Characteristics of the Vector-system are the linear movement of the instruments parallel to the tooth surface and an indirect application of the ultrasound's energy on the tissues to be treated due to a liquid film adhering to the instrument, or by particle suspension. 24 subjects (14 male, 10 female, age: 37 - 64 yrs.) were recruited for a clinical trial aimed at assessing the effect of the Vector periodontal therapy. The treated periodontal areas showed no endodontic disorder and the pockets measured (pressure calibrated probe) between 5 mm and 14 mm. After a baseline examination including assessments of oral hygiene standards, attachmemt level, bleeding on probing (BOP) and suppuration the patients received oral hygiene instructions. For the initial periodontal treatment the metallic Vector-instruments and the Vector-hydroxylapatite (HA)-suspension was used according to the manufacturer's instructions. By using a split mouth design on the same patients, diluted HA-suspension with a pH of 7 (control) and diluted citrus acid solution with a pH of 5.5 modified analogous HA-suspension (test group) were assessed. After 6 weeks, 3 months, 6 months and 12 months all of the results were re-evaluated. The participants reveived a professional oral prophylaxis by using the Vector fiber-reinforced resin-recall-instruments and analogous suspensions, areas with persistent BOP were re-treated. Six weeks after the initial treatment a significant reduction of the pocket depths and of the number of periodontal areas with positive BOP was attained (Kruskal/Wallis; Wilcoxon Mann-Whitney). Suppurations had completely disappeared. Twelve months after the initial treatment an attachment gain of more than 2 mm was recorded on 21 out of 24 patients on more than three periodontal areas. No gender specific significant differences existed; data of both the test and control group was derived from the same population. The pH of the Vector coupling fluid seems to have a minor influence on the treatment outcome. Schlagwörter: periodontitis, Vector, Initial Treatment, Supportive Periodontal Therapy