Release of nickel ions from stainless steel alloys used in dental braces and their patch test reactivity in nickel-sensitive individuals

Metallic Dental Implants Wear Mechanisms, Materials, and Manufacturing Processes: A Literature Review

OBJECTIVES

From the treatment of damaged teeth to replacing missing teeth, dental biomaterials cover the scientific interest of many fields. Dental biomaterials are one of the implants whose effective life depends vastly on their material and manufacturing techniques. The purpose of this review is to summarize the important aspects for metallic dental implants from biomedical, mechanical and materials science perspectives. The review article will focus on five major aspects as mentioned below. Tooth anatomy: Maximizing the implant performance depends on proper understanding of human tooth anatomy and the failure behavior of the implants. Major parts from tooth anatomy including saliva characteristics are explored in this section. Wear mechanisms: The prominent wear mechanisms having a high impact on dental wear are abrasive, adhesive, fatigue and corrosion wear. To imitate the physiological working condition of dental implants, reports on the broad range of mastication force and various composition of artificial saliva have been included in this section, which can affect the tribo-corrosion behavior of dental implants. Dental implants classifications: The review paper includes a dedicated discussion on major dental implants types and their details for better understanding their applicability and characteristics. Implant materials: As of today, the most established dental implant materials are SS316L, cobalt chrome alloy and titanium. Detailed discussion on their material properties, microstructures, phase transformations and chemical compositions have been discussed here. Manufacturing techniques: In terms of different production methods, the lost wax casting method as traditional manufacturing is considered. Selective Laser Melting (SLM) and Directed Energy Deposition (DED) as additive manufacturing techniques (AM) have been discussed. For AM, the relationships between process-property-performance details have been explored briefly. The effectiveness of different manufacturing techniques was compared based on porosity distribution, mechanical and biomechanical properties.

SUMMARY

Despite having substantial research available on dental implants, there is a lack of systematic reviews to present a holistic viewpoint combining state-of-the-art from biomedical, mechanical, materials science and manufacturing perspectives. This review article attempts to combine a wide variety of analyzing approaches from those interdisciplinary fields to deliver deeper insights to researchers both in academia and industry to develop next-generation dental implants.

Preparation and characterization of acrylic resins with bioactive glasses

This study aimed to prepare a bioactive acrylic material by adding different types of glasses. Commercially available polymerized acrylic resin was mixed with 10% of four different types of glasses in the powder form and cured. Flexural strength, sorption, and solubility of the samples were tested according to ISO 20795-1:2013. The total number of samples used in the tests were 60. The materials were placed in artificial saliva of pH 4 and 7, and elution was performed for 0, 1, 28, and 42 days. The collected samples were analyzed using inductively coupled plasma atomic emission spectrometry to detect Ca, P, and Si ions and using ion chromatography to detect F ions. The materials obtained after modification with glasses showed lower compressive strength compared with pure polymethyl methacrylate but met the standard requirements. Two glass types showed higher solubility values compared with the value defined by the ISO standard. Biomin C and S53P4 released Ca, P, and Si ions, respectively, after 42 days in artificial saliva. Acrylic resins modified with 10% Biomin C and S53P4 glasses can be a valuable source of Ca and P ions under acid conditions for 28 and 42 days.

Comparative Investigation on Corrosion Resistance of Stainless Steels Coated with Titanium Nitride, Nitrogen Titanium Carbide and Titanium-Diamond-like Carbon Films

In this study, the corrosion resistance of titanium nitride (TiN), nitrogen titanium carbide (TiCN) and titanium-diamond-like carbon (Ti-DLC) films deposited on 316L stainless steel (SS) were compared via differences in the surface and section-cross morphologies, open circuit potential tests, electrochemical impedance spectroscopy and potentiometric tests. The corrosion resistance of the TiCN and Ti-DLC films significantly improved because of the titanium carbide (TiC) crystals that obstruct the corrosive species penetrating the as-deposited film in the electrolyte atmosphere. TiN exhibited the lowest corrosion resistance because of its low thickness and high volume of defects. The Ti-DLC film showed the lowest corrosion current density (approximately 4.577 μA/cm2) and thickness reduction (approximately 0.12 μm) in different electrolytes, particularly those with high Cl− and H+ concentrations, proving to be the most suitable corrosion protection material for 316L SS substrates.

