ARTÍCULOS ORIGINALES

Changes in pH of irrigating solutions after contact with human root dentón

 

Gabriela L. López^1,2, María L. de la Casa², Alberto M. Manlla³, María del M. Sáez², María E. López¹

¹ Department of Biological Chemistry.
² Department of Endodontics, School of Dentistry, National University of Tucumán.
³ IT Department, School of Agronomy and Zootechnics, National University of Tucumán, Tucumán, Argentina

CORRESPONDENCE Od. Gabriela Lucia Lopez Catedra de Endodoncia. Facultad de Odontologia. Av. Benjamin Araoz 800 (4000)-San Miguel de Tucuman-Argentina E-mail: gabrielallopez@gmail.com

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ABSTRACT

The aim of this study was to analyze the in vitro behavior of the pH of different irrigating solutions, used alone or consecutively, after contact with extracted human teeth. Mandibular human premolars were selected. The middle thirds were divided into 6 parts. The specimens obtained were divided into 6 groups and treated with irrigating solutions: 1) distilled water; 2) 1% NaOCl; 3) 1% Citric Acid (CA); 4) 17% EDTA; 5) 1% CA + 1% NaOCl; 6) 17% EDTA + 1% NaOCl. Specimens were immersed in 1 mL of each solution at 37oC, those of groups 1, 2, 3 and 4, for 5 minutes, and the rest, consecutively for 2.5 minutes in each solution. Initial and final pH of the solutions were determined. Data were analyzed by the T Test, one-way analysis of variance (ANOVA) and Tukey multiple comparison Test. At 2.5 and 5 minutes there were significant differences between the initial and final pH for all solutions. The pH values decreased for distilled water and NaOCl, while they increased for CA and EDTA. In vitro, the pH of all solutions was modified after contact with root dentin at both test times (2.5 and 5 min).

Key words: pH; Irrigating solutions; Dentin.

RESUMEN

Variaciones del pH de soluciones de irrigación endodónticas en contacto con dentina radicular humana

El objetivo de este trabajo fue estudiar in vitro el compor - tamiento del pH de diferentes soluciones de irrigacion endodonticas, usadas solas o en forma consecutiva, despues del contacto con dientes humanos extraidos. Se seleccionaron premolares inferiores. El tercio medio radicular se dividio en 6 partes. Los especimenes obtenidos se dividieron en 6 grupos, de acuerdo a la solucion de irrigacion empleada: 1) agua destilada; 2) NaClO 1%; 3) Acido Citrico 1% (AC); 4) EDTA 17%; 5) AC 1% + NaClO 1% ; 6) EDTA 17% + NaClO 1%. Los especimenes fueron sumergidos en 1 mL de cada solucion a 37°C. Aquellos del grupo 1, 2 y 3 durante 5 minutos, y el resto, consecutivamente 2,5 minutos. Se determinaron pH inicial y final para cada solucion. Los datos fueron analizados utilizando Test T, ANOVA y Test de comparaciones multiples de Tukey. A los 2,5 y 5 minutos de exposicion hubo diferencias estadisticamente significativas entre el pH inicial y final en todas las soluciones. El pH disminuyo en el caso de agua destilada e NaClO, mientras que aumento en AC y EDTA. In vitro, el pH de todas las soluciones se modifico despues del contacto con dentina radicular humana en ambos periodos de tiempo (2,5 y 5 minutos).

Palabras clave: pH; Irrigacion; Dentina.

