Acute pain or discomfort during orthodontic treatment is commonly reported. A study done in 2002 found that 87% of patients experienced pain after orthodontic visits. Additionally, "feeling pain" has been identified as the primary treatment concern for many patients prior to orthodontic treatment. More so, it can negatively affect patient compliance and attitude toward treatment.

Numerous studies have shown that pain varies in intensity and duration among orthodontic patients. The placement of orthodontic separators is a standard procedure to facilitate placement of orthodontic bands by creating a small amount of space between posterior teeth. Separator placement reliably produces acute discomfort to patients. Pain generated from orthodontic separator placement originates in the periodontal ligament (PDL) as compression forces are applied to the PDL unequally to open a small space (less than 0.5 mm) between the teeth. This compression triggers sterile necrosis or hyalinization in some areas of the PDL, leading to acute pain. The course of pain generated from orthodontic separators typically begins 4 hours after placement, reaching highest pain intensity approximately 24 hours after placement, and continuing to decrease in intensity until returning to pre-placement baseline after seven days.

Variation in reported pain intensity across orthodontic patients is of interest to any practitioner who desires to improve patient outcomes. In an attempt to enhance the orthodontist ability to understand pain and its predicting factors, researchers have examined pain from orthodontic treatment relative to patient demographics, personality traits, psychological factors, perceived need and attitude toward treatment, among others. Okeson asserts that pain is not directly related to the extent of tissue injury. Noxious stimuli originating in peripheral neurons (such is the case with separators) are subject to modulation at multiple levels through a complex central inhibitory system, where many other factors participate in decreasing or increasing the pain experience. Hence, an individual's emotional state, pain expectation and perception of control, as well as activities or distractions that will differ brain attention (Gate Control) can significantly influence the pain experience. Perceived stress, or the degree to which situations in an individual's life exceed their ability to cope, could be a good predictor of experienced pain. The Perceived Stress Scale is the most widely used screening form to evaluate perceived stress and asks subjects to recall the frequency of feeling overloaded and overwhelmed in the past month.

Recently, more attention has been given to the role of physical activity (PA) in reducing pain in patients that undergo orthodontic treatment. Physical activity has been shown to be an effective mediator of acute pain tolerance and pain sensitivity, an effect known as Exercise Induced Hypoalgesia (EIH). One study reported that a 1-mile run decreased pain intensity evoked from a weight being placed on the index finger. A similar decrease in pain response to pressure applied to the finger was found in subjects in another study who performed 30 minutes of aerobic exercise. It has also been demonstrated that exercise increased dental pain thresholds in response to electrical stimulation of the pulp. The exact mechanism involved in EIH remains elusive. Still, several pathways have been implicated including activation of the endogenous opioid pathway, increased Adrenocorticotropic Hormone release, and a conditioned pain the pain perceived in another area of the body.

Researchers have demonstrated that higher self-reported physical activity reduced the pain levels generated by placement of orthodontic separators when compared to patients with low physical activity. Self-reported measurements of physical activity carry limitations. The Physical Activity Questionnaire (PAQ) used in previous studies have demonstrated an only moderate correlation with direct activity observation (r=0.45), and with an activity monitoring device (r=0.57). The PAQ asks participants to report pain in the last seven days, and if given before treatment was performed, provides no data on physical activity during the week when subjects are experiencing pain. To further explore the correlation between physical activity and acute pain during orthodontic treatment, a more reliable measure of physical activity is warranted.

Actigraphy sensors provide an objective measure of physical activity. Actigraphy sensors include pedometers, which count steps over a defined time interval, and accelerometers, which measure acceleration in "activity counts" that are then extrapolated to the Metabolic Equivalent of Task (METS) to measure energy expenditure. No other paper has evaluated the effect of physical activity measured with pedometers on acute pain following separators placement during orthodontic treatment. Because not all patients experience pain at the same level, it would be beneficial for clinicians to identify which patients are likely to experience more intense pain before beginning treatment. To this end, the purpose of this study is to test the effect of physical activity measured by pedometer on acute pain produced by the placement of separators.