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An ultraviolet device for the destruction of bacteria on contaminated dental handpiece surfaces (concluded)
Endodontia AN ULTRAVIOLET DEVICE ON CONTAMINATED
FOR THE DESTRUCTION OF BACTERIA DENTAL HANDPIECE SURFACES (CONCLUDED)*
VICTORH. DIETZ, D.D.S., PH.D., (Continued
from
the Novmber
ANN
ARBOR,
MICH.
issue, page 1467.)
A R&mm6 of the Total Procedure
1. The three identical handpieces and contra-angles were sterilized in liquid silicone at 300° F. This ideally lubricates the six pieces with the silicone which does not smolder when subsequently dry-heat sterilized. 2. These six pieces after being adequately drained are combined within the folds of a sterile towel to make the three handpiececontra-angle assemblies. Each assembly will be referred to, hereinafter, simply as the handpiece. 3. The three handpieces, wrapped within a sterile towel, are now blotted thoroughly and placed in the hot air oven where they are maintained at 160-170° C. for one and one-half hours. 4. Once the silicone treatment has been given it may be omitted for not over ten subsequent tests by resorting to dry heat sterilization exclusively. However, after each test these handpieces must be separated and scrupulously wiped with a clean towel. 5. After the handpieces have cooled sufficiently, they are aseptically placed within the rotating apparatus. A paper shield is applied to mask out the pulley end of the sheath beyond the knurling (Fig. 5), and a thoroughly washed and disinfected plastic tray is inverted over this. The plastic tray does not touch the handpieces. 6. The type 152 DeVilbiss all-purpose atomizer is used for nebulizing the saliva into the air. Having autoclaved this atomizer, fresh paraffin-stimulated saliva is collected in it by the use of a small sterile glass funnel. The spraying head is inserted and the atomizer is attached to the air jet of the dental unit. The atomizer is completely disassembled and thoroughly flushed with distilled water after each test. 7. It is advisable to carry out this procedure in the absence of air currents and without any persons being present. The operator should wear a surgical mask even though the saliva be his own. 8. The swivel tip of the atomizer is directed up at a right angle to the spray tubes. The nebulization of saliva is now begun holding the tube vertically and using full pressure. The amount of saliva used has been standardized at 25 ml. The time factor is less important and, depending essentially on the viscosity of the saliva, this amount will ordinarily require 2+$$-3ysminutes to be ejected. Nebulization is effected at a height of approximately one meter over the level *The W. K. Kellogg Foundation Institute University of Michigan. 1565
of Graduate and Postgraduate Dentistry,
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of the handpieces and is observably carried as a fine misty dispersion to a height almost two meters beyond this. F‘resh saliva when so dispersed will increase its odor many-fold but lasts not noticeably longer than approximately ten minutes. 9. lmmediately upon completing the ejection of the 2.5 ml. quantity of saliva exactly one minute is permitt,ed to elapse. The plastic tray is removed and the motor begun. Preliminary experiments have shown that most droplets agglomerate within the first minute giving a spotty distribution. For each succeeding minute up to five minutes the rate is quite constant and the droplets well dispersed (Fig. 6). After this time there is a negatively accelerating This was determined by subjecting blood agar plates to the diminution. immediate vicinity of nebulization at one-minute intervals. After a threeminute exposure of the synchronously revolving handpieces the motor is turned off, the plastic tray immediately replaced, and the rotating apparatus carried from the nebulized field to the laboratory with an elapse of time not over one minute.
Fig. 5.-Showing the application of the shield over the pul!ey end of the handpieces. This sharply terminates the deposition of bacteria upon the handpieces not above the knurling at the pulley end of the sheath. This photograph also shows the Position of the open Petri dish, as used in the preliminary experiments, in order to evaluate the distribution of bacteria by the method of nebulization.
10. Each handpiece is immersed in 35 ml. of sterile PSS (Fig. 7) in a 50 ml. test tube. When the tube is held at an angle of 45O, the water level includes all of the knurled surface of the sheath. The insertion of the handpiece causes approximately a 2 cm. rise in the water level. Should the surface level go beyond the end of the knurling, it does not matter as the shield of the rotating apparatus sharply demarcates the contaminated from the uncontaminated surfaces. The handpiece, in the tube, is briskly rotated for approximately thirty seconds. It is then removed and the tube reca.pped with the sterile rubber stopper. The
Fig. 6.-A, Six blood agar plates on which a suspension of Bncillus sz~btilis was Ileposited. The suspension contained abwt 1.000 This remarkably uniform distribution. effected in bacteria per ml.. and the suspending fluid, F’S, had 0.05 per cent agar added to it. Each plate was exposed to the nebulized fleld for three minutes on separate the nebulized field, represents forty-eight-hour cultures. Complete nebulization was carried out before each test and the inoculation started after a one-minute interval. B, A fortyoccasions. eight-hour blood agar plate showing the distribution of viable bacteria deposited upon the surface after a three-minute exposure in A great variety of colonies are macroscopically identifiable. Numerous hemolytic colonies may be observed and the nebulised fleld. The majority of these colonies are obviously not clones but were deposited in groups or packets within some exerting antibiotic effects. This plate was subjected to a single droplet. The use of microscopic slides in the nebulized field further substantiated this feature. nebulized whole saliva which accounts for the variety of bacteria that may be observed.
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three tubes, one for each handpiece, are identically prepared. The tubes are rapidly shaken along their long axes for approximately thirty seconds. This produced, by serial tests, a uniform suspension of bacteria. Three 0.1 ml. samples, from each of three tubes, showed an average variation not over 10 per cent despite the fact that this was one of the preliminary tests using the less accurate spreading technique, on blood agar plates, for viable count determinations.
Fig. T.-In the preparation of the bacterial “ride” in the butt of the tube and it is thoroughly to remove over 99 per cent of the bacteria.
suspension agitated
the contra-angle for thirty seconds.
is allowed to This proved
11. After the “wash off” suspensions of bacteria are thoroughly agitated, 0.1 ml. is pipetted from each tube into three Petri dishes. Blood agar pour plates are then made with 5 per cent defibrinated rabbit’s blood in a brain heart infusion (Difco) base containing 2 per cent agar. The consistency in the viable plate counts resulting from this procedure may be seen (Table II). The designations “left, ” ‘(center, ” and “right” refer to the positions of the handpieces in the rotating apparatus. It is now apparent that all positions are quite unisaliva formly subjected to the deposition of bacteria. Fresh paraffin-stimulated from the same individual was used for each test. Tests I and II were performed on one day and Tests III, IV, and V, on the following day. In the tests designed to determine the uniformity of contaminating handpieces by this method, it may be observed that the greatest single variation occurred in Test II (Table II) between the counts of 119 and 186. Even this variation is not much greater than 36 per cent in this instance, and the average variation for all tests is approximately 10 per cent. This constitutes a considerable improvement over the method of immersing the handpieee in saliva for experimental contamination. It is apparent, as would be expected, that one wdpiece must always be used as a control for each test with the three handpmces, for each sample of saliva. Arbitrarily, the handpiece in the center was chosen as the most plausible one to use as the control in subsequent experiments.
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The average bacterial count with a 0.1 ml. inoculum being slightly over 200, and washed off into 35 ml. of saline solution, indicates that the average total deposition of bacteria on a handpiece is of the magnitude of 70,000. This density of bacterial deposition compares favorably with Knighton’s experiments’s using handpieces with contra-angle or right-angle attachments. His “wash off” technique and bacteriologic procedures are also quite comparable. His actual clinical contamination of the handpieces indicates that: “All of the ten handpieces tested immediately after operation showed a positive bacterial growth, with an average colony count of 61,000.” However, considerable variation will occur with different salivary specimens. TABLE
Test
Test
Test
II.
