Kamal Fareed, BDS, MS
Department of Restorative Dental Sciences, College of Dentistry, King Saud University, P.O.Box60169,
Riyadh 11545, Saudi Arabia.
 

The form and reproducibility of pantographic tracings under the influence of relaxant drugs and in patients with muscle dysfunction and TMJ disorders, tend to emphasize the dominance of the neuromuscular factors. The purpose of this study was to demonstrate the effect of nitrous oxide induced psychosedation, on the reproducibility of pantographic tracings of border movements of the mandible. This study included four male subjects (with no signs and symptoms of muscular dysfunction and temporomandibular joint problems). Operator guided border tracings were recorded using the Denar pantograph. Three sets of tracings were recorded: (1) three tracings prior to sedation (Tracing I); (2) one tracing prior to sedation and two after sedation (Tracing II); (3) three tracings after psychosedation (Tracing III). The coincidence of tracings I, II, and 111 were statistically analyzed applying the chi-square (X2) analysis. There was a significant difference in the coincidence of tracings between Tracings 1 and II (X2 = 14.892). There was no significant difference in the coincidence of tracings between Tracings I and III (X2 = 1.338). This suggests that nitrous oxide psychosedation produces a centrally induced relaxation of the musculature, by possibly eliminating the extraneous anxiety producing factors.

 
The architecture of the temporomandibular joints (TMJ), the ligaments, and the neuromusculature of the masticatory system, constitutes the basis for
border movements. There is a lack of general agreement with regard to the extent to which each of these dictates function.1,6

The reproducibility of pantographic tracings appears to suggest the fixed ligamentous and bony elements as the primary factors.1,6,7Studies demonstrating a definitive change on both the form and reproducibility of the tracings, under the influence of relaxant drugs8-11 and in patients with muscle dysfunction and TMJ disorders,12-16 tend to emphasize the dominance of the neuromuscular factors.

Studies have used syccinylcholine and curare, muscle   relaxants   which   interfere   with   basic neuromuscular physiology1, 8, 9 and valium, orally and intravenously, where the degree of sedation cannot be titrated from individual to individual.10-11

Also, the reproducibility of pantographic trac­ ings of the mandible involves not only considerable skill by the operator, but also the need for patient cooperation. The latter, in itself, is a limitation since the elaborate pantographic equipment used could also induce a stressful situation in the patient.Nitrous oxide psychosedation creates an envi­ ronment in both patient and operator, where the elements producing anxiety are greatly suppres­ sed. It is the oldest gaseous anesthesia in use today. The exact mechanism by which it exerts its effect is currently unknown.17

The degree of sedation can be controlled by the use of nitrous oxide psychosedation and this would eliminate the extraneous anxiety producing fac­ tors, allowing for centrally induced relaxation of the musculature without the loss of conscious­ ness.18. This investigation evaluates the effect of nitrous oxide psychosedation on the reproducibility of pantographic tracings.

Four male subjects were selected for the study to possess:

1. Class I occlusal relationship and freedom from of any signs, or symptoms, of TMJ problems or muscular dysfunction.

2. Sufficient natural teeth to facilitate the cementation and retention of the clutches.

3. No undue resistance to operator-guided mandibular border movements.

4. No recent history of upper respiratory tract infection.

The subjects had a normal night's sleep, and were asked to avoid any stimulants.

Operator-guided border tracings were recorded using the Denar pantograph (Denar Corp.Anaheim, Calif., USA). Clutches were fabricated according to the manufacturer's instructions and adapted to the teeth. The pantographic procedure produces six sets of tracings recorded on six tables of the pantograph which have pressure-sensitive paper.

Three sets of operator-guided border tracings were recorded prior to sedation (Tracing I). Then the recording papers were replaced, and one set of operator-guided border tracing was recorded prior to sedation. The subjects were then psychosedated with nitrous oxide, and two more operator-guided border tracings were recorded on the same paper. Therefore, these recording papers had one tracing prior to sedation and two after sedation (Tracing II) These recording papers were again replaced, and then three sets of operator-guided border tracings were recorded with the subjects psychosedated for at least five minutes (Tracing 111).

In order to evaluate the sets of tracings for the four subjects accurately, the tracings were enlarged to twice their size, using a photocopying machine. The laterotrusive and mediotrusive border tracings were then evaluated for coincidence from centric relation positions using a magnifying lens. If there were more than one line present on a tracing being evaluated, it was considered to be non-coincident. If there was a line greater than 0.5 mm width, it was considered to be two lines and, therefore, non-coincident.

The coincidence of tracings I, II, and III to com­ pare the non-sedated and the psychosedated states for all the subjects, were studied.

Psychosedation Technique

The procedure was first explained to the sub­ jects. The nose mark was adjusted to ensure the participants' comfort. A flow of oxygen, 100% at 7 liters/minute was maintained for one minute.

