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A quantitative method for evaluating topical anesthetic potency
Anesthesiology A QUANTITATIVE
METHOD ANESTHETIC
FOR EVALUATING POTENCY
Il~:o~~~rt~>ILWOPORT, B.S., T).T).S.,* AND EDWARD I?. lh313s, BALTIMORE, MD.
TOPICAL
I).D.Y.,
F.A.C.I).,'"
F
OR over half a century vast amounts of research have been channeled into t.he field of local anesthesia, with the prime purpose in mind, so far as dentist’ry is concerned, of making the dental operation as safe and as painless as possible. In spite of the advances and improvements made, improvements that have rendered the majority of dental procedures absolutely painless, there has been a certain reluctance on the pa.rt of a rather wide segment of the population to submit to local anesthesia. Much of this reluctance may be traced to the fact that the insertion of the needle, in itself, gives rise to pain. This, together with the psychologic apprehension attending the injection, is often sufficient reason to warrant the patients seeking other forms of anesthesia, or of avoiding t,he dental operation altogether. Realizing this, there has been a distinct effort on the part of the profession to develop topical anesthetics, which when applied to the oral mwoxa would eliminate the pain of needle insertion. Unfortunately there has not been developed a sufficiently satisfactory topical anesthetic which will render the injection absolutely painless. To complicate matters further there has been no completely satisfactory method of evaluating topical anesthetic potency. Of necessity all tests mustbe purely subjective in nature. Because of individual variation these tests have been, to a great extent, practically inconclusive. With this in mind we hare attempted to eliminate AS many variables as possible. Previous methods of testing consist,& essentially of applying the 01’ tinie, ant.1 thert t&&g topical anest hetic*, waiting for a l)rescribcd lrllgth for anwthesia I)\; l)lt~itlls of it shat.l, t~sl)l(~l~(~1~.It is quite apparent that these ?1*StS6’tt!lt~it~‘Wl SIII’IL \‘;tl’iiiltlt% iIS; ( I I this shitt’l;ness iif thch <-siti t!1c ;irl!olllr? ot’ pwss11?? CY$211 111~individual palient’s pain thrcsholris: erted. T11ortler to eliminate thcsc variables the instrument shown in F’ig. 1 was devised. blood lnncet in which the Essentially. the inst,rumrnt is a converted blunted tip is placed against the part, to be tested and procure applied. AS *Instructor in Depar-tmfmt of Maryland. **Professor of Pharmacology,
I’niversity
of
Pharmacology,
Raltimwe
College 615
Saltimore of IBmt:rl
College Surge!‘~-,
of Cnivcrsity
Dental
Surgery,
of Maryland.
616
LEONARD
RAI’OIWRT
ASD
ED\VARD
C.
DOBBS
the pressure is applied the hub mol-es upward revealing notches which have previously been cut into the plunger, permitting it, to function as a scale. The same instrument may be used over and over on limitless numbers of patients without affecting its accuracy. Since the tip is quite large and blunt,, sharpness is not a factor. So far as pressure is concerned this can be measured very accurately. Before the instrument was placed in use 4 notches were cut into the plunger. Measurements were made to determine the a,mount of pressure which must be exerted against the tip to cause the plunger to move upward notch by notch. These were the results: first notch, 295 Gm. ; second notch, 333 Gm.; third notch, 353 Gm.; fourth notch, 373 Grn. I-293 2 -333 3 -353 4 -373
Fig.
l.- -Instrument
used
in
testing
topical
anesthetic
potency.
Periodically, after every 15 or 20 tests the instrument was re-evaluated and it was noted that no measurable changes occurred. With the eventual idea in mind of weighting topical anesthetics numerically, or according to a topical anesthetic index, the authors assigned unit values as well as descriptive terms to each demarcation inscribed on the plunger. Accordingly: (1) no perceptible movement of the plunger was assigned the numerical value of 0, and described as no anesthesia; (2) slight
EVAI,C.\TIS(;
TOPIC’.\L
ISESTHETIC
617
POTEX:CY
movement of the plunger was assigned the value of 1, and described as mild of the plunger to the second notch was assigned the tcne.sthe.sicr; (3) movement value of 2, and described as yml trnP.sthsi~~; (4) movement of the plunger between the srcwld ancl fourth notches was assigned the value of 3, and described as profound crncsthpsitr; (5) ll~ovemellt of the plnngrr to or hcyo~ld the fourth notch was assigned the value of 4, and described as tq(;q ~~c~(o~nd anesthesia. Before testing was begun it was decided, for ~~uqJoses of accuraclv, that the same anatomic area be used on all individuals studied. Ac:~ortlingl,v,, the area selected was the medial portion of the ltpI)er left canine eminence, high in the mucolahial fold.