I
II
III
ORGANISMS RECOVERABLE FROM AN 0.1 ML. INOCULUM WASH OFF SUSPENSION OF THE CONTAMINATED HANDPIECES
VIABLE
Left Center Right
141
Left Center Right
119 136
Left Center Right
Test
179
IV
126 (Control) 186
159 196
Teat (Control)
V
Left Center Right Left Center Right
FROM
THE
274 303
(Control)
257 227 255
(Control)
270
(Control)
177
Before proceeding with the ultraviolet radiation tests, by rotating the handpieces, a series of static tests were performed in order to determine the efficiency of irradiation on all surfaces of the handpieces. The three handpieces were placed in the various positions in the rotating apparatus as shown (Fig. 4) but were not revolved. In the actual procedure, the three handpieces were placed in the identical position for each test. These were then subjected to the impact of ultraviolet energy in the device for an arbitrary five-minute period. Only four tests were performed by this method, all with a single sample of saliva. In this way at least two tests for each surface could be performed. In all instances the handpiece was inserted in the ultraviolet device in a standard “sagittal” position (if a bur were inserted it would be pointing down). The bacteriological procedures were the same, and the controls were not irradiated. The results (Table III) indicate that the top surfaces of the handpieces in the direct ultraviolet stream were most efficiently reduced in numbers (about 70 per cent). The surprising finding was the fact that approximately a 50 per cent reduction in the number of bacteria was found for both sides of the handpiece. One side was directed toward the back reflecting surface and the other side toward the plastic door. Apparently, then, the plastic door, to little or no extent, constitutes a “blind spot” which would diminish reflectivity. This equal effectiveness is undoubtedly due to the slight forward “off centering” of the lamp intended to overcome any “blind spot” effect by using a plastic door. The plastic door not only enhances the appearance of the device but enables the operator to see whether or not the contra-angle is attached and what type of bur or stone was last placed therein. The bottom of the handpiece,
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as would be expected, showed only little better than a 40 per cent reduction in the bacterial count. It should be remembered that even the sides of the handpiece, when contaminated and placed in the standard “sagittal” position, receive the incident, rays on approximately one half of their contaminated surfaces. The bottom of the handpiece, in contradistinction, can receive no direct rays upon its contaminated surface. This finding indicates the pot,ential advantage of using a multiple lamp device. TABLE III.
STATIC TESTS TO DETERMINE EFFICIENCY OF ~RRALUATION OK THE T.'ARIOW RURFACJ~S
Test 1.
Top of handpiece Control 90 31 Left 23 Right
Test
Right side of handpiece Control 144 Left 76 Right 81
Il.
(in direct path of incident
Test III.
Left side of handpiece 202 Control 114 Left Right 09
Test IV.
Bottom Control Left Right
of handpiece 187 100 111
(toward
(toward
(toward
rays)
flat, back, reflecting
plastic
surface)
door)
are of circular
reflecting
surface)
The following experiments (Table IV) were carried out in the routine fashion by rotating the handpieces and subjecting them to the various periods of time in the ultraviolet device. Before instituting the test, a one-hour warm-up period was allowed in order to stabilize the temperature in the radiation chamber. With temperature determinations made at the very center of the chamber and starting at 21’ C., there is about an 8* C. rise in one hour. The ambient operating temperature, with a room temperature of 22-23O C., and with the occasional opening of the door, is about 26O C. A single test, over a period of eight hours with a room temperature fluctuation between 21 and 25O C., and with the door unopened, gave a final temperature of 29Li” C. The temperature factor is apparently not too critical. Nevertheless, Buttolph4” showed that ultraviolet energy is most efficiently bactericidal within a temperature range of 70-80’ 5’. The device, therefore, need not be louvered as the average 26O C. (78.8’ F. j is safely within the most efficient range of bactericidal ultraviolet activity. For each test a fresh specimen of paraffin-stimulated saliva was used. The marked rise in the number of bacteria found in certain salivary specimens appeared particularly if the specimens should have been collected for some time after a meal. As is well known, t,he dehydration of organisms may contribute to a spontaneous decrease in their viable numbers. Hence, in all tests of one to four minutes’ exposure, the control handpiece was the last to be washed off to make the bacterial suspension. In those tests of eight minutes’ duration and over,
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the control handpiece was immersed as nearly between the times that the two experimental handpieces were washed off. It was thought at the conclusion of Test IV (eight minutes) that the residual organisms may have remained within the bur opening and that these were not receiving the direct ultraviolet impact. A short series of tests established this fact to be true in five out of six handpieces irradiated for sixteen minutes each. These tests are entirely qualitative as they were performed by inserting sterile pipe cleaners into the full length TABLE IV.
THE DESTRUCTION OF BACTERIA AT “DOUBLING” INTERVALS FROM ONE MINUTE TO SIXTY-FOUR MINUTES. THE NUMBERS INDICATE THE NUMBER OF VIABLE ORGANISMS IN 0.1 ML. OF THE SUSPENSXON
Test 1
(1 minute) Saliva A Control 233 Left 197 Right 200
Saliva B 123 152 115
Saliva C 206 197 166
Test II
(2 minutes) Saliva A Control 88 Left 50 Right 44
Saliva B 308 217 190
Saliva C 250 146 164
(4 minutes) Saliva A Control 179 Left 122 Right 90
Saliva 13 148 70 76
Saliva C 111 73 50
(8 minutes) Saliva A Control 222 Left 100 Right 96
Saliva B 102 30 35
Saliva C 93 42 29
Saliva B 199 2
Saliva C 143 19 10
Saliva B 110
Saliva C 154
1:
1:
Saliva B 242 10 4
Saliva C 206 6 8
Test
III
Test IV
Test V
Test VI
Test VII
(16 minutes) Saliva A Control 175 Left 15 Right 22 (32 minutes) Saliva A Control 202 Left Right 1; (64 minutes) Saliva A Control 140 Left 3 Right 4
of the bur openings. The pipe cleaners, contaminated in this way, were then used to inoculate nutrient broth. Five of the six culture tubes were grossly positive after forty-eight hours’ incubation. However, the b,ur opening is not the only place where bacteria can reside with impunity. The bur lock is also a very likely site for such residence. These data indicate that a 50 per cent reduction in the number of viable bacteria lies somewhere between four and eight minutes’ exposure time, and that approximately a 95 per cent kiI1 may
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be expected in a half hour. From an analysis of the data of Test VII it is apparent that in about one hour we are approaching the theoretical “99 per cent kill. ’ ’ To the present time, only one handpiece has been subjected to irradiation for two hours and one for four. These latter two also showed an average “99 per cent kill. ” It is possible that at this point we have reached the limit of ultraviolet effectiveness with this device. As ButtolphjO stated : “Too little is known, however, regarding the relative clinical values of the higher rates of kill represented by 99 per cent and 99.99 per cent, the latter representing, for example, a survival of 1 organism in 10,000.” There is evidence that periods of irradiation of thirty seconds or less may actually be stimulatory to the proliferation of bacteria. The differences found are certainly not entirely due to t,he effect of dehydration of bacteria on the control handpieces in such a short time. The differences found are difficult to ascribe entirely to dehydration also due to the fact that there is no difference in the environmental temperature between the experimental and control handpieces. The control handpieces, frequently showing a lower count when the experimental handpieces were irradiated for periods of thirty seconds, lent credence to the assumption that some inherent bactericidal factor in the saliva may have been inactivated upon irradiation. Such factors are well known since the investigations of Clough,5’ Hine,52 Bibby et a1.,53and Hi11.54 In order to demonstrate this possibility, a nonhemolytic strain of streptococcus was lightly seeded over the surface of a blood agar plate. A 5 ml. quantity of fresh “resting” saliva was collected and 1 ml. of each was placed in the undersurface of st,erile Coplin jar lids. This quantity was flowed out to cover the surface of the lid to the inner rim. The film was approximated to be about one-quarter to one-half mm. in thickness. Two specimens were irradiated, at the “handpiece level ” for periods of fifteen and thirty seconds. The control filtrate was not irradiated. The three filtrates were then Micro-Seitz filtered to These specimens were filtered directly into yield about a 0.5 ml. quantity. sterile microcolorimetric cups. These are preferred over Florey cups because The imof their very small size and the fact that they prevent evaporation. bibition of the saliva filtrate by the media is also better confined to the area of the cup. These cups are arranged in a group upon a sterile flat jar lid. The blood agar plate is then inverted upon these cups which readily adhere to the media. A sterile bibulous cap is placed over the Petri dish to enable it to be incubated right side up. The results of this procedure (Fig. 8) indicate that some inhibitory substance is inactivated upon subjection to a fifteen-second or longer irradiation. The inhibitory action of the saliva filtrate is quite weak and ephemeral. A slight stimulatory effect may be observed after twenty-four hours’ incubation at the periphery of the zone of inhibition. After forty-eight hours, growth is just as luxuriant over the zone of inhibition. Thus it is evident that the inhibition of the bactericidal factor is possibly as important as dehydration. These phenomena, along with a possible stimulatory effect due to a may have contributed to the frequently very short exposure to irradiation, higher counts of experimentals over controls in the preliminary thirty-second tests.
