 A multiple regression model is calculated for the dependent variable bony fill with the independent variables baseline clinical parameters CAL-V, PD, GI, PI, postsurgical medication DOXYPLAC, defect parameters INFRA, 1, 2, 3wall component, baseline A. actinomycetemcomitans, age, sex, centre, smoking, EHI. Sex, centre, and smoking habits are defined by indicator variables. All patients that are recruited and treated according to the study protocol are considered for analysis intent to treat: ITT. If a patient left the study before finishing all re-examinations the respective data of the last re-examination are entered into the analysis last observation carried forward: LOCF. Statistical analysis is performed using a PC program SystatTM for Windows Version 10, Systat Inc. Evanston, IL, USA. 