Elemental analysis of contemporary dental materials regarding potential beryllium content
grid.5963.9Department of Prosthetic Dentistry, Faculty of Medicine, Medical Center, Center for Dental Medicine, University of Freiburg, Freiburg, Germany
grid.7892.40000 0001 0075 5874Institute of Applied Materials, Applied Material Physics (IAM-AWP), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany
grid.5963.9Faculty of Medicine, Medical Center –Clinic of Respiratory Medicine, University of Freiburg, Freiburg, Germany
Abstract
Exposure to beryllium (Be) can lead to lung pathologies, such as chronic beryllium disease (CBD). This occupational illness has been more prevalent among dental technicians compared to the non-exposed population. Although most manufacturers state that dental materials are Be-free, this prevalence raises the question of whether the materials are completely devoid of Be-traces. Thus, the objective of the present study was to analyze the elemental composition, with emphasis on Be, of a wide range of commercially available dental materials frequently used by dental laboratories. Samples of 32 different materials were collected and analyzed using inductively coupled plasma-optical emission spectrometry (ICP-OES) and X-ray fluorescence spectroscopy. The results showed that the Be content was below the limit of quantification in all included samples (< 0.00005 mass-%). Therefore, it can be concluded that possible traces of Be were below clinical relevance in dental materials. Exposure of dental technicians to alternative Be sources should be further evaluated.
Introduction
Beryllium (Be) is a chemical element and naturally occurring lightweight metal that finds industrial application in electronics, aerospace, and defense equipment1–3. In the field of dentistry, Be has been used in nickel–chromium4,5 alloys with contents of up to 2.05 mass.%6 for the fabrication of prosthetic reconstructions. Be reduces the melting temperature, decreases the surface tension, and increases the bond strength between metals and ceramics7. Furthermore, it improves the castability and polishing of non-precious alloys.
Manufacturing and processing of Be-containing materials is highly toxic, and workers are exposed to the inhalation of Be particles, fumes, or solutions8. Brief exposure can lead to the development of a rare condition called acute berylliosis9, while long-term contact can cause Be sensitization (BeS)10 and chronic Be disease (CBD), also known as chronic berylliosis10,11. An official statement of the American Thoracic Society assessed the prevalence of BeS between 0.9 and 14.6% and of CBD between 0.0 and 7.8%1. BeS represents an immunologically-mediated response to the metallic element without evidence of disease, while CBD is considered an incurable occupational lung condition and is often misdiagnosed with sarcoidosis or other granulomatous lung disorder10. Symptoms of CBD are cough, dyspnea, fatigue, fever, night sweats, and weight reduction3,8 with potential progression to the loss of respiratory function12. A history of occupational exposition to Be, positivity to the beryllium lymphocyte proliferation test (BeLPT) and a bioptic examination, confirming a granulomatous inflammation of the lungs, are considered signs for definitive diagnosis of CBD1. The incubation periods can last up to three decades13. Due to the available evidence of carcinogenicity in humans and the risk of developing lung cancer by occupational exposure, Be and Be compounds have also been classified as category 1 carcinogens by the International Agency for Research on Cancer14.
As a consequence of the increased occupational exposure to Be in dental laboratories, dental technicians appear at a higher risk of primarily developing CBD8,15–18. Therefore, to protect workers, the Occupational Safety and Health Administration recently established a new limit of 0.2 µg of Be per cubic meter of air for an exposure duration of eight hours or of < 2 µg of Be per cubic meter of air for more than 15 min18. According to the current ISO standard for fixed and removable restorations (ISO 22674:2016), the limit value for Be in metallic materials is 0.02% (mass fraction)19. Exposure to Be is considered the causal agent for CBD development, and it remains unclear why dental technicians might be more affected. Therefore, the present study aimed to determine the elemental composition of commonly used dental materials and assess the exact amount of Be. Both, non-precious and precious metal alloys used to fabricate prosthetic reconstructions were included. Furthermore, different types of dental ceramics, titanium alloys, polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), and polycarbonate were analyzed. Inductively coupled plasma-optical emission spectrometry (ICP-OES) represents a highly sensitive analytical technique with wide elemental coverage and was applied in the present study20,21 The null hypothesis at study conceptualization assumed that evaluated materials contain traces of Be.
