Introduction

Pediatric endodontic procedure helps in maintaining teeth in dentition, until their normal exfoliation time [ 1 ]. An accurate evaluation of root canal length determines the success of an endodontic procedure.

American Academy of Endodontics (2003) defined working length as ‘the distance from a coronal reference point to the point at which canal preparation and filling should terminate’ [ 2 ]. Accurate working length (WL) determination is extremely important, as it has an impact on ideal canal preparation, disinfection, and apical seal of root canal system [ 3 ]. The correct root canal length of primary teeth is difficult to predict because of the root resorption pattern, which could be either physiological or pathological. There is continuous alteration in size, shape, and position of root apices of primary teeth, [ 4 ] that causes difficulty in accurate determination of root canal length [ 5 ]. Traditional methods for establishing WL include conventional radiography, tactile sensation, moisture on a paper point, and knowledge of root canal anatomy.

After the introduction of digital radiography (DR), the first commercial integrated digital imaging system in dentistry was radiovisiography (RVG) which comprises an intraoral sensor instead of the conventional X-ray film [ 6 ]. DR is based on digital image capture and uses a charge-coupled device [ 3 ]. The advantages of a digital radiography above the conventional method are; predominantly a faster image procurement, lower radiation dose and image editing ability [ 7 ]. Although both conventional and DR methods offer some advantages, such as direct observation of root canal anatomy, presence of any periapical lesion and canal curvatures, there are limitations associated with them, such as radiation exposure and image distortion, which results in difficulty in identification of resorbed root apices [ 3 ]. Electronic apex locators (EAL) have been introduced to overcome the disadvantages of the above techniques. It is used in dentistry to determine where the apical constriction is located in the root canal [ 8 ]. It is a more accurate, easy, and painless technique, which is very useful in uncooperative children. Various advantages of EAL include; lesser radiation dosage as well as procedure time, which helps in maintaining patient cooperation. The efficacy of EAL has been proven even in the presence of root resorption, which is frequently encountered in primary teeth [ 9 ]. Considering the importance of WL determination for pediatric endodontic treatment and its maintenance until normal exfoliation, the aim of this systematic review was to compare the accuracy of EAL and DR for WL determination in primary teeth.

Materials and Method

Protocol registration and review reporting

The present systematic review was registered with protocol ID CRD42020222326 at the International Prospective Register of Systematic Reviews (PROSPERO). This systematic review was reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist (PRISMA 2020) [ 10 ].

Research question

Research question for this systematic review was structured in PICOS format (participant, intervention, comparison, outcome and study design), depicted in Table 1.

Is there a difference in accuracy between an EAL and DR for WL determination in primary teeth?

Eligibility criteria

The eligibility criteria (Table 2) in this study were formulated to find studies based on the PICOS format. All studies were chosen in accordance with the criteria specified in this review.

Information sources and search strategy

Databases used in the search strategy included; Cochrane Library, National Library of Medicine (MEDLINE PubMed), Google scholar, EBSCOhost, Open grey literature, including both electronic and printed literature. The concept table (Table 3) denotes the terms used for search strategy, which included key concepts, as well as free text terms. Boolean operators such as OR/AND were used to combine search terms with other keywords relating to the review's goal. Additional articles were searched by looking through the references of the chosen publications, as well as previously published reviews on the topic, textbooks and publications, that met the inclusion criteria of the study.

Articles published or studies conducted from January 1, 2005 to January 31, 2023 were included for this systematic review.

Study selection

Selection of a study was done in three stages. In stage one, assessment of all the titles of the studies obtained through search strategy were done by two independent reviewers (IA and SP). Stage 2 involved screening of the abstracts, which was followed by screening of the full texts of relevant studies in stage 3. In case of disagreements between the two reviewers, a third reviewer (FK) was called in for a final decision. Only studies with full text reports were examined in this systematic review. Due to differences in the data supplied in abstract and those provided in the final report [ 11 ], literature published only as abstracts were excluded from the study. Authors were contacted for a full text of the relevant abstracts wherever possible.

Data collection and data items extracted

After defining the inclusion criteria for the selected articles, data extraction was performed independently by two review authors (IA and SP). Any disagreements in data extraction from the selected studies were discussed and resolved by a third (FK) and fourth (DP) reviewer. This information included authors name, year of publication, number of teeth included, demographic details of the patients (age in years), intervention, comparison, outcomes, study design and results.

Study of risk of bias assessment

The risk of bias assessment was performed by two independent reviewers (IA & SP); using a modified version of the methodological items for nonrandomized studies (MINORS) scale (Annexure 1) [ 12 ]. A third reviewer (FK) validated all modifications to the MINORS scale. Cohen kappa coefficient for overall inter reviewer reliability was 0.725, indicating moderate agreement [ 13 ]. Any disagreements regarding risk of bias assessment, between the two reviewers (IA & SP), were resolved by a consensus between third (FK) and fourth (DP) reviewer. The items in MINORS scale were scored 0 (if not reported), 1 (if reported but inadequate) or 2 (if reported but adequate). The ideal score for comparative studies is 24. The checkpoints 6, 7 and 10 were excluded, as it was not applicable for this review. Hence, for the present systematic review 9 check-points were considered. The total score considered for the present review was 18. The score reported between 1 and 11 indicated high risk of bias, whereas score between 12 and18 indicated low risk of bias.