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In the course of preliminary experiments there was some evidence that the curved reflecting surface may have been designed to converge the rays too sharply, hence concentrating a greater lethal intensity within the center of the handpiece than at either end, To determine this possibility the method of Novak and Lacy55 was applied to irradiated handpieces and their respective controls. This was attempted for three tests (nine handpieces) as follows. For each test three handpieces were contaminated as described, and two irradiated for ten minutes, the third being used as the control. These handpieces were placed in a refrigerator (5-loo C.) for ten minutes, then removed and each
Fig. 8.-Showing the microcolorimetric cups “inverted” upon a blood agar plate. A single specimen of saliva was used for all of these tests. The center cup was Alled with about 0.5 ml. of fresh whole saliva. In this instamP bacterial growth may be observed but no zone of inhibition or imbibition. The latter is conceivably due to the viscosity of the saliva. a shows only a slight imbibition zone with the salivary specimen having been heat-inactivated (56” C./one hour). B shows a deAnite zone of inhibition with a sample OP the saliva that was seitz-flltered. C shows no apparent zoning in a seitz-filtered sample of the saliva which was irradiated for only flfteen seconds. D is identical to C but was irradiated for thirty seconds. The particulate matter observable in E is an imbibition control using 0.5 ml. of sterile PSS. CUPS A to E are. in part. Alterable crystalloidal substances but mainly reflection artifacts.
rotated in a separate trough of agar media thermostatically maintained between 43 and 45O C. These were carefully withdrawn and rotated in the air to effect uniform thickness until solidified. For this agar coating technique, troughs are essential as the handpieces must at all times be held horizontally. The handpiece, thus coated and incubated, should demonstrate the growth of organisms in situ. The coated handpieces were incubated, in position, within the disinfected rotating apparatus and covered with the disinfected plastic tray. Sterile distilled water, to a depth of about an inch, was placed in each compartment to effect humidification in order to prevent the agar from drying out to a thin, brittle film. However, the surfa.ce of the handpiece is not easily coated and
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the incubation of the troughs in all instances indicated that over 90 per cent The sparse counts of the organisms were washed off in the coating procedure. in the arbitrary zones (Fig. 9) were completely erratic and unreliable and the procedure was a.bandoned. A zonal immersion t,echnique was carried out in two t,ests (6 handpieces). The total length of the handpiece could be arbitrarily divided into three zones of 4 cm. length each as shown (Fig. 9). Zone A was washed off to make a bacterial suspension, by the immersion technique. in the usual 35 ml. of sterile PSS. The handpiece was then transferred to a second tube and immersed to include Zones A and B. This was repeated for the same handpiece in another tube to a depth including all three zones. Although only two tests were performed, the data shown in Table V are very interesting. The bacteriologic procedure was the same except, to ensure an adequate count, a 1.0 ml. inoculum was used. The “zonal” immersion method is far from infallible but the data strongI> substantiate the fact, that the design of the apparatus does concentrate the ultraviolet light within the middle third of the handpiece. It is obvious, therefore, that a modified design of the reflecting surfaces of the radiation chamber would be more effective. Parabolic curvatures, parallel rather than at right angles to the curvature of t,he handpiece sheath, would greatly rectify this condition. A more efficient, diffuse reflecting surface combined with an increased number of lamps and wattage can, theoretically, increase the bactericidal efficiency tenfold. A new design was contemplated which should assure a 99 per cent kill in less than five minutes. However, a rather intricate design, but theoretically capable of assuring a 99 per cent kill in about one minute, will first be attempted if the engineering problems do not prove to be insurmountable.
Fig. I).-The three arbitrary zones, of exactly 4 cm. length each, conveniently at the obtuse angle of the contra-angle, at the end of the contra-angle, and at the end knurling of the sheath.
divide of the
At the present no attempt has been made to determine which types of organisms survive. To date it is evident, however, that lactobacilli, staphylococci, and streptococci are quite readily killed. The experimental procedure, nevertheless, was desirably carried out with saliva and its polymicrobic flora actually to test the “floracidal” effect of ultraviolet light. Burs were not inserted in the contra-angle as they would only have been extraneous to the test. Burs clogged with debris cannot be sterilized by this method. In actual use a sterile bur is inserted before or after irradiating the handpiece. This device has had only a limited clinical application over a period of two years. The arrangement of the device is seemingly ideal in every respect. The
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door-pedal mechanism, handpiece retaining device, and other features function with utmost simplicity. In no way does the use of this device encumber any dental procedure. Its use simply entails inserting the handpiece in the device rather than hanging it upon the conventional hook. The operator will find himself quickly habituated to this procedure. The clinical application of this device has been limited to endontic procedures in which instance the rubber dam has at all times been applied. The straight handpiece has a microhead contra-angle attached. This contra-angle permits burs to protrude another third in length from the head over some of With this arrangement the contrathe conventional contra-angle attachments. angle need never actually touch tooth surfaces. TABLE V. THE SURVIVAL OF BACTERIA WITHIN THE THREE ZONES UPON TEN MINUTES' ULTRAVIOLET RADIATION FOR EACH HANDPIECE OTHER THAN THE CONTROLS. THE COUNTS REPRESENT A 1.0 ML. INOCULUM ZONE A
ZONE B
ZONE C
Test I
Control Left Right
543 92 184
460 49 47
419 60 124
Test
Control Left Right
703 115 167
661 32 93
520 115 127
II
In the experimental clinical application following procedure has been observed :
over a period
of two years the
1. The handpiece and contra-angle were silicone-sterilized according to the method of Crowley and Ostrander.56 Excess silicone was drained for a day within the folds of a sterile towel. These parts were assembled and attached to the handpiece spindle aseptically. This assembly, hereinafter again referred to only as the handpiece, was aseptically placed in the ultraviolet device. The lamp was burned for two hours. 2. The following morning a tooth was isolated by the use of a rubber dam and the field liberally swabbed with full-strength iodine. The ultraviolet lamp had been b,urning for at least an hour before using the handpiece the day after the initial insertion of the handpiece in the device. The pulp chamber was entered and the approach adequately extended. This bur was removed and a flame-shaped bur inserted. This enabled the operator to complete the approach Upon completion this bur was imby carrying out the’ usual conical cavity. mediately removed and the tooth debris falling on the contra-angle head was wiped off within the folds of a sterile towel. 3. The handpiece was replaced in the device until again needed for the Grasping the pulley end of the handpiece it was frequently wiped next patient. off in its entirety with a sterile towel during the first week as the silicone had a tendency to work its way out of the mechanism, imparting an oily film to the surface. 4. The handpiece was always irradiated for a period. of not less than one half hour between patients, and often an hour or much longer. The reason for
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this variation is simply that the ultraviolet device is turned on the “first thing” in the morning and turned off as the “last thing ” after the day’s work is done. However, there is no objection to irradiating the handpiece through the night. Obviously, however, the burning of the lamp about sixteen hours additionally every day would abbreviate the lamp-life on the basis of its burning expectancy. 5. luring a six-month period the full brunt of responsibility for disinfecting; the handpiece was thrown upon the ult,raviolet device. During this period thirty-five patients were attended and teeth were entered sixty-three times. These cases were especially selected, and in forty-two primary entrances into teeth, only sixteen demonst,rated the presence of viable bacteria. In no instance was t,here any evidence of bacterial cont,amination from one patient to the next on the basis of a negative culture or according to the type or species of bacteria previously encountered. The random sequence in the bacteriologic cultures was entirely fortuitous and would not have been possible if, in this special series of cases, a high percentage of the initial cultures had not been negative. Had the sequence of patients been such as to encounter, e.g., XtreptoCOCCUS z’iridans two or three times successively from consecutive patients, even then proof of contamination would not have been absolute. However, had such been the case, the evidence would have been strongly suggestive of contamination. Staphylococci, occasionally demonstrable on the operator’s hands, were never encountered in the initial cultures.
