Odontogenic maxillary sinus disease: a cone-beam computed tomography surveillance.

The maxillary sinus is vulnerable to microbial infection spread via dental pathology. It is well documented that upper bicuspids and molars with necrotic pulp may promote the direct extension of the endodontic infection into the maxillary sinus [ 1 , 2 , 3 , 4 ]. A five class classification of the vertical relationship (Type I to Type V) and a three class classification of the horizontal relationship (Type 1 to Type 3) between the roots’ apices of maxillary molars and the sinus floor were described based on anatomical close vicinity [ 5 ]. Commonly, during the evolution of chronic apical periodontitis occurs a bone resorption circumscribing the root apex, which allows the imagistic identification of the lesion on radiographs [ 6 , 7 , 8 ]. When root apex is situated in the immediate anatomical proximity of the maxillary sinus floor the progressive bony destruction initiated by chronic apical periodontitis involves the antral cortical bone and result in an additional alteration of the Schneiderian membrane [ 9 , 10 , 11 ]. The spread of endodontic infection into the maxillary sinus, which is directly related to the distance between root apices and sinus floor, was termed endo-antral syndrome (EAS) [ 2 , 12 , 13 , 14 ]. However, in developing an odontogenic maxillary sinus disease may be involved some other sources of dental infections such as inadequate root canal treatments, marginal leakage of faulty restorations, periodontal bone loss, vertical root fractures, sinus perforation or root tips forced into the sinus following the tooth extraction, bone grafts for root form implants as well as endodontic surgical procedures [ 15 , 16 , 17 , 18 ]. The reported frequency of EAS fluctuates to a large extent among all maxillary sinusitis ranging commonly between 4.6% and 47%. The highest value recently mentioned for dental etiology of maxillary sinusitis was even 80% [ 2 , 19 , 20 ]. However, the hyperplasia of sinus mucosa, which is the main radiographic sign of sinusitis, arrives at 10.6% to 12.3% [ 21 ]. Cone-beam computed tomography (CBCT) scanning proved to be a reference diagnostic aid for detecting the etiological relationship between odontogenic infections, mainly chronic apical periodontitis, and maxillary sinusitis [ 22 , 23 , 24 ]. Moreover, this imagistic method provides extremely valuable data concerning the maxillary sinus abnormalities and mucosal changes associated with periapical inflammation of upper molars and premolars that are anatomically situated in the proximity of the sinus floor [ 25 , 26 , 27 , 28 ]. The aim of this CBCT study was to find out in case of chronic apical periodontitis the influence of distance between closely positioned root apices and sinus floor on subsequent mucosal changes typical to EAS.

The frequency of maxillary sinusitis according to sex (Figure 1 ) shows, according to the χ2 (chi-squared) test (p<0.05), a statistically significant difference (Table 1 ). Distribution of patients according to sex Frequency of maxillary sinusitis according to sex Sex Normal sinus [%] Sinusitis [%] p Males 15 85 0.01 Females 37 63 The age of patients has a median of 42 years. The most frequent affected patients belonged to the age range between 31–50 years (66%), recording a maximum value (34%) for the group between 41–50 years (Figure 2 ). According to the Mann–Whitney test, the difference between normal and inflammatory affected sinuses is not statistically significant (p=0.734). Distribution of patients according to age According to Fisher’s exact test, there was no statistically significant difference between pulp necrosis and chronic apical periodontitis concerning the odontogenic etiology of maxillary sinusitis (Table 2 ). Pulp diagnosis Normal sinus [%] Sinusitis [%] p Chronic apical periodontitis 27 73 >0.999 Pulp necrosis 33 67 Out of 109 upper teeth involved in EAS, the highest number of teeth was recorded in second molars (35). It followed in descendent order first molars (60), second premolars (9), and first premolars (5) (Figure 3 ). Upper teeth that induced endo-antral syndrome: M1 (first molar), M2 (second molar), P1 (first premolar), P2 (second premolar) According to Fisher–Freeman–Halton exact test, no statistically significant difference (p=0.320) was found between anatomical type of teeth and maxillary sinusitis (Table 3 ). Frequency of maxillary sinusitis according to anatomical type of upper teeth Upper teeth Normal sinus [%] Sinusitis [%] p First premolar 60 40 0.320 Second premolar 33 67 First molar 29 71 Second molar 27.5 72.5 Healthy/diseased status of maxillary sinus related to anatomical location of chronic apical periodontitis vs sinus floor Subsequent relationship of chronic apical lesions location to the sinus status of health showed increasing