A critical analysis of research methods and experimental models to study working length determination and the performance of apex locators - A narrative review with recommendations for the future.

Outcome studies have repeatedly shown that the apical endpoint of root canal preparation and filling is a determinate factor for the outcome of root canal treatment. Accurate determination of root canal length enhances the efficacy of chemo-mechanical disinfection and prevents over-/under-instrumentation and over-/under-filling in relation to the canal terminus. Long and short root canal fillings are consistently reported to be associated with higher rates of post-treatment endodontic disease. Although standards for undertaking and reporting diagnostic accuracy studies are available, publications dealing with the determination of root canal length are highly heterogeneous and describe procedures inconsistently. The aim of this review is to critically assess the methodology of publications in the past three decades. The process of planning, performing and analysing working length studies are presented stepwise with suggestions to optimize research methods.

Accreditation of postgraduate speciality training programmes in Endodontology. Minimum criteria for training Specialists in Endodontology within Europe.

This consensus statement from the European Society of Endodontology (ESE) sets out the minimum criteria for training Specialists in Endodontology within Europe. The case is made for recognizing Endodontology as a distinctive dental discipline throughout Europe. Guidelines are presented on the requirements of a specialist and of a specialist training programme in Endodontology. The aims, objectives and curriculum content of a specialist training pathway are outlined, with guidelines on trainee appraisal, and the expectations of faculty and institutional commitment. In publishing these guidelines, the ESE is responding to a public and professional need for consistently high standards of training and specialist clinical service within Europe.

Homogeneity and adaptation of a new gutta-percha paste to root canal walls.

A new flowable root canal filling material (GuttaFlow) was tested. Under simulated clinical conditions, the middle and coronal thirds of 90 human teeth with 169 root canals were shaped with 6% taper rotary HERO instruments and the apical third with rotary LightSpeed instruments. The root canals were divided into three similar groups and were filled with GuttaFlow (GF), conventional cold laterally condensed gutta-percha (LC), and warm vertically condensed gutta-percha (VC). Roots were sectioned at five levels, digitally photographed and traced. The percentage of voids area showed a statistically significant difference between GF and both LC and VC [GF 1.9% (95% CI = 1.4-2.4), LC 4.4% (95% CI = 2.2-6.6), VC 6.8% (95% CI = 5.4-8.1)]. The frequency of voids was significantly different between all groups [GF 37% (95% CI = 34%-40), LC 10% (95% CI = 8-12), VC 22% (95% CI = 19-24)]. In most sections, GuttaFlow completely filled the prepared root canal, but small voids were frequently present within the core of the filling material.

The ability of root ZX apex locator to reduce the frequency of overestimated radiographic working length.

The aim of this in vitro study was to evaluate the ability of the Root ZX device to avoid instrumentation beyond the apical foramen in premolars after conventional working length radiography. Thirty extracted premolars with 43 root canals were subjected to radiographic and electronic working length determination. Radiographic working length determination resulted in overestimation in 51% of the root canals, although the measuring file tip was located to be 0 to 2 mm short of the radiographic apex. Electronic working length measurements with the Root ZX reduced the percentage of overestimation to 21%. In 6 root canals (14%), both radiographic and electronic working length measurements led to overestimation. It is concluded that complementing radiographic working length determination with electronic apex locator measurements may help to avoid overestimation beyond the apical foramen in premolars.

Efficiency of hand and rotary instruments in shaping oval root canals.

This study was designed to determine the efficiency of hand and rotary instruments in shaping oval root canals. Seventy-five oval canals were equally divided into three groups. The apical third was prepared with rotary LightSpeed instruments either to size 52.5 (mandibular incisors) or to size 57.5 (distal root of mandibular molars). The middle third with an oval cross-section was shaped with Hedström hand files using circumferential technique, with 6% taper rotary Hero files in a circumferential filing movement or with rotary LightSpeed instruments in a step-back technique. Instrumentation was performed under clinical conditions in a phantom head. The teeth were sectioned at two levels in the middle third of the root. An assembly technique allowed comparing the canal outline before and after instrumentation. The photographed root sections were superimposed and traced under a stereomicroscope. The ratio of prepared to unprepared canal outline was calculated for each section. The lowest values were observed in the LightSpeed group (mean: 0.42; 95% confidence interval (CI): 0.37; 0.47). Significantly higher values were recorded in the Hero group (mean: 0.58; 95% CI: 0.53; 0.64) and in the Hedström group (mean: 0.56; 95% CI: 0.49; 0.62). No instrumentation technique was capable of completely preparing dentin walls of oval root canals. Circumferential filing of the middle third of oval root canals with either 6% taper Hero files or conventional Hedström hand files gave comparable results.

