The aim of this randomized placebo- controlled clinical trial is to evaluate the effects of Lactobacillus rhamnosus SP1- containing probiotic tablets and azithromycin tablets as an adjunct to scaling and root planning (SRP).

Material and methods: Fifty-four chronic periodontitis patients will be recruited and monitored clinically, immunologically and microbiologically at baseline, 3, 6, 9 and 12 months after therapy. All patients will receive scaling and root planning and randomly will be assigned over an probiotic experimental (SRP + probiotic, n=18), antibiotic experimental (SRP + Azithromycin, n=18) or control (SRP + placebo, n=18) group. Probiotic will be used once per day during 3 months. Antibiotic will be used once per day during 5 days.

Inclusion Criteria:

• 14 natural teeth, excluding third molars
• 10 posterior teeth
• 35 years old
• 5 teeth with periodontal sites with probing depths ≥5mm, clinical attachment loss ≥3mm Bleeding on probing ≥20% of sites Extensive bone loss determined radiographically

Exclusion Criteria:

• Periodontal treatment before the time of examination
• Systemic illness
• Pregnancy Anticoagulant, antibiotics and non- steroid anti- inflammatory therapy in the 6-month period before the study