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.

Motives for studying dental medicine in Germany.

INTRODUCTION: Aim of this study was to investigate the motives for studying dental medicine of pupils and students accepted for first semester. METHODS: Motives of pupils from secondary schools (grades 10-12) around Tübingen and accepted students at the Dental School Tübingen were evaluated using a five-level Likert scale. Information about age, gender, family, apprenticeship and university enrolment was also included in the assessment. RESULTS: A total of 402 out of 409 participants filled out the questionnaires. Of these, 390 (280 females and 110 males) could be evaluated; the mean age was 17.4 years. Sixty-one planned an apprenticeship and 64 already completed it; 93 were readily accepted at university. All participants highly rated the motives "help patients" and "good career prospects." As next, women chose "diversified activity" and men "scientific interest." Participants who planned an apprenticeship rated "help patients" significantly higher than the other participants, whilst the motive "high responsibility of the dental profession" amongst interviewees with completed apprenticeship was highly significant in comparison with the rest. CONCLUSION: Empathy for patients and high responsibility of the dental profession are more important than prestige or social standing. An apprenticeship seems to greatly influence the career choice by giving more weight to "high responsibility of the dental profession." In future, such results can help universities design selection tests to target specific groups. The high proportion of female dentists and the attitude towards work and family of the generations Y and Z may bring change to the traditional practice model in Germany.

Real-Time Guided Endodontics with a Miniaturized Dynamic Navigation System Versus Conventional Freehand Endodontic Access Cavity Preparation: Substance Loss and Procedure Time.

INTRODUCTION: This study aimed to evaluate substance loss and the time required for access cavity preparation (ACP) using the conventional freehand method (CONV) versus a miniaturized dynamic navigation system of real-time guided endodontics (RTGE) in an in vitro model using 3-dimensional-printed teeth. METHODS: Nine human anterior maxillary teeth were selected and micro-computed tomographic scanned. Root canals were virtually reduced to 2 mm below the cementoenamel junction. The teeth were digitally duplicated and mirrored to yield 6 different models with 6 single-rooted teeth each. The models were 3-dimensionally printed using radiopaque resin and consecutively mounted on a dental mannequin for ACP. Two operators with 12 and 2 years of clinical experience, respectively, received 6 models (36 teeth) each and performed ACP on half of the models using RTGE (after digital planning) and CONV on the other half 2 weeks later. The time was recorded. Postoperative substance loss was measured by cone-beam computed tomographic imaging. The differences in time and substance loss between the methods and operators were evaluated by the t test. RESULTS: Overall, substance loss was significantly lower with RTGE than CONV (mean = 10.5 mm3 vs 29.7 mm3), but both procedures took a similar time per tooth (mean = 195 vs 193 seconds). Operator 1 (more experienced) achieved significantly less substance loss than operator 2 with CONV (mean = 19.9 vs 39.4 mm3) but not with RTGE (mean = 10.3 vs 10.6 mm3). CONCLUSIONS: RTGE is a practicable, substance-sparing method performed in comparable time as CONV. Moreover, RTGE seems to be independent of operator experience.

Apical Pressure Generated Using Conventional Syringe Irrigation in Immature Teeth-An In Vitro Study.

This in vitro study aimed to evaluate apical pressure during irrigant delivery with syringe irrigation in immature teeth with an open apical foramen. Conventional syringe irrigation was performed in a 3D-printed immature incisor. A 5 mL syringe combined with 25 G and 30 G cannulas was used. Open-ended and side-vented needle tip designs were assessed. Cannulas were placed at tooth length (TL), TL -1 mm, TL -2 mm, and TL -4 mm. The syringe plunger was moved with a force of 10 N, 20 N, 40 N, and 80 N to simulate clinical conditions. A pressure sensor measured periapical pressures during irrigation. Each experiment was repeated 10 times. Data were analyzed descriptively (maximum, mean, standard deviation, 95% CI) with the critical threshold indicative of extrusion set at 7.64 mbar. 30 G cannulas with both needle tip designs never exceeded the threshold at any TL with a plunger force of 10-40 N. At 80 N, 30 G open-ended cannulas exceeded the threshold in 10%, 30 G side-vented in 20-60% of the measurements. At any TL, 25 G open-ended cannulas and 25 G side-vented cannulas never crossed the threshold with forces of 10-20 N and 10 N, respectively. Consequently, 30 G cannulas with both designs can be recommended for irrigant delivery in immature teeth. 25 G cannulas ought to be used with caution.

Microarchitecture of medication-related osteonecrosis of the jaw (MRONJ); a retrospective micro-CT and morphometric analysis.

