Morphological Pattern of the Atrophic Posterior Maxillae

* Images were included if: 1. Pristine maxillary posterior atrophic ridges (between premolars and molars) as a result of missing single or multiple teeth for over than 12 months. 2. Residual ridge height (RH) was \< 10 mm. 3. Presence of teeth adjacent to or opposing the edentulous area so the location of the edentulous ridges corresponding to the tooth site could be identified. 4. The maxillary sinus to be measured was visible from its floor to at least 15 mm from the alveolar crest of the edentulous ridge. * Images were excluded if: 1. Images were unclear or incomplete due to scattering or other reasons 2. Edentulous ridge height was more than 10 mm 3. Ridge preservation/augmentation simultaneous/delayed to tooth extractions 4. Grafted maxillary sinus for implant-supported prosthesis 5. The location of the edentulous ridge cannot be determined 6. Implants or other prosthetic device restoring the posterior ridge 7. Presence of sinus pathology that made the measurement impossible 8. The outline of the edentulous ridge cannot be identified due to low 'grey scale' density