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Dental Tribune United Kingdom Edition

November 201314 Endo Tribune United Kingdom Edition page 13DTß to the apical third can be en- hanced by using ultrasonic and sonic devices that demonstrate acoustic micro-streaming and cavitation.79,81,90,91 Acoustic micro- streaming is defined as the move- ment of fluids along cell mem- branes, which occurs as a result of the ultrasound energy creating mechanical pressure changes within the tissue. Cavitation is defined as the formation and col- lapse of gas and vapour-filled bubbles or cavities in a fluid. The Apical Vapour Lock theo- ry, proven in vitro by Tay, has been clinically demonstrated92 to also include the middle third by Vera: “The mixture of gases is origi- nally trapped in the apical third, but then it might grow quickly by the nucleation of the smaller bub- bles, forming a gas column that might not only impede penetra- tion of the irrigant into the apical third but also push it coronally af- ter it has been delivered into the canal.” However, more recently Munoz93 demonstrated that both: passive ultrasonic irrigation (PUI) and EndoVac are more effective than the conventional endodon- tic needle in delivering irrigant to WL of root canals. This begs the efficacy ques- tion. Two recently published stud- ies examined this issue with both systems by testing their ability to eliminate microorganisms during clinical treatment from infected root canal systems.94,95 Paiva found that after a supplementary irrigation procedure using PUI with NaOCl that 23 per cent of the samples produced positive cul- tures. Cohenca’s study examin- ing the clinical efficacy of the En- doVac found no microbial growth either after post instrumentation irrigation or at the one-week92 ob- turation appointment. When questioning these di- verse results one must remem- ber that microbial hydrolysis via NaOCl is an equilibrium reaction. Hand demonstrated that a 50 per cent reduction of NaOCl concen- tration resulted in a 300 per cent reduction in dissolution activity. Accordingly, one must consider both the delivery of the irrigant to full working length, via PUI or apical negative pressure and the total volume of NaOCl exchanged. The volume of an instrumented root canal 19mm long shaped to a #35 with a six per cent instrument equals .014 cc. Paiva described placement of NaOCl via a Nav- iTip (ULTRADENT) at WL - 4mm during instrumentation and dis- cussed using PUI with #15 Kfile at WL - 1mm. Prior to PUI, 2ml of NaOCl was injected into the ca- nal; however, this could not have filled the apical four millimeters95 due to the apical vapour lock. According to Munoz, the ca- nal was most likely immediately filled with ultrasonically activated NaOCl for one minute92 , but as just described - only about .014cc would have been effectively avail- able for this exchange and activa- tion. In contrast, the Apical Nega- tive Pressure protocol described by Cohenca et al. approximately 2ml of NaOCl actively passes through the complete WL for one92 minute.96 The difference in volumetric exchange equals 2/.014 = 14,200 per cent and likely explains the disinfection differen- tial. The plastic rotary F File Although sonic or ultrasonic in- strumentation is more effective at removing residual canal debris than rotary endodontic files are,104 and irrigation solutions are often unable to remove this during en- dodontic treatment, many clini- cians still do not incorporate it into their endodontic instrument armamentarium. The common reasons given for not using sonic or ultrasonic filing are that it can be time-consuming to set up, un- willingness to incur the cost of the equipment, and lack of aware- ness of the benefits of this final in- strumentation step in endodontic treatment. It is for these reasons that an endodontic polymer-based rotary finishing file was developed. This new, single-use, plastic rotary file has a unique file design with a di- amond abrasive embedded into a non-toxic polymer. The F File will remove dentinal wall debris and agitate the NaOCl without enlarg- ing the canal further. Pressure-alternation devices Rinsendo irrigates the canal by using pressure– suction technol- ogy. Its components are a hand- piece, a cannula with a 7mm exit aperture, and a syringe carrying irrigant. The handpiece is pow- ered by a dental air compressor and has an irrigation speed of 6.2ml/min. Research has shown that it has promising results in cleaning the root canal system, but more research is required to provide scientific evidence of its efficacy. Periapical extrusion of ir- rigant has been reported with this device.101, 102 The EndoVac apical negative- pressure system The EndoVac apical negative- pressure irrigation system has three components: the Master Delivery Tip, MacroCannula and MicroCannula. The Master Deliv- ery Tip simultaneously delivers and evacuates the irrigant (Fig. 2). The MacroCannula is used to suc- tion irrigant from the chamber to the coronal and middle segments of the canal. The MacroCannula or MicroCannula is connected via tubing to the high-speed suction of a dental unit. The Master Delivery Tip is connected to a syringe of irri- gant and the evacuation hood is connected via tubing to the high- speed suction of a dental unit.56 The plastic MacroCannula has an open end of ISO size 0.55mm in diameter with a 0.02 taper and is attached to a handpiece for gross, initial flushing of the coronal and mid-length parts of the root canal. The MicroCannula contains 12 microscopic holes and is capable of evacuating debris to full work- ing length.102 The ISO size 0.32mm