Effect of toothbrushing on elemental release from dental casting alloys

Usefulness of lymphocyte transformation test and in vitro cytokine release in differentiating between independent and cross-reacting nickel/palladium allergy

BACKGROUND

Often concomitant patch test (PT) reactivity to palladium (Pd) and nickel (Ni) is found.

OBJECTIVES

To determine whether lymphocyte transformation test (LTT) could be useful in discrimination between cross-reacting or distinct PT results, and to compare the results with in vitro cytokine production upon Pd or Ni stimulation.

MATERIALS AND METHODS

The study population consisted of two groups: 13 individuals with Pd PT reactions (10 with concomitant Ni PT reaction, 3 individuals with only Pd PT reactivity) and 10 Ni/Pd PT negative individuals. LTT and assessment of cytokine release (interferon-gamma, interleukin-5 [IL-5], IL-8, IL-17A, tumor necrosis factor alpha) by cytometric bead assay were performed.

RESULTS

All 10 patients with positive PT to Ni and Pd showed positive LTT to Ni (P < .05) as compared with the 10 Pd/Ni PT negative patients-but had no significant LTT reaction to Pd. In all, 9 out of 10 Pd/Ni PT negative patients were also LTT negative to Ni and 10 out of 10 to Pd. In the 3 only Pd PT reactors 2 out of 3 remained LTT negative to Ni and 0 out of 3 to Pd. As a major finding, cytokine production gave clearly enhanced IL-5 response to Ni in Ni PT positive individuals (P < .05), whereas Pd PT reactivity was not linked with such enhanced IL-5 production in vitro to Pd.

CONCLUSIONS

Pd and Ni sensitization are mostly found concomitantly, and cross-reactivity is questioned. By different LTT reactions and particularly IL-5 production in vitro, predominant Ni sensitization becomes more evident.

Delayed-type hypersensitivity to metals in connective tissue diseases and fibromyalgia

Rheumatic diseases include a group of autoimmune disorders with environmental and genetic etiology that are characterized as a subgroup of connective tissue diseases (CTD). Rheumatoid arthritis (RA) often involves the small joints of the hands in a symmetrical fashion that can lead to loss of joint function, and RA, as well as Sjögren's syndrome (SS) and other rheumatic diseases, are often accompanied by sensitivity to metals. Numerous investigations on metal sensitivity were evaluated in this review. A detailed metal exposure history was collected by different evaluation of studies. In all subjects, the main source of metal exposure was nickel, mercury, gold, palladium, titanium, and chromium. All of SLE (systemic lupus erythematosus), RA and SS patients appeared to have an increased frequency of metal delayed-type hypersensitivity (DTH) (Type IV allergy). As dental restorative materials release minor amounts of their metals (including mercury, gold, and nickel), many adults are commonly exposed to these metal ions by vapor or corrosion into saliva. Metal-related DTH in these patients will induce an inflammatory response. Such inflammations are important factors in CTD progress. It is hypothesized that metal-specific T cell reactivity can act as an etiological agent in the propagation and chronification of rheumatic inflammation. The key responses of metal delayed-type hypersensitivity in autoimmunity are precipitating as an appealing challenge for further investigations.

Nylon Bristles and Elastomers Retain Centigram Levels of Triclosan and Other Chemicals from Toothpastes: Accumulation and Uncontrolled Release

Triclosan (TCS), a broad-spectrum antimicrobial, is used in commercial toothpastes with reported dental benefits. Our studies on 22 popular manual toothbrushes in the U.S. showed that common toothbrush head components can accumulate substantial amounts of TCS after brushing with TCS-formulated toothpastes (TCS-TPs). After simulated 3-month brushing with a commercial best-selling TCS-TP, over one third of the adults' toothbrushes showed a cumulative TCS uptake of 21-37.5 mg, equivalent to 7-12.5 doses of the TCS used per brushing. Similar results were observed on children's toothbrushes with small pea-size heads. Elastomer components were found to be the main contributor while both nylon bristles and elastomers could act as absorptive sinks for TCS during brushing. Studies on six different TCS-TPs containing 0.3 wt% TCS showed similar profiles of TCS accumulation. The absorbed TCS was gradually released into toothpaste slurries after switching to TCS-free alternatives. Release of TCS, which typically measured at a fraction (<75%) of the standard dose using the TCS-TPs, continued for over 2 weeks and occurred most rapidly in peroxide-containing "whitening" toothpastes, followed by alkaline and surfactant-rich toothpastes. The accumulating effect was not exclusive to TCS but was commonly observed on several chemicals identified in TCS-TPs and a range of regular toothpastes.

