The Source of Mineral Salts in Subgingival Calculus

W HILE it is generally agreed that the organic matrix of calculus (both supragingival and subgingival) is built up by microorganisms-mainly actinomyces and leptothrix'0-there are 2 opposing opinions on the source of the mineral salts in subgingival calculus. One group2 ' 6, 8, 9, 11, 12, 14 contends that they are precipitated from the saliva, and that the saliva is constantly circulating to the bottom of even very deep pockets. Another group " 1 5, 10 13, 15 maintains that the mineral salts in subgingival calculus are derived from the blood, being precipitated from exudate and pus entering the pocket from the surrounding soft tissue. No experiment proving that saliva can or cannot enter into gingival pockets has, however, been undertaken. For the further study of the formation of subgingival calculus, it is of the greatest importance to make sure from which of the previously mentioned sources the mineral salts are derived. As there are no means by which it can be decided whether or not saliva penetrates into normal and pathologic pockets, an investigation was made with the aim of finding out to which extent vital