Oral Hypersensitivity Reactions

Allergic contact hypersensitivity reactions of the oral mucosa pose a significant medical concern for some patients. Oral hypersensitivity reactions can result from a vast number of allergenic chemicals, but occur commonly from dental materials, flavorings, and preservatives. Clinical presentation is varied and often overlaps with other oral conditions, complicating their diagnosis and management. The most common clinical entities associated with oral hypersensitivity reactions are oral lichenoid reactions and allergic contact cheilitis. In addition to reviewing these conditions and their most common corresponding allergens, this article summarizes the pathogenesis of oral hypersensitivity reactions and addresses patch testing pearls.

Metals and Metalloids Release from Orthodontic Elastomeric and Stainless Steel Ligatures: In Vitro Risk Assessment of Human Exposure

Elastomeric ligatures are increasingly used as a part of esthetic orthodontic treatment, particularly in children. The aim of the present study was to experimentally test whether these appliances may contribute to exposure to toxic elements. In the present study, elastomeric ligatures (ELs) were incubated in artificial human saliva for 1 month (a typical period of their use) and the release of 21 metals (Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mg, Mo, Ni, Pb, Rb, Tl, Ti, Sb, Sr, Sn, Zn, U, V) and 2 metalloids (As and Ge) was studied using inductively coupled plasma-mass spectrometry. For comparison, stainless steel ligatures (SLs) were incubated for 1, 3, and 6 months (since sometimes their use is prolonged) under similar conditions. The determined metal levels were compared to the corresponding safety limits for human exposure. During 1 month, the ELs released Cd, Co, Cr, Mn, Ni, and Sn at total mean ± SD level of 0.31 ± 0.09, 0.98 ± 0.30, 3.96 ± 1.31, 14.7 ± 8.5, 13.8 ± 4.8, and 49.5 ± 27.7 μg, respectively. Other elements were always below the detection limits. In case of SL, the release of Co, Cr, Fe, Ni, Mn, and Sn was observed, and the determined values increased over the studied period. After 6 months, their total mean ± SD levels amounted to 28.6 ± 0.2, 21.7 ± 0.2, 623.5 ± 3.0, 1152.7 ± 1.8, 5.5 ± 0.3, and 22.6 ± 0.2 μg, respectively. The released metal levels from both ligature types were always below safety limits. The release of Ni from SL during 6 months would constitute 5.0 and 11.5% of tolerable intake in adults and children, respectively. The results of this in vitro study highlight that the use of ligatures in orthodontic treatment can be considered safe in terms of metal exposure although elastic ligatures replaced on a monthly basis appear to be advantageous in comparison to the prolonged use of stainless steel appliances.

Immunostimulatory capacity of dental casting alloys on endotoxin responsiveness

STATEMENT OF PROBLEM

Oral metal exposure has been associated with systemic and local adverse reactions, probably due to elemental release from the alloys. Although supraphysiological concentrations of salts from dentally applied metals can activate innate cells through TLR4 (Ni, Co, Pd) and TLR3 (Au), whether direct exposure to solid alloys can also trigger innate immune reactivity is still unknown.

PURPOSE

The purpose of this in vitro study was to determine whether dental cast alloy specimens can activate innate cells and influence their responsiveness to bacterial endotoxin.

MATERIAL AND METHODS

Human monocyte-derived dendritic cells (MoDC) and THP-1 cells were cultured on top of different alloy specimens (Ni-Cr, Co-Cr, Pd-Cu, Pd-Ag, Ti-6Al-4V, amalgam, gold, and stainless steel) or in alloy-exposed culture medium with or without endotoxin (lipopolysaccharide [LPS]; Escherichia coli 055:B5). Interleukin-8 (IL-8) production was used as the parameter for innate stimulation and evaluated by enzyme-linked immunosorbent assay after 24 hours of culture. The statistical significance of the effects of various casting alloys on the secretion of IL-8 was analyzed by using the nonparametric Wilcoxon rank sum test (α=.05).

RESULTS

Dental cast alloys induced IL-8 production in MoDC and THP-1 cells, with Au and Pd-Cu providing the strongest stimulation. The alloy-exposed culture media tested contained sufficient stimulatory metal ions to induce detectable IL-8 production in THP-1 cells, except for the Ni-Cr and stainless steel exposed media. Au and Pd-Cu alloys were also most effective in potentiating LPS responsiveness as measured by IL-8 production.

CONCLUSIONS

Using an in vitro culture system to expose MoDC and THP-1 cells to different alloy specimens this study showed that contact with the solid alloys, in particular when they contain Pd or Au, can trigger innate immune responses and augment responsiveness to bacterial endotoxin.

