Bertl K, et al. - Experts evaluated the sinus width (SW) at different height levels of posterior teeth and the possible factors influencing SW. They also assessed whether or not a simple/meaningful sinus classification based on SW is possible. In SW depending on the height level within the sinus and on tooth position, a large variation was noted, which does not permit a simple/meaningful classification of each sinus as “narrow”, “average”, or “wide”. However, in the premolar region, the narrow sinuses are rather prevalent, while wide sinuses bare prevalent in the molar region. Moreover, they noted an association of a wider and shorter residual alveolar ridge.