Outcomes and data synthesis

The mean differences and their standard deviations were extracted and used in the presentation of results. The meta-analysis was not performed due to a high degree of heterogeneity seen in data extraction from different studies and methodologies.

Results

Study selection

PRISMA flowchart (2020) describing the process of selecting studies is shown in Figure 1 (Page et al. 2020). Electronic literature search yielded 746 results. In the initial step of the screening process, duplicates were removed (299) using Mendeley software for Windows (Mendeley Ltd, Version 1803 Elsevier, London UK). A total of 447 articles were then evaluated, in accordance to the PRISMA standards [ 10 ]. In the next step of the screening process, 409 articles were removed due to ire-levance based on titles and abstracts. Finally, 38 full text articles were assessed and checked for eligibility criteria. Following full-text screening, 28 articles (Table 4) were eliminated, as they were not in accordance to inclusion criteria [ 14 - 41 ]. Any inconsistency over final inclusion was discussed and resolved amongst two review authors (IA and SP), whereas, a third reviewer (FK) acted as mediator. Thus, ten full text articles that meteligibility criteria and were included in present systematic review. Detailed summary of data selection was presented in the form of PRISMA 2020 flow diagram (Figure 1).

Figure 1. PRISMA 2020 flow diagram of the study

Study characteristics

The study characteristics of 10 included studies were listed in Table 5. The included studies were published from January 1, 2005 to January 31, 2023. Five of the studies were in vitro study [ 42 - 46 ], four were ex vivo [ 3 - 4 , 47 - 48 ] and one was in vivo study [ 6 ]. No randomized and non-randomized clinical trials were found. The sample size of included studies ranged from 20-90 extracted human primary teeth. Age of the participants in the in vivo and vivo studies varied from five to fifteen years. EAL used in the intervention group were Formatron D 10, Root ZX, Joypex 5, Root ZX mini, DentaPort ZX, COXO C Smart-1 Pro, iPex, Apex ID and Propex II, whereas DR used were size #0 and size #1. Accuracy was evaluated under stereomicroscopy using direct observation of apical exit of advancing K file, until tip of the file was visible at apical foramen or apical resorption level. Outcomes were assessed by comparing the difference among the actual length, DR and apex locator working length measurement. A statistically insignificant difference between EAL and DR was seen in seven out of 10 articles, whereas, other three studies showed statistically significant difference, indicating that EAL was more closely related to actual working length than DR.

Risk of bias assessment

The methodological quality assessment of the selected studies using modified version of MINORS criteria was depicted in Figure 2. It demonstrates the reviewer’s assessment, regarding each risk of bias, which has been presented as percentages across all the included studies. This scale was modified because no clinical trials were found during the search study. Thus, only in vivo, in vitro and ex vivo studies were included. The scores were categorized as low, unclear, and high risk of bias. Low risk of bias indicates plausible bias that was not likely to change the results seriously, unclear risk of bias indicates bias that raised doubts about the results, and high risk of bias indicates bias that does not inspire confidence in the results.

Figure 2. Risk of bias graph: review author’s judgments about each risk of bias item presented as percentages across all included studies

The summary of risk of bias presented in Table 6 show, seven studies by Mello Moura et al. [ 47 ], Wankhade et al. [ 4 ], Kumar et al. [ 3 ], Sahni et al. [ 44 ], Kayabasi et al. [ 45 ], Pol et al. [ 46 ] and Khan et al. [ 48 ], that presented low risk of bias which indicates high quality of evidence.

The remaining three studies conducted by Subramaniam et al. [ 42 ], Neena IE et al. [ 6 ], and Sherif et al. [ 43 ], showed high risk of bias, which indicates low quality of evidence. The summarized findings show that the included studies are of moderate quality overall, with a high risk of bias evident only at definite points.

Discussion

Early loss of primary teeth can cause space closure resulting in malocclusion of permanent dentition. Pulpectomy procedure involves complete removal of both coronal and radicular pulp. WL determination is an essential step in pulpectomy procedure, as it decides the position of apical foramen and thus the extent of obturation.

It is hard to judge the root canal anatomy of primary teeth because of continuous ongoing resorption and root canal shape. [ 49 ] The position of canal terminus and measurement of WL can be done by various techniques.

