Palatonasal recess on medial wall of the maxillary sinus and clinical implications for sinus augmentation via lateral window approach.

BACKGROUND: Anatomic variations of the maxillary sinus determine the degree of difficulty in performing sinus augmentation. Whereas some variations, e.g., the septum and morphology of the sinus, have been extensively studied, the structure of the medial wall has never been investigated. The aims of this study are to measure the location and angulation of the palatonasal recess (PNR) on the medial wall and identify risk sites that are related to the shape of the PNR. METHODS: Cone-beam computed tomography (CBCT) scans were screened from the University of Michigan School of Dentistry database. Edentulous sites with <10 mm between the floor of the maxillary sinus and the alveolar crest were selected. The residual ridge height (RH), the distance between the PNR and the alveolar crest, and the angulation of the PNR were measured on the selected sagittal planes. The percentage of sites (risk sites) with recesses that were <90 degrees and <15 mm from the alveolar crest was calculated. The PNR location and angulation were compared among premolar and molar edentulous sites. RESULTS: Two hundred seventy-four sites were studied. The mean +/- SE PNR location was 14.2 +/- 2.8 mm, 13.1 +/- 2.2 mm, and 12.5 +/- 2.5 mm for the second premolar, first molar, and second molar sites, respectively, with significant differences between the second premolar and second molar sites. The mean PNR angulation was 109.8 degrees +/- 25.3 degrees , 121.6 degrees +/- 22.1 degrees , and 144.9 degrees +/- 23.1 degrees in the corresponding sites, with significant differences among the site groups. The respective percentages of risk sites were 15%, 8.2%, and 2.4% in the second premolar, first molar, and second molar sites. CONCLUSIONS: Maxillary sinuses with acute-angled PNRs might present a challenge for performing sinus augmentation. Therefore, this anatomic structure should be carefully evaluated.