Quantifying the Effects of Bichectomy on the Middle and Lower Thirds of the Face: A Two-Dimensional Assessment

Technical Summary: Quantifying the Effects of Bichectomy on the Middle and Lower Thirds of the Face

Problem Statement
The aesthetic perception of the face is defined by the volumetric relationship between the facial skeleton and soft tissues, particularly the Bichat's fat pad (BFP). While the BFP contributes significantly to the volume and contour of the middle third of the face, its removal via bichectomy surgery (BS) is often performed to enhance zygomatic prominence and create a more defined facial contour. However, there is a lack of standardized, quantitative data demonstrating the specific impact of BFP removal on facial dimensions. The study addresses the need to objectively measure whether BS results in a measurable reduction in the area and linear distances of the middle and lower thirds of the face, and to determine if these changes correlate with the volume of fat removed or the patient's Body Mass Index (BMI).

Methodology
This study employed a retrospective, cross-sectional, experimental design involving 17 patients (ages 24–60) who underwent BS in a private clinical setting between 2021 and 2023.

• Surgical Protocol: All procedures were performed by a single dentist under local anesthesia using an intraoral approach. The technique involved a precise incision in the buccal mucosa, dissection of the buccinator muscle, and the excision of the buccal portion of the BFP. The excised fat volume was measured immediately using a 5 mL syringe, with removals ranging from 3.00 to 6.65 cm³ per side.
• Data Acquisition: Standardized pre- and postoperative (90-day follow-up) photographs were captured using a fixed camera setup (105mm focal length, ISO 100, f/8 aperture) to ensure consistency in lighting, distance, and perspective.
• Measurement Variables: Using GIMP®, Adobe Photoshop®, and ImageJ® software, the study analyzed pixel-based measurements. Key variables included:
  1. The distance from the sagittal line to the gonion.
  2. The distance from the sagittal line to the zygomatic region.
  3. The total facial area of the middle and lower thirds (defined by the silhouette between the eye centers, gonion, and zygomatic region).
  4. Patient BMI.
• Statistical Analysis: Descriptive statistics (mean and standard deviation) were calculated. Inferential analysis utilized a nonparametric bootstrap resampling test (n=300) to assess robustness, followed by One-way ANOVA with Tukey's post hoc test to evaluate significant differences between pre- and postoperative measurements. The null hypothesis ($H_0$) posited no difference between the volume of fat removed and the measured distances/areas.

Key Results
The study found statistically significant reductions in all measured facial parameters following the removal of the BFP:

• Linear Distances: There was a significant reduction in the distance from the sagittal line to the gonion ($p = 0.013$) and the distance from the sagittal line to the zygomatic region ($p = 0.005$). The average percentage reduction was 2.95% for the sagittal-gonion distance and 1.76% for the sagittal-zygomatic distance.
• Facial Area: A highly significant reduction in the total facial area of the middle and lower thirds was observed ($p = 0.000$), averaging a reduction of approximately 10,000 pixels.
• Fat Volume: The average volume of fat removed was 4.10 ± 1.04 ml per side.
• BMI Correlation: Crucially, the study found no statistical relationship between the patient's BMI and the volume of fat removed or the resulting variation in facial area. This indicates that BMI does not predict the degree of facial reduction achieved through BS.

Significance and Claims
The paper claims that the aesthetic effects of bichectomy on the middle and lower thirds of the face can be objectively quantified using 2D digital photographs and pixel-based measurements. The primary contribution is the demonstration that removing an average of 4.10 ml of BFP results in statistically significant, measurable reductions in facial width and area, thereby enhancing the projection of the zygomatic region and defining the jaw angle.

The authors emphasize that these results support a personalized approach to facial aesthetic surgery. They argue that because the reduction in facial area is not dependent on the patient's BMI, surgical planning cannot rely solely on body mass to predict outcomes. Instead, the volume of fat removed directly influences facial proportions, suggesting that careful, individualized assessment is required to avoid excessive volume loss that could lead to an aged or skeletal appearance. The study concludes that the subtle changes perceived by patients can be scientifically validated through the reduction of pixel counts in specific facial regions, providing a reproducible metric for evaluating surgical success.