For an individual who is either standing or sitting, the vertical position of his/her mandible relative to the maxilla remains fairly stable. This position is very critical in the field of dentistry and is called the ‘rest’ position. Due to its role in establishing the height of artificial full dentures, the highest occlusal plan of the upper and lower teeth must be placed so that the lower denture is not dislodged by the tongue. There should also be an appropriate space between the upper and lower teeth so that the teeth do not click together when the subject talks, and the height of the face is maintained for aesthetic and functional reasons. In addition, the reconstructive maxillofacial surgeon may also use the rest position. The rest position is defined by the Glossary of Prosthetic Terms as ‘’the postural relation of the mandible to the maxilla when the patient is resting comfortably in the upright position, and the condyles are in an unstrained position in the glenoid fossae’’ (1977). On the other hand, Yemm (1975) defines the mandibular rest position as a state of equilibrium between the elastic components of the opposed groups of elevator and depressor muscle. Various procedures and devices have been used in an attempt to establish a reproducible rest position.
Rest position has also been explained clinically and graphically. Although the exact mechanism of the clinical rest position is somewhat elusive, three explanations have been suggested based on muscle tonus, myotatic reflexes, and gravity-elasticity. Moyers defines rest position as the contraction of the postural muscles of the mandible resulting in a rest position of balance between the opening and closing muscles. He also states that the rest position is likely to be a position of least muscular activity and not a true rest position because postural muscles are very rare. On the other hand, Ramfjord et al (1971) found gravity elasticity to be another physiological explanation for the rest position which means that there is a force between the effects of gravity and the elastic nature of the soft tissues (mainly the muscles) surrounding the mandible. This force then affects the mandible. All these explanations are relevant.
Wagner did a comparison of four clinical procedures of obtaining the rest position. Each method produces different rest positions; simply resting position produces less high and low readings, saying ‘’mmm’’ produces the largest RVD, and swallowing the smallest. This would suggest that simply resting is the most reliable technique. However, other research studies found all these methods to be unreliable and as such, care is required.
The majority of dentists today would use the Willis gauge, a pair of dividers, or a ruler to measure the distance between two reference marks placed on the tip of the nose and the chin. These methods are very inaccurate indeed. Originally, the rest position was thought to be stable throughout life (Thompson, 1946). However, the majority of the research studies now show that the clinical rest position could vary according to the head position, loss of teeth, environmental changes, and muscle tone.
In his study, Olsen (1951) found out that the rest position is not rigidly stable and could vary for many reasons. On the other hand, Atwood states that the degree of variability of the clinical rest position in a patient depended on the relative values of and complex interplay between some 30 influential factors.
EMG
Clinicians always face difficulties in determining rest position and for this reason, many studies have been conducted to develop precise methods. Electromyography (EMG) is one such method. The accuracy of determining rest position by the electromyography method has been a subject of controversy (Satish et al.1987). The difference between the rest position determined by conventional methods and the electromyography method was found by Sheppard and Sheppard (1975). A similar conclusion was drawn by Satish et al (1987). To compare the resting position determined by electromyography with that obtained using conventional methods. Feldman, Leupold, and Staling (1978) reported that the mean resting position was similar for both methods produced by a more consistent reproducible determination of the position than did the conventional technique.
Hickey, Williams, and Woelfel (1961) used electromyography to determine the position of the mandible at which the voltage from temporalis and digastrics muscles was lowest. This was used in combination with the phonetic method to obtain the rest position which was then recorded with a cephalometric radiograph. The study indicated that electromyography could produce a consistent jaw position, but the experimental method did not indicate to what degree this position coincided with that obtained phonetically (Hickey et al 1961).
It has been suggested that it would be better to refer to the rest position as a postural position because it is not a position of rest due to some degree of activity (Lyons, 1988). Therefore some EMG activity should be accepted. However, dental literature has not universally agreed that ‘’ no’’ ‘’little,’’ or ‘’minimal’’ EMG activity should be anticipated at the clinical rest position (Lawrence, 1982). Minimal activity is not necessarily synonymous with the clinical (physiological) rest position. Moller (1966) has confirmed ‘’little’’ or no EMG activity at the clinical rest position. Ramfjord and Ash (1966) have gone further to report that there was minimal EMG activity at and beyond the clinical rest position (a vertical dimension increase that obliterates the interocclusal space). The active theory is supported by Moller(1966), who demonstrated electomygraphyically that the elevator muscles exhibit slight activity when the mandible is in the rest position. He also found that when a subject whose jaw is in the rest position moved from an upright position to a supine position, a reduction in the electrical activity of the temporalis muscle could be demonstrated and this was cited as evidence for a servo-controlled mechanism producing a response to changes in position (Moller,1966). However, Yemm (1969) reported that stress induced by the experimental environment can initiate muscle activity and this could account for the activity recorded at the rest position that is reduced through the diminution of anxiety when the subject assumes a supine position. In addition, the activity in muscles shown by EMG could be due to other sources such as electrical activity or electronic noise generated within the amplification circuits (Yemm, 1969).
