title: Susceptibility of oral Candida species to calcium hydroxide in vitro.
abstract: OBJECTIVE
  The susceptibility of common oral Candida species to saturated aqueous calcium hydroxide solution was studied.
  
  
  METHODS
  The yeast species tested were C. albicans (16 strains). C. glabrata (three strains), C. guilliermondii (three strains), C. krusei (two strains), and C. tropicalis (two strains). At least one reference strain of each species was used; the others were clinical isolates either from persistent apical periodontitis or from marginal periodontitis. The susceptibility of Enterococcus faecalis (ATCC 29212) was studied for comparative purposes. Standardized inocula of the strains were incubated in aqueous calcium hydroxide solution, pH 12.4, for time-periods ranging from 5 min to 6 h. Volumes of 0.1 mL of the test suspension were cultured directly on Brucella blood agar and incubated in air at 37C. The plates were inspected for growth at 24 and 48 h and the colonies were counted. The time required to reduce the number of colony-forming units to less than 0.1% of the initial number was determined for each strain.
  
  
  RESULTS
  The sensitivity of the C. albicans strains was generally low, with 16 h of incubation required to kill 99.9% of the colony-forming units. No differences in susceptibility between C. albicans strains isolated from root-canal infections and from periodontitis were found. Both strains of C. tropicalis were killed between 3 and 6 h of incubation, whilst strains of C. guilliermondii were killed after only 1020 min of incubation. All strains of C. glabrata survived 20 min, but not 1 h, of incubation, whilst 13 h were required to kill C. krusei. Compared with E. faecalis, all Candida spp. showed either equally high or higher resistance to aqueous calcium hydroxide.
  
  
  CONCLUSIONS
  This study indicates that Candida spp. are resistant to calcium hydroxide in vitro, which may explain the isolation of yeasts from cases of persistent apical periodontitis.
authors.affiliation: Department of Cariology, Institute of Dentistry, University of Helsinki, Finland. tuomas.waltimo@helsinki.fi
authors.forename: T M
authors.initials: TM
authors.lastname: Waltimo
authors.forename: E K
authors.initials: EK
authors.lastname: Sirén
authors.forename: D
authors.initials: D
authors.lastname: Orstavik
authors.forename: M P
authors.initials: MP
authors.lastname: Haapasalo
mesh_terms: D002126:Calcium Hydroxide / Q000494:pharmacology*; D002175:Candida / Q000187:drug effects* / Q000302:isolation & purification; D002176:Candida albicans / Q000187:drug effects / Q000302:isolation & purification; D015169:Colony Count, Microbial; D003786:Dental Pulp Cavity / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D010485:Periapical Periodontitis / Q000188:drug therapy / Q000382:microbiology*; D012388:Root Canal Irrigants / Q000494:pharmacology*
chemical_list: D012388:Root Canal Irrigants; D002126:Calcium Hydroxide