- Abstract The effect of a degradable controlled release system containing cetylpyridinium chloride (CPC) on plaque accumulation and gingivitis was evaluated when applied on the anterior teeth of volunteers (16–17 years) over 4 weeks. At baseline, plaque index (PI) and gingival index (GI) of the Ramfjord teeth were measured in the experimental and placebo groups, including 23 and 21 participants respectively. Following scaling and root planning, the participants were instructed to brush, using one brush stroke, the film-forming solution on the buccal surface of the maxillary and maudibular incisors, 1 × a day before bedtime. The applied active solution contained 9 mg of CPC (approximately 80 mg of 11% CPC solution), while the placebo solution was identical in formation, but without, the active agent. After 4 weeks, in the CPC-applied group, the recorded PI scores were 0.52 (±0.56) in the anterior area and 1.31 (±0.80) in the posterior area, whereas the corresponding areas in the placebo group reached 1.25 (±0.74) and 1.51 (±1.00), respectively. The P)=0 frequency in the buccal anterior surfaces after 4 weeks was 54.6% (±38.7%) in the experimental group as compared with 21.9% (±29.0%) in the placebo group (p = 0.005). In contrast to the anterior teeth, there was no significant difference between groups with respect to the PI scores in the non-applied posterior teeth. It may be postulated that the impressive 58% inhibition of plaque accumulation at the site of application is the result of an increase of the substantivity of the CPC due to its incorporation in the film–forming degradable controlled release system.