Unmet diagnostic needs in contact oral mucosal allergies

The oral mucosa including the lips is constantly exposed to several noxious stimuli, irritants and allergens. However, oral contact pathologies are not frequently seen because of the relative resistance of the oral mucosa to irritant agents and allergens due to anatomical and physiological factors. The spectrum of signs and symptoms of oral contact allergies (OCA) is broad and a large number of condition can be the clinical expression of OCA such as allergic contact stomatitis, allergic contact cheilitis, geographic tongue, oral lichenoid reactions, burning mouth syndrome. The main etiological factors causing OCA are dental materials, food and oral hygiene products, as they contain flavouring agents and preservatives. The personal medical history of the patient is helpful to perform a diagnosis, as a positive history for recent dental procedures. Sometimes histology is mandatory. When it cannot identify a direct cause of a substance, in both acute and chronic OCA, patch tests can play a pivotal role in the diagnosis. However, patch tests might have several pitfalls. Indeed, the presence of metal ions as haptens and specifically the differences in their concentrations in oral mucosa and in standard preparation for patch testing and in the differences in pH of the medium might result in either false positive/negative reactions or non-specific irritative reactions. Another limitation of patch test results is the difficulty to assess the clinical relevance of haptens contained in dental materials and only the removal of dental materials or the avoidance of other contactant and consequent improvement of the disease may demonstrate the haptens' responsibility. In conclusion, the wide spectrum of clinical presentations, the broad range of materials and allergens which can cause it, the difficult interpretation of patch-test results, the clinical relevance assessment of haptens found positive at patch test are the main factors that make sometimes difficult the diagnosis and the management of OCA that requires an interdisciplinary approach to the patient.

Allergic Reactions to Dental Materials-A Systematic Review

INTRODUCTION

Utility of various dental materials ranging from diagnosis to rehabilitation for the management of oral diseases are not devoid of posing a potential risk of inducing allergic reactions to the patient, technician and dentist. This review aims to develop a systematic approach for the selection and monitoring of dental materials available in the market thereby giving an insight to predict their risk of inducing allergic reactions.

MATERIALS AND METHODS

Our data included 71 relevant articles which included 60 case reports, 8 prospective studies and 3 retrospective studies. The source of these articles was Pub Med search done with the following terms: allergies to impression materials, sodium hypochlorite, Ledermix paste, zinc oxide eugenol, formaldehyde, Latex gloves, Methyl methacrylate, fissure sealant, composites, mercury, Nickel-chromium, Titanium, polishing paste and local anaesthesia. All the relevant articles and their references were analysed. The clinical manifestations of allergy to different dental materials based on different case reports were reviewed.

RESULTS

After reviewing the literature, we found that the dental material reported to cause most adverse reactions in patients is amalgam and the incidence of oral lichenoid reactions adjacent to amalgam restorations occur more often than other dental materials.

CONCLUSION

The most common allergic reactions in dental staff are allergies to latex, acrylates and formaldehyde. While polymethylmethacrylates and latex trigger delayed hypersensitivity reactions, sodium metabisulphite and nickel cause immediate reactions. Over the last few years, due to the rise in number of patients with allergies from different materials, the practicing dentists should have knowledge about documented allergies to known materials and thus avoid such allergic manifestations in the dental clinic.

Evaluation of ionic degradation and slot corrosion of metallic brackets by the action of different dentifrices

OBJECTIVE

To evaluate the in vitro ionic degradation and slot base corrosion of metallic brackets subjected to brushing with dentifrices, through analysis of chemical composition by Energy Dispersive Spectroscopy (EDS) and qualitative analysis by Scanning Electron Microscopy (SEM).

METHODS

Thirty eight brackets were selected and randomly divided into four experimental groups (n = 7). Two groups (n = 5) worked as positive and negative controls. Simulated orthodontic braces were assembled using 0.019 x 0.025-in stainless steel wires and elastomeric rings. The groups were divided according to surface treatment: G1 (Máxima Proteção Anticáries®); G2 (Total 12®); G3 (Sensitive®); G4 (Branqueador®); Positive control (artificial saliva) and Negative control (no treatment). Twenty eight brushing cycles were performed and evaluations were made before (T0) and after (T1) experiment.

