Drs. Kathryn L. Aasen, Brian E. Bergeron, Mark D. Roberts, Van T. Himel, Thomas E. Lallier, and Kent A. Sabey evaluate the effectiveness of debris removal in mesial roots of mandibular molars
Introduction: The purpose of this study was to evaluate the effectiveness of debris removal in mesial roots of mandibular molars using Max-i-Probe® (Dentsply Rinn) conventional positive pressure needle, EndoVac® Negative Pressure Irrigation System (SybronEndo), or Photon Induced Photoacoustic Streaming (PIPS) irrigation.
Methodology: Forty-five extracted mandibular molars were match paired for curvatures and randomly assigned to each irrigation technique group (n=15). Mesial canals were prepared to a size 20/.04 at working length using rotary NiTi files and sterile water irrigation. Teeth were mounted in resin using a custom-designed Bramante style K-Kube and sectioned at 3 and 5 mm from the apex. Specimens were reassembled in the K-Kube, and mesial canals only were cleaned and shaped using rotary instrumentation and 6% NaOCl. Protocols for final preparation size of the mesial canals, irrigation sequence between instruments, and final irrigation followed manufacturers’ recommendations. Images of canals and isthmuses were taken prior to and following instrumentation/irrigation to evaluate presence of debris. Comparisons of cleanliness were made using paired t-tests, and the groups were compared with ANOVA (P < 0.001).
Results: In the mesial canals and isthmuses, there were no significant differences between the overall cleaning ability of the three irrigation techniques at 3 and 5 mm from the apex. Final cleanliness of the uninstrumented distal canals was significantly greater in the PIPS group when compared to the other two groups (P < 0.001). Conclusion: Within the limitations of this study, Max-i-Probe, EndoVac, and PIPS irrigation techniques demonstrated similar ability to clean mandibular molar mesial canals and isthmuses at 3 and 5 mm from the root apex.
It has been well established that microorganisms are responsible for the development and progression of apical periodontitis.1-2 Overall success rate of initial nonsurgical root canal therapy has been quoted as high as 96%.3 Multiple in vivo studies have shown significantly lower success rates when there is evidence of pretreatment periapical pathology.4-5
Further in vivo studies have also shown decreased success rates when cultivable bacteria are detectable immediately prior to obturation.6-7 Sjogren, et al., found viable bacteria in 40% of infected canals after cleaning and shaping using 0.5% NaOCl irrigation. Although 68% of these teeth were successful, this rate was much lower than the 94% success rate in teeth with negative cultures prior to obturation.6 The number and type of microorganisms that must be eliminated from a canal system to prevent endodontic failure is unknown. Therefore, the quest to improve overall success rates of initial endodontic therapy should begin with the elimination of all microorganisms from the canal system.
Cleaning and shaping a root canal system to render it void of organic debris and microorganisms is challenging.8 Chemomechanical procedures have been shown to significantly decrease the numbers of bacteria left in canals but have not achieved total elimination of bacteria and debris in all canals.9-10 This, in part, is due to the complex anatomy found in many root canal systems.11-12 Bacteria can reside in canal isthmuses, accessory canals, dentinal tubules, and canal recesses.13 Microorganisms may survive the process of cleaning and shaping simply due to the irrigant’s inability to penetrate these areas.14-15
Conventional positive pressure needle irrigation with NaOCl has been the gold standard to which many other systems have been compared. One of the drawbacks of this technique is its inability to express irrigant greater than 1 mm past the needle tip.16 Since the reduction of debris in the apical one-third of the canal is partially dependent on the volume of NaOCl irrigation directly contacting it, the apical preparation size must be large enough to accommodate placement of the irrigation needle.17-18 Klyn, et al., showed conventional positive pressure irrigation was least effective at removing canal isthmus debris 1 mm from the working length when compared to debris removal at 3 and 5 mm from the working length.19 An additional concern of conventional positive pressure irrigation is its safety.20 Desai and Himel demonstrated apical extrusion of NaOCl when using a positive pressure irrigation technique.21
A number of irrigation devices have been developed in attempts to improve the safety and effectiveness of irrigation delivery into all areas of the canal system. The EndoVac Negative Pressure Irrigation System draws irrigant apically by way of evacuation. The manufacturer’s recommended minimal apical prep size is 35/.04. This allows the placement of the microcannula to working length during final irrigation. The EndoVac’s negative apical pressure decreases the potential for apical irrigant extrusion. In a study evaluating safety, the EndoVac had the lowest frequency of irrigation extrusion when compared to the EndoActivator® (Dentsply Tulsa Dental Specialties, Tulsa, OK), passive ultrasonic irrigation, and syringe irrigation with a side-vented needle.22