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INTRODUCTION

Endodontic instrumentation produces a smear layer and plugs of organic and inorganic particles of calcified tissue and organic elements such as pulp tissue debris, odontoblastic processes, microorganism and blood cells in dentinal tubules¹. Irrigation is considered the best method for removing tissue remnants and dentin debris during instrumentation^2,3. Irrigating agents also provide lubrication, destruction of microbes and dissolution of tissues. The efficiency of irrigating agents depends on root canal length, penetration depth of the substance, application time, dentin hardness, and concentration and pH of the solutions^2,4,5. Because each solution is most effective at a specific pH, changes in pH value could modify its properties. It has been suggested that chelating agents improve chemical-mechanical debridement in the root canal treatment by removing the smear layer from the root canal and demineralizing and softening dentin. The most commonly used chelating agents are based on different concentrations of ethylenediaminetetraacetic acid (EDTA) and citric acid (CA)^6,7. Other nonchelating agents, such as sodium hypochlorite (NaOCl), have also widely been recommended as irrigants.
Initially, the use of EDTA solution was proposed by Ostby (1957) to assist with the instrumentation of calcified, narrow or blocked canals because of its ability to foster the chelation of the calcium ions at a pH close to neutral8. Its efficiency in removing inorganic dentin particles, preventing the formation of smear layer during instrumentation has been demonstrated^9-12. It is used at 15-17% and pH ^7-8. CA, a weak organic acid, has a chelating deminer - alizing effect on calcified dentin components¹³. It has been previously applied on root surfaces altered by periodontal disease and flap surgery in order to increase cementogenesis and to accelerate healing, regeneration and normal periodontal attachment¹⁴. In operative dentistry, CA has been proposed as a mild etchant for hard dental tissues, particularly for dentinal conditioning, and enhanced smear layer and plug removal6. In endodontic treatments it is used at a concentration of 1%-50% and pH 0.8-1.9. NaOCl has been widely recommended as an irrigant for chemical-mechanical debridement of root canals due to its solvent activity for necrotic and living tissues, in addition to its ability as an effective agent against broad spectrum bacteria^15-17. It is used at a concentration of 1%-5.25% and at pH 11.9. For maximum effect during and after instrumentation, chelating agents should be followed by tissue solvents. Alternating the use of EDTA or CA and NaOCl solutions has gained wide acceptance as an effective irrigation regimen^18-20. The aim of this study was to evaluate in vitro the behavior of the pH of different irrigating solutions, used alone or consecutively, after contact with extracted human teeth.

MATERIAL AND METHODS

Experimental teeth and solutions
Ten recently extracted single-root human mandibular premolars were selected on the basis of their similarity in morphology and size. They were kept in distilled water at 4oC until used. Debris, calculus and soft tissue remnants on the root surfaces were cleaned using a Gracey curette (Hu-Friedy, NC, USA). The crowns were sectioned at the cement-enamel junction using a high speed bur # 2200 (KG Sorensen, SP, Brazil) and water-irrigation. Cementum was removed using a Gracey curette. Root canals were enlarged up to a number 50 K-file (Maillefer, East Lansing, MI, USA), ), at a working length of 1mm from the apex. They were cleaned and shaped using the step-back technique. After each instrument change, root canals were irrigated with 2 mL of distilled water, using a 25G needle (BD Precision Glide, Curitiba, Brazil). The apical and coronal third of the roots were removed and the remaining parts were cut transversally into three parts using a high speed bur # 2200 (KG Sorensen, SP, Brazil) (Fig. 1 and 2). Each slice was then bisected in buccolingual direction, obtaining a total of six sections of each root (Fig. 3). Sections of the same teeth were used to compare all the solutions. The sections were weighed on a precision scale (Acculab, BA, Argentina) (accuracy ≤0.1 mg) and found to have an average weight of 46.0 mg 13 mg. Then they were stored at 4oC until use. The 60 specimens were divided into six experimental groups (ten specimens each) and treated with different irrigating solutions: group 1 (Control), distilled water (DW) pH 7; group 2, 1% NaOCl pH 11.6; group 3, 1% CA pH 1.8; group 4, 17% EDTA pH 7.2; group 5, 1% CA pH 1.2 + 1% NaOCl pH 11.6; group 6, 17% EDTA pH 7.2 + 1% NaOCl pH 11.6. The specimens in groups 1, 2, 3 and 4 were immersed in 1 mL of the irrigant at 37oC for 5 minutes, and those in groups 5 and 6 were left in contact with 1 mL of each solution for 2.5 minutes resulting in a 5-minute immersion. Specimens were not washed between irrigants. All specimens were then removed and the pH of each solution was analyzed.

Fig. 1: Root dentin segments. A: coronal third; B, C and D: middle thirds; E: apical third.

Fig. 2: Root middle third segments.

Fig. 3: Sections of root dentin middle third segments.

pH measurement
The pH of each solution was determined before and after contact with the dentin specimens using a digital pH meter (Broadley-Yames Corp. Irvine, Ca, USA) for small volumes (accuracy ≤0.01). The pH was determined by placing the refillable Calomel electrode in a 30 μL sample on a slide for 10 sec. The electrode was washed with distilled water and wiped dry between readings.

Statistical analysis
Data were analyzed using the T Test to compare the initial and final pH of each solution for related samples, and the final pH at different times for independent samples. Finally, one-way analysis of variance (ANOVA) was performed to compare the pH of the NaOCl solution when it was used alone or consecutively to CA or EDTA. Means were compared using the Tukey multiple comparison test.

