Frequency and distribution of proximal overlappings on posterior bitewing radiographs.

4374 proximal surfaces on 791 posterior bitewing radiographs were classified according to overlappings. Six categories were used: 1) no overlapping, 2) blurred contact areas, 3) less than half of the enamel overlapped, 4) more than half of the enamel overlapped, 5) dentin overlapped, and 6) unclassifiable overlappings. Filled surfaces and surfaces not in contact were excluded. Only 19% of the surfaces did not have overlappings 65% exhibited mild overlappings (categories 2 and 3), and 16% severe overlappings (categories 4, 5 and 6). The frequencies of no overlappings varied from 7% to 40% for single tooth surfaces. The relationship between distribution of overlappings and tooth surfaces was statistically significant at the 0.05% level. Principles of excluding overlapping surfaces have been inconsistent in previous epidemiologic studies and clinical trials. The use of exact criteria for exclusion is recommended.