Patients diagnosed with stage III or IV periodontitis that exhibit mandibular first or second molars with increased periodontal probing depth (PPD > 4 mm) and class II buccal mandibular furcation defects (horizontal probing depth of >= 3 mm ) will be recruited. This study will be a non-inferiority, prospective, randomized, double-blind controlled clinical trial with a parallel design. Patient will be recruited from the clinics of the School of Dentistry at the Aristotle University of Thessaloniki and private dental practices in Thessaloniki, Greece. Initially, non-surgical periodontal treatment will be performed through scaling and root planning in combination with oral hygiene instructions and motivation. The re-evaluation will be performed 4-6 weeks following the treatment and the patients who meet the inclusion criteria will be included in the study. Patients will be randomly allocated at a 1:1 ratio to either subgingival debridement and flapless application of EMD (test group) into the affected furcation defect or to periodontal surgery in combination with EMD application (control group). Periodontal and radiographic parameters, patient reported outcomes, oral cavity measurements and gingival crevicular fluid will be collected before as well as up to 9 months following the treatment.

The first step in periodontal therapy aims to successfully remove supragingival dental biofilm, improve oral hygiene and control potential risk factors. During the second step of treatment, the "cause-related therapy", non-surgical periodontal treatment consisting of subgingival debridement aiming to reduce plaque accumulation, calculus deposits, gingival inflammation, pocket depths is performed,which is effective for gaining attachment level. However, non-surgical periodontal treatment per se rarely translates into periodontal regeneration. In patients with severe periodontal disease residual periodontal pockets may remain after an initial therapy. Furcation defects often do not respond favourably to non-surgical periodontal therapy and are associated with elevated risk of progression. The elimination of these residual periodontal pockets can be achieved at the thirdstep of the treatment by resective or regenerative procedures based on the morphology of the defect or alternatively repeated subgingival instrumentation with or without adjunctive therapies can be carried out. Regeneration of the periodontal tissues includes cementum, periodontal ligament (PDL) and alveolar bone. Currently, several flap designs and biomaterials have been utilized and tested in the literature aiming at periodontal regeneration including bone grafts, bone substitute materials, growth factors, enamel matrix derivative proteins (EMD), guided tissue regeneration or even a combination of these materials. Although the application of EMD in conjunction with non-surgical periodontal treatment has shown a positive effect with evidence of regeneration, its effectiveness remains inconclusive.

Further studies in various disease conditions (intrabony defects, furcation defects, suprabony defects) are needed to confirm the potential benefit of adjunctive EMD application in combination with subgingival debridement (non surgical periodontal therapy). No study to our knowledge has tested the efficacy of flapless application of EMD in the healing of molars with furcation involvement.

Study design: Non-inferiority, double-blind, randomized, controlled clinical trial with parallel design.

Null Hypothesis: The adjunctive flapless use of enamel matrix derivative (EMD) during subgingival debridement in patients diagnosed with Stage III or IV periodontitis that exhibit class II buccal mandibular furcation involvement leads to inferior outcomes in clinical and radiographic as well as in biomarkers in comparison with surgical periodontal treatment with EMD.

Hypothesis: The adjunctive flapless use of enamel matrix derivative (EMD) during subgingival debridement in patients diagnosed with Stage III or IV periodontitis that exhibit class II buccal mandibular furcation involvement results in noninferior/equivalent outcome in clinical and radiographic variables as well as in biomarkers in comparison with surgical periodontal treatment with EMD.

Aim: The aim of this study is to investigate the non-inferiority of the flapless application of enamel matrix derivate (EMD) in addition to subgingival debridement in class II buccal mandibular furcationsin regards to the clinical and radiographic outcome as well as the level of biomarkers related to periodontal disease activity, inflammation and regeneration compared with periodontal surgery with EMD.

Methods: Patients diagnosed with stage III or IV periodontitis that exhibit mandibular first or second molars with increased periodontal probing depth (PPD > 4 mm) and class II buccal mandibular furcation defects (horizontal probing depth of >= 3 mm)will be recruited. This study will be a non-inferiority, prospective, randomized, double-blind controlled clinical trial with a parallel design.