Material and methods
Study design
The analytical work was performed by the Institute of Applied Materials–Applied Material Physics of the Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany. The study proposal for cooperation between the Department of Prosthetic Dentistry and Clinic of Respiratory Medicine of the University of Freiburg, Freiburg, Germany, and the KIT has been approved and accepted by the Karlsruhe Nano Micro Facility in 2020.
Investigated materials and interdisciplinary cooperation
Four non-precious (Co–Cr) and five precious (Au) alloys were evaluated in the present investigation. In addition, seven ZrO2-based ceramics, two feldspathic ceramics, one lithium disilicate glass-ceramic (Li2Si2O5), one nano-fluorapatite glass-ceramic, and one nano-hybrid composite for veneering were included. Furthermore, five implant-supported abutments made of titanium or ZrO2, three PMMA-based materials, one polycarbonate, and one PEEK were examined. The evaluated samples represented a selection of the most frequently used materials for each category in two German dental laboratories, which provided the samples for elemental analysis. An overview of the investigated materials and their commercial name and article number is given in Table 1.Manufacturer Article no. Sample name Material Kulzer H-01028 Heraenium EH Co–Cr alloy Kulzer M-01068 Heraenium PW Co–Cr alloy Dentaurum 102-620-00 Remanium Star Co–Cr alloy Shera 401,070 Sheraheavy-Metal Co–Cr alloy Kulzer SW12002-10 Mainbond EH Au alloy Kulzer SW12004-10 Bio Herador GG Au alloy Kulzer SW12035-0010 Bio Maingold SG Au alloy Kulzer SW12016-10 Heraloy G Au alloy Koos Edelmetalle 30,033 Ecobest Au alloy Zirkonzahn ZRAB8001 ICE Zircon Translucent Oxide ceramic Kuraray Noritake 6951 Katana™ Zirconia ML 3Y-TZP Zirkonzahn ZRFC8021A02 Prettau® 4 Anterior® Dispersive® 5Y-TZP Ivoclar Vivadent 725,196 IPS e.max ZirCAD Prime 3Y-TZP + 5Y-TZP Pritidenta 220,841 priti®multidisc ZrO2 Extra Translucent 4Y-TZP Dental Direkt G852017 DD cubeX2® ML 5Y-TZP Zirkonzahn ZRAB8001 ICE Zircon Translucent A3 Oxide ceramic Ivoclar Viviadent 247,590 IPS e.max Press LT Lithium disilicate glass-ceramic Ivoclar Vivadent 168,424 IPS e.max Ceram Nano-fluorapatite glass-ceramic GC Europe 622,643 Gradia™ Plus Nano-hybrid composite Kuraray Noritake 35,101,010 Ex-3 Feldspathic ceramic Kuraray Noritake 901,053 Cerabien™ ZR Feldspathic ceramic Zirkonzahn ZRAD8001 Prettau® Zirkon 95H10 Oxide ceramic Straumann 48,710 RN Variobase Implant abutment SIC 935,727 SIC Standard Abutment Implant abutment Kulzer 30,503,871 cara i-abutment® titanium Implant abutment Zirkonzahn BSAF0893 Set ZZ Base B-C-ABCH Implant abutment Tizian Blank 624,939 Tizian Blank Zirkoniumdioxid Implant abutment Organical CAD/CAM BL00067-3700 Organic PMMA ECO PMMA Organical CAD/CAM N/A Organic PMMA DISC Multicolour 5-Layer PMMA Organical CAD/CAM N/A Organic PMMA ECO Clear PMMA Ernst Hinrichs Dental 242,774 JUVORA™ PEEK PEEK Schütz Dental 220,361 Tizian Blank Polycarbonate
Preanalytical sample procession
The samples were divided into seven different groups depending on their different chemical composition. In Table 2 the preanalytical preparations and the chemical digestion are described for each group.Sample name Cutting(1) Pestle(2) Etching(3) Sample weight(4)
mgChemical decomposition Acid mixture Fill up graphite oven (5) flux (6) micro wave (7) ml Volume Solution min
°CLiBO2/LiBr
g
°Cmin
°CHF
suprapureHCl
subb
(ml)HNO3