RESULTS

The Wilcoxon test showed no difference in ionic concentrations of titanium (Ti), chromium (Cr), iron (Fe) and nickel (Ni) between groups. G2 presented significant reduction (p < 0.05) in the concentration of aluminium ion (Al). Groups G3 and G4 presented significant increase (p < 0.05) in the concentration of aluminium ion. The SEM analysis showed increased characteristics indicative of corrosion on groups G2, G3 and G4.

CONCLUSION

The EDS analysis revealed that control groups and G1 did not suffer alterations on the chemical composition. G2 presented degradation in the amount of Al ion. G3 and G4 suffered increase in the concentration of Al. The immersion in artificial saliva and the dentifrice Máxima Proteção Anticáries® did not alter the surface polishing. The dentifrices Total 12®, Sensitive® and Branqueador® altered the surface polishing.

Microbiologically influenced corrosion of orthodontic metallic appliances

Biocorrosion (microbiologically influenced corrosion; MIC) occur in aquatic habitats varying in nutrient content, temperature, stress and pH. The oral environment of organisms, including humans, should be one of the most hospitable for MIC. Corrosion of metallic appliances in the oral region is one cause of metal allergy in patients. In this study, an inductively coupled plasma-optical emission spectrometer revealed elution of Fe, Cr and Ni from stainless steel (SUS) appliances incubated with oral bacteria. Three-dimensional laser confocal microscopy also revealed that oral bacterial culture promoted increased surface roughness and corrosion pits in SUS appliances. The pH of the supernatant was lowered after co-culture of appliances and oral bacteria in any combinations, but not reached at the level of depassivation pH of their metallic materials. This study showed that Streptococcus mutans and Streptococcus sanguinis which easily created biofilm on the surfaces of teeth and appliances, did corrode orthodontic SUS appliances.

Release of metal ions from fixed orthodontic appliance: an in vitro study in continuous flow system

OBJECTIVE

To evaluate the release of metal ions from fixed orthodontic appliances.

MATERIALS AND METHODS

A new system for in vitro testing of dental materials was constructed and consisted of a thermostatic glass reactor that enabled immersion of the studied material. Experimental conditions reflected the human oral cavity, with a temperature of 37°C and a saliva flow rate of 0.5mL/min. The simulated fixed orthodontic appliance made of stainless steel was evaluated. Sampling was performed at several time points during the 28-day study, and the metal ion concentration was determined by inductively coupled plasma optical emission spectrometry.

RESULTS

The total mass of released metal ions from the appliance during 4 weeks of the experiment was as follows nickel 18.7 μg, chromium 5.47 μg, copper 31.3 μg.

CONCLUSIONS

The estimated doses of nickel, chromium, and copper determined by extrapolation of experimental data released during the treatment period were far below the toxic dose to humans. This shows that orthodontic treatment might not be a significant source of exposure to these metal ions.

Inhalation toxicity of 316L stainless steel powder in relation to bioaccessibility

The Globally Harmonized System for Classification and Labelling of Chemicals (GHS) considers metallic alloys, such as nickel (Ni)-containing stainless steel (SS), as mixtures of substances, without considering that alloys behave differently compared to their constituent metals. This study presents an approach using metal release, explained by surface compositional data, for the prediction of inhalation toxicity of SS AISI 316L. The release of Ni into synthetic biological fluids is >1000-fold lower from the SS powder than from Ni metal, due to the chromium(III)-rich surface oxide of SS. Thus, it was hypothesized that the inhalation toxicity of SS is significantly lower than what could be predicted based on Ni metal content. A 28-day inhalation study with rats exposed to SS 316L powder (<4 µm, mass median aerodynamic diameter 2.5–3.0 µm) at concentrations up to 1.0 mg/L showed accumulation of metal particles in the lung lobes, but no signs of inflammation, although Ni metal caused lung toxicity in a similar published study at significantly lower concentrations. It was concluded that the bioaccessible (released) fraction, rather than the elemental nominal composition, predicts the toxicity of SS powder. The study provides a basis for an approach for future validation, standardization and risk assessment of metal alloys.

Metal release from stainless steel powders and massive sheets--comparison and implication for risk assessment of alloys

Industries that place metal and alloy products on the market are required to demonstrate that they are safe for all intended uses, and that any risks to humans, animals or the environment are adequately controlled. This requires reliable and robust in vitro test procedures. The aim of this study is to compare the release of alloy constituents from stainless steel powders of different grades (focus on AISI 316L) and production routes into synthetic body fluids with the release of the same metals from massive sheets in relation to material and surface characteristics. The comparison is justified by the fact that the difference between massive surfaces and powders from a metal release/dissolution and surface perspective is not clearly elucidated within current legislations. Powders and abraded and aged (24 h) massive sheets were exposed to synthetic solutions of relevance for biological settings and human exposure routes, for periods of up to one week. Concentrations of released iron, chromium, nickel, and manganese in solution were measured, and the effect of solution pH, acidity, complexation capacity, and proteins elucidated in relation to surface oxide composition and its properties. Implications for risk assessments based on in vitro metal release data from alloys are elucidated.

