As subjects, teeth having been considered as non-preservable and thus extracted are used and several teeth of each tooth type are selected and subjected to measurement. Then, the lost periodontal ligament area (SL) of each tooth is calculated on the basis of the sample attachment level (M) and total periodontal ligament area (S) thereof. Next, the relationship between the bite force coefficient (B), which reflects the bite force of each tooth and varies from tooth type to tooth type, and the lost periodontal ligament area (SLB) at loosing of each tooth is statistically processed for each tooth group. By taking advantage of the linear relationship between these factors existing in this step, a linear equation representing the relationship between the bite force coefficient (B) and the lost periodontal ligament area (SLB) at tooth loosing is formed. Thus, [remaining periodontal ligament area modified by bite force (SSB)]/total periodontal ligament area (S)]×100 (%) is calculated, on the basis of the lost periodontal ligament area (SLB) at tooth loosing, as a periodontal index modified by bite force (BPI) that shows the degree of the progress of periodontitis.En tant que sujets, sont utilisées des dents ayant été considérées non conservables et ainsi arrachées, et plusieurs dents de chaque type de dent sont sélectionnées et soumises à une mesure. La zone du ligament parodontal perdue (SL) de chaque dent est alors calculée sur la base du niveau de fixation de léchantillon (M) et de sa zone de ligament parodontal totale (S). Ensuite, la relation entre le coefficient de force de morsure (B), qui reflète la force de morsure de chaque dent et varie dun type de dent à lautre, et la zone de ligament parodontal perdue (SLB) lors de la perte de chaque dent est statistiquement traitée pour chaque groupe de dents. En tirant avantage de la relation linéaire entre ces facteurs existant à cette étape, une équation linéaire représentant la relation entre le coefficient de force de mo