percentage of sinusitis depending on the anatomical distance to the sinus floor. The maximum incidence of sinusitis was recorded in chronic apical inflammatory lesions having a protruding contact with sinus mucosa (Figure 4 ). Excepting the protruding contact of chronic apical periodontitis with sinus floor (p=0.01), according to Fisher–Freeman–Halton exact test, other etiological relationships between location of apical lesions and maxillary sinusitis are not statistically significant (Table 4 ). Frequency of maxillary sinusitis depending on distance between apical lesion and sinus floor Distance Normal sinus [%] Sinusitis [%] p >2 mm 69 31 0.01 1–2 mm 25 75 Tangent contact 26 74 Protruding contact 0 100 In molars, the highest frequency was recorded for tangent contact (66%), equally followed by the group with protruding contact (14%) and the teeth situated at over 2 mm distance (14%). The last group (9%) represented molars situated at 1–2 mm distance (Figure 5 ). In premolars, the highest frequency was noticed when the apical lesions were in tangent contact (58%) with sinus floor, equally followed by lesions situated at over 2 mm distance (21%) and 1–2 mm distance (21%). The protruding contact in premolars was absent (Figure 6 ). Anatomical location of chronic apical lesions related to the sinus floor in upper molars Anatomical location of chronic apical lesions related to the sinus floor in upper premolars Commonly, the chronic apical lesions of posterior upper teeth are the outcome of untreated necrotic root canals or poor previous endodontic treatment (Figure 7A ). However, undetected fissures in the wall of pulp chamber that are extending in the root (Figure 7B ) or complex endodontic system of second upper premolars may also be contributory factors (Figure 7C ). The abnormalities revealed on CBCT scans in our survey were described as mucosal hyperplasia (Figure 7D , 7E ), dome-shaped opacification (Figure 2 ), periostitis (Figure 9E , 9F , 9H and 9I ), and sinus opacification with air-bubbles (Figure 10C , 10D ). The mucosal thickening of the maxillary sinus is not mandatory depending on the anatomical distance separating the root tips from sinus floor. However, the lesion definitely is more severe if the root tip overlaps the sinus floor, as in case of palatal root of upper first molar, compared to second premolar where is observed a gap between the sinus floor and the periapical lesion (Figure 7D , 7E ). The dome-shaped radiopacity in the maxillary sinus situated above the poorly treated or even untreated roots of upper posterior teeth (Figure 8D , 8F ) may be associated with a general thickening of sinus mucosa (Figure 8C ). When an extended chronic apical lesion situated in direct contact with sinus floor progresses lengthy in maxillary sinus, periosteal reactions and radiopaque structures caused by osteogenesis may be observed (Figure 9E , 9H ). Usually, mucosal thickening and dome-shaped radiopacity are also associated (Figure 9I ). Periosteal reactions in EAS can occur despite the correct conventional radiographic images of root fillings (Figure 9A ) or working length measurements (Figure 9B ). Internal root resorption might be a challenging factor (Figure 9B , 9C ). Additional frequent etiologies of periosteal reactions are undisclosed periradicular lesions (Figure 9D ) and missed root canals (Figure 9G ). Sometimes the maxillary sinusitis induced by chronic apical lesions is observed as an extended opacification of the involved sinus and air bubbles, which suggests the presence of a fluid (Figure 10C ). The common cause may be failed endodontic treatment (Figure 10A ), or a furcation lesion identified only by CBCT (Figure 10B ). However, various features of sinus pathology such as the high thickening of mucosa and dome-shaped opacifications may be also present (Figure 10D ). Mucosal hyperplasia of the maxillary sinus: (A) Periapical radiography of upper right premolars and molars showing poor previous endodontic treatment and apical radiolucency in the second premolar (tooth 15); in the first molar (tooth 16) is observed a discrete widening of periodontal ligament around the tip of palatal root; in tooth 15 is observed a distinct distance between the root tip and the sinus floor compared to tooth 16, which palatal root tip overlaps the sinus floor; (B) Operatory microscope image disclosing at first molar (tooth 16), after the access cavity preparation, a distinct fissure in the distal wall of pulp chamber suggesting that it is extended in the root; (C) CBCT axial view showing that the already treated upper right second premolar has two root canals; (D) CBCT sagittal view showing that the periapical lesion overlaps the maxillary sinus floor and is associated with mucosal thickening; (E) CBCT coronal view showing the direct contact of periapical lesion associated to