## 4 Discussion  
The aim of the present study was to evaluate the correlation between the clinical signs considered pathognonomic for the diagnosis of VRF and the actual reference standard, using the principles of evidence-based dentistry by means of systematic review of the literature. The fundamental principle of evidence-based dentistry, is the usage of the best available clinical evidence to support the practitioner's everyday practice [16; 17; 18]. Evidence-based dentistry is based on the process of methodically finding, evaluating, and using investigative findings as the basis for clinical decision making [16; 17; 18; 19; 20; 21; 22]. In the present systematic review, the methodological quality of the included studies was appraised, and risk of bias was calculated for each study according to Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy parameters [23]. All included studies were graded to have a low risk of bias. Various studies regarding the diagnosis of VRF and the clinical and radiographic features of vertically root-fractured teeth have been published. However, their study design, VRF definition, VRF confirmation methods, and assessed clinical and radiographic data have been highly variable, which results in the publication of varying and unclear results [1]. In  
Figure 1: A flow chart of the systematic search process. the present systematic review, we included studies that used VRF confirmation methods in agreement with the one of the defined reference standards: The VRF being confirmed during surgical procedure, the VRF being confirmed following tooth extraction, or the VRF being identified radiographically as a distinctly discernable separation of segments of fracture. In the current study, a detailed literature search of several electronic databases was conducted. To overcome the heterogeneity of data, strict inclusion and exclusion criteria were applied to the identified studies. Only three studies fulfilled the criteria [8; 9; 10]. Meta-analysis was not preformed because of the small number of the articles. It has been reported in the literature that deep periodontal pocket was found in VRF clinical studies at a rate between 23.9% to 100% [8; 9; 13; 15; 24; 25; 26]. In the present study, it was found in 51% of the cases. Another clinical sign usually associated with VRF is the presence of sinus tract. From previous studies, sinus tracts associated with VRF, different to those that result from a typical chronic periapical abscess, were not typically located in the apical area, but rather located several millimeters below the gingival margin [10]. In our systematic review, sinus tract was found in 46% of the cases, and there were no data regarding the position of the sinus tract [8; 9; 10]. In 2008, the AAE has published a statement saying that when there is a combination of deep pocket and a sinus tract in endodontically treated tooth it is considered \"pathogonomic\" for the presence of a VRF. [20] The three articles which were included in our systematic review showed that the \"pathognomic combination\" was found only in 28% of the VRF-confirmed teeth. The real prevalence of this combination might be different, and there are many more articles observing the clinical signs and symptoms of VRF-confirmed teeth which detail the finding of deep pocket and a sinus tract, but did not address the cases in which they appear together. The lucent \"halo\" radiographic appearance, which is associated with VRF [27], was found in 44% of the cases in this study. This radiographic heterogeneity could be clarified by the time that has passed until VRF was diagnosed, which affects the amount and pattern of bone destruction [12; 28]. Cone beam CT (CBCT) has been suggested in some studies as a preferable method to diagnose VRF compared with periapical radiographs. However, there is still lacking evidence to suggest the advantage of CBCT over conventional radiographs to detect VRF [23].