Immunotherapy of allergic contact dermatitis

The term 'immunotherapy' refers to treating diseases by inducing, enhancing or suppressing immune responses. As allergy is an excessive, detrimental immune reaction to otherwise harmless environmental substances, immunotherapy of allergic disease is aimed at the induction of tolerance toward sensitizing antigens. This article focuses on the historical developments, present state and future outlook for immunotherapy with haptens as a therapeutic modality for allergic contact dermatitis. Inspired by the effectiveness of immunotherapy in respiratory allergies, attempts were undertaken at curing allergic contact dermatitis by means of controlled administration of the sensitizing haptens. Animal and human experiments confirmed that tolerance to haptens can be induced most effectively when the induction of tolerance precedes attempted sensitization. In real life, however, therapy is sought by people who are already sensitized and an effective reversal of hypersensitivity seems more difficult to achieve. Decades of research on Rhus hypersensitivity led to a conclusion that immunotherapy can suppress Rhus dermatitis, however, only to a limited degree, for a short period of time, and at a high risk of side effects, which makes this method therapeutically unprofitable. Methodological problems with most available studies of immunotherapy of contact allergy to nickel make any definite conclusions impossible at this stage.

Dermatitis in patients undergoing the Nuss procedure for correction of pectus excavatum

BACKGROUND

The Nuss procedure was introduced in 1987 for the correction of pectus excavatum. In this procedure, a stainless steel bar is placed underneath the sternum.

OBJECTIVES

To report cutaneous reactions associated with Nuss bar placement.

METHODS

Over a period of 30 months, 50 patients underwent the Nuss procedure. The study population was limited to those who developed clinically significant cutaneous reactions postoperatively. Patient information was obtained from electronic medical records. All patients had been patch tested preoperatively with stainless steel discs supplied by the bar manufacturer. When performed, expanded patch testing was carried out in accordance with the North American Contact Dermatitis Group guidelines.

RESULTS

Postoperatively, 3 patients developed areas of protuberant granulation tissue at one or more incision sites. One patient developed localized oedema, dermatitis, and lymphadenopathy. Two of these 4 patients underwent further patch testing. Of these 2, 1 with dermatitis had a positive reaction to nickel and the other, with granulation tissue, tested negative for metal allergy.

CONCLUSIONS

Despite clinical evidence of cutaneous reactions or putative allergy, no patient required early removal of the bar(s). Cutaneous testing with stainless steel discs supplied by the bar manufacturer does not provide accurate screening for allergy to the implant used in the Nuss procedure.

Release of metal ions from orthodontic appliances by in vitro studies: a systematic literature review

In the present work, a systematic literature review on release of metal ions from orthodontic appliances under in vitro conditions is described. Detailed and schematic analysis of used materials and applied methods (immersion media, incubation time, temperature, and analytical techniques) is provided. The PubMed search identified 40 studies, among which eight met the selection criteria. One additional study was included in the review. All the authors agreed that the doses of released metal ions were far below the toxic level and the dietary intake. Although the concentrations of metal ions in immersion media greatly differed, the general conclusions were coherent. It must be underlined that the main disadvantage of in vitro tests was that the experimental setup did not reflect in vivo conditions, e.g., the presence of biofilm, which grows on the surface of the materials in oral cavity. The presence and activity of microflora to a large extent is responsible for the process of corrosion, in particular, biodeterioration. The further scheme of in vitro research should incorporate changeable conditions of oral cavity environment (pH, dynamic conditions-saliva flow) and the presence of microbiological flora (microbiological attack) in the experimental design and, first of all, the real proportions of appliance elements.

Nickel sensitisation in mice: a critical appraisal

BACKGROUND

The market release of new domestic and industrial chemical and metal products requires certain safety certification, including testing for skin sensitisation. Although various official guidelines have described how such testing is to be done, the validity of the available test models are in part dubious, for which reason regulatory agencies and research aim to further improve and generalise the models for testing of skin sensitisation.

