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Inside Dentistry
February 2023
Volume 19, Issue 2

Conservative Treatment to Close Black Triangles

Composite injection overmolding offers a predictable and affordable solution

David Clark, DDS | Charles Regalado, DDS

The treatment of open gingival embrasures, which are sometimes referred to as "black triangles," has recently reached a significant threshold of consciousness among both patients and clinicians. In addition, many orthodontists have begun to acknowledge that postoperative black triangles that appear after adult orthodontics are a real concern. Approximately one third of the individuals who undergo orthodontics as adults suffer from black triangles following the completion of treatment.1 Besides being unsightly and prematurely aging the smile, black triangles are prone to accumulate food debris and excessive plaque.2,3 The occurrence of black triangles after adult orthodontics is upsetting enough to the patients that some orthodontists have become gun-shy about treating adult crowding cases or adult cases in general.4-8

The age of the patient, duration of active treatment, crown morphology, and degree of crowding are all involved in black triangle manifestation, and development of the condition can readily be predicted before orthodontics is initiated.9-14 In a landmark study, Cunliffe and Pretty analyzed patient concerns and showed that patients were more concerned about black triangles than they were about dark teeth or crowded teeth, which may be surprising to many esthetic-minded clinicians who prescribe whitening treatments and adult orthodontics.15 A quick internet search for "dental black triangles" yields seemingly endless results regarding patient questions, patient complaints, and now even lawsuits related to adult orthodontic treatment and papilla loss resulting from periodontal therapy. Instead of sweeping these problems under the rug, cosmetic dentists can view this clinical and esthetic dilemma as a unique opportunity to improve the functionality, esthetics, health, and confidence of these patients through appropriate restoration.

This article presents two case reports involving the treatment of black triangles. Both of these cases were treated using a composite injection overmolding protocol (Bioclear Method, Bioclear) involving specific matrices, gauges, heated composites, and finishing and polishing materials and instruments.

Case Report 1: Treating Extreme Black Triangles

A 38-year-old female patient presented to the practice with severe bone and soft-tissue loss that had resulted in the development of extreme black triangles between several teeth (Figure 1 through Figure 4). A complete clinical examination was performed, and pretreatment radiographs were acquired. She noted that the appearance of her upper smile was the most important to her. The patient was referred by her periodontist, who confirmed that she had demonstrated excellent compliance over a course of prescribed treatment that included full-mouth scaling and root planing and laser-assisted regeneration using the laser-assisted new attachment procedure (LANAP). In addition, she had consistently attended periodontal maintenance appointments at 3-month intervals. Her inflammation was under control, and despite the severe loss of her periodontium, her teeth demonstrated relatively low mobility with nothing beyond a 1 or 1+ designation. She expressed that she was highly motivated and eager to proceed with having her black triangles closed.

Treatment Options

The presence of an extreme amount of unfamiliar negative space presents a challenge to both the patient who must endure the emotional impact and to the dentist who must treat the case. Patients who present with a severe degree of bone and soft-tissue loss have been treated with invasive procedures, including ones involving extractions, block grafts, and implants.16 Oftentimes, a prosthesis utilizing pink porcelain is needed to hide the remaining negative space.17 If the patient cannot afford implants or they are not deemed predictable, then extractions and removable prosthetics may be considered. Alternatively, full crowns are often recommended. Each of these options carries its own risk to reward ratio, and the cost of these treatments extends over a wide range. Patients often find themselves at a crossroads when it comes to their desire for a better smile. When more ideal options are financially out of reach for patients, dentists should pursue treatments that can provide satisfactory solutions while maintaining or even improving existing health conditions.

For the patient in this case, closing the black triangles with injection-molded composite would provide an affordable alternative. However, with such large negative spaces to be closed, there were concerns about how that would affect the final tooth size, shape, and proportions.18 Two questions were considered: could the spaces be closed esthetically, and should all of the spaces be closed? Closing the spaces could result in unacceptable tooth proportions, and not closing all of the spaces could miss the mark from the patient's perspective regarding the desired outcome. In this clinician's experience, most patients select the option that results in the least invasive procedure and find the results more than satisfactory. The perception of a beautiful smile is what matters most, even when there are some compromises that must be made.19 These issues were relayed to the patient to manage expectations and avoid any disappointment.

