Root Canal Preparation with a Novel Nickel-Titanium Instrument Evaluated with Micro-computed Tomography: Canal Surface Preparation over Time

Assessing accumulated hard-tissue debris using micro-computed tomography and free software for image processing and analysis

INTRODUCTION

The accumulation of debris occurs after root canal preparation procedures specifically in fins, isthmus, irregularities, and ramifications. The aim of this study was to present a step-by-step description of a new method used to longitudinally identify, measure, and 3-dimensionally map the accumulation of hard-tissue debris inside the root canal after biomechanical preparation using free software for image processing and analysis.

METHODS

Three mandibular molars presenting the mesial root with a large isthmus width and a type II Vertucci's canal configuration were selected and scanned. The specimens were assigned to 1 of 3 experimental approaches: (1) 5.25% sodium hypochlorite + 17% EDTA, (2) bidistilled water, and (3) no irrigation. After root canal preparation, high-resolution scans of the teeth were accomplished, and free software packages were used to register and quantify the amount of accumulated hard-tissue debris in either canal space or isthmus areas.

RESULTS

Canal preparation without irrigation resulted in 34.6% of its volume filled with hard-tissue debris, whereas the use of bidistilled water or NaOCl followed by EDTA showed a reduction in the percentage volume of debris to 16% and 11.3%, respectively. The closer the distance to the isthmus area was the larger the amount of accumulated debris regardless of the irrigating protocol used.

CONCLUSIONS

Through the present method, it was possible to calculate the volume of hard-tissue debris in the isthmuses and in the root canal space. Free-software packages used for image reconstruction, registering, and analysis have shown to be promising for end-user application.

Irrigation of human prepared root canal--ex vivo based computational fluid dynamics analysis

AIM

To analyze the influence of the needle type, insertion depth, and irrigant flow rate on irrigant flow pattern, flow velocity, and apical pressure by ex-vivo based endodontic irrigation computational fluid dynamics (CFD) analysis.

METHODS

Human upper canine root canal was prepared using rotary files. Contrast fluid was introduced in the root canal and scanned by computed tomography (CT) providing a three-dimensional object that was exported to the computer-assisted design (CAD) software. Two probe points were established in the apical portion of the root canal model for flow velocity and pressure measurement. Three different CAD models of 27G irrigation needles (closed-end side-vented, notched open-end, and bevel open-end) were created and placed at 25, 50, 75, and 95% of the working length (WL). Flow rates of 0.05, 0.1, 0.2, 0.3, and 0.4 mL/s were simulated. A total of 60 irrigation simulations were performed by CFD fluid flow solver.

RESULTS

Closed-end side-vented needle required insertion depth closer to WL, regarding efficient irrigant replacement, compared to open-end irrigation needle types, which besides increased velocity produced increased irrigant apical pressure. For all irrigation needle types and needle insertion depths, the increase of flow rate was followed by an increased irrigant apical pressure.

CONCLUSIONS

The human root canal shape obtained by CT is applicable in the CFD analysis of endodontic irrigation. All the analyzed values -irrigant flow pattern, velocity, and pressure - were influenced by irrigation needle type, as well as needle insertion depth and irrigant flow rate.

The permanent deformation of the self-adjusting files when used in canals of extracted teeth

AIM

To examine the permanent deformation of self-adjusting files (SAF) when used by endodontists with no previous experience with this system.

METHODOLOGY

The canals of extracted human molars were initially prepared with glide path up to size 20 K-file. The operators were first instructed on the use of the SAF in simulated canals in plastic blocks then applied the SAF in natural root canals of extracted teeth. Every 4 min, each file was withdrawn from the canal and inspected for integrity. If intact, it was used in another canal for an additional 4 min and checked again. This was repeated until all 19 SAF files were deformed. The files were collected for inspection at ×50 magnification. All teeth were then examined radiographically for the presence of any metal fragments in the root canals. Permanent deformation was categorized according to the type and location occured. Three types were defined as follows: (i) detachment of one component of the file at one end while the component is retained (ii) detachment of a component at both ends and the component missing and (iii) permanent twisting of the component. Recordings were made and statistically analysed using McNemar's test.