palatal root of tooth 16 and the generalized thickening of maxillary sinus mucosa; a complex bone resorption affecting the sinus floor is also extending around the apical third of the palatal root. CBCT: Cone-beam computed tomography Dome-shaped radiopacity: (A) Periapical radiography of upper right last two molars showing both an inappropriate endodontic treatment in tooth 17 associated with localized hypodense image of maxillary sinus and the roots tips of vital healthy tooth 18 which are extending inside the sinus; (B) CBCT image showing in axial plane a dome-shaped radiopacity in maxillary sinus corresponding to the tooth 17; (C) CBCT image in sagittal plane showing the dome-shaped radiopacity in maxillary sinus corresponding to the tooth 17 associated with generalized mucosal thickening; the root tip of tooth 18 is extending inside the sinus; (D) Coronal view of CBCT showing the dome-shaped radiopacity and tooth 17; (E) Axial view of upper right last molars (teeth 17, 18) disclosing no endodontic fillings in both mesio-buccal root canals (MB1 and MB2) of the second molar (tooth 17); the palatal canal is also unobturated; (F) CBCT image in sagittal plane; the mesio-buccal and disto-buccal root tips of the upper right second molar (tooth 17) touches the sinus floor; a dome-shaped radiopacity in maxillary sinus is situated above the poorly treated disto-buccal and untreated mesio-buccal roots of the tooth 17. Periosteal reactions in endo-antral syndrome: (A) Preoperative radiography of upper right first premolar (tooth 14) showing a chronic apical periodontitis despite the conventional apical limit of previous fillings in both root canals; the first molar (tooth 16) also presents a chronic apical lesion of the mesio-buccal root; (B) Periapical radiography confirming the roots length measurement in upper right first molar (tooth 16); an internal resorption is also evidenced in the mesio-buccal root; (C) Postoperative control radiography of upper right first molar (tooth 16); (D) CBCT axial view of upper right lateral teeth disclosing the periradicular lesions in first molar (tooth 16) and first premolar (tooth 14); (E) CBCT sagittal view of upper right lateral teeth confirming the chronic periradicular lesions revealed on preoperative periapical radiography; the extended apical lesions in the first molar (tooth 16) are in direct contact with sinus floor; a periosteal reaction and radiopaque structures due to osteogenesis are observed in maxillary sinus; (F) CBCT coronal view of upper right first premolar relieves an extended chronic apical lesion and poor previous root canal treatment; though there is a distinct distance between the lesion and the sinus floor, periosteal and mucosal reactions in maxillary sinus are beyond doubt present; (G) CBCT axial view of upper right lateral showing the poor endodontic treatment in first premolar (tooth 14); (H) CBCT sagittal view of upper right lateral teeth showing the chronic apical lesions and the subsequent changes induced in maxillary sinus: periosteal reaction associated with osteogenesis and thickening of sinus mucosa; (I) CBCT coronal view of upper right first premolar various pathological changes in maxillary sinus such as a dome-shaped hypodense structure, periosteal osteogenic reactions, and thickening of sinus mucosa Maxillary sinus opacification with air-bubbles: (A) Periapical radiography of upper left last two molars (teeth 26 and 27) with previous root canal fillings; periradicular bony rarefaction observed in tooth 27 is the consequence of failed root canal obturations, short to the apex; moreover, in tooth 27, a canal transportation was generated in mesio-buccal root; (B) CBCT image in axial plane showing the unfilled apical third in buccal roots of tooth 26, as well as a bony rarefaction in the furcation area; (C) CBCT view in coronal plane showing a global opacification of the left maxillary sinus suggesting the presence of fluid as well as air bubbles; the palatal root is situated closer to sinus floor compared to buccal roots; the image resembles maxillary sinusitis; (D) CBCT view in sagittal plane showing various features of pathology: a highly thickened mucosa, dome-shaped opacifications and air bubbles compatible to sinusitis

