BACKGROUND Despite the broad use of crown-lengthening surgery (CLS), there is no complete agreement as to the desired amount of exposed sound tooth structure needed to accommodate both the restorative needs and the reformation of the supraosseous gingiva (SOG). Classically, it has been proposed that approximately 3 mm of SOG, the amount considered by most to be present before surgery, will be reformed after CLS. The purpose of this study was to test the viability of transsulcular probing (TSP) and to determine whether the SOG that forms after CLS is the same as that measured preoperatively. METHODS Nineteen patients underwent CLS with the surgical tooth acting both as the control and the test site. The SOG dimension was measured by TSP before and 6 months after surgery. Stents were used as fixed reference points. Intraclass correlations were calculated to test for the reliability of TSP measurements versus direct-bone-level (DBL) measurements. A Wilcoxon signed-rank test was used to compare the means for the mean buccal, mean lingual, and overall mean SOG dimensions at baseline to corresponding measurements at 6 months. RESULTS Intraclass correlation coefficients for TSP measures of SOG to DBL measures of SOG ranged from 83.4% agreement to 91.9% agreement, with all correlations being highly significant (P <0.001), indicating a high degree of agreement between TSP and DBL. The differences in SOG dimensions, 6 months after surgery compared to baseline, were as follows: mean buccal, 0.51 mm; mean lingual/palatal, 0.61 mm; overall mean, 0.56 mm. These differences were significant for all three comparisons (P <0.001, P <0.004, and P <0.001, respectively). CONCLUSIONS TSP is an accurate alternative method to DBL in clinically determining SOG dimensions. Six months after CLS, the SOG dimension was reduced by 0.51 to 0.61 mm compared to the presurgical measurement, with these mean differences being statistically significant.