Abstract
Aim
The present study investigated the accuracy of root canal preparation with regard to the integrity of the apical constriction (AC) using two different working length determination approaches: (1) the electronic method of working length determination (EWLD), and (2) the radiologic “gold standard” method (GS).
Methodology
Simulation models were constructed by arranging extracted human teeth by means of silicon bolstered gingiva masks, along with a conductive medium (alginate). Electronic working length determination (group 1; EWLD) and radiologic plus initial electronic working length determination for posterior comparability (group 2; GS) preceded manual root canal preparation of teeth in both groups. Master cones were inserted according to working lengths obtained from the group specific method. Subsequently, root apices (n = 36) were longitudinally sectioned using a diamond-coated bur. The distance between the achieved apical endpoint of the endodontic preparation and the apical constriction (AC) was measured using digital photography. Then, distances between radiologically identified apical endpoints and AC (GS–AC) were compared with the corresponding distances EWLD–AC. Moreover, the postoperative status of the AC was examined with regard to both preparation approaches.
Results
Differences between distances GS–AC and EWLD–AC were not statistically significant (p > 0.401) (Mann-Whitney-U). Among EWLD samples, 83% of the master cones exhibiting tugback at final insertion terminated close to the apical constriction (±0.5 mm), and no impairment of the minor diameter’s integrity was observed.
Conclusions
The sole use of EWLD allowed for a high accuracy of measurements and granted precise preparation of the apical regions.
1
Introduction
During root canal instrumentation, maintaining the integrity of the existing apical constriction (AC) is considered essential. Regarding the small diameter of this anatomic structure (0.15–0.35 mm) and its varying average distance towards the most apical part of the root (0.5–2.0 mm) , it seems challenging to protect the AC from alterations during preparation procedures. The latter might result in impaired biological functions of the periodontium, along with an increased probability of apical extrusion of used sealers, and with a decreased prognosis for the whole treatment .
Previous studies have proven that enlargement of the apical constriction in the course of root canal preparation induced inflammatory reactions and stronger postoperative nociception due to an increased transmission of bacteria to the periapical tissues . In case of any foraminal enlargement the postoperative perception of pain occurred significantly more often, whereby both an increased severity of pain and a prolonged interval of postoperative nociception has been described; this represented a remarkable contrast if compared to the control group with a maintained apical constriction’s integrity . A preparation approximating the apical constriction as precise as possible thus might chemo-mechanically reduce the microorganisms in the canal system to the greatest extent. In addition, the following risks would seem to decrease: For one thing the transmission of debris and bacteria causing periapical inflammation, and for another the extrusion of root canal filling materials initiating inflammatory foreign body reactions in the periapical tissue . The complete root canal instrumentation terminating at the apical constriction might prevent the development of chronic inflammatory periapical periodontitis, thus reducing further corrective treatment needs (like endodontic revisions and/or apicoectomies) .
Nowadays, determination and localization of the apical constriction is possible using electronic root canal length measurement devices (ERCLMD), also known as electronic apex locators (EAL). Considering the high reliability, accuracy, and reproducibility of electronic measurements, this method has gained wide acceptance by both the scientific community and many practitioners . Under clinical conditions, ERCLMD alone (or in combination with conventional radiography) has been reported to reduce the risk of instrumenting and filling beyond the apical foramen . Thus, recommendations of the German Society for Dental, Oral and Maxillofacial Medicine (DGZMK) with respect to the endodontic working length determination suggest that the combination of electronic working length determination (EWLD) and radiologic methods (“gold standard”; GS) provides the most accurate measurements . Moreover, both the American Association of Endodontists (AAE) and the European Society of Endodontology (ESE) have recommended to confirm the electronically determined working lengths by means of additional radiographs .
However, it remains unclear to which extent this additional radiologic approach does influence the success of the mechanical part of the root canal treatment. On the one hand, radiography (except for clinically not well established 3D radiographs for endodontic purposes) seems to be suitable for adequate working length determination only to a limited degree ; on the other hand, the use of ERCLMD indeed allows for identification of the apical constriction . Notwithstanding, there is only limited information on the AC’s integrity after completion of the root canal preparation performed by sole use of the ERCLMD. Previous studies have demonstrated that for all investigated tooth types the average position of the apical constriction is located between 0.51 and 0.59 mm coronally to the major diameter; likewise, the ability of ratio-method based endometric devices to locate the constriction with an average distance of 0.54 mm has been documented .
