Electron-microscopic Observations on Soft Carious Human Dentin

¹ Departments of Dentistry and Dental Research and Anatomy, University of Rochester School of Medicine and Dentistry

An electron-microscopic study was conducted on soft carious human dentin fixed in buffered osmic acid, 10 per cent neutral formalin, or 70 per cent alcohol and imbedded in butyl methacrylate. Some material was studied without fixation and imbedding. For observations on the inorganic phase of the tissue and collagen-crystallite relationship, unstained sections and tissue homogenates were employed. For study of the organic phase, sections were stained in phosphotungstic acid. It was found that even in advanced dentinal caries the typical morphologic pattern of dentin is recognizable with massive bacterial colonies covering the surface of the lesion and extending into the dentinal canals and intercanalicular matrix. A general and possibly selective demineralization of the inorganic phase appeared to be the first phase in the carious process, leaving a sparse distribution of crystallites in the intercanalicular matrix and a distinct, heavily mineralized pericanalicular layer. The finding of an abundance of apparently normal collagenous fibrils indicated that collagen breakdown followed a general tissue demineralization. The final stage in tissue destruction apparently involves the more or less simultaneous dissolution of remaining crystallites and depolymerization of the collagen fibrils.