Arh urd Bid. Vol. Ii, pp.1 129-I 13.5 1966. k’erganlon hebs Ltd. Printed in Cit. Britain.

AN INVESTIGATION INTO THE REPUTED DESENSITIZING EFFECT OF APPLYING SILVER NITRATE AND STRONTIUM

CHLORIDE TO HUMAN DENTINE

D. J. ANDERSON and B. MATTHEWS

Department of Physiology, Guy’s Hospital Medical School, London, S.E.1, England

Summary-Using osmotic stimulation of human dentine, the reputed desensitizing action of silver nitrate and strontium chloride was investigated. Two cavities were prepared in the crown of a lower premolar and the desensitizing agent was used on one while the other served as control. All experiments were carried out on freshly cut dentine and on the same dentine after filling the cavity for a week with gutta percha. The effect of silver nitrate was tested with one application just before the second experimental session. Strontium chloride, however, was applied after every stimulating solution (8 times) in both experimental sessions. Neither silver nitrate nor strontium chloride had a desensitizing action judged by the number of reports of pain from test and control dentine.

INTRODUCTION

THE LITERATURE contains numerous references to clinical procedures designed to reduce the sensitivity to stimulation of dentine exposed as a result of recession of the supporting tissues at the neck of teeth. Among the agents for which desensitizing activity has been claimed are silver nitrate and zinc chloride (MILLER, 1950), sodium fluoride (HOYT and BIBBY, 1943) and strontium chloride (COHEN, 1961; SMITH and ASH, 1964; MEFFERT and HOSKINS, 1964). The last has been incorporated in tooth- paste which, if it is effective, offers a convenient method for patients themselves to deal with the problem of sensitive dentine. Conflicting reports as to its effectiveness have appeared. COHEN (1961) for example, concluded that a toothpaste containing strontium chloride in a 10% concentration used by a group of patients with histories of “hypersensitive dentine”, was effective in controlling pain in about 75 per cent of the group. This conclusion was arrived at from reports given by the patients them- selves without any tests having been applied by the investigator.

SMITH and ASH (1964) attempted a more objective assessment of the effects of strontium chloride in toothpaste by using mechanical and thermal stimuli, both of which could be accurately quantitated. This toothpaste also contained strontium chloride in a concentration of 10% by weight. These investigators adopted the double blind procedure. Their conclusion was that no significant change occurred in sensitivity to mechanical or thermal stimuli. However, immediately following this paper was one in the same journal by MEFFERT and HOSKINS (1964) with the same dentifrice investigated without double blind technique. In their series complete

1129

P

1130 D. J. ANDERSON AND B. MATTHEWS

relief was reported by twenty-two out of forty-five patients-almost 50 per cent of the total-and only three patients obtained little or no relief.

Pain can be induced at the neck of the tooth by temperature change-commonly a fall in temperature, by touch and by chemical constituents of the food. It is possible that osmotic pressure is an important factor in the pain-producing power of food materials but no reports have appeared in which the effectiveness of desensitizing agents to osmotic stimuli has been investigated, other than that of ANDERSON (1963) in which the reputed desensitizing effect of silver nitrate was tested. The present report will deal with further experiments on silver nitrate and with a new series on strontium chloride.

METHODS AND MATERIALS

The general procedure was similar to that employed in previous experiments (ANDERSON and RONNING, 1962b). The subjects were students in the age range 17-21 years and the teeth were lower premolars showing early signs of caries in the occlusal enamel.

Silver nitrate experiments These experiments follow a smaller series, the results of which have been reported

already (ANDERSON, 1963). The procedure was to cut two cavities in each tooth and to stimulate both with a sugar syrup, 2 Molal, 6 Molal and saturated solutions of calcium chloride, exerting calculated osmotic pressures in the range of 200-2800 atm. The solution was introduced into the cavity at 37°C on a pledget of cotton wool and was removed after 30 sec. After every stimulation, the cavity was rinsed with warm water and the subject was then asked to report any sensation he had felt. Every solution was applied twice and in random order. At the end of the sequence the cavities were filled with gutta percha and, after a week, the same pattern of stimulation was repeated. However, just prior to the second session of stimulation, ammoniacal silver nitrate (Howe’s, U.S.N.F.) was applied to one of the cavities for 2 min, followed by eugenol for 3 min. This is the routine sequence followed clinically. Silver nitrate is generally considered to penetrate the dentinal tubules deeply, and this has been confirmed in our laboratory in four out of five premolar teeth treated in this way in vivo (ANDERSON and RONNING, 1962a).

In planning the experiments with silver nitrate, the object of restricting the silver nitrate to one application just before the second session was to test its effectiveness on dentine made hypersensitive by gutta percha. This preparation was chosen in spite of the fact that the mechanism of hypersensitivity produced in this way may differ from that responsible for hypersensitivity found in dentine exposed at the neck of the tooth, since it would have been difficult to obtain suitable patients prepared to take part in lengthy experiments which might welI have exacerbated their condition. As the results of this and previous experiments show, silver nitrate did not modify sensation in any way that we could determine.

