Pain in the oral region is a major reason people consult their dentist, and the clinician should acknowledge this simple fact by specifically asking about pain as a part of the basic dental examination. The assessment of pain symptoms may provide valuable clues to the differential diagnosis, to the evolution of an underlying pathology, to the treatment efficacy, and most importantly, to the patient’s wellbeing. Pain may also have a variety of effects on other biologic and psychosocial functions. The assessment of pain should therefore be considered indispensable to provide optimal care and service.
The definition proposed by the International Association for the Study of Pain (IASP) emphasizes both sensory and affective-emotional aspects of pain and implies that clinicians evaluate both of these dimensions in their patients. A variety of measurement techniques are described in the following pages that rely on subjective report to evaluate these basic aspects of pain perception. Complementary behavioral and physiologic measures that offer additional indices of pain states are also briefly described. Recent advances in medical imaging that provide measurements of pain-related brain responses are discussed to further demonstrate that self-reports of pain reflect pain-related activity within the central nervous system (CNS).
Basic Characteristics of Measures
The gold standard for measurement of clinical or experimentally induced pain must fulfill a series of criteria.1 A valid pain measure should be sensitive to changes in pain produced by variations in nociceptive input or by effective analgesic procedures (criterion-related validity). It should also enable a clinician to discriminate different pain conditions (eg, inflammatory vs neuropathic pain) in patients (discriminant validity). Pain measures should also be reliable—ie, stable in time and not affected by the experimenter testing a human volunteer in a pain experiment or the clinician taking the measurement from a pain patient. In addition to being highly valid and reliable,2 a good pain measure should (1) allow for a comparison of the magnitude of changes in pain across treatments and pain conditions, (2) be relatively free of bias, (3) be useful for assessing both experimental and clinical pain, (4) allow for comparisons with neurobiologic measures in humans and animals to study underlying mechanisms, and (5) be relatively easy to use. In the broader context of clinical pain assessment, valid sets of measures should further sample the various dimensions of the pain experience and its effect on the patient’s ability to function (content validity).
The first category of measures relies on the collaboration with the subject to produce a response that reflects the pain experience as precisely as possible (Box 10-1).
|Box 10-1 Pain measurements|
|• Pain threshold: the least experience of pain that a subject can recognize; the lowest stimulus intensity at which a subject perceives pain|
|• Pain tolerance: the greatest level of pain a subject is prepared to tolerate|
|• Pain scales (see Fig 10-1)|
|Nominal and ordinal scales: translation of the pain experience according to discrete categories|
|Magnitude estimation scales: translation of the pain experience on a continuum|
|Pain questionnaires: evaluation of multiple dimensions of the pain experience via a combination of scales|
|Spontaneous motor/behavioral responses|
|• Facial: pain and emotional expression|
|• Vocal: nonverbal oral expression (eg, crying in neonates)|
|• Motor/behavioral: reduced motility, postural adjustments, changes in gait, protective behaviors, pain complaints, analgesic consumption|
|• Motor: nociceptive withdrawal reflex|
|• Autonomic: sympathetic and parasympathetic responses|
|• Endocrine: neurohormonal responses|
|• Neurophysiologic: activity within primary afferent nerve fibers, motor and sympathetic efferents, and the CNS|
Pain threshold and tolerance
Threshold measurement is the simple detection of pain in response to a stimulus. Pain thresholds can be measured by asking subjects to report when they feel pain during a gradual and controlled increase in stimulus intensity (method of limits), or in response to the repeated administration of discrete stimuli of different intensities (method of constant stimulus). The threshold is defined as the average point at which subjects start to feel pain, or as the stimulus intensity at which pain is felt in 50% of the trials. Reliable thresholds have been obtained with a variety of stimuli applied to skin, muscle, gingiva, and tooth pulp.