Pneumatization of the maxillary sinus and resorption of the residual alveolar ridge following tooth extraction can compromise the dental implant placement. Similarly, extension of the dental implants inside the maxillary sinus cavity is not rare. Some studies have observed some differences in relation to the depth of the implant extension inside the sinus cavity. When the implants penetrate inside of the sinus cavity less than 2 mm, spontaneous covering of the implants with the sinus mucosa seems to occur [34, 35]. Also, new bone formation above dental implants has been described, especially if the implants exposed to the maxillary sinus do not tear the Schnederian membrane [34,35,36,37,38]. Nevertheless, when the implant extension inside the maxillary sinus is greater (more than 2 mm), the maxillary membrane do not repair spontaneously and debris accumulate on the exposed surfaces of the implants that were not covered by bone inside the antral cavity [34], which could lead to sinusitis. However, the long-term consequences of debris accumulation over the implants extended inside the maxillary sinus and perforating the Schneiderian membrane were not systematically evaluated before.

In relation to the long-term consequence of these different levels of implant protrusion, it was observed in this review that there were no statistically significant differences in implant survival, between implant penetrating ≤ 4 mm or > 4 mm, with a survival rate of 99.5% and 98.5% respectively.

Survival rate of the present review is in accordance with survival rates reported in a systematic review by Corbella et al. [39] in which the analyzed survival rates of different techniques for the treatment of atrophic posterior maxilla were as follows: short implants showed a survival rate from 86.5 to 98.2%, osteotome technique showed a survival rate from 95.4 to 100%, and sinuses augmentation through lateral technique showed an implant survival rate from 75.57 to 100%.

The secondary outcome of this review was the analysis of the clinical and radiological complications related to the penetration of implants in the maxillary sinus. Clinical complication among the different authors ranges from 0 to 14.3%, with a weighted mean complication rate of 3.4%, without finding statistical difference according to the level of implant penetration. The most common clinical complication was epistaxis, which can be considered a minor complication and that did not lead to major complications. Radiographic complication has also been shown low, weighted complication rate of 14.8%, without finding statistical difference according to the level of implant penetration. The most common complication was thickening of sinus membrane without having relevance at the clinical level. This is in concordance with the mongrel-dog study of Jung et al. [35], who observed after 6 months follow-up that the mucosa in the maxillary sinus cavity showed no inflammatory signs when dental implants perforating inside the maxillary sinus, suggesting that the extending implants do not make the maxillary sinus vulnerable to complications and do not cause any effect to the sinus physiology and resulting with no local or systemic pathology at all.