Introduction

It is known that cleaning and shaping plays a critical role in the success of root-canal treatment (1). Davis found that even in canals where proper preparation has been performed, there are uninstrumented areas with organic and inorganic debris present (2, 3). Debris present on root canal surfaces, after hand or rotary instrumentations, prevents the complete removal of vital or necrotic pulp tissues and microorganisms, making difficult a complete disinfection of the root canal system (4-6). Removal of organic tissues with the use of sodium hypochlorite (NaOCl) and removal of inorganic components of the smear layers with Ethylene Diamine Tetraacetic acid (EDTA) has been reported to be a useful adjunct to biomechanical preparation of the canals (7, 8).

In a review of the literature, passive ultrasonic irrigation (PUI) was described as an adjunctive treatment for cleaning the root canal system and was more effective than syringe irrigation. Although acoustic streaming and cavitation appears to play an important role in its efficacy, the exact physical mechanism has not been explained (9). Others studies demonstrated that passive ultrasonic irrigation is an effective technique that improves debris removal from inside the canals and isthmuses (6, 11, 12), but the difference in efficacy between the use of passive sonic irrigation and ultrasonic irrigation has been debated (10-12).

Recently, two new activating devices have been introduced to the market: the Endoactivator (Dentsply, Tulsa Dental) and the F-file (Plastic Endo®, LLC). The EndoActivator uses sonic activation of the irrigants with a strong, flexible, medical-grade polymer composition tip. Sonic devices produce a larger disturbance of the irrigating solution around the tip and the mode of vibration is less affected by wall contact than when ultrasonic devices are used (13, 14). Preliminary trials have shown significantly cleaner canals using EndoActivator when compared with traditional irrigation (15). The F™ file is a single-use, plastic rotary file which has a unique file design with a diamond abrasive embedded into a non-toxic polymer. The F- file will remove dentinal wall debris and agitate the irrigant without further enlarging the canal.

A review of the literature reveals that presently there are a few published studies on the cleaning ability of F-Files. The purpose of this in vitro study is to evaluate the ability of EndoActivator, F-file and passive ultrasonic irrigation to clean canals when compared to syringe irrigation.

Methods and Materials

Sample Selection

Root Canal Instrumentation

Final Irrigation

Specimen Processing and Evaluation

The specimens were then longitudinally sectioned, using a serrated laboratory diamond disk (Brasseler, Savannah, GA) to groove the buccal and lingual of each root. A 15 blade was tapped with a mallet along the groove to separate the halves. During sectioning, care was taken to avoid penetration into the canal space. Each half was dried for a minimum of 24 hours in a vacuum desiccator, attached to coded stubs, sputtered coated, and viewed with a scanning electron microscope (JOEL JSM – 6400).

Three photographs for each specimen were taken at a magnification of 500x to visualize the coronal, middle, and apical portion of the root canal system. The areas examined for each sample were standardized using parameters similar to those described by AL-Hadlaq (16) and Schafer (5). A digital photograph of the coronal, middle, and apical thirds were taken of each half of each specimen. A total of 336 images were independently analyzed by 2 calibrated, blinded evaluators using the following scoring system as previously described (17): Score 1, clean surface with very little to no debris, presenting open dentinal tubules throughout the canal wall (Fig 1A); Score 2, clean surface with some scattered debris and/or thin homogenous smear layer with some open or partially open dentinal tubules (Fig 1B); Score 3, mostly unclean surface containing debris and smear layer with few visible open or partially open dentinal tubules (Fig 1C); Score 4, unclean surface with large amount of debris and smear layer with no visible dentinal tubules (Fig 1D). When a disagreement in scoring occurred, an additional analysis was performed with both evaluators together until a consensus was reached. After scoring the samples, the code was broken and data was analyzed by Kruskal-Wallis statistical test set at significance level of P≤0.05.