Elimination As has bee11 previously mcntionetl. may be fairly well eliminated through
Sharpness of Point.-Since is felt that this factor was blunted and had times the instrument measurable change in
cannot be a diameter was used the relative
of Variables we feel that three clistinct variables use of the instrument described.
the same instrument was used in all tests it. considered variable. The end of the plunger of 1.95 mm. Irrespective of the number of there could not conceivably have been any sharpness or dullness of the point.
Individual Pain Threshold Variations.-Before testing was begun we felt that a great source of error in topical anesthetic evaluation stemmed from the variations in individual patient’s pain t,hreshold. In order to eliminate or reduce this intlividual variation each patient was first tested for pain threshold and those with high thresholds were eliminated. to the test, area imcdial portion The test consist4 of apylpillg thr iustrumellt of left, canine c~minencc) RIK~ esertillg pressure until the patient, signified that pain was felt. Tf the plunger moved, even slightly, before the patient, gave such a sign, that, patient was inlmetliatrly rliminatetl as having too high a threshold for testing purposes. It may 1~: 01 interest IO note that ;\l)~~)rosi~rl;ltely 40 per cent of all those tested were rliminatctl from the filial tests l~nuse of high threshold values. This large proportion, if not previously weetlecl out, coultl have materially influenced the statistical findings.
Amount of Pressure Exerted.-----c)11eoi’
the
pdmt*
*Tainter. JI. I,.. II. Further Observations on the Gums and Oral
S. 31.: Throndson A. H.. an<1 Moose. on ttw IZtficacy of tile JIore Cvmmon Mucosa. J. Am. Iknt. A. 24:1486, 1937.
iv f (xstinp I he cXl)lOWr point has the ol)rrator.
\~;trial)les
effectiveness of topical anesthetics liy liicans 4 ;I Shill’]> Iteen the amount of pressure csertrd ctn the t,spiorer by By the usr of this instrumenl the tlrroI nrigirlatirry First. we wtw’ able to 1ll~ilSllJ’e l)elirved to be eliminated. Stuclics Local
from
this
sours
is
-\-isibly the amount in Topical .\nesthetics
Anesthesia. \!‘hen ITsed
618
LEOXARD
R.\I'Ol'ORT
ASD
EDWARD
C. DOBBS
Second, of pressure which was exerted against the tip of the instrument. the constancy of this pressure coul(1 be checked any number of times simply by re-evaluating the instrument as was done after approximately every 15 or 20 tests.
The Method of Testing In this series of studies the patients used were students in the dental clinic. The reason for using students was that they were more easily accessible to the laboratory in which the tests were conducted and because the operators felt that they would more intelligently and scientifically define their sensations than lay individuals. When the patient was seated in the chair the first thing to be done was to explain roughly the mechanism of the test. It is to be emphasized that the preliminary test was carried out without applying any medication to the mucosa. If sufficient pressure was exerted against the tip of the instrument such that the plunger moved upward, without the patient signifying the presas having too high ence of pain, that individual was immediately “discarded” a pain threshold for purposes of the test. Once it was ascertained that the patient’s threshold was satisfactory the topical anesthetic to be testecl was applied by dipping a cotton swab into the solution, expressing the excess liquid against the side of the l:ottle, and wiping the saturated swab three times across the medial aspect of the upper left canine eminence, high in the mucolabial fold. In the testing of pastetype anesthetics, this technique was, of necessity, modified by squeezing a moderate portion of the paste onto the swab and applying in the manner just described. Concomitant with the application of the topical anesthetic a stop watch was placed in operation so that the degree of anesthesia could be tested at precisely one-minute intervals. At the expiration of each minute for a period of ten minutes, the patient was tested for degree of anesthesia by use of the instrument previously described. As each patient indicated that pain was felt the instrument was read to determine how much pressure had been exerted to produce the pain. The unit, values to 0 to 4 inclusive, previously described, were used to designate this point and tabulation was made on a series of 25 “threshold acceptable” patients. This same procedure was followed for each topical anesthetic studied.
