- Open Access
Thickness of the Schneiderian membrane and its correlation with anatomical structures and demographic parameters using CBCT tomography: a retrospective study
© The Author(s). 2018
- Received: 29 January 2018
- Accepted: 27 August 2018
- Published: 19 October 2018
The aims of the present study were to determine the thickness of the Schneiderian membrane and identify the width of the maxillary sinus, which is indicated by the buccal and lingual walls of the sinus angle between. Furthermore, to investigate the possibility of a correlation between the aforementioned structures and also other anatomical and demographic parameters using CBCTs for dental implant surgical planning.
The study included CBCT images of 76 consecutive patients with field-of-view 15 × 12 or 12 × 8cm. Reformatted cross-sectional CBCT slices were analyzed with regard to the thickness of the Schneiderian membrane designated by the medial and the lateral walls of the sinus, in three different standardized points of reference. Age, gender, and position of the measurement were evaluated as factors that could influence the dimensions of the anatomical structures, using univariate and multivariate random effects regression model.
The mean thickness of the Schneiderian membrane was 1.60 ± 1.20 mm. The average thickness revealed now differentiation by age (p = 0.878), whereas gender seemed to influence the mean thickness (p = 0.010). Also, the thickness of the Schneiderian membrane increased from medial to distal (p = 0.060). The mean value of the angle designated by buccal and lingual walls of the sinus was 73.41 ± 6.89 °. The angle measurements revealed no correlation with age, but a tendency towards lower mean angles in females (2.5 ° on average, p = 0.097). According to the anatomical position of the measurement, a differentiation was also detected. No correlation between thickness of the Schneiderian membrane and the angle of the walls of the sinus was concluded (p = 0.662).
This study demonstrated that the thickness of the Schneiderian membrane and the width of the maxillary sinus can only be affected by gender and anatomical position, but not by the age of the patient.
- Schneiderian membrane
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) [2–6]. 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 .
The Schneiderian membrane is the mucous membrane that covers the inner part of the maxillary sinus cavity . 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 . 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.
The study sample included 76 patients, of which 39 were females and 37 were males. In total, 120 sinuses (44 both left- and right-sided, 21 right-sided, and 11 left-sided) were evaluated as suitable for the present study and were measured. The total sample was classified in four age groups (below 45 years, 45–54 years, 54–64 years, and over 65 years of age). The mean age value of the sample is 58 years (ranging from 19 to 65 years of age).
All patients were Greek adults, and all CBCT examinations were performed to evaluate the posterior maxilla for future implant surgery. All patients were either patients of our clinic or had been referred to our clinic by their private dentist for implant or other pre-implant surgery. The minimum acceptable alveolar process was 5 mm. Patients with previous implant therapy or/and maxillary sinus augmentation in their history as well as patients with active periodontal disease, cysts, polyps, sinusitis, allergic rhinitis, or other pathological entities in their maxillary sinuses were excluded from our study. Other exclusion criteria were the presence of systematic diseases impacting the metabolism and quality of the bones in patients’ history, such as thyroid disease, hyperparathyroidism, diabetes, chronic renal disease, osteoporosis, and no development or acquired craniofacial or neuromuscular deformities. None of the patients previously or currently received medication including vitamin D, human growing hormone (HGH), or bisphosphonates. All the collected data were anonymous.
The CBCT images were obtained with NewTom VGI Tomograph (NewTom, Verona, Italy) with a voxel size of 0.3 mm. Operating parameters were set at 5.28 mA, 110 kV, exposure time 3.60 s, and field of view (FOV) of 15 × 12 or 12 × 8 cm. Panoramic reformatted images with thickness of 1 mm were chosen for the present study.
All measurements were performed in millimeters using the ruler contained in the NNT Viewer®.
Using the built-in ruler of the NNT Viewer®, we measured the angle EDF for each cross-sectional image created by the aforementioned method. This angle indicates the width of the maxillary sinus in each location. As this angle increases, so does the width of the maxillary sinus.
Angle ≤ 65o: small
65o < angle < 80o: moderate
Angle ≥ 80o: large
Evaluation of the images
The CBCT images were initially evaluated by an oral surgeon and then they were re-evaluated and measured by two experienced dentists who were involved in the patients’ treatment and follow-up. In case of any disagreement, both parties re-evaluated and remeasured the related CBCT imaging.
All analyses were performed using Stata version 13.1 (Stata Corp., TX, USA).
Sinuses’ thickness by gender and overall
Average thickness (mm)—all points
Average thickness by age group
Average thickness (mm)—overall
Thickness by point of measurement (all measurements)
Sinuses’ angles by gender and overall
Average angle (°)—all points
Angle of the walls of the sinus by age groups
Results from a multivariable random effects regression model of all angles on age (in groups) gender and point of measurement
(− 5.7, 3.9)
(− 5.5, 2.8)
(− 5.0, 3.9)
(− 5.4, 0.5)
It is very important to pre-operatively evaluate the thickness of the Schneiderian membrane to plan the surgical procedure in the region that involves the membrane, such as a sinus lift augmentation, which increases the possibility of membrane perforation or other complications.
