Push-out Bond Strength of Mineral Trioxide Aggregate in the Presence of Alkaline pH Mohammad Ali Saghiri, BSc, MSc,* Noushin Shokouhinejad, DDS, MSc, † Mehrdad Lotfi, DMD, MSc, ‡ Mohsen Aminsobhani, DMD, MSc, † and Ali Mohammad Saghiri, BSc, MSc § Abstract Introduction: The aim of this study was to evaluate the effect of a range of alkaline pH values on the push-out strength of white mineral trioxide aggregate (WMTA). Methods: The standardized lumens of root slices prepared from extracted single-rooted human teeth were filled with white ProRoot MTA. The specimens were then randomly divided into 4 groups (n = 20) and wrapped in pieces of gauze soaked in synthetic tissue fluid (STF) (pH, 7.4) and STF buffered in potassium hydroxide at pH values of 8.4, 9.4, or 10.4. The samples were incubated for 3 days at 37  C. The push-out bond strengths were then measured by using a universal testing machine. Failure modes after the push-out test were examined under a light microscope at 40 magni- fication. The data were analyzed by using one-way anal- ysis of variance and Tukey post hoc tests. Results: The greatest (9.46  0.63 MPa) and lowest (5.68  0.83 MPa) mean push-out bond strengths were observed after exposure to pH values of 8.4 and 10.4, respec- tively. There were significant differences between the groups (P = .001). The bond failure was adhesive for all experimental groups. Conclusions: Push-out bond strength of WMTA could be influenced by different alka- line pH values. (J Endod 2010;36:1856–1859) Key Words Alkaline, mineral trioxide aggregate, MTA, pH, push-out bond strength M ineral trioxide aggregate (MTA) has been widely used for pulp capping (1), pul- potomy (2), repair of root perforations (3), root-end filling during apical surgery (4), apical barrier formation in nonvital teeth with open apices (5), and root canal filling (6). It has been shown that physical and chemical properties of MTA are affected in an acidic environment (7). Reduced diametric tensile strength (8), push-out bond strength to dentin (9), surface hardness (10), and impaired sealing ability of MTA (11) have been reported in low pH situations. Scanning electron microscopy studies revealed the development of a porous surface and lack of needle-like crystals in MTA samples exposed to low pH environments (10, 11). Calcium hydroxide has been widely used as an intracanal medicament because of its well-known antimicrobial activity (12), which is directly related with its high pH (13). Furthermore, it has denaturing effect on proinflammatory mediators (14). It has been recommended to use calcium hydroxide paste as an interappointment medi- cament to eliminate or reduce bacterial contamination before placement of MTA (15). The effect of pretreatment with calcium hydroxide on the properties of MTA is contro- versial. Hachmeister et al (16) have not found adverse effects of pretreatment with calcium hydroxide on the sealing ability of MTA as an apical barrier. In contrast to this finding, another study showed that pretreatment with calcium hydroxide adversely affects the sealing ability of white MTA (WMTA) (17). Interestingly, a recent study on the effects of an alkaline environment on WMTA has revealed significantly lower surface hardness as well as more porosity and unhydrated structure in normal (pH, 7.4) and high alkaline environment (pH, 10.4) compared with pH values of 8.4 and 9.4 (18). To date, the effect of alkaline situations on properties of MTA has not been well- documented. The exposure of MTA to an alkaline environment after pretreatment with calcium hydroxide might affect the properties of MTA. To the best of our knowledge, there is no published article regarding the effect of alkaline environment on the bond strength of WMTA to intraradicular dentin. Therefore, this study was conducted to compare the push-out bond strength of WMTA after exposure to a range of alkaline pH values. Materials and Methods Preparation of Specimens Forty extracted, single-rooted human teeth, stored in 0.5% chloramine-T, were selected for this study. The mid-root dentin was sectioned perpendicular to the long axis into 1.00  0.05 mm thick serial slices by using water-cooled diamond blade on a Labcut 250B cutting machine (Extec Corp, Enfield, CT). The lumens of the root slices were drilled with #2 to #5 Gates-Glidden burs (Dentsply Maillefer, Ballaigues, Switzerland) to obtain 1.3-mm diameter standardized cavities. White ProRoot MTA (WMTA) (Dentsply Tulsa Dental, Tulsa, OK) was mixed following the manufacturer’s instructions and placed inside the lumens of the root slices. Saline-moistened Gelatamp (Roeko-Colte ` ne/Whaledent, Langenau, Germany) was used as a matrix to prevent extru- sion of the MTA. The specimens were then randomly divided into 4 groups (n = 20). In group A, the root slices were wrapped in pieces of gauze soaked in synthetic tissue fluid (STF) that was prepared as follows: 1.7 g of KH 2 PO 4 , 11.8 g of Na 2 HPO 4 , 80.0 g of NaCl, From the *Department of Dental Material, School of Dentistry, Tehran Branch, Islamic Azad University, Tehran, Iran; † Department of Endodontics, School of Dentistry/Dental Research Center, Tehran University of Medical Sciences, and Iranian Center for Endodontic Research, Tehran, Iran; ‡ Research Center for Pharmaceutical Nanotechnology and Department of Endodontics, Dental Faculty, Tabriz University (Medical Sciences), Tabriz, Iran; and § Department of Computer Engi- neering, Amirkabir University of Technology/Kamal Asgar Research Center (KARC), Tehran, Iran. Address requests for reprints to Mohammad Ali Saghiri, Instructor, Department of Dental Material, School of Dentistry, Tehran Branch, Islamic Azad University, Tehran, Iran. E-mail address: saghiri@gmail.com. 0099-2399/$ - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.08.022 Basic Research—Technology 1856 Saghiri et al. JOE — Volume 36, Number 11, November 2010