The current retrospective cross-sectional study investigated the association between endodontic prognostic factors and four dependent variables including PL presence, its size, CBD, and BPBH, on CBCT scans. Our findings revealed that missed canals, perforation, underfilled, and overfilled canals were significantly correlated with the presence of PL. Specifically, missed canals emerged as the primary factor affecting the PL volume. Therefore, the null hypothesis was rejected. In addition to the missed canal, perforation and separated instrument could significantly diminish BPBH. On the other hand, none of the factors mentioned could exert a statistically considerable effect on CBD.
PL status
The overall prevalence of PL in this study was found to be 49.3% in endodontically treated teeth, which was in line with several previous papers [
4,
30,
32‐
35]. However, there are other publications in the literature reporting less [
3,
36,
37] or more [
8,
38‐
41] prevalence regarding PLs. Discrepancies in the reported prevalence might stem from differences in sample size and the radiographic techniques of choice implemented to detect PLs. Overall, endodontic treatment significantly increases the probability of PL in teeth, with an OR being reported as high as 25.17 [
36].
During the present study, no significant difference was found between gender and the presence of PL (
P = .360), confirming previous research [
10,
34,
42,
43]. Nevertheless, Dutta et al. reported that PL prevalence was significant towards gender with women (OR = 37.78) having higher odds than men (OR = 17.05) [
32]. On the other hand, Bürklein et al. found men to be more affected by PL in their root-filled teeth than women [
3]. The heterogeneous findings could be explained by variations in the sample size and uniformity, as some studies focused exclusively on root-filled teeth, while others included untreated teeth as well.
Moreover, no statistical difference was established regarding PL prevalence in maxillary/mandibular teeth in the multivariate-adjusted model (OR = 1.427,
P = .342). However, when performing an unadjusted chi-square analysis, PL appeared to be significantly more prevalent in the maxilla (
P = .001), which corroborates previous studies [
3,
4,
42]. This trend has been attributed to the variation in bone structure between the upper and lower jaws with the mandible exhibiting a denser osseous pattern which limits the expansion of the PL. Nevertheless, accounting for predictive variables collectively by conducting an adjusted analysis limits bias, thereby ensuring more reliable results [
44].
As the most prevalent technical error in this study, 72% and 15% of maxillary and mandibular molars (50.4% of all samples) were associated with a missed canal, respectively, of which 70.4% were accompanying a PL (OR = 10.022,
P < .05). This significant association has been addressed in several publications so far, with reported OR spanning from 2.9 [
3] to 6.25 [
7] in various studies. Baruwa and colleagues reported a 12% prevalence of missed canals in their study, of which 82.6% were correlated with a PL (OR = 4.4) [
6]. Meirinhos et al. demonstrated a 79% prevalence of PL in root-filled teeth with untreated canals [
30]. The increased odds identified in our results could be a product of our homogenous study population, exclusively involving teeth that had undergone endodontic treatment.
The prevalence of MB2, which is an additional canal in maxillary molars, can be observed in as much as 60% of cases involving the first and second maxillary molars [
45]. At the root level, both first and second maxillary molars predominantly exhibited missed MB2 canals, followed by missed ML canals in the lower molars, which precisely corroborates the findings of previous authors [
4,
6‐
8]. This finding is substantiated by considering the complexity of the anatomy and the difficult accessibility of these canals. However, Karabucak et al. found the second distal canal as the most commonly missed canal in the mandibular first molars [
8]. The approximate prevalence of this canal has been reported to be 22% [
46]. Additionally, a recent cross-sectional study conducted across multiple countries has revealed the presence of middle mesial canals in approximately 7% of the lower first molar teeth [
47]. The presumption of a three-canal system could probably avert the clinician from further negotiating for an additional distal or mesial canal upon discovering the initial ones. These results could suggest that clinicians may allocate greater attention to MB2, ML, and second distal canals in their practice to further prevent PL formation.
Obturation length was a significant predictor for PL (
P < .05), with overfilled canals exhibiting a more prominent effect (OR = 15.859) in increasing the chance of PL than underfilled canals (OR = 3.725). A short filling was prevalent in 24.1% of cases of which 69.1% had led to the presence of a PL. Overfillings existed in only 1.7% of cases of which 80% were accompanying a PL. In this regard, Bürklein et al. reported that 31.2% and 1% of cases were underfilled and overfilled, respectively [
3]. While the likelihood of association with PL regarding overfilled canals was smaller in our study than theirs (OR = 27,
P < .05), the results for underfilled cases in our study relatively corroborated their findings (OR = 4.37,
P < .05). In the study by Kabak et al., 29.6% and 8.3% of root-filled teeth were underfilled and overfilled, respectively [
36]. Corresponding to our results, overfilled cases (OR = 5.42,
P < .05) were associated with odds of PL more intensely than underfilled (OR = 2.59,
P < .05) cases. El Ouarti et al. reported that inadequately filled roots were associated with PLs with an OR of 1.93 (
P = .004) in a Moroccan subpopulation [
39], while Frisk et al. reported the OR for the same association to be 2.77 (
P < .05) in a Swedish population [
10]. On the other hand, another author reported no significant difference between overfilled canals and the ones with adequate root filling length [
4].