Photon Induced Photoacoustic Streaming is an innovative irrigation system that uses the Fotona LightWalker Er:YAG laser (Technology4Medicine) at sub-ablative power levels in conjunction with a patented tip that is effective when placed exclusively into the coronal access cavity. This technique allows all canals to be irrigated at the same time. The cleaning ability of PIPS appears to be associated with rapid irrigant motion caused by expansion and implosion of laser-induced bubbles.23 Using single canal premolars, Peters, et al., demonstrated significantly less bacteria at the 1 mm level after PIPS activation when compared to ultrasonically activated irrigation and conventional irrigation.24
In evaluating the effectiveness of irrigation devices, previous studies have either measured debris removal or elimination of bacteria. Debris removal measurement allows visualization of the extent of irrigation penetration into canal intricacies. The complex canal anatomy of mesial molars with isthmuses makes irrigation and debris removal more challenging. Von Arx, using endoscopic inspection during periradicular surgery, noted mesial canal isthmuses in 83% of mandibular first molars.25 Mannocci also evaluated mesial roots of mandibular molars and found isthmuses were present 17%, 37%, and 50% at 1, 2, and 3 mm from the apex, respectively.26 There are a number of studies evaluating debris removal in mesial root isthmuses of mandibular molars using the EndoVac, passive sonics, ultrasonics, and conventional positive pressure irrigation. These studies have not demonstrated complete removal of debris in the apical 6 mm. The PIPS laser technique has yet to be evaluated in this manner. The aim of this study was to compare the cleaning effectiveness of conventional Max-i-Probe needle irrigation, the EndoVac system, and PIPS laser technique using mesial canal isthmuses of mandibular molars.
Materials and Methods
This study followed a similar protocol used by Klyn, et al., and Howard, et al.19,27 Forty-five extracted mandibular molars were evaluated for the presence of mesial canal isthmuses in the apical 5 mm using cone beam computed tomography (i-CAT, Imaging Sciences International). Teeth were stored in 0.1% thymol before use. The occlusal surface of each tooth was flattened so that a reproducible working length (WL) reference point was established. A standard access was performed and a #10 C-File (Dentsply Maillefer) was placed into the mesial and distal canals until the tip of the file was visible at the apical foramen. Working length was determined by subtracting 1 millimeter from the above measurement. A size #20/.04 glide path was accomplished in the mesial canals using stainless steel K-files (Miltex, Inc.) and Hyflex® CM™ NiTi files (Coltène/Whaledent Inc.). The glide path allowed for easier file placement into the canals after sectioning. The mesial canals were irrigated with 1 mL sterile saline between files. The distal canals were not instrumented. Access openings were covered with a moist cotton pellet and Cavit™ (3M™ ESPE™). Triad® gel (Dentsply Trubyte) was used to seal the mesial and distal foramen to prevent mounting resin from entering canals. The roots were covered with two coats of nail polish prior to mounting.
Each tooth was embedded into a custom-made metal cube (K-Kube), filled with EpoxiCure® resin (Buehler) up to the level of the cementoenamel junction. The K-Kube (Figure 1) is based on the Bramante technique with the addition of a compression component.28 Compression eliminates the 0.3 mm gap created by each saw blade cut. The K-Kube facilitates the disassembly and reassembly of each tooth so that canal and isthmus debris can be evaluated prior to and after instrumentation and irrigation. In this technique, each root canal system serves as its own control. After setting, the embedded specimens were removed from the K-Kube and stored in 100% humidity.
The resin-mounted specimens were sectioned at right angles to the root canal at 3 and 5 mm from the mesial root apex using an Accutom 50 precision saw (Struers) equipped with a 0.30-mm-thick, high concentration diamond blade (Precision Surfaces International). The coronal surface of each section was used for evaluation and scoring.
Each specimen served as its own control. The teeth were match paired for curvatures and randomly placed into one of the following three groups:
- Irrigation with conventional 30 gauge Max-i-Probe (n=15)
- Irrigation with PIPS (n=15)
- Irrigation with the EndoVac system (n=15)
Images of each section were made using a digital camera (Nikon CoolPix 5400, Nikon Inc.) attached to a stereomicroscope (Nikon SMZ-2T, Nikon Instruments Inc.) at the highest magnification to allow complete visualization of canals and isthmus. The color images were viewed on a high-resolution iMac® monitor (Apple) and the outer surfaces of the ML, MF, D root canals, and isthmus were traced. The debris present in the canals and isthmuses was also outlined. Image J software (National Institutes of Health, v1.39a) was used to calculate the surface area of the root canal, isthmus, and the debris present. This data was used to calculate a cleanliness percentage for each canal and isthmus prior to instrumentation and after final irrigation.