Increased frequency of delayed type hypersensitivity to metals in patients with connective tissue disease

BACKGROUND

Connective tissue disease (CTD) is a group of inflammatory disorders of unknown aetiology. Patients with CTD often report hypersensitivity to nickel. We examined the frequency of delayed type hypersensitivity (DTH) (Type IV allergy) to metals in patients with CTD.

METHODS

Thirty-eight patients; 9 with systemic lupus erythematosus (SLE), 16 with rheumatoid arthritis (RA), and 13 with Sjögren's syndrome (SS) and a control group of 43 healthy age- and sex-matched subjects were included in the study. A detailed metal exposure history was collected by questionnaire. Metal hypersensitivity was evaluated using the optimised lymphocyte transformation test LTT-MELISA(®) (Memory Lymphocyte Immuno Stimulation Assay).

RESULTS

In all subjects, the main source of metal exposure was dental metal restorations. The majority of patients (87%) had a positive lymphocyte reaction to at least one metal and 63% reacted to two or more metals tested. Within the control group, 43% of healthy subjects reacted to one metal and only 18% reacted to two or more metals. The increased metal reactivity in the patient group compared with the control group was statistically significant (P<0.0001). The most frequent allergens were nickel, mercury, gold and palladium.

CONCLUSIONS

Patients with SLE, RA and SS have an increased frequency of metal DTH. Metals such as nickel, mercury and gold are present in dental restorative materials, and many adults are therefore continually exposed to metal ions through corrosion of dental alloys. Metal-related DTH will cause inflammation. Since inflammation is a key process in CTDs, it is possible that metal-specific T cell reactivity is an etiological factor in their development. The role of metal-specific lymphocytes in autoimmunity remains an exciting challenge for future studies.

Nickel alloys in the oral environment

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

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.

A clinical evaluation of cobalt-chromium metal-ceramic fixed partial dentures and crowns: A three- to seven-year retrospective study

STATEMENT OF PROBLEM

In severely compromised dentition, loading of long-span and cantilever metal-ceramic fixed partial dentures (FPDs) could result in framework deformation and porcelain fractures. The use of cobalt-chromium (Co-Cr) alloys may be advantageous, but there is little information on the longevity of, and complications with, prostheses made with these alloys.

PURPOSE

The aim of this retrospective study was to report the survival and complication rates of Co-Cr metal-ceramic FPDs and crowns followed over a 3- to 7-year period.

MATERIAL AND METHODS

The study included 42 patients with a total of 51 FPDs and 12 single crowns assigned to 1 of 3 groups. The 3 groups comprised patients with abutment teeth with a questionable prognosis (n=10), advanced chronic periodontitis (n=19), or abutment teeth with a positive prognosis (n=13). The FPDs had a mean of 9.7 units (range of 3-14). Of the FPDs, 32 were provided with a cantilever on 1 side (n=24) or both sides (n=8). The mean observation time was 51 months (range of 28-82). All patients were examined by 2 independent prosthodontists using the California Dental Association (CDA) assessment system for evaluation. One-way ANOVA with Fisher's LSD post hoc test and the Mann-Whitney U test were used for statistical analyses (alpha=.05).

RESULTS

Seventeen (34%) of the FPDs had biological and/or technical complications. Six (12%) FPDs were completely or partially removed during the observation period, 1 framework fractured, and 9 (17.6%) FPDs had ceramic fractures. Fifteen of the 21 fractured FPD units were related to FPDs that were placed in 3 patients with bruxing habits. The CDA rating for marginal integrity was "excellent" for more than 98% of the abutments. No patients reported adverse reactions to the material.

CONCLUSIONS

Metal-ceramic FPDs made of cobalt-chromium alloy performed acceptably in the questionable prognosis and advanced chronic periodontitis groups.

