Variation in bucco-palatal maxillary sinus width does not permit a meaningful sinus classification.

There is a large variation in SW depending on the height level within the sinus and on tooth position, which does not permit a simple/meaningful classification of each sinus as "narrow," "average," or "wide." Nevertheless, narrow sinuses (<10 mm) are rather prevalent in the premolar region, while wide sinuses (>15 mm) in the molar region; further, a wider and shorter residual alveolar ridge is associated with a wider SW.