Aging

Aging changes the oral epithelium by thinning the epithelium and diminishing keratinization, which can result in reduced papillae height.

Ko-Kimura et al. assessed the relation between age and presence of black triangles after orthodontic treatment and concluded that open gingival embrasures were more frequently found in patients over 20 years of age than in younger patients.

To explain this phenomenon, Chang measured the papillary height on standardized periapical radiographs of maxillary central incisors in 180 adults and found the interdental distance increased and papillary height decreased with age.

Based on this evidence, orthodontic management of older patients involves risk of papilla loss and presence of black triangles; this risk cannot be modified.

Periodontal biotype

Gingival Biotype can be classified as thin and scalloped or thick and flat. Because of the restricted blood supply, the thin biotype is more friable and shows more risk of recession following trauma as surgeries or inflammations ( Fig. 2 ).

(A) Thin biotype. (B) Underlying thin bone with dehiscence or fenestration.

Less than 1.5 mm gingival thickness is considered thin tissue biotype and often exists with underlying thin bone with dehiscence or fenestration ( Fig. 2 ). On the other hand, the thick tissue responds better to procedures, reacting with no recessions but with deeper periodontal pockets. Chow et al. found a positive association between interproximal gingival thickness and presence of gingival papilla presence in 96 adult patients. Tissue thickness is most easily assessed by placing a metal instrument, usually a periodontal probe in the facial sulcus. Thickness can also be assessed by transgingival probing, or ultrasonic measurement, but since it may induce discomfort it is usually performed under local anesthesia.

Based on this evidence, biotype evaluation prior to the start of orthodontic therapy may identify patients at risk for black triangles. Such a susceptible patient can be referred for interceptive periodontal therapy.

Distance from the crest of alveolar bone to the contact point

Increased distance from the crest of the alveolar bone to the interproximal contact is significantly related to presence of black triangles. According to the classic study from Tarnow et al, when the distance from the contact point to the alveolar bone was less or equal to 5 mm, the papilla was present in 98% of the times, while at 6 mm it dropped to 56% and at 7 mm it was only present 27% of the times. These findings indicate that the papilla will extend only a limited distance from the alveolar crest to the interproximal contact ( Fig. 3 ). Wu et al. found similar results. A distance of 5, 6, and 7 mm resulted in an open embrasure in 2, 44, and 73% of the cases respectively. These observations indicate that papilla was present in almost 100% of the cases if the distance from the alveolar crest to the contact point was 5 mm or less. When the distance was more than 7 mm, most patients had an open gingival embrasure. Based on this evidence, orthodontists can mitigate the risk for black triangles by developing treatment plans with the alveolar bone to contact point distance in mind.

Radiographic bone crest to contact point.

Crown shape

Divergent or triangular shaped crown forms are associated with posttreatment black triangles. ( Fig. 4 ) Due to this crown shape, the interproximal contact is more incisally located, increasing the roots distance, the length of embrasure area and the distance from the crest of the alveolar bone to the interproximal contact point. Burke et al. showed the association between tapered crowns and black triangles presence. Kurth and Kokich also showed that the mesial crown form of maxillary central incisors is significantly related to open gingival embrasures. The lower mean crown form ratio in patients with open gingival embrasures suggests a slightly more divergent crown form in these subjects. A pretreatment crown shape analysis which results in identifying triangular crown shape alerts the risk for black triangles. Thin scalloped periodontium that can often be found around slender triangular shaped crowns and is usually paired with narrow keratinized tissue width can easily be diagnosed. The overlying gingiva is thin and clear, this allows the probe to be visible through it . Risks stemming from thin tissue can be mitigated through gingival grafting.

Triangular crown shape.

Interproximal contact point

The length of the interproximal contact is another factor related black triangles. On average, the interproximal contact, in patients with black triangles, was shorter or located 1 mm more incisally than in patients with normal gingival embrasures. Since the incisal edge is a fixed reference point, the mean difference in contact position is probably due to a difference in length of the interproximal contact.

The length of the contact point presumably has an effect on the distance from the contact to the alveolar bone crest in that the longer the contact point, the closer it is to the bone crest. In the case of central incisors, this dimension is easily modified. However, in other anterior teeth, bilateral symmetry of the contacts on the opposite side must be kept in mind. Modified contact points involving laterals, canines, and premolars require similar contact point modifications on the other side so as to maintain symmetry. This point opens the door to multidisciplinary treatment and places the orthodontist in a central management position.

Root angulation

Burke et al. concluded that orthodontic movement of crowded anterior teeth can separate the roots and stretch the interdental papilla, increasing the presence of black triangles between incisors after orthodontic treatment.

Kurth and Kokich, with even more details, showed that root angulation of the maxillary central incisors is related to black triangles. Mean root angulation in normal gingival embrasures converges at 3.65°. When mesial crown form, alveolar bone interproximal contact, and interproximal contact incisal edge variables are constant, a 1° increase in root divergence increased the odds of an open gingival embrasure by 14–21%.

Distance between roots

Cho et al. investigated the existence of interdental papillae at certain distances from the contact point to the alveolar crest, depending on the interproximal distance between roots. They found that the number of papillae that filled the interproximal space decreased with increasing interproximal distance between roots and became more prominently decreasing with the increasing distance from the contact point to the alveolar crest. Treatment planning to decrease this distance mitigates the risk of developing black triangles.

Morphology of embrasure area

The size of the gingival embrasure area is a significant determinant of black triangles. Patients with open gingival embrasures have significantly larger mean embrasure areas than patients with normal gingival embrasures.

Chang assessed standardized periapical radiographs of the maxillary central incisors from 330 adult patients to analyze the association between embrasure morphology and central papilla recession. The author concluded that central papilla recession as a result of ageing is most frequently associated with a wide interdental width and long distance between proximal cementoenamel junction and contact point.

These findings allow the orthodontist to not only identify patients whose age puts them at risk for losing papilla, but also to vet the many methods to reduce the embrasure area.

Orthodontic treatment

Burke affirmed that a black triangle is a frequent sequela of aligning crowded maxillary central incisors. One third of orthodontic patients can be expected to have crowded central incisors. Two-fifths of those can be expected to have a post-orthodontic black triangle.

An et al. found association between black triangles and lingual movement of the incisors, large antero-posterior overlap between the two central incisors before treatment in the maxilla. The authors still demonstrated that a large amount of intrusion of the mandibular incisors can aggravate the severity of open gingival embrasures.

Ikeda et al. found a positive correlation between the duration of active orthodontic treatment and open gingival embrasures.

Uribe et al. showed that more than two thirds of the patients who had a mandibular incisor extracted had a black triangle embrasure at the end of treatment. And that the open gingival embrasures are noticeable by 52% those patients. The magnitude of an open gingival embrasure is moderately to very noticeable in 52% of these patients.

Agreeing with Uribe, Phyton et al. concluded that black spaces after mandibular incisor extraction had negative repercussions with regard to dental esthetics for the dentist, the dental student, and the layperson. Although mandibular incisors are less visible than maxillary, the presence of a black triangle may still be considered unacceptable; it is worth risk assessment.

Understanding the pathways by which black triangles can form empowers clinicians assess risks for development and to hedge those risks through treatment plans which avoid those risks.