The purpose of this study was to approve the possibility of clinical application of selftesting technique to confirm the cleanness status of the tooth surface after mechanical toothbrushing. Thirty-two periodontal patients who did not compromise any other systemic diseases were divided into two groups. Control group was instructed only the Bass method for toothbrushing, and then experimental group was demonstrated the Bass method and self-testing technique respectively for plaque control during this experiment. Selftesting technique is composed the comparison of roughness of the labial surface of maxillary central incisor and other toothsurface with touch sense using the tip of tongue. Plaque score and Gingival index were measured as clinical parameters at baseline and 1, 2 and 4 weeks after scaling and root planing. The results were as follows ; 1. Plaque scores and gingival index of 1, 2, and 4 weeks of two groups were statistically significant differences when compared with baseline value (p<0.05). 2. Plaque scores and gingival index of baseline and 1 week between two groups were not significant differences (p<0.05). 3. Plaque scores and gingival index of 2 and 4 weeks of test group were statistically significant difference when compared with control group (p<0.05). From the above results, self-testing technique which decides necessity of additional toothbrushing when tongue tip of subjects touch the maxillary molar buccal surfaces and mandibular molar lingual surfaces nd compares with maxillary anterior labial surfaces after toothbrushing appeared to effect the motivation of subjects. This study suggests that self-testing technique for cleanness after toothbrushing should be effect on the maintenance of oral hygiene when it is applied to clinical practice.