One of the widely used methods is the radiographic method for WL determination. However, measurement by this method is generally one or a half-millimeter (mm) short of the radiographic apex, where the apical constriction is generally thought to be located [ 50 ]. To eliminate the many problems associated with the radiographic methods, apex locator is now being used clinically and has become an essential part of the armamentarium of root canal procedure. Several studies have compared WL determination done by EAL and DR in primary teeth; only nine studies have been considered for inclusion in this systematic review.

The sample size is important to make any inferences about a population from a sample. Sample size was 20 to 90 primary teeth for the included studies. None of the studies revealed any details about the sample size calculation. This could lead to an increased chance of risk of bias of individual studies. The amount of physiologic root resorption can affect the determination of WL in an endodontic procedure. Amount of root resorption was reported in majority of the studies, however, three studies, Subramaniam P et al. [ 42 ], Neena IE et al. [ 6 ] and Sherif B et al. [ 43 ], inadequately reported the amount of root resorption. The threshold file size for working length measurements should be size # 15 K, as the tip diameter of the No # 10K files is less than 120 micrometers, which is not identifiable [ 6 ]. This finding was in accordance with studies by Kumar L V et al. [ 3 ], Sherif B et al. [ 43 ] and Sahni A et al. [ 44 ], Kayabasi M et al. [ 45 ]. Density profile plot analysis for digital images found that size #20 files were employed for radiographic length computation, because size #15 and size #10 files have decreasing perceptibility of file length [ 51 ].

Because of anatomical variances, anatomical structure interference, and projection problems, determining the precise radiographic root canal length is difficult [ 52 ]. Kumar L V et al. [ 3 ], Mello Moura et al. [ 47 ], Neena IE et al. [ 6 ], Sherif B et al. [ 43 ] and Kayabasi M et al. [ 45 ] employed the paralleling technique which is difficult to perform on paediatric patients. However, in the remaining four studies, they have not reported about the projection technique. These variables may result in over-instrumentation and over-filling of canals, causing permanent tooth bud injury [ 1 , 53 ].

As calibrated digital measurements are more accurate than un-calibrated ones [ 54 ], digital image calibration was performed, prior to WL determination, using an on-screen calibration tool. Kim et al. [ 55 ] demonstrated in their study that radiographic measurement of WL using an onscreen straight-line measurement was effective.

Apex locators are classified based on their generations. The first and second generations of EALs are obsolete, and are no longer manufactured or utilized in the modern era of dentistry. Nasiri et al. [ 56 ] performed a systematic review and meta-analysis and found that all generations are equally beneficial and accurate in WL evaluation.

The real WL was calculated by subtracting 0.5mm from the distance between the apical foramen and the apical constriction, which is roughly 0.5-1.0 mm [ 57 ]. A 0.5 mm margin was employed in numerous researches evaluating the accuracy of WL. Amongst the included studies, five studies, by Kumar L V et al. [ 3 ], Sahni et al. [ 44 ], Kayabasi M et al. [ 45 ], Pol D S et al. [ 46 ] and Khan SA et al. [ 48 ], determined WL by subtracting 0.5mm from apical foramen, while five studies by Wankhade AD et al. [ 4 ], Neena IE et al. [ 6 ], Subramaniam P et al. [ 42 ], Sherif B et al. [ 43 ] and Mello Moura et al. [ 47 ] did not report about the same. When compared to DR, it was found that the WL measurement provided by the EAL was near to the real WL determination in all of the included studies. This was in line with a number of research studies [ 42 , 58 ] that measured the precision of the apex locator in primary teeth. The radiographic length determination is difficult in primary teeth because of constant change in apex position due to continuous ongoing root resorption. However, only a few studies have found that in roots with wider apical foramen, EAL measurements are much shorter than the true WL [ 59 ]. In primary dentition, however, most studies found EAL accuracy rates of 64 to 96 percent [ 58 , 60 ]. In a study by Sahni et al. [ 44 ], a substantial correlation was discovered between the WL of the reference technique and EAL, and this was in agreement with Shabahang et al. [ 61 ], who concluded that EAL reliably determines the root end even in cases when root resorption is present. Furthermore, this is consistent with the findings of other researchers who reported the great accuracy of EALs in primary teeth.

The disparity in accuracy of WL may be due to variation in study designs, sample sizes, rate of resorption, file size, reference point, radiographic technique, and different generations of EAL used in the included studies.

This review has some limitations, one of which was usage of limited databases for search strategy. Another limitation was use of English literature only as, articles published in other languages were excluded. Finally, caution should be exercised before applying the results of this review in a clinical scenario, as all the included studies were of in vitro design.

Conclusion

Within the limitation of present systematic review, we found moderate quality of evidence to suggest accuracy of EAL and DR for WL determination. Majority of studies showed statistically insignificant difference between EAL and DR. However, in few studies, electronic measurement was close to actual WL as compared to DR. Based on the evidence that is currently available, EAL can be considered as an alternative for working length measurement in primary teeth. However, future research should include information about the study populations, blinding and sufficient documentation.

Conflict of Interest:

The authors declare that they have no conflict of interest.

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