subb
(ml)H2O2
suprapureH2SO4
suprapureUltrapure water ml RN Variobase x – x 90–120 12080 – 1 6 2 – – 2 50 Ultrapure water SIC Standard Abutment cara i-butment® titanium Set ZZ Base B-C-ABCH Tizian Blank Zirkoniumdioxide x – – 120–220 – – 3 / 30150 / 250 – – 6 – 4 – 50 Ultrapure water JUVORA™ PEEK Mainbond EH(8) x – – 180–240 24080 – – – 12 4 – – – 50 10% HCl Bio Herador GG Bio Maingold SG(8) Heraloy G Ecobest(8) Tizina Blank x – – 88–185 - - 5/15150/180 – – 10 2 – – 50 Ultrapure water Organic PMMA ECO Organic PMMA DISC Multicolour 5-Layer Organic PMMA ECO Clear ICE + Farbe – x – 150 – 2/0.02 1000 – – HCl 1:125 HNO3 1:125 – – – 100 Ultrapure water ICE Zircon Transluzent KatanaTM Zirconia ML Prettau® 4 Anterior® Dispersive® IPS e.max ZirCAD Prime priti®multidisc ZrO2 Extra Translucent DD cubeX2® ML Sheraheavy-Metal x – – 100–129 72090 – – 2 6 2 – – 2 50 Ultrapure water Heraenium EH(8) Heraenium PW(8) Remanium Star(8) e.max Press LT – x – 120–150 - 2 / 0.02 1000 – – – HNO3 10%50 – – – 100 Ultrapure water e.max Ceram GradiaTM Plus Ex-3 Cerabien™ ZR Prettau® Zirkon 95H10
Inductively coupled plasma-optical emission spectrometr
Each sample solution was diluted several times depending on the concentration of the various elements. Instead of using volumetric dilution methods, the sample solution and ultrapure water were weighed (XP 205, Mettler-Toledo, Gießen, Germany). Analysis of the elements was accomplished with four different calibration solutions and an internal standard (Sc) by ICP-OES (iCAP 7600 ICP-OES Duo, Thermo Fisher Scientific Inc., Waltham, MA, USA) (Table 3). For Be the solution was, if necessary, matrix adapted (Ti, Co, Cu, Zr, Mo, Pd, In, W, Pt, Au). The range of the calibration solutions extended from 0.0005 to 0.01 mg/l. One to three wavelengths of Be were used for the calculation.ICP Peristaltic pump Mira Mist peek nebulizer Gas flow 0.6 (L/min) Cyclon teflon spray chamber Ceramic torch with ceramic injector tube RF power (W) 1150 Auxiliary gas flow 0.5 (L/min) for main compounds 1.0 (L/min) for high matrix content Wavelength (nm) Be 234.861; 313.042; 313.107 Al 176.638; 308.215; 394.401; 396.152 Si 212.412; 221.667; 251.611 K 766.490; 769.896 Ti 323.452; 334.188; 334.941; 337.280; 338.376 V 268.796; 292.464; 309.464 Cr 205.560; 206.157; 267.716 Co 228.616; 230.786; 238.892 Cu 213.598; 324.754; 327.396 Zn 202.548; 206.200; 213.856 Ga 287.424; 294.364; 403.298; 417.206 Y 371.030; 377.433; 437.494 Zr 339.198; 346.823; 348.115; 349.621; 357.685; 383.676 Mo 202.030; 203.844; 204.598 Pd 324.270; 340.458; 360.955 Ag 243.779; 32.068; 338.289 In 230.606; 303.936; 325.609; 410.172 Sn 175.790; 189.989; 181.120 Ba 230.424; 233.527; 413.066 Hf 251.303; 264.141; 277.336 W 207.911; 220.448; 224.875 Pt 177.709; 203.646; 214.423; 224.552 Au 197.819; 208.209; 211.068; 242.795; 267.595
X-ray fluorescence spectroscopy
All samples were analyzed semiquantitative via X-ray fluorescence spectroscopy (XRF) (Pioneer S4, Bruker AXS, Karlsruhe, Germany) against different universal calibrations depending on the material of the samples (metal, oxide, etc.).
Quality control
The certified ICP calibration solutions (Aesar, Thermo Fisher (Kandel) GmbH, Karlsruhe, Germany, CPAChem, Bogomilovo, Bulgaria) were controlled with another certified ICP solution from a different producer (Agilent, Waldbronn, Germany; Merck, Darmstadt, Germany). The recovery of these standards in matrix-adapted solutions was between 95 and 105%.
