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BACKGROUND: Adjunctive locally delivered antibiotics during maintenance may favor the control of periodontal infections. This study evaluated the long-term clinical and microbiologic effects of yearly locally delivered controlled-release doxycycline as an adjunct to mechanical debridement.

METHODS: A total of 128 periodontal maintenance patients having at least four teeth with probing depth (PD) \textgreater or =5 mm were randomly assigned to local application of doxycycline gel at baseline and 1 and 2 years as an adjunct to mechanical debridement (test) or mechanical debridement only (control). Supportive periodontal therapy (mechanical debridement, polishing, and oral hygiene reinforcement) was provided every 6 months. Plaque, bleeding on probing (BOP), PD, and relative attachment level (RAL) were scored at baseline; 3 months; and 1, 2, and 3 years. Subgingival plaque samples were taken at each examination and analyzed for their content of 40 bacterial species. Data analyses were performed on an intention-to-treat basis with the subject as the statistical unit.

RESULTS: Significant reductions in BOP, PD, RAL, and the mean counts of a number of target species between baseline and 3 years were documented for both treatment groups, whereas plaque scores remained unchanged. A statistically significant difference in favor of the adjunctive doxycycline therapy was found between the two groups only at the 3-month examination for BOP, PD, and RAL and for a minority of bacterial species at 2 years.

CONCLUSION: Although short-term effects on clinical parameters were found with the adjunctive use of locally delivered doxycycline, repeated applications annually had no clinical or microbiologic effects beyond those observed with mechanical debridement alone in maintenance patients.