pH CHANGES OF FIVE DIFFERENT CALCIUM HYDROXIDE AND MINERAL TRIOXIDE AGGREGATE MIXTURES USED FOR INTRACANAL MEDICATON AND PULP CAPPING

Abstract

(Tables 4a and 4b). all calculated F values are higher than the F values for P=0.05. [...]at all time intervals, when each group was considered separately, intra-group differences were statistically significant for different time periods (P <0 .05). According to our results for both MTA and Ca(OH)2 mixtures with local anaesthetics, the final pH was reached after one week, which shows that the reaction is slower and consistent with the conclusions of other authors. According to our study, MTA mixed with CHX, attributing to its inhibition on setting reaction, gave lower pH values. [...]it can be concluded that all selected vehicles in our study are as suitable as distilled water or as saline solutions for preparing calcium hydroxide pastes.

Headnote

Abstract

The aim of this study was to evaluate the pH changes of five different calcium hydroxide (Ca(OH)2) and mineral trioxide aggregate (MTA) mixtures used for Intracanal medication and pulp capping. We prepared mixtures with distilled water, a local anaesthetic solution, physiological saline solution, chlorhexidine (CHX) and glycerine. The pH of each dressing material was determined using a digital pH meter. pH measurements were determined at 3 min, 10 min, 1 h, 3h, 24 h, 48 h and 7 days, respectively. All vehicles demonstrated similar pH changes, ranging within pH 11-12, when mixed with calcium hydroxide. In MTA groups, three different vehicles also showed similar pH changes values with calcium hydroxide, while the MTA+local anaesthetic solution and MTA +CHX mixtures demonstrated lower pH change values. Also, all MTA mixtures showed lower pH values against calcium hydroxide mixtures.

Keywords: calcium hydroxide, mineral trioxide aggregate, anaesthetic solution, pH value , chlorhexidine, glycerine, pulp capping, intracanal dressing.

1.INTRODUCTİON

Since its introduction in dentistry, in endodontics (Ca(OH)2) became one of the gold standard, due to its ability to induce hard tissue formation, its antibacterial behavior and tissue-dissolving capability [1,2]. Tronstad et al. [3] suggested that calcium hydroxide placement in the root canal elevates the pH, producing an alkaline environment in the surrounding tissues by the diffusion of hydroxyl ions through the dentinal tubule. An increased pH is bacteriocidal and inhibits osteoclastic activity, as well [1-6]. MTA is a new bio-compatible material, also considered as one of the gold standard in endodontics, due to its low solubility, biocompatibily, adequate sealing ability, low cytotoxicity, good tissue tolerance and possible induction of mineralized tissue formation [2,4,5,7-14]. MTA promotes an alkaline pH and has a mechanism of action similar to calcium hydroxide, in terms of increasing pH and releasing calcium ions [2,5,7,10,13,15]. Calcium hydroxide has a pH ranging from 11 to 13, while the pH of MTA has an initial pH of 10.2, which rises to 12.5 after 3 hours of mixing [8,15]. It is recomended that the selected vehicle should not affect the pH of calcium hydroxide and MTA, responsible for their biological activity [5,8,15]. Calcium hydroxide powder for root canal dressing has been mixed with various vehicles, such as distilled water, saline, anesthetic solution, Ringer's solution, camphorated monochlorophenol cresatin and glycerine [4,5,15-17], while MTA powder has been mixed with water [2,8,15]. Manufacturers' instructions on the usage of MTA typically recommend sterile or distilled water and liquid's mixing with the MTA powder [2,7,8,14,15,18]. To see the possible effects of the selected vehicle to MTA, and to compare it with Ca(OH)2, the pH values of calcium hydroxide and MTA mixtures in combination with either distilled water, local anaesthetic solutions, physiological saline, chlorhexidine (CHX ) and glycerine solution were determined in this study.

2.MATERİALS AND METHODS

The Ca(OH)2 and MTA combinations were prepared using five different solutions. Details on the groups are listed in Table 1. Details on the materials and equipments used in this study are listed in Table 2. Ca(OH)2 and MTA powder was added to 1 mL of the vehicle until the solution was saturated. All sealers were mixed according to manufacturers' instructions.

100 polyethylene tubes 5 mm in height and 1.5 mm in internal diameter were filled with cement mixtures to be evaluated. Samples from each group were immersed in glass test tubes containing 2 mL of distilled water. After specific periods described below, pH is determined with a pH meter. Analysis of pH: A digital pH meter was calibrated with known standard pH solutions of 4.01, 7.00 and 9.21. The pH of each solution prior to mixing with powders and later on, of each prepared combination, was determined. pH measurements were determined at 3 min, 10 min, 1 h, 3 h, 24 h, 48 h and 7 days after mixing. The pH values were recorded at the above mentioned time intervals and statistical analysis of data was performed using two-way ANOVA. All statistical analyzes were performed by SPSS Version 18 (SPSS Inc.,Chicago, IL, USA) software.

3.RESULTS AND DİSSCUSİON

The mean pH values recorded for our experimental groups are presented in Table 3, and the two-way ANOVA statistical analyzes are presented in Table 4.

