Braces and Possible Biomarkers for Root Resorption

Orthodontic braces are made from a variety of materials, including stainless steel, nickel titanium, ceramic, and clear plastic, but the underlying biology of tooth realignment remains essentially the same. Braces are attached directly to the crowns of the teeth, resulting in stresses along the tooth roots and within the periodontal ligament. The periodontal ligament, strain­ed to accommodate the stress, alters its normal blood flow, allowing specialized cells to dissolve bone in the tooth socket and gradually move the tooth away from the pressure. As the tooth moves, bone-forming cells fill in behind to permanently reposition it in a straighter, more desirable position. But sometimes biology can play tricks. As a misaligned tooth straightens, its roots can also erode to varying degrees. In the worst-case scenario, badly eroded roots will kill the tooth, leaving patients to cope with its associated emotional and economic costs. Researchers have yet to pin down what exactly triggers root resorption. Nor do they have the means to predict who is at risk. The best that orthodontists can do is take periodic radiographs, which might detect the resorption—but always after the fact. 

In the August issue 2009 of Orthodontic Craniofacial Research, National Institute of Dental and Craniofacial Research (NIDCR) grantees take a preliminary step forward in learning to detect root resorption as it happens. The scientists confirmed that certain telltale molecules accumulate at higher concentrations in the gingival crevicular fluid of treated orthodontic patients with mild and severe root resorption compared to those who had not yet received braces. The molecules included the well-known bone matrix proteins osteopontin and osteoprotegerin as well as the immune signaling compound receptor activator of NF-kappaB ligand, or RANKL. The low-but-measurable protien content of gingival crevicular fluid generally derives from the gingival tissues, serum, and/or nearby oral bacteria. Ortho­dontists can readily and noninvasively collect the fluid using filter paper strips. The study authors noted that future studies are needed to evaluate the RANKL/osteoprotegerin ratio in particular during tooth movement and root resorption. These studies will need to be larger than the current investigation, which included 40 treated patients and 20 untreated, or control, subjects.