The purpose of the present study was to explore the maxillary sinus anatomy, its variations and volume in patients with a need for maxillary implant placement.
Maxillary sinus data of 101 consecutive patients who underwent spiral computed tomography (CT) scans for preoperative implant planning in the maxilla at the Department of Periodontology, University Hospital, Catholic University of Leuven, Leuven, Belgium were retrospectively evaluated. The alveolar bone height was measured on serial cross-sectional images between alveolar crest and sinus floor, parallel to the tooth axis. In order to describe the size of the maxillary sinus anteroposterior (AP) and mediolateral (ML) diameters of the sinus were measured.
The results indicated that the alveolar bone height was significantly higher in the premolar regions in comparison to the molar region (n = 46, P < 0.01). The age showed negative relation to bone dimension (r = - 0.32, P = 0.04).
Anterior and posterior border of the maxillary sinuses were mostly located in the first premolar (49%) and second molar (84%) regions, respectively. Maxillary sinus septa were indentified in 47% of the maxillary antra. Almost 2/3 (66%) of the patients showed major (> 4 mm) mucosal thickening mostly at the level of the sinus floor. The present sample did not allow revealing any significant difference (P > 0.05) in maxillary sinus dimensions for partially dentate and edentulous subjects.
Cross-sectional imaging can be used in order to obtain more accurate information on the morphology, variation, and the amount of maxillary bone adjacent to the maxillary sinus.
The use of oral implants for the treatment of partially as well as totally edentulous
patients has increased incredibly. Nowadays more imaging techniques have become
available for the preoperative planning of oral implant surgery, each with their
own strength and weaknesses and specific indications [
In particular, placement of dental implants in the posterior maxilla can be jeopardized
by several factors. The predominant problem is undoubtedly the lack of bone quantity.
Considering that maxillary sinus floor elevation surgery may be indicated when dealing
with cases of insufficient bone below the maxillary sinus, a closer look to its
anatomical variations seems a necessity. It should be considered that the maxillary
sinus has a close relation to the roots of the maxillary molars and bicuspids. Normally
tooth apices and the maxillary floor are separated by cortical bone, but some teeth
(such as the first and second maxillary molar) are only separated from the maxillary
sinus floor by a thin mucosal layer [
Because of the intimate relationship between teeth and maxillary sinus, periapical
infections might result in reactive mucosal response within the sinus. Maxillary
sinus mucosal thickening is twice as common in patients with dental disease as in
the general population [
Although surgical interventions involving the maxillary sinus are increasing,
the presurgical planning continues using two-dimensional radiographs for maxillary
sinus visualization [
Maxillary sinus computed tomography (CT) data of 101 consecutive patients (edentulous and partially dentate) visiting the department of Periodontology, University Hospital, Catholic University of Leuven, Leuven, Belgium were assessed. While 30 patients (14 males, 16 females; aged 20 to 70 years; mean age = 53.8 years) were edentulous, 71 were partially edentulous (36 males, 35 females; aged 22 to 80 years; mean age = 52.8 years). They all gave informed consent to undergo maxillary spiral CT scans as part of the clinical procedure for preoperative planning of implant placement in the maxilla.
Spiral CT was carried out by Somaton Plus R CT scanner (Siemens, Erlangen, Germany) at 120 kV, 165 mAs, 500 µm reconstructed voxel size at the Department of Radiology University Hospital Catholic University of Leuven, Leuven, Belgium. The axial plan was positioned parallel to the hard palate of the maxilla. For the computer-assisted navigation system, a dual scanning procedure was used to allow the prosthetic model to be visualized together with the jaw bone reconstruction. The latter included a scanning of the patient with the scan prosthesis and some radio-opaque markers included, followed by another scanning of the prosthesis only. This set-up allowed identification of the respective edentulous sites with standardized linear measurements of the bone height at the level of each tooth site.
Below is an overview of the measurement of the patient's spiral CT scans employed for exploration of the maxillary sinus anatomy, its variation and volume.