Apical constriction: location and dimensions in molars-a micro-computed tomography study.

INTRODUCTION: The existence of the apical constriction has been repeatedly questioned. The aim of the present study was to validate the existence of the apical constriction and determine its location and dimensions in molars by using substantial micro-computed tomography analysis. METHODS: Ninety human molars with 271 canals were evaluated. Teeth with resorption, defects, or incomplete root formation as well as wisdom teeth were excluded. Patients' age was categorized into 3 groups. Teeth were scanned by micro-computed tomography with a resolution of 27 µm. Multi-threshold segmentation was performed to trace the canal outline in a total of 25,093 sections. In each cross section, 88 parameters, eg, area, circumference, and maximum and minimum diameter were recorded and analyzed. The apical constriction (AC) was defined to be the narrowest area extending along a distance of 0.1 mm or more at the apex. Size and form of the constriction were recorded as well as the distance to the apical foramen (AC-AF) and apex (AC-A). RESULTS: The mean distance of AC-AF was 0.2 mm (99% confidence interval, 0.15-0.24; range, 0-0.6 mm), and of AC-A it was 0.9 mm (99% confidence interval, 0.86-1.0; range, 0.1-1.7 mm). The type of canal had no influence on AC-AF and AC-A. In 76% of all canals the apical constriction was parallel. The mean size of constriction in molars was instrument size 30. Patients aged 30 or younger had significantly wider constrictions. CONCLUSIONS: The apical constriction was found to be located at or close to the foramen. The most common form was the parallel form.

Increased apical enlargement contributes to excessive dentin removal in curved root canals: a stepwise microcomputed tomography study.

INTRODUCTION: To determine whether increased apical enlargement would result in a complete preparation of curved canals and to progressively assess shaping quality using multiple microcomputed tomography (MCT) scans. METHODS: Ninety root canals with a curvature of 25° to 50° were selected. Five MCT scans, 1 preoperative and 4 postoperative, were acquired from each canal. Canal preparation was performed up to size 50 using 3 techniques, nickel-titanium (NiTi) hand files, Mtwo (VDW, Munich, Germany), and ProTaper (Maillefer, Ballaigue, Switzerland), by experienced operators in a dental mannequin so as to simulate the clinical conditions. At a level of 1 mm short of the working length, 2 parameters were evaluated in each of the 4 postoperative acquisitions: the percentage of the prepared outline and the amount of dentin removed (the prepared area). RESULTS: Statistically, there was no significant difference between the 3 systems used regarding the prepared outline. The maximum prepared outline was achieved by the use of NiTi hand files (63%; confidence interval [CI], 54%-73%), whereas Mtwo and ProTaper amounted to 58% (CI, 50%-66%) and 60% (CI, 51%-70%), respectively. In contrast, the dentin area removed by ProTaper was significantly higher than that of Mtwo and NiTi hand files. CONCLUSIONS: Increased apical enlargement of curved canals did not result in a complete apical preparation, whereas it did lead to the unnecessary removal of dentin.

Determining the apical preparation size in premolars: part III.

OBJECTIVE: The objective of this study was to investigate cross sections of the apical part of premolar root canals and determine recommendations for their optimal apical preparation size. METHODOLOGY: A total of 140 root canals from extracted human premolars (86 maxillary, 54 mandibular) were selected. After preflaring, the electronic working length (WL) was measured to identify where the apical preparation size (APS) should be established. Subsequently, nontapered, noncutting special instruments (SI) were used to reach the WL. The diameter of the largest SI width that reached the WL was defined as d(SI). The roots were apically sectioned at 2 levels, and the diameter of a potential rotary instrument was determined, allowing complete circumferential cutting of the root canal wall for each section. The estimation of APS was then related to d(SI). RESULTS: Apically enlarging upper premolars with 2 canals and lower premolars to an individual APS of d(SI) +0.3 mm (6 file sizes) resulted in a 71% to 75% complete preparation of the root canal walls, whereas an enlarged preparation of d(SI) +0.4 mm (8 file sizes) reached 82% to 96%. In upper premolars with a single canal, an APS of d(SI) +0.3 mm completely processed the root canal walls in only 37%, whereas an APS of d(SI) +0.4 mm reached 63%. CONCLUSIONS: The APS in 2-canal upper premolars and mandibular premolars should be at least 6 sizes larger than the first apically binding file, whereas in upper premolars with a central canal, the APS should be enlarged to 8 sizes larger. Normally, this implies shaping premolars with 1 canal to #60 to 70 and with 2 canals to #40 to 50.

Homogeneity and adaptation of endodontic fillings in root canals with enlarged apical preparation.

