Introduction

The main purpose of endodontic treatment (ET) is to prevent and treat acute and chronic apical periodontitis (AP). From a biomechanical point of view, this means cleaning, shaping, and disinfecting the root canal system to allow three-dimensional filling at a later stage. Achieving these goals is a prerequisite for therapeutic success [1-3].

ET is a multi-stage process in which a number of factors must be taken into account. One of the factors is radiological control after ET. Radiologic features of appropriate ET are as follows:

During diagnosis and treatment planning, it is extremely important to know the morphology of the root canal system and its deviations from the norm, as well as the shape and size of the pulp chamber. This knowledge allows for thorough treatment planning and increases the likelihood of a positive treatment outcome [5]. A successful ET can be well defined by the absence of apical periodontitis and the absence of clinical symptoms after a period of observation.

Intraoral radiographs are an essential diagnostic tool used during the planning of ET. They provide information on tooth anatomy, the presence of periapical lesions, their progression, and treatment results. Periapical lesions are visible on radiographs if there has been a loss of bone mineralisation in the range of 30 to 50%. For this reason, periapical lesions are not always visible on X-rays [6-8]. X-rays are two-dimensional images of a three-dimensional structure, which means that some features of the examined area may not be sufficiently visible. In addition, differences in the density of the bone surrounding the examined tooth and the difficulty in obtaining reproducible images can affect the interpretation of this type of tissue imaging [6,9]. The introduction of cone-beam computed tomography (CBCT) into daily practice has enabled three-dimensional imaging of the dentition, the maxillofacial skeleton, and the interrelationships of anatomical structures. CBCT imaging, however, has some disadvantages. These include the increased radiation dose absorbed by the patient, the generation of artifacts, and the occurrence of scattered radiation that makes a substantial contribution to the image noise [10-12].

CBCT offers the possibility of using different sizes of the imaging area (FOV – field of view), which ranges from 3 to 20 cm. Using CBCT for endodontic diagnosis, it is important to follow the principle of using the smallest possible FOV, the smallest possible voxel size and the shortest possible patient exposure time when operating with pulsed emission mode [13,14].

The purpose of this study was a retrospective cross-sectional study of the Polish subpopulation performed to evaluate the quality of ET and the condition of periapical tissues of permanent teeth based on CBCT images and the influence of the quality of ET on the occurrence of periapical lesions.

Material and methods

A retrospective cross-sectional study included a group of patients who underwent a CBCT in the period from 01/01/2015 to 04/06/2021 at the University Dental Clinic of the Pomeranian Medical University in Szczecin, Poland. The entire material was collected retrospectively based on the available medical records. The CBCT images used in this study were acquired for a variety of indications, i.e. orthodontic, implant, orthognathic, surgical, and ET planning. The consent of the Bioethics Committee of the Pomeranian Medical University in Szczecin was obtained to conduct the study, with consent number KB-0012/191/04/18.

Inclusion criteria for the study group were as follows: patients over 18 years of age, permanent teeth, the teeth and their periapical region visible on all the multiplanar views (axial, coronal and sagittal), CBCT field of view 6 × 8, 8 × 8, 8 × 15, voxel size ≤ 200 μm (4-16 mA, 57-90 kV, 6.1-2.3 s). Cases not fulfilling these criteria were excluded from the study. Maxillary and mandibular third molars, impacted teeth, and records with poor quality were also excluded from the analysis.

The CBCT scans were recorded using the Cranex^® 3Dx (Soredex Oy, Tuusula, Finland). The scans were evaluated using the OnDemand 3D program (Cybermed Co, Seoul, Korea) in a darkened room by one endodontist with 6 years of clinical experience (KLB), who was calibrated before the start of the study. Intra-observer reliability for PESS index was assessed by calculating Cohen’s k by a double scoring of 50 randomly selected CBCTs at one-month intervals. All kappa values exceeded 0.80. In cases of difficult assessment, the images were consulted by a senior endodontist (AN).

No CBCT study has been performed specifically for this study. The age, sex, total number of teeth, number of endodontically treated teeth, and number of teeth with AP of each patient included for the study were recorded.

The periapical and endodontic status scale (PESS) was used to assess the quality of ET and the extent of apical periodontitis on CBCT. The first part of the PESS is the Complex Periapical Index (COPI), which was designed for evaluation of periapical lesions. The second part of the PESS is the Endodontically Treated Tooth Index (ETTI), which was designed for ET quality evaluation [15]. The COPI was used to assess the AP in each tooth included in the analyses. The relationship between root and radiolucent lesion (R) was assessed only for multi-rooted teeth. The ETTI was used to make canal-by-canal assessments of each endodontically treated tooth (Figure 1). For the purposes of this study, the ETTI has been modified by adding the H3 score to assess the homogeneity of the root canal filling. The H3 score refers to the absence of a root canal filling in the case of previous pulp amputation or canals missed in previous ET (filling material visible only in the aspect of the pulp chamber). The periapical and endodontic status scale is presented in Table 1.

