Dentin hypersensitivity can be a major problem for periodontal patients. The relationship between dentin hypersensitivity and the patency of dentin tubules in vivo has been established. Thirteen adult patients with teeth scheduled for extraction were selected and a stent fabricated to confirm location of the root surface being examined. Response to a constant air blast was recorded on a numeric pain rating scale (from 0 to 4) during the course of treatment. The tooth surface was initially treated with 0.5 molar EDTA (pH = 7.4), to remove the smear layer and expose tubules. The region was then treated with either a 3% monopotassium-monohydrogen oxalate solution or a 3% sodium chloride solution, both at pH = 2.4. Solutions were prepared to be indistinguishable to the examiner. Response to air was evaluated before and after EDTA treatment and after treatment with a desensitizing agent. The patient was anesthetized and the treated tooth extracted. Specimens were sectioned, critical point dried, sputter coated with gold, and examined under the scanning electron microscope. Photomicrographs were analyzed by computer assisted digital analysis to evaluate the degree of tubule occlusion. Statistical analysis by repeated measures ANOVA for univariate tests of hypothesis for within subject effects showed the sodium chloride solution was more effective in reducing dentin sensitivity than the potassium oxalate solution. Scanning electron micrographic analysis revealed a mean dentin tubule aperture size of 1.720 square microns following EDTA treatment alone, 0.564 square micron following potassium oxalate treatment, and 0.386 square micron following sodium chloride treatment.(ABSTRACT TRUNCATED AT 250 WORDS)