Abstract:

Objective To identify risk factors for the occurrence of black triangle of lower anterior teeth after orthodontic treatment in non-extraction patients with crowded lower anterior teeth. Methods A total of 151 orthodontic patients who completed orthodontic treatment in Orthodontic Department of the Affiliated Stomatological Hospital of Nanjing Medical University from January 2017 to December 2021 were selected as research subjects. The patients were divided into normal group and black triangle group according to whether there was a black triangle between mandibular central incisor teeth after the treatment. According to the clinical data of intraoral photos, digital models and CBCT, parameters related to tooth alignment and tooth movement before and after treatment were measured and analyzed. Results The incidence of black triangle between mandibular central incisor teeth was 23.2% in non-extractive patients with crowded lower anterior teeth. There were statistical differences between the normal group and the black triangle group in age, crowding degree, antero-posterior and transverse overlap of the two central incisors, angle formed by the incisal edges of the two central incisors, and CEJ-CEJ distance. Regression analysis showed that age, antero-posterior overlap, ICP-CEJ distance and CEJ-CEJ distance were significantly correlated with the occurrence of black triangle. Conclusion The incidence of black triangle is low in patients with crowded lower anterior teeth without tooth extraction, but it is more likely to occur in adult orthodontic patients and patients with severe labial-lingual dislocation of mandibular central incisor teeth or large gingival interproximal space.

Key words: black triangle, mandibular central incisor teeth, orthodontic treatment, open gingival embrasure