# Biphasic Injection for Masseter Muscle Reduction with Botulinum Toxin
## 3 Results  
One patient experienced asymmetric smiling, which self-resolved within 4 weeks from the injection; at 1 month follow up no asymmetry was recorded. In another case, the patient claimed sagging. All the patients, if asked, claimed a mild temporary massication force decrease for about 3 weeks after BoNTA injection, but no one claimed it as distressing. No cases of paradoxical bulging were observed (Table 1). Out of 98 treatments accomplished on 42 patients, we observed a mean reduction of the left masseteric angle of 8.23\({}^{\circ}\)\(\pm\) 2.21\({}^{\circ}\) and a mean reduction of the right masseteric angle of 8.52\({}^{\circ}\)\(\pm\) 2.92\({}^{\circ}\) (Table 2). Statistical Analysis was performed using SPSS Software version 24.0 (IBM Corp., Armonk, NY, USA). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Patient**} & \multirow{2}{*}{\begin{tabular}{c} **LEFT** \\ **ISIDE** \\ **PRE-OP (\({}^{\circ}\))** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **RIGHT** \\ **SIDE** \\ **POST-OP** \\ **(\({}^{\circ}\))** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **RIGHT** \\ **SIDE** \\ **PA (\({}^{\circ}\))** \\ \end{tabular} } \\ \hline \#1 & 8 & \(-1\) & 9 & 7 & \(-2\) & 9 \\ \#2 & 4 & \(-1\) & 5 & 3 & 0 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the pre and post treatment angles and the overall variation (\(\Delta\)), per side. Unit of measure: grade (\({}^{\circ}\)). Positive angles are formed by masseteric lines lateral to the zygomatic arch line. Negative angles are when the masseteric line falls medial to the perpendicular zygomatic arch line. Figure 5: The angle between the zygomatic arch line and the masseter line was calculated in pre-operative picture (**A**) and 6 months post-operative picture (**B**) to assess the reduction of masseteric projection in order to achieve lower face recontouring. smile [50] or difficulty in mouth opening were described in our experience. Even if the most reported side effect is a decreased chewing power [8; 9; 10; 50], in this study, no patient claimed transient muscle weakness as distressing. Moreover, none of our patient experienced bruising, the second most frequent complication reported in the literature [50]. Differently from what was reported by [PERSON] et al., no cases of dizziness and headache occurred in our practice [58]. A case of asymmetric smiling self-resolved within a week, without the need for further BoNTA injection as described by [PERSON] and [PERSON] [50]. Only one patient claimed sagging; this finding was consistent with previously described studies but with a lower incidence [57; 58]. Paradoxical bulging is described by several authors as a reported complication related to injection level [55; 56]. However, no cases of paradoxical bulging were reported with our biphasic injection approach. The technique is tailored according to masseteric muscle anatomy injecting both deep and superficial belles, thus avoiding the risk of muscular fiber overactivity. Regarding the operative method, several approaches are described with important differences determined by the number of sites of injection and the injective technique. In the technique described by [PERSON] et al., a reference line is drawn from tragus to the mouth and BoNTA is administrated into 2 points, over the masseteric prominence. Two additional points are injected, 1 cm above and 1 cm below the reference line [59]. As reported in the literature [58; 60], we consider this approach risky for a sunken cheek appearance especially in patients with high middle third projection, because 2 points of injection are just below zygomatic arch. Otherwise, a two-point technique is described with injection points placed in the center of masseteric area [41]. Moreover, variation of this technique includes injecting 3 to 4 sites, 1.5 cm above the angle of the mandible [8]. [PERSON] et al. use a distributed injection points technique: six sites are marked in a grid-like fashion [57].