OF THE SPECIFIC RADIOGRAPHIC AT PANORAMIC RADIOGRAPHY INDICATING POSSIBLE CLOSE RELATIONSHIP OF POSTERIOR TEETH AND SURROUNDING ANATOMICAL STRUCTURES: A CBCT STUDY

Background / Aim. In the planning of posterior teeth extraction it is necessary to determine their position and correlation with the surrounding anatomical structures. The aim of this study was to perform CBCT analysis in order to evaluate predictive value of specific OPT radiographic signs in determining the proximity of posterior upper teeth to the maxillary sinus and lower teeth to mandibular canal. Methods. In a prospective study, 460 cases out of 423 patients were analyzed. Seven OPT radiographic signs were assessed to determine the correlation of the third molars to the mandibular canal, while five radiographic signs were followed to determine the correlation of the maxillary sinus floor to the upper posterior teeth. For each OPT radiographic sign a precise analysis of the axial slices of the CBCT was performed . Results. Interruption of the white line is a radiographic sign showing statistically significant interruption of the integrity of the mandibular canal on the CBCT axial slices (p=0.002). Also, diversion of the inferior alveolar canal at the axial sections shows statistically significant interruption of the continuity of the mandibular canal (p=0.003). Radiographic sign darkening of the root showed superimposition of the anatomical structures, a close relationship with the tooth but often with preserved mandibular canal integrity ( p<0.001). Absence of lamina dura, interruption of the maxillary sinus floor's cortex and projection of the root apices in the sinus cavity are radiographic signs that were statistically the most commonly associated with interruption of maxillary sinus integrity on CBCT axial slices (p<0.001). Conclusion. The results of our study indicate that the presence of certain radiographic signs on the OPT may have predictive significance. The exact relationship between anatomical structures and posterior teeth cannot be accurately estimated on OPT. The precise position of the molars and correlation to the mandibular canal and the maxillary sinus can be accurately determined by CBCT imaging.


Introduction
In planning posterior teeth extraction, it is necessary to determine their exact position and relationship with the surrounding anatomical structures to prevent intraoperative and postoperative complications. 1,2 During preoperative preparation and planning of the extraction of the lower molars, it is essential to determine the exact position of the tooth and its relationship with the mandibular canal to avoid damaging the neurovascular contents of the mandibular canal. 3,4 The particular importance for the upper posterior teeth extraction is the position of the tooth root apices and their relation to the floor of the maxillary sinus. 5,6 The most commonly used radiographic method for analyzing the posterior teeth position and the relationship with mentioned anatomical structures is orthopantomography (OPT). 7,8 On OPT images, referring relationship of the posterior teeth to the surrounding anatomical structures for diagnosis, treatment plan, and preoperative preparation were analyzed. 9,10 Rood and Shehab recommended altogether seven radiographic signs with aim to determine correlation of the posterior tooth and the mandibular canal on the OPT. Four of them occur on the tooth (darkening of the root, deflected roots, narrowing of the root, dark and bifid root) and the other three on the canal (interruption of the white line(s), diversion of the inferior alveolar canal, narrowing of the inferior alveolar canal). 11 According to Luciana J Lopes et.al, for evaluating the relationship between the upper molars and the maxillary sinus floor, presence or absence of the following radiographic signs should be followed: Projection of the root apices in the sinus cavity, interruption of the maxillary sinus floor's cortex, lamina dura, darkening of the root apical region, upward curving of the sinus floor enveloping the tooth root partially or completely. 12 Cone Beam Computed Tomography (CBCT), has been widely used in dentistry in recent years due to lower radiation dose than the conventional computed tomography (CT). 13,14 However, higher radiation dose compared to OPT, additional costs and less availability were responsible that CBCT has not been introduced as a routine additional diagnostic method. 15,16 The aim of this study was to perform CBCT analysis in order to evaluate the predictive value of the specific OPT radiographic signs used in determining the proximity of posterior upper teeth to the maxillary sinus and lower teeth to the mandibular canal.

