Fracture strength of bovine incisors after intra-radicular treatment with MTA in an experimental immature tooth model E. A. Bortoluzzi 1 , E. M. Souza 1 , J. M. S. N. Reis 2 , R. M. Esberard 1 & M. Tanomaru-Filho 1 1 Department of Dentistry and Endodontics; 2 Department of Dental Materials and Prosthodontics, Araraquara Dental School, Sa ˜o Paulo State University, Sa ˜o Paulo, Brazil Abstract Bortoluzzi EA, Souza EM, Reis JMSN, Esberard RM, Tanomaru-Filho M. Fracture strength of bovine incisors after intra-radicular treatment with MTA in an experimental immature tooth model. International Endodontic Journal, 40, 684–691, 2007. Aim To evaluate, using an experimental immature tooth model, the fracture resistance of bovine incisors submitted to different reinforcement treatments with mineral trioxide aggregate (MTA). Methodology An immature tooth model was cre- ated by sectioning the coronal and apical portions of 40 bovine incisors 8 mm above and 12 mm below the cementoenamel junction. The root canals were irri- gated with 1.0% sodium hypochlorite. They were enlarged both coronally and apically using number 703 carbide burs (ISO: 500–104-168-007-021) and their internal diameter was standardized to 2.1 mm. The specimens were assigned to four groups (n ¼ 10): GI-control (without filling); GII-apical MTA plug + filling with gutta-percha and endodontic sealer; GIII- filling with MTA; GIV-apical MTA plug + filling with MTA + metallic post (Reforpost I). A polyether impres- sion material was used to simulate the periodontal ligament. The specimens were submitted to a compres- sive load at a crosshead speed of 0.5 mm min )1 in a servo-hydraulic universal testing machine (MTS 810) applied at 45° to the long axis of the tooth until failure. Data were submitted to statistical analysis by the Kruskal–Wallis test at 5% significance level. Results GIV presented the highest fracture resistance (32.7N) and differed significantly from the other groups (P < 0.05). No statistically difference was found between GII (16.6N) and GIII (23.4N) (P > 0.05). GIII had a significantly higher fracture resistance than GI (P < 0.05). Conclusions The use of MTA + metallic post as an intra-radicular reinforcement treatment increased the resistance to fracture of weakened bovine teeth in an experimental immature tooth model. Keywords: apexification, bovine teeth, fracture resistance, metallic post, mineral trioxide aggregate. Received 1 September 2006; accepted 16 February 2007 Introduction Dental trauma is most frequent in children aged 8–12 years and most commonly affects the maxillary central incisors possibly causing pulp necrosis (And- reasen & Andreasen 1994). In these cases, teeth with incomplete root development and periapical pathosis should undergo a treatment to induce apexification. The clinical management of pulpless, immature teeth is challenging because of the open, divergent apical morphology and weak, underdeveloped root dentine walls (Lawley et al. 2004). Calcium hydroxide [Ca(OH) 2 ] is widely accepted as an inter-appointment intracanal medicament (Bystrom et al. 1985) during root canal treatment and its use in apexification procedures has been described (Frank 1966). When placed within the root canal system, Correspondence: Ma ´rio Tanomaru-Filho, Rua Humaita ´, 1901, apto. 182, Centro, 14801-385 Araraquara, SP, Brazil (Tel.: +55 16 3301 6390; fax: +55 16 3301 6392; e-mail: tanomaru@uol.com.br). doi:10.1111/j.1365-2591.2007.01266.x International Endodontic Journal, 40, 684–691, 2007 ª 2007 International Endodontic Journal 684