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I 39roots3_2010 look are necessary for locating this canal. Lower inci- sors also have a second canal more than 40 per cent of the time, with the second canal often placed more lingually. We regularly treat teeth that have no peri-apical infectionsbuthavetechnicallyinadequateroot-canal treatments. The conventional wisdom is that if plan- ning to place crowns or bridges on teeth with techni- cally inadequate treatments, one takes responsibility for such treatment, as it will form the foundation forsubsequentwork.Successratesareexpectedtobe 94 per cent in this situation, which is phenomenally high and offers predictability for subsequent work. _Case report The following case is an example of a retreatment case that was referred to our practice for an opinion and treatment, if required. The patient was asympto- maticonpresentationfortheinitialconsultationwas no history of symptoms. Initial root-canal treatment had been initiated over ten years ago. The #32 was unrestored while the #31 had an amalgam and a previous root-canal filling. Sensitiv- ity tests revealed that the #32 responded positively, whereasthe#31gaveanegativeresponse.Therewere no probing defects greater than 3 mm. There was no buccal swelling or expansion of the bone, and the teeth were not tender to percussion or palpation. A large multilocular peri-apical lesion measuring 25mmby10mmwasnotedtobeassociatedwiththe #31 and #32 (Fig. 1). A provisional diagnosis of chronic apical perio- dontitis was made. The likely cause of the lesion was intra-radicular bacteria. During a recent course, the majority of dentists suggested that the treatment of choice was to extract the tooth and possibly enucle- ate the lesion. It is important to remember that one cannot diagnose whether a lesion is odontogenic or non-odontogenic by radiography alone. There are two types of cysts: true cysts and bay cysts. Bay cysts areconnectedtotheroot-canalsystemandwouldbe expected to heal following conventional endodontic therapy. Theoretically, true cysts are independent of the root-canal space and may not heal by root-canal treatment alone. (Much evidence suggests that the size of the lesion does not influence the outcome of healing, although it may be true that the greater the size of the lesion, the greater the likelihood of its being cystic.) The treatment recommended to the patient in this instance was root-canal retreatment with a review in six months to assess healing. There wasanobviouspossiblesourceofinfectionintheun- treated mesial canals, while the distal canals had had atechnicallyinadequateroot-canaltreatment(Fig.1). AD case report _ retreatment I