1. The minimum and maximum alveolar bone height was measured on cross-sectional
images between alveolar crest and maxillary sinus floor (
Cross-sectional image showing measurement of the alveolar bone height below the sinus at the level of the respective (prosthetic) tooth: the distance between the floor of the maxillary sinus (A) and the alveolar crest (B) was considered to be the alveolar bone height below the maxillary sinus floor.
2. The size of the maxillary sinus according to anteroposterior (AP) and mediolateral
(ML) diameters of the sinus was measured (
Serial axial slice showing measurement of the maxillary sinus dimensions: anteroposterior (AP) and mediolateral (ML) measures were performed at 5, 10, 15 and 20 mm above the most apical level of the maxillary sinus floor.
3. Mucosal thickening of the maxillary sinus was defined as the existence of soft tissue structures thickness > 4 mm.
All measures were done using an accurate measuring tool (with an accuracy to the nearest = 0.1 mm) in the viewing software, by using a diagnostic screen (SGI, Fremont, CA, USA). Measures were performed by two observers D.X. and R.J. (1 oral surgeon and 1 dentomaxillofacial radiologist), and 10% of the measures was repeated to determine the intra- and inter-subject variability. The latter yielded a non-significant variability, with a coefficient of variation below 4% for both intra- and inter-observer measurements.
The maxillary sinus was also assessed morphologically, by determining the anterior and posterior extends of the maxillary sinus, in relation to the respective teeth or estimated tooth sites, in case of edentulism. This morphological rating was done on axial, sagital and panoramic slices. At the same time the occurrence of sinus septa was noted on axial and sagital slices. This morphological assessment allowed a general scoring on sinus morphology and the occurrence of any asymmetry (which was also confirmed dimensionally, see previous paragraph).
Morphologic measures were done by the same observers (D.X., R.J.) using the same viewing software and the same diagnostic screen (SGI, Fremont, CA, USA).
Above mentioned data were pooled and averaged for further analysis. Descriptive variables included dental status, the number of septa in the maxillary sinus, the respective location and morphologic variation of the sinus. Statistical analysis was performed using the statistical package of NCSS 2000 (Kaysville, Utah, USA). Data were tested for normality which yielded a skewed data set necessitating non-parametric analysis. Descriptive statistics were used for all linear measurements. Afterwards, Wilcoxon matched pairs test was applied for non-parametric analysis. The Pearson rank correlation was used to test the correlation between age and alveolar bone height. Differences were considered as statistically significant when P-values were less than 0.05.
The outcome of the linear bone measurement in edentulous and partially dentate
patients is shown in
Minimum alveolar bony heighta in edentulous and partially dentate patient as measured in parallel to respective (prosthetic) tooth axis
Groups | Statistics | Tooth position and value of minimum bony height | |||||
---|---|---|---|---|---|---|---|
15 | 16 | 17 | 25 | 26 | 27 | ||
9.2 (4) | 7.3 (4.6) | 6.7 (4.3) | 8 (5.3) | 4.9 (2.8) | 5.1 (3.5) | ||
5 - 16.7 | 1.1 - 17.9 | 1.1 - 14.5 | 2.2 - 20.5 | 1.3 - 9.0 | 1.1 - 11.7 | ||
14 | 15 | 13 | 13 | 15 | 15 | ||
9.5 (5.1) | 6.2 (3.5) | 5.7 (3.2) | 10 (5.1) | 6.3 (3.9) | 6 (3.3) | ||
2.6 - 22.4 | 1.3 - 12.1 | 1.1 - 12 | 2.3 - 18.2 | 1.4 - 12.5 | 1.3 - 12.4 | ||
32 | 31 | 27 | 27 | 28 | 26 | ||
|
0.95c | 0.57c | 0.57c | 0.17c | 0.31c | 0.40c |
aAlveolar bony height values in mm.
bTested between the dentate and edentulous patients dimensions.
cThe mean differences are not significant at 95% significance level.
SD = standard deviation.
