Patients of all ages now routinely seek orthodontics treatment. In this chapter, we investigated whether age-dependent biologic responses to orthodontic force correlate with the rate of tooth movement. Results from our clinical study are presented, showing that although the cytokine and osteoclast markers increased significantly in both adolescents and adults in response to orthodontic forces, the increases are greater in adults. Interestingly, the rate of tooth movement in adults are significantly slower than in adolescents with adults reporting significantly more discomfort and pain. In this chapter, we discuss the clinical implications and possible explanations for these surprising results.