Descriptive statistics
Results of the elemental analysis are described in Tables 2, 3, 4, 5 and 6 as the mean outcome, standard deviation (SD) and measurement uncertainty ( ±). Data regarding the oxides are semiquantitative results determined with XRF against a universal calibration. The results were normalized to 100.Element Unit LOQ Heraenium EH Heraenium PW Remanium Star Sheraheavy-Metal Mean SD ± Mean SD ± Mean SD ± Mean SD ± Be mass-% 0.00001 < 0.00001 – – < 0.00001 – – < 0.00001 – – < 0.00001 – – Cr mass-% 0.1 26.9 – 2.7 23.0 – 2.3 23.0 1.2 30.9 0.1 1.5 Mn mass-% 0.100 0.568 – 0.114 0.677 – 0.169 < 0.100 – - 0.515 0.103 Fe mass-% 0.050 0.012 – 0.003 4.160 – 0.416 0.034 – 0.009 0.564 – 0.056 Co mass-% 0.1 63.4 – 6.3 54.7 – 5.5 59.8 4.6 3,0 59.1 0.2 3.0 Ga mass-% 0.37 < 0.37 – – < 0.37 – – < 0.37 – – < 0.37 – – Mo mass-% 0.09 7.57 – 1.14 < 0.09 – 0.22 – 4.97 0.01 0.25 In mass-% 0.06 < 0.06 – – < 0.06 – < 0.06 – < 0.06 – Sn mass-% 0.03 < 0.03 – – < 0.03 – < 0.03 – < 0.03 – W mass-% 0.07 < 0.07 – – 15.90 - 1,59 9.56 – < 0.07 – – Pt mass-% 0.05 < 0.05 – – < 0.05 – < 0.05 – < 0.05 – – Au mass-% 0.05 < 0.05 – – < 0.05 – < 0.05 – < 0.05 – – Total mass-% 98.44989 98.43700 92.61400 96.04884 Element Unit LOQ Mainbond EH Bio Herador GG Bio Maingold SG Heraloy G Ecobest Mean SD ± Mean SD ± Mean SD ± Mean SD ± Mean SD ± Be mass-% 0.000004 < 0.000004 – – < 0.000004 – – < 0.000004 – – < 0.000004 – – < 0.000004 – – Fe mass-% 0.200 < 0.200 – – 0.983 – 0.246 < 0.200 – – 0.318 – 0.080 0.230 – 0.058 Cu mass-% 0.53 7.43 0.03 0.37 < 0.53 – – 12.1 0.1 0.6 < 0.53 – – < 0.53 – – Zn mass-% 0.100 0.482 0.003 0.024 < 0.100 – – 0.473 0.006 0.024 < 0.100 – – 1.36 0.01 0.07 Ga mass-% 0.13 n.a – – < 0.13 – – n.a – – 1.97 0.02 0.10 n.a – – Pd mass-% 0.40 < 0.40 – – < 0.40 – – < 0.40 – – 35.9 0.1 3.6 9.73 0.10 0.49 Ag mass-% 0.30 15.2 – 1.52 n.a – – 14.3 – 1.43 n.a – – 29.1 – 2.9 In mass-% 0.30 < 0.30 – – 1.65 0.01 0.08 < 0.30 – – 8.21 0.11 0.41 3.96 0.01 0.20 Pt mass-% 0.12 8.36 0.04 3.59 11.2 0.1 3.59 3.85 0.01 3.59 < 0.12 - - < 0.12 – – Au mass-% 0.2 69.0 0.5 4.2 84.6 0.8 5.2 70.2 0.5 4.3 50.8 0.5 3.1 56.3 0.3 3.4 Total mass-% 100.472 98.433 100.923 97.198 100.680 Element Unit LOQ ICE Zircon Transluzent Katana Zirconia ML Prettau® 4 Anterior® Dispersive® IPS e.max ZirCAD Prime priti®multidisc ZrO2 Extra Translucent DD cubeX2® ML ICE Zircon Transluzent A3 Mean SD ± Mean SD ± Mean SD ± Mean SD ± Mean SD ± Mean SD ± Mean SD ± Be mass-% 0.00005 < 0.00005 – – < 0.00005 – – < 0.00005 – – < 0.00005 – – < 0.00005 – – < 0.00005 – – < 0.00005 – – Y mass-% 0.01 4.29 0.03 0.21 5.58 0.13 0.28 6.49 0.03 0.32 5.38 0.05 0.27 5.24 0.02 0.26 7.56 0.13 0.38 4.25 0.08 0.21 Zr mass-% 2.6 68.0 0.6 3.4 67.3 1.5 3.4 66.1 0.3 3.3 67.5 0.8 3.4 67.3 0.3 3.4 65.3 1.2 3.3 67.9 1.3 3.4 Hf mass-% 0.02 1.49 0.01 0.07 1.29 0.03 0.06 1.29 0.01 0.06 1.50 0.02 0.08 1.45 0.01 0.07 1.42 0.03 0.07 1.55 0.03 0.08 Total mass-% 73.78 74.17 73.88 74.38 73.99 74.28 73.70