DESENSITUINC EFFECT OFSILVER NITRATE AND STRONTIUM CHLORIDE 1131

Strontium chloride experiments In the strontium chloride experiments, the general procedure was the same as

already described for the silver nitrate experiments. However, with the object of providing the maximum opportunity for any desensitizing effect of strontium chloride to make itself apparent, a saturated solution of strontium chloride was used, rather than the usual concentration of 10% by weight in toothpaste. Two cavities were cut in the same tooth and strontium chloride was applied to one of the cavities (to be referred to as the test cavity) for 30 set after all of the eight stimulations. Thus, although the first stimulation to the test cavity was not affected by previous appli- cations of strontium chloride, all subsequent stimulations followed strontium chloride. The object of this arrangement was to allow for the possibility that strontium chloride might completely abolish sensation. If it did so and if it had been applied before any stimulating solution, then its effect could not be distinguished from the occasional occurrence of a tooth which failed to respond to any stimulation. For control purposes, water was applied to the other cavity (the control cavity) after each stimulating solution. Thus, seven of the eight stimulations were preceded by strontium chloride in the test cavity and by water in the control cavity. This procedure was adopted in both sessions, e.g. immediately following cavity preparation and a week later after filling the cavity with gutta percha in the interim period.

Silver nitrate experiments

RESULTS

Table 1 shows the results from the experiment on five subjects previously reported (ANDERSON, 1963), followed by data from the twelve subjects of the present series. There is clearly no difference between the silver nitrate-treated cavities and the controls in terms of the total number of reports of pain.

TABLE 1. THEEFFECTOFONEAPPLICATIONOFSILVERNITRATESOLUTIONONTHE NUMBER OF REPORTS OF PAIN FROM HUMAN DENTINE

The silver nitrate was applied to Cavity 2 once for 2 min, followed by eugenol for 3 min, just prior to Session 2. Data on Subjects 1-5 comes from ANDERSON (1963)

Session 1

Cavity I Cavity 2

Session 2 ________-__- --.

Cavity 2 tAgNO,-

Cavity 1 treated)

Subjects l-5 2.5 20 25 28 Subjects 6-17 39 41 51 52

- - Total reports of pain 64 61 76 80

- 136

- - Maximum possible 136 136 136

Strontium chloride experiments Since the first application of strontium chloride clearly failed to abolish response

to subsequent stimulation, it was necessary to look for a gradual decline in sensitivity.

1132 D. J. ANDERSON AND 3. MATTHEWS

However, a decline in sensitivity was to be expected during repeated stimulation whether strontium chloride was used or not. ANDERSON and RONNING (1962b) and ANDERSON, MATTHEWS and SHELTON (1966) demonstrated this phenomenon with the same range of solutions as was employed in the present series. To be accepted as exerting a true desensitizing effect, treatment with strontium chloride must result either in a complete abolition of sensation, or a steeper decline in sensitivity than was shown by the control cavities.

The results of the sixteen applications in twelve subjects are set out in Figs. 1A and 1B. In session 1 there was a possible maximum of twelve reports of pain for all the

Session 1.

lo-

9.

2-

l-

O_

T

.

.l

Control SrC12 - treated

1A

FIGS. 1A and 1B. Reports of pain from control and SrCl *-treated cavities following eight stimulations. The results in Fig. 1A are from twelve subjects and in Fig. 1B from eleven subjects. The total number of reports of pain in response to each successive stimulation from one to eight is represented by a column. Maximum possible number of reports of pain is twelve in every column in Fig. 1A. In Fig. 1B the maximum is eleven in every column except in the last column of control and test, in which it is ten.

stimulations in both test (strontium chloride-treated) and control (water-treated) cavities. In session 2, one of the twelve subjects dropped out and with one of the re- maining eleven subjects, the last stimulation was accidentally omitted in the second session. Therefore the maximum possible in all the columns of Fig. 1B is eleven, except in the last in which it is ten. Judged by the numerical results, strontium

1XSENSITIZING EFFECT OF SILVER NITRATE AND STRONTIUM CHLORIDE 1133

-

LB

SrC12 - treated

chloride has no effect. However, the subjects frequently made comparisons between sensations evoked, although not asked to do so, and from these comparisons it appeared that in response to the same stimulating solution, strontium chloride-treated cavities were sometimes less painful than the controls. Since the experiments were not designed to obtain this kind of information, it can only be regarded as a pointer for further experiments. An additional finding was the ability of saturated solutions of strontium chloride at 37°C to cause pain. This occurred in 36 per cent of the applications.

DISCUSSION

From these experiments it seems clear that neither silver nitrate nor strontium chloride reduced the sensitivity to osmotic stimulation of dentine. Comparisons made by some of the subjects between the sensation experienced from treated cavities and control cavities indicated that the intensity of the pain may have been reduced by strontium chloride and this calls for further investigation. However, the application of a saturated solution of strontium chloride in the first session did not diminish the total number of reports of pain, and did not prevent the anticipated rise in sensitivity after filling with gutta percha for a week. Furthermore, it did not reduce the total number of reports of pain from the teeth made sensitive by the temporary filling.

