A computer-implemented periodontal index creation method, comprising: a measurement step of using a plurality of teeth extracted, because they are judged to be unconservable, as objects, and measuring a sample attachment level, which is a dimension ranging from the cementoenamel junction of each tooth or the crown margin of the tooth with a veneer crown to a lowermost site of a submarginal dental calculus deposited portion of the tooth in a plurality of samples taken for each tooth type from the teeth; a periodontal membrane area computation step of finding the lost periodontal membrane area (S L) of each tooth based on the total periodontal membrane area of each tooth and the sample attachment level; a bite force coefficient computation step of finding a bite force coefficient for each tooth, with the cusp of each tooth being taken as the point of action of a lever and the condyle of the temporomandibular joint as the fulcrum of the lever, based on the ratio between the distance from the cusp to the condyle and the distance from a specific reference tooth giving a reference position to the condyle, and the ratio between the length of the reference tooth and the length of each tooth, the distances and the lengths being given preliminarily; a straight line preparation step of preparing a bite force-lost periodontal membrane straight line which is a linear equation showing the relationship between the bite force coefficient and the lost periodontal membrane area (S L), by utilizing the fact that there is a linear relationship between the value of the bite force coefficient different according to the tooth type alone and the value of the lost periodontal membrane area (S L) when statistically processing the relationship between the bite force coefficient and the lost periodontal membrane area (S L) for each type of tooth; a lost periodontal membrane area detection step of finding an at-time-of-loss lost periodontal membrane area (S L), which is a lost periodontal membrane area (S L) at the time of loss of each tooth, corrected in consideration of the bite force coefficient, based on the bite force-lost periodontal membrane straight line obtained in the straight line preparation step; and an at-time-of-loss periodontal index computation step of calculating (at-time-of-loss remaining periodontal membrane area/total periodontal membrane area)×100 (%) as a periodontal index at the time of loss of each tooth, based on an at-time-of-loss remaining periodontal membrane area (S S) determined by subtracting the at-time-of-loss lost periodontal membrane area (S L) from the total periodontal membrane area. a measurement step of using a plurality of teeth extracted, because they are judged to be unconservable, as objects, and measuring a sample attachment level, which is a dimension ranging from the cementoenamel junction of each tooth or the crown margin of the tooth with a veneer crown to a lowermost site of a submarginal dental calculus deposited portion of the tooth in a plurality of samples taken for each tooth type from the teeth; a periodontal membrane area computation step of finding the lost periodontal membrane area (S L) of each tooth based on the total periodontal membrane area of each tooth and the sample attachment level; a bite force coefficient computation step of finding a bite force coefficient for each tooth, with the cusp of each tooth being taken as the point of action of a lever and the condyle of the temporomandibular joint as the fulcrum of the lever, based on the ratio between the distance from the cusp to the condyle and the distance from a specific reference tooth giving a reference position to the condyle, and the ratio between the length of the reference tooth and the length of each tooth, the distances and the lengths being given preliminarily; a straight line preparation step of preparing a bite force-lost periodontal membrane straight line which is a linear equation showing the relationship between the bite force coefficient and the lost periodontal membrane area (S L), by utilizing the fact that there is a linear relationship between the value of the bite force coefficient different according to the tooth type alone and the value of the lost periodontal membrane area (S L) when statistically processing the relationship between the bite force coefficient and the lost periodontal membrane area (S L) for each type of tooth; a lost periodontal membrane area detection step of finding an at-time-of-loss lost periodontal membrane area (S L), which is a lost periodontal membrane area (S L) at the time of loss of each tooth, corrected in consideration of the bite force coefficient, based on the bite force-lost periodontal membrane straight line obtained in the straight line preparation step; and an at-time-of-loss periodontal index computation step of calculating (at-time-of-loss remaining periodontal membrane area/total periodontal membrane area)×100 (%) as a periodontal index at the time of loss of each tooth, based on an at-time-of-loss remaining periodontal membrane area (S S) determined by subtracting the at-time-of-loss lost periodontal membrane area (S L) from the total periodontal membrane area.