This book gives an insight of how the forces exerted by orthodontic tooth movement cause several metabolic changes in the periodontal tissues. Many studies have evaluated such modifications by analysis of various host metabolites released into the gingival crevicular fluid (GCF). This study used a cross-sectional design to examine the lactate dehydrogenase (LDH) activity in GCF to assess whether GCF LDH can be proposed as a sensitive marker for periodontal tissue modifications during orthodontic tooth movement. Thus the association between clinical parameters and tissue remodeling represented by GCF alterations can be useful to biologically monitor and predict orthodontic treatment.