Results
Detailed results of the ICP-OES elemental analysis are shown in Tables 4, 5, 6, 7 and 8.Element Unit LOQ IPS e.max Press LT IPS e.max Ceram GradiaTM Plus Ex-3 Cerabien™ ZR Prettau® Zirkon 95H10 Mean SD ± Mean SD ± Mean SD ± Mean SD ± Mean SD ± MW SD ± Be mass-% 0.00002 < 0.00002 – – < 0.00002 – – < 0.00002 – – < 0.00002 – – < 0.00002 – – < 0.00002 – – Na2O mass-% – 0.42 – – 3.69 – – 0.21 – – 4.71 – – 4.15 – – - – – MgO mass-% – 0.26 – – - – – – – 0.32 – – 0.30 – – - – – Al2O3 mass-% – 2.22 – – 8.08 – – 6.89 – – 15.9 – – 12.6 – – 0.6 – – SiO2 mass-% – 76.0 – – 49.1 – – 49.8 – – 64.9 – – 71.70 – – 5.41 – – P2O5 mass-% – 1.98 – – 0.12 – – 0.03 – – - – – - – – - – – SO3 mass-% – 0.06 – – 0.05 – – 0.74 – – 0.04 – – 0.03 – – – – – K2O mass-% – 7.53 – – 7.67 – – 0.16 – – 11.0 – – 7.81 – – 0.24 – – CaO mass-% – 0.06 – – 1.99 – – 0.13 – – 0.80 – – 0.75 – – 0.06 – – TiO2 mass-% – – – – 1.41 – – 0.30 - - - - - - - - 0.05 – – Cr2O3 mass-% - 0.12 – – 0.04 – – – – – 0.07 – – 0.08 – – – – – MnO mass-% – – – – – – – – – – – – – – – – – – – Fe2O3 mass-% – 0.26 – – 0.09 – – 0.09 – – 0.15 – – 0.15 – – 0.26 – – Co2O3 mass-% – – – – – – – – – – – – – – – – – – – NiO mass-% – – – – – – – – – – - – – – – – – – – CuO mass-% – – – – – – – – – – - – – – – – 0.03 – – ZnO mass-% – 4.67 – – 5.01 – – – – – 0.22 - - 0.06 – – 0.06 – – SrO mass-% – 2.70 – – 8.37 – – 0.35 – – - - - – – – – – Y2O3 mass-% – - – – 0.53 – – – – – 0.10 - - 0.15 – – 5.03 – – ZrO2 mass-% – 1.40 – – 9.49 – – – – – 0.64 - - 0.56 – – 85.80 – – Nb2O5 mass-% – – – – – – – – – – – – – – – – 0.71 – – SnO mass-% – – – – 3.78 – – – – – – – – – – – – – – Sb2O3 mass-% – – – – – – – – – – 1.15 – – 1.24 – – – – – BaO mass-% – – – – – – – 41.3 – – – – – – – – – – – La2O3 mass-% – 0.50 – – – – – – – – – – – – – – – – – CeO2 mass-% – 1.00 – – 0.58 – – – – – – – – 0.42 – – – – – Tb2O3 mass-% – 0.82 – – – – – – – – – – – – – – – – – HfO2 mass-% – – – – – – – – – – – – – – – – 1.80 – – Total mass-% 100.00 100.00 100.00 100.00 100.00 100.00 Element Unit LOQ RN Variobase SIC Standard Abutment cara i-abutment® titanium Set ZZ Base B-C-ABCH Tizian Blank Zirkoniumdioxid Mean SD ± Mean SD ± Mean SD ± Mean SD ± Mean SD ± Be mass-% 0.000004 < 0.000004 – – < 0.000004 – – < 0.000004 – – < 0.000004 – – < 0.000004 – – Al mass-% 0.04 < 0.04 – – 5.74 0.08 0.15 5.88 0.11 0.16 5.62 0.10 0.15 n.a – – Ti mass-% 0.2 100.0 0.5 2.4 89.8 0.1 2.2 89.9 0.1 2.2 90.2 0.1 2.2 11.3 0.2 2.3 V mass-% 0.13 < 0.13 – – 4.06 0.02 0.09 3.97 0.03 0.08 3.84 0.02 0.08 n.a - - Total mass-% 100.0 99.60 99.75 99.66 11.30
Oxide ceramics
