Multiple choice Cases that do not respond to therapy and recur for unknown reasons belong to acute periodontitis chronic periodontitis refractory periodontitis bacute periodontitis Reveal answer Fill a bubble to check yourself C Correct answer Explanation Refractory Periodontitis was coined in 1989 classification of periodontal diseases. It existed for a decade as a separate disease till 1999 when it was removed from the classification. A new term called recurrent periodontal disease was coined.