OBJECTIVE

We applied a recently published murine model of nickel allergy as to test its applicability in a regulatory setting and to study and better understand the events leading to type-IV hypersensitivity. Nickel was chosen as model hapten since it induces allergic contact dermatitis with high incidence in the general population.

METHOD

Typically, C57BL/6 mice were sensitised and challenged by intradermal applications of nickel, and cutaneous inflammation was analysed by the mouse ear-swelling test, by histology, and by lymphocyte reactivity in vitro.

RESULT

Surprisingly, the study suggested that the skin reactions observed were results of irritant reactions rather than of adaptive immune responses. Non-sensitised mice responded with cutaneous inflammation and in vitro lymphocyte reactivity which were comparable with nickel-sensitised mice. Furthermore, histological examinations as well as experiments in T-cell deficient mice demonstrated that lymphocytes were not involved and that nickel caused an irritant contact dermatitis rather a true allergic type-IV contact dermatitis.

CONCLUSION

The authors question the validity of the described murine model of nickel allergy.

Face and neck dermatitis from a stainless steel orthodontic appliance

Although nickel is the most common cause of contact allergy, nickel-containing orthodontic appliances seldom cause adverse reactions that result in discontinuation of treatment. We report on an eruption of dermatitis in the face and neck of an adult female patient after placement of a rapid maxillary expansion appliance (RME). Because the patient suspected nickel allergy, her tolerance to the appliance material was tested intraorally before treatment by cementing bands on four teeth for a week. No visible adverse reactions were seen during the test. One week after cementation of the RME appliance, the patient reported strong itching of the face and a red rash. Clinical examination showed itchy papular erythema on the face and neck. No intraoral reactions or symptoms were present. The RME appliance was removed, and symptoms disappeared in 4 to 5 days. The patient was referred for a nickel patch test, which gave a strong positive result. Adverse patient reactions of potential allergic origin should be diagnosed carefully, and their possible impact on further treatment should be evaluated accordingly.

Release of Palladium from Biomechanical Prostheses in Body Fluids Can Induce or Support PD-Specific IFNγ T Cell Responses and the Clinical Setting of a Palladium Hypersensitivity

The increased use of Palladium (Pd) for biomedical applications, which has more than doubled in the last ten years, appears to be associated with an increased frequency of adverse reactions to Pd. The aim of this study is to investigate the relationship between the implant of a biomechanical apparatus containing Pd and the setting of a hypersensitivity to Pd by determining the levels of the metal released in biological fluids, assessing the effects of Pd on peripheral blood mononuclear cell (PBMC) cytokine production and exploring the clinical setting of skin sensitization. Of a total of 3,093 subjects examined in 2006, sensitization to Pd alone or in association with nickel (Ni) was observed in 1.6% and 13.03% of the individuals, respectively. Of these, a group of six subjects positive to Pd and negative to Ni at patch testing were selected on the basis of the oral clinical symptoms in order to measure both the levels of Pd in biological fluids and the degradation of the dental prostheses. Specific Pd measurements were carried out on salivary fluid, urine and serum samples by High Resolution Inductively Coupled Plasma-Mass Spectrometry. In addition, the degradation of the dental prostheses was assessed by both a “leaching test” and an analysis of the micro morphology of orthodontic prostheses. The induction of IFN-γ production by Pd was assessed in PBMC by the ELISpot assay. Skin sensitization to Pd was evaluated by patch testing and clinical examination. Ten healthy subjects were comparatively tested as controls. We found a specific induction of an IFN-γ response by Pd in PBMC collected from all the subjects positive to Pd at patch testing. On the contrary, control subjects did not show any response to Pd as assessed by IFN-γ ELISpot assay or by skin testing. Remarkably, the levels of Pd in all biological samples (saliva, sera, urine) were significantly higher in Pd-sensitized patients than in those collected from controls, reaching the highest concentrations in the urine. The leaching studies gave additional evidence that the dental appliances can release measurable levels of Pd in saliva. Oral clinical symptoms in patients with Pd dental prostheses were associated with measurable levels of Pd in the biological fluids, the induction of Pd-specific IFN-γ responses in PBMC and the clinical evidence of skin sensitization to Pd. These data suggest that dental appliances may represent an active source of Pd in the body, and this, in turn, can favour the clinical setting of a hypersensitivity to this metal.

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.