Discussion The ultraviolet device herein described is not to be construed as an absolute method of sterilization. That it is a distinct aid in suppressing the bacteria with which a handpiece has been contaminated has been adequately demonstrated. There are, oftentimes, minor or relatively imperceptible breaks in the technique of manipulating a sterile handpiece. When these breaches occur the handpiece should be immediately replaced in the ultraviolet device for a few minutes. Evidence is not yet complete but the few bacteria that may be transferred b,y a contra-angle ‘ ‘ clicking ’ ’ against an instrument handle appear to succumb in a matter of seconds. This difference may be due to an absence of the apparently protective salivary mucin and the few or very superficially disposed bacteria. The simplicity of using the ultraviolet device for operative (Fig. 10) and surgical procedures (Fig. 11) is shown. In the experimental method of contaminating the handpiece with whole saliva, mucin, food debris, and other extraneous substances may easily shield bacteria. In addition bacteria are demonst,rably deposited in clumps and, as pointed out by Duggar,“’ “. . . it is possible that when bacteria are present in clumps some of them may escape the bactericidal effect of the lamps.” Porter” further elucidated the significance of the bacterial population in his statement: “The relation between the amount of ultraviolet radiation and the percentage of bacteria killed in a given culture is determined by the distribution of bacteria of varying resistance to the radiation and is not due to the probability of hitting a vital spot in a given organism by a photon.” Nevertheless, this experiment was designed to determine the actual effectiveness of the ultraviolet device herein
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This was attempted under condescribed under the least artificial conditions. ditions which embodied certain features which may be encountered in the various clinical applications other than in endodontic procedures where it is apparently quite effective. It seems especially desirable to employ the device immedia.tely after silicone or oil sterilization as these fluids persist in creeping over the surfaces of the handpiece as a thin film and easily pick up dust and air-borne bacteria, if unprotected. During the intermittent use of the handpiece, on the same patient, it should repeatedly be inserted in the device. In surgical procedures the straight handpiece is most commonly employed; however, with the aid of an The dentist holds the assistant the changing of burs constitutes no problem. handpiece and inserts the bur while the assistant stabilizes the pulley wheel and secures the bur. The assistant may present the surgeon with the handpiece, removing it by the pulley wheel, and may similarly receive and reinsert it.
Fig.
10.
Fig.
11.
Fig. lO.-This demonstrates the simple removal of the handpiece by the pedal elevation of the plastic door during an operative procedure. Fig. Il.-The use of the device in oral surgery demonstrates the operator’s ability to maintain lip retraction while removing the handpiece by a single deft movement.
As previously indicated, the all-day operation of the lamp is not generally advised from the standpoint of lamp economy. However, the cost for operating a lamp continuously over an eight-hour period does not exceed one cent a day. It should be remembered that the suppression of the bacteria by the use of ultraviolet light is only exerting its effect on the surface. A grossly contaminated handpiece is best sterilized by the method of Crowley and OstrandeP and its sterility maintained before and durin g any operation by the use of the
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ultraviolet device. The use of subsequent dry heat sterilization, as described herein, was merely a requisite experimental procedure. Once saturated with liquid silicone, dry heat sterilization for approximately ten subsequent times has not been found injurious. This at,tests to the maintenance of high viscosity by silicone at 160-170° C. for a period of two hours. This contrasts sharply with the findings of Harvey, LeMay, and Shuttlewort,hGO who, in reference to the dry heat sterilization of handpieces, lubricated with ordinary oil or grease, stated : “Relubrication is then necessary. ” The opening and closing of the door of the ultraviolet device is of no consequence as to the possibility of bacterial contamination from the air. Air-borne bacteria are quite dry and unprotected, and as such are immediately destroyed upon being wafted into an ultraviolet stream. The intensity of the lamp “is sufficient for almost instantaneous destruction of bacteria introduced by the opening and closing of the cabinet, door. . . ,” therefore, “a 4-watt germicidal lamp provides ultraviolet intensities on the instrument surfaces ranging from 0.5 to 1.0 watt per square foot.“6’ The Ba.cillus subtilis and its allied species are ubiquitous air inhabitants and it is of interest that Schreiber,62 as early as 1896, demonstrated t,hat the B. subtilis was unable to form spores when exposed to direct sunlight for one hour. This early work marks one of the first experiments with ultraviolet light in the guise of sunlight. His procedure was very good for his time as he eliminated the infra-red and other heat wave effects by placing cultures in the active stage of growth in tubes that were partially immersed in running water. In respect to the vegetative forms he found that, their content became granular, the protoplasm contracted, and involution forms appeared. Modern investigators have substantiated t,hese findings while working with ultraviolet light. The Bacillus subtilis is one of the most resistant of the air-borne bacteria to ultraviolet radiation and yet it readily succumbs at intensities not much greater than those required for Escherichia coli which is the organism considered as most representative of average resistance. Wherever there is considerable human traffic there is a profound increase in the transient air flora from the human source. Generally, it may be said that these bacteria are more readily destroyed than is the representative Escherichia coli. BurketG3 using a commercial ultraviolet cabinet designed for destroying bact,eria upon dental instruments and burs, found, under the conditions of his experiment, that the apparatus was ‘I. . . bactericidal for the usual oral flora (saliva), and pure cultures of beta streptococcus, Staphylococcus aureus and albus, Escherichia co&i, and Ba~cillus subtilis including spore forms. Radiation for thirty minutes of blood agar plates streaked with eighteen-hour cultures of these organisms prevented growth.” Burket concluded that “improvements in design of the ultraviolet generator, the sterilizing cabinet, and the burr holder may result in a more efficient instrument which would be practical for the sterilization of dental burrs.” In the author’s experience, ultraviolet light is quite inadequate for the In fact. sterilization of ‘ ‘ clogged ’ ’ burs and certain other dental instruments.
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OF BACTERIA
1579
the utilization of bactericidal rays has nothing to recommend them for those instruments that we are able to sterilize by comparatively simple, rapid, and absolutely positive methods. The handpiece alone remains an exception, and the auxiliary use of ultraviolet light is especially desirable. Numerous workers have reported sensational results with similar intensities of ultraviolet light when applied to a great number of variable procedures. Such reports maintain the complete destruction of bacteria, or, at least, a SOcalled 99 per cent kill, in a matter of seconds rather than minutes or even an hour. Unfortunately, no such spectacular results can as yet be reported with the present device. However, the data herein reported are relentlessly factual for just one thing, the survival of .some bacteria. The streptococci and staphylococci are readily destroyed, and these are of chief concern in pulp infections and also in mixed infections involving the dental apparatus. Public health officers of glassware in public recommending ultraviolet cabinets for the “sterilization” dining establishments realize that ultraviolet intensities must be of considerable magnitude to ‘ ‘burn through” lipstick smudges occasionally remaining after the otherwise thorough mechanical washing of cups and glasses. Similarly, this device must be potentiated to such an extent that the apparent protective effect of saliva is immediately annihilated and that the initial stimulatory effect upon bacteria is reduced to only a few seconds. Summary 1. An ultraviolet device, attached to the dental unit, has been described for the destruction of bacteria upon the contaminated dental handpiece. 2. The device serves a secondary function by deodorizing oils and greases used for the lubrication of handpieces. It may also be used as an aid in deodorizing the dental office. 3. After two years’ clinical trial, during which time the device was frequently used all day, there has been no harm to the operator, or any of the patients, due to the escape of the ultraviolet rays incident to opening and closing the door. 4. Grossly contaminated handpieces showed a 99 per cent reduction of the surface bacteria in approximately one hour of irradiation. 5. A new method is described for experimentally contaminating dental handpieces which affords greater consistency in the distribution and density of organisms. This method also enables a control handpiece to be used in each instance. 6. It has been demonstrated that periods of irradiation of thirty seconds or less may not only stimulate the proliferation of bacteria b,ut also are apparently capable of inhibiting some bactericidal factor in the saliva. . 7. A six months’ clinical trial indicated that this device was quite efficient in a. series of endodontic procedures in which instance the rubber dam was always applied. 8. After the use of a positive method of sterilizing the handpiece, the device may be used in operative and surgical procedures for the purpose of suppressing contamination before and during use on a patient.
1580
VICTOR
H.
DIETZ
9. From a practical standpoint, this device is very simple to use in any dental procedure and constitutes not the slightest encumbrance thereto. 10. All mechanical features are now completely satisfactory and a new extremely powerful device is contemplated which should afford a 99 per cent kill of surface bacteria in not more than one or two minutes.
References 1. Editorial. 2. Knighton.
