Felice 2009a.

Methods	Randomised trial of split‐mouth design, 1 year post‐loading follow‐up. No withdrawals
Participants	Patients having 4 to 6 mm of alveolar height with a thickness of 8 mm or more below the sinus. Adults treated in dental hospitals/university clinics in Bologna, Roma and Chieti, Italy. Exclusion criteria were: general contraindications to implant surgery, patients irradiated in the head and neck area, immunosuppressed or immunocompromised patients, patients who took or are taking bisphosphonates intravenously, patients with untreated periodontitis, poor oral hygiene and motivation, uncontrolled diabetes, pregnancy or lactation, addiction to alcohol or drugs, psychiatric problems, lack of opposite occluding dentition in the area intended for implant placement, patients with an acute or chronic infection inflammation in the area intended for implant placement. 15 patients were treated and all patients were followed up to 1 year after loading, therefore there were no drop‐outs
Interventions	Comparison 1: short implants without augmentation versus long implants with augmentation 1 to 3 5 mm long implants of 6 mm in diameter versus 1 to 3 10 mm or longer implants of 4 mm in diameter placed in 2‐stage laterally augmented sinus with 100% bovine anorganic bone (Bio‐Oss, Geistlich Pharmaceutical, Wolhusen, Switzerland) with their lateral windows sealed with a resorbable collagen membrane (OsseoGuard, Biomet 3i, Palm Beach, FL, USA) 4 months before. All augmentation procedures were performed under local anaesthesia. All implants were left to left to heal submerged for 4 months. Rescue implants (MegaGen Implant Co. Lld., Gyeongbuk, South Korea) as short implants and EZ Plus (MegaGen) as long implants, all with internal connection were used. Implant site preparation was also different since a 5 mm diameter trephine was used initially to prepare the osteotomy sites for Rescue implants. Provisional screw‐retained reinforced resin prostheses were replaced after 4 months by definitive screw‐retained metal‐ceramic prostheses
Outcomes	Prosthesis and implant failures, complications, peri‐implant marginal bone levels, and patient preference
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Article: "A computer generated restricted randomisation list was created"
Allocation concealment (selection bias)	Low risk	Article: "Only one of the investigators (ME), not involved in the selection and treatment of the patients, was aware of the randomisation sequence and could have access to the randomisation list stored in his pass‐word protected portable computer. The randomised codes were enclosed in sequentially numbered, identical, opaque, sealed envelopes. Envelopes indicating which site to augment were opened sequentially just prior to the augmentation procedure. Therefore, treatment allocation was concealed to the investigators in charge of enrolling and treating the patients"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Article: "One dentist (GP) not involved in the treatment of the patients performed all clinical and radiographic assessments without knowing group allocation, therefore the outcome assessor was blinded, however the Bio‐Oss augmented sites could be identified both clinically when testing implant stability because of the different diameters and on radiographs because they appeared more radio‐opaque and implants were different"
Incomplete outcome data (attrition bias) All outcomes	Low risk	All data presented, no drop‐outs
Selective reporting (reporting bias)	Low risk	All planned outcomes were reported
Other bias	High risk	Implants of small diameter (4 mm) and of different design were inserted with a different surgical technique in the augmented group instead of the originally planned identical but longer implants Patients had always the augmentation procedure performed first and then had implant placement bilaterally. This may have affected patient preference since patient could not experience the benefit of having the prosthesis 4 months earlier