Although the diagraph rh occurring at the beginning of a syllable in a word of Greek origin is ordinarily changed to rrh when a prefix or other lexical element is placed before it, the r is not doubled in this word. Inflammatory destruction of tissues immediately around the root of a tooth, i.e., pericementum, cementum, and approximating layers of alveolar bone. [peri- + G. rhiza, root, + klasis, destruction]