Patient will be recruited from the clinics of the School of Dentistry at the Aristotle University of Thessaloniki and private dental practices in Thessaloniki, Greece.

Pre-treatment: Non-surgical periodontal treatment will be performed through scaling and root planning in combination with oral hygiene instructions and motivation. The reevaluation will be performed 4-6 weeks following the treatment and the patients who meet the inclusion criteria will be included in the study. Patients will be randomly allocated at a 1:1 ratio to either subgingival debridement and flapless application of EMD (test group) into the affected furcation defect or to periodontal surgery in combination with EMD application (control group). Periodontal and radiographic parameters, patient reported outcomes, oral cavity measurements and gingival crevicular fluid will be collected before as well as up to 9 months following the treatment.

Sample size calculation An estimate of the expected PPD reduction from OFD+EDTA+EMD was drawn from Casarin et al. 2010. The mean PPD reduction following OFD+EDTA+EMD was 1.9 +/- 1.6 mm and 1.0 +/-1.3 mm when OFD+EDTA was only performed. The differential effect of using EMD in a surgical periodontal treatment amounts about 1 mm. The sample size calculation was performed using α=0.05 and 90% power to detect a difference of 1 mm between treatment groups (MINST+Flapless EMD vs MIST+EMD) which is clinically significant and detectable. The estimated standard deviation was 1 mm. The required sample size was calculated to be 18 individuals in each group (total 36). Considering that some patients might be lost during the follow-up, a total of 44 participants will be enrolled (dropout rate of 20%). When the power was set to 80%, the required sample size is 13 patients per group (total 26). Considering a dropout rate of 20%, a total of 32 patients will be enrolled.

Statistical methods Descriptive statistics will be used to present the results of the sample's characteristics (mean and standard deviation for age, number of teeth, clinical periodontal and radiographic parameters; counts and percentages for categorical variables such as gender, medical and smoking history etc). The distribution of the sample will be measured with the Shapiro-Wilk test. In case of normal distribution: paired and unpaired t-tests will be utilized. In case a non-parametric test is used, Wilcoxon signed-rank and Mann Whitney U tests will be utilized. Chi-square test will be also used to compare categorical variables. GCF and periodontal measurements can be correlated with Spearman or Pearson rank correlation test. A statistical significant result will be set to a threshold level of <=0.05.

Inclusion Criteria:

• Individuals of at least 18 years of age with a diagnosis of stage III or IV periodontitis.
• Have at least one class II furcation defect with PPD >4 mm and horizontal probing depth of >= 3 mm in a mandibular first or second molar.
• Teeth have to be vital or properly treated endodontically.
• Gingival recession ≤ 2mm on furcation site
• Proper oral hygiene: full-mouth plaque score (FMPS) ≤20%.
• Systemically healthy (absence of systemic conditions such as diabetes mellitus that can affect the treatment outcome of periodontal therapy)
• Ability to understand the study procedures and comply with them through the length of the study.
• Given written informed consent form for participation in the study.

Exclusion Criteria:

• Pregnant or lactating female (self-reported).
• Current acute infection.
• Non-surgical periodontal treatment within the last 6 months or/and surgical periodontal treatment the last 12 months before the initial pre-treatment.
• Need for antibiotic premedication.
• Antibiotic treatment in the previous 3 months.
• Allergy to any materials or medications that could be used during or after the procedure.
• Teeth having an improper endodontic therapy with clinical signs of infection or subgingival restorations.
• Tooth mobility of 2nd and 3rd degree.
• History of radiation therapy in the head and neck region.
• Chronic use of medications that may alter the response of periodontal tissues.
• Smoke ≥ 10 cigarettes/day.

The selected sites will be randomly assigned to test and control groups using an online software for randomization. The therapist will be kept unaware of treatment allocation until the treatment. The outcomes assessor will be unaware of the treatment allocation.