Atwood (1956) reported that the EMG silence at the clinical rest position is dependent on the sensitivity of the equipment, the judgment of the operator, and the patient’s state of rest. Most physiologists agree that the EMG shows complete relaxation (zero EMG activity) when the muscles are at rest (Basmajian, 1967; Pruzansky, 1955). Moyers (1950) found by using EMG that there is a range of mandibular positions about which minimal activity occurs. In addition, minimal activity or silence over a range of jaw positions has been reported by Jarabak (1957), Garnick &Ramfjord (1962), Yemm &Berry (1969), and by Manns et al. (1981). Some authors described an EMG silence or minimum EMG activity at mandibular postural position and during passive movements of the jaws along the habitual path of closure (Arturo et al, 1981). The view that relaxed bodily posture is not maintained by tonic muscle activity induced by the stretches reflex is now widely accepted (Watkinson, 1987).
Hypnosis is an altered state of consciousness in which the patient awareness’s of the surrounding world, including somatic sensation, is diverted to an awareness of a more comfortable world within his or her mind (Goldman, 1989). Hypnosis comprises a range of procedures that can be used to help a patient achieve a psychological state which we call a trance. It is also important to recognize that the trance state is not always accompanied by eye closer or even relaxation (Auld, 1989). However, Kirsch (2001) states that hypnosis is a naturally occurring phenomenon during which the body remains relaxed while the mind goes into a highly focused state. Hypnosis is not new. It is as old as mankind (Slone, 1961).
Ericson et al (1976) reported that during a hypnotic session, patients are encouraged to focus on the hypnotherapist’s voice and pleasant images and to fix their gaze in a particular manner. During this induction phase, the patient begins to enter a hypnotic trance. A trance is associated with many physiologic changes that include flattening of facial muscle, decrease in orienting movements, immobility, changes in blinking and swallowing, catalepsy in a limb, autonomous motor behavior, altered breathing and pulse (Simon and Lewis, 2000). As subjects enter a trance, the conscious mind becomes less and less vigilant to the immediate surroundings. The word ‘hypnosis’ however is relatively new, dating back to 1841 when the physician Dr. James Braid Manchester named this state of mind after the goddess of sleep, Hypnos (James,2010).
During hypnosis therapy, the patient focuses on the stimuli of images offered by the therapist’s voice and this is called hetero-hypnosis, which is done by one individual (an operator) to another (subject) (Johanson et al., 1983; Moss and Magaro, 1989). On the other hand, when individuals undergo self-hypnosis, they take themselves into a focused state by using their awareness as the operator. Some research studies have proved that self-hypnosis is an easy and cost-effective method (Ghonemi, 2000). Health care providers who specialize in treating oral-facial pain may want to consider medical hypnosis as a valuable treatment modality for their patients who are reluctant to try conservative treatment (Simon and Lewis, 2000). Hypnosis has advantages over biofeedback because it can be administered to groups and does not require expensive or unwieldy equipment. Hypnosis also has advantages over habit reversal because such techniques involve extensive office monitoring, coaching, and practice, and they are still not appropriate for the exceedingly common patient with TMD who clenches or grinds during sleep.
Many studies have shown the application of hypnosis in dentistry. For instance, Gerschman (1989) reported in his study in Australia that hypnosis can minimize dental phobia anxiety, and pain. Gottfredson’s study adds further support to a growing body of evidence relating hypnotisability to both the acquisition and management of pain. However, many dentists have been reluctant to use hypnosis in controlling pain because pain control is associated with deep trance which takes time to achieve. Simon and Lewis (2000) found that after hypnosis treatment, subjects exhibited a significant decrease in symptoms in terms of reduced frequency, duration, and intensity of their TMD pain. Additionally, they reported a significant improvement in their overall daily functioning. In addition to the previous use to hypnosis Barsby (1994) found that hypnosis is very effective in the management of ‘’gagging’’ and intolerance to dentures.