Methods
This prospective study was conducted at Department for Dentistry, Medical Faculty, University of Pristina -Kosovska Mitrovica, on the sample of 423 patients (460 cases analyzed). A criterion for including in the study was identified radiographic sign on OPT.
The patients identified with the radiographic sign on OPT were referred for CBCT imaging. The exclusion criteria from the study were relative or absolute contraindication for radiographic imaging, unclear images and the absence of mandibular canal on OPT or CBCT (plexiform canal). Written informed consent was obtained from all participants for their data to be used in the study.

Statistical data analysis
The proportions of radiographic signs between the classes were analyzed using the Chisquaree test. All p values less than 0.05 were considered significant. The Statistical Package for the Social Science Program (version 22, SPSS Inc., Chicago, IL, USA) was used in the statistical analysis.

Results
The total number of examined subjects was 460 cases with identified OPT radiographic sign. On 234 images (50.87%) the proximity of posterior teeth to the maxillary sinus was analyzed, and 226 radiographic images (49.13%) implied an analysis of the inferior alveolar nerve canal position in relation to mandibular molars.

Results of OPT and CBCT analysis of the relationship between the mandibular canal and the molar teeth
Taking into account the total number of analyzed images, 13.3% or 30 cases belong to the first and second class with subclasses (1a, 1b, 2a, 2b). The statistical analysis revealed that radiographic sign Darkening of the root was statistically significantly more frequent Radiographic sign Darkening of the root was confirmed in 52.4% cases in the Class 4a.
There was statistically significantly more frequency in the Class 4a, compared to the presence in other classes (p = 0.002). (Figure 4) In determining the bucco-mesial localization of the mandibular canal, the frequency of lingual localization of the mandibular canal was observed in 59 cases, while the occurrence of buccal-localization appeared in 50 cases. In 117 cases, the apical localization of the mandibular canal was observed.

The OPT and CBCT results analysis of the relationship between the roots of maxillary teeth and the maxillary sinus
The Darkening of the root apical region was confirmed in 71% of subjects in group with Type 1 finding on the CBCT. The darkening of the root apical region was statistically significantly more frequent in group with Type 1 findings on the CBCT compared to other findings on the CBCT (p=0.007).
Upward curvature of the sinus floor enveloping the tooth root partially or completely was confirmed in 39% of subjects in group with Type 2 finding on the CBCT. Upward sinus floor curvature partially or completely was statistically significantly more frequent in group with Type 2 findings on the CBCT compared to other types (p <0.001).

Interruption of the maxillary sinus floor's cortex was present in 15% of patients in a group
with Type 4 findings on the CBCT. Interruption of the maxillary sinus floor's cortex was statistically significantly more frequent in group with Type 4 findings on the CBCT compared to other types (p<0.001).
The presence of radiographic findings Absence of lamina dura was also diagnosed in 15% of patients in group with Type 4 finding on the CBCT and was significantly more common than other types (p<0.001).
Projection of root apices in the sinus cavity was confirmed in 66 (55%) cases in a group with Class 4 finding on the CBCT. Projection of root apices in the sinus cavity was statistically significantly more frequent in a group with Class 4 findings on the CBCT compared to other types (Table 3.)

Discussion
Several studies dealt with a relationship among different anatomical structures on OPT images have shown that a presence of certain radiographic indicators indicates a possibility of postoperative complications. 18,19 The use of radiographic signs during the analysis of two-dimensional OPT images may point out a close relationship between the mandibular canal and impacted third molars, According to the analogous clinical trials, assessing the importance of this radiographic sign, a frequent close relationship and direct contact between anatomical structures can be seen on radiograph images, as well as the appearance of clinical post-operative complications such as paraesthesia 20,21 The American Dental Association (ADA) study recognizes superimposition as a sign leading to neurosensory complications in some cases. 19 Their research has been supported by the findings of other authors indicating the presence of two or more signs on panoramic radiography, the deep horizontally impacted mandibular molar represent factors associated strongly with close proximity of the impacted tooth to mandibular canal and an increased risk of complications. 22,23,24 Our study showed that it is impossible to determine the bucco-oral localization of the mandibular canal on the OPT, while at the axial sections of

Conclusion
The results of our study indicate that the presence of certain radiographic signs on the OPT may have predictive significance. The exact relationship between anatomical structures and posterior teeth cannot be accurately estimated on OPT since the precise position of the molars and correlation to the mandibular canal and the maxillary sinus can be accurately performed only on the CBCT.