Nitrous oxide was then administered at 1 liter/ minute, and oxygen was reduced by 1 liter/minute till a baseline of the following was achieved.The subjects were asked to report the onset of any of the following symptoms: A warm feeling, a comfortable glow through the body, pleasant sen­ sations, tingling of the fingers, toes or lips, floating and buzzing sensations, and heaviness of the limbs. The patients were monitored for the following signs: respiration, eye movements, skin color, and unusual body movements. The subjects were not allowed to fall asleep.

The procedure lasted for a maximum of twenty minutes.

For the four subjects, 48 sets of tracing were evaluated for Tracings I, II, and III, respectively.

The tracings were evaluated in the following categories:

1.  Tracings I vs. Tracings II (Table I).

2.  Tracings I vs. Tracings III (Table II).

The data were statistically analyzed applying the chi-square (X2) analysis with 1 degree of free­ dom.19

The chi-square analysis showed the following:

1.  There was a significant difference in the coincidence of the tracings between Tracings I and II.

2.  There was no significant difference in the coincidence of the tracings between Tracings I and III.
  

Four normal subjects were tested in this prelimi­ nary study demonstrating an effect of nitrous oxide psychosedation on pantographic tracings. The results suggest that the use of nitrous oxide seda­ tion, Tracing II, probably increased the anxiety of the patients and disturbed the neuromuscular bal­ ance. Therefore, the tracings were not reproduci-ble when compared to Tracing I. After a period of time and when the psychosedation base-line was achieved, Tracings III were reproducible when compared to Tracings I.

While establishing that the architecture of the TMJ, the ligaments, and the neuromuscular com­
plex constitute the basis for border movements, the literature also reveals lack of general agreement with regard to the extent to which each of these dic­ tate the function.

Pantographic tracings of mandibular border movements have been shown to be reproducible in subjects with normal muscle and TMJ function. This has been the parameter used in various studies, using different forms of sedation, on the effect of neuromuscular factors.8-11

Posselt1 made tracings of the posterior border movement on three conscious subjects. After plac­ ing these subjects under general anesthesia and curare, he traced the border movements. He found no change in the position of these movements, and concluded that the ligaments were responsible for limiting the posterior border movements of the condyles.

Boucher and Jacoby8 studied tracings in an experiment similar to Posselt. They found that the patients, under anesthesia and curare, could be moved farther posteriorly than the conscious post­ erior border position. They concluded that the muscles were responsible for limiting posterior bor­ der movements of the mandible.

McMillen9 conducted a study similar to Posselt and Boucher and Jacoby, except that succinyl-
choline chloride (Anectine) was used to produce complete muscle flaccidity and an extraoral pan­ tograph was used. Operator-guided tracings were recorded. In all ten subjects recorded, wider lateral border movements were recorded when the mus­ cles were made flaccid. Posterior mandibular dis­ placement was slight. He concluded that the mus­ cles, ligaments, and the bony structures all share the role of limiting mandibular movement.

Dedmon and Scandrett10 studied the effects of intravenous diazepam on pantographic tracings. The dose used was 15 to 20 mg. They found no widening of the tracings after the medication. No clinical advantages, or benefits, resulted from diazepam pre- medication.

Jackson11 studied the effect of administering Val­ ium (2 mg), orally on the reproducibility of pantog­ raphic tracings of three subjects. There was a signif­ icant difference in the reproducibility between the medicated and non-medicated subjects. The per­ centage coincidence of border tracings increases significantly, when the patient is pantographed while under the influence of medication. No signif­ icant difference in the reproducibility of border tracings relative to time (1, 1 1/2, 2 and 2 1/2
hours), after medication was recorded. He also concluded that the neuromusculature appears to
be the overriding factor governing border move­ ments.

Other studies have shown that the reproducibil­ ity of pantographic tracings improves after the insertion of occlusal splints and with occlusal therapy. These studies suggest that border move­ ments and muscle dysfunction may be interre­ lated.12-14

Pantographic border movement tracings have also been used in studies involving patients with TMJ problems and muscular dysfunctions. These studies demonstrate that patients, with such prob­ lems, are characterized by low reproducibility of the pantographic tracings. They also show that the reproducibility is improved when the dysfunction symptoms were improved.15-16

Anxiety is considered to be an important factorin patients with muscle dysfunction and TMJ prob­ lems. Nitrous oxide and pantographic procedures could be used to assess the role of the anxiety fac­ tors associated with these disorders.

Pantography is a procedure often used during extensive restorative procedures. It is imperative to have the neuromusculature in a relaxed state to obtain reproducible tracings for each patient. Nitr­ ous oxide psychosedation offers a safe and easy mode of complimenting the efficacy of such a pro­ cedure, simply because the psychosedation facility is included in most dental operatories, and mastery in this technique involves no great effort.

From this preliminary study, the following can be concluded:

1. The neuromusculature is a significant factor in governing border movements.

2. Nitrous oxide psychosedation produces a centrally induced relaxation of the muscula­ ture, when the baseline is properly achieved, by possibly eliminating the extraneous anxiety producing factors.

3. The effect of nitrous oxide and pantographic procedures on patients, with muscle dys­ function and TMJ problems, needs to be studied.

The author would like to express his gratitude to Dr. Paul Salins, formerly Assistant Professor, Biomedical Dental