Maximum alveolar bony heighta in edentulous and partially dentate patient as measured in parallel to respective (prosthetic) tooth axis
Groups | Statistics | Tooth position and value of maximum bony height | |||||
---|---|---|---|---|---|---|---|
15 | 16 | 17 | 25 | 26 | 27 | ||
12.2 (3.8) | 10.4 (4.9) | 9.7 (4.8) | 11.8 (4.4) | 8.8 (4.6) | 8.6 (4.4) | ||
8.2 - 19.6 | 3.2 - 21.2 | 1.3 - 16.9 | 5.8 - 20.9 | 3 - 17.9 | 1.9 - 16.1 | ||
14 | 15 | 13 | 13 | 15 | 15 | ||
13.0 (4.6) | 10.2 (4.6) | 8.2 (3.4) | 13.9 (4.8) | 10.3 (4.7) | 8.6 (3.5) | ||
4.9 - 21.5 | 2.6 - 22.7 | 2.9 - 14.9 | 5 - 20.2 | 2.7 - 19.4 | 2.8 - 14.7 | ||
32 | 31 | 27 | 27 | 28 | 26 | ||
0.51c | 0.98c | 0.29c | 0.18c | 0.31c | 0.86c |
aAlveolar bony height values in mm.
bTested between the dentate and edentulous patients dimensions.
cThe mean differences are not significant at 95% significance level.
In order to describe the size of the maxillary sinus, AP (length) and ML (width)
dimensions were determined and the mean values in partially dentate and edentulous
patients are shown in
Anteroposterior (AP) and mediolateral (ML) dimensionsa of the sinus in partially dentate and edentulous patient in right and left side
Sinus | Dentate patients
(n = 71) | Edentulous patients
(n = 30) | Pb value | ||
---|---|---|---|---|---|
AP dimension | ML dimension | AP dimension | ML dimension | ||
37.4 (4.7) | 24.8 (4.6) | 38 (5.2) | 25.5 (5.2) | 0.49c | |
37 (5.2) | 25.1 (5.3) | 36.8 (5.9) | 23.5 (5.1) | 0.77c |
aAnteroposterior and mediolateral dimensions expressed as mean values (standard deviation) in mm.
bTested between the dentate and edentulous patients dimensions.
cThe mean differences are not significant at 95% significance level.
The data also showed that almost 2/3 of patients (66%) showed major (> 4 mm) mucosal thickening, mostly located on the maxillary sinus floor, with a complete absence of swelling only found in 11% of the cases. Furthermore, 11 cases of mucosal retention cysts in the left (n = 5) and right (n = 6) side of the maxillary sinus were observed.
According to the present study, the anterior borders of the maxillary sinus were
located mostly at the level of the premolar region with first premolar being 44.7%
and 52.6% for right and left sides respectively. Meanwhile 78.8% right sinus and
89.5% left sinus extended distally to the second molar region (
Patient left and right maxillary sinus anterior and posterior border location in accordance to the tooth position
Borders | Maxillary teeth | Maxillary Sinus | ||
---|---|---|---|---|
Right (n [%]) | Left (n [%]) | Pooled (n [%]) | ||
Canine | 3 (7.9) | 2 (5.3) | 5 (6.6) | |
First premolar | 17 (44.7) | 20 (52.6) | 37 (48.7) | |
Second premolar | 16 (42.1) | 12 (31.6) | 28 (36.9) | |
First molar | 2 (5.3) | 4 (10.5) | 6 (7.8) | |
Second premolar | 1 (2.6) | 0 (0) | 1 (1.3) | |
First molar | 3 (7.9) | 2 (5.3) | 5 (6.6) | |
Second molar | 30 (78.8) | 34 (89.5) | 64 (84.2) | |
Third molar | 4 (10.5) | 2 (5.3) | 6 (7.9) |
The shape and size of the maxillary sinus could alter throughout the life. In this study half of the patients (50%) showed a somewhat symmetric morphology. One third (33%) of the patients had some differences at several levels while the remaining patients (17%) showed a predominant asymmetric morphology.