Data of the three most present elements are semiquantitative and determined with XRF against a universal calibration. The concentration data can vary from more than 25 to < 5%. The results were normalized to 100. Be concentration of the tested oxide ceramics resulted below the measuring limit of 0.5 mg/kg (Table 6). All the oxide ceramics investigated had a Zr content between 66.1 and 68 mass%. Y was contained in all samples and DD cubeX2® ML (7.6 mass-%) showed the highest content. Furthermore, Hf, which belongs to the group of heavy metals, was detected in all samples ranging between 1.29 and 1.55 mass %.
Other ceramics
As for the oxide ceramics, semiquantitative results were obtained with XRF against a universal calibration. The concentration data can vary by more than 100% at concentrations < 5% and the results were normalized to 100. None of the evaluated samples contained Be (limit of quantitation < 0.2 mg/kg) (Table 7). IPS e.max Press contained 76 mass-% SiO2, while IPS e.max Ceram contained 49.1 mass-% SiO2 with a higher content of ZrO2 (9.49 mass-%) compared to the other groups. Gradia™ Plus is the only investigated nano-hybrid composite containing BaO (41.3 mass-%), the second-largest component in this material after SiO2 (49.8 mass-%).
Implant abutments
The elemental analysis of the implant abutments showed that the SIC standard abutment and the cara i-abutment ® titanium had a similar elemental composition (Table 8). Both consisted of approximately 90 mass-% Ti, 4 mass-% V and 6 mass-% Al. The RN Variobase abutment was measured to be 100 mass-% Ti (with a standard deviation of 0.5 mass-% and measurement uncertainty of 2.4 mass-%). The values for Al, Ti and V were below the respective detection limit. Therefore, a possible Be content was below the detection limit for all the evaluated samples.
PMMA, PEEK, polycarbonate
The analysis of the three PMMA, one PEEK, and one polycarbonate material revealed a Be content < 0.08 mg/kg for all the evaluated samples (Table 9).Juvora PEEK Tizian Blank Organic PMMA Eco A3 Organic PMMA DISC Multicolor 5-Layer Organic PMMA Eco Clear Element Unit LOQ Mean SD ± Mean SD ± Mean SD ± MW SD ± MW SD ± Be mg/kg 0.04 < 0.04 – < 0.08 – < 0.08 – < 0.08 – < 0.08 –
Discussion
The objective of this study was to investigate multiple currently used dental materials concerning their possible Be content. To our best knowledge, no studies have conducted an elemental analysis for the detection of Be using a comparable broad spectrum of different dental materials, which includes precious and non-precious alloys, ceramics, PMMA, PEEK, and polycarbonate. Importantly, due to the low occupational exposure limits (0.2 mg Be/m3 air), a very sensitive methodology is necessary to determine the concentration of Be at ultra-trace levels.
