Abstract

The objective of this study was to assess the influence of chlorhexidine (liquid and gel) and zinc oxide in calcium hydroxide (CH) pastes on root pH in simulated external resorption. One hundred human anterior teeth with a single root canal were selected. After decoronation and root canal instrumentation, the specimens were divided into 4 experimental groups and 1 control group (without intracanal paste): CH + saline (CH+S), CH + 2% chlorhexidine liquid (CH+ CHX), CH + 2% chlorhexidine gel (CH+ CHXg), and CH + 2% chlorhexidine gel + zinc oxide (CH+ CHXg+ZnO). pH was measured using a microelectrode at 3 and 24 h, and 1, 2, 3, and 4 weeks after inserting intracanal pastes. Data were analyzed statistically using an ANOVA and Tukey’s test (p < 0.05). The CH+CHXg+ZnO group had the highest pH values throughout (p<0.05). The CH+S and CH+ CHX groups had the highest pH values after 1 week and the CH+ CHXg group after 2 weeks. CH+ CHXg maintained the highest pH until the fourth week compared with CH+ CHX (p < 0.05). The control group remained at a neutral pH at all evaluated times. It can be concluded that chlorhexidine solution or gel maintained the alkaline pH of CH, and chlorhexidine gel allowed a slower decrease in pH over time. CH+ CHXg+ZnO showed the highest pH values and was an effective intracanal medication for maintaining alkaline root pH in the area of resorption.

Chlorhexidine; Zinc Oxide; Calcium Hydroxide, Endodontics

Introduction

External inflammatory root resorption represents a challenge for dentists because it can lead to tooth loss when diagnosis is delayed. ¹1. Fuss Z, Tsesis I, Lin S. Root resorption: diagnosis, classification and treatment choices based on stimulation factors. Dent Traumatol. 2003 Aug;19(4):175-82. https://doi.org/10.1034/j.1600-9657.2003.00192.x
https://doi.org/10.1034/j.1600-9657.2003... ^,22. Lima TF, Gamba TO, Zaia AA, Soares AJ. Evaluation of cone beam computed tomography and periapical radiography in the diagnosis of root resorption. Aust Dent J. 2016 Dec;61(4):425-31. https://doi.org/10.1111/adj.12407
https://doi.org/10.1111/adj.12407... For resorption to occur, the protective barriers of the dental root, which are represented by the cementoblasts and the pre-cementum, must be destroyed and an inflammatory process must be initiated. This process can be potentiated in teeth with pulp necrosis because bacteria and their metabolic products can diffuse through the dentinal tubules, acting as a stimulant to inflammation on the external root surface. ³3. Abbott PV. Prevention and management of external inflammatory resorption following trauma to teeth. Aust Dent J. 2016 Mar;61 Suppl 1:82-94. https://doi.org/10.1111/adj.12400
https://doi.org/10.1111/adj.12400... Usually, such lesions appear as sequelae after severe dental trauma, such as luxations and avulsions. ⁴4. Andreasen JO, Bakland LK, Flores MT, Andreasen FM, Andersson L. Traumatic Dental Injuries - A manual. 3rd ed. West Sussex: Wiley-Blackwell; 2011. pp. 18-21.

Calcium hydroxide (CH) pastes have traditionally been used as an intracanal medicament to treat external inflammatory root resorption. ³3. Abbott PV. Prevention and management of external inflammatory resorption following trauma to teeth. Aust Dent J. 2016 Mar;61 Suppl 1:82-94. https://doi.org/10.1111/adj.12400
https://doi.org/10.1111/adj.12400... ^,55. McHugh CP, Zhang P, Michalek S, Eleazer PD. pH required to kill Enterococcus faecalis in vitro. J Endod. 2004 Apr;30(4):218-9. https://doi.org/10.1097/00004770-200404000-00008
https://doi.org/10.1097/00004770-2004040... CH has a high pH, antimicrobial activity, and inhibits the clastic cells responsible for the progression of resorption. ⁶6. Trope M, Moshonov J, Nissan R, Buxt P, Yesilsoy C. Short vs. long-term calcium hydroxide treatment of established inflammatory root resorption in replanted dog teeth. Endod Dent Traumatol. 1995 Jun;11(3):124-8. https://doi.org/10.1111/j.1600-9657.1995.tb00473.x
https://doi.org/10.1111/j.1600-9657.1995... ^,77. Siqueira Junior JF, Lopes HP. Mechanisms of antimicrobial activity of calcium hydroxide: a critical review. Int Endod J. 1999 Sep;32(5):361-9. https://doi.org/10.1046/j.1365-2591.1999.00275.x
https://doi.org/10.1046/j.1365-2591.1999... ^,88. Cvek M. Endodontic management and the use of calcium hydroxide in traumatized permanent teeth. In: Andreasen JO, Andreasen FM, Andersson L, editors. Textbook and color atlas of traumatic injuries to the teeth. 4th ed. Oxford: Blackwell; 2007. p. 598-657.^,99. Forghani M, Mashhoor H, Rouhani A, Jafarzadeh H. Comparison of pH changes induced by calcium enriched mixture and those of calcium hydroxide in simulated root resorption defects. J Endod. 2014 Dec;40(12):2070-3. https://doi.org/10.1016/j.joen.2014.09.006
https://doi.org/10.1016/j.joen.2014.09.0... An appropriate vehicle must be used for CH to have the desired effect. Saline, distilled water, anesthetic solutions, and propylene glycol are commonly recommended vehicles. ¹⁰10. Mohammadi Z, Dummer PM. Properties and applications of calcium hydroxide in endodontics and dental traumatology. Int Endod J. 2011 Aug;44(8):697-730. https://doi.org/10.1111/j.1365-2591.2011.01886.x
https://doi.org/10.1111/j.1365-2591.2011...

