In this blog we review black triangles. Why they occur and what influence orthodontics has in both their formation, as well as the solutions available.
A black triangle is the cervical embrasure space to the interproximal contact point, in other words, it is the loss of the interdental papilla. A black triangle is a noticeable aesthetic concern to patients and ranked the third most disliked feature of an unaesthetic smile Cunliffe 2009. It commonly occurs following orthodontic treatment, with a recent systematic review showing an incidence of nearly 1 in 2, with 44.8% on average Rashid 2022, it is more common in adults, with a smaller incidence in those below 20 years of age with 1 in 5 affected, 18% Ahmed 1999. It is more common in the lower arch and also greater in size in the lower arch An 2018 To put the frequency into context, it is similar for adults to white spot lesions (42% Enaia 2011) yet it seems not to make a mention in commonly used consent forms (AAO or BOS).
The papilla itself consists of free gingival fibres which extends both buccally and lingually, with an interconnecting area below the interproximal contact point. The key component to the behaviour / misbehaviour of the papilla is the arrangement of the interpapillary gingival fibres, which are horizontal extending buccally to lingually.
How large does a black triangle have to be before it is noticed? Kokich explored this with modifying smile photos, and a black triangle of 2mm (vertical discrepancy) was observed reliably by orthodontists, and 3mm for lay people Kokich 2005. This makes for interesting reading as not every black triangle is of aesthetic concern, similar to a Bolton’s discrepancy, the relevance is not just in its presence, but the magnitude of its presence, incidentally 2mm for both black triangles and a Bolton’s discrepancy Othman 2007.
The loss of the papilla has a number of causes, we will focus on the main three; teeth, bone and the gingiva. There is a consistent theme to black triangle formation with regards to the teeth and bone, the stretching of the papilla. If we consider the papilla a water balloon (Farooq’s favourite analogy and summer pastime), the more the papilla is stretched in width and length, the less height it will have due to the horizontal orientation of the gingival fibres.
Tooth shape plays a key role in the shape the gingiva, and therefore the papilla as well. A triangular tooth has a greater distance between the roots (and therefore greater stretching) due to a slender mesial-distal width of the root at the cervical aspect. Another flaw of the triangular tooth is that the root is wider at the labio-lingual aspect cervically, this results in wider (labio-lingual) interproximal bone. with greater horizontal stretch of gingival fibres and consequently less height Singh 2013.
The distance between the roots at the cervical aspect has an association with black triangle formation, with 2.4mm or greater likely to result in a black triangle Martegani 2007. The distal tip of the roots has also been associated with black triangles. With a normal papilla at 3.65o , and for every 1o higher the odds of a black triangle forming increased by 14-21% Kurth 2001.
Classification papilla loss: Nordland and Tarnow 1998
The distance from the base of the contact point to the crestal bone relates to the papilla formation. The ‘5mm rule’, established by the landmark study by Tarnow 1992 states for a 5mm distance from the base of the contact point to the crestal bone, the papilla is 98% likely to be present, and for every 1 mm above 5 mm, the likelihood of a papilla being present reduced by 50%. This rule isn’t always true, as it was found an increased interradicular distance resulted in a black triangle, even with a 5 mm distance from the base of contact to the crestal bone Martegani 2007 , however it remains a factor. The final flaw of the triangular tooth as the base of contact point is more incisal, there is a greater chance of there being a 5 mm distance when compared to square shaped tooth.
Although the contact point remains static, bone loss has an association with aging, with 1.5mm of bone loss expected between 24-45 years of age Persson 1998, although small, this loss of marginal bone height can significantly affect the ‘5 mm rule’.
The thickness of the gingiva also affects the resistance to recession, with thin gingiva (less than 1.5 mm) more likely to recede Seibert 1989. The shape of the gingiva also plays a factor, with a high scalloped gingiva predisposed to recession when compared to a flat phenotype Singh 2013.
The answer is yes, but it depends. Nearly half of all adults and 1 in 5 adolescent orthodontic patients will have a black triangle at the end of treatment, the evidence points to orthodontics as the culprit. During the alignment phase of overlapping incisors, the interdental distance is increased and in doing so we can breach the 2.4mm inter-radicular distance described earlier, therefore the papilla is stretched by the underlying interdental gingival fibres which reduces the height. Of crowded incisors 41% were found to have a black triangle after alignment Burke 1994. The starting point is not the same though of the papilla in crowded incisors as it is for aligned incisors, as the papilla in the case of crowded teeth is narrower, and therefore less papilla is likely to be present Burke 1994.
The percentages are even higher for lower incisor extraction cases, where 68% of patients have black triangles (Uribe et. al., 2011). Labial movement has also shown a reduction of gingival tissues and greater black triangles Athar 2020.
Orthodontics, can redeem itself in the case of black triangles, orthodontic tooth movement now comes to the rescue:
Curettage has been described as a method of reconstructing gingival fibres through a purposeful hyperplastic inflammatory reaction, however it is unpredictable and based on the aetiology of necrotising gingivitis rather than crowding Shapiro 1985
Dermal filler. The use of hyaluronic acid into the base of the papilla (2-3mm from the tip) re-creates the papilla. However repeat treatments are required, and studies are restricted to case series and animal studies. It can also give rise to pseudo-pocketing and collect plaque.
Surgical management: Three broad options are available. A papilla can be reconstructed with coronal reposition flap, either a split thickness or free gingival graft can be used to re-create the papilla Han 2000, the challenge with this form of surgery is the trauma from the incision itself may result in necrosis of the gingival tissues. Papilla preservation surgery on the other hand is designed to avoid incision into the papilla, and repositions the apical position of the papilla incisally, giving it a ‘lift’. Bone grafts can be used increase the bone volume and therefore reduce the distance from the crestal bone to the base of the contact point.
Restorative management: Composite bonding or veneers alter the shape of the teeth, moving the contact point apically, and checking the ‘5 mm rule’ box, however it does not reduce the inter-radicular distance, unless the restoration is placed subgingivally. A gingival veneer (prosthetic papilla) can be used as a removable cosmetic solution.
The formation of black triangles are common in orthodontic treatment, however with one hand orthodontics faults, with the other it remedies, offering three clear methods to resolve black triangles. Black triangles increase in prevalence with age, and in writing this blog we have considered the management of smaller black triangles of younger patients, in order to reduce the occurrence and size as our patient’s age. I (Farooq) have included details i use to consent patients for black triangles, and hope it is useful.
A variety of factors relate to the formation of a black triangle, and the main ones have been discussed, which are described as either linear or angular measurements, however the interdental volume would seem to be of better value, combining several variables, and would help understand the influence different factors on the papilla. the relatively fixed tissue volume.
A paraphrased statement of balance by Burke on the topic of black triangles, we should balance orthodontic ideals (such as angulation) with aesthetics of managing black triangles Burke 1994
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We hope you have enjoyed this blog, This blog started with a conversation between Kerolos AlHakeem, Farooq Ahmed and James Andrews, to follow more conversations, clinical tips and commentaries on orthodontics please check us out on Instagram / facebook