diam- eter stainless-steel MicroCannula has four sets of three laser-cut, laterally positioned offset holes adjacent to its closed end, 100μ in diameter and spaced 100μ apart. This is attached to a finger piece for irrigation of the apical part of the canal when it is positioned at working length. The MicroCan- nula can be used in canals that are enlarged with endodontic files to ISO size 35.04 or larger. During irrigation, the Master Delivery Tip delivers irrigant to the pulp chamber and siphons off the excess irrigant to prevent overflow. Both the MacroCannula and MicroCannula exert negative pressure that pulls fresh irrigant from the chamber, down the ca- nal to the tip of the cannula, into the cannula, and out through the suction hose. Thus, a constant flow of fresh irrigant is delivered by negative pressure to working length. A recent study showed that the volume of irrigant deliv- ered was significantly higher than the volume delivered by conven- tional syringe needle irrigation within the same period,46 and re- sulted in significantly more debris removal at 1mm from working length than did needle irrigation. During conventional root ca- nal irrigation, clinicians must be careful when determining how far an irrigation needle is placed into the canal. Recommendations for avoiding NaOCl incidents in- clude not binding the needle in the canal, not placing the needle close to working length, and us- ing a gentle flow rate when us- ing positive-pressure irrigation.103 With the EndoVac, in contrast, ir- rigant is pulled into the canal at working length and removed by negative pressure. Apical nega- tive pressure has been shown to enable irrigants to reach the api- cal third and help overcome api- cal vapour lock.46,104 In addition, with respect to isthmus cleaning, although it is not possible to reach and clean the isthmus area with instruments, it is not impossible to reach and thoroughly clean these areas with NaOCl when the method of irri- gation is safe and efficacious. In studies comparing the EndoActi- vator,105 passive ultrasonic,105 the F File,105 the manual-dynamic Max- i-Probe (DENTSPLY Rinn),105,106 the Pressure Ultrasonic111 and the EndoVac,106 only the EndoVac was capable of cleaning 100 per cent of the isthmus area. Apart from being able to avoid air entrapment, the EndoVac sys- tem is also advantageous in its ability to deliver irrigants safely to working length without caus- ing their undue extrusion into the periapex,46,102 thereby avoiding NaOCl incidents. It is important to note that it is possible to cre- ate positive pressure in the pulp canal if the Master Delivery Tip is misused, which would create the risk of a NaOCl incident. The manufacturer’s instructions must be followed for correct use of the Master Delivery Tip. Sodium hypochlorite incidents Although a devastating endodon- tic NaOCl incident is rare,107 the cytotoxic effects of NaOCl on vital tissue are well established.108 The associated sequelae of NaOCl ex- trusion have been reported to in- clude life-threatening airway ob- structions,109 facial disfigurement requiring multiple corrective sur- gical procedures,110 permanent paraesthesia with loss of facial muscle control,69 and - the least significant consequence - tooth loss.111 Althoughtheexactaetiologyof the NaOCl incident is still uncer- tain, based on the evidence from actual incidents and the location of the associated tissue trauma, it would appear that an intravenous injection may be the cause. The patient shown in Figure 3 demon- strates a widespread area of tissue trauma that is in contrast to the characteristics of NaOCl incident trauma reported by Pashley.108,112 This extensive trauma, and par- ticularly involving the pattern of ecchymosis around the eye, could only have occurred if the NaOCl had been introduced intrave- nously to a vein close to the root apex through which extrusion of the irrigant occurred and the irrigant then found its way into the venous complex. This would require positive pressure api- cally that exceeded venous pres- sure (10mg of Hg). In one in vitro study, which used a positive-pres- sure needle irrigation technique to mimic clinical conditions and techniques, the apical pressure generated was found to be eight times higher than the normal ve- nous pressure.113 This does not imply that NaO- Cl can or should be excluded as an endodontic irrigant; in fact, its use is critical, as has been dis- cussed in this article. What this does imply is that it must be deliv- ered safely. Safety first In order to compare the safety of six current intra-canal irrigation delivery devices, an in vitro test was conducted using the worst- case scenario of apical extrusion, with neutral atmospheric pres- sure and an open apex.102 The study concluded that the Endo- Vac did not extrude irrigant after deep intra- canal delivery and suctioning of the irrigant from the chamber to full working length, whereas other devices did. The EndoActivator extruded only a very small volume of irrigant, the clinical significance of which is not known. Mitchell and Baumgartner tested irrigant (NaOCl) extrusion fromarootcanalsealedwithaper- meable agarose gel.114 Significant- ly less extrusion occurred using theEndoVacsystemcomparedwith positive-pressure needle irriga- tion. A well-controlled study by Gondim et al. found that patients experienced less post-operative pain, measured objectively and subjectively, when apical nega- tive-pressure irrigation was per- formed (EndoVac) than with api- cal positive-pressure irrigation.115 Efficacy Fig. 2 EndoVac set-up. Fig. 3 Irrigation accident with widespread trauma.