The purpose of this investigation is to evaluate 2 different methods for reducing cortical wall thickness in sinus floor augmentation surgery. A manual bone scraper was compared in terms of efficacy, speed, and safety to an ultrasonic insert for osteoplasty, in a randomized controlled clinical trial with a split-mouth design. Twenty-five patients with severe posterior maxillary atrophy were treated with bilateral sinus floor elevation with lateral approach. Antrostomies were randomly performed by eroding the cortical wall with a manual bone scraper (test site) or with an ultrasonic insert (control site) until the membrane was visible under a thin layer of bone, before outlining the window with a piezoelectric device. Occurrence of membrane perforation, laceration of vascular branches, and surgical time were recorded. Mean surgical time of the antrostomy in the test sites was 9'18", while in the control sites was 9'47". No significant differences were found in terms of surgical time, incidence of membrane perforation during antrostomy (4.3% in both groups), or other intraoperative complications between the 2 techniques. Both surgical approaches represent effective options for performing lateral antrostomies during sinus floor elevation procedures in a safe and predictable way.