Rat tissue reaction to MTA FILLAPEX Ò Generally the main goal of root canal therapy is the proper cleaning and shaping of the root canal system followed by filling of the canal with gutta-percha and sealer. Ideally, sealers should have favorable physical and chemical properties (1). In addition, it is highly desirable for sealers to be biocompatible because they can come in direct contact with the periodontal tissues through the apical foramen and accessory communica- tions. Because they could delay wound healing, it is important to study the reaction of tissues to these sealers before their clinical use (2). The presence and release of substances from sealers may generate different reactions when in contact with tissues. The reaction varies according to the substance, the amount released, and the resorption speed. Sealapex Ò (SybronEndo, Glendora, CA, USA) is a sealer that contains calcium oxide (CaO), which in contact with water forms calcium hydroxide (Ca(OH) 2 ) (3, 4). Seal- apex Ò has been shown to induce only a mild inflammatory reaction when it contacts the periapical tissues (2, 3, 5). Mineral trioxide aggregate (MTA) has been exten- sively studied. It was designed to be used in pathologic or iatrogenic root perforations and in root-end cavities (6, 7). Studies have shown that MTA promotes favorable tissue reactions characterized by the absence of severe inflammatory reactions, the presence of a fibrous cap- sule, and the induction of mineralized repair tissue (8, 9). However, despite its favorable characteristics, MTA does not exhibit the physical properties needed to be used as a sealer, owing to its working time, setting time, and difficult handling (1, 10). An MTA-based sealer (Angelus Ò ; Londrina, Parana´, Brazil) was recently introduced to the market. It is a paste–paste sealer whose composition is a trade secret. However, it is known that synthetic Portland Cement clinkers, which are dark gray nodular materials made by heating ground limestone and clay at a temperature of about 1400–1500°C, and disalicylate are the basic components and form an ionic polymer. According to the manufacturer, it has the following physical proper- ties: working time, 35 min; flow capacity, 27.66 mm; setting time, 130 min; optical density, 77%; and solubil- ity, 0.1%. Moreover, it is easily manipulated. However, no study has evaluated its biological characteristics. Thus, the aim of this study was to compare the tissue reactions of MTA FILLAPEX, Sealapex and Angelus MTA in the subcutaneous connective tissues of the rat, including their ability to stimulate mineralization. Material and methods Thirty male 4- to 6-month-old Wistar Albino rats, weighing 250–280 g, were used in the study. The animals were housed in temperature-controlled rooms and Dental Traumatology 2011; doi: 10.1111/j.1600-9657.2011.01096.x Ó 2011 John Wiley & Sons A/S 1 Joa ˜ o Eduardo Gomes-Filho, Simone Watanabe, Carolina Simonetti Lodi, Luciano Tavares Angelo Cintra, Mauro Juvenal Nery, Jose ´ Arlindo Otoboni Filho, Elo ´ i Dezan Jr, Pedro Felı ´cio Estrada Bernabe ´ Department of Endodontics, Arac ¸atuba School of Dentistry, University of Estadual Paulista, Sa ˜o Paulo, Brazil Correspondence to: Dr Joa ˜o Eduardo Gomes-Filho, Department of Endodontics, Arac ¸atuba School of Dentistry, University of Estadual Paulista, R. Jose ´ Bonifa ´cio, 1193, Arac ¸atuba, Sa ˜ o Paulo, Brazil Tel.: +0055 18 36363252 Fax: +0055 18 36363279 e-mail: joao@foa.unesp.br Accepted 6 November, 2011 Abstract – The aim of this study was to evaluate the rat subcutaneous tissue reaction to implanted polyethylene tubes filled with mineral trioxide aggregate (MTA) FILLAPEX Ò compared to the reaction to tubes filled with Sealapex Ò or Angelus MTA Ò . These materials were placed in polyethylene tubes and implanted into the dorsal connective tissue of Wistar rats for 7, 15, 30, 60, and 90 days. The specimens were stained with hematoxylin and eosin or Von Kossa or left unstained for examination under polarized light. Qualitative and quantitative evaluations of the reaction were performed. All materials caused moderate reactions after 7 days, which decreased with time. The reactions were moderate and similar to that evoked by the control and Sealapex Ò on the 15th day. MTA FILLAPEX Ò and Angelus MTA caused mild reactions beginning after 15 days. Mineralization and granulation birefringent to polarized light were observed with all materials. It was concluded that MTA FILLAPEX Ò was biocompatible and stimulated mineralization.