The research protocol was submitted to and approved by the Ethical Committee of the University of Medical Sciences, School of Dentistry, Havana, Cuba (prot. 013/2013).

Eight female Pelibuey sheep, with a mean body weight of approximately 35 kg and a mean age of approximately 3 years, were provided by the Centro Nacional para la Producción de Animales de Laboratorio (CENPALAB) in Havana, Cuba. The surgical sessions were performed at the Centro de Cirugía Experimental (CENCEX) Facultad de Medicina “Victoria de Girón”, Universidad de Ciencias Médicas in Havana, Cuba. The animals were kept at the facilities of CENPALAB during the experimental period.

The ARRIVE checklist was followed as a guide. According to the Three R requirements [20], aiming to reduce the number of animals, the interferences among animals was eliminated, adopting a split-mouth design. No previous experiments were available that studied healing at the repositioned bony plate, so to describe the event of healing with sufficient approximation, a relevant difference in bone formation within the sinus was set to 10%, assuming a standard deviation of approximately 8%. Considering these values clinically relevant, seven pairs of subjects were calculated to be able to reject the null hypothesis that this response difference is zero with a power of 0.8 and α = 0.05.

Two different procedures for antrostomy closure were adopted, one using a resorbable membrane (control site) and the other repositioning the bone plate (experimental site). The randomisation was performed electronically (www.randomization.com) by an author not involved in any surgical procedures (DB). The surgeon (AP) was informed of the treatment randomly selected only at the end of the grafting procedure.

The examiner of the histological slides (AP) was carefully trained before the evaluation. The measurements were performed twice, and mean values used.

The animals fasted for 24 h preoperatively, but were allowed to drink water ad libitum. Anaesthesia was induced by 0.4 mg/kg of midazolam (Dormicum; Roche, Basel, Switzerland) and 10 mg/kg of ketamine (Ketamina-50; Liorad, Havana, Cuba), and orotracheal intubation was performed. The anaesthesia was maintained with a mixture of oxygen and 2–3% isoflurane (Isoflurane-vet; Merial, Toulouse, France) at a rate of 5 L/min. The surgical sites were rinsed with 0.12% chlorhexidine digluconate (Periogard™; Colgate-Palmolive Ltd, New York, NY, USA) and trichotomy was performed. After general anaesthesia, 1.5–2 cc of 2% mepivacaine HCI with 1:100,000 epinephrine was injected at the surgery site. All surgeries were performed under sterile conditions, using good clinical and laboratory practices.