The Sterilization of the Dental Handpiece, J-. Am. Dent. A. 36: 325, 1948. Holmes T.: Unnublished data. (Professor of Bacteriolaev. -” , Washington .I -University School of D&tistry, St. Louis, ‘MO.) ibid., p. 327. 3. Editorial, Howard: (Engineering Department, General Elec4. Haynes, Personal communication. tric Co., Nela Park, Cleveland.) 5. Luckiesh, M., and Taylor, A. H.: Transmittance and Reflectance of Germicidal (h2537) Energy, J. Optic. Sac. America S6: 227, 1946. Barnard, J. E., and Morgan, H. deR.: Proe. Roy. Soe., London, B, 72: 126, 1903. 7h: Porter, J. R.: Bacterial Chemistry and Physiology, New York, 1946, John Wiley & Sons, Inc., p. 154. 8. Duggar, B. M., and Hollaender, Irradiation of Plant Viruses and of Micro-organA.: isms With Monochromatic Light, J. Bact. 27: 219 and 241, 1934. 9. SharD. D. G.: Lethal Bction of Short IJltraviolet Ravs Y on Several Common Patho genie Bacteria, J. Bact. 37: 447, 1939. Radiation on Tubercle BaK. C.. and Lavin. G. I.: Effects of Ultraviolet 10. Smithburn, cilli, km. Re;. Tuberc. 36: 782, 1939. Effect of Ultraviolet H. C., Nagy, R., and Mouromseff, G. J.: Bactericidal 11. Rentschler, Radiation, J. Bact. 4.1: 745, 1941. 12. Porter, J. R.: Ibid., p. 159. Ueber die Abtiitung von Bakterien durch Licht, Arch. f. 13. Thiele, H., and Wolf, K.: Hvp. 60: 29. 1907. 0.: ’ Ueber den hiechanismus 14. Ehri&a>n, der bactericiden Wirkung ultravioletter Strahlen, Ztschr. f. Hyg. u. Infektionskr. 111: 618, 1930. 15. Wyss, O., Clark, J. B., Haas, F., and Stone, W. S.: The Role of Peroxide in the Biological Effects of Irradiated Broth, J. Bact. 56: 51, 1948. Action of Ultraviolet Light; Absorption of Ultra16. Gates, F. L.: Studv of Bactericidal violet Light bi Bacteria., J. Gen. Physiol. 14: 31, 1930. ” Wirkung monochromatischen O., and Noethling, W.: Ueber die bactericide 17. Ehrismann, Lichtes, Ztschr. f. Hyg. u. Infektionskr. 113: 597, 1932. Effect of Ultraviolet Radiation on 18. Hollaender, 9., and Claus, W. D.: ‘Bactericidal Escherichia coli in Liquid Suspensions, J. Gen. Physiol. 19: 7.53, 1936. 19. Bucholz, J., and Jeney, A. V.: Ueber das Wesen der bakteriziden Wirkung van monochromatischen ultravioletten Strahlen, Zentralbl. f. Bakt. 133: 299, 1935. 20. Wyckoff, R. W. G.: Killing of Colon Bacilli by Ultraviolet Light, J. Gen. Physiol. 15: 351, 1932. 21. Emmons,. C. W., and Hollaender, A.: The Influence of Monochromatic Ultraviolet Radiation on the Rate of Variant Production in Trichophpton Mentagrophytes, Genetics 24: 70, 1939. (Abst.) 22. Mackinnon, R. (:.: Vitamin Deficiencies of Seven J. I;:., and Artagaveytia-Allende, Strains of Ectothrix, Large-Spored Trichophgtons Isolated From Man and Cattle, J. Bact. 56: 91, 194% L. J.: Germicidal Protection and Disinfection. General EXectrie Co.. Enrrineer23. Buttolah. ing ‘Division, Lamp Department, Cleveland, Ohio, ‘November, 1947, p. 4. .’ 24. Jordan, E. O., and Burrows, W.: Textbook of Bacteriology, ed. 14. Philadelphia, 1947, W. B. Saunders Company, p. 62. Mercurv Lamos. General Electric Co.. Engineering 25. Weitz. C. E.. and Amick. C. L.: division: Lamp Department, Clevelan& Ohio; August, 1947. (Preface.) y I’ of Germicidal, Erythemal, and Infrared Energy, qew M. : Applications 26. Luckiesh, York, 7946, D. Van Nostrand Company, Inc. +>7 Lurie, M. B.: G-E Germicidal Lamps, General Quoted from the brochure (Y690): Electric (‘o., Nela Park, Cleveland, Ohio? p. 10. 28. Buttolph, I,. .T.: Germicidal Ajr Disinfection, General Electric (‘o., Engineering Dvision, Lamp Department, Cleveland, Ohio, February, 1947, p. 8. of Dental Instruments: Questions and Answers. .J. Am. 29. Crowley, M. C.: Disinfection WI.
Dent.
30. Buttolph,
A. 37:
T,. .T.:
243,
Zbicl.
1948.
DEVICE
FOR
DESTRUCTION
OF BACTERIA
1581
Bacteria in Water Under Pressure, 31. Luckiesh, M., Kerr, J. P., and Knowles, T.: Killing G. E. Review 50: 16, 1947. Textbook of Biochemistry, ed. 4, Philadelphia, 1946, W. B. Saun32. Harrow, Benjamin: ders Company, p. 213. Water by Means of Germicidal Lamps, 33. Luckiesh, M., and Holladay, L. L:: Disinfecting G. E. Review 47: 45, 1944. 34. Luckiesh, M., Kerr, J. P., and Knowles, T.: Ibid., u. 3. Germicidal Radiatidn-Medical-Research Reports (Reprint G. S. l), 35. Buttolph; L.‘J.: General Electric Co., Engineering Division, Cleveland, Ohio, January, ” 1945. (Preface.) Director, Bureau of Disease Control, Michigan 36. Leeder, F. S.: Personal communication. Department of Health, Lansing. 37. Germicidal Radiation-Medical Research Reports (Reprint G. 8. l), General Electric Co., Engineering Division, Cleveland, Ohio, January, 1945. 38. Duggar, B. M.: Biological Effects of Radiation, New York, 1936, McGraw-Hill Book Company, Inc. Air Contamination and Air Sterilization, Am. J. 39. Quoted by Robertson, C. E., et al.: Dis. Child. 58: 1023, 1939. Control of Cross Infections of the 40. Sauer, L. W., Minsk, L. L., and Rosenstern, I.: Respiratory Tract, J. A. M. A. 118: 1271, 1942. Control of Epi41. Wells, W. F., Wells, M. W., and Wilder, T. 8.: The Environmental demic Contagion. I. An Epidemiologic Study of Radiant Disinfection of Air in Day Schools, Am. J. Hyg. 35: 97, 1942. 42. Greene, D., Barenberg, L. H., and Greenberg, B.: Effect of Irradiation of the Air in a Ward on the Incidence of Infections of the Respiratory Tract With a Note on Varicella, Am. J. Dis. Child. 61: 273, 1941. Principles of Ultraviolet D&infection of Enclosed Spaces. From a 43. Buttolph, L. J.: paper presented at the Annual Meeting of the American Public Health Association, New York City, Oct. 3, 1944. 44. Crowlev. M. C.. and Ostrander. F. D.: Silicone Fluid for Sterilization of Dental Handpieces, Science 12: 542, lQ48. 45. Spizizen, J., Hampil, B., and Carter, J. E.: The Inactivation of Viruses in Human Plasma by Uitravioiet Irradiation, Proc. Sot. Am. Bact. 1: 77, 1948. Sur la loi de la vitease d’hemolyse des hkmaties sous 46. Dreyer, G., and Hanssen, 0.: l’action de la lumihre. de la chaleur et de auelaues cores Comet. I hemolvtiaues. LIL, 1 rend. Aead. d. SC. 145: ‘234, 1907. of Air, Arch. Phvs. Theranv_I 23: 143. 1942. 47. Wells, W. F.: Radiant Disinfection 48. Knighton, Holmes T.: Unpublished data. ’ Germicidal Protection and Disinfection, General Electric Co., En49. Buttolph, L. J.: gineering Division, Lamp Dept., Cleveland, Ohio! November, 1947, p. 4. 50. Buttolph, L. J.: Principles of Ultraviolet Disinfectron of Enclosed Spaces. From a paper presented at the Annual Meeting of the American Public Health Association, New York City, Oct. 3, 1944. 51. Claugh, 0. W.: Inhibitory Effect of Saliva on L. acidophilus, J. D. Res. 15: 213, 1935. 52. Hine, M. K.: Daily Observations of Bacterial Inhibition by Saliva, J. D. Res. 15: 305, 1936. Action of Human Saliva, 53. Bibby, B. G., Hine, M. K., and Clough, 0. W.: Antibacterial J. Am. Dent. A. 25: 1290, 1938. Salivarv Factor Which Influences Growth of L. acidoohilus and Is Ex54. Hill. T. J.: ‘pression of Susceptibility or Resistance to Dental Caries, J. km. Dent. A. 26: 239, 1939. 55. Novak, M., and Lacy, A. M.: Quantitative Method for Determining Bacterial Count of Restaurant Glassware, Am. J. Hyg. 36: 316, 1942. 56. Crowley, M. C., and Ostrander, F. D.: Ibid. 57. Duggar, B. M.: Ibid. 58. Porter, J. R.: Ihid., p. 156. 59. Crowley, M. C., and Ostrander, F. D.: Zbicl. 60. Harvey, W., LeMay, C. H., and Shuttleworth, C. W.: Sterilization of Dental Handpieces, Proc. Roy. Sot. Med. 40: 507, 1947. 61. Buttolph, L. J.: Germicidal Protection and Disinfection, General Electric Co., Engineering Division, Lamp Department, Cleveland, Ohio, November, 1947, p. 5. 62. Schreiber, 0.: Ueber die physiologischen Bedingungen der endogenen Sporenbildung bei Bacillus anthracis, subtilis, und tumescence, Zentralbl. f. Bakt. P. Abt. I, original, 20: 353, 1896. The Bactericidal Action of Ultraviolet Radiation on the Oral Flora 63. Burket, L. W.: and Its Effectiveness for Dental Burr Sterilization, Am. J. Orthodontics and Oral Surg. (Oral Surg. Sect.) 30: 533-538, 1944. CLUB BLDG., GRAND AND WASHINGTON, ST. LOUIS 3, MO. PRESENT ADDRESS : UNIVERSITY I
I
FOR THE DESTRUCTION OF BACTERIA DENTAL HANDPIECE SURFACES (CONCLUDED)*
VICTORH. DIETZ, D.D.S., PH.D., (Continued
from
the Novmber
ANN
ARBOR,
MICH.
