The maxillary sinus is the largest of the paranasal air-filled spaces, and it develops firstly in utero [1, 2]. Anatomically, the maxillary sinus is a pyramid-shaped cavity located in the facial skull with a mean volume of 12.5 mL (min 5 mL and max 22 mL) [2,3,4,5,6]. The size, the shape, and the wall thickness of every maxillary sinus not only vary among the population, but also between the two sides of an individual skull [6].

The Schneiderian membrane is the mucous membrane that covers the inner part of the maxillary sinus cavity [7]. Histologically, it consists of an overlaid periosteum with a thin layer of a pseudo-stratified ciliated epithelium and highly vascularized connective tissue [1, 7]. According to Kim et al. 2009, it has been proved that mesenchymal stem cells from the sinus membrane have an ability of bone formation, which plays a vital role in sinus floor elevation procedures [8]. Many studies have measured the thickness of the Schneiderian membrane using different methods such as cadaver examinations, CTs, and CBCTs. Normally, the thickness of the Schneiderian membrane is approximately 1 mm [6, 9]. However, in everyday clinical practice, mucosal thickening of the maxillary sinus is a common radiographic finding in asymptomatic patients; therefore, mucosal lining of more than 4 mm is considered to be pathological [6, 9].

When planning any surgical treatment for the maxilla that includes the posterior region, not only the dimensions and abilities of the Schneiderian membrane, but also the anatomical variations of the maxillary sinus are very significant for every clinician. Cone-beam computed tomography provides essential three-dimensional information regarding the inner part of the maxillary sinus in order to increase the success rate of every surgical procedure and, simultaneously, in order to limit the intra- and post-operative complications.

In the international literature, there is a limited number of studies that quantify the dimensions of the Schneiderian membrane using CBCTs. Therefore, the aim of the present retrospective study is to measure the thickness of the Schneiderian membrane and to identify the width of the maxillary sinus, which is indicated by the angle between the buccal and lingual walls of the sinus in a given height, using CBCT imaging. Furthermore, the present study detects possible correlations between the aforementioned factors and also between each of these factors with anatomical locations and demographic parameters.