I trends _ re-treatment Figs. 7a–9b_Clinical cases re-treated using the concepts above with the Twisted File and RealSeal bonded obturation. Fig. 7a Fig. 7b nal micro-leakage once their crowns are accessed. This micro-leakage appears in the form of odour, moisture, unset restoratives and voids, amongst other visual clues. Assuring that the post-endodontic result will be sealed correctly is best accomplished through removal of the crown, re-treatment procedures and the placement of a new coronal build-up. Owing to its ease of use and durability, Dr Mounce uses Maxcem (Kerr) for build-ups, a self-etching, selfadhesive composite cement. 4) Removal of posts and coronal obstructions of all types including the build-up While a comprehensive discussion of post and obstruction removal is beyond the scope of this paper, it should be mentioned that the overriding principle in removal of all obstructions is to remove as little dentine as possible in order to minimise both perforation and the risk of vertical root fracture. As a result, the greater the extent to which procedures can be performed that both cools the tooth to prevent overheating during ultrasonic vibration and conserves tooth structure, the greater the probability of clinical success. The Ruddle Post Removal System is invaluable in this regard if used correctly. Post removal involves selecting the correct ultrasonic tips. The coronal access must be ideal before either the orifice is managed or the clinician progresses beyond the orifice. Attempting to remove obturation material or shape the orifice without attaining straight-line access is contraindicated. 5) Removal of canal contents The coronal access must be ideal before either the orifice is managed or the clinician progresses beyond the orifice. Attempting to remove obturation material or shape the orifice without attaining straight-line access is contraindicated. The removal of canal contents is passive, gentle and done is three waves (heat, mechanical and solvents). The Elements Obturation Unit (EOU) is an excellent source of heat for removing gutta-percha. The heat plugger of the EOU is used in the same motion as the System B down-pack. Approximately half of the gutta-percha can be removed with one to two down-pack motions per canal. Removal of gutta-percha with the heat tips also creates a space into which the RNT instruments can be placed to remove shreds of gutta-percha that remain along the walls. Both the removal of gutta-percha with heat and with RNT instruments is done dry. These two successive steps allow the vast majority of gutta-percha to be removed and if performed correctly minimise the amount of solvent to be placed in the presence of hand files and time required to achieve patency. It is essential that the RNT files that are used to remove gutta-percha entered passively and gently, and used with an upward brush-stroke away from the furcation. Placing them apically with force into the mass of gutta-percha can easily lead to strip perforation, particularly if the existing dentinal wall next to the furcation is relatively thin from the start, owing to previous overzealous shaping. 26 I roots 4_ 2009