The prevalence of one or more septa in overall study population was 47%. No correlation
was found between the number of septa and the sinus morphology. However, the statistical
analysis between the number of the septum and AP dimension showed that the AP dimension
was smaller in patients without septum as compared to patients with various sinus
septa, but only in left side (P = 0.04)(
Anteroposterior (AP)a dimension of the patients' left and right sinus depending on sinus septa presence
Sinus | N | Sinus without septum | N | Sinus with septa | Pb value |
---|---|---|---|---|---|
56 | 36.9 (5) | 42 | 38.6 (4.5) | 0.21c | |
50 | 35.8 (6.1) | 48 | 37.9 (3.8) | 0.04d |
aAnteroposterior dimension expressed as mean values (standard deviation) in mm.
bTested between AP dimensions of maxillary sinus with and without septa.
cThe mean differences are not significant at 95% significance level.
dThe mean differences are significant at 95% significance level.
Results of the present study demonstrated a considerable difference in mean values of the alveolar bone height for the two groups of patients (edentulous and partially dentate). Extreme differences were observed when contrasting the first molar region in edentulous patients (4.9 [SD 2.8] mm; range 1.3 - 9 mm) to the second premolar region in dentate subjects (13.9 [SD 4.8] mm; range 5 - 20.2 mm). It is striking that after tooth extraction such a drastic difference can exist between posterior maxillae with and without teeth (on average 9 mm difference). Thus placement of dental implants in these patients requires preprosthetic surgical procedures such as alveolar ridge or sinus floor augmentation with bone grafting.
Although there is a wide range of maxillary sinus dimensions in different studies
that may reflect the influential effects like human variability and triggering of
pneumatisation [
Yet, it should be considered that linear measures, as used in the current study, do not fully reflect a three-dimensional volume of maxillary sinus.
It is obvious that the use of volumetric measures of the sinus may be more precise and could thus reveal distinct results. Further studies are needed to study the behaviour of the maxillary sinus in conjunction to tooth extraction, implant placement and sinus grafting procedures. In such future studies, the current problem of an unequal sample size (30 edentulous, 71 dentate) should also be dealt with.
Significant mucosal thickening was observed in 66% of the study group and is
presumably related to periapical or periodontal diseases. Others also found that
the presence of restorative dentistry and periapical infection can result in focal
mucosal thickening in the floor of the maxillary sinus [
The extension of the maxillary sinus is variable in the population. In the present
study the anterior border was in the premolar region and posterior border located
mostly in second molar region, but in some studies the posterior border of the maxillary
sinus in third molar and tuberosity area was reported [
In 83% of patients a symmetric morphology or small differences at some levels
in maxillary sinus was shown, while the remaining patients (17%) showed a predominant
asymmetric morphology. There is not much data concerning the asymmetry of the maxillary
sinus. Some studies considered neighbouring cartilages or bony structures as an
influencing factor in shape and enlargement of the paranasal sinuses [
Mucosal retention cysts in the sinus are mostly found by accident as clinical
signs and symptoms are limited and majority of these cysts have spontaneous regression
[
The presence of anatomic variations within the maxillary sinus, such as septa,
can increase the risk of sinus membrane perforation during sinus elevation procedures
[
The incidence of antral septa varies from 16% to 69% in different studies [
It seems obvious that there are lots of variations in the maxillary sinus anatomy
and a three-dimensional imaging yields much more information than plain film. In
this respect, CT is a valuable imaging modality for three-dimensional evaluations
of the anatomical structures but its major drawback remains the inherent costs and
the radiation concern. Current low dose CT protocols may however enable low dose
imaging of the paranasal sinuses [
In the present study, higher mean values in alveolar bone height were observed in the premolar region, while more bone loss occurred in older individuals. Anterior and posterior border of the maxillary sinus were located in the first premolar and second molar respectively. Most of the patients (83%) showed symmetric or small differences sinus morphology in both sides, while almost half of the subjects showed sinus septa. Mucosal thickening was seen in 2/3 (66%) of the patients mostly in the sinus floor.
We would like to acknowledge the immense amount of work put into the initial project by Professor Johan van Cleynenbreugel, Oral Imaging center, Faculty of Medicine, Catholic University of Leuven, Leuven, Belgium, who passed away during the course of this research.
The authors declare that they have no conflict of interest.