The EAS relies on pulpal and sinusal changes. The dental signs of a tooth that approximates the sinus floor are loss of vitality, periapical radiolucency, and the resorption of lamina dura that radiological separates the alveolus from sinus [ 2 ]. There were observed in our study four categories of anatomical rapports between chronic apical lesions and maxillary sinus floor, such as tangent contact, protruding contact, 1–2 mm separating interval, and over 2 mm separating interval. Commonly, the sinusal signs are a localized or generalized thickening of the sinus mucosa or varying degrees of sinus radiopacity, mainly dome-shaped. Other described abnormalities are antral pseudocyst, nonspecific opacification, periostitis and anthrolits [ 2 , 27 ]. The most frequent change of maxillary sinus radiographic image in chronic maxillary sinusitis is mucosal hyperplasia, which was reported to be associated to around 80% of chronic apical periodontitis [ 2 , 11 ]. If localized hyperplasia it is disclosed as a slightly radiopaque mass above the apex of the endodontically affected tooth, whereas in case of a generalized inflammatory reaction of the sinus mucosa is observed like a quite uniform radiopaque band covering the floor of the maxillary sinus [ 4 ]. In our study, the frequency of hyperplasia (63%) was higher than that of Estrela et al. (44%) and lower (8%) in partial obstruction (15.8%). Similar results of maximum values concerning sinus inflammatory pathology triggered by chronic apical periodontitis for 41–50 years group of age recorded in our study are also reported by Estrela et al. [ 29 ]. However, altogether in both partial and total obstruction exceeds the Estrela et al. findings (17%) [ 30 ]. Occasionally, directly above an upper posterior tooth with chronic apical periodontitis may be seen a localized thickening of the sinus mucosa that appears as a dome-like radiopaque image [ 31 ]. Usually, this mucosal change is symptom-less and restores to health after a thorough orthograde root canal treatment of the chronic apical periodontitis [ 4 ]. The mucosal thickening may be flat (less than 5 mm) or polypoidal (higher than 10 mm) [ 11 ]. However, presently there is no consensus regarding the thickness of mucosa in order to be classified as mucosal thickening, so that the reported cutoff values are between 2 mm and 6 mm [ 26 ]. According to Lu et al., the mucosal thickening can be mild (2–4 mm), moderate (4–10 mm) or severe (over 10 mm) [ 9 ]. In a study was found that various degrees of mucosal thickening with a mean value of 2.78 mm were present in 46.2% of maxillary sinuses [ 9 ]. When a bone interval separated the periapical lesion from sinus floor, the prevalence of mucosal thickening was 77.3%. The expected increase of mucosal thickening prevalence when periapical lesions touched or entered the sinus floor accounted for at least 80% [ 9 ]. At times, in chronic apical periodontitis may be observed small prominences of the sinus floor, when the root apices of offending teeth projects into the sinus. These chronic apical lesions may displace the periosteum of the maxillary sinus floor stimulating bone deposition in its inner border by reactional osteogenesis and expanding it as a hyperdense imagistic halo, sometimes dome-shaped though anatomically the chronic inflammatory tissue does not penetrate the sinus cavity [ 4 , 19 , 30 ]. However, this slight dislocation triggers a periosteal response resulting in a deposition of a thin layer of newly produced bone. On radiographs may be observed both this periapical osteoperiostitis and its possible resolution after a proper root canal treatment of the affected tooth [ 4 ]. Though the etiological association between chronic apical periodontitis and sinus pathology was for the first time signalized at the beginning of 40’s, the EAS was properly described merely some decades later [ 2 , 12 ]. Conventionally, in dental office, the assessment of a possible EAS was basically accomplished by using mainly two modalities of imaging examination as periapical and panoramic radiographs. Nevertheless, according to literature, over recent years the CBCT gradually became the “gold standard” tool of diagnosis in endodontics, treatment planning and follow-up. CBCT scanning is much more accurate than former radiographic diagnosis tools, avoiding ambiguous image interpretations and insufficient information about important details of periradicular and sinus floor area [ 2 , 4 , 11 , 15 , 25 , 26 , 27 , 32 ]. Despite the advantages of CBCT imaging, the periapical and panoramic radiographs are still extremely useful since they at first may signalize both anatomical and pathological features of the maxillary sinus [ 2 , 4 ]. On properly angled periapical radiographs, the thin layer of cortical bone, which corresponds to the benchmark of sinus floor, normally appears as a slight radiopaque line, highlighting the anatomic relationship between the sinusal cavity and the root apices of upper premolars and molars. Actually, this thin bone layer is the radiographic fusion of the sinus floor and the lamina dura of corresponding tooth alveolus [ 2 ]. The periapical radiographs are also helpful in disclosing the presence of chronic apical periodontitis and their various locations related to the sinus floor, since a chronic apical lesion may be situated at distinct distance, may touch or even overlap the inferior border of maxillary sinus [ 2 , 4 ]. The