Recent investigations have revealed the presence of interproximal groove lesions on the dentitions of several prehistoric California Indians. These lesions are associated with interproximal caries and/or periodontal disease. The grooves are most likely caused by the use of dental probes during life as part of a palliative or therapeutic function. Another possible explanation is the stripping and thinning of sinew through the interproximal spaces of the teeth. Problems arise in the interpretation of this particular lesion because of the relative lack of specimens. In addition, a large majority of individuals who are affected by interproximal caries and/or periodontal disease do not display interproximal grooves. Potential explanations are provided.