Evaluation of odontometric methods in immature permanent teeth: research for a better practice

Background/Aim. Determination of correct working length is one of the keys to success in root canal treatment. It provides efficient canal cleaning and shaping, a three-di-mensional chermetic obturation and an optimal healing procees following root apex formation. The aim of this work was to evaluate and compare the accuracy and applicability of working lengths determined in permanent immature teeth in vivo using different clinical methods. Methods. The research was conducted at the Dental Clinic of Vojvodina in Novi Sad, the Department of Pediatric and Preventive Den-tistry. A sample of 30 canals of young permanent teeth were selected for the research. Inclusion criteria were: a need for endodontic treatmant, young permanent teeth, teeth with incomplete apex formation according to Demirijans stages F and G determined on radiography. Exclusion criteria: more than 3 years from eruption, pathological and iatrogenic resorption of the apex. The canal lenght was measured first on the initial radiograph used later as the parameter for comparison with various clinical methods. Results. The greatest average difference of measured working lengths was found by using electroodontometry and the paper point method afterwards. Regarding individual measurements, the most unprecise reading was with electroodontometry and tactile method up to 5 mm difference, and 4.6 mm was the maximal deviation for radiographic method. A deviation was defined by matching the measurements with a canal length measured on the initial radiograph. Our results showed that there was a difference between observed methods, although there was no statistical significance. Conclusion. The radiographic method and tactile method stand out as dominant methods for odontometry in permanent immature teeth, thanks to highly accurate readings, while the electroodontometry is considered the most unreliable method for determining working length in immature permanent teeth.


Introduction
Determination of correct working length is one of the keys to success in root canal treatment.It provides for efficient canal cleaning and shaping, a three-dimensional chermetic obturation and an optimal healing procees following root apex formation.In clinical practice the presence of a wide apex may provide challenges in endodontic treatment.A routine root canal procedure can not be performed in these cases and the success of the treatmant is unpredictable [1].
Immature permanent teeth have open or wide apices at the time of their erruption as a physiologic phase during root development.Apical closure occurs approximately 3 years after eruption [1].Open apices can also be present as a consequence of trauma, caries or pathological resorption.They can also be iatrogenic as a result of overinstrumentation or root resection [2].An open apex may develop in a previously mature apex owing to extensive resorption after orthodontic treatment or severe periapical inflammation [1].An open apex and thin dentinal walls make the endodontic treatment difficult and there is a higher risk of post-treatment root fracture under occlusal or traumatic forces [1,3,4].The walls of the apex may diverge, converge or be parallel depending on the stage of root development [5].
The aim of determining the working length is to enable the root canal to be prepared as close to the apical constriction as possible.There is general agreement that the apical constriction is appropriate for termination of canal preparation and opturation [6].The location of the apical constriction normally varies between 0.5 and 2 mm from the radiographic apex in fully developed permanent teeth [6].However, in cases of wide apices, the apical constriction is not formed and, consequently this guideline can not be followed.A lackof research in this field and no defined protocol, nor golden standard test for working lenght determination in immature teeth has led to variable methods and rendered the question of working lenght determination a controversy.
Long-term medication with calcium hydroxide is used widely to induce apexification of immature teeth with pulpal necrosis before a definitive obturation [7].The success rate of apexification with calcium hydroxide is about 95%.With Mineral Trioxide Aggregate (MTA) the success rate of apexification is comparable or higher [3].The advantages of MTA are fewer visits and faster development of a calcific barrier, even though the longterm success rate of MTA apexification is yet to be determined [8].Calcium hydroxide, also MTA should be placed in the soft tissue region at the apex, in order to promote apexification [3].In contrast to using calcium hydroxide or MTA, the literature highlights the benefits and a better long term prognosis with regenerative endodontic therapy, eventhough there are no standardized protocols for its application as well.

Objectives
Given the lack of clinical research in the field of odontometry in immature permanent teeth and precise clinical protocols for determining working length, the study aims to evaluate and compare the accuracy and applicability of working lengths determined in permanent immature teeth in vivo using different clinical methods: electroodontometry, radiographic method, tactile method and paper point method.