After consulting with the patient, she chose to proceed with black triangle closure using injection-molded composite restorations and to have as much space closed as possible because her condition had such a negative impact on her public interactions. Her goal was to achieve a confident and pleasing smile, untethered to the norms in dentistry that are often used to evaluate "ideal" smiles.20


At the beginning of the appointment, the proper shade of composite was chosen to match the patient's existing color and appropriately sized matrices were selected. The key to correct matrix selection is to do a simple try-in of the various sizes prior to placement of the rubber dam. The use of a rubber dam is highly recommended to achieve total isolation and to expose more tooth structure below the visible gingival margin. The goals in matrix selection are to preview that the black triangle will indeed be closed adequately and that there will be no hindrances to being able to seat the matrices completely into the sulcus of each tooth. If this step is performed after the rubber dam is placed, the dam can compress the tissue apically and result in the selection of too large a matrix and excess lateral pressure to the papilla after injection molding. Excess pressure can distort the shape of the papilla that will be formed with this procedure. The correct matrix size and shape will allow just enough composite to close the black triangle and apply side pressure to support the papilla, enhancing the long-term result (Figure 5 and Figure 6). An ideally sized matrix (Anterior Matrix DC Series [DC201], Bioclear) was chosen to close the space between the maxillary central incisors and for the distal surfaces of the central incisors as well. A smaller matrix (Anterior Matrix DC Series [DC203], Bioclear) would be used for the mesial and distal surfaces of the lateral incisors. All of the matrices were set aside into designated and marked containers.

To begin the procedure, a rubber dam was placed over the anterior segment, and after properly tucking it into the sulci, the teeth were dried, disclosed with a disclosing solution (Dual Color Disclosing Solution, Bioclear) and rinsed after 30 seconds. Teeth Nos. 7 through 10 were then cleared of all biofilm and pellicle with the use of aluminum trihydroxide powder in a high-pressure water spray (Bioclear Blaster, Bioclear). Prior to placing the matrices, the interproximal contacts were entered with handheld saws and then lightly sanded with diamond sanders (TruContact, Bioclear). This facilitated the further removal of biofilm in these tight areas and reduced the contact tightness to permit complete seating of the matrices. The final amount of black triangle closure was visualized by placing the matrices before the rubber dam was applied. In this case, the matrices were correct to close the space; however, if they were not, they could either be customized or replaced with others that might improve the outcome.

Tooth No. 8 was chosen to be injection-molded first. A 37% phosphoric acid solution was used to etch the entire tooth for 15 seconds, then it was rinsed, and the excess water was removed. A universal adhesive (3M Scotchbond Universal Adhesive, 3M Oral Care) was then applied, scrubbed into the exposed dentin areas for 20 seconds, and air thinned. Next, the entire tooth was copiously wetted with additional adhesive to act as a surfactant for the composite as it was injection molded. The adhesive was not precured. With the adhesive applied, the designated matrices for the mesial and distal surfaces were placed and seated into the sulcus. This formed a full 360º envelope or "aquarium" around the tooth. The matrices chosen for the mesial surfaces of teeth Nos. 7 and 9 were placed on their respective surfaces to act as "shield" matrices. These help to guard against the over encroachment of composite into the interproximal space during the injection-molding process, eliminating the accidental curing of composite beyond the desired shape provided by the matrix.

Warmed flowable composite (3M Filtek Supreme Flowable Restorative, 3M Oral Care) was slowly injected into each matrix around tooth No. 8 by placing the tip of the syringe into the interproximal area on the facial side and allowing the composite to slowly flow to the lingual half of the tooth. The lingual halves of the tooth were then filled to completion. Great care was taken to ensure that the flowable composite was free of voids and had filled much of the matrix system. Once the flowable composite was placed, a warmed universal paste composite (3M Filtek Supreme Ultra Universal Restorative, 3M Oral Care) was injected into the matrix system. The warmed paste composite displaced the excess adhesive as well as much of the flowable composite, leaving a dense monolithic mass composed chiefly of the paste composite. The goal was to achieve a ratio of approximately 90% paste composite to 10% flowable composite. After cleaning up the excess material with a composite instrument (Curved Sculpting Paddle, Bioclear) and dry brushes along the gingival areas, the composite was light cured from both the facial and lingual aspects for a minimum of 20 seconds per side. Once the composite was cured, a coarse, flame-shaped diamond bur (Flame FG Turbine, Komet Dental) and coarse polishing discs (3M Sof-Lex Finishing and Polishing Discs [coarse], 3M Oral Care) were used to shape the tooth to roughly 80% of the final desired contours.

This protocol was then followed to restore tooth No. 9 and, subsequently, the lateral incisors. Final shaping was completed with the coarse polishing disc, and then the teeth were polished using pre-polishing paste (Magic Mix, Bioclear) followed by a polishing cup (RS Polisher, Bioclear) (Figure 7). The rubber dam was removed, and the patient's smile was evaluated for facial harmony. Adjustments were not needed because she was pleased with all of the aspects of her smile (Figure 8 and Figure 9). Postoperative radiographs were acquired to assess for excess composite and compared to the preoperative radiographs to assess the quality of the technique (Figure 10 and Figure 11). The matrices and technique employed facilitated the creation of smooth "infinity edges," which were essential to the patient's healthy tissue response.

Final Result

Although there were concerns regarding the effect of the added volume of composite and how it might negatively affect the tooth contours and thus the esthetics of the overall smile, the results were highly acceptable to the patient, who was pleased that she opted for injection-molded composite restorations to solve her dilemma. With the wide variation of perceived beauty in a smile, this is not surprising.20-22 One of the greatest benefits of using injection-molded composites to close black triangles is the added stability that periodontally weak teeth can obtain. In this case, stability had improved even further at the 2-year mark (Figure 12 and Figure 13). As is often seen following cosmetic dentistry, the dramatic improvements resulted in a more relaxed and confident smile.

