This multicenter randomized controlled clinical trial aims to compare the clinical, radiographic, microbiological and molecular outcomes of two collagenated xenogeneic bone substitutes (GTO® and GenOs®) used in combination with the Non-Incised Papilla Surgical Approach (NIPSA) for the treatment of intrabony periodontal defects. The study will evaluate whether differences exist between the two biomaterials with respect to clinical attachment gain, defect resolution, wound healing and biological markers of regeneration.

Background Periodontal reconstructive surgery has demonstrated favourable long-term outcomes in the treatment of intrabony periodontal defects, including challenging defects with limited remaining bony walls. Periodontitis is a chronic inflammatory disease associated with progressive destruction of the tooth-supporting tissues and alveolar bone loss. Intrabony defects are associated with an increased risk of disease progression and tooth loss and therefore represent an important therapeutic challenge.

Recent advances in minimally invasive periodontal surgery aim to improve regenerative outcomes while reducing patient morbidity. The Non-Incised Papilla Surgical Approach (NIPSA) is a minimally invasive surgical technique that provides access to the intrabony defect through an apical incision while preserving the papillary and marginal soft tissues. This approach may improve wound stability, clot protection, vascularisation, and soft tissue preservation.

In parallel, collagenated xenogeneic bone substitutes have been developed to enhance periodontal regeneration. GenOs® is a collagenated xenogeneic particulate bone substitute with a preserved collagen matrix and documented regenerative potential. GTO® is a collagenated xenogeneic bone substitute consisting of cortico-cancellous granules incorporated into a cohesive collagen gel composed of type I and III collagen. Differences in biomaterial composition and physical form may influence wound healing, tissue stability, and regenerative outcomes.

Aim The aim of this multicenter randomised controlled clinical trial is to compare the clinical, radiographic, microbiological, and molecular outcomes of GTO® and GenOs® used in combination with the NIPSA surgical approach for the treatment of intrabony periodontal defects. The study will evaluate whether the two biomaterials result in comparable improvements in periodontal regeneration and biological markers associated with bone formation and healing.

Materials and Methods This study is designed as a multicenter, parallel-group, randomised controlled clinical trial conducted at the School of Dental Medicine, University of Belgrade (Serbia), and the Department of Periodontology, University of Cagliari (Italy).

Thirty patients diagnosed with Stage III periodontitis and presenting with at least one intrabony periodontal defect with probing depth greater than 5 mm following completion of non-surgical periodontal therapy will be enrolled. Participants will be randomly allocated in a 1:1 ratio to one of two treatment groups:

Test group: GTO® combined with the NIPSA surgical technique. Control group: GenOs® combined with the NIPSA surgical technique. Allocation concealment will be achieved using sequentially numbered, opaque, sealed envelopes. The operator will be informed of the assigned biomaterial after defect preparation, while the examiner responsible for clinical measurements, radiographic assessment, and outcome evaluation will remain blinded to treatment allocation throughout the study.

Clinical parameters, including probing depth (PD), clinical attachment level (CAL), bleeding on probing (BOP), and plaque index (PI), will be recorded at baseline and 6 months after surgery. Standardized periapical radiographs will be obtained at baseline, immediately after surgery, and at 6 months.

Microbiological analysis will be performed using real-time PCR. Molecular analyses will evaluate gene expression associated with osteogenesis and bone remodelling (RANKL, OPG, ALP, RUNX2, OCN), vascularisation (VEGF, HIF-2, eNOS), and growth factors (FGF and TGF). Particular attention will be given to the RANKL/OPG ratio as a marker of the balance between bone resorption and bone formation.

Clinical Relevance This study will provide comparative evidence regarding the regenerative potential of two collagenated xenogeneic bone substitutes used in conjunction with a minimally invasive periodontal surgical approach. The findings may contribute to optimising biomaterial selection and improving treatment predictability in regenerative periodontal therapy.

Inclusion Criteria:

• Age ≥ 18 years
• Diagnosis of Stage III periodontitis
• At least one intrabony periodontal defect with probing depth > 5 mm following completion of non-surgical periodontal therapy
• Full-mouth plaque score (FMPS) < 20%
• Full-mouth bleeding score (FMBS) < 20%
• Ability to understand the study procedures and provide written informed consent

Exclusion Criteria:

• Systemic medical contraindications to periodontal surgery
• History of head and neck radiotherapy
• Poor oral hygiene or lack of motivation/compliance
• Uncontrolled diabetes mellitus
• Pregnancy or lactation
• Treatment with antiresorptive medications or other drugs affecting bone remodeling
• Heavy smoking (>20 cigarettes/day)