The clinical picture of CMD (craniomandibular dysfunction) describes the pathological condition of a functional disorder or mechanical misload of the masticatory muscles. The clinical picture also includes the connective tissue supporting the masticatory muscles (fascia, tendon) with secondary dysfunction and damage to the temporomandibular joints, teeth, periodontium and, more rarely, the soft tissues of the oral cavity when biting the cheeks, tongue or lips.
According to current knowledge, the clinical picture must be extended to include functional disorders/damage to the neck, nape and (with restrictions) also the back muscles and the associated spinal joints.
The terminological diversity of earlier names for CMD since its first description by Costen indicates the pathognomic complexity of this disease and the associated involvement of various specialist disciplines in addition to dentistry.
Functionally healthy versus dysfunctional
According to epidemiological studies, around six percent of the European population live functionally healthy lives, whereas the prevalence of objective findings of CMD without evidence of subjective complaints is 85 percent.
According to this, a large proportion of the population is confronted with triggering disruptive factors and reacts with progressive and/or regressive tissue adaptations. These structural changes can be neuronally compensated or tolerated for years and remain clinically inconspicuous in the sense of a silent CMD. Only around nine percent of the population have developed full CMD with persistent objective and subjective symptoms. In this group, tolerance to the disruptive factors has been lost and, as a result, the neuronal ability to compensate has collapsed.
Women more frequently affected than men
In a gender comparison, women are affected by CMD around five times more frequently than men, with the peak age being between 30 and 34 years. The prevalence values of typical CMD complaints also increase dramatically when symptoms such as tension headaches, migraine complaints, neck and back pain, ringing in the ears or tinnitus, hearing loss, balance disorders, dizziness, swallowing difficulties, speech and taste disorders, which were previously not primarily attributed to “dental diseases” but to diseases from other specialist areas (see above), are included in the evaluation.
CMD-triggering disruptive factors
The evaluation of the relevant specialist literature regarding the etiology of CMD reveals four triggering disruptive factors, which makes the multi-causality or multifactorial genesis of the disease clear. The following causes are described in detail, which can of course also occur in combination:
- Dento-occlusal interference factors
- Traumatic surgical disruptive factors
- Orthopaedic disruptive factors
- Psychosocial disruptive factors
At this point, it should be mentioned that hyperfunction of the masticatory muscles in central hyperkinesia due to diseases of the extrapyramidal motor system has been described as a concomitant symptom of affective psychoses or as an undesirable side effect of psychopharmacological medication (e.g. with the neuroleptic drug haloperidol). Trismus or masticatory and facial muscle spasms have also been observed in tetanus, tetany, epilepsy, meningitis, skull base fractures and oromandibular dystonia. However, as these muscular disorders are not specific to the masticatory muscles, but can affect the entire skeletal musculature, it is not justified to define further disruptive factors.
Dento-occlusal interference factors
Dento-occlusal interference factors and traumatic-surgical interference factors fall into the specialist areas of dentistry, oral and maxillofacial surgery, pediatrics, speech therapy, orthopedics and manual medicine.
Dento-occlusal interference factors are classified as pre- and postnatal developmental defects of the teeth and acquired diseases of the teeth and periodontium, including periodontal remodeling processes and factors caused by dental intervention. They therefore relate to malocclusions after tooth migration or tilting or due to sliding obstacles, supraocclusions during elongation or early contact, non-occlusions or infraocclusions due to tooth loss and tilting, incorrect jaw relationships with condyle displacements due to forced occlusions or incorrect bites for prosthetic restorations and orthodontic, conservative and prosthetic treatments.
Dental interventions during jaw and muscle growth of the two dentitions can cause much more extensive damage than corresponding treatments in adults, whose bone and muscle tissue can only be remodeled to a limited extent, due to the still pronounced biological ability of the developing organism to adapt its shape. The problem of iatrogenic orthodontic treatment errors lies in the influence on the natural tooth angulations, whereby corrections to the axial position of the upper first molar represent the greatest risk factor for a dento-occlusal disorder, because the 6-year molar influences the angulations of all replacement and growth teeth that erupt after it, with the exception of the anterior teeth. Therefore, the leveling of Spee’s curve, which is the aim of the straight-wire technique, must be considered a treatment error in the legal sense.
Traumatic surgical disruptive factors
The traumatic surgical disruptive factors relate to mechanical injuries and maxillofacial surgery on the jaws (especially on the ascending branch and the condyle), the teeth, the temporomandibular joint and the spinal joints as well as the associated musculature, resulting in changes in size, shape and position as well as underdevelopment (e.g. condylar asymmetries) after wound healing is complete.
Orthopaedic disruptive factors
The orthopaedic disruptive factors are located in the specialist fields of orthopaedics, manual medicine, pediatrics, speech therapy, dentistry and oral and maxillofacial surgery. They relate to pre- and postnatal developmental defects and acquired diseases of the bones, joints and muscles of the spine with resulting postural or positional defects of the cervical spine, including developmental defects and acquired diseases of the jaws, temporomandibular joint, masticatory muscles and tongue (e.g. as growth inhibition due to thumb sucking habit resulting in persistent infantile swallowing) as well as orthopaedic surgical interventions on the spine.
Psychosocial disruptive factors
Psychosocial disruptive factors are naturally assigned to the fields of psychiatry and psychology.
Surprisingly, only very few studies have been published that deal with the question of the epidemiological distribution or demographic frequency of the named disruptive factors. However, there is current data on the increasing dominance of psychosocial disruptive factors over the last few decades. The mechanisms by which psychosocial stress (as a synonym for disruptive factors) can contribute to the development of CMD were described by Gameiro et al. in a review. According to this, stress can profoundly modulate the processes of pain conduction and perception in the sense of a psychosomatic projection (somatization or somatoform disorder). Furthermore, bruxism and compressio dentalis (teeth clenching) can be seen as a sign of a stress management strategy and serve to protect against chronic stress-related illnesses. The non-physiological increase in teeth grinding and clenching can be convincingly explained by Lazarus and Laurier’s transactional stress model, according to which each person has individual stress coping skills (active and passive coping). In active coping according to the frustration-aggression theory, the aggressive reaction occurs on a somatic-muscular level as an archaic fight response. In the passive coping strategy, frustration triggers resignation and subsequently depression.
Parafunctions
Just like the psychosocial stress factors, the three other disruptive factors also generate neuronally controlled muscle hyperactivity or hypertonization of the masticatory muscles with a lack of rest phases, which is defined by the term parafunctions and triggers primary structural and functional damage to the musculature. These are then the cause of secondary consequential damage to the temporomandibular joints, periodontium, teeth, adjacent soft tissues, neck muscles and cervical spine joints.