Fig. 1

Distances from root tip to the maxillary sinus floor measured in the coronal section are divided into four types by the method of Shahbazian. a Distance larger than 0.5 mm; b distance less than or equal to 0.5 mm but larger than 0 mm; c distance equal to 0 mm, root tip attached to the sinus floor; d roots protruded into the sinus, distance recorded as negative