In vitro evaluation of the antimicrobial activity of calcium hydroxide combined with chlorhexidine gel used as intracanal medicament Brenda Paula Figueiredo de Almeida Gomes, DDS, MS, PhD, a Morgana Eli Vianna, DDS, MS, b Neylla Teixeira Sena, DDS, b Alexandre Augusto Zaia, DDS, MS, PhD, a Caio Cezar Randi Ferraz, DDS, MS, PhD, a and Francisco José de Souza Filho, DDS, MS, PhD, a Piracicaba, SP, Brazil STATE UNIVERSITY OF CAMPINAS -UNICAMP The aim of this study was to investigate the antimicrobial activity of calcium hydroxide (Ca(OH) 2 ) combined with 2% chlorhexidine gluconate (CHX) gel against endodontic pathogens and to compare the results with the ones achieved by Ca(OH) 2 mixed with sterile water and by CHX gel alone. Two methods were used: the agar diffusion test and the direct contact test. Ca(OH) 2  2% CHX gel produced inhibitory zones ranging from 2.84 to 6.5 mm, and required from 30 seconds to 6 hours to eliminate all tested microorganisms. However, 2% CHX gel showed the largest microbial growth zones from 4.33 to 21.67 mm, and required 1 minute or less to inhibit all tested microorganisms. A paste of Ca(OH) 2 plus sterile water inhibited only the microorganisms with which it was in direct contact and required from 30 seconds to 24 hours to kill all tested microorganisms. In conclusion, 2% CHX gel  Ca(OH) 2 showed better antimicrobial activity than Ca(OH) 2 manipulated with sterile water. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;102:544-50) One of the major factors associated with endodontic failure is the persistence of microbial infection in the root canal system and periradicular area. 1 The chances of a favorable outcome of root canal treatment are significantly higher when microorgan- isms have been effectively eradicated before sealing the root canal system. However, microorganisms may per- sist in the root canal after root filling, increasing the risk of treatment failure. 2,3 The intracanal dressings tend to be effective against microorganisms that may have resisted the root canal preparation. Besides, medicaments control persistent exudation and destructive action of osteoclasts present in external dental resorption. 4 Ca(OH) 2 is believed to to have many of the proper- ties of an ideal root canal dressing, mainly due to its alkaline pH. 5,6 It is bactericidal 7 and neutralizes the remaining tissue debris in the root canal system. 8 Ca(OH) 2 also promotes an alkalinizing osteogenic en- vironment on the surrounding tissues through the con- tinuous release of OH - ions. 9,5 Furthermore, Ca(OH) 2 mediates the neutralization of lipopolysaccharides 10 and thus helps in cleansing the root canal. 8 Estrela et al. 11 claimed that Ca(OH) 2 inhibits bacte- rial enzymes by means of hydroxyl ions of the bacte- ria’s cytoplasmic membrane, generating the antibacte- rial effect. It activates tissue enzymes such as alkaline phosphatase, leading to the mineralizing effect. The chemical and biological dynamics that occur in the ionic dissociation of Ca(OH) 2 and its effect through tissue and bacterial cellular alterations deserve careful discussion and investigation. For calcium hydroxide to act effectively as an intra- canal dressing, it should ideally occupy all the pulp space thereby diffusing into areas inaccessible to in- a Associate Professor, Department of Restorative Dentistry, State Uni- versity of Campinas, Piracicaba, SP, Brazil. b Postgraduate Student, Department of Restorative Dentistry, State University of Campinas, Piracicaba, SP, Brazil. 1079-2104/$ - see front matter © 2006 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2006.04.010 544 Vol. 102 No. 4 October 2006 ENDODONTOLOGY Editor: Larz S. W. Spångberg