Quality of Endodontic Treatment and Prevalence of Apical Radiolucencies in a Bulgarian Subpopulation: a CBCT Analysis

Introduction: The advent of Cone Beam Computed Tomography (CBCT) in endodontics has enhanced the diagnosis of periapical radiolucencies and the assessment of endodontically treated teeth. Aim: The purpose of this study was to assess the prevalence of periapical radiolucencies in a Bulgarian subpopulation and the quality of previous endodontic treatment using CBCT scans. Materials and methods: This study included 2795 roots from 160 Large FOV CBCT which were evaluated by two independent examiners using two scoring systems: CBCT-PAI and PESS. Results: The inter-examiner agreement spanned from strong to almost perfect (0.892 and 0.983). The prevalence of periapical lesions according to the two scoring systems was 23.1% and 12.9 %, respectively. The prevalence of endodontically treated teeth was high (34.1%). Sixty-five percent of them presented with signs of periapical radiolucencies, while only 1.4% of all non-treated roots had a periapical lesion. A significant association between periapical disease, poor quality of the root canal filling and inadequate coronal seal was found (p<0.001). Conclusions: The prevalence of periapical disease in endodontically-treated teeth in the Bulgarian subpopulation was high. Poor quality of the root canal filling and inadequate coronal seal were assessed as prognostic determinants of treatment failure. CBCT techniques can augment conventional diagnostic techniques in the field of endodontics.


INTRODUCTION
The progression of microorganisms from the infected root canal space to the periapical area evokes an inflammatory response during which pathophysiological changes occur leading to bone resorption. 1,2 The condition is known as chronic apical periodontitis and is represented radiographically as a radiolucent area around the apex of the tooth.
Recent epidemiologic research documents that the prevalence of periapical radiolucencies varies among patients aged 20 to 30 by 33%, aged 30 to 40 by 40%, aged 40 to 50 by 48%, 50 to 60 by 57%, and in patients older than 60 years of age by 62%. 3 The prevalence of chronic apical periodontitis in Bulgaria is high -between 2.0% and 18%. 4 Furthermore, the prevalence of periapical radiolucencies in teeth with root canal treatment is also very high -71.3%. 4 Therefore, chronic periapical pathosis is regarded as a socially and economically significant disease and a public health problem.
The contemporary method that is most widely used in day-to-day clinical practice for evaluation of the periapical area is the periapical radiography (conventional or digital). [5][6][7] However, it provides a two-dimensional view of three-dimensional (3D) structures. [8][9][10] Several studies have reported on the limitations of periapical radiography in detecting periapical lesions due to bone characteristics, lesion location, morphologic variations, surrounding bone density, x-ray angulations and radiographic contrast. 5,8,11 Histologic analysis is considered the most accurate diagnostic method but its application is limited to endodontic surgery only due to its invasive nature. 12 Recently, CBCT has been successfully implemented in the field of endodontics as it provides a 3D reconstruction of the anatomical structures. Several studies have confirmed the increased accuracy of CBCT in detecting periapical lesions in comparison with conventional radiographic techniques. [13][14][15][16][17] Therefore, CBCT can be beneficial to endodontic diagnosis. The purpose of this study was to describe the periapical health status of a Bulgarian subpopulation via CBCT measurements and estimate the prevalence of disease and treatment.

Cases Selection
The retrospective study was approved by the institutional review board of the Medical University of Plovdiv, with accordance to the ethical standards of the Declaration of Helsinki and with a waiver of informed consent due to the design of the study. Large FOV CBCT images of 120 patients were selected from the database of a dental radiology laboratory in Plovdiv, Bulgaria. The patients included in the study were aged 18-64 (mean age 48.5 years) with a minimum of 10 teeth.

Imaging methods and analysis
The CBCT images were obtained with the Planmeca Pro-Max 3D Max dental X-ray unit. The scans' parameters were voxel size of 0.200 & 0.200 & 0.200 mm, 15 bits. The CBCT volumetric data were evaluated by two independent and calibrated examiners with the Planmeca Romexis Dental Imaging Software. Monitor settings concerning brightness and contrast were adjusted to the preferences of the examiners. A slice thickness of 0.2 mm to 0.5 mm was used for the multiplane views in accordance with the examiner's preferences.
A total of 2795 roots (1843 teeth) were examined. The root was adopted as the unit of observation and each root was scored with two previously published indices. The CBCT-PAI by Estrela et al. 10 scores the size of the lesion, its location, and relationship with the roots of the tooth ( Table 1). The PESS index by Venskutonis et al. 18 is a complex scoring system evaluating lesion size, root canal treatment quality and possible complications. It consists of two scoring systems -COPI, the complex periapical index ( Table 2), designed for the identification and classification of periapical bone lesions, and ETTI, the endodontically treated tooth index (Table 3), designed for endodontic treatment quality evaluation. For the assessment of the endodontic treatment, the scores were distributed in the following categories: the scores of L2, L3 and L4 were labeled as an inadequate length of the root canal filling, the scores of H2 -as an inadequate quality of the root canal filling and the scores of CS2 -as an inadequate coronal restoration.  The variables E (expansion of cortical bone) and D (destruction of cortical bone) were added to each score when either of these conditions was detected in the CBCT analysis.

