Abstract This study evaluated the effect of coronal scaling (CS), root planing (RP), modified Widman surgery (MW) and flap with osseous resectional surgery (FO) upon the presence of gingival suppuration and supragingival plaque. 75 patients completed split-mouth therapy and 2 years of maintenance care. Data were collected prior to the initiation of therapy, following initial therapy, following surgical therapy and yearly during 2 years of maintenance care. All 4 types of therapy reduced the prevalence of suppuration with RP, MW and FO producing a greater reduction than CS in sites 5 mm. Sites were grouped according to presence of suppuration at 2 consecutive examinations. The mean changes in probing depth and probing attachment level for each time period were compared. Sites that began to suppurate between 2 exams or were suppurating at both exams had a less favorable response in mean probing depth reduction and mean probing attachment gain when compared to sites that stopped suppurating between exams or did not suppurate at either exam. The prevalence of supragingival plaque decreased during active therapy and 2 years of maintenance. There was no difference in the prevalence between the therapy groups except for FO-treated sites showing more plaque accumulation after surgical therapy. The presence or absence of supragingival plaque at specific sites was dynamic, frequently converting to a new status between 2 examinations.