Assessment of risk factors for black triangle formation after orthodontic treatment with premolar extractions

TL;DR

This study identifies risk factors for black triangles after orthodontic treatment, focusing on the distance between the contact point and alveolar crest.

Contribution

The study demonstrates that mandibular contact point to alveolar crest distance is a significant predictor of black triangle formation.

Findings

Patients with black triangles showed a significant increase in mandibular contact point to alveolar crest distance post-treatment.

The vertical distance from contact point to alveolar crest is critical in minimizing black triangle formation.

Variables like tooth angulation and treatment duration had limited impact on black triangle formation.

Abstract

Black triangles (open gingival embrasures) result from a reduction in the height of the interdental papilla below the contact point and can lead to food impaction, alveolar bone loss, difficulties in plaque control, compromised esthetics, and speech problems. Since achieving a harmonious and esthetic smile is one of the primary goals of orthodontic treatment, identifying risk factors associated with these spaces is of great clinical importance. The aim of the present study was to investigate and compare risk factors related to the occurrence of black triangles after orthodontic treatment.

Records of 47 patients between the ages of 14-34 years old, all treated with fixed orthodontics using the MBT 0.22 system and bilateral premolar extraction, were retrospectively analyzed. Patients were divided into two groups based on the presence (n=25) or absence (n=22) of black triangles after treatment. Pre- and post-treatment panoramic radiographs, lateral cephalograms, and intraoral photographs were calibrated and analyzed using ImageJ and Dolphin Imaging software. Measurements included distance from contact point to alveolar crest, horizontal and vertical incisor movements, tooth morphology, interproximal CEJ distance, axial inclination of incisors, Little’s irregularity index, contact area, and treatment duration. Data were analyzed using paired and independent t-tests, Mann-Whitney U test, and Fisher’s exact test (significance level set lesser than 0.05).

The findings revealed that the distance from the contact point to the alveolar crest showed a statistically significant difference between the two groups in the mandibular arch (p = 0.006) and in the total of both arches combined (p = 0.003). However, the difference in the maxillary arch was not statistically significant (p = 0.127). Moreover, in patients without black triangles, the mean distance from the contact point to the alveolar crest showed a slight, nonsignificant decrease in both arches(P>0.05). In contrast, patients with black triangles exhibited no significant maxillary change but a significant mandibular increase from 3.44 mm pre- treatment to 4.19 mm post-treatment (p = 0.021). Other variables, including horizontal and vertical incisor movements, tooth morphology, interproximal CEJ distance, axial inclination, irregularity index, contact area, and treatment duration, did not show statistically significant differences (P>0.05).

Maintaining a short vertical distance between the contact point and the alveolar bone crest plays a critical role in minimizing black triangle formation after orthodontic treatment. When treatment procedures are standardized, variables such as tooth angulation, crown shape, and treatment duration appear to have limited impact. This study demonstrated that patients who developed black triangles showed a significant post-treatment increase in the mandibular contact point to the alveolar crest distance. Recognizing this relationship can help clinicians refine treatment strategies to improve aesthetics and preserve periodontal health.

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