SOME PHYSICOCHEMICAL FACTORS IN RELATION TO THE CAUSATION OF INTERPROXIMAL CARIES

¹ University of Otago Dental School, Dunedin, New Zealand

1. The conditions affecting the rate of loss of acid from narrow spaces between contiguous curved and flattened surfaces have been investigated.

2. The experimental method was designed to simulate some of the purely physicochemical factors obtaining in the dental arch.

3. Where the shape of the space and the acid concentration were constant, the effect of external buffer capacity was of importance, though tending to reach a limiting value.

4. The physical factor of spacing was of much greater importance than the buffering capacity of the external medium. An alteration in width of 0.07 mm. equalled the effect produced by a ninefold change in buffer capacity.

5. Increasing the depth of a parallel-sided space had a similarly very pronounced effect.

6. Variations in the shape of interproximal areas would seem to adequately explain differences in caries susceptibility for different interproximal surfaces of the same tooth, and may be fundamental to all variations in susceptibility between different parts of the dental arch.

7. The foregoing findings are consistent with the theory that acid decalcification of the enamel surface is the initial lesion of interproximal caries. Above the pH level at which acid decalcification begins (and for a constant rate of acid production), these results indicate that the resulting rate of fall in pH in interproximal spaces is dependent on (a) the degree of separation of the teeth and (b) the shape and width of the contact or capillarity areas, and to a much lesser extent, the buffering capacity of the saliva. Once the critical pH is reached, hydrogen ions will also be removed by their interaction with the inorganic constituents of the tooth enamel.