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.arrow shows the root canal.)RENEGOTIATING THE ROOT CANALFOLLOWING DISMANTLINGIrritation dentine, pulp stones and other calci-fications may make the location of root canalorifices or negotiation of a root canal difficult.Exposing the Canal OrificesMicroscopic magnification and illuminationcombined with ultrasonic tips are invaluablein this situation and provide the most pre-Figure 6.22dictable means of locating canal orifices.15Matrix material has been plugged through the perforationUltrasonics allow the precise removal of den-into the bony defect.The root canal has been sealed withtine from the pulp floor with minimal risk ofgutta percha.perforation.Ultrasonic diamond-coated tipscan be used dry in intermittent bursts toremove dentine.The assistant uses a Stropkoroot canal system is cleaned in the usual irrigator to puff away dentine chips.A solu-manner, dried and obturated with gutta tion of 17% EDTA is excellent for clearing thepercha and sealer.area under exploration.The pulp chamberIf the root canal is relatively straight and the should be flooded with EDTA solution forperforation site can be located, obturating the 2 minutes.Dentine chips and other debris cancanal with MTA may be feasible.This can be a then be washed away with sodium hypochlo-useful technique for teeth that are to be rite.The pulp floor is explored with a DG16restored with a post crown, as it can some- probe or micro-debrider to locate the canal ori-times be difficult to place sufficient gutta fices.If the canal is very fine, highly curved orpercha and sealer to provide an adequate seal.sclerosed, then a fine hand instrument such asSometimes, a surgical approach may be a C file (Dentsply-Maillefer, Ballaigues,required (Figure 6.25).Switzerland) can be used to gauge a pathway. 122 ADVANCED ENDODONTICS: CLINICAL RETREATMENT AND SURGERY3If there is sufficientcoronal tooth substanceremaining forrestoration withoutpost, fill the perforation1 2 site and canal withGutta percharepair materialBone Matrix packedthrough defectGranulationtissueLateralPerforation repairroot perforationmaterialPost holeFigure 6.24Internal matrix perforation repair.A thorough knowledge of the anatomy of instruments should be advanced graduallythe pulp floor and the likely location of and a confirmatory radiograph exposed tothe canal orifices is essential.The pulp floor ascertain orientation of the instrument withinmap and the relationship of the floor to the canal.Under the microscope, it is oftensurrounding tooth structure should give possible to distinguish between irritationsome idea of the location of root canals dentine occluding the original canal and that(Figures 6.26, 6.27).of the root wall.The area that needs to beThe pulp floor tends to be darker than the removed tends to be darker (Figure 6.29).walls.Dyes, such as iodine in potassiumiodide or methylene blue, have been used todemonstrate the location of canal orificesThe Location of Canals in(Figure 6.28).Specific SituationsThe orifices tend to be located at animaginary point directly apical to the origi-The Second Mesiobuccal Canal ofnal location of the cusp tip.Dentine needs toMaxillary Molarsbe removed very carefully when attemptingto locate sclerosed canals.Ultrasonic tips Approximately 60% of maxillary molars havesuch as the CPR 2 and 3 allow precise two mesiobuccal canals.The orifice of theremoval of dentine from the floor of the pulp second mesiobuccal canal (MBII) often lieschamber.Swan-necked LN burs can also be under a lip of dentine on the mesial wallvery useful.(Figure 6.30).If the canal is completely sclerosed for There may be two separate orifices butseveral millimetres apical to the pulp floor, occasionally the MBII branches off the primary PERFORATION REPAIR AND RENEGOTIATION FOLLOWING DISMANTLING 123Figure 6.27The correct orifices have now been accessed and flared.Figure 6.25In this maxillary central incisor, there was a possibilitythat the root canal had been perforated by previous postspace preparation.Because the root canal was very large,it was decided to obturate the apical region with MTA,which will seal any potential perforation (arrow).Figure 6.28An indicator dye such as Canal Blue (Dentsply,Weybridge, Surrey, UK) has been used to identify orificesof any remaining root canals in this maxillary molar.Figure 6.26until the second orifice is located.An estima-The pulp floor map has not been used in a previoustion for the location of the MBII orifice can beattempt to find the root canals (blue arrows indicate canalmade by visualizing a point at the intersectionorifices)
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