As seen in Fig 1. the pH values after mixing were lower than the final results. The lowest pH values were obtained when CHX was used both in Ca(OH)2 and MTA groups. For our statistical analyzes. (Tables 4a and 4b). all calculated F values are higher than the F values for P=0.05. Therefore. at all time intervals, when each group was considered separately, intra-group differences were statistically significant for different time periods (P <0 .05). At all time intervals, the differences between MTA and the calcium hydroxide groups were statistically significant (P <0 .05). Differences between the pH changes of the tested solutions were statistically significant between all groups P<0 .05). The pH values ranged between 11.73 and 12.70. All final pH values for calcium hydroxide mixtures are higher than 12 (Table 3). Calcium hydroxide mixtures have higher values than MTA mixtures. All types of liquids used in this study were found to be viable for preparing Ca(OH)2 pastes. The range of pH values was between 9.375 and 12.705 in all MTA experimental groups. MTA mixtures have lower pH values than calcium hydroxide mixtures. In MTA mixtures, B1 and B4 groups have high values (pH >12). Distilled water, saline, glycerine and CHX solution groups of MTA mixtures final pH values are higher than 11. CHX mixtures of MTA reach a pH 11 at day 7. Anesthetic solution mixtures of MTA have lower pH values (Table 3).

Ca(OH)2 and MTA are routinely used as dressing materials in endodontic therapy [1-5]. When used as intra-canal medicaments, they have shown to be effective in eliminating bacteria from the root canal space. Their high pH has a destructive effect on bacterial cell membranes and protein structures [19]. Most bacteria present in the root canal system grow best at a pH around 6.5 to 7.5, and most microorganisms are destroyed at pH 9.5, though a few can survive up to pH 11 or higher. The high pH of the medications may also neutralize the acids and thus help prevent further destruction of mineralized structures [5,17,18 20,21]. An aqueous preparation of these materials can potentially maintain their high pH for a long time in the root canal [16]. It is also suggested that the high pH could be vasoconstrictive, and therefore, beneficial for hemostasis [10]. The methodology for evaluating the material pH in our study is to fill standardardized tubes containing test materials and immerse them in distilled water. We mesured pH from that solution. This method seems to be the most common one, as literature indicates that most authors used it [2,3,5,6,18,19,21]. Sjogren et al. [21], who studied the antimicrobial effect of calcium hydroxide, reported that the effective destruction of microorganisms was complete after 1 week. The results of this study indicate that at least 7 days were required for total destruction of microorganisms. In many studies, although the working time intervals vary slightly, a final period of at least 7 days is predicted, as in our study [5,6,18,20,21]. Ca(OH)2 and MTA have been studied with different vehicles, such as distilled water, deionized water, saline solution, local anaesthetics, camphorated paramonochorophenol, chlorhexidine, iodine, potassium iodine, erythromycin, clindamycin, tetracycline and glycerine [1,4,5,8,16,17,22]. Calcium hydroxidedistilled water or calcium hydroxide-saline solution mixtures have commonly been used as intracanal medicaments with a pH ranging from 11 to 13 [5,8,17,22]. In our study, the pH values of each solution exceeded 12, and our results were completely consistent. MTA-distilled water mixtures are also commonly used in endodontic theraphy [8]. Watss et al. [22] mixed MTA with distilled water and local anesthetic solutions to see the effect of pH on temporal settings of MTA. They advised that MTA must be mixed with distilled water. Our study was consistent with this idea, as MTA-Distilled water and MTA-Saline solution have higher pH levels than the other groups considered in our study. Accorinte et al. [14] recommend that MTA with a pH ranging nearly to 10 should be mixed with distilled water and a saline solution. For some authors [8,23], the pH of MTA has an initial pH of 10.2, which rises to 12.5 after 3 hours of mixing. This agrees with our findings, as it gave similar results. Filho et al. [6], who evaluated the pH changes in White MTA-distilled water mixtures, found out that the pH changes between 8.2 to 10. Kuga et al. [18] evaluated the pH of MTA-based sealers and found out pH values ranging from 8.89 to 9.39. Our results indicate pH values ranging from 11.75 to 12.60 for MTA (ProRoot). Additives in White MTA and MTA-based sealers can affect the final physical properties of materials, like their pH levels [8,23]. The acid pH of local anaesthetics might modify the alkaline pH of materials [4,5,19,32], or the reactive products could cause a reduction in pH over an extended period of time [22]. In our study, calcium hydroxide-local anaesthetic mixtures maintained their alkaline pH levels higher than 12 after 3 hours. On the other hand, it is reported that MTA powder versus local anesthetic solutions will give slower setting reactions, and that the set material has less compressive strength [8,22,24]. According to our results for both MTA and Ca(OH)2 mixtures with local anaesthetics, the final pH was reached after one week, which shows that the reaction is slower and consistent with the conclusions of other authors. Souza et al. [17] mixed Ca(OH)2 with a CHX gel and found out a pH between 12.5-12.7. The high pH levels are exactly the same as in our CHX- Ca(OH)2 group. For Kogan et al. [24], CHX is not suitable, because it completely prevents the setting reaction of MTA. Malhotra et al. [23] suggested that the use of 2% CHX and 0.12% CHX in combination with MTA has been reported to significantly increase the anti-bacterial effect of MTA, but with reduced pH. According to our study, MTA mixed with CHX, attributing to its inhibition on setting reaction, gave lower pH values. The effect of glycerine for pH values to Ca(OH)2 and MTA mixtures was not studied before. In both Ca(OH)2 and MTA mixtures, we obtained pH values > 11. This vehicle seems to be available to mix with Ca(OH)2 and MTA powders to obtain higher pH values.

4.CONCLUSİONS

The results of this study show that five different vehicles demonstrate similar pH changes in combination with calcium hydroxide. Accordingly, it can be concluded that all selected vehicles in our study are as suitable as distilled water or as saline solutions for preparing calcium hydroxide pastes. In preparing MTA pastes, local anaesthetics and CHX seem not viable for obtaining high pH values.

References

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