This systematic review and subsequent meta-analysis follow the guidelines of the PRISMA statement.

The following focus question was developed: Is the intrusion of dental implants into the sinus cavity during implant drilling or implant placement, without regenerative procedure (lateral sinus lift or transalveolar technique) and graft material, has an effect on implant survival or increase clinical and radiographic complications? (Fig. 1) (Table 1).

Implant survival was defined as no pain on function, no mobility, 2–4 mm radiographic bone loss, and no exudates history.

Implant success was defined as no pain or tenderness upon function, no mobility, +2 mm radiographic bone loss from initial surgery, and no exudates history.

An electronic literature search was conducted by two independent reviewers (GMR and BE) based on the inclusion criteria in several databases, including MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials, and the Cochrane Oral Health Group Trials Register databases, covering articles written in English up until January 2018. Because no randomized controlled trials were found in the screening process, the included studies were analyzed with Newcastle-Ottawa scale (NOS). Both reviewers compared decisions, and their eligibility for this review was confirmed after discussion. Full articles were obtained for all the investigations deemed eligible for inclusion in this paper and further evaluated by both reviewers. If needed, a third reviewer was consulted to ensure consensus.

Literature search was conducted in several databases including MEDLINE (PubMed) and EMBASE from 1980 to 2018. All article titles and abstracts were screened in order to eliminate non-qualifying studies. Next, full-text evaluation of each article was performed in order to confirm the eligibility based on the inclusion and exclusion criteria. Combinations of controlled terms (MeSH and EMTREE) and keywords were used whenever possible, with “[mh]” representing the MeSH terms. In addition, other terms not indexed as MeSH and filters were applied. The key terms used were the following: (((((((((((((“maxillary sinus”) OR “schneiderian membrane” [MeSH Terms]) OR “schneiderian membranes” [MeSH Terms]) OR “dental implant” [MeSH Terms]) AND “perfor*”) OR “penetrat*”) OR “intruding*”) OR “sinus perforat*” OR “membrane perforation*”) OR “schneiderian membrane peforation*”). References of full-text-evaluated investigations were also screened. In addition, a manual search in periodontics/implantology-related journals, including “Clinical Oral Implant Research,” “Journal of Dental Research,” “Journal of Clinical Periodontology,” “Journal of Periodontology,” “Clinical Implant Dentistry and Related Research,” and “The International Journal of Periodontics & Restorative Dentistry,” from 1980 up to 2018, was also performed to ensure a thorough screening process.