Canal preparation and irrigation
Each sample was reassembled into the K-Kube. The Cavit and cotton pellet were removed, and a #20/.04 file was placed at WL to verify proper reassembly. After coronal flaring with Gates Glidden drills (Dentsply) sizes #2-4, the canals in the EndoVac and conventional Max-i-Probe irrigation group were prepared with .04 Hyflex rotary files to a master apical file size #35 using a crown-down technique. The canals in the PIPS group were prepared with .04 and .06 Hyflex rotary files using a crown-down technique to a master apical file size #25/.06 per manufacturer’s recommendations. Irrigation was as follows:
Groups A/B: Conventional Max-i-Probe and PIPS laser
A 30-gauge Max-i-Probe irrigation needle was placed into the canal 1 mm from binding and no further than 1 mm coronal to the WL. One mL 6% NaOCl irrigation was used between each file size to irrigate the canal. Time per irrigation cycle was 30 seconds.
Group C: EndoVac
Per manufacturer’s recommendations, between each file the EndoVac master delivery tip (MDT) was placed above the access opening, and 6% NaOCl was simultaneously delivered and evacuated keeping the canal and chamber replenished with irrigant. The macrocannula was inserted into each canal while the MDT continually replenished the canal and chamber with 6% NaOCl. Insertion of the macrocannula was to a point just short of binding, and it was slowly moved up and down in the canal for 30 seconds.
Group A: Conventional Max-i-Probe
The Max-i-Probe delivered 1.0 mL of 6% NaOCl over 30 seconds in each canal, and the NaOCl was allowed to remain passively in the canals for an additional 30 seconds. In each canal, 0.5 mL 17% EDTA was delivered over 10 seconds and allowed to remain passively for 50 seconds. Finally 1.0 mL 6% NaOCl was delivered over 30 seconds to each canal and then allowed to remain passively for 30 seconds.
Group B: PIPS laser
The irrigation technique followed manufacturer’s recommendations for final irrigation. The 2940 nm Er:Yag LightWalker laser at 20 mJ (15 Hz, 50 microsecond pulse duration) was equipped with a 600 micron stripped tip. In each cycle, the PIPS laser tip was placed exclusively into the pulp chamber, short of any canal orifice.
Cycles 1-3: 30-second continuous cycles of 6% NaOCl activated by the PIPS laser
Cycle 4: 30-second continuous cycle of sterile water activated by the PIPS laser
Cycle 5: 30-second continuous cycle of 17% EDTA activated by the PIPS laser
Cycle 6: 30-second continuous cycle of sterile water activated by the PIPS laser
Group C: EndoVac
The irrigation technique followed manufac-turer’s recommendations. Final irrigation followed the MicroCycle technique for two canals (purging and charging canals). MicroCycle 1: The microcannula was placed in the first canal to working length while the MDT delivered 6% NaOCl for 10 seconds. The MDT was quickly removed, and the microcannula was allowed to suction the NaOCl from the canal (purged). The cycle was repeated. On the third cycle, after the initial 10 seconds, the microcannula was quickly withdrawn from the canal allowing the MDT to fill the canal with 6% NaOCl (charged). The NaOCl was allowed to sit in the canals for an additional 30 seconds. During this time, the irrigation sequence was repeated on the second canal. MicroCycle 2: Again using the microcannula and MDT, each canal was irrigated with 1.0 mL 17% EDTA over 10 seconds, then the canal was charged. The 17% EDTA remained passively in the canals for an additional 50 seconds. MicroCycle 3: 6% (NaOCl) was the same as MicroCycle 1.
After final irrigation, all specimens were removed from the K-Kube, and each sample slice was examined for remaining debris similar to the initial evaluation. Percent canal cleanliness was statistically analyzed for significant differences between each group, section, canal total, isthmus total and pre-instrumentation, post-final irrigation techniques.
The amount of debris present before instrumentation and after final irrigation was compared with paired t-tests, and the groups were compared with repeated measures analysis of variance (P < 0.001).
One specimen in the EndoVac group and five specimens in the conventional Max-i-Probe group were lost either during processing or lacked a detectable isthmus. There were no statistically significant differences in mesial canal and isthmus cleanliness among all three groups at all sections prior to instrumentation or after final irrigation (Table 1, Figure 2). All canals and isthmuses were significantly cleaner after final irrigation compared to before instrumentation. Within each group, there was no statistically significant difference in canal cleanliness at 3 or 5 mm from the mesial root apex (Figure 3). The distal canals in the PIPS group post-final irrigation were significantly cleaner than the uninstrumented distal canals in the other two groups (P < 0.001). The cleanliness of the distal canals in the EndoVac and Max-i-Probe conventional needle irrigation groups was not significantly different (Figure 4).
