Existence of a Neutral-Impact Maxillo-Mandibular Displacement on Upper Airways Morphology

Abstract

Current scientific evidence on how orthognathic surgery affects the airways morphology remains contradictory. The aim of this study is to investigate the existence and extension of a neutral-impact interval of bony segments displacement on the upper airways morphology. Its upper boundary would behave as a skeletal displacement threshold differentiating minor and major jaw repositioning, with impact on the planning of the individual case. Pre- and post-operative cone beam computed tomographies (CBCTs) of 45 patients who underwent maxillo-mandibular advancement or maxillary advancement/mandibular setback were analysed by means of a semi-automated three-dimensional (3D) method; 3D models of skull and airways were produced, the latter divided into the three pharyngeal subregions. The correlation between skeletal displacement, stacked surface area and volume was investigated. The displacement threshold was identified by setting three ∆Area percentage variations. No significant difference in area and volume emerged from the comparison of the two surgical procedures with bone repositioning below the threshold (approximated to +5 mm). A threshold ranging from +4.8 to +7 mm was identified, varying in relation to the three ∆Area percentages considered. The ∆Area increased linearly above the threshold, while showing no consistency in the interval ranging from -5 mm to +5 mm.

Keywords: 3D analysis method; OSAS; bioengineering; maxillofacial surgery; orthognathic surgery; upper airways.

Figure 1

(a): Example of skull and maxillary bones segmentation in 3D Slicer software. (b): Example of upper airways segmentation in 3D Slicer software.

Figure 2

Superimposition of post- to pre-operative upper airways 3D models following point-pairs picking alignment in CloudCompare software. (a) Posterior view. (b) Sagittal view. (c) Colorimetric surface map following iterative closest point (ICP) to refine alignment in CloudCompare software (Sagittal view).

Figure 3

Upper airways 3D models evaluation and partitioning into bounding boxes in Matlab software. One single case is reported (left: pre-operative, right: post-operative).

Figure 4

Plotted data of upper airways (UA) ∆Area variation in relation to maxillary bones displacement. (a) The X axis reports the maxillary antero–posterior repositioning (AP) movement, while the Y-axis reports the average percentage ∆Area variation of the slices of the corresponding patient for each subregion. Red circles indicate an average percentage reduction in area while blue circles indicate an average increase. (b) The X axis reports the mandibular AP movement, while the Y-axis reports the average percentage ∆Area variation of the slices of the corresponding patient for each subregion. Red circles indicate an average percentage reduction in area while blue circles indicate an average increase.

Figure 5

ROC curves relative to the +50% area increase; maxillary displacement for the three subregions analysed. (A) Nasopharynx. (B) Oropharynx. (C) Hypopharynx.

Figure 6

ROC curves relative to the +50% area increase; mandibular displacement for the three subregions analysed. (A) Nasopharynx. (B) Oropharynx. (C) Hypopharynx.