Purpose: To evaluate the clinical performance and postoperative sensitivity of noncarious Class V restorations with and without the use of a potassium oxalate-based desensitizing agent over a period of 18 months. Materials and Methods: One hundred forty cervical lesions (40 patients) were selected and randomly divided into four groups: group 1 (G1) - teeth restored with the application of a potassium oxalate-based desensitizing agent (BisBlock) after acid etching and before the application of the adhesive Adper Single Bond 2; group 2 (G2) - teeth restored using the same adhesive system used in G1, without the use of any desensitizing agent; group 3 (G3) - similar to G1, but using the adhesive One-Step; group 4 (G4) - similar to G3, but without the application of BisBlock. All restorations were evaluated (double blind) after 1 week and 2, 6, 12, and 18 months according to the modified USPHS criteria. The McNemar and chi-square tests were used to analyze the results (p <= 0.05). Results: There were no statistical differences between groups restored with or without the use of a desensitizing agent for postoperative sensitivity. After 18 months, retention rates proved to be statistically significantly lower for One-Step than Adper Single Bond 2. Conclusion: The use of potassium oxalate-based desensitizing agent did not decrease postoperative sensitivity when it was used under composite resin restorations. Keywords: clinical evaluation, dentin desensitizer, potassium oxalate, dentin hypersensitivity, noncarious cervical lesions