 - Control: 200 mg placebo. Doxycycline and placebo are packaged identically and stored in sealed envelopes that were marked with the randomization code. Patients receive doxycycline or placebo after regenerative surgery is accomplished. Patient and clinician are blinded. Block randomization by smoking status current smoking: smokersformer and never smoking: non smokers is provided by the manufacturer of the doxycycline August Wolff GmbH Co. Arzneimittel, Bielefeld, Germany. 