issue, page 1467.)
A R&mm6 of the Total Procedure
1. The three identical handpieces and contra-angles were sterilized in liquid silicone at 300° F. This ideally lubricates the six pieces with the silicone which does not smolder when subsequently dry-heat sterilized. 2. These six pieces after being adequately drained are combined within the folds of a sterile towel to make the three handpiececontra-angle assemblies. Each assembly will be referred to, hereinafter, simply as the handpiece. 3. The three handpieces, wrapped within a sterile towel, are now blotted thoroughly and placed in the hot air oven where they are maintained at 160-170° C. for one and one-half hours. 4. Once the silicone treatment has been given it may be omitted for not over ten subsequent tests by resorting to dry heat sterilization exclusively. However, after each test these handpieces must be separated and scrupulously wiped with a clean towel. 5. After the handpieces have cooled sufficiently, they are aseptically placed within the rotating apparatus. A paper shield is applied to mask out the pulley end of the sheath beyond the knurling (Fig. 5), and a thoroughly washed and disinfected plastic tray is inverted over this. The plastic tray does not touch the handpieces. 6. The type 152 DeVilbiss all-purpose atomizer is used for nebulizing the saliva into the air. Having autoclaved this atomizer, fresh paraffin-stimulated saliva is collected in it by the use of a small sterile glass funnel. The spraying head is inserted and the atomizer is attached to the air jet of the dental unit. The atomizer is completely disassembled and thoroughly flushed with distilled water after each test. 7. It is advisable to carry out this procedure in the absence of air currents and without any persons being present. The operator should wear a surgical mask even though the saliva be his own. 8. The swivel tip of the atomizer is directed up at a right angle to the spray tubes. The nebulization of saliva is now begun holding the tube vertically and using full pressure. The amount of saliva used has been standardized at 25 ml. The time factor is less important and, depending essentially on the viscosity of the saliva, this amount will ordinarily require 2+$$-3ysminutes to be ejected. Nebulization is effected at a height of approximately one meter over the level *The W. K. Kellogg Foundation Institute University of Michigan. 1565
of Graduate and Postgraduate Dentistry,
1566
VICTOR
H.
DIET2
of the handpieces and is observably carried as a fine misty dispersion to a height almost two meters beyond this. F‘resh saliva when so dispersed will increase its odor many-fold but lasts not noticeably longer than approximately ten minutes. 9. lmmediately upon completing the ejection of the 2.5 ml. quantity of saliva exactly one minute is permitt,ed to elapse. The plastic tray is removed and the motor begun. Preliminary experiments have shown that most droplets agglomerate within the first minute giving a spotty distribution. For each succeeding minute up to five minutes the rate is quite constant and the droplets well dispersed (Fig. 6). After this time there is a negatively accelerating This was determined by subjecting blood agar plates to the diminution. immediate vicinity of nebulization at one-minute intervals. After a threeminute exposure of the synchronously revolving handpieces the motor is turned off, the plastic tray immediately replaced, and the rotating apparatus carried from the nebulized field to the laboratory with an elapse of time not over one minute.
Fig. 5.-Showing the application of the shield over the pul!ey end of the handpieces. This sharply terminates the deposition of bacteria upon the handpieces not above the knurling at the pulley end of the sheath. This photograph also shows the Position of the open Petri dish, as used in the preliminary experiments, in order to evaluate the distribution of bacteria by the method of nebulization.
10. Each handpiece is immersed in 35 ml. of sterile PSS (Fig. 7) in a 50 ml. test tube. When the tube is held at an angle of 45O, the water level includes all of the knurled surface of the sheath. The insertion of the handpiece causes approximately a 2 cm. rise in the water level. Should the surface level go beyond the end of the knurling, it does not matter as the shield of the rotating apparatus sharply demarcates the contaminated from the uncontaminated surfaces. The handpiece, in the tube, is briskly rotated for approximately thirty seconds. It is then removed and the tube reca.pped with the sterile rubber stopper. The
Fig. 6.-A, Six blood agar plates on which a suspension of Bncillus sz~btilis was Ileposited. The suspension contained abwt 1.000 This remarkably uniform distribution. effected in bacteria per ml.. and the suspending fluid, F’S, had 0.05 per cent agar added to it. Each plate was exposed to the nebulized fleld for three minutes on separate the nebulized field, represents forty-eight-hour cultures. Complete nebulization was carried out before each test and the inoculation started after a one-minute interval. B, A fortyoccasions. eight-hour blood agar plate showing the distribution of viable bacteria deposited upon the surface after a three-minute exposure in A great variety of colonies are macroscopically identifiable. Numerous hemolytic colonies may be observed and the nebulised fleld. The majority of these colonies are obviously not clones but were deposited in groups or packets within some exerting antibiotic effects. This plate was subjected to a single droplet. The use of microscopic slides in the nebulized field further substantiated this feature. nebulized whole saliva which accounts for the variety of bacteria that may be observed.
1568
VICTOR
H.
DIRT2
three tubes, one for each handpiece, are identically prepared. The tubes are rapidly shaken along their long axes for approximately thirty seconds. This produced, by serial tests, a uniform suspension of bacteria. Three 0.1 ml. samples, from each of three tubes, showed an average variation not over 10 per cent despite the fact that this was one of the preliminary tests using the less accurate spreading technique, on blood agar plates, for viable count determinations.
Fig. T.-In the preparation of the bacterial “ride” in the butt of the tube and it is thoroughly to remove over 99 per cent of the bacteria.
suspension agitated
the contra-angle for thirty seconds.
is allowed to This proved
11. After the “wash off” suspensions of bacteria are thoroughly agitated, 0.1 ml. is pipetted from each tube into three Petri dishes. Blood agar pour plates are then made with 5 per cent defibrinated rabbit’s blood in a brain heart infusion (Difco) base containing 2 per cent agar. The consistency in the viable plate counts resulting from this procedure may be seen (Table II). The designations “left, ” ‘(center, ” and “right” refer to the positions of the handpieces in the rotating apparatus. It is now apparent that all positions are quite unisaliva formly subjected to the deposition of bacteria. Fresh paraffin-stimulated from the same individual was used for each test. Tests I and II were performed on one day and Tests III, IV, and V, on the following day. In the tests designed to determine the uniformity of contaminating handpieces by this method, it may be observed that the greatest single variation occurred in Test II (Table II) between the counts of 119 and 186. Even this variation is not much greater than 36 per cent in this instance, and the average variation for all tests is approximately 10 per cent. This constitutes a considerable improvement over the method of immersing the handpieee in saliva for experimental contamination. It is apparent, as would be expected, that one wdpiece must always be used as a control for each test with the three handpmces, for each sample of saliva. Arbitrarily, the handpiece in the center was chosen as the most plausible one to use as the control in subsequent experiments.