Methods
The research was conducted at the Dental Clinic of Vojvodina in Novi Sad, Department of Pediatric and Preventive Dentistry.The study protocol was approved by the local ethics committee, and patients/parentsgave their informed consent.The selection of patients was made by two experienced clinicians, one pedodotistand onegeneral dentist with 15 years of experience.The endodontic procedures and measurments were performed after the dentists were calibrated, with a kappa intraexaminer concordance index score of 0.84.Inclusion criteria were: need for endodontic treatmant, young permanent teeth and teeth with incomplete apex formation according to Demirijan'sstages F and G determined with radiography [5].Exclusion criteria were: more than 3 years from eruption, pathological and iatrogenic resorption of the apex.All patients had endodontic treatmants throughout multiple visits.The treatmants were done with Calcium hydroxide or MTA.For the purpose of this research paper, the clinical protocol remained unchanged and additional diagnostic procedures were not included.
The clinical examination began with thorough history of subjective symptoms, following diagnostic tests and radiographic examination.The diagnosis of pulpal status was irreversible pulpitis or pulpal necrosis.The canal lenght was measured firstly on the initial radiograph, which was later used as the parameter for comparison between various clinical methods.The retroalveolar radiograph was made with a digital x ray (SironaHeliodentVario, Sirona Dental Systems GmbH) using bisecting angle method.The lenght was measured on the x ray between a reference point on a cusp or incisal edge at 1 mm shorter than the visible edge of the rooth on the radiograph.The estimated canal lenght was measured with a mm ruler and 2x magnification with two clicks (1 click at the reference point and the second click 1 mm shorter than the apex).
Local anaesthesia was used if pain was expected regarding the diagnosis, patients requested and a patients/parental consent was gained.If not approved, anaesthesia was not given.
After isolating the tooth with rubber dam, an access cavity was prepared to allow removal of all inflamed or necrotic pulp tissue.Next a nerve file was inserted.At this point some of the pulp tissue was removed by rotating and withdrawing a nerve file.Irrigation was done with NaOCl 0,5%.
Tactile measurements were completed firstly, using asuitable file.Local anaesthesia was not used when these measurements were performed.The tip of the file was placed against a dentinal wall in the root canal and displaced apically until it reached the edge of dentinal wall at the apex and provoked sensitivity or haemorrhage.The length was adjusted and measured.This procedure was repeated to circumferentially probe all dentinal walls, if a shorter length was determined, the ring on the file was readjusted, thus representing the tactile working length.Electronic measurements were done next using the Raypex 5 electronic apex locator (VDWGmbH, Munich, Germany), a fourth generation apex locator.After a copious irrigation with NaOCl 0,5%, a file was chosen which was four degrees smaller than the file which was earlier defined as suitable for tactile method.After slightly drying the canals, the chosen file was introduced until a constant beep (around 5 seconds) was evoked.This was repeated and the correct lenght noted.The next step was to record radiographic measurements with a file in the canal placed in the canal, in length which corresponds to the lenght on the initial radiograph.The steps of radiographic imaging were standardized.If the obtained results differed more than 3mm, the x ray was repeated.If the difference was less than 3mm, the lenght of the instrument was measured again and the working length was corrected adding or subtracting for adequate length.The measuring was done with a mm ruler and x2 magnification with 2 clicks ( 1 click at the reference point and the second click at the file tip).
Odontometry using paper points was done next.An initial paper point was placed 0.5 mm short of the indicated length determined by the tactile method done earlier.The point advanced apically until some fluid wass noticed on the tip.Another paper point was used just short of this point.The working length was then determined as the maximum length that a paper point could be placed into the canal and remained dry after brief contact [9].
Working length measured by apex locator, tactile method, paper point and radiographic method was compared to the canal lenght measured on the initial radiograph.Data was collected and statistical analysis was carried out with the use of SPSS (Statistical Package for the Social Sciences) Windows version12.0.Statistical analysis included standard descriptive statistical analysis, the differences between investigated groups were compared using one-way Anova test (absolute values and SD in mm were compared for all determined working lengths) with the level of significance set at p<0.05.Average differences, maximal and minimal deviations, standard deviations were determined for each individual measurment method.The deviations from the average values (both positive and negative values) were calculated in all measurements, and the correlation coefficient between employed clinical methods was calculated.

Results
The sample consisted of 21 patients (9 female, 12 male), mean age 8.3±1.7 years.A sample of 22 immature permanent teeth including 13 upper central incisors, 2 upper lateral incisors, 2 upper praemolars and 2 upper and 3 lower molars with total 30 canals were selected for the research.The results of this study are shown in Table 1.The greatest average difference of measured working lengths was found using electroodontometry, then the paper point method.Regarding individual measurements, the most unprecise reading was with electroodontometry and tactile method with 5 mm difference, and 4.6 mm was the maximal deviation for radiographic method.Minimal deviation meant that the single measurements corresponded to the parameter measured on the initial radiograph.Our results showed that there was a difference between observed methods, although there was no statystical significance.In two cases there was a problem in defining the correct canal length with paper point method, when repeatedly a dry canal could not be obtained, while some uncertainties were present in one case using the tactile method, when the mean value of four measurements was applied.In Figure 1.every method and all measurements of working lengths are shown.
The correlation between deviations in all clinical methods was 0.79.