Chlorhexidine (CHX) digluconate is a bisguanide known for its antimicrobial action against bacteria. ¹¹11. Gomes BP, Vianna ME, Zaia AA, Almeida JF, Souza-Filho FJ, Ferraz CC. Chlorhexidine in endodontics. Braz Dent J. 2013;24(2):89-102. https://doi.org/10.1590/0103-6440201302188
https://doi.org/10.1590/0103-64402013021... For endodontic purposes, CHX can be used in a liquid or in a gel presentation and it has been suggested as an alternative vehicle for CH. ¹¹11. Gomes BP, Vianna ME, Zaia AA, Almeida JF, Souza-Filho FJ, Ferraz CC. Chlorhexidine in endodontics. Braz Dent J. 2013;24(2):89-102. https://doi.org/10.1590/0103-6440201302188
https://doi.org/10.1590/0103-64402013021... This combination is associated with excellent antimicrobial activity and high pH, without alteration of the biological characteristics or action as a physical barrier preventing the reinfection of the canal. ¹¹11. Gomes BP, Vianna ME, Zaia AA, Almeida JF, Souza-Filho FJ, Ferraz CC. Chlorhexidine in endodontics. Braz Dent J. 2013;24(2):89-102. https://doi.org/10.1590/0103-6440201302188
https://doi.org/10.1590/0103-64402013021... ^,1212. Gomes BP, Vianna ME, Sena NT, Zaia AA, Ferraz CC, Souza Filho FJ. In vitro evaluation of the antimicrobial activity of calcium hydroxide combined with chlorhexidine gel used as intracanal medicament. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 Oct;102(4):544-50. https://doi.org/10.1016/j.tripleo.2006.04.010
https://doi.org/10.1016/j.tripleo.2006.0...

Depending on the stage of root resorption, CH pastes must be renewed within the canal for several weeks. ³3. Abbott PV. Prevention and management of external inflammatory resorption following trauma to teeth. Aust Dent J. 2016 Mar;61 Suppl 1:82-94. https://doi.org/10.1111/adj.12400
https://doi.org/10.1111/adj.12400... Abbott ³3. Abbott PV. Prevention and management of external inflammatory resorption following trauma to teeth. Aust Dent J. 2016 Mar;61 Suppl 1:82-94. https://doi.org/10.1111/adj.12400
https://doi.org/10.1111/adj.12400... states that the intracanal medicament can remain in the canal for 6-12 months, being replaced every 3 months. Chamberlain ¹³13. Chamberlain TM, Kirkpatrick TC, Rutledge RE. pH changes in external root surface cavities after calcium hydroxide is placed at 1, 3 and 5 mm short of the radiographic apex. Dent Traumatol. 2009 Oct;25(5):470-4. https://doi.org/10.1111/j.1600-9657.2009.00806.x
https://doi.org/10.1111/j.1600-9657.2009... suggests changing CH pastes at shorter intervals because, after 4 weeks, the pH decreases substantially. Although this type of treatment is well accepted, the constant changes of CH paste are a clinical disadvantage. In addition, renewal and prolonged exposure to CH may alter the mechanical properties of dentin, reducing fracture resistance. ¹⁴14. Yassen GH, Vail MM, Chu TG, Platt JA. The effect of medicaments used in endodontic regeneration on root fracture and microhardness of radicular dentine. Int Endod J. 2013 Jul;46(7):688-95. https://doi.org/10.1111/iej.12046
https://doi.org/10.1111/iej.12046... ^,1515. Valera MC, Albuquerque MT, Yamasaki MC, Vassallo FN, Silva DA, Nagata JY. Fracture resistance of weakened bovine teeth after long-term use of calcium hydroxide. Dent Traumatol. 2015 Oct;31(5):385-9. https://doi.org/10.1111/edt.12185
https://doi.org/10.1111/edt.12185... ^,1616. Andreasen JO, Munksgaard EC, Bakland LK. Comparison of fracture resistance in root canals of immature sheep teeth after filling with calcium hydroxide or MTA. Dent Traumatol. 2006 Jun;22(3):154-6. https://doi.org/10.1111/j.1600-9657.2006.00419.x
https://doi.org/10.1111/j.1600-9657.2006... ^,1717. Rosenberg B, Murray PE, Namerow K. The effect of calcium hydroxide root filling on dentin fracture strength. Dent Traumatol. 2007 Feb;23(1):26-9. https://doi.org/10.1111/j.1600-9657.2006.00453.x
https://doi.org/10.1111/j.1600-9657.2006...

