Periodontal bone height in relation to number and type of teeth in dentate middle-aged women. A methodological study.

Assessing the average periodontal bone height of the total dentition in large samples of individuals is a time-consuming and tedious task. The purpose of this investigation was to study the possibility of facilitating epidemiological work by representing the average bone height of the entire dentition by an index based on measurements in limited parts of the dentition. The correlation coefficient, which in several studies has been used as a measure of the agreement between mean bone heights in different regions of the dentition, cannot prove the degree of any such agreement. Only a comparison of the magnitude of these means can serve this purpose. Consequently, the first step was a detailed study of the average bone height in different regions of the dentition on a large sample (862 dentate middle-aged women). The proximal bone heights were assessed by measurements on orthopantomograms by means of a five degree plastic ruler (modified Schei ruler, Björn & Holmberg 1966), whereby the bone heights were related to the entire lengths of the teeth. The results confirmed that the variations in periodontal breakdown between different regions of the dentition are substantial in middle-aged populations. The average bone height was lower in the upper than in the lower jaw in all regions except the incisor areas. In subsamples of subjects having at least one remaining tooth of each type (molars, premolars, canines and incisors) in both jaws, the differences in bone heights were smallest and not significant between the means for the mandibular molars and the total means. In subsamples of individuals having lost all mandibular molars, the mean bone score for the combination of mandibular incisors and canines seemed to be the index of choice for representing the total dentition.