(1) Grenz-ray studies indicate that decalcification rather than fracture is the initial lesion of caries in rats and man. (2) Optical studies of ground sections show marked variations in appearance of carious enamel. (3) Poor calcification (mottled enamel) does not affect the liability of enamel to caries, but does affect rate and extent of caries. (4) X-ray and Grenz-ray studies of incipient enamel-caries indicate that remineralization of these lesions does not occur. (5) Grenz-ray studies show increased density of primary dentin under caries in some cases. Special stains show fatty metamorphosis of contents of dentinal tubules under caries ; another reaction is formation of secondary dentin. (6) Human dentin and enamel are permeable; reduction of their permeability (sclerosis) diminishes rate of caries. (7) Internal resorption of teeth differs from caries; i.e., the former is due to cellular activity, the latter to bacteria.
References: J. Den. Res., 1931, 1932, 1938; Den. Cosmos, 1932, 1933, 1935, 1936; Bull. N. Y. State Den. Soc., 1938.