panoramic radiographs show bilaterally an overview of the anatomic relationship between the upper posterior teeth and the floor of maxillary sinus. The presence, location, size, and type of the periapical and sinus pathology are also displayed [ 2 , 4 ]. Some years ago, a useful means of diagnosis was also computed tomography (CT) but presently was replaced with CBCT since, despite the high sensitivity, its specificity was rather low [ 4 ]. However, it is worthy to remind that both CT and CBCT provide a qualitative apparent similar visualization of maxillary sinus. However, CT gives a higher radiographic contrast and additional information on soft tissue [ 25 ]. It was revealed that though CBCT is accurate in diagnosing chronic periapical lesions because it has a high sensitivity (approaching 1), on the other hand its specificity is relatively low (0.73). Accordingly, it results in a significant risk for false positive diagnostics [ 33 ]. However, while assessing the diagnostic value of CBCT images with periapical radiographs it was found that the sensitivity of CBCT was higher, but the specificity was similar [ 32 ]. By using CT and particularly CBCT scanning, presently may be observed 30% more chronic apical periodontitis and four times more sinus mucosa thickening than in periapical radiographs [ 19 ]. Moreover, it has to be highlighted that the current limited CBCT systems are better suited for endodontic field since offer higher image resolution and more details [ 9 ]. Introduced in 1998, CBCT, the more recent 3D imaging modality, has an improved clinical value since provides a higher resolution and a shorter scanning time [ 9 , 25 ]. The present CBCT scanners have a spatial resolution of isotropic voxel size that extends between 0.08 and 0.4 mm, providing a comprehensive and detailed radiographic image of anatomical structures [ 25 ]. Moreover, the effective dose of radiation, as high as 40 to 50 μS, places this 3D technology in a range similar to that of conventional 2D periapical radiographs [ 23 ]. In the case of the CBCT scan, it is mandatory that the potential diagnostic benefit outweighs the risk of ionizing radiation. Accordingly, smaller size FoV CBCT scans are highly recommended since their use complies with both radiological principles of as low as reasonably achievable (ALARA) and as low as reasonably practicable (ALARP) [ 10 , 32 ]. Though CBCT images proved in case of upper posterior teeth to accurately reproduce both the anatomical relationship of their apices with the floor of maxillary sinus and the subsequent mucosal changes induced by chronic apical periodontitis, some papers question if the higher-voxel resolution of the FoV CBCT scans provide a better radiographic image of sinus mucosal changes compared to the full-field CBCT scans [ 34 ]. The voxel size resolution of CBCT scanner used in our study (0.125 mm) provided a sufficient detailed image that allowed to accurately describe several radiographic changes, such as mucosal hyperplasia, dome-shaped opacification, compact sinusitis, periostitis, and sinus opacification with air-bubbles. Based on these findings, in case of EAS we consider that a top quality CBCT image can also reveal the real anatomical relationship of upper molars and premolars with sinus floor. Accordingly, we suggest four classifications of maxillary sinusitis induced by chronic apical periodontitis related to the distance between the apical lesion and sinus floor, as follows: Class 1 (tangent contact), Class 2 (protruding contact), Class 3 (1–2 mm interval), and Class 4 (over 2 mm interval). In order to avoid a misdiagnosis though CBCT scan proved to be a powerful tool in visualizing the chronic periapical lesions, it seems that a special caution has to be taken while interpreting CBCT images for healthy periapical tissues. The reason is the surprisingly significant variations of the periodontal ligament space width in vital teeth as the CBCT examination found its increased dimension ranging between 0–1 mm [ 33 ]. Moreover, by using both periapical index (PAI) [ 30 ] and CBCT–PAI indexes [ 32 ], while analyzing the 3D images provided by a small FoV and high resolution (0.08 mm voxel) CBCT scan, it was found that in 72% of teeth with healthy pulp status CBCT–PAI score was higher than PAI score [ 33 ]. Therefore, if in teeth with necrotic pulp the widening of periodontal ligament space greater than 1–2 mm is considered a normal emergence, in case of vital teeth any widening might question the value of conventional radiographic reading in differentiating a vital from a non-vital tooth [ 33 ]. Though the literature reports showed that odontogenic maxillary sinus disease account for only 10% to 12–15% of all cases of maxillary sinusitis, it has to be highlighted that the various clinical and radiological features of this condition may raise