Another proposed intracanal medicament for the treatment of external inflammatory resorptions is the combination of 2% CHX gel, zinc oxide, and CH. ¹⁸18. Soares AJ, Lima TF, Nagata JY, Gomes BP, Zaia AA, Souza-Filho F. Intracanal dressing paste composed by calcium hydroxide, chlorhexidine and zinc oxide for the treatment of immature and mature traumatized teeth. Braz J Oral Sci. 2014 Jan;13(1):6-11. https://doi.org/10.1590/1677-3225v13n1a02
https://doi.org/10.1590/1677-3225v13n1a0... This medicament presents greater radiopacity when compared with medicaments without zinc oxide, and remains in the root canal for longer periods without the need for periodic changes. However, no studies in the literature have evaluated how long this medicament remains at a high pH, a critical factor for the control of external inflammatory root resorption.

In view of the above information, the aim of this study was to assess the influence of CHX and zinc oxide in CH medications on pH in simulated external root resorption.

Methodology

This study was approved by the Research Ethics Committee of the Health Sciences Center of Federal University of Paraiba (protocol number: 44722715.4.0000.5188).

Sample size was calculated according to a previous study with similar methodology. ⁹9. Forghani M, Mashhoor H, Rouhani A, Jafarzadeh H. Comparison of pH changes induced by calcium enriched mixture and those of calcium hydroxide in simulated root resorption defects. J Endod. 2014 Dec;40(12):2070-3. https://doi.org/10.1016/j.joen.2014.09.006
https://doi.org/10.1016/j.joen.2014.09.0... The minimal sample size to detect a difference with a power of 80% at 95% confidence interval was 12. (G*Power 3.1.7 software for Windows; Heinrich Heine, Universität Düsseldorf). However, additional specimens were used to compensate for possible sample loss.

One hundred anterior permanent human teeth with similar anatomic characteristics were selected. Before the analysis, all teeth were radiographed in the buccolingual and mesiodistal directions to confirm the presence of a single canal with no curvature. Teeth with morphological alterations, cavities, or destruction of the root cementum were excluded from the study sample.

The teeth were decoronated 15 mm from the apex to create roots of equal length. Confirmation of the root length was performed with a digital caliper. The procedure was followed by instrumentation of the canals using a Reciproc 50.05 instrument (VDW GmbH, Munich, Germany) in accordance with the manufacturer’s instructions. The working length was 1 mm short of the apical foramen. A K-file 15 (Dentsply, Bailagues, Switzerland) was inserted up to the apical foramen for maintaining apical patency. Canal irrigation was performed with 15 mL of 2.5% sodium hypochlorite. On completion of the instrumentation, the canals were irrigated with 5 mL of 17% EDTA, and 10 mL of distilled water.

To simulate external root resorption, cavities on the buccal surface of the roots were created with a 1.4-mm high-speed diamond round bur (Brasseler, Savannah, USA). Only one defect was created on each tooth. The cavities were positioned 5 mm above the root apex, in the middle third, and were 4 mm in diameter. To remove the smear layer, the simulated root resorptions were irrigated with 3 mL of 17% EDTA and then with 5 mL of distilled water.

Division of experimental groups and analysis of root pH

The specimens were divided into four experimental groups and one control group, as shown in Table 1 .

Before material placement, all canals were dried with paper points. The intracanal pastes for each group were manipulated on a glass plate, adding CH to the vehicle in a ratio of 1:1 until a creamy consistency was obtained. The insertion into the root canals was performed using lentulo spirals, filling the entire root canal. For the CH+CHXg+ZnO group, manipulation was also performed on a glass plate, adding CH, CHX gel, and zinc oxide in a ratio of 2:1 2 as described by Soares et al. ¹⁸18. Soares AJ, Lima TF, Nagata JY, Gomes BP, Zaia AA, Souza-Filho F. Intracanal dressing paste composed by calcium hydroxide, chlorhexidine and zinc oxide for the treatment of immature and mature traumatized teeth. Braz J Oral Sci. 2014 Jan;13(1):6-11. https://doi.org/10.1590/1677-3225v13n1a02
https://doi.org/10.1590/1677-3225v13n1a0... The consistency of this intracanal paste is similar to that of Coltosol (Coltene/Whaledent, Mahwah, USA). This medicament was inserted incrementally with an endodontic condenser (Odous de Deus, Belo Horizonte, Brazil) until it filled the root canal. Complete placement of CH pastes was verified radiographically.