Be has been widely used in the past decades to manufacture dental appliances22,23. To date, Be-exposure is considered "a modern industrial hazard"24 which can lead to sensitization and CBD, chronic lung disease2. A key factor for the management of CBD is the prevention of workplace-related and environmental Be exposure25. Frye et al. described a cluster of workers in an industry not directly related to Be processing and suffering from BeS caused by the high levels of Be contained in the concrete dust25. Appropriate protective equipment and preventive measures are mandatory to reduce the risk of respiratory diseases. In addition, routine medical examinations should be provided as for other high-exposure worker categories. Although exposure to Be in working places is being strictly regulated by the Occupation Health and Safety Administration, controlling is difficult26. Dental technicians are at higher risk of developing occupational respiratory disorders such as pneumoconiosis, caused by exposure to dust while handling dental materials27–30. They still seem to represent a population at higher risk of Be-associated disorders as compared to non-exposed workers despite the increasingly use of Be-free materials17,31. Furthermore, while the term "beryllium free" is used by several manufacturers to name their dental products, the concentration threshold for defining a material "free" from Be is still not defined. Further research groups aimed to assess the amount of Be contained in dental materials. Alkmin et al. investigated the microstructural characteristics of eight Ni–Cr alloys in the commerce6. The samples were analyzed using an inductively coupled plasma spectrometer (ICP-OES). Of the eight investigated alloys, five presented Be traces up to 2.05 mass-% and in two of these cases, the Be amount was not reported by the manufacturer.
There are different methods for ICP elemental analysis. On one side, inductively coupled plasma mass spectrometry relies on a high-temperature ionization source paired with a mass spectrometer. After nebulization, the samples are atomized, and ions are generated for the mass analysis20,21. On the other side, ICP-OES technology is based on the light transmission at specific wavelengths by atoms that move to a lower energy level. Element type and concentration are calculated based on the position and the intensity of the photon rays. All the analytical investigations of this study were performed with ICP-OES, which allows for precise multi-element tracing with high sensitivity and low detection limits.
Within the limit of quantification of the adapted methodic, Be traces ranged from below 0.000004 to 0.00005 mass-% depending on the group of materials analyzed. Based on these analyses, conducted at the ultra-trace level, it can be assessed that traces of Be are not of clinical significance in the evaluated samples. Therefore, the null hypothesis of the present investigation, assuming traces of Be are contained in the investigated dental materials, has to be rejected. Be was not found in the investigated materials, but further independent studies should address the elemental composition of used dental materials, focusing on heavy metals. A thorough understanding of health risks and the development of strategies to minimize occupational exposure to hazards should be continually pursued.
These results, however, raise further questions regarding the increased prevalence of Be-associated disorders in dental technicians and an evidence-based explanation. Firstly, some of the studies were conducted several years ago8,15,32, and the identification of health hazards, as well as the consequent restrictions adopted, might have caused the modification of the material compositions by the manufacturers. Secondly, despite the large-scale screening, the analyzed samples represent only a minimal fraction of the materials currently used in dental laboratories. Finally, it should also be considered that this study included only materials used in German dental laboratories, while most recent articles describing the prevalence of Be-associated diseases in dental technicians were assessed in other countries17,31,33. Despite the analyses of a large amount of samples by several sensitive methods, this study has a few limitations, including the restriction of the geographic area to Germany and to certain types of material. Analogue evaluations should be considered in future investigations involving a broader group of materials and different countries.
Conclusions
Based on the described elemental analysis, the following conclusions can be drawn:
- The applied ICP-OES method allowed for a highly sensitive elemental analysis at ultra-trace levels.
- Be concentration was below the respective limit of quantification (< 0.00005 mass-%) for all the evaluated samples.
- Further studies are needed to assess the Be amount in currently commercialized dental materials.
Abbreviations
- CBD
- Chronic Beryllium disease
- BeLPT
- Beryllium lymphocyte proliferation test
- 3Y-TZP
- 3 Yttria-stabilized tetragonal zirconia polycrystal
- 4Y-TZP
- 4 Yttria-stabilized tetragonal zirconia polycrystal
- 5Y-TZP
- 5 Yttria-stabilized tetragonal zirconia polycrystal
- BeS
- Be sensitization
- ICP
- Inductively coupled plasma
- ICP-OES
- Inductively coupled plasma-optical emission spectrometry
- PEEK
- Polyether ether ketone
- PMMA
- Polymethyl methacrylate
- XRF
- X-ray fluorescence spectroscopy
Acknowledgements
The authors thank MDT Ulrich Lamott (Lamott Zahntechnik GmbH, Emmendingen, Germany) and MDT Wolf Woerner (Labor Woerner GmbH, Freiburg, Germany) for their support to this investigation by kindly providing the investigated samples.
Funding
Open Access funding enabled and organized by Projekt DEAL.
Data availability
All data generated or analysed during this study are included in this published article.
Competing interests
The authors declare no competing interests.