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

Material and methods: Thirty six chronic periodontitis patients will be recruited and monitored clinically, immunologically and microbiologically at baseline, 3 and 6 months after therapy. All patients will receive scaling and root planning and randomly will be assigned over an experimental (SRP + probiotic, n=18) or control (SRP + placebo, n=18) group. The tablets will be used once per day during 3 months.

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