Statistical analysis
Data were typed into a spreadsheet, and SPSS software (version 17; SPSS Inc., Chicago, IL) was used to perform the analysis. The Cohen kappa was calculated to assess the inter-examiner agreement for each parameter for the indexes. The Mann-Whitney test was used as the univariate approach to detect statistically significant differences between the categories. Correspondence analysis was used for the assessment of the association of the quality of endodontic treatment and status of the apical periodontium. The level of significance adopted was 1%. Folia Medica I 2021 I Vol. 63 I No. 1

S0
Widening of the periodontal ligament not exceeding two times the width of the lateral periodontal ligament S1 The diameter of small well-defined radiolucency up to 3 mm S2 Diameter of medium well-defined radiolucency 3-5 mm

S3
Diameter of large well-defined radiolucency >5 mm R (Relationship between root and radiolucent lesion)

R0
No radiolucency, when widening of the periodontal ligament is not exceeding two times the width of the lateral periodontal ligament R1 Radiolucent lesion appears on one root R2 Radiolucent lesion appears on more than one root

DISCUSSION
Radiographically detectable periapical radiolucencies mark the presence of a chronic destructive inflammatory process. These chronic lesions are either of primary or secondary endodontic origin and patients generally do not present with any symptoms. Even persistent endodontic lesions can provide functionality and comfort to the patients and they may never seek further treatment until complications arise. 19 Therefore, the cases chronic apical periodontitis tend to accumulate in given population. Effective screening methods are needed for their successful diagnosis and timely treatment.
The high proportion of endodontically treated teeth presented with periapical radiolucency which correlates with previous reports. [19][20][21] These results can be due to a variety of factors. While endodontically compromised teeth are retained successfully through root canal treatment as it is the effective way to reduce the symptoms and treat periapical disease, unsuccessful treatments do not always present as functional or symptomatic failures and accumulate over time in a population. 22 Furthermore, radiographic screening and cross-sectional studies are an effective way of assessing the prevalence, severity and origin of the problem. However, these snapshot studies cannot distinguish between healing and persistent lesions. 19 One of the limitations of the present retrospective study is that our evaluation was only based solely on the radiographic analysis. No data about the dental history of the patients were available.
The overall prevalence of periapical disease in the Bulgarian subpopulation was higher than previous reports based on conventional radiographic techniques. 4 This can be explained with higher sensitivity of CBCT in the detection of periapical radiolucencies. 23 The prevalence also varied according to the two scoring systems. This is due to the different disease threshold criteria in their design. The conventional strict criteria for endodontic success on conventional two-dimensional radiographs include a complete absence of periradicular radiolucency along with the re-establishment of a normal periodontal ligament space and a defined lamina dura. established in clinical practice. 24 With the advent of the new high-resolution three-dimensional images new, universal criteria need to be established for the successful evaluation of treatment success and prevention of unnecessary treatment.
An evaluation of the quality of pervious endodontic treatment was performed with the ETTI scoring system. The high resolution CBCT images provided for the comprehensive assessment of any factors that could have impacted treatment success. Our results indicate that incomplete obturation of the root canals and a compromised coronal seal increase the risk of secondary infection of the root canal system and are associated the development of periapical disease. The results are in accordance with previous reports and underline the need for optimized treatment strategies. [25][26][27][28][29][30] The best treatment results were associated with a root canal obturation ending 0-2 mm short of the apex, which is compliant with the accepted standards. The cases examined in this study do not represent a statistically significant sample of the Bulgarian adult population. Nevertheless, the results provide an insight into the poor quality of endodontic treatment and the prevalence of periapical radiolucencies.

CONCLUSIONS
The present study revealed high prevalence of periapical radiolucencies in endodontically treated teeth among the Bulgarian subpopulation. Our findings underline the need of strict post-treatment endodontic evaluation protocols and continuous post-operative monitoring and care. Within the limitations of the present study, it was concluded that the quality of endodontic treatment in Bulgaria is not up to the accepted clinical standards.