Although residual alveolar ridge height has been associated with sinus mucosal thickening [36], our study did not find a significant association between these two parameters. Acharya et al. [36] reported that lower available bone height in the subsinus region was related to thickened sinus membranes within an Asian-Indian and Hong Kong-based Chinese population. Differences in the ethnic composition and geographic location of this population might explain the different findings compared to our study, which was primarily comprised of a Caucasian cohort in North America. Also, in their study, the majority of patients (80.53%) had some degree of periodontal disease, which might have directly influenced their outcome analysis. Since residual bone height depends highly on the rate of bone remodeling and sinus pneumatization after tooth extraction [37], future prospective clinical trials are needed to investigate the relationship between changes in maxillary sinus dimension and mucosal thickness.

This study presents new data on maxillary sinus mucosal thickening derived from a carefully defined data set; however, there were some limitations in the study. One limitation was the limited sample size. However, as discussed, our stringent case selection criteria yielded a more uniform data set for analyses. Other limitations were related to the actual measurements of the maxillary sinus. In order to normalize the data, specific planes were used as the basis for measurements. However, due to anatomical variations in patients, it was not always possible to orient each plane in the exact position. In those instances, the plane of orientation was set as close to ideal as possible. For example, it was not possible to orient the entire hard palate horizontally in some patients if it had a curvature. In addition, since the maxillary sinus is a three-dimensional structure with many variations among patients, situations arose where mucosal thickening extended from the septa or lateral walls instead of just on the floor of the sinus. In these situations, best judgment was utilized in order to decide if these areas of thickening would have an impact on the implant placement area. Also, variations in the anatomical features made orienting CBCT scans at times challenging, and this may have influenced the study outcomes.