RO0211

16 I I special _ laser ments. The LightSpeed LSX (Discus Dental) file is a unique, extremely flexible, taperless, NiTi instrument capable of cleaning to the WW. The final apical size is the instrument size that completes WW preparation and is determined when the LSX file binds 4mm (or more) from the working length (WL), and requires a firm push to reach WL. The customised apical prepa- rations created are critical for predictably successful endodontics and provide significant advantages: _effective removal of infected material, debris, inflamedandnecrotictissuefromtheapicalregion; _allows placement of irrigating needle to WL for negative pressure apical irrigation; _facilitates placement of intra-canal medication deeper within the canal; and _facilitatesplacementofradial-firinglasertipwithin 1mm of WL. Negativepressureapicalirrigation There are two main reasons that irrigants fail to reach the critical last 3mm of a root canal. Firstly, using positive pressure irrigation with a side-vented needle there is little flushing beyond the depth of the needle.11 Mostoftheirrigantfollowsthepathofleast resistance and backs out of the canal, with apical flushing penetrating only 1 to 2mm apical to the endoftheneedle.Toachieveeffectiveapicalflushing, the needle tip needs to be placed 1mm from WL, which dramatically increases the risk of a sodium- hypochlorite accident. Secondly, the presence of apical vapour lock fromairtrappedinthecanal,aswellasammoniaand carbon dioxide released from the dissolving action of sodium hypochlorite on pulp tissue, prevents pen- etration of irrigants into the apical third. This vapour lock cannot be removed with hand or rotary files, sonic or ultrasonic activation. In a recent study, vapour lock resulted in “gross retention of debris and smear layer remnants” in the apical 0.5 to 1.0mm of closed root-canal systems.12 The EndoVac (Discus Dental) is a true apical negative pressure irrigating system that provides continuous, high-volume irrigation of fresh fluids to the canal terminus with simultaneous evacuation. It is comprised of a master delivery tip (Fig. 3) that delivers fluid to the pulp chamber and a macro- and micro-cannula (Fig. 4) that draw the fluid from the chamber to the canal terminus by way of evacuation. This system eliminates vapour lock and provides superior cleaning, disinfecting and smear layer re- moval, while virtually eliminating the threat of sodium hypochlorite accident.13 When compared to positive pressure irrigation with a ProRinse needle, EndoVac produced canals that were 366 and 671% cleaner 1 and 3mm from WL, respectively.14 When EndoVac was used in combination with LightSpeed LSX instrumentation, canals were 99 and 99.5% free of debris 1 and 3mm from WL, respec- tively.15 roots2_2011 Fig. 9 Fig. 9_Technique for laser tip positioning in canal.