Figure 2.

Determination of landmarks for the natural ostium and accessory maxillary ostium. (A) Three-dimensionally constructed nasal airway and left maxillary sinus. The natural ostium and accessory maxillary ostium can be found from the lateral view of the nasal airway. (B,C) Landmarks of the natural ostium, accessory maxillary ostium, and adjacent anatomic structures. After three-dimensional coordinates (x, y, z) for each landmark were obtained, the horizontal and vertical dimensions of the natural ostium and accessory maxillary ostium and the spatial position of the natural ostium and accessory maxillary ostium related to the adjacent anatomic landmarks, such as the maxillary sinus floor, anterior maxillary sinus wall, and orbital floor, were obtained. The definitions of each landmark are described in Table 1. NO, natural ostium; AMO, accessory maxillary ostium.