Methods Used in Evaluating
Data
For purposes of brevity we will henceforth refer to the numerical values assigned to the instrument as the “T.A. index” (topical anesthetic index). The first method of handling the data was to ascertain the lo-minute T.A. index for each individual patient by averaging the ten separate T.A. indices obtained at the expiration of each minute. Practically, this is of no great consequence since such an index indicates very little when individual variation is considered. Accordingly, the operators reasoned that to atone for certain individual peculiarities or unanticipated results a T.A. index for each minute, covering
EVALCATISG
TOPICAL
ANESTHETIC
619
POTEXCT
This was done by averaging the T.-A. all 25 patients, should be determined. index at one-minute periods for all of the ‘15 patients, with each of the anesthetics used. The results are found talmlated in Yigs. 2 to 6 and the graphs made from It is our opinion t,hnt conthese tabulations arc placed immediately following. siderable significance may he attached to these graphs. Iqirst of all, the elinical value of topical anesthetics may lx determined at a glatlce, t+t:und, the shape of the graph indicates the recummendecl clinical application of the topBy way of example, an anesthetic which shows ical anesthetic in question. a slow gradual rise and maintains the rise for sume time would be a poor selection for application to oral mucous meml)rane prior to needle injection, beOn the other cause of the length of time required to produce anesthesia. hand it might be ideally used in scaling ol)erations where prolonged anesthesia is desirable. Of course, the ideal topical anesthetic for scaling would produce its anesthesia quickly, in addition to maintaining it for a prolonged period. T-A
INDEX
BY
MINUTES
MINUTE
I
2
3
4
5
6
INDEX
1.60
I.16
.80
.40
.32
.I2
I
2
3
4
5
7 0
6
7
8
9
IO
0
0
0
8
A high T.A. bides for the first Ininuie ur t \Vo: tllell il ra j)id dl,i)[) Such a graph ~voul(I indicate result in a graph pattern of spiking. prtGn,jectir)n anesthetic. but a poor choice for prolongetl work.
9
IO
n-ould a good
Summary and Conclusions The work was begun wit,11 the prime factory, more scientific, and I~OJ’C accurate
purpose of finding a JIIUW satisltlethod of evaluating topical an-
620
LEONARD
1-A
RAPOPORT
INDEX
AND
BY
MINUTES
EDWARD
C. DOBBS
MINUTE
I
2
3
4
5
6
7
6
9
IO
lNDEX
.64
1.08
1.44
2.32
2.60
2.92
3.00
3.06
2.84
2.76
4.0 3.5
TIME Fig.
S.-Graph
IN
pattern
1-A
for
9
I
I
6
5
8
7
---1
IO
MINUTES Cook-Waite
INDEX
BY
Tropical Paste-Pontocaine chloride 0.2 per cent.
2 per
Trialkonium
cent.
MINUTES
MINUTE
I
2
3
4
5
6
7
8
9
IO
INDEX
1.20
.92
.80
0
0
0
0
0
0
0
a #i
2.0 I.5 l.O0.5I
TIME Fig.
L.-Graph
pattern
2
IN for
3
4
5
6
Co;;nt
Co.), . active
7
I 8
9
Id
MINUTES Emulcaine
(G.H.
ingredient.
Benzocaine
21 per
EVALUATING
T-A
TOPICAL
BY
INDEX
ANESTHETIC
621
POTENCY
M lNUTES
MINUTE
I
2
3
4
5
6
7
8
9
IO
INDEX
1.60
1.64
.80
.40
.I2
.08
0
0
0
0
T-A
INDEX
MINUTE
\
INDEX
I. I6
BY
MINUTES
2
3
4
5
6
7
8
9
10
.60
.40
20
.20
.08
.04
0
0
0
3.5 3.0 t: g
2.5
-
2.0
a
&L I.5
L
2
I TIME
IN
3
MINUTES
4
5
6
I
7
8
J
9
IO
622
LEONARD
RAPOI’ORT
AKD
EDWARD
C. DOBBS
It has long been evident that, alesthetic preparations in human subjects. though animal expetirnents can be carried out with a fair degree of accuracy, the results obtained do not always coincide with the findings in clinical practice. In order to utilize the response obtained from human beings and at the same time to eliminate as many extraneous variables as possible, an instrument was devised which reduced some of these factors. A weighting system was assignetl to the instrument so that topical anesthetics might be mathematically evaluated for efficiency in terms of an index, in the same manner that alcohols are weighted by proof or percentage of alcoholic content. It was not our intent to evaluate the various topical anesthetics in vogue today, but rather to develop an instrument which could be used to measure the potency of topical anesthetics. The findings were rather enlightening, indicating that certain types of topical anesthetics are practically worthless, others designed for specific purposes, and that none of those tested could be wholeheartedly recommended for all types of work. Another important outgrowth of the work was the finding that a T.A: index of at least 2 should be sought for if pain is to be eliminated. It is our hope that a new avenue of approach to the evaluation of topical anesthetics has been opened and that this work will be but the forerunner of further investigation in this field.