Medication-related osteonecrosis of the jaw (MRONJ) is a severe side effect of antiresorptive (AR) drugs such as bisphosphonates (BP) and denosumab (Dmab). Although several risk factors are described, the etiology of MRONJ is still not fully elucidated. Bone-strengthening is the primary aim of antiresorptive therapy; however, overly increased bone mass and microcrack accumulation are also discussed in MRONJ etiologies. The aim of this study is to evaluate the microarchitecture of jaw bones with micro-computed tomography (micro-CT) in AR-treated patients with or without MRONJ. Human jaw bone samples of AR-treated patients were separated into 11 groups by AR treatment bisphosphonate (BP), denosumab (Dmab), both (M) and control groups. Subgroups were divided according to the clinical localization as AR-exposed vital jaw bone (BPexp, Dmabexp, Mexp), osteonecrosis-margin of a sequestrum (BPOmar, DmabOmar, MOmar) and osteonecrosis-sequestrum (BPOseq, DmabOseq, MOseq). Healthy jaw bone (CHB) and osteoporotic jaw bone (COP) represent control groups. Samples underwent retrospective micro-CT and morphometric analysis in representative units by bone volume fraction (BV/TV), bone surface density (BS/BV), trabecular thickness (Tr.Th.), trabecular number (Tr.N.), trabecular space (Tr.Sp.), Euler characteristic for bone connectivity, bone mineral density (BMD) and tissue mineral density (TMD). A total of 141 samples from 78 patients were analyzed. BV/TV of Mexp group (mean: 0.46 ± 0.27) was significantly higher than in the COP group (mean: 0.14 ± 0.05; p = 0.0053). Tr.Th. differed significantly between the BPexp group (mean: 0.32 ± 0.15) and the Mexp group (mean: 0.57 ± 0.20; p = 0.0452) as well as between the BPOseq group (mean: 0.25 ± 0.10) and the MOseq group (mean: 0.39 ± 0.18; p = 0.0417). Signs of trabecular thickening and unorganized trabecular microarchitecture from AR-exposed- to sequestrum groups, were analyzed in 3D reconstructions. However, BS/BV, Tr.N., and Tr.Sp. showed no significant differences. Euler characteristic of the BPOseq group (median: 7.46) doubled compared to that of the BPexp group (median: 14.97; p = 0.0064). Mineralization parameters BMD and TMD were similar in all groups. Findings show evidence of enhanced bone mass and suspect microarchitecture in some AR-treated jaw bone compared to osteoporotic jaw bone. Despite increased bone mass, some MRONJ samples showed decreased trabecular connectivity by Euler characteristic compared to AR-treated jaw bone. These samples may indicate extensive ossification and ineffective bone mass with superficially higher bone mass without existing or even reduced mechanical stability, indicated by connectivity loss. This result might also suggest a high risk to microcrack accumulation. At some point, possibly some kind of over-ossification could lead to under-nourishment and microarchitectural weakness, creating instability, subsequently increasing vulnerability to MRONJ.

The Effect of Various Plasma Gases on the Shear Bond Strength between Unfilled Polyetheretherketone (PEEK) and Veneering Composite Following Artificial Aging.

This study investigated the effect of different gaseous plasma surface treatments on the shear bond strength between unfilled polyetheretherketone (PEEK) and veneering composite resin. The study followed ISO 10477 guidelines in preparing, bonding, and testing the samples. Specimens of unfilled PEEK were distributed to one of the following six surface treatment groups: reference, adhesive, argon, nitrogen, oxygen, and air plasmas. After milling, the specimens were wet polished using (P320) polishing discs. Bonding procedures were done according to the manufacturer's instructions using (Opaquer + Dentine), except in the adhesive group (Visio.link + Opaquer + Dentine). Afterwards, thermal cycling for 5000 cycles between 5 and 55 °C in distilled water was conducted. Finally, the shear bond strengths of all groups were calculated, and mode of fracture was determined. Nitrogen surface treatment had the highest mean shear bond strength of 10.04 (±1.84) MPa, while the reference group showed the lowest value of 5.38 (±2.90) MPa. Regarding mode of fracture, all the specimens showed a 100% adhesive failure mode. Plasma surface treatment can be a reliable alternative method to the traditional protocol of bonding veneering composite resin to unfilled PEEK material.

Guided Endodontics versus Conventional Access Cavity Preparation: A Comparative Study on Substance Loss Using 3-dimensional-printed Teeth.