Coronal sealing was performed with Coltosol (Coltene/Whaledent, Mahwah, USA) and composite resin (Filtek 3M Espe, Sumaré, Brazil). Apical sealing was performed with cyanoacrylate and sticky wax. Subsequently, the specimens were inserted into individual devices containing non-buffered saline solution. The cap of each device was filled with sticky wax to allow fixation of the specimens and prevent their displacement. The specimens were stored in an incubator at 37 °C until the root pH was assessed.

To measure the pH, the teeth were removed from the individual devices and washed with distilled water. A digital pH meter with a microelectrode (HI1093B, Hanna instruments, São Paulo, SP, Brazil) was used to verify root pH changes. The microelectrode was calibrated with solutions of known pH (4.7 and 9) before every five measurements. The assessments were performed at 3 h, 24 h, and 1, 2, 3, and 4 weeks after inserting the intracanal pastes. The methodology and the periods of analysis were based on previous studies. ⁹9. Forghani M, Mashhoor H, Rouhani A, Jafarzadeh H. Comparison of pH changes induced by calcium enriched mixture and those of calcium hydroxide in simulated root resorption defects. J Endod. 2014 Dec;40(12):2070-3. https://doi.org/10.1016/j.joen.2014.09.006
https://doi.org/10.1016/j.joen.2014.09.0... ^,1313. Chamberlain TM, Kirkpatrick TC, Rutledge RE. pH changes in external root surface cavities after calcium hydroxide is placed at 1, 3 and 5 mm short of the radiographic apex. Dent Traumatol. 2009 Oct;25(5):470-4. https://doi.org/10.1111/j.1600-9657.2009.00806.x
https://doi.org/10.1111/j.1600-9657.2009...

Statistical analysis

Kolmogorov-Smirnov analysis of the raw data indicated a bell-shaped distribution. Therefore, the data were analyzed with a one-way analysis of variance (ANOVA) and the groups were compared using Tukey’s multiple comparison test (with a 95% confidence interval, p = 0.05). Data were analyzed using SPSS 11.5 statistical software (SPSS Inc, Chicago, USA)

Results

Table 2 shows the mean pH values, standard deviation, and statistical differences found in the between-group and within-group analyses. The CH+CHXg+ZnO group presented the highest pH values at all evaluated times, differing statistically from the other groups (p < 0.05). The maximum pH values of the CH + S and CH + CHX group were 9.5 and 9.92, respectively, reached in the first week. The CH + CHXg group reached the peak pH value (9.99) in the second week; it decreased more slowly until the fourth week compared with the CH + S and CH + CHX groups (p < 0.05).

