SA2 - Establishing Facial Soft Tissue Types in the Orthognathic Patient Evaluation

Oral Abstract Presenter(s)

• 

  Marcus Crayton, DDS (he/him/his)

  Resident
  Department of Oral and Maxillofacial Surgery/Howard University Hospital
  Washington, District of Columbia

  Handouts

Co-Author(s)

• EL

  Ermina Lee, BS

  Medical Research Scholars Program Research Fellow
  NIH/NIDCR
  Bethesda, Maryland
• XL

  Xiaobai Li, PhD

  Biostatistics and Clinical Epidemiology Service Staff
  NIH/NIDCR
  Bethesda, Maryland
• 

  Konstantinia Almpani, DDS, MSc

  Assistant Research Physician
  NIH/NIDCR
  Bethesda, Maryland
• DJ

  Dana Jackson, DDS

  Department Chair, Program Director, & Clinical Associate Professor
  Department of Oral and Maxillofacial Surgery/Howard University Hospital
  Washington, District of Columbia
• JL

  Janice S. Lee, DDS, MD, MSc

  Clinical Director
  NIH/NIDCR
  Bethesda, Maryland

Abstract: The facial soft tissue (ST) profile is extensively discussed in the oral and maxillofacial literature, with focus on identifying predictive ratios for ST changes following orthognathic surgery. Postoperative swelling may also be influenced by ST biotype. Although validated methods for three-dimensional (3D) ST evaluation exist, research into the ST response to surgery remains limited due to the lack of a standardized, clinically accessible technique for assessing biotype.<sup>1 As a result, ST evaluation is provider-dependent and not quantifiable. In this study, we conduct a targeted examination and propose a framework for ST envelope classification.

This is a retrospective, IRB approved study using Cone Beam Computed Tomography scans (CBCTs) acquired preoperatively for orthognathic surgery. All CBCTs were configured to the same coordinate system (Invivo 7.0) and annotated with a validated set of 3D skeletal cephalometric landmarks covering the surfaces of the frontal bone, face, maxilla, and mandibe.2 ST measurements were obtained by first bisecting the CBCT volume in the sagittal plane at each landmark. Manual software was then used to measure the linear projection of the cephalometric point to the edge of the soft tissue profile (Figure 1). The protocol was performed by a single investigator and reviewed by a senior investigator. Twenty-two landmarks were initially considered and tested regarding their reproducibility. Ten landmarks were omitted due to poor reproducibility (bilateral Gonion, Antegonion, Zygomatic arch) or were obscured due to the chin resting position (B point, Pogonion, Gnathion, Menton). Descriptive and correlation statistical analyses were conducted on the ST thickness measurements corresponding to the remaining 12 skeletal landmarks (Table 1).

Thirty-two surgical patients (19 female; 25 skeletal Class III, 7 Class II) were included, with a mean age of 25.8 years (range: 16-45) and BMI of 26.5 (range: 18.8-45.5). Spearman’s correlation revealed that the ST thickness at Prosthion had a strong positive association with ST thickness at Frontozygomatic arch right (ρ = 0.63, P < .0001) and left (ρ = 0.60, P = .0003), a moderate association with the one at Nasion (ρ = 0.50, P = .0036), and weak association with the one at A point (ρ = 0.39, P < .0001). Correlation analyses further revealed that the ST thickness at Nasion had a moderate positive association with the ones at Supraorbitale right (ρ = 0.57, P = .0007) and left (ρ = 0.50, P = .0035). No other pairwise comparison of landmark-based ST thickness demonstrated statistically significant correlation, except between symmetric points, demonstrating protocol validity. Age was not correlated with any landmark-based ST thickness measurement, and BMI demonstrated an association only with the thickness at Nasion (ρ = 0.38, P = .0301). The results of the Wilcoxon rank-sum test indicated that ST thickness was greater in males compared to females at Nasion (U = 306, P = .0002), Supraorbitale right (U = 322, P < .0001) and left (U = 325, P < .0001), Prosthion (U = 265, P = .028), and A point (U=273, P = .013). Compared to Class II, those with Class III had thicker ST at Prosthion (U = 49, P = .0013).

Using a set of validated, easily reproducible skeletal cephalometric landmarks to anchor ST thickness measurements, we establish a framework for CBCT-based ST evaluation. The thickness at Prosthion demonstrated moderate variability, and is promising for the stratification of thick versus thin biotype at its mean value. Nasion is also promising for biotype stratification given its correlation with ST thickness at Prosthion and placement away from regions directly affected by orthognathic surgery. Our measurement protocol enables objective classification of ST biotype, enhancing consistency in assessment.

1. Piombino P, Esposito E, Committeri U, et al. Facial soft tissue thickness measurement method and relationship with BMI, age and sex. J Stomatol Oral Maxillofac Surg. 2023;124(4):101420. doi:10.1016/j.jormas.2023.101420
2. Liberton DK, Verma P, Contratto A, Lee JS. Development and Validation of Novel Three-Dimensional Craniofacial Landmarks on Cone-Beam Computed Tomography Scans. J Craniofac Surg. 2019;30(7):e611-e615. doi:10.1097/SCS.0000000000005627
Table 1 Preoperative Soft Tissue Thickness (mm) Figure 1 Skeletal Cephalometric-Based Soft Tissue Thickness Protocol Demonstration</sup>