J. J. DOEL ET AL: 'Protective effect of salivary nitrate and microbial nitrate reductase activity against caries', EUROPEAN JOURNAL OF ORAL SCIENCES, vol. 112, no. 5, 1 October 2004 (2004-10-01), DK, pages 424 - 428, XP055392242, ISSN: 0909-8836, DOI: 10.1111/j.1600-0722.2004.00153.x