Discussion

Pulp necrosis is one of the factors responsible for the progression of external inflammatory root resorption, because bacteria and their metabolic products can diffuse through the dentinal tubules, reach the root surface, and increase destruction in this area, thus making endodontic treatment necessary. ³3. Abbott PV. Prevention and management of external inflammatory resorption following trauma to teeth. Aust Dent J. 2016 Mar;61 Suppl 1:82-94. https://doi.org/10.1111/adj.12400
https://doi.org/10.1111/adj.12400... As CH has an active influence on the reduction of osteoclastic activity and induction of repair, it plays an important role in controlling resorption. ¹³13. Chamberlain TM, Kirkpatrick TC, Rutledge RE. pH changes in external root surface cavities after calcium hydroxide is placed at 1, 3 and 5 mm short of the radiographic apex. Dent Traumatol. 2009 Oct;25(5):470-4. https://doi.org/10.1111/j.1600-9657.2009.00806.x
https://doi.org/10.1111/j.1600-9657.2009... ^,1919. Tronstad L, Andreasen JO, Hasselgren G, Kristerson L, Riis I. pH changes in dental tissues after root canal filling with calcium hydroxide. J Endod. 1981 Jan;7(1):17-21. https://doi.org/10.1016/S0099-2399(81)80262-2
https://doi.org/10.1016/S0099-2399(81)80... ^,2020. Estrela C, Holland R. Calcium hydroxide. In: Estrela C, editor. Endodontic science. São Paulo: Editora Artes Medicas Ltda; 2009. p. 744-821. Such effects are possible because of the pH of CH. ¹⁰10. Mohammadi Z, Dummer PM. Properties and applications of calcium hydroxide in endodontics and dental traumatology. Int Endod J. 2011 Aug;44(8):697-730. https://doi.org/10.1111/j.1365-2591.2011.01886.x
https://doi.org/10.1111/j.1365-2591.2011... Pure CH paste has a high pH (12.5 to 12.8) and it is classified as a strong base. ¹⁰10. Mohammadi Z, Dummer PM. Properties and applications of calcium hydroxide in endodontics and dental traumatology. Int Endod J. 2011 Aug;44(8):697-730. https://doi.org/10.1111/j.1365-2591.2011.01886.x
https://doi.org/10.1111/j.1365-2591.2011... pH values found in this study varied from 8.4 to 11.1 because the pH was measured on the root surface. Other studies with a similar methodology found similar pH values. ⁹9. Forghani M, Mashhoor H, Rouhani A, Jafarzadeh H. Comparison of pH changes induced by calcium enriched mixture and those of calcium hydroxide in simulated root resorption defects. J Endod. 2014 Dec;40(12):2070-3. https://doi.org/10.1016/j.joen.2014.09.006
https://doi.org/10.1016/j.joen.2014.09.0... ^,1313. Chamberlain TM, Kirkpatrick TC, Rutledge RE. pH changes in external root surface cavities after calcium hydroxide is placed at 1, 3 and 5 mm short of the radiographic apex. Dent Traumatol. 2009 Oct;25(5):470-4. https://doi.org/10.1111/j.1600-9657.2009.00806.x
https://doi.org/10.1111/j.1600-9657.2009... The decrease in pH on the root surface can be explained because the diffusion of hydroxyl ions along the dentinal tubules was probably slowed by the buffering capacity of dentin. ²¹21. Wang JD, Hume WR. Diffusion of hydrogen ion and hydroxyl ion from various sources through dentine. Int Endod J. 1988 Jan;21(1):17-26. https://doi.org/10.1111/j.1365-2591.1988.tb00949.x
https://doi.org/10.1111/j.1365-2591.1988...

Aqueous solutions are recommended as vehicles for CH because they allow rapid release of ions. In the present study, the use of saline confirmed this. The maximum pH peak was reached after 1 week, remaining above pH 9 until the second week. Thereafter, the decrease was significant. Chamberlain et al. ¹³13. Chamberlain TM, Kirkpatrick TC, Rutledge RE. pH changes in external root surface cavities after calcium hydroxide is placed at 1, 3 and 5 mm short of the radiographic apex. Dent Traumatol. 2009 Oct;25(5):470-4. https://doi.org/10.1111/j.1600-9657.2009.00806.x
https://doi.org/10.1111/j.1600-9657.2009... verified the pH changes in simulated external root resorption in canals completely or partially filled with CH, and also observed that the pH values began to decrease significantly after the second week. However, the authors used UltraCal XS (UltraDent Products Inc., South Jordan, USA), which also has an aqueous vehicle, and stated that this medication must be renewed within the canal after 4 weeks. The results of this research confirm the need for renewal to maintain the alkaline pH of the root surface when saline is used as a vehicle.

CHX is a substance used as an endodontic irrigant and its pH ranges from 5.5 to 7. ¹¹11. Gomes BP, Vianna ME, Zaia AA, Almeida JF, Souza-Filho FJ, Ferraz CC. Chlorhexidine in endodontics. Braz Dent J. 2013;24(2):89-102. https://doi.org/10.1590/0103-6440201302188
https://doi.org/10.1590/0103-64402013021... CHX in combination with CH is an intracanal medicament advocated by several authors who claim that the antimicrobial activity of CH is potentiated by the addition of CHX. ¹²12. Gomes BP, Vianna ME, Sena NT, Zaia AA, Ferraz CC, Souza Filho FJ. In vitro evaluation of the antimicrobial activity of calcium hydroxide combined with chlorhexidine gel used as intracanal medicament. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 Oct;102(4):544-50. https://doi.org/10.1016/j.tripleo.2006.04.010
https://doi.org/10.1016/j.tripleo.2006.0... ^,2222. de Souza-Filho FJ, Soares AJ, Vianna ME, Zaia AA, Ferraz CC, Gomes BP. Antimicrobial effect and pH of chlorhexidine gel and calcium hydroxide alone and associated with other materials. Braz Dent J. 2008;19(1):28-33. https://doi.org/10.1590/S0103-64402008000100005
https://doi.org/10.1590/S0103-6440200800...

23. Gomes BP, Souza SF, Ferraz CC, Teixeira FB, Zaia AA, Valdrighi L et al. Effectiveness of 2% chlorhexidine gel and calcium hydroxide against Enterococcus faecalis in bovine root dentine in vitro. Int Endod J. 2003 Apr;36(4):267-75. https://doi.org/10.1046/j.1365-2591.2003.00634.x
https://doi.org/10.1046/j.1365-2591.2003...

