THE BIOLOGY OF ORTHODONTIC TOOTH MOVEMENT AND THE IMPACT OF ANTI-INFLAMMATORY DRUGS

摘要

Orthodontic tooth movement (OTM) results from complex biological mechanisms, more knowledge of which is needed for optimized orthodontic treatment. The biology of OTM is characterized by a cascade of events, triggered by the strain of the periodontal ligament fibers, leading to an inflammatory process that allows appropriate tissue remodeling. However, this inflammatory process may evoke side effects, such as pain, for which the use of non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol (acetaminophen) has been advocated. In vitro and in vivo studies have demonstrated that the arachidonic acid (AA) pathway represents a main step of the molecular events governing tissue remodeling during OTM. Through this pathway, important pro-inflammatory prostaglandins (PGs) are synthesized by three isoforms of a key enzyme referred as cyclooxygenase (COX), which catalyzes the conversion of AA into prosta-glandin G_2 (PGG_2), the precursor of all of the other PGs. Interestingly, among the downstream effects of these PGs also are the main side effects of OTM, pain and root resorption. The NSAIDs thus act by non-specifically blocking either all of the COX isoforms or the isoform 2 (COX-2), while paracetamol specifically blocks the isoform 3 (COX-3). The different tissue distribution and action of these COX isoforms likely would be responsible for some differences in the clinical effects produced by NSAIDs and paracetamol. Current animal and human studies show that all NSAIDs, including paracetamol, generally are useful in controlling pain associated to OTM while not affecting root resorption. However, only paracetamol does not appear to inhibit OTM and, therefore, may represent the drug of choice to control pain during OTM. Moreover, specific inhibitors for the COX-2 have not been reported to have significantly different effect on OTM as compared to all the non-specific inhibitors. The choice between these two classes of drugs, therefore, should be made on the basis of whether the patient has other systemic conditions, such as gastric or cardiovascular diseases. Although general indications for the use of these NSAIDs during OTM now are available, future investigations on both the basic biology underlying OTM and on the mechanisms of action of these drags are warranted to further optimize orthodontic treatments.