The present study assumed that the average thickness of the Schneiderian membrane is 1.60 ± 1.20 mm.
Year of study
Method of study
Tos and Mogesen et al.
Aimetti et al.
0.97 ± 0.36 mm
Pommer et al.
0.09 ± 0.045 mm
Janner et al.
2.16–3.11 mm (mid-sagittal regions) and 0.9–1.84 mm (lateral-median regions)
Pazera et al.
1.58 mm (95% CI 1.17–1.98)
Cakur et al.
0.5 ± 0.49 mm
Pommer et al.
Anduze-Acher et al
1.99 ± 2.10 mm
Zheng-Ze Guo et al.
1.93 ± 2.00 mm
Shih-Cheng Wen et al.
1.78 ± 1.99 mm
Yen-Hua Lin et al.
1.32 ± 0.87 mm
Insua et al.
1.36 ± 0.42 mm
Lozano-Carrascal et al.
1.82 ± 1.59 mm
Talo Jildirim et al.
4.19 ± 5.84 mm
1.60 ± 1.20 mm
In this study, it was detected that 27.5% of the measurements made (99 out of 360) were more than 2 mm. However, all X-ray examinations that showed a visually detectable pathology were excluded from our study. For this reason, our study cannot conclude that the limit of 2 mm is an accurate limit to evaluate a sinus membrane as healthy or pathological. The limit of 2 mm as a criterion is used by Shanbhag et al. 2014, Ji-Young Yoo et al. 2011, Janner et al. 2011, and Cagici et al. 2008 [10–13]. On the contrary, Eggesbo et al. 2006 and Cakur et al. 2011 set the limit of 4 mm as a safe threshold to evaluate a sinus membrane as pathological [9, 14]. Furthermore, Lozano-Carrascal et al. 2017 accept a threshold of 3 mm of membrane thickness for pathology existence . In our study, the membrane thickness of 6.94% of our sample was over 4 mm. For this reason, we can accept a thickness over 4 mm as a safer limit to evaluate if there is a pathology in the sinus or not.
Comparing the thickness of the membrane between the two genders, males seem to have thicker membranes than females. Vallo et al. 2010, Janner et al. 2011, Ji-Young Yoo et al. 2011, Cakur et al. 2013, and Jildirim et al. 2017 [9, 11, 12, 16, 17] also come to this conclusion. Our study assumed that this difference is of the order of 40%. On the contrary, Pazera et al. 2010 concluded that there is no significant difference between thickness of the mucosa and gender (p = 0.294) .
The aforementioned differences can be attributed to the fact that every study has evaluated different populations and has also set different criteria in the selection of their sample.
In our study, there is no statistically significant influence when comparing the thickness of the mucosa and age (p = 0.878). Janner et al. 2010, Vallo et al. 2010, and Jildirim et al. 2017 also come in accordance with our results [12, 16, 17]. The age factor does not seem to affect the anatomical characteristics of the sinus. Unlike a state of inflammation, allergy, smoking of the patient does not affect the sinus thickness or wideness .
As regards the width of the maxillary sinus, the mean angle value was found to be 73.4 ± 6.9 °. It seems that there is a tendency towards greater angle values in the male group, but the difference is not statistically significant in order to conclude that wider angles and widths exist in male patients. The aforementioned results can be also associated with the results of the study of Gosau et al. 2009, which showed that female sinuses tend to have lower average volume values than male sinuses . The study of Lozano-Carrascal et al. 2017 also measured the same angle but only in the region of the upper first molar and found a mean value of 73.39 ± 15.23 ° . The present study is more accurate because the mean angle results from three different measurements taken from three different points of the maxillary sinus.
In the present study, it was also concluded that the width of the sinus increases from mesial to distal. Male sinuses had higher prevalence of high angle values compared to female sinuses, but the majority of angle values and widths was characterized as moderate.
In an attempt to correlate the membrane biotype regarding thickness with the sinus width, it was proven that there is no correlation between the thickness and width of the sinus (p = 0.695).
In conclusion, the present study demonstrated that male patients tend to have a thicker membrane than female patients. The angles of the sinus seemed to increase in width from mesial to distal, and they have no significant correlation with any of our parameters. Thickness of the mucosa and width of the maxillary sinus did not seem to correlate. Future studies including larger groups of participants should be necessarily conducted in order to establish additional possible correlations between the anatomical structures of the maxillary sinus and their variations.
Availability of data and materials
The data will not be shared, but are available upon request.
DK evaluated and selected the CBCT images for the present study. AK and SP conducted all the required measurements. All four authors interpreted and analyzed the data collected. KT critically revised and approved the article. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Patient recruitment and data collection for this study took place at National and Kapodistrian University of Athens, School of Dentistry, Greece. The research was approved by the Ethics Committee of the National and Kapodistrian University of Athens, Greece, and all activities were conducted in full accordance with ethical principles, including the World Medical Association Declaration of Helsinki. We described the purpose of the study to patients, and the data obtained anonymously.
Consent for publication
Written informed consent was obtained from the patients for the publication of this study and any data.
Authors Demos Kalyvas, Andreas Kapsalas, Sofia Paikou, and Konstantinos Tsiklakis declare that they have no competing interests.
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