Traumatic injuries of teeth are a frequent occurrence and usually involve the anterior teeth of young patients. Pulpal necrosis is a frequent sequel of trauma and if microbial infection occurs, this will result in the development of a periapical lesion (Sundqvist 1976). Conventional root canal treatment is aimed primarily at eliminating these bacteria as completely as possible (Weiger et al. 2000). Treatment options to manage large periapical lesions range from non-surgical root canal treatment and/or apical surgery to extraction. Current philosophy in the treatment of teeth with large periapical lesions includes the initial use of non-surgical root canal treatment. When this treatment is not successful in resolving the periradicular pathosis, additional treatment options should be considered. Such treatment may include non-surgical retreatment to rule out morphological abnormalities or treatment inadequacies. Surgery may occasionally be required. Surgical treatment of persistent extensive periradicular lesions most often involves curettage and apical resection. However, simpler approaches such as marsupialization or tube decompression may be alternatives for large cystic lesions (Hoen et al . 1990).
Radiographic differentiation of periapical cysts and granulomas is notoriously difficult. Natkin et al . (1984) analysed the data of various studies relating radiographic lesion size to histology. They stated that with a radiographic lesion size of 200 mm 2 or larger, the incidence of cysts was almost 100%. If the lesion is separate from the apex and with an intact epithelial lining (apical true cyst, Nair 1998), it may have developed into a self-perpetuating entity that may not heal when treated non-surgically. On other occasions, a large periapical lesion may have a direct communication with the root canal system (apical pocket cyst, Nair 1998) and respond favourably to non-surgical treatment (Hoen et al . 1990). Some clinical studies have confirmed that simple non-surgical treatment with proper infection control can promote healing of large lesions (Çalı ; kan & < en 1996, Weiger et al . 2000). An awareness of root canal morphology and careful interpretation of preoperative radiographs is necessary for adequate access and infection control in endodontic therapy. This is likely to have a critical bearing on outcome. Mandibular incisors are often anatomically complex, with 45% displaying second canals (Kartal et al. 1992). Such teeth may fail to respond to treatment if important anatomy is missed. They may also fail to respond well to surgery if infection has not been controlled.
The following case report describes the endodontic treatment of traumatized mandibular incisors which were associated with a large periapical lesion.

A 12-year-old male patient was referred to the Department of Endodontics in the Dental Faculty of Ankara University for treatment of mandibular left and right central and lateral incisor teeth. The patient stated that he was involved in a bicycle accident when he was 7 years old and had not seen a dentist, since he had no complaint. The patient’s history did not reveal whether the teeth were luxated, intruded or extruded. Until the age of 12, he sometimes had mild pain but no swelling in the mandibular anterior region. Clinical examination of soft tissues showed no signs of scarring or fistulae. None of these teeth were discoloured. Both the central and lateral incisors were slightly sensitive to percussion and palpation, but there was no mobility. Mandibular right and left lateral and right central incisor teeth failed to respond to electric pulp testing, whereas the mandibular left lateral incisor responded within normal limits.

Figure 1. Preoperative radiograph showing mandibular central and lateral incisors with large periapical lesion.


Figure 2. Follow-up 3 months after completion of endodontic treatment. Periapical radiograph shows healing of the periapical lesion.


Figure 3. Radiograph taken immediately after endodontic treatment.

Periapical radiographs demonstrated a large radiolucent lesion around the apices of the mandibular incisors with a well-defined margin around the apex of the mandibular left lateral incisor (Fig. 1). This tooth gave a normal response to electric pulp tests.
Despite this positive sensitivity test, root canal treatment was initiated on all mandibular incisors. The mandibular left lateral incisor was anaesthetized and rubber dam applied. Following access cavity preparation, vital pulp tissue was extirpated and the working length was estimated as being 1 mm short of the radiographic apex. The canal was prepared with size 15–40 K-files using a step-back technique. The other three incisors that had necrotic pulp tissue were accessed and size 15 K-files were passed beyond the apical foramen. Copious, mucopurulent fluid was drained through the root canals. When drainage ceased, the canals were prepared 1 mm short of the radiographic apices with size 15–40 K-files using a step-back technique. Canals were irrigated copiously with 0.2% chlorhexidine gluconate. Calcium hydroxide powder (Merck, Darmstadt, Germany) was mixed with sterile

Figure 1. Radiograph taken at follow-up examination 6 months after completion of endodontic treatment. Healing of periapical lesion is evident.