METHOD ANESTHETIC
FOR EVALUATING POTENCY
Il~:o~~~rt~>ILWOPORT, B.S., T).T).S.,* AND EDWARD I?. lh313s, BALTIMORE, MD.
TOPICAL
I).D.Y.,
F.A.C.I).,'"
F
OR over half a century vast amounts of research have been channeled into t.he field of local anesthesia, with the prime purpose in mind, so far as dentist’ry is concerned, of making the dental operation as safe and as painless as possible. In spite of the advances and improvements made, improvements that have rendered the majority of dental procedures absolutely painless, there has been a certain reluctance on the pa.rt of a rather wide segment of the population to submit to local anesthesia. Much of this reluctance may be traced to the fact that the insertion of the needle, in itself, gives rise to pain. This, together with the psychologic apprehension attending the injection, is often sufficient reason to warrant the patients seeking other forms of anesthesia, or of avoiding t,he dental operation altogether. Realizing this, there has been a distinct effort on the part of the profession to develop topical anesthetics, which when applied to the oral mwoxa would eliminate the pain of needle insertion. Unfortunately there has not been developed a sufficiently satisfactory topical anesthetic which will render the injection absolutely painless. To complicate matters further there has been no completely satisfactory method of evaluating topical anesthetic potency. Of necessity all tests mustbe purely subjective in nature. Because of individual variation these tests have been, to a great extent, practically inconclusive. With this in mind we hare attempted to eliminate AS many variables as possible. Previous methods of testing consist,& essentially of applying the 01’ tinie, ant.1 thert t&&g topical anest hetic*, waiting for a l)rescribcd lrllgth for anwthesia I)\; l)lt~itlls of it shat.l, t~sl)l(~l~(~1~.It is quite apparent that these ?1*StS6’tt!lt~it~‘Wl SIII’IL \‘;tl’iiiltlt% iIS; ( I I this shitt’l;ness iif thch <-siti
I’niversity
of
Pharmacology,
Raltimwe
College 615
Saltimore of IBmt:rl
College Surge!‘~-,
of Cnivcrsity
Dental
Surgery,
of Maryland.
616
LEONARD
RAI’OIWRT
ASD
ED\VARD
C.
DOBBS
the pressure is applied the hub mol-es upward revealing notches which have previously been cut into the plunger, permitting it, to function as a scale. The same instrument may be used over and over on limitless numbers of patients without affecting its accuracy. Since the tip is quite large and blunt,, sharpness is not a factor. So far as pressure is concerned this can be measured very accurately. Before the instrument was placed in use 4 notches were cut into the plunger. Measurements were made to determine the a,mount of pressure which must be exerted against the tip to cause the plunger to move upward notch by notch. These were the results: first notch, 295 Gm. ; second notch, 333 Gm.; third notch, 353 Gm.; fourth notch, 373 Grn. I-293 2 -333 3 -353 4 -373
Fig.
l.- -Instrument
used
in
testing
topical
anesthetic
potency.
Periodically, after every 15 or 20 tests the instrument was re-evaluated and it was noted that no measurable changes occurred. With the eventual idea in mind of weighting topical anesthetics numerically, or according to a topical anesthetic index, the authors assigned unit values as well as descriptive terms to each demarcation inscribed on the plunger. Accordingly: (1) no perceptible movement of the plunger was assigned the numerical value of 0, and described as no anesthesia; (2) slight
EVAI,C.\TIS(;
TOPIC’.\L
ISESTHETIC
617
POTEX:CY
movement of the plunger was assigned the value of 1, and described as mild of the plunger to the second notch was assigned the tcne.sthe.sicr; (3) movement value of 2, and described as yml trnP.sthsi~~; (4) movement of the plunger between the srcwld ancl fourth notches was assigned the value of 3, and described as profound crncsthpsitr; (5) ll~ovemellt of the plnngrr to or hcyo~ld the fourth notch was assigned the value of 4, and described as tq(;q ~~c~(o~nd anesthesia. Before testing was begun it was decided, for ~~uqJoses of accuraclv, that the same anatomic area be used on all individuals studied. Ac:~ortlingl,v,, the area selected was the medial portion of the ltpI)er left canine eminence, high in the mucolahial fold.