Dose dependence of oral tolerance to nickel

The dose dependence of oral nickel tolerance was analyzed by comparing three different subsets of C57BL/6 mice: Ni(very low) mice were reared in a nickel-reduced environment, Ni(low) and Ni(high) mice were reared in a stainless steel-containing environment and the latter received oral NiCl(2) (10 mM). In spleen and feces, Ni(very low) mice exhibit significantly lower nickel concentrations than Ni(low) and Ni(high) mice. In contrast to Ni(very low) mice that can be sensitized with a single intradermal administration of NiCl(2) alone, Ni(low) mice can only be sensitized in the presence of an adjuvant and Ni(high) mice cannot be sensitized at all. This dose-dependent resistance to nickel sensitization (i.e. Ni(high) > Ni(low) > Ni(very low)) correlates with differences in the number and type of nickel-specific T regulatory (Treg) cells. Adoptive transfer studies into Ni(very low) recipients showed that Ni(very low) mice completely lack specific Treg cells whereas Ni(low) and Ni(high) mice harbor them, albeit their numbers and/or suppressive strength are much higher in Ni(high) than Ni(low) mice. The principal Treg subset in Ni(low) mice consists of CD4(+)CD25(+) cells, among which CD4(+)CD25(+)alpha(E)beta(7)(+) cells are the most effective. In Ni(high) mice, CD4(+)CD25(+) Treg cells co-exist with an ensemble of CD8(+) Treg and CD4(+)CD25(-) suppressor-inducer cells.

Nickel release from nickel particles in artificial sweat

Nickel is widely used in a broad range of products, primarily made of alloys, used by humans on a daily basis. Previous assessments have shown that skin contact with some such products may cause nickel allergic contact dermatitis, induced by the release of nickel. However, data on nickel release from small nickel particles in artificial sweat for assessment of potential risks of workers in nickel-producing and nickel-using facilities are not available. The objective of this study was to fill this knowledge gap by determining nickel release from fine nickel powder ( approximately 4 microm diameter) of different loadings varying from 0.1 to 5 mg/cm(2), when immersed in artificial sweat. The amount of nickel released increased with increasing particle loading, whereas the highest release rate per surface area of particles was observed for the medium particle loading, 1 mg/cm(2), at current experimental conditions. All particle loadings showed time-dependent release rates, reaching a relative steady-state level of less than 0.1 microg/cm(2)/hr after 12 hr of immersion, whereby less than 0.5% of the nickel particle loading was released. Nickel release from particles was influenced by the surface composition, the active surface area for corrosion, particle size, and loading.

Resistance to sliding of titanium brackets tested against stainless steel and beta-titanium archwires with second-order angulation in the dry and wet states

INTRODUCTION

With the increased awareness of Ni allergies, alternative alloys for orthodontic products must be identified. The properties of these new products must be determined.

METHODS

Rectangular (0.017 x 0.025 in) stainless steel (SS) and beta-titanium (beta-Ti) archwires were tested against commercially pure titanium brackets (CP-Ti, 0.018-in slot) in the dry state and with whole human saliva. Resistance to sliding (RS) was measured as a function of 5 normal forces (N, 200 to 950 cN), 32 angles (theta, -12 degrees to +12 degrees), and 1 interbracket distance (IBD, 18 mm).

RESULTS

With clearance between the archwire and the bracket (passive region, theta < or =theta(c)), the frictional coefficients (mu) of the SS archwire and the CP-Ti bracket couples were 0.12 and 0.13 for the dry and wet tests, respectively; for the beta-Ti archwire and the CP-Ti bracket couples, the mu values were 0.29 and 0.28 for the dry and wet tests, respectively. For an theta without clearance (active region, theta > or =theta(c)), RS increased as a function of theta and N. To examine the rates of binding (mu(BI)) in this active region, the value of classical friction (mean of the passive region data) was subtracted from RS to yield BI, and the value of theta(c) was subtracted from each theta to yield relative contact angles (theta(r)). Because of the unique relationship between the frictional and mechanical properties of these SS and beta-Ti archwires tested against the CP-Ti brackets at a large IBD, the mu(BI) values for these archwire-bracket couples were nominally equivalent (24 to 30 cN per degree). Clinical outcomes would be unaffected by this 6 cN per degree (approximately 0.2 oz-force per degree) difference. When all kinetic data in the elastic region (theta(r) < or =5 degrees ) were combined, mu(BI) equaled 28 cN per degree. Above this region (theta(r) > or =5 degrees ), the data for the SS archwire and CP-Ti bracket couples were less scattered than those for the beta-Ti archwire and the CP-Ti bracket couples. This demarcation from linearity was designated as theta(z) and indicated the end of the elastic region and the beginning of the plastic region, above which sliding can eventually cease. This region (theta > or =theta(z)), the binding region (theta(c) < or =theta < or =theta(z)), and the classical friction region (theta < or =theta(c)) were described in a model.

