▁did ▁not ▁find ▁that ▁the ▁data ▁supported ▁the ▁traditional ▁general ization ▁that ▁pre val ence ▁and ▁sever ity ▁of ▁period ont itis ▁is ▁marked ly ▁increased ▁in ▁African ▁and ▁Asian ▁populations . ▁ ▁Inc idence ▁of ▁Period ont itis ▁Like ▁measurements ▁of ▁pre val ence ▁of ▁period ont itis , ▁the ▁measurement ▁of ▁inc idence ▁will ▁vary ▁depending ▁upon ▁the ▁case ▁definition ▁of ▁the ▁disease . ▁ ▁O ften ▁“ inc idence ” ▁refers ▁to ▁new ▁sites ▁that ▁meet ▁the ▁definition ▁of ▁period ont itis , ▁even ▁if ▁they ▁occur ▁within ▁a ▁person ▁that ▁already ▁has ▁other ▁dise ased ▁sites . ▁ ▁Beck ▁ 1 9 9 7 ▁found ▁that ▁past ▁disease ▁predicted ▁subsequent ▁C AL , ▁although ▁not ▁usually ▁at ▁the ▁same ▁site . ▁ ▁Also , ▁persons ▁with ▁greater ▁attachment ▁loss ▁at ▁bas eline ▁were ▁more ▁likely ▁to ▁lose ▁teeth ▁over ▁the ▁next ▁ 5 ▁years . ▁ ▁Beck ▁ 1 9 9 7 ▁– ▁looked ▁at ▁inc idence ▁density ▁such ▁that ▁the ▁numer ator ▁was ▁attachment ▁loss ▁greater ▁or ▁equal ▁to ▁ 3 mm ▁while ▁the ▁denomin ator ▁was ▁the ▁time ▁at ▁risk ▁for ▁each ▁site . ▁ ▁The ▁incident ▁density ▁for ▁all ▁subjects ▁was ▁ 0 . 0 0 1 7 ▁per ▁site ▁per ▁month . ▁ ▁In ▁other ▁words , ▁if ▁ 1 0 0 0 ▁sites ▁were ▁followed ▁for ▁one ▁month , ▁ 1 . 7 ▁sites ▁would ▁lose ▁ 3 mm ▁or ▁greater ▁attachment . ▁ ▁In ▁one ▁year , ▁ 2 0 . 6 ▁sites