The release of chlorhexidine from an ethyl cellulose-based dosage form (SRD) has been shown to be effective in the reduction of the flora associated with periodontal pockets as well as in reducing probing depths. In this study, treatment with this dosage form was compared to routine maintenance therapy (RMT) in a 2-year, split mouth clinical trial. Ten patients with 84 pockets greater than or equal to 5 mm who had not received any periodontal therapy or systemic antibiotics over the last 6 months were included. The patients all received a full mouth scaling and root planing together with through oral hygiene instruction. Two months later (baseline) plaque index (P1I), bleeding on probing (BOP), pocket probing depth (PD), and attachment levels (AL) were assessed at all selected sites. Pockets on the control side then received RMT while the experimental pockets were treated with the SRD only. Treatment was repeated every 3 months for 2 years. The SRD treatment resulted in an improvement of greater than or equal to 3 mm in PD of at least 1 pocket in 8 of 10 patients, while RMT resulted in a similar improvement in only 1 of 10 patients (P = 0.012). Similarly a gain of attachment of greater than or equal to 3 mm was found in at least 1 SRD pocket in 8 of 10 patients. The RMT resulted in a similar improvement in only 2 patients (P = 0.012).(ABSTRACT TRUNCATED AT 250 WORDS)