RESULTS

Table 1 shows the pH values of the experimental solutions after contact with the sections of root dentin. At 5 minutes there were statistically significant differences (p≤ 0.01) between the initial and final pH values for all the solutions, including the control solution (p≤ 0.05). The pH values decreased for DW and NaOCl and increased for CA and EDTA. When the irrigating solutions were used consecutively (Table 2), similar results were obtained: the pH values for DW and NaOCl decreased significantly (p≤ 0.01), while for CA and EDTA, they increased significantly (p≤ 0.01) after remaining in contact with the dentin for 2.5 minutes.

Table 1: Initial and final pH of irrigating solutions after contact with human root dentin.

Table 2: Initial and final pH of consecutively used irrigating solutions after contact with human root dentin.

A comparison of the final pH values for DW, CA and EDTA solutions at both exposure times (5 minutes and 2.5 minutes) (Tables 1 and 2) showed no difference (p≥ 0.05) between the pH values of the DW and EDTA groups. However, CA showed statistically significant differences (p≤ 0.05) resulting in even higher pH values at 2.5 minutes than at 5 minutes contact time. Regarding NaOCl solutions (Table 3), after the use of CA, and even more so with EDTA, pH was significantly lower (p≤ 0.01) at 2.5 minutes contact time compared to the pH value at 5 minutes.

Table 3: Final pH of NaOCl solution alone and consecutively used after contact with human root dentin.

DISCUSSION

The decalcifying action of CA, which has an acid pH, is greater than its chelating action, as reported in a paper by Machado-Silveiro et al. 2004²¹ comparing CA to sodium citrate. They considered that sodium citrate may only have the chelating activity of the original acid, which is low and may explain why sodium citrate has lower decalcifying activity than CA. De-Deus et al. 2006²², reported that 10% CA caused peritubular and intertubular dentin erosion. Machado-Silveiro et al. 2004 also found stronger results with 1% and 10% CA than with 17% EDTA, while Spano et al. 2009 contradict these results reporting that, when used for 5 min, 15% EDTA removed more calcium ions than 10% CA. Di Lenarda et al. 200023 found similar results for 1 ml.L-1 CA and 15% EDTA. Haznedaroglu 200324 studied the effect of pH variation on the chelating effectiveness of CA, concluding that pH is a more important factor than concentration. These results are in agreement with Hennequin et al. 1994⁸. Thus, decalcification was higher with a CA solution at pH 1.19. In addition to the pH variations of CA, EDTA and NaOCl with exposure time, we have demonstrated in other studies that these irrigating solutions did not significantly affect organic and inorganic human dentin composition at 2.5 minutes or 5 minutes exposure time²⁵.
Renewal of the solution increases the effectiveness of its action compared to a single continuous application over the same period of time²⁶ because it maintains the pH at natural levels, thereby increasing its moisturizing and decalcifying capacity²⁷. Zehnder et al. 2005²⁸ reported that CA and EDTA may interfere with NaOCl action and should therefore be used separately. Both CA and EDTA immediately reduce the available chlorine in solution, rendering the sodium hypochlorite irrigant ineffective on bacteria and necrotic tissue. In our experience, NaOCl, like DW, did have lower pH after contact with the dentin, as if some acidic component of the exposed root tissue could be slightly sensitive to solubilization. On the other hand, CA and EDTA as chelating agents may act on the calcium dentin component, which may be responsible of the rise in the pH of the solution. However, exposure time might not affect the action of EDTA, as was demonstrated for CA, which had lower pH at 5 minutes than at 2.5 minutes, as if the dentin had shown buffering capacity. After the application of CA and EDTA, the solubilization effect of NaOCl may be much greater, since the dentinal tissue would be much more destabilized. However, it should be taken into consideration that cementum was absent from the root specimens in this experiment. Dentin exposed to NaOCl may be sensitive to solubilization, an effect that may appear after the application of CA and EDTA, which may act on dentinal calcium. The exposure time used may not affect the pH of NaOCl and EDTA as it did for CA, which may provide evidence of dentinal buffering capacity at 5 min.
Further studies are needed to determine the pH behavior of the solutions, used alone and consecu - tively, in contact with human root dentin at higher exposure times. This study should be complemented with others to determine biocompatibility of these drugs when used in endodontic treatments.

ACKNOWLEDGMENTS

The authors wish to acknowledge the technical assistance of Lic. Biochemist Maria Mercedes Salas. The work was funded by grants from Research Council of the National University of Tucuman (CIUNT) and School of Dentistry of the National University of Tucuman (FOUNT).

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