Elimination As has bee11 previously mcntionetl. may be fairly well eliminated through
Sharpness of Point.-Since is felt that this factor was blunted and had times the instrument measurable change in
cannot be a diameter was used the relative
of Variables we feel that three clistinct variables use of the instrument described.
the same instrument was used in all tests it. considered variable. The end of the plunger of 1.95 mm. Irrespective of the number of there could not conceivably have been any sharpness or dullness of the point.
Individual Pain Threshold Variations.-Before testing was begun we felt that a great source of error in topical anesthetic evaluation stemmed from the variations in individual patient’s pain t,hreshold. In order to eliminate or reduce this intlividual variation each patient was first tested for pain threshold and those with high thresholds were eliminated. to the test, area imcdial portion The test consist4 of apylpillg thr iustrumellt of left, canine c~minencc) RIK~ esertillg pressure until the patient, signified that pain was felt. Tf the plunger moved, even slightly, before the patient, gave such a sign, that, patient was inlmetliatrly rliminatetl as having too high a threshold for testing purposes. It may 1~: 01 interest IO note that ;\l)~~)rosi~rl;ltely 40 per cent of all those tested were rliminatctl from the filial tests l~nuse of high threshold values. This large proportion, if not previously weetlecl out, coultl have materially influenced the statistical findings.
Amount of Pressure Exerted.-----c)11eoi’
the
pdmt*
*Tainter. JI. I,.. II. Further Observations on the Gums and Oral
S. 31.: Throndson A. H.. an<1 Moose. on ttw IZtficacy of tile JIore Cvmmon Mucosa. J. Am. Iknt. A. 24:1486, 1937.
iv f (xstinp I he cXl)lOWr point has the ol)rrator.
\~;trial)les
effectiveness of topical anesthetics liy liicans 4 ;I Shill’]> Iteen the amount of pressure csertrd ctn the t,spiorer by By the usr of this instrumenl the tlrroI nrigirlatirry First. we wtw’ able to 1ll~ilSllJ’e l)elirved to be eliminated. Stuclics Local
from
this
sours
is
-\-isibly the amount in Topical .\nesthetics
Anesthesia. \!‘hen ITsed
618
LEOXARD
R.\I'Ol'ORT
ASD
EDWARD
C. DOBBS
Second, of pressure which was exerted against the tip of the instrument. the constancy of this pressure coul(1 be checked any number of times simply by re-evaluating the instrument as was done after approximately every 15 or 20 tests.
The Method of Testing In this series of studies the patients used were students in the dental clinic. The reason for using students was that they were more easily accessible to the laboratory in which the tests were conducted and because the operators felt that they would more intelligently and scientifically define their sensations than lay individuals. When the patient was seated in the chair the first thing to be done was to explain roughly the mechanism of the test. It is to be emphasized that the preliminary test was carried out without applying any medication to the mucosa. If sufficient pressure was exerted against the tip of the instrument such that the plunger moved upward, without the patient signifying the presas having too high ence of pain, that individual was immediately “discarded” a pain threshold for purposes of the test. Once it was ascertained that the patient’s threshold was satisfactory the topical anesthetic to be testecl was applied by dipping a cotton swab into the solution, expressing the excess liquid against the side of the l:ottle, and wiping the saturated swab three times across the medial aspect of the upper left canine eminence, high in the mucolabial fold. In the testing of pastetype anesthetics, this technique was, of necessity, modified by squeezing a moderate portion of the paste onto the swab and applying in the manner just described. Concomitant with the application of the topical anesthetic a stop watch was placed in operation so that the degree of anesthesia could be tested at precisely one-minute intervals. At the expiration of each minute for a period of ten minutes, the patient was tested for degree of anesthesia by use of the instrument previously described. As each patient indicated that pain was felt the instrument was read to determine how much pressure had been exerted to produce the pain. The unit, values to 0 to 4 inclusive, previously described, were used to designate this point and tabulation was made on a series of 25 “threshold acceptable” patients. This same procedure was followed for each topical anesthetic studied.
