The Collaborative International Dictionary of English v.0.48:

periodontitis \per`i*o*don*ti"tis\
   (p[e^]r`[=e]*[-o]*d[o^]n*t[imac]"t[i^]s), n. (Med.)
   A disease that attacks the gum and bone around the teeth.

   Syn: periodontal disease.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

periodontitis
    n 1: a disease that attacks the gum and bone and around the
         teeth [syn: periodontal disease, periodontitis]