title: The effects of outward forced convective flow on inward diffusion of potassium across human dentin.
abstract: OBJECTIVE
  To measure the inward flux of potassium across human dentin disks, in vitro, in the absence and then in the presence of a simulated pulpal pressure (PP), before and after brushing with two desensitizing dentifrices.
  
  
  METHODS
  Dentin discs were made from extracted unerupted third molars and etched with 6% citric acid to remove the smear layers. The hydraulic conductance (Lp or outward fluid movement) of the discs was measured before and after brushing for 2 minutes with two desensitizing dentifrices, Colgate Sensitive Maximum Strength or Sensodyne Fresh Mint, both dentifrices containing 5% potassium nitrate. The potassium flux was measured at a pressure of 0 cm H2O, and a simulated pulpal pressure of 20 cm H2O.
  
  
  RESULTS
  The results showed the Colgate-brushed specimens had lower Lp (P < 0.05) than specimens brushed with Sensodyne or with saline. The Colgate-brushed specimens had a corresponding lower K+ flux, at a PP = 0 cm H2O, than specimens brushed with saline, but were not significantly different than specimens brushed with Sensodyne dentifrice. However, when the pressure was increased from 0 to 20 cm H2O, to simulate outward dentin fluid pressure, there were significant decreases in K+ flux across all three treatment groups, but the K+ flux of the Colgate-brushed specimens were affected the least, resulting in the Colgate-brushed specimens having significantly (P < 0.05) greater K+ fluxes than the saline or Sensodyne dentifrice-brushed groups. The magnitude of reduction in K+ flux in going from 0 cm H2O to 20 cm H2O was demonstrated to be linearly related to the magnitude of the Lp of the brushed specimens. Hence, a small Lp corresponded to a small reduction in K+ flux, and a correspondingly large K+ flux at 20 cm H2O. An explanation of this phenomenon is that a decrease in the Lp of dentin, produced by brushing, corresponds to a decreased outward dentin fluid flow. This lowers the outward K+ convective flow and also lowers the inward K+ diffusion. However, since the decrease of the outward K+ convective flow is greater than the decrease of the inward K+ diffusion, and the net flux is the algebraic sum of these two terms, the result is greater net inward K+ flux through the dentin. Therefore, the Colgate-brushed specimens, which exhibited the lowest Lp, provided the greatest inward K+ flux at simulated dentin fluid pressure.
authors.affiliation: Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA. dpashley@mail.mcg.edu
authors.forename: David H
authors.initials: DH
authors.lastname: Pashley
authors.forename: Kelli
authors.initials: K
authors.lastname: Agee
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Anita
authors.initials: A
authors.lastname: Smith
authors.forename: Edward A
authors.initials: EA
authors.lastname: Tavss
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Gambogi
mesh_terms: D000704:Analysis of Variance; D045424:Complex Mixtures; D003802:Dentifrices / Q000493:pharmacokinetics; D003804:Dentin / Q000378:metabolism*; D003806:Dentin Permeability; D003807:Dentin Sensitivity / Q000378:metabolism*; D019234:Dentinal Fluid / Q000502:physiology*; D004058:Diffusion; D004338:Drug Combinations; D005459:Fluorides / Q000493:pharmacokinetics; D006801:Humans; D006874:Hydrostatic Pressure; D009566:Nitrates / Q000493:pharmacokinetics*; D010710:Phosphates / Q000493:pharmacokinetics; D011188:Potassium / Q000378:metabolism*; D017680:Potassium Compounds / Q000493:pharmacokinetics*; D012212:Rheology; D012965:Sodium Chloride / Q000493:pharmacokinetics; D018709:Statistics, Nonparametric; D014099:Toothbrushing
chemical_list: D045424:Complex Mixtures; D003802:Dentifrices; D004338:Drug Combinations; D009566:Nitrates; D010710:Phosphates; D017680:Potassium Compounds; C097427:Sensodyne; C444700:colgate sensitive; D012965:Sodium Chloride; D005459:Fluorides; C023844:potassium nitrate; D011188:Potassium