INTRODUCTION: The aim of this in vitro study was to compare endodontic access cavities in teeth with calcified root canals prepared with the conventional technique and a guided endodontics approach regarding the detection of root canals, substance loss, and treatment duration. METHODS: Six identical sets of upper and lower jaw models were produced with 3-dimensional-printed incisors that had simulated calcified root canals. Splints for guided access preparations were fabricated based on 3-dimensional surface scans and cone-beam computed tomographic data sets. Under simulated clinical conditions, 3 operators with different levels of experience prepared access cavities on each front tooth with the conventional technique and guided endodontics (8 teeth per technique and operator). Access cavities were volumetrically assessed on postoperative cone-beam computed tomographic scans. Statistical significance was tested by examining the overlap of 95% confidence intervals (CIs). RESULTS: Canal location was successful in 10 of 24 cases (41.7%) using the conventional technique and 22 of 24 cases (91.7%) with the guided approach. The mean substance loss of the conventional access and the guided access was 49.9 mm3 (95% CI, 42.2-57.6 mm3) and 9.8 mm3 (95% CI, 6.8-12.9 mm3), respectively. The treatment lasted 21.8 minutes (95% CI, 15.9-27.7 minutes) for the conventional technique and 11.3 minutes (95% CI, 6.7-15.9 minutes) for guided endodontics. The success of the guided approach was not influenced by the experience of the operator. CONCLUSIONS: Guided endodontics allows a more predictable and expeditious location and negotiation of calcified root canals with significantly less substance loss.

Clinical course and therapeutic outcomes of operatively and non-operatively managed patients with denosumab-related osteonecrosis of the jaw (DRONJ).

PURPOSE: Details regarding risk factors, onset, and outcomes for denosumab-related osteonecrosis (DRONJ) are sparse. This study examines the clinical characteristics and operative and non-operative therapeutic outcomes in patients with DRONJ not previously exposed to other antiresorptives. METHODS: A retrospective medical record review was conducted, and data were collected, including clinical findings, management, healing outcomes, and radiologic, histologic, and micro-computed tomography (CT) analyses. RESULTS: Seventeen patients were treated with denosumab, with 14.1 ± 8.3 doses before DRONJ onset. The majority of lesions were observed at sites of dental prostheses (41%) and dental extractions (35%). Sixteen patients were managed non-operatively (10/16) or operatively (6/16) with either major (5/6) or minor surgery (1/6) and included in the follow-up analysis. Complete healing was significant in patients treated with major surgery (80%) compared to the non-operative group (20%; p < 0.035). Denosumab was discontinued in 60% of non-operative patients and major surgery patients with no effect on healing. Histologic findings of 4 patients analyzed exhibited a decreased number of osteocyte lacunae, and micro-CT of 3 patients scanned revealed trabecular thickening. CONCLUSION: DRONJ lesions occurred mostly at sites of prostheses sores after a mean of 14 doses of denosumab. Major surgery demonstrated more complete healing than non-operative management, and denosumab cessation did not improve healing outcomes.

Treatment of calcified root canals in elderly people: a clinical study about the accessibility, the time needed and the outcome with a three-year follow-up.

OBJECTIVE: Determination of accessibility, time needed and outcome of endodontic treatment of teeth with calcified root canals in a sample of elderly participants in a private practice limited to endodontics. BACKGROUND: Due to demographic changes, gerodontology is becoming more and more important, also in the field of endodontology. Elderly patients can show up with severe calcifications of root canals. Root canal treatment, when needed, can be very challenging in these cases. Only few data exist about the treatment of calcified root canals and its outcome, especially in an elderly population. MATERIALS AND METHODS: Forty-one participants (median age: 72 years) needing a root canal treatment were included. The total number of treated teeth was 41 with 114 negotiated root canals. A specialist limited to endodontics performed the treatment in a private practice. Outcome was assessed by applying the periapical index score on the basis of recall radiographs provided by the referring dentists. Likewise, time required to localise the root canals was measured. RESULTS: All root canals have been detected using the operating microscope, and full working length could be established in 90% of the cases. Success rate was 80% after an observation time of 3 years. In three of five teeth, root canals could be localised within 15 min. CONCLUSION: Calcified root canals of older people treated in this study were all accessible within a maximum of 60 min. The success rate after a follow-up of 3 years was 80%.

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.

Neurosensory impairment of the mental nerve as a sequel of periapical periodontitis: case report and review.

Apical periodontitis of endodontic origin rarely leads to sensory impairment of the inferior alveolar or mental nerve. This article reviews and documents a clinical case of neurological disorder where paresthesia and hypesthesia of the mental nerve resulted as a sequel of apical periodontitis of a mandibular second premolar. The healing process and long-term results 3 years after conventional root canal treatment are presented.

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."

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.

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.

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.