Validation of a minimally-invasive regeneration technique to improve open gingival embrasures using a rat model

Abstract

Open gingival embrasure, so called the "black triangle", is one of the unsolved dilemmas in esthetic dentistry. Although various techniques were introduced to esthetically improve the black triangles in the recent years, the lack of reproducible experimental models and clinical trials have prevented the development of successful protocols to regenerate or to compensate the loss of the interdental papilla. Therefore, the objective of this study was first to develop a reliable animal model of open gingival embrasure, and then to validate a non-invasive injection technique using the hyaluronic acid (HA) filler to augment the interdental papilla. To reproduce open gingival embrasure in SD (Sprague Dawley) rats, rapid space opening was induced between the lower incisors by the attachment of a compression spring. The loss of interdental papilla height was morphologically evaluated and calculated using standardized serial photographs, microCT and histological sections. Afterwards, HA fillers or PBS was locally injected and changes in the interdental papilla were evaluated. The results were as follows: 1. Following 7 days of space opening, the margin of the interdental papilla between the lower incisors gradually became irregular and flat indicating a condition similar to the open gingival embrasure (p<0.05). 2. Local injection of HA filler induced augmentation effect of the interdental papilla compared to the injection of PBS (p<0.05). 3. Interdental papilla became convex and inner granules containing HA were detected within the submucosal layer following its injection. Open gingival embrasure was reproduced reliably in vivo. Local injection of HA filler was validated as a meaningful minimally-invasive procedure to improve open gingival embrasure.