24. Vianna ME, Horz HP, Conrads G, Zaia AA, Souza-Filho FJ, Gomes BP. Effect of root canal procedures on endotoxins and endodontic pathogens. Oral Microbiol Immunol. 2007 Dec;22(6):411-8. https://doi.org/10.1111/j.1399-302X.2007.00379.x
https://doi.org/10.1111/j.1399-302X.2007...

25. Gomes BP, Sato E, Ferraz CC, Teixeira FB, Zaia AA, Souza-Filho FJ. Evaluation of time required for recontamination of coronally sealed canals medicated with calcium hydroxide and chlorhexidine. Int Endod J. 2003 Sep;36(9):604-9. https://doi.org/10.1046/j.1365-2591.2003.00694.x
https://doi.org/10.1046/j.1365-2591.2003...

26. Basrani B, Tjäderhane L, Santos JM, Pascon E, Grad H, Lawrence HP et al. Efficacy of chlorhexidine- and calcium hydroxide-containing medicaments against Enterococcus faecalis in vitro. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003 Nov;96(5):618-24. https://doi.org/10.1016/S1079-2104(03)00166-5
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27. Schäfer E, Bössmann K. Antimicrobial efficacy of chlorhexidine and two calcium hydroxide formulations against Enterococcus faecalis. J Endod. 2005 Jan;31(1):53-6. https://doi.org/10.1097/01.DON.0000134209.28874.1C
https://doi.org/10.1097/01.DON.000013420...

28. Gomes BP, Montagner F, Berber VB, Zaia AA, Ferraz CC, Almeida JF et al. Antimicrobial action of intracanal medicaments on the external root surface. J Dent. 2009 Jan;37(1):76-81. https://doi.org/10.1016/j.jdent.2008.09.009
https://doi.org/10.1016/j.jdent.2008.09....

29. Sirén EK, Haapasalo MP, Waltimo TM, Ørstavik D. In vitro antibacterial effect of calcium hydroxide combined with chlorhexidine or iodine potassium iodide on Enterococcus faecalis. Eur J Oral Sci. 2004 Aug;112(4):326-31. https://doi.org/10.1111/j.1600-0722.2004.00144.x
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30. Zerella JA, Fouad AF, Spångberg LS. Effectiveness of a calcium hydroxide and chlorhexidine digluconate mixture as disinfectant during retreatment of failed endodontic cases. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2005 Dec;100(6):756-61. https://doi.org/10.1016/j.tripleo.2005.05.072
https://doi.org/10.1016/j.tripleo.2005.0... ^-3131. Podbielski A, Spahr A, Haller B. Additive antimicrobial activity of calcium hydroxide and chlorhexidine on common endodontic bacterial pathogens. J Endod. 2003 May;29(5):340-5. https://doi.org/10.1097/00004770-200305000-00006
https://doi.org/10.1097/00004770-2003050... Other advantages of this association are: high pH, ²²22. de Souza-Filho FJ, Soares AJ, Vianna ME, Zaia AA, Ferraz CC, Gomes BP. Antimicrobial effect and pH of chlorhexidine gel and calcium hydroxide alone and associated with other materials. Braz Dent J. 2008;19(1):28-33. https://doi.org/10.1590/S0103-64402008000100005
https://doi.org/10.1590/S0103-6440200800...

23. Gomes BP, Souza SF, Ferraz CC, Teixeira FB, Zaia AA, Valdrighi L et al. Effectiveness of 2% chlorhexidine gel and calcium hydroxide against Enterococcus faecalis in bovine root dentine in vitro. Int Endod J. 2003 Apr;36(4):267-75. https://doi.org/10.1046/j.1365-2591.2003.00634.x
https://doi.org/10.1046/j.1365-2591.2003...

