The present experiment aimed to study the influence on the healing after the placement of autogenous bone on the antrostomy and in the subjacent region after maxillary sinus elevation. After 8 weeks of healing, in the antrostomy region, a trend of higher bone formation in the treated compared to the untreated sites was observed. No statistically significant difference was found. In the subjacent region (close-to-window region), a higher content of new bone was found in the treated compared to the untreated region, being the difference statistically significant. A trend of higher proportions of new bone was observed in all the remaining regions within the elevated space in the treated compared to the untreated regions. However, none of the differences reached statistical significance.

The protection of the access window with membranes after sinus floor elevation using lateral access has been propagated as a procedure that yields higher implant success rate [3]. However, both clinical and experimental studies have shown that, despite the use of collagen membrane, complete closure of the antrostomies after sinus floor elevation might not be always achieved. In a clinical study [12], after 9 months from sinus floor elevation in which collagen membranes were used to cover the antrostomy, biopsies were harvested at the grafted sites from both the crestal region and the antrostomy. The histological analysis showed 40.1% of mineralized bone and 40.1% of marrow spaces in the biopsies retrieved from the alveolar crest while those from the antrostomy presented proportions of 26.0% and 23.4%, respectively. Moreover, only 3.9% of connective tissue was found in the crestal regions while in the antrostomy the respective proportion was 19.7%. This amount of connective tissue was mainly due to a few antrostomies that showed incomplete healing of the lateral window.

Experimental studies as well have reported incomplete healing of the antrostomies. In an experiment in sheep [19], at the test sites, perforation of the sinus mucosa was carried out and then protected with a collagen membrane. The elevated space was filled with biphasic calcium phosphate (60% HA/40% beta-TCP) on both test and control sites. The antrostomy was protected with a membrane made of polylactic acid and citric acid ester acetyl. After 12 weeks of healing, the bone was found formed from the margin of the antrostomy. However, none of the antrostomies was completely obliterated, presenting connective tissue occupying the central regions of the access window. In another similar experiment in sheep [20], a collagen membrane was placed only at the test sites subjacent to an intact sinus mucosa. The elevated space was filled with deproteinized bovine bone mineral (DBBM) and a collagen membrane was placed on the access window, both at the test and control sites. After 4 months of healing, the antrostomies of both sites presented high amounts of new bone (35–39%). Marrow spaces and residues of DBBM were found at proportions of 12–13% and 16–20%, respectively. However, connective tissue was found at high proportions in both sites (27–36%), interposed between the margins of the antrostomy.