diagnostic difficulties and postpone the adequate treatment [ 9 , 18 , 21 , 35 ]. The clinical practice also proved that the sinus mucosal inflammatory changes induced by chronic apical periodontitis though initially asymptomatic if persistent may increase the local inflammation and predispose to airborne infections [ 19 ]. According to a systematic review and meta-analysis of maxillary sinusitis evaluating CBCT images, about 50% of this condition is of odontogenic etiology, namely chronic apical lesions or chronic marginal periodontitis [ 36 ]. Therefore, in maxillary sinusitis sometimes are possible concurrently symptoms produced by both etiologies, dental and otorhinolaryngological, so that the undiagnosed patients are commonly shuttled between dentist and otorhinolaryngologist. Differential diagnosis is hard to be performed only on clinical bases and the imagistic examination is crucial despite the mandatory careful examination of upper posterior teeth [ 1 , 19 ]. Moreover, considering a maxillary rhinosinusitis as an alternative cause of patient’s complaints while running the differential diagnosis, an iatrogenic attitude might be avoided since the root canal treatment of respective teeth is definitely unnecessary [ 18 ]. Even asymptomatic both the initial outcome of chronic apical periodontitis, the periapical mucositis expressed on CBCT by mucosa thickening or its dome-shaped enlargement and the osteoperiostitis restricted to sinus floor, require the root canal treatment of causal tooth in order to avoid their future progress to partial or total obstruction of the maxillary sinus [ 19 ]. Nevertheless, in EAS the healing of maxillary sinus may occur if the root canals of the affected tooth are successfully treated by conservative management. In view of the proper clinical approach, a detailed assessment of the sinus pathological status prior to endodontic treatment is highly recommended. Considering this base line at the onset of root canal cleaning and shaping, the practitioner may run an efficient follow-up of the clinical success or failure [ 13 ]. Healing is also achieved in case of refractory response to routine root canal treatment if the tooth is removed by extraction [ 2 , 4 , 12 , 34 , 35 , 37 ]. As a rule, in dental practice any radiographic examination should not be accomplished before the clinical examination. A yearly imagistic postoperative control in chronic apical periodontitis, at least during the first five years, is recommended to be done by conventional periapical radiographs.

The odontogenic maxillary sinus disease, also known as EAS, is directly related to the spread of endodontic infections from upper bicuspids and molars with necrotic pulp. CBCT imaging proved to be a reference diagnostic aid for detecting the etiological relationship between odontogenic infections and maxillary sinusitis. The abnormalities revealed on CBCT scans of maxillary sinus in our survey have been mucosal hyperplasia, dome-shaped opacification, periostitis, and sinus opacification with air-bubbles. A four class classification related to the anatomical distance between the chronic apical lesions and sinus floor, such as protruding contact, tangent contact, 1–2 mm separating interval, and over 2 mm separating interval it was suggested.

The authors deny any conflict of interests related to this study.

There were retrospectively evaluated a total of 109 CBCT images (47 men and 62 women, mean age 42 years, range 17–73 years) from a pool of CBCT scans taken for routine diagnosis and treatment planning in consecutive 353 patients. Intraoral and extraoral clinical examinations were performed, including vitality pulp test, axial tooth percussion test and recording of sinus tracts. In all patients, the medical histories were noncontributory. The CBCT images were acquired with Veraviewepocs three-dimensional (3D) P (R100) equipment (J. Morita MFG Corp., Kyoto, Japan). The scan parameters were 90 kV, 5 mA, 9.4 s exposure time, 125 μm spatial resolution and 40×40 mm field of view (FoV). All images were two-dimensional (2D) visualized in sagittal, axial and coronal sections. The study was carried out in total agreement with the World Medical Association (WMA) Declaration of Helsinki. Informed consent of the patients was obtained. The random selection of CBCT scan followed as inclusion criteria the good quality of radiographic images, the presence of sinus pathology, and fully erupted upper first and second molars and first and second premolars. There were excluded the cases with insufficient FoV, bone abnormalities, traumatic lesions or tumors of the maxilla and the oroantral fistulas as well. The CBCT scans examination was performed by an experienced radiologist. Mucosal thickening was taken into consideration when its width was greater than 1–2 mm as in previous studies [ 9 , 11 , 15 ].