Figure 1

Assessment of endodontic treatment (L2H1CS1CF5) and apical periodontitis (S2RxD1) using the PESS index. L2 – root canal filling > 2 mm from radiographic apex, H1 – complete obturation (homogenous appearance of the root canal filling), CS1 – adequate coronal seal, CF5 – endodontically treated root with radiolucency, S2 – diameter of medium well-defined radiolucency 3-5 mm, Rx – no assessment, D1 – radiolucency around the root

Results

Of the 1351 CBCT records, after applying the exclusion criteria, 180 scans were available for statistical analysis (85 male and 95 female, mean age 41.85 ± 15.51 years), containing 4158 permanent teeth. The distribution of patients by age and gender is shown in Table 2. Apical periodontitis was found in 248 teeth (6%), ET was found in 413 teeth (9.9%), and both ET and AP were observed in 159 teeth (3.8%).

Discussion

Knowing the condition of endodontically treated teeth and the status of periapical tissues can help predict future oral health needs in patients of the examined population. In addition, the assessment of the quality of dental treatment in a given population can influence the educational program of future dentists and the direction of their professional development [7,16]. The present cross-sectional study was conducted on the basis of available CBCT examinations, so it does not represent a random sample of the Polish subpopulation. Therefore, extrapolation of results to the general population should be done with caution. According to Pak et al. [17] a cross-sectional survey is the best way to study health status, disease. and treatment provided in a population. Ideally, the study would have been conducted in a randomised setting, but performing CBCT in healthy patients does not follow American Association of Endodontists (ASE) and European Society of Endodontology (ETE) guidelines [13,14]. In CBCT imaging, the level of risk associated with increased radiation exposure compared to conventional imaging should be outweighed by the potential benefits.

In this study, 4158 teeth in 180 patients were evaluated. To date, the largest group of patients was evaluated by Meirinhos et al. [18], who examined 20,836 teeth in 1160 patients, and Aysal et al. [19], who examined 20,606 teeth. In these studies, a full-arch scan with voxel size of 200 μm or less was used. Van der Veken et al. [20] studied 11,117 teeth in 631 patients. Unfortunately, the authors did not provide CBCT imaging parameters (FOV and voxel size). Due to the aforementioned need for radiation protection of patients, CBCT examinations were also conducted on groups of smaller size. Paes da Silva et al. [21], Mashyakhy et al. [22], and Dutta et al. [23] in their CBCT-based cross-sectional studies evaluated, respectively, 3595 teeth in 245 patients with a voxel size of up to 0.3 mm, 5504 teeth in 208 patients with a voxel size of 0.25 mm (unfortunately, the authors did not provide information about the FOV), and 5585 teeth in 214 patients using voxel sizes of 0.25 mm and 0.3 mm and FOVs of 6, 8, and 13 cm. Cross-sectional studies based on orthopantomogram images in relation to CBCT were characterised by study groups with larger populations. In a study conducted by Huumonen et al. [24] on 6101 patients, the authors managed to evaluate as many as 120,635 teeth. Archana et al. [25] conducted their observations on a smaller group of 1340 patients (30,098 teeth evaluated). Kielbassa et al. [26] managed to include 1000 patients (22,584 evaluated teeth) in their study group.

In the present study, of all assessed teeth, AP was found in 6%, while AP co-occurred with ET in 3.8%. The findings of studies evaluating the prevalence of periapical lesions in other populations using CBCT imaging were as follows: Paes da Silva et al. [21] observed 3.4% of teeth affected by periapical lesions, and Dutta et al. [22], Van der Veken et al. [20], and Meirinhos et al. [18] found 5.8%, 5.9%, and 10.4% of such teeth, respectively. Endodontically treated teeth with co-existing AP accounted for 2.3%, 2.6%, 4.0%, and 6.1% in the studies by Dutta et al. [22], Paes da Silva et al. [21], Van der Veken et al. [20], and Meirinhos et al. [18], respectively. The presence of AP in teeth with correct ET may suggest the presence of a true periapical cyst, which have a completely enclosed lumina, unlike a pocket cyst which is open to the root canal. Pocket cysts heal after proper ET [27].

Our study showed that periapical lesions were most commonly observed in patients in the third decade of life, with an incidence rate of 1.4%. Similar observations were made by Van der Veken et al. [20] in a study of the Belgian population. Among subjects in the fourth decade of life, the percentage of teeth with a periapical lesion was 1.3%. Studies based on panoramic images and dental status yielded more varied results, as shown in Table 6. These differences may be due to several factors, such as the quality of imaging, the social status of the study population, the background of the study population, the level of education of the dentists in the study area, or the time at which the study was performed.