Toothbrushing causes elemental release from dental casting alloys over extended intervals

The release of elements from dental alloys has been linked to alloy biocompatibility. Much of the research measuring elemental release has been done in vitro under passive conditions. The current study supplements a previous report that measured elemental release from dental alloys during and after the equivalent of 1 week of toothbrushing. In the current study, toothbrushing times were extended to the equivalent of 2 years, and elemental release was measured during and after brushing, with and without toothpaste. The results showed that for the major classes of dental alloys, brushing alone caused no significant elemental release during the brushing, and only minor increases after brushing. Brushing with toothpaste caused significant increases in elemental release for all elements of all alloys, but the largest increases were for the two nickel-based alloys. Nickel released during brushing with toothpaste reached 600-800 microg/cm(2) of alloy surface. Both beryllium-containing and non-beryllium-containing nickel-based alloys behaved similarly, refuting claims that non-beryllium alloys are superior in this regard. Thus, brushing with toothpaste under these extended in vitro conditions appears to increase the biological liabilities from elemental release for all alloys, but primarily for nickel-based alloys.

Palladium--a review of exposure and effects to human health

Palladium is a metal the output and use of which has more than doubled in the past ten years. It is used in dental appliances, chemical catalysts, electrical appliances and jewelry, but the greatest increase in Pd demand has been in automotive emission control catalysts. Studies on Pd concentrations in ancient ice and recent snow samples reflect the increase in mining, smelting and use of palladium in the last decades. Increases of palladium in the environment have been shown in air and dust samples. There is no data as yet available to assess the effect of this exposure. A major source of health concern is the sensitization risk of Pd as very low doses are sufficient to cause allergic reactions in susceptible individuals. Persons with known nickel allergy may be especially susceptible. Workers occupationally exposed to Pd include miners, dental technicians and chemical workers. The latter are exposed mainly to Pd salts several of which may cause primary skin and eye irritations. It is advised that persons with known Pd allergy should not work with Pd compounds. The general population may come into contact with palladium mainly through mucosal contact with dental restorations and jewelry containing palladium and possibly via emissions from Pd catalysts. Protection of the public from related adverse effects may be achieved by the use of alloys with high corrosion stability and thus minimal release of palladium. In general, in dental patients who are sensitive to Pd, restorations using Pd-containing materials should not be used although Pd has been used without allergic effects in some of these individuals. Further, those patients who have an allergy to nickel should be informed that use of Pd-containing dental materials may cause Pd allergy, though this risk appears to be low.

Do powered toothbrushes contaminate toothpaste with metals?

Replaceable brush units of powered toothbrushes (PTBs) can contain metal parts made of nickel and chromium bearing alloy. These alloy ingredients have allergenic potential, and may contaminate toothpaste and the mouth during use. Here I quantify metals abraded from PTBs. A leading brand of PTB was used in a simulated intraoral environment with three leading brand toothpastes, and post-brushing samples were analysed for iron, chromium, nickel, molybdenum, and manganese by certified laboratories using standard methods. Results showed tartar control toothpaste abraded most metal, and caused discolouration of toothpaste slurry. Discolouration of toothpaste slurry, as a useful indicator of metal abrasion, was limited to one toothpaste brand, and not useful across brands.

Elemental release from dental casting alloys into biological media with and without protein

OBJECTIVE

The objective of this study was to determine the role of proteins in affecting elemental release from a variety of clinically available dental casting alloys. An important role for proteins was suspected based on previous reports about the corrosion of stainless steel and the cytotoxicity of alloys after exposure to a saline-protein solution.

METHODS

Clinically available alloys with compositions ranging from 0 to 94at.% noble elements were exposed for 1 week to either saline, saline with 3% bovine serum albumin (BSA), or complete cell-culture medium with 3% serum. Atomic absorption spectrophotometry was used to measure the release of elements from the alloys. Elemental release was normalized for the exposed surface area of the alloys.

RESULTS

In general, more elemental release occurred into the saline-BSA solution compared to saline alone for all released elements (Ag, Cu, Pd, and Zn) except for Ni. Ni release from the NiCr alloy was lower in the presence of BSA. Each element responded somewhat differently with Pd being the least predictable in its behavior. Elemental release was less in the cell-culture medium than in the saline-BSA solution for most elements. For alloys which released multiple elements, all elements responded similarly but not identically to the presence of protein. A high elemental release during exposure to the saline-BSA solution correlated with a low alloy cytotoxicity post-exposure to the saline-BSA.

SIGNIFICANCE

This study demonstrates the importance of defining exactly the composition of biological solutions used to assess in vitro corrosion and biocompatibility of dental casting alloys. Other molecules in addition to proteins appeared to be critical to the corrosion of these alloys in vitro.