24. Vianna ME, Horz HP, Conrads G, Zaia AA, Souza-Filho FJ, Gomes BP. Effect of root canal procedures on endotoxins and endodontic pathogens. Oral Microbiol Immunol. 2007 Dec;22(6):411-8. https://doi.org/10.1111/j.1399-302X.2007.00379.x
https://doi.org/10.1111/j.1399-302X.2007... ^-2525. Gomes BP, Sato E, Ferraz CC, Teixeira FB, Zaia AA, Souza-Filho FJ. Evaluation of time required for recontamination of coronally sealed canals medicated with calcium hydroxide and chlorhexidine. Int Endod J. 2003 Sep;36(9):604-9. https://doi.org/10.1046/j.1365-2591.2003.00694.x
https://doi.org/10.1046/j.1365-2591.2003... substantivity as a result of the presence of CHX, ¹²12. Gomes BP, Vianna ME, Sena NT, Zaia AA, Ferraz CC, Souza Filho FJ. In vitro evaluation of the antimicrobial activity of calcium hydroxide combined with chlorhexidine gel used as intracanal medicament. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 Oct;102(4):544-50. https://doi.org/10.1016/j.tripleo.2006.04.010
https://doi.org/10.1016/j.tripleo.2006.0... ^,2828. Gomes BP, Montagner F, Berber VB, Zaia AA, Ferraz CC, Almeida JF et al. Antimicrobial action of intracanal medicaments on the external root surface. J Dent. 2009 Jan;37(1):76-81. https://doi.org/10.1016/j.jdent.2008.09.009
https://doi.org/10.1016/j.jdent.2008.09.... as a physical barrier against the reinfection of the canal, ¹²12. Gomes BP, Vianna ME, Sena NT, Zaia AA, Ferraz CC, Souza Filho FJ. In vitro evaluation of the antimicrobial activity of calcium hydroxide combined with chlorhexidine gel used as intracanal medicament. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 Oct;102(4):544-50. https://doi.org/10.1016/j.tripleo.2006.04.010
https://doi.org/10.1016/j.tripleo.2006.0... radiopacity, ²⁹29. Sirén EK, Haapasalo MP, Waltimo TM, Ørstavik D. In vitro antibacterial effect of calcium hydroxide combined with chlorhexidine or iodine potassium iodide on Enterococcus faecalis. Eur J Oral Sci. 2004 Aug;112(4):326-31. https://doi.org/10.1111/j.1600-0722.2004.00144.x
https://doi.org/10.1111/j.1600-0722.2004... and diffusion through the dentinal tubules, ²⁹29. Sirén EK, Haapasalo MP, Waltimo TM, Ørstavik D. In vitro antibacterial effect of calcium hydroxide combined with chlorhexidine or iodine potassium iodide on Enterococcus faecalis. Eur J Oral Sci. 2004 Aug;112(4):326-31. https://doi.org/10.1111/j.1600-0722.2004.00144.x
https://doi.org/10.1111/j.1600-0722.2004... which is an important factor for the treatment of external inflammatory root resorption.

The maximum mean pH values reached in the root surface by the pastes containing CHX liquid and gel were 9.92 and 9.99, respectively. Such results concur with those of other studies that found pH values between 9 and 12. ³²32. Agrafioti A, Tzimpoulas NE, Kontakiotis EG. Influence of dentin from the root canal walls and the pulp chamber floor on the pH of intracanal medicaments. J Endod. 2013 May;39(5):701-3. https://doi.org/10.1016/j.joen.2012.12.039
https://doi.org/10.1016/j.joen.2012.12.0... ^,3333. Duarte MA, Midena RZ, Zeferino MA, Vivan RR, Weckwerth PH, Santos F et al. Evaluation of pH and calcium ion release of calcium hydroxide pastes containing different substances. J Endod. 2009 Sep;35(9):1274-7. https://doi.org/10.1016/j.joen.2009.05.009
https://doi.org/10.1016/j.joen.2009.05.0... ^,3434. Pacios MG, Casa ML, Angeles Bulacio M, López ME. Calcium hydroxide’s association with different vehicles: in vitro action on some dentinal components. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003 Jul;96(1):96-101. https://doi.org/10.1016/S1079-2104(02)91705-1
https://doi.org/10.1016/S1079-2104(02)91... ^,3535. Yücel AC, Aksoy A, Ertaş E, Güvenç D. The pH changes of calcium hydroxide mixed with six different vehicles. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007 May;103(5):712-7. https://doi.org/10.1016/j.tripleo.2006.10.016
https://doi.org/10.1016/j.tripleo.2006.1... However, Carvalho et al. ³⁶36. Carvalho CN, Freire LG, Carvalho AP, Siqueira EL, Bauer J, Gritti GC et al. The influence of dentine on the pH of calcium hydroxide, chlorhexidine gel, and experimental bioactive glass-based root canal medicament. ScientificWorldJournal. 2015;2015:686259. https://doi.org/10.1155/2015/686259
https://doi.org/10.1155/2015/686259... observed that when CHX was used as the vehicle, the peak pH was achieved immediately after preparation of the medication (pH = 9); after 7 days, the pH was neutral. These authors have questioned the efficacy of the combination of CHX and CH. In the present study, the use of CHX did not decrease the alkalinity of CH, because when this vehicle was used, the pH values in the first week were higher than with saline. Basrani et al. ³⁷37. Basrani B, Ghanem A, Tjäderhane L. Physical and chemical properties of chlorhexidine and calcium hydroxide-containing medications. J Endod. 2004 Jun;30(6):413-7. https://doi.org/10.1097/00004770-200406000-00009
https://doi.org/10.1097/00004770-2004060... affirmed that addition of CHX to CH lowers its contact angle and improves the wettability of the medication on the root canal, favoring the penetration of ions into the dentinal tubules.