Methods Used in Evaluating
Data
For purposes of brevity we will henceforth refer to the numerical values assigned to the instrument as the “T.A. index” (topical anesthetic index). The first method of handling the data was to ascertain the lo-minute T.A. index for each individual patient by averaging the ten separate T.A. indices obtained at the expiration of each minute. Practically, this is of no great consequence since such an index indicates very little when individual variation is considered. Accordingly, the operators reasoned that to atone for certain individual peculiarities or unanticipated results a T.A. index for each minute, covering
EVALCATISG
TOPICAL
ANESTHETIC
619
POTEXCT
This was done by averaging the T.-A. all 25 patients, should be determined. index at one-minute periods for all of the ‘15 patients, with each of the anesthetics used. The results are found talmlated in Yigs. 2 to 6 and the graphs made from It is our opinion t,hnt conthese tabulations arc placed immediately following. siderable significance may he attached to these graphs. Iqirst of all, the elinical value of topical anesthetics may lx determined at a glatlce, t+t:und, the shape of the graph indicates the recummendecl clinical application of the topBy way of example, an anesthetic which shows ical anesthetic in question. a slow gradual rise and maintains the rise for sume time would be a poor selection for application to oral mucous meml)rane prior to needle injection, beOn the other cause of the length of time required to produce anesthesia. hand it might be ideally used in scaling ol)erations where prolonged anesthesia is desirable. Of course, the ideal topical anesthetic for scaling would produce its anesthesia quickly, in addition to maintaining it for a prolonged period. T-A
INDEX
BY
MINUTES
MINUTE
I
2
3
4
5
6
INDEX
1.60
I.16
.80
.40
.32
.I2
I
2
3
4
5
7 0
6
7
8
9
IO
0
0
0
8
A high T.A. bides for the first Ininuie ur t \Vo: tllell il ra j)id dl,i)[) Such a graph ~voul(I indicate result in a graph pattern of spiking. prtGn,jectir)n anesthetic. but a poor choice for prolongetl work.
9
IO
n-ould a good
Summary and Conclusions The work was begun wit,11 the prime factory, more scientific, and I~OJ’C accurate
purpose of finding a JIIUW satisltlethod of evaluating topical an-
620
LEONARD
1-A
RAPOPORT
INDEX
AND
BY
MINUTES
EDWARD
C. DOBBS
MINUTE
I
2
3
4
5
6
7
6
9
IO
lNDEX
.64
1.08
1.44
2.32
2.60
2.92
3.00
3.06
2.84
2.76
4.0 3.5
TIME Fig.
S.-Graph
IN
pattern
1-A
for
9
I
I
6
5
8
7
---1
IO
MINUTES Cook-Waite
INDEX
BY
Tropical Paste-Pontocaine chloride 0.2 per cent.
2 per
Trialkonium
cent.
MINUTES
MINUTE
I
2
3
4
5
6
7
8
9
IO
INDEX
1.20
.92
.80
0
0
0
0
0
0
0
a #i
2.0 I.5 l.O0.5I
TIME Fig.
L.-Graph
pattern
2
IN for
3
4
5
6
Co;;nt
Co.), . active
7
I 8
9
Id
MINUTES Emulcaine
(G.H.
ingredient.
Benzocaine
21 per
EVALUATING
T-A
TOPICAL
BY
INDEX
ANESTHETIC
621
POTENCY
M lNUTES
MINUTE
I
2
3
4
5
6
7
8
9
IO
INDEX
1.60
1.64
.80
.40
.I2
.08
0
0
0
0
T-A
INDEX
MINUTE
\
INDEX
I. I6
BY
MINUTES
2
3
4
5
6
7
8
9
10
.60
.40
20
.20
.08
.04
0
0
0
3.5 3.0 t: g
2.5
-
2.0
a
&L I.5
L
2
I TIME
IN
3
MINUTES
4
5
6
I
7
8
J
9
IO
622
LEONARD
RAPOI’ORT
AKD
EDWARD
C. DOBBS
It has long been evident that, alesthetic preparations in human subjects. though animal expetirnents can be carried out with a fair degree of accuracy, the results obtained do not always coincide with the findings in clinical practice. In order to utilize the response obtained from human beings and at the same time to eliminate as many extraneous variables as possible, an instrument was devised which reduced some of these factors. A weighting system was assignetl to the instrument so that topical anesthetics might be mathematically evaluated for efficiency in terms of an index, in the same manner that alcohols are weighted by proof or percentage of alcoholic content. It was not our intent to evaluate the various topical anesthetics in vogue today, but rather to develop an instrument which could be used to measure the potency of topical anesthetics. The findings were rather enlightening, indicating that certain types of topical anesthetics are practically worthless, others designed for specific purposes, and that none of those tested could be wholeheartedly recommended for all types of work. Another important outgrowth of the work was the finding that a T.A: index of at least 2 should be sought for if pain is to be eliminated. It is our hope that a new avenue of approach to the evaluation of topical anesthetics has been opened and that this work will be but the forerunner of further investigation in this field.