Aged Alkaline Phosphatase--blood Alveolar Bone Loss--blood Anti-Bacterial Agents--therapeutic use Biomarkers--blood Bone Density--drug effects Bone Density Conservation Agents--therapeutic use Bone Diseases, Metabolic--drug therapy Child Collagen Type I--blood Double-Blind Method Doxycycline--therapeutic use Female Humans Linear Models Middle Aged Osteocalcin--blood Peptides--blood