RESULTS

Mechanical failures on the 5-arch-side of SAF (odd side) were significantly more frequent in comparison with the even side (P = 0.039). Similarly, mechanical failures in arches on the odd side were also significantly more frequent compared with the even ones (P = 0.012) Longitudinal beams fractured significantly less often compared with arcs or struts (P < 0.001). In no case did complete file fracture occur, nor were metal fragments retained in the root canal.

CONCLUSIONS

Deformation of SAF files occurred mainly as detachment of one of the arches or struts at connection points on the odd side of the file. In no case did its mechanical failure result in metal fragment retention in the root canal.

A comparative study of biofilm removal with hand, rotary nickel-titanium, and self-adjusting file instrumentation using a novel in vitro biofilm model

INTRODUCTION

This study sought to present a standardized biofilm model in extracted teeth with an artificial apical groove to quantify the efficacy of hand, rotary nickel-titanium, and self-adjusting file (SAF) instrumentation in biofilm bacteria removal.

METHODS

Thirty-six extracted single-rooted teeth with oblong canals were selected. Each tooth was split longitudinally, and a 0.2-mm-wide groove was placed in the apical 2 to 5 mm of the canal. After growing mixed bacteria biofilm inside the canal under an anaerobic condition, the split halves were reassembled in a custom block, creating an apical vapor lock. Teeth were randomly divided into 3 treatment groups (n = 10 per group) using the K-file, ProFile (Dentsply Tulsa Dental Products, Tulsa, OK), and the SAF (ReDent-Nova, Ra'anana, Israel). Irrigation consisted of 10 mL 3% NaOCl and 4 mL 17% EDTA. Six teeth received no treatment. Areas inside and outside the groove were examined using a scanning electron microscope.

RESULTS

The scanning electron microscope showed a consistently thick layer of biofilm grown in the canals of the control group after 4 weeks. Within the groove, a smaller area remained occupied by bacteria after the use of the SAF compared with the ProFile and the K-file (3.25%, 19.25%, and 26.98%, respectively; P < .05). For all groups, significantly more bacteria were removed outside the groove than inside (P < .05). No statistical differences were found outside the groove (P > .05).

CONCLUSIONS

Although all techniques equally removed bacteria outside the groove, the SAF reduced significantly more bacteria within the apical groove. No technique was able to remove all bacteria. This biofilm model represents a potentially useful tool for the future study of root canal disinfection.

Effectiveness of ethylenediaminetetraacetic acid (EDTA) and MTAD on debris and smear layer removal using a self-adjusting file

OBJECTIVE

The aim of this study was to investigate the cleaning ability of a self-adjusting file (SAF) system regarding debris and smear layer removal using ethylenediaminetetraacetic acid (EDTA) or MTAD.

STUDY DESIGN

In total, 45 maxillary incisor teeth were randomly divided into 2 different irrigation groups of 20 canals each and a negative control group of 5 canals. The canals in each of the irrigation groups were irrigated using sodium hypochlorite (1.3%) as an initial irrigant during the first 2 minutes of operation, followed by 2 minutes continuous irrigation with either 17% EDTA or MTAD in a closed system. The negative control group was irrigated using 1.3% sodium hypochlorite. The roots were split longitudinally and subjected to scanning electron microscopy (SEM). The presence of debris and smear layer in the coronal, middle, and apical thirds of the canal was evaluated using a 5-grade scoring system with ×200 and ×2,000 magnification, respectively.

RESULTS

The SAF operation with 2-minute continuous irrigation using MTAD resulted in root canal walls that were free of smear layer in 85%, 70%, and 60% and of debris in 95%, 90%, and 95% of the coronal, middle, and apical thirds of the root canals, respectively. The SAF operation with continuous irrigation using EDTA resulted in root canal walls that were free of smear layer in 85%, 60%, and 50% and of debris in 95%, 90%, and 85% of the coronal, middle, and apical thirds of the root canals, respectively. Teeth in the negative control group were totally covered with debris. Evaluation by SEM showed no significant difference between the tested irrigants in removing the smear layer and debris among the different regions of the root canal. Both groups were significantly different from the negative control group.

CONCLUSIONS

When using the SAF, the protocols used in this study were effective for debridement for all regions of the root canal even for the apical thirds.

