## 4 Discussion  
The prevalence of black triangles is considered to be between 15% and 41.9% in the general population depending on the dental procedure performed and the age of the patient [19,20]. Reconstruction of the interdental papilla has been approached from various reconstruction techniques. Most of them include surgical techniques with not always predictable results. The minimally invasive HA approach has the potential advantage of being effective, predictable, and minimally invasive with only slight injury as compared to surgical treatments. In addition, it has few side effects. Although, its application is limited to small defects. This systematic review and meta-analysis were based on the application of HA to treat the presence of black triangles. A total of 166 papillae in 126 patients were included in the evaluated studies. The study by [PERSON] et al. [12] included 13 papillae adjacent to implants in 21 patients (12 women and 9 men) who were injected with HA. The manufacturer's recommended technique was used in the study (Hyadent Barrier Gel, Elaf Medical Supplies, Zagreb, Croatia). Thus, 0.36 mL of HA were injected, of which 5.76 mg were crosslinked HA and 0.72 mg were non-crosslinked HA. The average papilla defect at the beginning of the study was 2.0 \(\pm\) 1.1. At the end of the study (6 months later), the average was 1.9 \(\pm\) 0.8. This difference was not statistically significant. In the first study by [PERSON] et al. [13], 10 patients (four men and six women) were studied and injected with HA (a total of 43 papillae adjacent to natural teeth). For the initial examination, papilla defects with cut-off values of 0.24 mm\({}^{2}\) for area, 1.0 mm in height, and 0.5 mm for width were chosen. In this study, a total of 0.01 cc was injected (Teosyal Puresense Global Action, Teoxane, Geneva, Switzerland), of which 0.25 mg consisted of crosslinked hyaluronic acid. A maximum of five sessions were performed or sessions were continued until black triangles were no longer visible. The initial mean area was 1.37 \(\pm\) 0.41 mm, which was reduced to 0.70 \(\pm\) 0.20 mm at 6 months. Their results represent a decrease in the percentage of area of the black triangle. The results show 100% total reconstruction at 29 sites and a partial reconstruction of the remaining 14 sites, with percentages between 39% and 96%. Taking the data as a whole, an average reconstruction rate of 92.55% was achieved following an average number of 3.42 injections. Of note was the 100% interdental papilla reconstruction rate in most cases \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & & & & \\ \hline Confusion Bias & & & & & & & & \\ \hline Selection Bias & & & & & & & & \\ \hline Classification Bias & & & & & & & & \\ \hline Intervention? & & & & & & & & \\ Intervention Bias & & & & & & & & \\ \hline Lost Data Bias & & & & & & & & \\ \hline Measurement Bias & & & & & & & & \\ \hline Results Bias & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Assessing risk of bias in included studies. All studies have moderate to high risk of bias. Low risk of bias = green (+), unclear risk of bias = yellow (? ), high risk of bias = red (-). for initial values of up to 0.25 mm\({}^{2}\) area and a height of up to 1 mm. However, when the area exceeded 0.25 mm\({}^{2}\) and the height was 1 mm, the results showed a statistically significant negative correlation in relation to the rate of reconstruction. An interesting finding was that the distance between the point of contact and the bone crest had to be less than 6 mm for optimal results to be achieved, a result consistent with those obtained by other authors [21; 22; 23; 24; 25]. In the second study by [PERSON] et al. [14], 13 patients (six men and seven women) with a total of 21 papillae from the anterior maxilla region were included. Only papillae that had adjacent teeth were included. In each session, a single dose per 0.002 cc HA (Teosyal Puresense Global Action, Teoxane, Geneva, Switzerland) was used with a maximum of five applications.