Tooth size and approximal decay in human teeth.

As PART of a study of spacing-crowding at the Burlington Orthodontic Research Centre, cognisance was taken of the presence of mesial and distal restorations in primary molars in the sample. Since at age nine, more than half the sample of primary molars which could be measured had such restorations, the validity of the spacingcrowding data could be questioned. Specifically, it was of interest to know whether the approximal restorations made the mesio-distal dimensions of the teeth so restored larger or smaller and whether the caries attack as represented by approximal restorations had a predilection for larger or smaller teeth. In answer to the first question, it was found possible to locate at least thirteen subjects who had approximal restorations in primary maxillary molars (substantiated radiographically) on one side only. Since left-right differences in unrestored primary molars were found in the larger study (HUNTER, 1960-l) to be of the average order of 0.03 mm, symmetry was assumed to have existed prior to restoration. The restored maxiUary primary molars proved to be, on the average, 0.18 mm smaller than their non-carious unrestored antimeres. A similar mandibular comparison for eight subjects showed the restored teeth to be on the average, 0.07 mm smaller than their unrestored antimeres. Therefore, it was concluded that the process of restoration of approximal decay did not, on the average, significantly enlarge the size of the primary molars but rather tended, to an insignificant extent, to diminish their size by the observed amounts. It is possible that the dentists of Burlington who completed these restorations had a slight tendency to underpack their restorations-possibly related to the difficulty of wedging primary molars. Some significance may then be attached to the finding that at age six, 491 restored primary molars were on the average 0.28 mm larger than 1365 unrestored molars. At age nine, 814 restored primary molars were found, on the average, to be 0.16 mm larger than 723 non-carious unrestored teeth. These differences exceed by a factor of 10 the average measurement errors found for the primary molar measurements. (HUNTER, 1960-l). Sixteen comparisons were made at the two ages, each involving at least eighteen subjects. Of the thirty-two comparisons made, thirty-one showed the restored molars to be larger and twenty of these differences were statistically significant at the 5 per cent level. Four representative comparisons are shown in Table 1 for mandibular left second primary molars. Similar comparisons were made for right mandibular second primary molars,