CONCLUSIONS

This model explains, in part, the equivalent values of mu(BI) for SS and beta-Ti archwires tested against CP-Ti brackets.

Dissolution of materials in artificial skin surface film liquids

The dissolution of chemical constituents from jewelry, textiles, cosmetics, drugs, industrial chemicals, and particles in direct and prolonged contact with human skin is often assessed in vitro using artificial skin surface film liquids (SSFL). To provide meaningful results, the composition of artificial SSFL should accurately mimic human sweat and sebum, and the conditions of the in vitro test system should accurately reflect in vivo skin conditions. We summarized the reported composition of human SSFL and compared it to 45 different formulations of artificial sweat and 18 formulations of artificial sebum (studies published from 1940 to 2005). Conditions of in vitro dissolution test systems were reviewed and compared to in vivo skin conditions. The concentrations of individual constituents and pH of artificial sweat and concentrations of artificial sebum constituents are not always within ranges reported for human SSFL. Nearly all artificial SSFL lack many of the constituents in human SSFL. To develop a comprehensive model SSFL, we propose a standard SSFL, modified from the two best published sweat and sebum formulations. Little is known concerning the influence of test system conditions on dissolution, including SSFL temperature, container material composition, agitation, and physicochemical properties of the test article on dissolution. Thus, both a need and an opportunity exist for standardizing the composition of artificial SSFL and in vitro dissolution test methodologies. To standardize in vitro dissolution test systems, we recommend: maintaining artificial SSFL at a biologically relevant temperature appropriate to the human activity being modeled, carefully selecting test and sample storage containers to avoid bias in dissolution measurements, accounting for friction between a test article and skin in a biologically plausible manner, and physicochemical characterization of the test article or material to better understand mechanisms of dissolution and potential mechanisms of toxic action of dissolved material. More accurate modeling and better understanding of chemical dissolution from articles in contact with the skin will ultimately improve risk decision making, thereby protecting even the most susceptible persons from adverse health effects resulting from skin exposure.

A follow-up study of patients with subjective symptoms related to dental materials

OBJECTIVES

The extent to which substances released from dental materials cause adverse health effects and whether removal of dental materials results in improvement of health is a matter of dispute. The aim of the study was to investigate changes in the intensity of subjective symptoms after replacement of dental materials in patients referred for adverse reactions related to dental materials, and to compare the profiles of symptoms with those found in the general population.

METHODS

Information was obtained from 142 patients referred to the Dental Biomaterials Adverse Reaction Unit in Bergen, Norway. At the time of examination, all patients completed a questionnaire regarding a range of subjective symptoms. A follow-up questionnaire was sent to all patients 1 to 2 years later. Similar questionnaires were sent to a reference group of 800 persons drawn from the general population.

RESULTS

The follow-up questionnaires were completed and returned by 84 patients, and 441 persons in the reference group. The patient group presented higher symptom indices than the reference group (P<0.001). Generally, there was some decrease in the intensity of different symptoms in patients who had replaced dental materials. The decrease was evident regarding intraoral symptoms (P=0.022) and total symptom index (P=0.041). The group of patients who had replaced materials still had significantly higher symptom indices than those of the reference group. Patients who had not replaced dental materials did not present any reduction in symptom indices.

CONCLUSION

The pattern of symptoms was similar for the groups investigated. At the group level, the intensity of local and some general subjective symptoms was reduced after replacement of the materials, but not to the level found in the general population.

Occupational allergens in dentistry

PURPOSE OF REVIEW

Dental professionals and their physicians frequently do not recognize, accurately diagnose or appropriately manage occupational allergies. Dental allergen identification, diagnostics and practical avoidance strategies are summarized in this review.

RECENT FINDINGS

Methacrylates, natural rubber latex proteins, rubber glove allergens, and glutaraldehyde are the predominant allergens in dentistry. Reactions range from cell-mediated contact allergy to urticaria and occupational asthma.

SUMMARY

Despite recent advances in allergen characterization and increased awareness of selected allergens, treatment of occupational allergies can be improved. Better information and improved cooperation between dental workers and their clinicians is needed.