[From translation by Rudolf Kronfeld.]
Caries can develop on an area of tooth surface only when an acid reaction persists there continuously for a considerable period. Every neutralization or reduction of acidity at this area, however transitory—beyond the isoelectric point of the organic substance of enamel or dentin (cervical caries)—causes precipitation of the calcium in solution in the prisms or dentinal tubules. An area of tooth surface in the earliest stages of caries becomes more resistant to acids than before, when the acidity of this area is temporarily neutralized or reduced below the isoelectric point; then other areas that formerly were poorly calcified or not at all (interprismatic substance, dentinal tubules) also become calcified. Alkalies are not suited for neutralization or reduction of the acidity, because they diffuse only slowly through the film on the tooth surface; but the acidity can be reduced almost to neutrality by physico-chemical buffering, or by substances which (locally or in the entire oral cavity) temporarily discontinue the acid fermentation under the film. The daily use of such substances in the mouth tends to prevent caries.
Caries can never progress from carious dentin left under a filling, if the borders of the cavity are absolutely free from caries, and the filling is well adapted to the margins (each amalgam filling should be underlaid with soft cement). Always to excavate into sound dentin is unwarranted because thus pulps are often exposed unnecessarily and have to be devitalized. If the tooth has never caused pain, it is therefore always better to leave carious dentin at the floor of the cavity than to expose the pulp by unnecessarily extensive excavation. The correctness of this procedure has been confirmed at the Dental Institute of the University of Frankfort, Germany (Kirchem, W., Thesis, 1935) and at eleven school dental clinics in Budapest, Hungary. In Budapest, 4000 teeth were treated according to this principle. The number of devitalizations was reduced by one-half. The failures (pulpitis, periodontitis) were 0.27 percent.
References: Z. Stom., 1931, 1933, 1934, 1935, 1936; D. Monat. Zahnh., 1931; Zahndrz. Rund., 1933.