Discussion
To the best of the authors knowlegde, no prospective clinical studies of working length determination in immature teeth have been published.By its design, this was a prevalence in vivo study aimed to clarify the dillema of odontometry in teeth with incomplete root formation.
There are many experimental in vitro studies about working lenght determination in immature teeth.The time taken to process an in vitro research and its conclusions versus an in vivo, clinical research is significantly less.The results from in vitro studies should be interpreted with caution, as in clinical situations, there is often a lack of ideal circumtances and controlled enviroment for precise measurment [10,11,12].Nevertheless,for a comprehensive understanding of this matter, knowledge for odontometry in permanent immature teeth should be validated through both in vitro and in vivo studies.
Apex locators have been shown to be highly accurate in locating the apical foramen and constriction in fully developed teeth [8].Their performance can be influenced by several factors: the diameter of apical foramen, the size of file in use, electrolytes, pulp tissue and blood.The third and later generation apex locators were constructed to overcome some of these limitations [1].Even though, various authors have determined that as the diameter of the apical foramen increases, the measured lenghts with apex locators become shorter than the actual canal lenght [13].A laboratory study showed that file size is irrelevant for apical size of 60, whereas, better fitting files are recommended to be used for apical sizes over 70 [1].Hulsmann & Pieper found that apex locators had an accuracy rate of only 62.7% in cases of teeth with wide apices, often showing shorter working length as incorrect measurements [9].Our results mainly correspond to these findings meaning that electroodontometry can be suprisingly unprecise in immature teeth with a tendency to record shorter working lenghts.Various studies have indicated that a difference of ± 0.5 mm in electroodontometry measurements is clinically acceptable [13,14,15].In our research, the average difference of working lenghts determined with electroodontometry is within this range, even though it varies the most from the initial working lenght in comparison to other methods.
In teeth with open apices the radiographic interpretation of canal length can be difficult due to a different apical structure and the missing periodontal ligament space at the root apex [16].Although, radiography is the main method of determining working lenght during endodontic treatment of immature permanent teeth, variations are frequent among the imaging tehnique used [1].With a correct imaging technique magnification and image distortion can be minimized, but a certain amount of these phenomena is unavoidable [17].
Radiographic methods may lead to overinstrumentation, due to showing a longer canal length [14].The main reason is the fact that the apical foramen is frequently (92%) located short of the apex and the length of the measuring file appears radiographically shorter than its actual length [15].In our study measurments with radiographic method were the most precise.This can be due to that the parameter for defining the deviations was the canal lenght measured on the initial radiograph.In the literature there are statements that the success rate of endodontic treatment using the Raypex5 electronic apex locator and radiographic measurement are quite similar [1].The benefits of electroodontometry in addition to eliminating radiation exposure is that apex locators are superior in reducing overestimation during odontometry compared to radiographic canal lenght deternination [18].In our study we conclude that comparing single measurements radiographic odontometric method is more precise, but there was no statistically significant difference comparing all the results gained with electroodontometry and radiographic method.
The accuracy of Tactile Method, measured in teeth with open apices was found to be high (over 97%) [13,14,16].ElAyouti et al. described a tactile method using a size 25 file with a bent tip, their results show that this method may offer an alternative to other methods, as 97,7% of measurements were in the range of ±0.5mm to actual canal lenght [19].Our results agree with these findings since the average difference for tactile method was 0.213 mm, also within the clinically acceptable range.During measuring usingtactile method there were some unscertainties in one case with 5 mm deviations observed in multiple working lenght determination attempts.
Using paper point method there were some issues with defining the correct length in two first molars, when repeatedly a dry canal could not be obtained.The control of moisture is difficult because the contact area to the periapical tissues is wide, especially in cases with periapical inflammation an excess moisture is inevitable [19,20].Also, to determine precise measurements the periapical tissue must be located at the same level of the apical foramen, a requirement which may not be present in immature permanent teeth, since periapical tissues can extend in the canal up to 3mm [21].
Our results agree with earlier published statements by ElAyouti et al. [19] and Gurtu et al [22] who noted difficulties in the usage of tactile and paper point method in curved and narrow canals, contrary to expected success in anterior teeth with wide canals withoptained moisture control.
Study limitations include the possible risk of error in reproducibility during measuring and relatively small sample sizes.Further the study reflects a single center experience.In two cases there was a problem in defining the correct lenght with paper point method, when repeatedly a dry canal could not be obtained.With tactile method there were some unscertainties in one case when the examinor decided to use the mean value of four measurements.

Conclusion
The radiographic method and tactile method stand out as dominant methods for odontometry in permanent immature teeth, thanks to highly accurate readings.On the other hand, electroodontometry is the most unreliable method for determining working length in immature permanent teeth.Defining a precise protocol and golden standard method for working lenght determination in permanent immature teeth remains to be an objective in the field of endodontics.

Figure 1 .
Figure 1.Differences between working lenghts measured (mm) on the initial radiograph and various clinical odontometric methods.

Table 1 .
Statystical analysis of measured working lengths using different clinical methods