The width of plaque-free zones on primary molars with attachment loss.

The width of plaque-free zones on stained surfaces of extracted primary molars showing attachment loss was measured. The teeth were divided into 4 groups: maxillary first and second molars, mandibular first and second molars. 30 measurements were made under a stereomicroscope on each of the 4 surfaces in every group. The plaque-free zone had a mean width of 1.75 +/- 0.49 mm and a range of 1.0-4.3 mm. The plaque-free zone was significantly (P less than 0.001) wider on the proximal surfaces (1.94 +/- 0.56 mm) than on the combined buccal and lingual surfaces (1.56 +/- 0.32 mm). There was no difference between the 2 proximal surfaces while the lingual surfaces gave higher values than the buccal ones. On the second and on the lower primary molars, the plaque-free zones were wider than on the first and on the upper molars.