title: Direct and transdentinal antibacterial activity of chlorhexidine.
abstract: OBJECTIVE
  To evaluate the antibacterial effect of different chlorhexidine (CHX) concentrations against Streptococcus mutans using the agar-diffusion method with and without human dentin discs placed between the bacteria and the test substances.
  
  
  METHODS
  For the direct application (agar-well technique), a base layer containing 15 mL of BHI agar and 300 microL of S. mutans inoculum (10(9) cfu/mL) was prepared in Petri dishes. Six wells per dish were made at equidistant points and immediately filled with CHX gels (0.12%, 0.2%, 1% and 2%), 35% phosphoric acid and pure natrosol (n = 6 wells/substance). Paper discs soaked in sterile distilled water served as control group (n = 6). For the indirect application (transdentinal diffusion), 0.2 mm- and 0.5 mm-thick human dentin discs (36 discs/thickness) had the hydraulic conductance determined, which allowed the homogeneous allocation of them to the experimental and control groups. The discs were placed at equidistant points on the Petri dishes containing BHI with the S. mutans inoculum (six discs per dish; one per substance) with the pulpal side in contact with the bacteria. In the discs treated with CHX gels, dentin surface was etched with H3PO4 and rinsed with distilled water before CHX gel application for 1 minute. After both direct and indirect application, the dishes were incubated for 24 hours and the bacterial growth inhibition zones formed around the wells and dentin discs were measured. Data were analyzed statistically by the non-parametric Kruskal-Wallis and Mann-Whitney tests at 5% significance level.
  
  
  RESULTS
  In the direct test, all CHX concentrations presented a dose-dependent antibacterial activity against S. mutans. In the indirect test, there were statistically significant differences (P < 0.05) among all groups and the largest microbial growth inhibition zones were observed when 2% CHX was applied on 0.2 mm-thick discs (P < 0.05). It was concluded that all evaluated CHX gels exhibited both direct and transdentinal antibacterial activity against S. mutans. This effect of CHX was strongly influenced by the CHX concentration as well as the dentin barrier thickness.
authors.affiliation: Department of Orthodontics and Pediatric Dentistry, University of São Paulo State, UNESP, Rua Humaitá, 1680--CEP: 14.801-903, Araraquara, SP, Brazil.
authors.forename: Fernanda Campos Rosetti
authors.initials: FC
authors.lastname: Lessa
authors.forename: Indri
authors.initials: I
authors.lastname: Nogueira
authors.forename: Fernanda da Silveira
authors.initials: Fda S
authors.lastname: Vargas
authors.forename: Denise Magdalena Palomari
authors.initials: DM
authors.lastname: Spolidorio
authors.forename: Josimeri
authors.initials: J
authors.lastname: Hebling
authors.forename: Franklin
authors.initials: F
authors.lastname: García-Godoy
authors.forename: Carlos Alberto de Souza
authors.initials: CA
authors.lastname: Costa
mesh_terms: D000362:Agar; D000891:Anti-Infective Agents, Local / Q000008:administration & dosage / Q000494:pharmacology*; D002710:Chlorhexidine / Q000008:administration & dosage / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003806:Dentin Permeability; D004058:Diffusion; D052978:Disk Diffusion Antimicrobial Tests; D004305:Dose-Response Relationship, Drug; D006801:Humans; D010756:Phosphoric Acids / Q000494:pharmacology; D018709:Statistics, Nonparametric; D013295:Streptococcus mutans / Q000187:drug effects*
chemical_list: D000891:Anti-Infective Agents, Local; D010756:Phosphoric Acids; D000362:Agar; C030242:phosphoric acid; D002710:Chlorhexidine