LETTERS TO THE EDITOR Comments regarding: Lucchetti MC, Fratto G, Valeriani F, De Vittori E, Giampaoli S, Papetti P, et al. Cobalt-chromium alloys in dentistry: An evaluation of metal ion release. J Prosthet Dent 2015;114:602-8 Dear Editor: We read with great interest the recently published article, “Cobalt-chromium alloys in dentistry: An evaluation of metal ion release” by Lucchetti et al.1 in which the authors aimed to investigate metal ion release of Co-Cr alloy that was manufactured both by direct metal laser sintering (DMLS) and conventional casting techniques. The material method of the study is very clear and detailed for both chemical and biological corrosion. For this reason we aimed to use this methodology as a reference in one of our in vitro studies. However, when we read the article in detail we detected an error in the given formula of artificial saliva. In literature, artificial saliva is often used in many formulas for in vitro studies to simulate in vivo conditions. 2-5 In the Lucchetti et al.1 article, the content of artificial saliva was formulated as: 2.0.10-2 M KCl, 1.4.10-3 M KH2PO4, and 1.5.10-2 M K2HCO3. The researchers indicate they used Mutlu-Sagesen et al5 and ISO 10271 standards6 in the material and method as reference. However, the referenced study of Mutlu-Sagesen et al5 gave the artificial saliva as: 7.69 g of K2HPO4, 2.46 g of KH2PO4, 5.3 g of NaCl, and 9.3 g of KCl added to 1000 ml of distilled water. When we search the literature, the material, K2HCO3, was not found in the formation of artificial saliva. Also, the pharmacists was not able to prepare artificial saliva for our study according to the formula that was given by Lucchetti et al.1 We believe there is a typographical error in the article that needs to be corrected to prevent encountering the same problem in the future studies. Faruk Emir, PhD Prosthodontist Dental Health Sciences Center Department of Prosthodontics Gülhane Military Medical Academy Ankara, Turkey Simel Ayyildiz, DDS, PhD Associate Professor Dental Health Sciences Center Department of Prosthodontics Gülhane Military Medical Academy Ankara, Turkey REFERENCES 1. Lucchetti MC, Fratto G, Valeriani F, De Vittori E, Giampaoli S, Papetti P, Spica VR, Manzon L. Cobalt-chromium alloys in dentistry: An evaluation of metal ion release. J Prosthet Dent 2015;114:602-8. 2. Matos IC, Bastos IN, Diniz MG,Mirana MS. Corrosion in artificial saliva of Ni-Cr-based dental alloy joined by TIG welding and conventional brazing. J Prosthet Dent 2015;114:278-85. 3. Ionta FQ, Mendonça FL, de Oliveira GC, de Alencar CRB, Honório HM, Magalhães AC, Rios D. In vitro assessment of artificial saliva formulations on initial enamel erosion remineralization. J Dent 2014;42: 175-9. 4. Almqvist H, Lagerlöf F. Effect of intermittent delivery of fluoride to solution on root hard-tissue de- and remineralization by I125 adsorptiometry. J Dent Res 1993;72:1593-8. 5. Mutlu-Sagesen L, Ergun G, Karabulut E. Ion release from metal-ceramic alloys in three different media. Dent Mater J 2011;30:598-610. 6. International Standards Organization. ISO 10271. Dentistry-corrosion test methods for metallic materials Geneva: ISO. Available at: http://www.iso.org/ iso/store.htm. Accessed July 3, 2014. Authors’ Response Dear Editor: We are glad our paper was of interest and very sorry if a clerical error occurred in reporting the formula in the manuscript.1,2 Indeed, that formula cannot chemically exist, not only because some components are missing, but because K2HCO3 geometry is clearly impossible for the valence bonds. We thank colleagues and referees for their observations and apologize to readers for any difficulty they may have encountered in trying to prepare this solution for artificial saliva. The correct composition is: 4.4 10-2 M K2HPO4, 1.8 10-2 M KH2PO4, 9.1 10-2 M NaCl, and 1.25 10-1 M KCl. In using the solution we did not encounter any problems and it was very stable for 4 weeks at 4C. Special care was not needed to solve the components THE JOURNAL OF PROSTHETIC DENTISTRY 1