Overfillings might provoke tissue irritation due to prior overinstrumentation. They may trigger an inflammatory response by pushing infectious residue to the periapex [
48]. Furthermore, overfillings might induce foreign body reactions in the periapical region even in the absence of microorganisms. This situation could result in PLs remaining asymptomatic for extended periods [
49]. Similarly, the infectious dentinal debris left in the unobturated portion of the underfilled canals could aggravate the treatment prognosis by elevating the risk of a sustained infection [
48].
Successful endodontic therapy relies on homogeneous obturation of the prepared roots along with a hermetic seal of the coronally destructed tooth portion, without one outweighing the other [
50]. However, quality assessment of coronal restorations in CBCT scans is subject to scattering artifacts which imposes challenges in evaluating restoration quality impeccably. Therefore, clinical examination and intraoral radiography stand out as more reliable methods for appraising the quality of coronal restorations [
4].
In the current study, neither the type of restoration nor the presence of a post could significantly influence the periapical status of the root-filled teeth, which corroborates the findings of a previous study [
39]. Conversely, according to Hommez et al., teeth with composite restorations demonstrated a higher association with PL than teeth restored with amalgam (
P < .01). Meanwhile, it was noted that the use of posts had no apparent effect on the status of PL [
51].
A previous study has demonstrated a significant association between crowns and PLs, while reporting no correlation toward PL status in teeth restored with plastic fillings [
4]. The observed correlation has been attributed to greater structural tooth loss preceding crown placement. However, Frisk et al. have reported a significant association between plastic restorations (composite and large mixed amalgam and composite) with PL (
P < .05) whereas they did not find a significant correlation regarding full crowns and PL status (
P = .06) [
10]. These inconsistencies could be accounted for by the retrospective nature of the research, which falls short of providing details about the condition of teeth prior to treatment. In sum, the integrity of the coronal restoration seems to hold more significance than the choice of material.
In this study, a 3.9% prevalence of perforation was noted, of which 90.9% were linked to a PL (OR = 15.216,
P = .013). Yamaguchi and colleagues have reported perforation as the second most important cause of treatment failure in 11.8% of root-filled teeth in a Japanese population [
52]. The inadvertent creation of a pathological connection between the root and its surrounding tissues could potentially result in complications severe enough to require the removal of the affected tooth. However, nonsurgical repair of perforations has been reported to display clinical success rates as notable as 70% [
53].
PL volume
The literature has covered various methods for measuring the volume of 3D objects, including the water displacement method (WDM), geometric-based models, magnetic resonance imaging, and CT-based techniques [
27,
54,
55]. WDM is considered the gold standard, providing optimal precision in determining the volume of an object by dipping it in a water-filled container and measuring the overflow [
56]. However, this measurement is only achievable with externally replicated PLs [
55]. CBCT scans have provided comparable results to WDM in terms of accuracy [
27,
54,
55]. However, precise detection of the PL borders via this method is a time-consuming and laborious procedure. Geometric-based models including partial frustum have demonstrated promising accuracy in cases where the previous two methods have been impossible to employ [
27]. Therefore, we implemented a partial frustum model on CBCT scans, as discussed in the
methods section, to have an accurate assessment of the PL volume.
The results suggested that the presence of missed canals was the only factor exerting a significant association with PL volume. The volume of PL was measured at 29.4 mm3 in the presence of missed canals and 7.73 mm3 in their absence (P < .05). Moreover, PL volume increased from 26.55 mm3 to 112.71 mm3 in teeth with one to three missed canals, respectively. Maxillary first molars had the greatest PL volume which was significantly larger than other types of teeth (P = .006). This larger volume could be attributed to the high prevalence of the missed MB2 canals in these teeth.
Limitations, strengths and recommendations
Cross-sectional studies present inherent shortcomings when assessing the progression of PLs. Due to the absence of information on teeth’s preoperative pulpal and periapical diagnosis, dental signs and symptoms, patients’ medical history, and the treatment date as the baseline, it is impossible to anticipate if PLs are healing or advancing. Thus, certain PLs associated with root-filled teeth may not indicate active diseases, thereby hindering the drawing of definitive conclusions regarding their association. Consequently, further rigorously controlled cohort or case-control studies are warranted. These studies should encompass all the aforementioned factors along with a comprehensive evaluation of the endodontic-periodontal relationship, to yield more generalized and valid results.
Another limitation of our study is the acquisition of CBCT scans from a single center. To enhance the results’ reliability, we recommend conducting similar research on a broader, multicenter national or international scale. Additionally, our method for measuring PL volume is relatively innovative, suggesting the need for further investigations using alternative approaches, such as specific CBCT software, to compare and improve the generalizability of results.
On the positive side, our study stands out by pioneering the PL volume measurement and exploring its correlation with endodontic prognostic factors. Moreover, we have performed an adjusted analysis to incorporate various prognostic factors, ensuring comprehensive statistical reporting of their collective impact. Comprehending this association, clinicians can precisely evaluate the treatment prognosis and establish an efficient treatment plan to enhance the patient’s well-being.