The results of this study demonstrated an overall mesial canal cleanliness of 94% in the conventional Max-i-Probe needle irrigation group. These results are similar to those of Klyn, et al., and Howard, et al., who demonstrated over 95% mesial canal cleanliness after final irrigation.19 Overall mesial canal cleanliness for the EndoVac in this study was 99%, which is in agreement with Howard, et al., who reported over 95% mesial canal cleanliness.27 We found a 93% overall isthmus cleanliness after using conventional irrigation; this is supported by Klyn, et al., with 90% isthmus cleanliness using conventional Maxi-i-Probe needle irrigation.19 Our overall isthmus cleanliness using EndoVac irrigation was 95%; this is much higher than 55% reported by Howard, et al.27 The differences in isthmus cleanliness results may be attributed to variations in isthmus width and length.
In this study, there were no statistically significant differences in canal and isthmus debridement at various levels between conventional Maxi-i-Probe needle, EndoVac, and PIPS laser irrigation. This is in agreement with Howard, et al., who also found no significant differences between canal and isthmus cleanliness when comparing the EndoVac with conventional irrigation.27 Additional studies have also evaluated debris removal using conventional and EndoVac irrigation. In a study by Siu and Baumgartner, the EndoVac showed significantly better debridement at 1 mm from working length compared to needle irrigation.29 When evaluating debris removal in narrow mesial canal isthmuses of mandibular molars, Susin, et al., found the EndoVac produced considerably cleaner isthmuses when compared to manual dynamic irrigation.30
In this study we used the NaOCl and EDTA irrigation protocol recommended by the manufacturers of the PIPS laser and EndoVac systems. The volume of NaOCL irrigation and contact times were not consistent between groups. Effectiveness of NaOCl is dependent on surface contact time, volume of irrigant, and exchange of solution.31 The PIPS protocol had a final apical preparation size of 25/.06. Therefore, there were fewer file and irrigation cycles in the PIPS group during mechanical instrumentation compared to the other two groups. Although fewer files may have produced less additional debris in the PIPS samples, decreased overall irrigation time and volume of NaOCl may have had an effect on the dissolution of organic debris. Also the PIPS final irrigation technique consisted of three 30-second intervals of continuous NaOCl irrigation, totaling 90 seconds for all canals. The final irrigation technique for the EndoVac and conventional needle irrigation had a total NaOCl irrigation time of 180 seconds. The EndoVac also had an advantage of continuous NaOCl exchange during the cleaning and shaping process, whereas the PIPS and conventional irrigation groups were limited to 1 mL NaOCl between files.
The PIPS technique is unique in that the tip of the laser is placed exclusively within the pulp chamber and not into the canal space below the orifice level. Through acoustic streaming, irrigant activated by the LightWalker laser has the potential to flow into all of the canals. In this study, the distal roots were retained so that the effect of PIPS on debris removal in a non-instrumented canal could also be observed. Although teeth were sectioned at 3 and 5 mm from the mesial root apex, the distance of the distal root sections from the distal root apices was not controlled within or between groups. The overall cleanliness of the distal roots was significantly greater (P < 0.001) in the PIPS group when compared to the EndoVac or conventional irrigation groups. The distal canal cleanliness in the EndoVac group compared to the conventional group was not significantly different. This data can only be noted as anecdotal, and further study would be required to confirm and expand on these observations.
The findings in this study showed no significant difference in debris removal of mandibular molar mesial canals and isthmuses when comparing the EndoVac, PIPS, and conventional Max-i-Probe needle irrigation. Although non-instrumented distal root cleanliness was not a controlled variable in this study, PIPS was significantly better at cleaning these uninstrumented canals when compared to the other two groups. A controlled study looking at PIPS ability to effectively clean canals with minimal instrumentation is warranted.
The authors wish to gratefully acknowledge Technology4Medicine for their generous donation of the PIPS laser patented tip and Dr. DiVito who personally oversaw the use of the Er:Yag laser. We would like to thank Dr. Cerniglia of Metarie, LA who graciously allowed us use his office space and Fotona LightWalker Er:Yag laser. We would also like to recognize Coltène/Whaledent for their generous donation of the Hyflex CM NiTi rotary files to facilitate this resident research. The authors deny any conflicts of interest related to this study. This article is the work of the United States government and may be reprinted without permission. Opinions expressed herein, unless otherwise specifically indicated, are those of the authors. They do not represent the views of the Department of the Air Force or any other department or agency of the United States government.
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