Causes for the absence of comprehensive statements regarding the post-operative integrity of the apical constriction are easily intelligible; clinical investigations using teeth worth preserving are not considered suitable to enlighten these questions for ethical reasons (except for teeth intended to being removed ), and in vitro models often do not fulfil the requested conditions for evaluation by means of ERCLMD . The present study aimed to develop an appropriate simulation model allowing for extra-oral electrometric working length determination, followed by investigation of the accuracy of root canal preparation including the status of the AC using EWLD and GS methods. By determining the distances of both GS–AC and EWLD–AC, it was hypothesized (H 0 ) that the accuracy of root canal preparation achieved by sole use of the ERCLMD would not differ from the accuracy of root canal preparation based on conventional radiography. H 0 was tested against the alternative hypothesis of a difference (H A ). In addition, the postoperative integrity of the apical constriction was assessed for both approaches.
2
Materials and methods
2.1
Samples
Extracted human single rooted premolars featuring complete root formation without external root resorption were purchased (Enretec, Velten, Germany); teeth presenting one apical foramen were selected using a stereomicroscope (OPMI pico; Zeiss, Jena, Germany). Exclusion criteria comprised existing large restorations, incompletely formed apices as well as previously performed root canal treatments. All teeth were numbered and separately stored in disinfecting solution (Chloramine-T 0.5%, pharmacy-made; Apotheke zum Engel, Krems, Austria) to prevent dehydration and alterations due to storage. Due to German regulations regarding the use of body materials, no ethical approval was mandatory .
2.2
Selection of appropriate teeth
The selection was conducted using an in-house developed radiographic holding device (Unvarying X-ray; Glaserei Salomon, Krems, Austria) to enable precise, non-overlapping assessments, and reproducibility. Integrated guidance elements allowed for repeated and constant alignment of the X-ray tube perpendicular to tooth and sensor, both arranged in parallel order . Thereby, samples were fixed in retrievable positions and constant distances towards both X-ray tube and sensor. SIDEXIS XG (Dentsply Sirona, Bensheim, Germany) and ImageJ v.1.50c4 (National Institutes of Health, Bethesda, MD, USA) were used for digital analysis. Calibration of electronic measurement instruments was performed by integration of a standardized lead ball. Based on its known diameter a generally valid spatial scale was defined, thus allowing for radiologic sample analyses. For each applicable specimen the pulp canal’s external circumscription was traced, and cross-section dimensions adjoining coronal and next to the minor diameter were measured ( Fig. 1 ; Panels I and III). Based on these premeasured initial radiographs, teeth (n = 36) were intentionally allocated with regard to each root canal’s apical diameter and curvature to groups A (EWLD) or B (GS), thus ensuring uniform distribution of root canal anatomies.
2.3
Model fabrication
The model was fabricated jointly by one of the investigators (MJG) and the technicians of the in-house dental laboratory (Danube Private University, Krems, Austria). Each group was arranged in the lateral regions of silicon bolstered gingiva masks that were inserted into universal X-ray models (A-RE; Frasaco, Tettnang, Germany). The apical part of each root was embedded in alginate blended with sodium chloride solution (0.9%, Ecoflac Plus; B. Braun, Melsungen, Germany) ; incorporation of one lip clip (VDW, Munich, Germany) per model assured a conductive environment providing appropriate conditions for impedance measurements. Stability during preparation procedures was ensured by use of a customized vacuum-formed matrix.
2.4
Treatment
Prior to the treatment, initial radiographs were taken using a paralleling technique, and these were evaluated to determine approximate working lengths. To simulate the clinical environment, the models were mounted into dental phantom heads (Frasaco) before implementing the preparation protocols . Subsequently, access cavities were prepared under copious water-cooling using a diamond-coated bur (# 806 314 5455 14 016; Komet, Lemgo, Germany). After exposure of the root canal orifices, exploration of the root canals with appropriate file sizes (≤ ISO size 15) (VDW) and coronal preflaring using FlexMaster IntroFiles (VDW) followed, thus allowing for pressureless insertion of the instrument into the canal lumen.
With the teeth of group A, an ISO 15 K-type file (VDW) was inserted until the third green LED was displayed on the ERCLMD (VDW.GOLD RECIPROC; VDW), thus indicating the desired working length. In case of initial non-accessibility of the working length, descending ISO sizes (files # 10, 08, and 06) were applied. With the teeth of group B, the initial instrumentation was performed by means of ISO 15 K-type files (VDW), adjusted to the preoperatively estimated working length resulting from subtraction of 1 mm from the distance between the coronal reference point and the radiographic apex, and followed by insertion of silver cones (30 mm; ISO 15; VDW).