DEVICE
FOR
DESTRUCTION
1569
OF BACTERIA
The average bacterial count with a 0.1 ml. inoculum being slightly over 200, and washed off into 35 ml. of saline solution, indicates that the average total deposition of bacteria on a handpiece is of the magnitude of 70,000. This density of bacterial deposition compares favorably with Knighton’s experiments’s using handpieces with contra-angle or right-angle attachments. His “wash off” technique and bacteriologic procedures are also quite comparable. His actual clinical contamination of the handpieces indicates that: “All of the ten handpieces tested immediately after operation showed a positive bacterial growth, with an average colony count of 61,000.” However, considerable variation will occur with different salivary specimens. TABLE
Test
Test
Test
II.
I
II
III
ORGANISMS RECOVERABLE FROM AN 0.1 ML. INOCULUM WASH OFF SUSPENSION OF THE CONTAMINATED HANDPIECES
VIABLE
Left Center Right
141
Left Center Right
119 136
Left Center Right
Test
179
IV
126 (Control) 186
159 196
Teat (Control)
V
Left Center Right Left Center Right
FROM
THE
274 303
(Control)
257 227 255
(Control)
270
(Control)
177
Before proceeding with the ultraviolet radiation tests, by rotating the handpieces, a series of static tests were performed in order to determine the efficiency of irradiation on all surfaces of the handpieces. The three handpieces were placed in the various positions in the rotating apparatus as shown (Fig. 4) but were not revolved. In the actual procedure, the three handpieces were placed in the identical position for each test. These were then subjected to the impact of ultraviolet energy in the device for an arbitrary five-minute period. Only four tests were performed by this method, all with a single sample of saliva. In this way at least two tests for each surface could be performed. In all instances the handpiece was inserted in the ultraviolet device in a standard “sagittal” position (if a bur were inserted it would be pointing down). The bacteriological procedures were the same, and the controls were not irradiated. The results (Table III) indicate that the top surfaces of the handpieces in the direct ultraviolet stream were most efficiently reduced in numbers (about 70 per cent). The surprising finding was the fact that approximately a 50 per cent reduction in the number of bacteria was found for both sides of the handpiece. One side was directed toward the back reflecting surface and the other side toward the plastic door. Apparently, then, the plastic door, to little or no extent, constitutes a “blind spot” which would diminish reflectivity. This equal effectiveness is undoubtedly due to the slight forward “off centering” of the lamp intended to overcome any “blind spot” effect by using a plastic door. The plastic door not only enhances the appearance of the device but enables the operator to see whether or not the contra-angle is attached and what type of bur or stone was last placed therein. The bottom of the handpiece,
1570
VICTOR
H.
DIETZ
as would be expected, showed only little better than a 40 per cent reduction in the bacterial count. It should be remembered that even the sides of the handpiece, when contaminated and placed in the standard “sagittal” position, receive the incident, rays on approximately one half of their contaminated surfaces. The bottom of the handpiece, in contradistinction, can receive no direct rays upon its contaminated surface. This finding indicates the pot,ential advantage of using a multiple lamp device. TABLE III.
STATIC TESTS TO DETERMINE EFFICIENCY OF ~RRALUATION OK THE T.'ARIOW RURFACJ~S
Test 1.
Top of handpiece Control 90 31 Left 23 Right
Test
Right side of handpiece Control 144 Left 76 Right 81
Il.
(in direct path of incident
Test III.
Left side of handpiece 202 Control 114 Left Right 09
Test IV.
Bottom Control Left Right
of handpiece 187 100 111
(toward
(toward
(toward
rays)
flat, back, reflecting
plastic
surface)
door)
are of circular
reflecting
surface)
The following experiments (Table IV) were carried out in the routine fashion by rotating the handpieces and subjecting them to the various periods of time in the ultraviolet device. Before instituting the test, a one-hour warm-up period was allowed in order to stabilize the temperature in the radiation chamber. With temperature determinations made at the very center of the chamber and starting at 21’ C., there is about an 8* C. rise in one hour. The ambient operating temperature, with a room temperature of 22-23O C., and with the occasional opening of the door, is about 26O C. A single test, over a period of eight hours with a room temperature fluctuation between 21 and 25O C., and with the door unopened, gave a final temperature of 29Li” C. The temperature factor is apparently not too critical. Nevertheless, Buttolph4” showed that ultraviolet energy is most efficiently bactericidal within a temperature range of 70-80’ 5’. The device, therefore, need not be louvered as the average 26O C. (78.8’ F. j is safely within the most efficient range of bactericidal ultraviolet activity. For each test a fresh specimen of paraffin-stimulated saliva was used. The marked rise in the number of bacteria found in certain salivary specimens appeared particularly if the specimens should have been collected for some time after a meal. As is well known, t,he dehydration of organisms may contribute to a spontaneous decrease in their viable numbers. Hence, in all tests of one to four minutes’ exposure, the control handpiece was the last to be washed off to make the bacterial suspension. In those tests of eight minutes’ duration and over,
DEVICE
FOR
DESTRUCTION
1571
OF BACTERIA
the control handpiece was immersed as nearly between the times that the two experimental handpieces were washed off. It was thought at the conclusion of Test IV (eight minutes) that the residual organisms may have remained within the bur opening and that these were not receiving the direct ultraviolet impact. A short series of tests established this fact to be true in five out of six handpieces irradiated for sixteen minutes each. These tests are entirely qualitative as they were performed by inserting sterile pipe cleaners into the full length TABLE IV.
THE DESTRUCTION OF BACTERIA AT “DOUBLING” INTERVALS FROM ONE MINUTE TO SIXTY-FOUR MINUTES. THE NUMBERS INDICATE THE NUMBER OF VIABLE ORGANISMS IN 0.1 ML. OF THE SUSPENSXON
Test 1
(1 minute) Saliva A Control 233 Left 197 Right 200
Saliva B 123 152 115
Saliva C 206 197 166
Test II
(2 minutes) Saliva A Control 88 Left 50 Right 44
Saliva B 308 217 190
Saliva C 250 146 164
(4 minutes) Saliva A Control 179 Left 122 Right 90
Saliva 13 148 70 76
Saliva C 111 73 50
(8 minutes) Saliva A Control 222 Left 100 Right 96
Saliva B 102 30 35
Saliva C 93 42 29
Saliva B 199 2
Saliva C 143 19 10
Saliva B 110
Saliva C 154
1:
1:
Saliva B 242 10 4
Saliva C 206 6 8
Test
III
Test IV
Test V
Test VI
Test VII
(16 minutes) Saliva A Control 175 Left 15 Right 22 (32 minutes) Saliva A Control 202 Left Right 1; (64 minutes) Saliva A Control 140 Left 3 Right 4
of the bur openings. The pipe cleaners, contaminated in this way, were then used to inoculate nutrient broth. Five of the six culture tubes were grossly positive after forty-eight hours’ incubation. However, the b,ur opening is not the only place where bacteria can reside with impunity. The bur lock is also a very likely site for such residence. These data indicate that a 50 per cent reduction in the number of viable bacteria lies somewhere between four and eight minutes’ exposure time, and that approximately a 95 per cent kiI1 may
1572
VICTOR
H.
