CBCT imaging has been recognized as a more sensitive imaging modality for identifying sinus thickening and pathoses in the posterior maxilla compared to panoramic radiography [21, 22]. This could explain why the current study identified a higher prevalence of mucosal thickening compared to earlier studies [23]. However, compared to other similar CBCT studies [21, 24, 25], the prevalence reported in the current study is still much higher than the previously published articles with a similar study design. Ritter et al. [25] in a retrospective CBCT study reported 38.1% of subjects presented with mucosal thickening. Similarly, Pazera et al. [24] reported a prevalence of 23.7% and Janner et al. [20] reported 37% of cases with membrane thickening. In a recent study, Brüllmann et al. [17] found 74% of evaluated sinuses had sinus findings upon CBCT examination. These differences in prevalence might result from the different inclusion criteria among the studies. Another potential explanation for these differences in the reported prevalence of mucosal thickening may be due to the ambiguous definition used in the early studies. Some studies suggested that 2 mm should be considered the threshold for identifying mucosal thickening [20], and thus the prevalence of slight mucosal thickening may have been underestimated. To avoid this situation, the current study analyzed the thickness of sinus membranes based on four different categories: no thickening (≤1 mm), minimal (>1 mm but ≤2 mm), moderate (>2 mm but ≤5 mm), and severe thickening (>5 mm). According to this index (Fig. 2), 93.1% of cases examined had maxillary sinus mucosal/tissue thickening and 65.5% had severe thickening.

The current study demonstrated that sinus mucosal thickening does not correlate with implant survival. This result is consistent with a previously published report by Jungner et al. [26]. In their study, the presence of sinus thickening was not significantly associated with implant failure. Similarly, our study found a 100% implant survival rate for both patients with and without sinus mucosal thickening. It is worth mentioning that none of the CBCT images evaluated in the current study showed signs of sinusitis or periapical pathoses, despite indications of physiologic mucosal thickening. All the selected images presented clear sinuses without signs of infection. Therefore, it could be postulated that physiologic mucosal thickening does not contribute to implant failure. However, an association between pathologic mucosal thickening and implant survival cannot be drawn. If sinusitis is suspected, it is suggested that clinicians consult the appropriate medical specialists before implant placement.