaque-free surfaces. Cell morphology was 50% spherical and 50% elongated. The surfaces that had had plaque attached demonstrated cell adherence in 84% of the given areas; those cells were spherical in 42% and elongated in 58%.

CONCLUSION

We conclude that individual oral hygiene habits during orthodontic treatment seem to have no effect on the biocompatibility of orthodontic bands, as we failed to discern a difference in either cell adherence or cell morphology in areas with and without prior plaque attachment.