Prediction and causes of open gingival embrasure spaces between the mandibular central incisors following orthodontic treatment.

An open gingival embrasure space (OGES) between the mandibular incisors, also known as a "black triangle" (BT), can be an undesirable outcome of adult orthodontic treatment.The purpose of this study was to determine the parameters that contributed most to the occurrence of an OGES between the mandibular central incisors, the area with the highest incidence of BT in the lower arch following orthodontic treatment.A stepwise regression model was used to identify the variables (age, crowding, treatment duration, alveolar bone height, and six variables describing crown morphology) related independently to OGES score. Intra-oral photographs taken before and after orthodontic treatment, study models and intra-oral radiographs of 60 patients were used. Embrasures between the mandibular central incisors were measured and classified into three types: papilla filling, pinpoint, and BT.Age at the first consultation, length of active treatment and maximum crown width were larger in the BT group than in the normal group. In contrast, incisal edge - centre of the contact point, upper contact point - lower contact point, mesial CEJ - distal CEJ, and mesial CEJ - distal CEJ / maximum crown width were smaller in the BT group than in the normal group. Variation in OGES score was explained by the independent contributions of age at the first consultation, duration of active treatment, maximum crown width, and mesial CEJ - distal CEJ width. The multiple regression coefficient was 0.98, and the regression coefficient square was 96 per cent.We conclude that age at the first consultation, duration of active treatment, and crown morphology are involved in OGES manifestation. We suggest also that BT occurrence may be predictable prior to treatment.