The paste containing CHX liquid reached the highest pH values after 1 week. The pH decreased significantly in the third and fourth weeks compared with the first one. By contrast, the paste containing CHX gel had higher pH values than did CHX liquid at all evaluated times, reaching the peak in the second week. Duarte et al. ³³33. Duarte MA, Midena RZ, Zeferino MA, Vivan RR, Weckwerth PH, Santos F et al. Evaluation of pH and calcium ion release of calcium hydroxide pastes containing different substances. J Endod. 2009 Sep;35(9):1274-7. https://doi.org/10.1016/j.joen.2009.05.009
https://doi.org/10.1016/j.joen.2009.05.0... found that 2% CHX gel associated with CH had higher pH values when compared with 1% CHX in propylene glycol; they attributed this result to natrosol gel, which is water-soluble and may favor the release of hydroxyl ions. In the present study, the decrease in pH over time was slower for CHX gel than for CHX liquid. In the third and fourth weeks, the pH of 2% CHX gel was also significantly higher. A reason for this is that natrosol may also allow the release of hydroxyl ions for a longer period, allowing the pH to remain alkaline in the fourth week.

One of the disadvantages of CH for the treatment of external inflammatory root resorption is the need for periodic renewals so that it can continue to exert its effects within the canal. Pastes containing zinc oxide can have a longer residence time in the root canal without the need for constant changes. The use of this paste was recommended for the treatment of traumatized teeth with external inflammatory root resorption and achieved good clinical results. ³⁸38. Herrera DR, Herrera CM, Lima AR, Nagata JY, Pereira AC, Silva EJ et al. Repair of apical root resorption associated with periodontitis using a new intracanal medicament protocol. J Oral Sci. 2014 Dec;56(4):311-4. https://doi.org/10.2334/josnusd.56.311
https://doi.org/10.2334/josnusd.56.311...

The CH+ CHXg+ZnO group had the highest pH values at all evaluated times. Souza-Filho et al. ²²22. de Souza-Filho FJ, Soares AJ, Vianna ME, Zaia AA, Ferraz CC, Gomes BP. Antimicrobial effect and pH of chlorhexidine gel and calcium hydroxide alone and associated with other materials. Braz Dent J. 2008;19(1):28-33. https://doi.org/10.1590/S0103-64402008000100005
https://doi.org/10.1590/S0103-6440200800... verified the antimicrobial effect and pH of this paste and observed that, compared with the combination of 2% CHX gel and CH, the pH was higher, which is in agreement with the present research. Guerreiro-Tanomaru et al. ³⁹39. Guerreiro-Tanomaru JM, Pereira KF, Nascimento CA, Bernardi MI, Tanomaru-Filho M. Use of nanoparticulate zinc oxide as intracanal medication in endodontics: pH and antimicrobial activity. Acta Odontol Latinoam. 2013;26(3):144-8. verified the effect of the addition of microparticulate and nanoparticulate zinc oxide in CH pastes and observed that the pH peak occurred after 14 days, remaining higher than 10 after 28 days. In the present study, the maximum pH was also observed in the second week, remaining alkaline until the fourth week. The results of this research suggest that, despite having higher viscosity than other pastes, the combination of 2% CHX gel, CH, and zinc oxide allowed the diffusion of ions inside the dentinal tubules, maintaining an alkaline pH in the area of resorption. Zinc oxide has a neutral pH when combined with inert vehicles, ³⁹39. Guerreiro-Tanomaru JM, Pereira KF, Nascimento CA, Bernardi MI, Tanomaru-Filho M. Use of nanoparticulate zinc oxide as intracanal medication in endodontics: pH and antimicrobial activity. Acta Odontol Latinoam. 2013;26(3):144-8. but the oxide behaves as an amphoteric oxide; ⁴⁰40. Mekki-Berrada A, Grondin D, Bennici S, Auroux A. Design of amphoteric mixed oxides of zinc and Group 3 elements (Al, Ga, In): migration effects on basic features. Phys Chem Chem Phys. 2012 Mar;14(12):4155-61. https://doi.org/10.1039/c2cp23613c
https://doi.org/10.1039/c2cp23613c... that is, it acts as an acid or a base depending on the medium. It is suggested that zinc oxide combined with CHX gel and CH may raise the pH of these medications, which are already alkaline. Further studies are recommended to verify the chemical association between these medicaments and to evaluate their efficacy in the treatment of external inflammatory root resorption.

According to the results of the present in vitro study, we can conclude that CHX solution or gel maintains the alkaline pH of CH, and that CHX gel allowed a slower decrease in pH over time. The combination of 2% CHX gel, CH, and zinc oxide had the highest pH values and was an efficient medication for maintenance of alkaline root pH in the area of resorption in this study.

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