Open gingival embrasures, also called "black triangles", may occur after surgical intervention or tooth replacement by an implant. They are perceived as anaesthetic by most patients and causing functional and phonetic problems. The aim of the present study is to assess the effect of injection of hyaluronic acid for papilla augmentation next to an implant restoration in a clinical controlled double-blinded randomized trial with 6 months follow-up.

Background Open gingival embrasures, also called "black triangles", may occur after surgical intervention or tooth replacement by an implant. They are perceived as anaesthetic by most patients and causing functional and phonetic problems. Although micro-surgical approaches in oral surgery have considerably improved, reconstruction of a missing papilla to close an open gingival embrasure is still amongst the most challenging surgical scenarios. None of the so far reported surgical interventions are predictable. Recently, injection of hyaluronic acid, an important component of the extracellular matrix, was introduced as a minimally invasive, simple, non-surgical method to augment missing papilla tissue. Yet, controlled clinical studies on the effect of hyaluronic acid to reconstruct a missing papilla are not available so far.

Aim The aim of the present study is to assess the effect of injection of hyaluronic acid for papilla augmentation next to an implant restoration in a clinical controlled double-blinded randomized trial with 6 months follow-up.

Materials and methods Forty patients seeking treatment for open gingival embrasures next to an implant restoration will be included. Patients will be randomly assigned to test group (n=20; injection of hyaluronic acid, Hyadent Barrier Gel, BioScience, Germany; CE certificated for Europe) or control group (n=20; injection of saline solution as a placebo control medium). The following clinical parameters will be assessed at baseline and after 1, 3, and 6 months: Modified papilla index score, distance between papilla tip and contact point, area and volume of black triangle, tissue texture and colour, probing depth, clinical attachment level, presence of plaque and/or bleeding on probing, aesthetic satisfaction of the patient and the examiner and sensation during injection. At baseline and after 6 months the distance between contact point and most cervical region of the alveolar bone crest will be assessed on periapical radiographs.

Inclusion Criteria:

• atrophic papillae in the maxilla or mandible anteriorly to 1st premolar next to an implant
• at least 18 years of age and adequate plaque control (full mouth plaque score < 20%)

Exclusion Criteria:

• open contact point, positive bleeding on probing and/or probing depth >5mm,
• presence of a labial recession (depth >3mm) at the neighboring teeth
• <2mm keratinized tissue at the gingival margin of the neighboring teeth/implant
• known systemic healing disorders (e.g. uncontrolled diabetes, malignancy, disease affecting connective tissue metabolism)
• regular intake of medications with an effect on mucosal healing (e.g. steroids)
• pregnancy or breast-feeding