Table 1 Definitions of pharyngeal airway and maxillary arch parameters

NPV

Nasopharyngeal airway volume: the volume between the superior border of the OPV, which was defined as the line from the posterior nasal spine perpendicular to the top limit of the OPV continuing superiorly to meet the posterior wall, and the outline of the pharynx (Fig. 2A, B)

NPA

Nasopharyngeal airway area: the area between the upper and lower limits of nasopharynx.Once the NPV border was established and the NPV computed, the nasopharyngeal airway area was calculated and shown automatically

OPV

The oropharyngeal airway volume (OPV) was identified as the volume of the pharynx between a line parallel to Frankfurt horizontal plane (FHP) crossing through the posterior nasal spine and another line parallel to FHP at the level of the tip of the epiglottis (Fig. 2C, D)

OPA

Oropharyngeal airway area: the area between the upper and lower limits of oropharynx,Once the OPV border was established and the OPV computed, the oropharyngeal airway area was calculated and shown automatically

TPV

Total volume of the pharyngeal airway: the nasopharyngeal volume plus the oropharyngeal airway volume

MWM

Maxillary width at the molars: a dimension between the deepest points of the bilateral posterior concavities in the maxilla (Fig. 3A)

IMW

Intermolar width: the dimension between the lingual alveolar bone crests of the maxillary bilateral first molars (Fig. 3B)

PH

Palatal height: the vertical dimension from the center of the IMW to the palate’s uppermost point (Fig. 3B)

PA

Palatal area: the area of the palate before the alveolar ridge boundaries from the bilateral maxillary first molars (Fig. 3C)

MWC

Maxillary width at the canines: the dimension between the deepest points of the bilateral maxillary middle concavities at the canines (Fig. 3D)

ICW

Intercanine width: the dimension between the lingual alveolar bone crests of the bilateral canines. (Fig. 3D)