An intraoral X-ray source (Heliodent Plus/SIDEXIS; Dentsply Sirona) was used for radiography. Based on each silver cone’s (VDW) actual length (L real ), its radiographic extent (L rad ), the distance between silver cone tip and radiologic apex (ΔL rad ), and the true distance (ΔL real ) were calculated by means of the formula: ΔL real = (L real × ΔL rad )/L rad . Subsequently, the root canals were prepared with K- and H-type files (VDW) using crown-down and step-back techniques, along with repeated irrigation using sodium hypochlorite (2.5%; Apotheke zum Engel). All instrumentations were performed to ISO size 35 of the master apical file, followed by a step-back procedure (in steps of 0.5 mm) to the final file (ISO size 50).
2.5
Investigation of the specimens
After finishing the preparation procedures, ISO size 35 master cones (VDW) exhibiting tugback at final insertion were placed according to the respective working lengths. To secure immobility of the master cones, access cavities were sealed with composite resin (G-ænial Flo A3; GC, Leuven, Belgium). For analysis, recollected and disassembled teeth were fixed using the aforementioned radiographic holding device. Each master cone recording was superimposed with the respective initial assessment of the radiograph; thus, the distance between the master cone’s tip and the minor apical diameter’s most coronal point could be determined ( Fig. 1 ; Panels II and IV). Then, to evaluate and to depict the actual outcome of the apical instrumentation, vertical cuts of the root apices were performed using a diamond-coated bur (# 806 314 156 514 012; Komet), along with an in-house constructed grinding/supporting device consisting of a cross table (Proxxon 20150 Kreuztisch KT 150; Proxxon, Föhren, Germany), a milling machine (Proxxon 20,000 Bohr- und Fräsbank BFB 2000; Proxxon), and a dedicated tooth fixture (Repladent; E. Hahnenkratt, Königsbach-Stein, Germany). Once the root canal was longitudinally exposed, it was selectively ground until its largest diameter was reached. Consequently, photographs were taken at 25-fold magnification using a video camera integrated to a stereomicroscope (Zeiss), followed by digital image processing (ImageJ) ( Fig. 2 ; Panels V and VII). Distances between AC and the radiologically (GS–AC) determined apical endpoints of the endodontic preparation were compared with the corresponding distances EWLD–AC. Finally, with respect to both preparation approaches the postoperative status of the AC was examined to allow for a percentage comparison.
2.6
Statistical analysis
Statistical analyses were performed using a dedicated statistical software package (SAS 9.3; SAS Institute, Cary, NC, USA). Data were checked for normal distribution using the Kolmogorov-Smirnov test. The differences between distances GS–AC and EWLD–AC were compared using Mann-Whitney-U-, Levene’s, and Student’s t -tests. The level of significance was set at p < 0.05.
2
Materials and methods
2.1
Samples
Extracted human single rooted premolars featuring complete root formation without external root resorption were purchased (Enretec, Velten, Germany); teeth presenting one apical foramen were selected using a stereomicroscope (OPMI pico; Zeiss, Jena, Germany). Exclusion criteria comprised existing large restorations, incompletely formed apices as well as previously performed root canal treatments. All teeth were numbered and separately stored in disinfecting solution (Chloramine-T 0.5%, pharmacy-made; Apotheke zum Engel, Krems, Austria) to prevent dehydration and alterations due to storage. Due to German regulations regarding the use of body materials, no ethical approval was mandatory .
2.2
Selection of appropriate teeth
The selection was conducted using an in-house developed radiographic holding device (Unvarying X-ray; Glaserei Salomon, Krems, Austria) to enable precise, non-overlapping assessments, and reproducibility. Integrated guidance elements allowed for repeated and constant alignment of the X-ray tube perpendicular to tooth and sensor, both arranged in parallel order . Thereby, samples were fixed in retrievable positions and constant distances towards both X-ray tube and sensor. SIDEXIS XG (Dentsply Sirona, Bensheim, Germany) and ImageJ v.1.50c4 (National Institutes of Health, Bethesda, MD, USA) were used for digital analysis. Calibration of electronic measurement instruments was performed by integration of a standardized lead ball. Based on its known diameter a generally valid spatial scale was defined, thus allowing for radiologic sample analyses. For each applicable specimen the pulp canal’s external circumscription was traced, and cross-section dimensions adjoining coronal and next to the minor diameter were measured ( Fig. 1 ; Panels I and III). Based on these premeasured initial radiographs, teeth (n = 36) were intentionally allocated with regard to each root canal’s apical diameter and curvature to groups A (EWLD) or B (GS), thus ensuring uniform distribution of root canal anatomies.
