METHODS	In a clinical trial , 19 students trained in the use of Gracey curettes for 10 weeks ( = 20 h ) ( GRA10 ) and Periopolisher system for 1 week ( = 2 h ) ( PP1 ) , and 20 students trained in the use of Gracey curettes for 1 week ( GRA1 ) and the Periopolisher for 10 weeks ( PP10 ) treated one patient each in a split-mouth design .\