It would not be justifiable to conclude from these negative findings that strontium chloride could not have some value when used clinically in the treatment of cervical

1134 D. J. ANDERSON AND B. MATTHEWS

hypersensitivity. The tissue under investigation in our experiments was virtually sound dentine under the occlusal surface of the tooth, exposed and made hyper- sensitive deli~rately. clinically hypersensitive dentine is at the neck of the tooth; it is not exposed by cutting and it is in contact with the fluids in the mouth over long periods. The state of this dentine and the underlying pulp almost certainly differs from that in our experiments and undoubtedly varies from patient to patient. It seems likely that the disagreement as to the clinical effectiveness of strontium chloride is the result of these variables. However, even allowing for the differences between our experiments and clinical studies, it is difhcult to understand previous success with a IO:/, concentration of strontium chloride and our faiiure with a saturated solution.

The finding that the saturated solution of strontium chloride caused pain in 36 per cent of the applications agrees with previous results. The calculated osmotic pressure of this solution is approximately 700 atm and its action corresponds well with that of a sugar syrup of similar osmotic pressure (ANDERSON 1966).

A~k~o~}/e~ge~e~l-These studies have been supported by a grant DE-01037-03 from the National Institutes of Health, U.S. Public Health Service.

Rbum&L’action desensibilisante bien connue du nitrate d’argent et du chlorure de strontium est ttudiee en utilisant la stimulation osmotique de la dentine humaine. Deux cavites sont preparees dans la couronne dune premoiaire inferieure et l’agent de d~sens~bilisation est test6 dam I’une des cavites alors que I’autre sert de temoin. Toutes les experiences sont realisees sur de la dentine fraichement preparee et sur la m&me dentine apres un pansement d’une semaine a la gutta percha. L’effet du nitrate d’argent est apprecie apres une application precedant immediatement le second essai experimental. Le chlorure de strontium, cependant, est Ctudit apres chaque application de la solution stimulante (8 fois) au tours des deux essais exptrimentaux. Ni le nitrate d’argent, ni le chlorure de strontium ont une action de desensibilisation, si l’on en juge par les douleurs ressenties sur la dentine contritle et la dentine soumise a l’ex~rimentation.

Zussamenfassung-Mit Hilfe osmotischer Stimulation des menschlichen Dentins wurde die bekannte desensibilisierende Wirkung von Silbernitrat und Strontium- chlorid untersucht. Zwei Kavitaten wurden in die Krone eines unteren Prlmolaren prlpariert, in einer wurde das de sensibilisierende Agens eingebracht, wahrend die andere ais Kontrolle diente. Alle U~tersuchungen wurden an frisch prlpariertem Dentin und am seiben Dentin nach FiMung der Kavitat mit Guttapercha wiihrend einer Woche ausgeftihrt. Die Wirkung con Silbernitrat wurde nach einer Anwendung unmittelbar vor der zwciten Versuchssitzung getestet. Strontiumchlorid wurde dagegen in beiden Versuchssitzungen nach Anwendung jeder stimulierenden Liisung (8 mal) verwandt. Weder Silbernitrat noch Strontiumchlorid zeigten eine desensibilisierende Wirkung, wie durch die Anzahl der Schmerzreaktionen an der Test- und der Kontroll- kavitlt im Dentin bewiesen wurde.

REFERENCES

ANDERSON, D. J. 1963. Sensory Mechanisms in Dentine. (Edited by ANDERSON, D. J.) pp. 88-93. Pergamon Press, Oxford.

ANDERSON, D. J. 1966. Advances in Oral Biology (Edited by STAPLE, P. H.), pp. l-29. Academic Press, New York.

ANDERSON, D. J. and RONNING, G. A. 1962a. Rye diffusion in human dentine. Archss oral Bio[. 7,505~512.

ANDERSON, D. J. and RONNING, G. A. 1962b. Osmotic excitants of pain in human dentine. Arckr oral Biol. 7, 513-523,

DESENSITIZING EFFECT OF SILVER NITRATE AND STRONTIUM CHLORIDE 1135

ANDERSON, D. J., MATTHEWS, B. and SHELTON, L. E. 1966. Variations in the sensitivity to stimulation of human dentine. Archs oral Biol. In press.

COHEN, A. 1961. Preliminary study of the effects of a strontium chloride dentifrice for the control of hypersensitive teeth. Oral Surg. 14, 1046-1052.

HOYT, W. H. and BIBBY, B. G. 1943. The use of sodium fluoride for desensitizing dentin. J. Am. dent, Ass. dent. Cosmos 30, 1372-1376.

MEFFERT, R. M. and HOSKINS, S. W. 1964. Effect of a strontium chloride dentifrice in relieving dental hypersensitivity. J. Periodont. 35, 232-235.

MILLER, S. C. 1950. Textbook of Periodontia (3rd ed.) Kimpton, London. SMITH, G. A. and ASH, M. M. 1964. A study of a desensitizing dentrifrice and cervical hyper-

sensitivity. J. Periodont. 35, 223-23 1.