Charles G. Widmer
The patient with orofacial pain is a challenge to health care providers because of the complexity of presenting signs and symptoms and the diversity of conditions that may elicit pain in this region. To accurately diagnose the cause of orofacial pain, a practitioner must have knowledge of a wide variety of disciplines including the basic biomedical sciences, epidemiology of orofacial pain conditions, validity and reliability associated with parameters used in diagnosis and treatment, pathologies that may present as pain in the orofacial region, and the psychosocial impact of pain on the individual.
The purpose of this chapter is to examine the current beliefs in the field of orofacial pain and to review an educational framework that has been proposed for orofacial pain curricula in dental schools.
Overview of Current Beliefs
Current beliefs regarding orofacial pain are quite diverse. Although the number of well-controlled randomized clinical trials is growing, most beliefs are still based on philosophic interpretations of clinical observations, rather than evidence-based practice (see chapter 18). The local dogma in each dental program will vary according to the philosophy of the department or the practitioner teaching about orofacial conditions. This general overview of the most important orofacial pain conditions emphasizes musculoskeletal pain, since this has traditionally generated the most controversy.
Intraoral pain conditions
Examples of orofacial pain conditions that have a well-understood etiology include odontalgia associated with either an irreversible pulpitis secondary to a caries infection, or a reversible pulpitis associated with trauma (see chapter 20). However, not all people who present with tooth pain have pulpitis. Some have atypical odontalgia, which has no clear etiology. This condition has been linked to several possible pathologies, including osteomyelitis and neuralgias. One variant of this condition, phantom tooth pain, occurs after an extraction of a tooth or group of teeth. Although the true etiologies of these persistent pain conditions have not been established, there is a tendency to group them with neuropathic pains (see chapters 7 and 24).
Mucosal and gingival pain associated with inflammation
Another orofacial pain that has a well-understood etiology is that associated with fungal infections (candidiasis) or viral infections (herpes simplex) of the oral mucosa. These infections respond to antifungal and antiviral agents, respectively. Acute necrotizing ulcerative gingivitis is associated with an acute gingival infection, whereas desquamative gingivitis is associated with abnormal hormonal levels or allergic reactions involving the gingival tissues, such as reactions to components of crowns or partial denture frameworks. These pains decline in a predictable fashion as the infections clear and the tissues repair. Chronic periodontal disease causes pain in only 6% of patients with the condition,1 which may be one of the reasons for its high prevalence in many population groups and the primary reason that it remains untreated in many patients (see chapters 2 and 23).
Until recently, most authors did not separate myalgia and arthralgia because they believed that both disorders had a common cause (see chapters 19 and 22). Some of the most common etiologic theories are listed below.
Dental and occlusal etiologies
Costen,2 an otolaryngologist, proposed that tooth loss was the cause of impaired hearing, stuffy ears, tinnitus, dull muscle and joint pain, dizziness, sinus symptoms, and headaches. He stated that correction of an overbite or replacement of lost molar support would remove the pressure that the displaced condyle was exerting on adjacent structures, including the dura mater and middle ear. In dentistry, this belief led to a major emphasis for five decades on occlusal-based treatment approaches and diagnostic devices for temporomandibular disorders (TMDs). Currently, this explanation is not generally accepted, although some practitioners still persist in occlusally based diagnostic and therapeutic approaches. Some evidence suggests that loss of posterior support, such as missing molars, may be linked to a higher incidence and severity of arthritis in the temporomandibular joint (TMJ),3 but these data must be interpreted with caution because of the possible link to a third variable—age.
Occlusal discrepancies, particularly centric occlusion interferences and balancing interferences, have also been cited as a cause of musculoskeletal pain. These concepts were based on the clinical observations of musculoskeletal pain improvement after elimination of nonideal contacts. However, epidemiologists have determined that a significant proportion of the population has these occlusal discrepancies without experiencing musculoskeletal pain.4 Others have placed experimental occlusal or placebo interferences in normal subjects, but these devices were not found to be associated with the development of TMD-like symptoms.5
One theory of masticatory and cervical musculoskeletal pain is that poor body alignment, including cervical posture (eg, forward head posture), pelvic tilt, and uneven leg lengths, can initiate and propagate the pain condition. To prove that poor body alignment is an etiologic factor, a practitioner would need to show that it predisposed the patient to musculoskeletal pain, but this has not been done. In fact, the prevalence of one of the misalignments that has frequently been invoked as a cause of TMDs, the so-called forward head posture, has been found to be as high as 93% in teenaged girls, suggesting that it is biologically very normal.6 Other postural or skeletal deviations from a philosophic ideal are probably just as high. For example, one concept states that the mandibular condyle should occupy a central position within the fossa. However, studies using tomography to examine the condylar position in asymptomatic participants and TMD patients found that variation from the ideal position was equally high in both samples.7,8
Another theory links orofacial pain with misalignment of the cranial bones coupled with stress along the sutures. The basis for this concept is the impression of improvement in musculoskeletal pain after cranial bone manipulation. To date, there is no evidence that the cranial bones are mobile in the adult, and no randomized clinical trials have been carried out to test the efficacy of manipulation.
The belief that patients with chronic pain are psychologically or emotionally disturbed is rather widespread. When no evidence of local pathology is found, the default diagnosis for some practitioners is a psychosomatic disorder. Although depression is a frequent symptom in patients with chronic orofacial pain, as it is in any chronic pain group, there is no evidence that depression, or indeed any psychologic trait or disorder, is a cause of TMDs or related conditions. Depression is likely to be secondary to the pain (see chapter 12).
Psychophysiologic theory of muscle pain
The psychophysiologic theory was proposed by Laskin9 to describe the relationship between stress, increased muscle activation patterns, and muscle and TMJ pain. As a group, patients with chronic pain show relatively high levels of stress10,11 ; however, most experimental studies of induced stress have not shown parallel changes in muscle activity and pain levels. Although a small increase of masticatory muscle electromyographic (EMG) activity (2 to 4 μV) during high relevant stress has been reported in a study12 using imagery or reaction times, this is not evidence that stress-induced hyperactivity causes TMD pain. In fact, this EMG activity may be caused by low-level activation of the />