Effects of two nickel-titanium instrument systems, Mtwo versus ProTaper universal, on root canal geometry assessed by micro-computed tomography

INTRODUCTION

The aim of this study was to compare the effects of Mtwo and ProTaper Universal (PTU) on root canal geometry three-dimensionally by using micro-computed tomography.

METHODS

A total of 20 canals were prepared with Mtwo or PTU system. Micro-computed tomography scanner was used to scan the specimens before and after instrumentation. Three-dimensional images were reconstructed. The parameters evaluated included canal surface area, volume, structure model index, thickness, straightening, canal transportation, and uninstrumented surface area.

RESULTS

Preparation significantly changed canal surface area, volume, structure model index, thickness, and canal curvature. There were no significant differences between instrument types concerning these parameters and uninstrumented surface area. The canals prepared with PTU showed larger values of transportation compared with those in Mtwo group at the apical third.

CONCLUSIONS

Both of the instrumentation systems produced canal preparations with adequate geometry. PTU produced larger transportation at apical third.

A high-resolution computed tomographic study of changes in root canal isthmus area by instrumentation and root filling

INTRODUCTION

The aim of this study was to obtain a three-dimensional analysis of the isthmus area of the mesiobuccal root canal system in mandibular molars using high-resolution micro-computed tomography (μ-CT) scanning and to measure the amount of debris and root filling material in the isthmus after instrumentation/irrigation and root filling.

METHODS

Mandibular molars with two separated mesial root canals (10 teeth) were scanned by using the Skyscan 1172 μ-CT system (Skyscan, Aartselaar, Belgium) before and after instrumentation and after filling using the Thermafil root filling technique. An isthmus was defined as the ribbon-shaped or thin connecting structure between two root canals after instrumentation. The characteristics of the isthmuses were quantitatively monitored during the whole treatment. The images were segmented and quantified. The surface area of the isthmus, volume of debris after rotary instrumentation, and volume of the filled space in the isthmus after obturation were evaluated.

RESULTS

Of the seven mesial roots, two had isthmus/anastomoses somewhere along its length in the apical 5 mm, and five had an isthmus that was continuous all the way from the coronal part to the apical part. The average percentage of isthmus surface area and isthmus volume after instrumentation was 21.4% and 9.4% of the whole root canal system, respectively. About 35.2% of the isthmus volume was filled with apparent hard tissue debris after instrumentation/irrigation. The average percentage of volume of filling material in the isthmus areas was significantly lower (57.5%) than in the main root canals (98.5%, p < 0.001).

CONCLUSIONS

A considerable amount of dentin debris is produced and packed into the isthmus area during rotary instrumentation of mesial canals of lower molars despite continuous irrigation during and after instrumentation. The debris may partly prevent penetration of the filling material and sealer into the isthmus area.

Root canal preparation of maxillary molars with the self-adjusting file: a micro-computed tomography study

INTRODUCTION

The aim of this study was to describe the canal shaping properties of a novel nickel-titanium instrument, the self-adjusting file (SAF), in maxillary molars.

METHODS

Twenty maxillary molars were scanned by using micro-computed tomography at 20-μm resolution. Canals were shaped with the SAF, which was operated with continuous irrigation in a handpiece that provided an in-and-out vibrating movement. Changes in canal volumes, surface areas, and cross-sectional geometry were compared with preoperative values. Canal transportation and the fraction of unprepared canal surface area were also determined. Data were normally distributed and compared by analyses of variance.

RESULTS

Preoperatively, mean canal volumes were 2.88 ± 1.32, 1.50 ± 0.99, and 4.30 ± 1.89 μm(3) [corrected] for mesiobuccal (MB), distobuccal (DB), and palatal (P) canals, respectively; these values were statistically similar to earlier studies with the same protocol. Volumes and surface areas increased significantly in MB, DB, and P canals; mean canal transportation scores in the apical and middle root canal thirds ranged between 31 and 89 μm. Mean unprepared surfaces were 25.8% ± 12.4%, 22.1% ± 12.0%, and 25.2% ± 11.3% in MB, DB, and P canals, respectively (P > .05) when assessed at high resolution.

CONCLUSIONS

By using SAF instruments in vitro, canals in maxillary molars were homogenously and circumferentially prepared with little canal transportation.