OBJECTIVE: The aim was to compare the homogeneity and adaptation of endodontic fillings placed in root canals with wide apical preparation. STUDY DESIGN: One hundred twenty root canals were prepared under simulated clinical conditions. The range of apical preparation size was 45 (narrow canals) to 60 (wide canals). The canals were filled using 4 techniques: Thermafil, GuttaFlow, apical cone, and vertical compaction. The root canals were sectioned at 5 levels. The adaptation and homogeneity of the filling were evaluated and statistically analyzed. RESULTS: The percentage of canal outline in contact with the filling in the Thermafil group (91.3% [95% confidence interval (CI) 88.8%-93.6%]) was statistically significantly lower than in the other groups. No statistically significant differences were found between GuttaFlow (96.6% [95% CI 95.7%-97.5%]), apical cone (98.6% [95% CI 98.0%-99.3%]), and vertical compaction (98.1% [95% CI 96.5%-99.7%]). Similarly, the percentage of void area in Thermafil group (4.0% [95% CI 2.6%-5.3%]) was statistically significantly higher than in the other groups (GuttaFlow 1.4% [95% CI 0.1%-1.8%], apical cone 1.6% [95% CI 0.7%-2.4%], and vertical compaction 0.1% [95% CI 0.1%-1.8%]). CONCLUSIONS: The tested filling techniques/materials provided similar high values for the homogeneity and adaptation to root canal walls after enlarged apical preparation, except for Thermafil at the most apical level.

Consistency of apex locator function: a clinical study.

The consistency of apex locators was determined by calculating the dysfunction frequency. Electronic working length (EWL) was determined in 507 patients requiring endodontic treatment. Different clinical parameters were recorded including tooth vitality, presence of obliteration, and metallic restoration. Two apex locators were used (Root ZX [Morita, Tokyo, Japan] and Raypex5 [VDW, Munich, Germany]). Apex locator performance was considered "consistent" when the scale bars were stable and moved only in correspondence to the movement of file in the root canal. A working length radiograph with files set to the EWL was performed. EWL were considered "acceptable" when the file tip was located 0 to 2 mm short of the radiographic apex. The function of apex locators was consistent in 85% of the patients (429/507 [99% confidence interval, 80-88]). The inconsistent measurements were strongly associated with partially or totally obliterated root canals (p < 0.0001). Radiographically, 97% of consistent measurements were "acceptable."

A clinical method to determine the optimal apical preparation size. Part I.

OBJECTIVE: To establish a new approach for determination of the optimal apical preparation size (APS). STUDY DESIGN: After preflaring 212 root canals from 80 extracted molars, electronic working length (WL) was measured to establish where the apical preparation size (APS) should be determined. Subsequently, nontapered, noncutting special instruments were used to reach WL. The diameter of the largest special instrument (SI) width that had to overcome some resistance to advance to WL was defined as d(SI). After sectioning the roots apically, the diameter of a potential rotary instrument was determined for each section, allowing a complete cutting of the root canal wall. The estimation of APS was related to d(SI). RESULTS: Theoretically, individual APS of d(SI) + 0.60 mm yielded circumferential apical preparations in 98% of the cases. When shaping palatal/distal root canals of molars to d(SI) + 0.40 mm, and mesiobuccal/mesiolingual/distobuccal root canals of molars to d(SI) + 0.30 mm, complete preparations of root canal walls resulted in 78% (95% CI, 69%-87%) and 72% (95% CI, 65%-80%) of canals, respectively. CONCLUSION: The described approach allowed evaluation of the APS for most root canals. Root canals should be shaped to larger sizes than normally recommended.

Extended apical enlargement with hand files versus rotary NiTi files. Part II.

OBJECTIVE: The objective of this study was to compare 2 preparation techniques performed under simulated clinical conditions with extended apical enlargement following determination of the optimal apical preparation size (APS). STUDY DESIGN: After preflaring 240 root canals, APS was evaluated as outlined in Part I. The apical portion was shaped to APS either with rotary NiTi Lightspeed instruments (LS) or NiTi hand instruments (HA) using the balanced force technique in a phantom head. After sectioning the apical area at 3 levels, every cross section was analyzed microscopically for circumferential removal of canal wall dentine. Loss of working length, instrument separation, and perforation were additionally recorded. RESULTS: In 70% (LS) and 69% (HA) of the root canals, 2 of 3 levels demonstrated that the root canal dentin was cut circumferentially. Neither loss of working length nor perforation occurred in both groups. Four LS instruments separated. CONCLUSIONS: APS frequently results in a nearly complete apical preparation regardless of the preparation techniques. In a few cases apical enlargement to APS does not achieve complete cutting of the canal walls. There was a rather slight risk of serious procedural errors.