The ozone therapy has been coming up as a new therapeutic modality. Medicine has been practicing since XIX century and counted great results. It is indicated for the treatment of 260 different pathologies. The researches in Dentistry has showed promising results, indicating a wide spread action in whole dental specialties. The great oxidative power of ozone provides a great antimicrobial effect and it increases the adenosine triphosphate (ATP) synthesis that can be considered as a general improvement of the cell metabolism, which can potentize the repair process. Thus, these facts justify the present study which will assess the increase of speed of apical periodontite repair.