Periapical lesions in roots with inadequate root canal filling were frequently detected on radiographs in the epidemiological studies mentioned above [9,18,19,25,26]. The results of the present study show that after ET, 38.5% of teeth were affected by AP. This is similar to the results of the Belgian study based on CBCT by Van der Veken’s team [20] and the Japanese study based on orthopantomogram images developed by Tsuneishi’s team [30]. The findings of this study showed that teeth with underfilled root canals were almost 2.5 times more likely to develop small periapical lesions, and teeth where the filling material was only visible in the pulp chamber were almost 3.5 times more likely to develop these lesions, compared with teeth where the ET had been carried out correctly. Aysal et al. [19] showed in their CBCT study that the risk of periapical lesions was just over 3 times higher in roots with underfilled canals, 5.5 times higher in roots with overfilled canals, and almost 3 times higher in teeth with inhomogeneously filled canals, compared to correctly treated teeth. A meta-analysis by Alves Dos Santos et al. [31] in 2022, based on CBCT studies, showed that homogeneous root canal filling and correct filling length (0-2 mm from the apex opening) have an impact on the success of ET. It should be mentioned that various filling materials (gutta-percha, glass fibre, metal posts) produce artifacts in the CBCT image that affect the assessment of canal filling (false positive cases of homogeneous filling) and complications such as vertical root fracture [32,33].

Similar correlations have been observed in studies based on orthopantomograms. Jersa et al. [29] showed a 3-fold increased risk of periapical lesions in teeth with poor quality ET compared to teeth with correctly performed ET. Similarly, Kamberi et al. [28] found a 5-fold increase in the risk of periapical lesions, while Huumonen et al. [24] found a 2-fold and 2.5-fold increase in the risk of these lesions for incorrect root canal filling in men and women, respectively, compared to correct root canal filling. Unfortunately, the aforementioned authors used a simplistic analysis to evaluate ET. They only considered correctly or incorrectly performed ET. Dugas et al. [34] and Kielbassa et al. [26] addressed this issue in more detail by including the homogeneity of the root canal filling material and the quality of the crown restoration after ET in their analyses. The former team found an almost 3-fold increase in the risk of periapical lesions for teeth with inhomogeneous root canal fillings compared with teeth with a homogeneous filling, and a 2.5-fold and almost 3-fold increase in the risk of periapical lesions for teeth with underfilled and overfilled root canals, respectively, compared with teeth with a proper root canal filling. Dugas et al. [34] also considered the quality of the crown restoration and found an almost 2-fold increased risk of periapical lesions in teeth with abnormal crown fillings compared to teeth with normal restorations. The second team’s findings showed an almost 2-fold increased risk of periapical lesions in teeth with incorrect root canal fillings and lack of root canal filling homogeneity compared to teeth with correct root canal fillings, and an almost 2-fold increased risk of periapical lesions in teeth with incorrect crown fillings compared to teeth with correct restorations [26].

The presented study is cross-sectional based on available CBCT studies; therefore, it does not represent a random sample of the population. Hence, extrapolation of results to the general population should be done with caution. According to Pak et al. [17], a cross-sectional study is the best way to examine health status, disease, and treatment in a given population. Ideally, the project would include a randomised study, but performing CBCT in healthy patients is not consistent with ASE and ETE guidelines [13,14]. The potential benefits of CBCT imaging must be balanced by the relatively higher level of risk associated with radiation exposure compared to conventional imaging. In a 2015 meta-analysis by Ludlow et al. [35], the mean effective doses for large, medium, and small FOV CBCT are 212 μSv, 177 μSv, and 84 μSv, respectively, while for small FOV, many devices achieve reasonable exposures of around 30 μS.

The development of artificial intelligence is very promising and interesting. Attempts have been made to use it to diagnose caries and AP based on 2D and 3D images [36,37]. The results show that it is more useful in assessing AP on CBCT than orthopantomogram [37]. It seems that future research should focus on the development of artificial intelligence in the diagnosis of dental pathology.

Based on the cited findings, our own results, and the new concept of ALADA – “as low as diagnostically acceptable”, which is a modification of ALARA – “as low as reasonably achievable”, routine use of CBCT with small FOV for ET of molars can be considered [35,38].

Conclusions

The quality of the ET provided to the Polish subpopulation is not satisfactory. The lack of homogeneity of the root canal filling is a significant risk factor for ET failure, most commonly affecting molars. Improper ET and poor quality of crown restoration after ET have an impact on the increased risk of occurrence, size, degree of root coverage, and extent of inflammatory periapical lesions in relation to adjacent anatomical structures.

Disclosures

1. Institutional review board statement: The study was approved by the Bioethics Committee of the Pomeranian Medical University in Szczecin, with approval number KB-0012/191/04/18.

2. Assistance with the article: None.

3. Financial support and sponsorship: None.

4. Conflicts of interest: None.