Clinical complications of endodontic treatment involve iatrogenic perforations of the canal walls, which may have an impact on the overall result of the treatment. The American Association of Endodontists define perforations as mechanical or pathological communication between the canal system and the external surface of the root. The most imminent causes of such perforation include inappropriate endodontic access, aggressive canal system preparation and non-axial preparation of the root post (1). Iatrogenic perforations are the second most frequent (9.6%) complication in endodontic treatment (2). A perforation located in the furcal area may cause pathological communication between the canal system and the periapical tissues, resulting in bacterial contamination. Therefore, a progressing destruction of the periodontal ligament may be observed, following permanent inflammation (3). The prognosis for a tooth with co-existing perforation depends on its location, time in which the canal system had direct contact with the periapical tissues, the extent of the periodontal ligament irritation and the technical feasibility of closing the perforation (2, 4, 5). Perforations located in the middle third section of the canal length have the best prognosis, while those located in the coronal third section and the pulpal floor have the worst one. In order to eliminate bacterial infection, immediate closing of the perforation is necessary, using bioactive materials with antibacterial properties and short setting time in various pH and moisture conditions, facilitating the regeneration of periodontal tissues and characterised by lack of resorption in tissue liquids, stability of dimensions and radiopacity (2, 4). The MTA (Mineral Trioxide Aggregate) is a material dedicated for perforation closing, which is a blend of Portland cement (70%), bismuth oxide (20%) and gypsum (5%), containing trace quantities of silicon, calcium and magnesium oxides, sulphur acid and sodium sulphate (2, 4, 6-8). Apart from its biocompatibility, the material induces biological response and is conducive for cell adherence and growth (7). Directly after the application, hydroxyapatite crystals are formed on its surface, which indicates its regenerative potential (8). The hydroxyapatites deposited act as scaffolds for further cell growth (5, 6). The MTA promotes cementogenesis owing to the adherence and growth of osteoblasts on its surface, which is followed by their secretion of genes encoding the proteins of mineralised tissues (6). These features of the MTA indicate its potential for usage in regenerative endodontic procedures.

This paper presents a case of the endodontic retreatment of the second lower molar tooth (tooth no. 37) with co-existing iatrogenic perforation of the pulpal floor, partially unfilled mesiolingual (ML) canal and vast periapical lesion. The patient E.M. aged 51, was referred in writing in September 2014 by a prosthodontist for restorative preparation preceding prosthodontic treatment. The referral letter also included the retreatment of the tooth 37. The Patient brought diagnostic radiographs, such as an orthopantomogram and cone beam computed tomography (CBCT) of the left side of the mandible. In her health questionnaire, the Patient mentioned respiratory allergies and asthma. In her dental questionnaire, the Patient did not report any subjective pain involving the tooth 37, which was endodontically treated in June 2011 due to acute pulpitis. As breathing problems made it impossible for the Patient to be treated in the ergonomic (recumbent) position with rubber dam coverage, the previous treatment was conducted in sitting position and without the rubber dam. The operating dentist had difficulties performing the endodontic procedure, of which the Patient was aware.