Bisphenol A and Dental Sealants: Olea's Response.

We have read the comments made by Imai on our recently published paper (1) and once again disagree with his interpretation of our findings. Unfortunately, we are unable to compare our results (1,2) with those cited by Imai because four of the papers he cited were published in the Dental Materials Journal which is not available in Europe. Because the British Library was unable to furnish copies of this journal, we assume that these articles are not available to the international scientific community. Perhaps these important papers should be published in more accessible journals.

Nevertheless, based on the account of the methodologic approach described by Imai in his letter, we believe that we used a superior analytical method: a) we set the wavelength of the UV detector at 280 nm, recommended for aromatic compounds (3); and b) we used a gradient that provided a better resolution and a shorter time for running the chromatogram. The methods that we used to detect bisphenols are now the international gold standard (4-7).

We believe that Imai's reading of our paper is both simplistic and erroneous. He produces interpretations of our figures which go beyond the actual data that they contain. Most of the concerns raised by Imai stem from his overinterpretation of our Figure 2 (1). For example, his comments on the peaks shown in our Figures 2C and 3 (1) imply that all of the information presented in Tables 3-10 should be depicted in a single figure. We chose to present one figure for each experiment. The figures show chromatograms selected from the set of tests that we performed. It would be more fruitful to discuss the results presented in the tables rather than measuring the X-axes and speculating on the basis of illustrations.

Furthermore, we consider the use of retention times for chemical identification, as described in Imai's letter, to be an inadequate method because these times are relative to the start of the chromatogram and follow a strict sequence. GC/MS should always be the method of choice for the interpretation of these chromatograms. Imai's charge of some confusion between bisphenol A and Bis-GMA-H can be easily refuted because the analytical conditions that we used clearly differentiated the two chemicals. Some of his other comments are equally speculative and lacking in scientific support. For instance, Bis-GMA is usually broken in GC/MS and is identified by its moieties.

In short, we cannot accept Imai's interpretation of our results. Above all, we regard as highly speculative his claim for the nonestrogenicity of Bis-GMA-based dental resins based on his group's findings of little bisphenol-A content. Unless he can demonstrate the absence of estrogenicity in these samples, his conclusions are tendentious and lacking in scientific rigor.

Work in progress is revealing the presence of bisphenol A in the saliva of Delton-treated patients several months after exposure. These data, together with growing evidence of estrogenic sealants and bisphenol A in composite resins and saliva (8-12), are increasing our concerns about the safety of Bis-GMA-based resins.

REFERENCES AND NOTES

(1.) Pulgar R, Olea-Serrano MF, Novillo-Fertrell A, Rivas A, Pazos P, Pedraza V, Navajas J-M, Olea N. Determination of bisphenol A and related aromatic compounds released from Bis-GMA-based composites and sealants by high performance liquid chromatography. Environ Health Perspect 108:21-27 (2000).

(2.) Olea N, Pulgar R, Perez P, Olea-Serrano F, Rivas A, Novillo-Fertrell A, Pedraza V, Soto AM, Sonnenschein C. Estrogenicity of resin-based composites and sealants used in dentistry. Environ Health Perspect 104:298--305 (1996).

(3.) Poskrobko J, Dejnega M, Kiedik M. High-performance liquid chromatography with multi-wavelength detection of the bisphenol-A impurities. J Chromatography A 883:291-297 (2000).

(4.) del Olmo M, Gonzalez-Casado A, Navas NA, Vilchez JL. Determination of bisphenol A (BPA) in water by gas chromatography-mass spectrometry. Anal Chem Acta 246:87-91 (1997).

(5.) del Olmo M, Zafra A, Gonzalez-Casado A, Vilchez JL. Use of beta-cyclodextrin inclusion complexes for the analysis of bisphenol A (BPA) residues in water by spectrofluorimetry. Int J Environ Anal Chem 69:99-103 (1998).

(6.) Gonzalez-Casado A, Navas NA, del Olmo M, Vilchez JL Determination of bisphenol A in water by microliquid-liquid extraction followed by silylation and gas chromatography-mass spectrometry. J Chromatogr Sci 36:565-569 (1998).

(7.) del Olmo M, Zafra A, Jurado AB, Vilchez JL. Determination of bisphenol A (BPA) in the presence of phenol by first-derivative fluorescence following microliquid-liquid extraction (MLLE). Talanta 50:1141-1148 (2000).

(8.) Moon HJ, Lee YK, Lim BS, Kim CW. Component elution from dental pit and fissure sealants. J Dent Res 79:191 (2000).

(9.) Noda M, Komatsu H, Sano H. HPLC analysis of dental resin composite components. J Biomed Mater Res 47:374-378 (1999).

(10.) Arenhold-Bindslev D, Breinholt V, Preiss A, Schmalz G. Time related bisphenol-A content and estrogenic activity in saliva samples collected in relation to replacement of fissure sealants. Clin Oral Invest 3:120-125 (1999).

(11.) Fung EYK, Ewoldsen NO, St Germain HA, Marx DB, Miaw CL, Slew C, Chou HN, Gruninger SE, Meyer DM. Pharmacokinetics of bisphenol A released from a dental sealant. J Am Dent Assoc 131:51-58 (2000).

(12.) Lewis JB, Rueggeberg FA, Lapp CA, Ergle JW, Schuster GS. Identification and characterization of estrogen-like components in commercial resin-based restorative materials. Clin Oral Invest 3:107-113 (1999).

Nicolas Olea Laboratory of Medical Investigations Department of Radiology School of Medicine HUSC-University of Granada Granada, Spain E-mail: [e-mail]