Figure 2. Recall radiograph taken 1 year after completion of treatment.

Radiographs showed that the radiolucent area was absent and that trabecular bone was forming. Clinical examination showed no sensitivity to percussion or palpation and the soft tissues were healthy. The next two radiographs at 6 months (Fig. 4) and 1 year (Fig. 5), revealed further bony healing.

Discussion.
The response to trauma can be varied. Some pulps remain apparently normal with no adverse effects, whereas others become necrotic. Necrotic pulps provide a good nutritional supply for pathogenic bacteria, which must be present for the development of a periapical lesion. In some cases periapical inflammation begins before the pulp is totally necrotic, and it is possible to have periapical radiolucency despite the presence of some vital tissue remaining in the root canal (Sundqvist 1976, Khayat et al . 1988). In the present case there was vital pulp tissue in the mandibular left lateral incisor despite the fact that there was a radiolucent lesion beyond the apex. Since this tooth was slightly sensitive to percussion and palpation, root canal treatment was initiated. The preoperative radiographic appearance of the mandibular left lateral incisor suggested the possibility of a second root. However, a further view at a different angle confirmed that the tooth had only one root.
Root canal treatment is based primarily on the removal of microbial infection from the complex root canal system. Irrigants aid in reducing the microbial flora of infected canals and if a tissue-solvent solution is used, can help to dissolve the necrotic tissue. Irrigating the canal system with chlorhexidine gluconate is an alternative to other irrigants (Jeansonne & White 1994, Ye ; ilsoy et al . 1995). Delany et al . (1982) tested chlorhexidine gluconate (0.2%) in a laboratory study using extracted teeth, and reported that it could be effective as an antibacterial agent when used as an endodontic irrigant. Kuruvilla & Kamath (1998) compared the antimicrobial efficacy of 2.5% sodium hypochlorite and 0.2% chlorhexidine gluconate. They reported that chlorhexidine gluconate was as effective, or possibly more effective in its antimicrobial activity than sodium hypochlorite. It has also been shown that chlorhexidinetreated root canals may be less susceptible to reinfection, which might be a clear advantage in the control of coronal leakage (Heling et al . 1992). However, chlorhexidine has none of the tissue-dissolving activity of sodium hypochlorite.
A calcium hydroxide-based paste was used as an antibacterial dressing and a calcium hydroxide containing sealer was used for permanent root canal obturation. Sjögren et al . (1991) found that the use of calcium hydroxide as a dressing for 1 week efficiently eliminates bacteria in the root canals. It has also been reported that treatment with calcium hydroxide resulted in a high frequency of periapical healing and some lesions, especially in young patients, were reduced or had completely disappeared only 1 or 3 months after treatment (Çalı ; kan & < en 1996, Çalı ; kan & Türkün 1997). Similarly, in the present case periapical healing appeared to be occurring 3 months after root canal obturation, and continued during the 12-month observation period. Radiographic signs such as density change within the lesion, trabecular reformation and lamina dura formation, especially around the apex of tooth 32, confirmed healing, particular when associated with the clinical finding that the teeth were asymptomatic and the soft tissues were healthy. It is difficult to determine with routine radiographic examination whether there is complete healing or whether decompression of the lesion reduced erosion of the cortical plates. More sophisticated techniques such as tomography and magnetic resonance may provide better intrabony imaging.

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