Purpose: This study aimed primarily to examine the relationship between maxillary sinus variations and dental implant placement in the atrophic maxillary premolar-molar region. Secondly, the preferences of experienced clinicians with regard to implant length in the bone and sinus were evaluated.

Materials and methods: The data were collected from panoramic radiographs of patients who had undergone dental implant surgery in the posterior maxilla. Parameters such as sinus pneumatization level, sinus floor elevation operation type, and length of dental implants in the sinus and bone (in millimeters) were evaluated. Groups were created for the categories mild-moderate-medial pneumatization and severe-extreme-medial pneumatization, with the subgroups severe and extreme medial pneumatization for medial pneumatization and "5 to 10 mm" and "≤ 5 mm" for inferior pneumatization of the maxillary sinus. The distribution of the data was evaluated with the Shapiro-Wilk test, and the Mann-Whitney U test was used to evaluate the millimeter measurements made in the groups.

Results: The mean implant length in bone tissue was measured as 6.3 mm in the mild-moderate-medial pneumatization group and 5.4 mm in the severe-extreme-medial pneumatization group (P < .001), whereas the mean implant length in the sinus was 3.6 mm in the mild-moderate-medial pneumatization group and 3.9 mm in the severe-extreme-medial pneumatization group, respectively (P < .001). The mean implant length in the sinus was 3.0 mm in the 5 to 10 mm group and 5.1 mm in the ≤ 5 mm group (P < .001), whereas the mean implant length in bone was measured as 6.6 mm in the 5 to 10 mm group and 3.6 mm in the ≤ 5 mm group (P < .001).

Conclusion: This was the first study in the literature in which classifications of inferior and medial pneumatization of the maxillary sinus were used for the same implants and their correlation was evaluated in the presence of sinus pneumatization. In this study, the mean implant length in the sinus was measured to be greater as sinus pneumatization progressed medially. Therefore, like inferior pneumatization, medial pneumatization may also have risks attributable to the need for internal or external sinus elevation operations in the atrophic maxilla, and this could be easily underestimated if CBCT is not used.