<prompt> The Russell periodontal index is calculated by:Adding all the tooth scores and dividing by the number of teeth examinedAdding all the tooth scores and multiplying by the number of teeth examinedAdding all the tooth scores and dividing by 32None of the above methods  <response>: The Periodontal Index PI was developed by Russell A.L. in 1956, over a trial period of ten years.The Russells rule states that When in doubt assign the lesser score.The Periodontal Index score PI score per individual is obtained by adding all of the individual scores and dividing by the number of teeth present or examined. PI score per person Sum of individual scoresNumber of teeth present.Ref: Soben peter, 5th edition pg no:326 