Case Report 2: Treating a Single Black Triangle

A 34-year-old male patient contacted the clinic after searching the internet for solutions to treat black triangles. Like many patients, his black triangles appeared during adult orthodontic treatment (Figure 14 and Figure 15). The patient received a complete examination, which included the acquisition of necessary radiographs and photographs. Proper photographs of the right and left lateral views are critical in these cases because the frontal view, which is what the patient sees, is different from the lateral views that everyone else sees (Figure 16 and Figure 17). Although the patient had developed three black triangles in the anterior mandible, he elected to only have the larger midline area black triangle treated. The limitations of treating this single area as opposed to pursuing more comprehensive treatment were discussed with the patient. In these types of cases, it is rare to treat only a single black triangle; therefore, this case provided an enlightening contrast of treated versus untreated areas at the 2-year follow-up.


For this case, a black triangle treatment system (Black Triangle Kit, Bioclear) was employed that contained the important components used in the first case report: matrices, dual-color disclosing solution, and handheld interproximal saws and sanders as well as a black triangle sizing gauge. The kit includes small and large matrices in four different color-coded emergence profiles that correspond with the colors on the sizing gauge. First, the black triangle gauge was inserted buccolingually below the contact to assess the mesiodistal size of the black triangle to be treated (Figure 18). The gauge bound in the pink zone, so a pair of correspondingly pink color-coded black triangle matrices were tried in for each embrasure.

Once the rubber dam was placed, the teeth were disclosed (Figure 19) and then blasted with the air/water/aluminum trihydroxide abrasive slurry (Figure 20). The saws and sanders were then used to groom the contact area to remove any calculus and to lighten the tension of the contact and allow the matrices to seat fully (Figure 21). Because the 37% phosphoric acid used to condition the teeth does not remove the soft, sticky biofilm, it is imperative that the teeth be aggressively cleansed before acid etching. In addition, the removal of the pellicle that coats the teeth improves the effectiveness of acid etching procedures.23 The interproximal area is extremely difficult to access with scalers and prophy cups and is, of course, the exact area that clinicians are attempting to bond to when treating black triangles.

In general, the black triangle gauge will indicate the appropriate matrices to restore the space, but in this case, the yellow-colored matrices, which have a more aggressive emergence profile, were chosen because of the unique shape of the patient's teeth, even though the gauge indicated to use the pink-colored ones (Figure 22). To begin, tooth No. 25 was injection molded using a protocol similar to that used in the first case report. First, the enamel was etched with the 37% phosphoric acid solution, then an adhesive (3M Scotchbond Universal Plus Adhesive, 3M Oral Care) was placed and air thinned but not light cured. Next, the warmed flowable composite was carefully injected using the uncured adhesive as a wetting agent, or surfactant, to minimize air entrapment and maximize the flow into the acute matrix-tooth interface. The flowable composite was injected from both the facial and lingual directions but not light cured. Finally, the warmed paste composite was injected from the facial direction. It easily displaced the flowable composite to the lingual and incisal vent areas. After the restoration was light cured, the matrix was removed from tooth No. 25 (Figure 23), and then tooth No. 24 was injection overmolded using the same protocol. This ensured a snug contact. The teeth were then rapidly sculpted together for the sake of symmetry and efficiency, placing infinity edge margins mid-tooth, and given a final polish using the 2-step system used in the first case report (Figure 24 and Figure 25).

Final Result

A comparison of the preoperative and postoperative radiographs demonstrates the imperceptible interface of composite to tooth as well as the void-free quality of the composite, which is the goal of injection overmolded monolithic composite restoration (Figure 26 and Figure 27). At the 1-year recall appointment, the treated area was essentially free of calculus and bacteria, but the neighboring untreated embrasure between teeth Nos. 25 and 26 was filled with calculus (Figure 28). The obvious hygiene benefit of black triangle closure is a bonus to the esthetic benefits, which is why the patient was counseled about pursuing complete treatment during the planning phase.


Traditional hand-spackled composite placement for the treatment of black triangles has historically been viewed with skepticism by many restorative dentists, orthodontists, and periodontists. Until the development of injection overmolded composite restorations, clinicians' confidence in treating black triangles was so guarded that most patients were told that there was no conservative option. They were either told that nothing should be done or offered aggressive and physiologically costly procedures, such as crowns, veneers, or inappropriate interproximal reduction during or at the end of orthodontic treatment. Although periodontal surgeries and dermal fillers rarely offer predictable, long-term solutions, injection overmolded composite restorations can provide patients with a conservative and affordable option.

About the Authors

David Clark, DDS
Bioclear Learning Centers International
Private Practice
Tacoma, Washington

Charles Regalado, DDS
Private Practice
Spokane, Washington


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