Figure 1

Figure 1

Figure 1 (A) This sample received a score of 1. It shows most of the dentinal tubules are open with a clean surface and very little debris. (B) This sample received a score of 2. It shows a clean surface with very little debris, a thin homogenous smear layer, and some partially open dentinal tubules. (C) This sample received a score of 3. It shows a mostly unclean surface containing debris and smear layer and few open dentinal tubules. (D) This received a score of 4. It shows an unclean surface with large amounts of debris and smear layer with no open dentinal tubules.

Results

The EndoActivator cleaned the apical and the middle third of the canals significantly better than the F files (p < 0.05). Ultrasonic and the Endoactivator performed better than the control group in all thirds of the canals. F file was significantly better than the control only in the middle third. All techniques cleaned the coronal third of the canal significantly better than the apical third and the F files and the Ultrasonic cleaned the middle third also significantly better than the apical third. No group demonstrated completely clean canals (Figure 2).

Figure 2

Figure 2

Figure 2 Dentin debris score (0-4) after activation of irrigation solutions (6.15% NaOCl and EDTA) with F-Files, EndoActivator (EA), Ultrasonic (US) and Control group (no activation).

Discussion

Although the removal of smear layer has been shown to improve disinfection of the canal, the currently available techniques fail to do so from the entire canal walls (8, 18). Sabins et al. (12) reported that passive sonic and ultrasonic activation for 30 and 60 seconds produce significantly cleaner canals than irrigation alone, with passive ultrasonic irrigation producing significantly cleaner canals than passive sonic irrigation. Evaluation of root canal and isthmus cleanliness with one minute of ultrasonic needle activation produced significantly cleaner canal walls and isthmuses of vital teeth (19). A study evaluating the effect of different irrigation and activation systems on the penetration of NaOCl into simulated laterals canals, showed that PUI has better penetration of irrigant into lateral canals (20). One minute of ultrasonic activation significantly reduced debris and biofilm on the root canal walls and isthmuses of necrotic teeth after cleaning and shaping (21).

In this in vitro study the apexes of the teeth were blocked using wax to simulate clinical situation with the tooth apex being surrounded by the boney socket (22). This has been reported to cause entrapment of gas in the apical third, also referred to as vapor lock, thus hindering the complete removal of smear layer from this region (22). This could explain the higher debris score for all specimens in the apical third. The greater taper of the root canal preparation has been shown to result in a better removal of the smear layer from the apical third. This was attributed to the greater penetration of the irrigation needle (23, 24). The analysis of the effect of needle penetration and fluid dynamics using a computer model, showed that placing the needle within 1mm from working length improve irrigants solutions cleaning properties at apical third (25), however clinically this could represent an unsafe situation where NaOCl can be extruded toward periapical tissues.

The inability of the different irrigation regimens to clear the smear layer from the apical third of the canal has led to research specifically aimed at this challenge (20, 26, 27). All of these studies relied on activation of the irrigants to achieve the desired results. In this study, activation of the irrigants with the EndoActivator and Ultrasonic improved the removal of smear layer in all thirds of the canals when compared to the control group. This is in agreement with the recently reported study where the use of an ultrasonic agitation increased the effectiveness of the final rinse procedure in the apical third of the canal walls (26). In the present study F-file did not perform better than the control in removal of smear layer from the apical and coronal third. A recent study which compared the F-Files to the ultrasonics found that the EDTA in the irrigation protocol was the significant contributor to the removal of smear layer rather than the activation technique itself (28). On the other hand Paragliola et al (26) found no difference between F-file and EndoActivator as irrigant agitation protocols in the penetration of an endodontic irrigant into dentinal tubules. Uroz et al concluded that EndoActivator did not enhance the removal of smear layer (27).

To conclude, in this in vitro study all teeth were found to have debris present, especially in the apical third. In summary, all techniques tested showed different degree of effectiveness in debris removal of the root canal system. The results demand the need for better irrigant protocols to completely remove debris from the apical third of the canal.