Effect of Irrigants and Cementum Injury on Diffusion of Hydroxyl Ions through the Dentinal Tubules Sherma Saif, DMD, MS,* Clifton M. Carey, PhD, † Patricia A. Tordik, DMD,* and Scott B. McClanahan, DDS, MS* Abstract This study measured hydroxyl ion diffusion through dentinal tubules into a bathing solution. Eighty single- canal, instrumented teeth were divided into 8 groups. Control groups 1 and 3 were irrigated with 10 mL 0.9% saline and 10 mL 6% sodium hypochlorite (NaOCl), respectively. Control groups 5 and 7 were irrigated with 3 mL and 1 mL 17% ethylenediaminetetraacetic acid (EDTA) and then 10 mL 6% NaOCl, respectively. Exper- imental groups 2, 4, 6, and 8 were irrigated as groups 1, 3, 5, and 7, followed by placement of calcium hydroxide (Ca(OH) 2 ) into canals. Bathing solution pH was recorded for 30 days, a cementum defect was made, and then pH was recorded for another 30 days. With a paired difference test, average pH during steady state was statistically different and higher after the defect (P  .001). With Tukey multiple comparisons, post-defect pH for group 6 was found to be significantly greater (P  .01) than in other groups. This study indicated final canal irrigation with 3 mL 17% EDTA and 10 mL 6% NaOCl before Ca(OH) 2 placement al- lowed the greatest hydroxyl ion diffusion to the root surface. (J Endod 2008;34:50 –52) Key Words Calcium hydroxide, diffusion, ethylenediaminetetraace- tic acid, hydroxyl ions, smear layer T he prognosis for avulsed or luxated teeth is unfavorably affected by surface resorp- tion, inflammation, or replacement resorption after replantation, repositioning, and stabilization (1, 2). In external inflammatory root resorption, the cementum and outer layer of dentin are resorbed. Pulp extirpation and introduction of calcium hydroxide (Ca(OH) 2 ) as an intracanal medicament within 7–10 days has been recommended to prevent or stop resorption (3, 4). Tronstad et al. (3) suggested that Ca(OH) 2 can influence local root resorption by increasing pH. Diffusion of hydroxyl ions through dentinal tubules and production of an alkaline environment in areas of resorption induce necrosis of osteoclasts and can inhibit inflammatory root resorption in monkeys (5). To prevent and treat external root resorption, Ca(OH) 2 must diffuse through dentin. Deardorf et al. (6) demonstrated the rate of Ca(OH) 2 diffusion differed accord- ing to tooth. Another study showed that hydroxyl ions did not significantly diffuse through an intact root surface (7). Foster et al. (8) observed that removal of smear layer with 10 mL of 17% ethylenediaminetetraacetic acid (EDTA) before Ca(OH) 2 placement might facilitate ion diffusion. The smear layer is an amorphous structure consisting of dentin, odontoblast processes, pulp tissue, and bacteria (9). It is found on canal walls of instrumented teeth and was measured to be 1–2 m thick, friable, loosely adherent, and packed up to 40 m into dentinal tubules (10). An effective method of smear layer removal from canal walls used 10 mL of 17% EDTA followed by 10 mL of 5.25% sodium hypochlorite (NaOCl) (11). Recommendations of contact time and irrigation volume required to effectively remove the smear layer by a chelating agent vary. Goldberg and Spielberg (12) suggested 15 minutes as the optimal working time for smear layer removal with EDTA and 0.84 g of a quaternary ammonium bromide (EDTAC). Zaccaro et al. (13) reported 20 mL of EDTA irrigation for 3 minutes as effective. It was also reported that 10 mL of 17% EDTA irrigation for 1 minute was effective, whereas 17% EDTA for 10 minutes caused dentin erosion (14). Crumpton et al. (15) demonstrated effective smear layer removal with a final 1-minute rinse of 1 mL of 17% EDTA followed by 3 mL of 5.25% NaOCl. To date, no study has reported a Ca(OH) 2 diffusion rate through radicular dentin when using reduced volumes of EDTA to remove the smear layer. The purpose of this study was to measure hydroxyl ion diffusion through dentinal tubules after root canal smear layer removal by using 1 or 3 mL 17% EDTA and then 10 mL 6% NaOCl before and after a cementum defect was made on a root surface. Materials and Methods Eighty anterior and premolar human, permanent teeth stored in 0.2 % sodium azide were decoronated at the cementoenamel junction with a #557 carbide bur (Henry Schein, Melville, NY) in a high-speed hand piece with water spray. Presence of a single root canal was verified with 2 digital radiographs (Schick Technologies, Long Island City, NY) in mesiodistal and buccolingual directions. A #10 FlexoFile (Dentsply Maillefer, Johnson City, TN) was placed in the canal until visible at the apical foramen and patency was verified. One millimeter was subtracted to establish working length. With a crown-down technique, all teeth were cleaned and shaped with ProFile 0.04 rotary instruments (Tulsa Dental, Tulsa, OK) to a master apical size #40. All were irrigated with 5 mL of 0.9% sodium chloride, USP (Baxter Healthcare Corp, Deerfield, IL) (saline) during canal instrumentation by using a 30-gauge Max-i-Probe (Dentsply Rinn, Elgin, IL), placing the irrigation tip 1 mm from working length. All canals were From the *Naval Postgraduate Dental School, Bethesda, Maryland; and † Paffenbarger Research Center, American Den- tal Association Foundation, National Institute of Standards and Technology, Gaithersburg, Maryland. Published by Elsevier Inc on behalf of the American As- sociation of Endodontists. Address requests for reprints to Dr Patricia A. Tordik, 8617 Augusta Farm Lane, Laytonsville, MD 20882. E-mail address: patricia.tordik@med.navy.mil. 0099-2399/$0 - see front matter Copyright © 2008 by the American Association of Endodontists. doi:10.1016/j.joen.2007.09.010 Basic Research–Technology 50 Saif et al. JOE — Volume 34, Number 1, January 2008