Treatment assignment To enter a patient into the study each investigator will fill in a screening and an entry form and fax them to the Central Registrar located at the Clinical Research support Unit of Periodontology, Dental Clinic, Dep. of Biological, Surgical and Dental Sciences, University of Milan, Fondazione IRCCS Ca' Granda Polyclinic Milan, Italy. Following receipt of these forms, the Registrar will proceed to verify satisfaction of all entry criteria and will enter the subject into the study. Patient codes will be assigned consecutively and will be made of a total of 2 digits that will encode the subject number (from 01 to 60). These will be assigned at the first visit, verifying the inclusion criteria and entering the patient into the study. After having been entered patients into the study, experimental patients will be randomly assigned by Central Registrar to one of the two treatment regimens according to pre-defined randomization tables.