DIET2
be expected in a half hour. From an analysis of the data of Test VII it is apparent that in about one hour we are approaching the theoretical “99 per cent kill. ’ ’ To the present time, only one handpiece has been subjected to irradiation for two hours and one for four. These latter two also showed an average “99 per cent kill. ” It is possible that at this point we have reached the limit of ultraviolet effectiveness with this device. As ButtolphjO stated : “Too little is known, however, regarding the relative clinical values of the higher rates of kill represented by 99 per cent and 99.99 per cent, the latter representing, for example, a survival of 1 organism in 10,000.” There is evidence that periods of irradiation of thirty seconds or less may actually be stimulatory to the proliferation of bacteria. The differences found are certainly not entirely due to t,he effect of dehydration of bacteria on the control handpieces in such a short time. The differences found are difficult to ascribe entirely to dehydration also due to the fact that there is no difference in the environmental temperature between the experimental and control handpieces. The control handpieces, frequently showing a lower count when the experimental handpieces were irradiated for periods of thirty seconds, lent credence to the assumption that some inherent bactericidal factor in the saliva may have been inactivated upon irradiation. Such factors are well known since the investigations of Clough,5’ Hine,52 Bibby et a1.,53and Hi11.54 In order to demonstrate this possibility, a nonhemolytic strain of streptococcus was lightly seeded over the surface of a blood agar plate. A 5 ml. quantity of fresh “resting” saliva was collected and 1 ml. of each was placed in the undersurface of st,erile Coplin jar lids. This quantity was flowed out to cover the surface of the lid to the inner rim. The film was approximated to be about one-quarter to one-half mm. in thickness. Two specimens were irradiated, at the “handpiece level ” for periods of fifteen and thirty seconds. The control filtrate was not irradiated. The three filtrates were then Micro-Seitz filtered to These specimens were filtered directly into yield about a 0.5 ml. quantity. sterile microcolorimetric cups. These are preferred over Florey cups because The imof their very small size and the fact that they prevent evaporation. bibition of the saliva filtrate by the media is also better confined to the area of the cup. These cups are arranged in a group upon a sterile flat jar lid. The blood agar plate is then inverted upon these cups which readily adhere to the media. A sterile bibulous cap is placed over the Petri dish to enable it to be incubated right side up. The results of this procedure (Fig. 8) indicate that some inhibitory substance is inactivated upon subjection to a fifteen-second or longer irradiation. The inhibitory action of the saliva filtrate is quite weak and ephemeral. A slight stimulatory effect may be observed after twenty-four hours’ incubation at the periphery of the zone of inhibition. After forty-eight hours, growth is just as luxuriant over the zone of inhibition. Thus it is evident that the inhibition of the bactericidal factor is possibly as important as dehydration. These phenomena, along with a possible stimulatory effect due to a may have contributed to the frequently very short exposure to irradiation, higher counts of experimentals over controls in the preliminary thirty-second tests.
DEVICE
FOR
DESTRUCTION
OF BACTERIA
1573
In the course of preliminary experiments there was some evidence that the curved reflecting surface may have been designed to converge the rays too sharply, hence concentrating a greater lethal intensity within the center of the handpiece than at either end, To determine this possibility the method of Novak and Lacy55 was applied to irradiated handpieces and their respective controls. This was attempted for three tests (nine handpieces) as follows. For each test three handpieces were contaminated as described, and two irradiated for ten minutes, the third being used as the control. These handpieces were placed in a refrigerator (5-loo C.) for ten minutes, then removed and each
Fig. 8.-Showing the microcolorimetric cups “inverted” upon a blood agar plate. A single specimen of saliva was used for all of these tests. The center cup was Alled with about 0.5 ml. of fresh whole saliva. In this instamP bacterial growth may be observed but no zone of inhibition or imbibition. The latter is conceivably due to the viscosity of the saliva. a shows only a slight imbibition zone with the salivary specimen having been heat-inactivated (56” C./one hour). B shows a deAnite zone of inhibition with a sample OP the saliva that was seitz-flltered. C shows no apparent zoning in a seitz-filtered sample of the saliva which was irradiated for only flfteen seconds. D is identical to C but was irradiated for thirty seconds. The particulate matter observable in E is an imbibition control using 0.5 ml. of sterile PSS. CUPS A to E are. in part. Alterable crystalloidal substances but mainly reflection artifacts.
rotated in a separate trough of agar media thermostatically maintained between 43 and 45O C. These were carefully withdrawn and rotated in the air to effect uniform thickness until solidified. For this agar coating technique, troughs are essential as the handpieces must at all times be held horizontally. The handpiece, thus coated and incubated, should demonstrate the growth of organisms in situ. The coated handpieces were incubated, in position, within the disinfected rotating apparatus and covered with the disinfected plastic tray. Sterile distilled water, to a depth of about an inch, was placed in each compartment to effect humidification in order to prevent the agar from drying out to a thin, brittle film. However, the surfa.ce of the handpiece is not easily coated and
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the incubation of the troughs in all instances indicated that over 90 per cent The sparse counts of the organisms were washed off in the coating procedure. in the arbitrary zones (Fig. 9) were completely erratic and unreliable and the procedure was a.bandoned. A zonal immersion t,echnique was carried out in two t,ests (6 handpieces). The total length of the handpiece could be arbitrarily divided into three zones of 4 cm. length each as shown (Fig. 9). Zone A was washed off to make a bacterial suspension, by the immersion technique. in the usual 35 ml. of sterile PSS. The handpiece was then transferred to a second tube and immersed to include Zones A and B. This was repeated for the same handpiece in another tube to a depth including all three zones. Although only two tests were performed, the data shown in Table V are very interesting. The bacteriologic procedure was the same except, to ensure an adequate count, a 1.0 ml. inoculum was used. The “zonal” immersion method is far from infallible but the data strongI> substantiate the fact, that the design of the apparatus does concentrate the ultraviolet light within the middle third of the handpiece. It is obvious, therefore, that a modified design of the reflecting surfaces of the radiation chamber would be more effective. Parabolic curvatures, parallel rather than at right angles to the curvature of t,he handpiece sheath, would greatly rectify this condition. A more efficient, diffuse reflecting surface combined with an increased number of lamps and wattage can, theoretically, increase the bactericidal efficiency tenfold. A new design was contemplated which should assure a 99 per cent kill in less than five minutes. However, a rather intricate design, but theoretically capable of assuring a 99 per cent kill in about one minute, will first be attempted if the engineering problems do not prove to be insurmountable.
Fig. I).-The three arbitrary zones, of exactly 4 cm. length each, conveniently at the obtuse angle of the contra-angle, at the end of the contra-angle, and at the end knurling of the sheath.
divide of the
At the present no attempt has been made to determine which types of organisms survive. To date it is evident, however, that lactobacilli, staphylococci, and streptococci are quite readily killed. The experimental procedure, nevertheless, was desirably carried out with saliva and its polymicrobic flora actually to test the “floracidal” effect of ultraviolet light. Burs were not inserted in the contra-angle as they would only have been extraneous to the test. Burs clogged with debris cannot be sterilized by this method. In actual use a sterile bur is inserted before or after irradiating the handpiece. This device has had only a limited clinical application over a period of two years. The arrangement of the device is seemingly ideal in every respect. The
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door-pedal mechanism, handpiece retaining device, and other features function with utmost simplicity. In no way does the use of this device encumber any dental procedure. Its use simply entails inserting the handpiece in the device rather than hanging it upon the conventional hook. The operator will find himself quickly habituated to this procedure. The clinical application of this device has been limited to endontic procedures in which instance the rubber dam has at all times been applied. The straight handpiece has a microhead contra-angle attached. This contra-angle permits burs to protrude another third in length from the head over some of With this arrangement the contrathe conventional contra-angle attachments. angle need never actually touch tooth surfaces. TABLE V. THE SURVIVAL OF BACTERIA WITHIN THE THREE ZONES UPON TEN MINUTES' ULTRAVIOLET RADIATION FOR EACH HANDPIECE OTHER THAN THE CONTROLS. THE COUNTS REPRESENT A 1.0 ML. INOCULUM ZONE A
ZONE B
ZONE C
Test I
Control Left Right
543 92 184
460 49 47
419 60 124
Test
Control Left Right
703 115 167
661 32 93
520 115 127
II
In the experimental clinical application following procedure has been observed :
over a period
of two years the
1. The handpiece and contra-angle were silicone-sterilized according to the method of Crowley and Ostrander.56 Excess silicone was drained for a day within the folds of a sterile towel. These parts were assembled and attached to the handpiece spindle aseptically. This assembly, hereinafter again referred to only as the handpiece, was aseptically placed in the ultraviolet device. The lamp was burned for two hours. 2. The following morning a tooth was isolated by the use of a rubber dam and the field liberally swabbed with full-strength iodine. The ultraviolet lamp had been b,urning for at least an hour before using the handpiece the day after the initial insertion of the handpiece in the device. The pulp chamber was entered and the approach adequately extended. This bur was removed and a flame-shaped bur inserted. This enabled the operator to complete the approach Upon completion this bur was imby carrying out the’ usual conical cavity. mediately removed and the tooth debris falling on the contra-angle head was wiped off within the folds of a sterile towel. 3. The handpiece was replaced in the device until again needed for the Grasping the pulley end of the handpiece it was frequently wiped next patient. off in its entirety with a sterile towel during the first week as the silicone had a tendency to work its way out of the mechanism, imparting an oily film to the surface. 4. The handpiece was always irradiated for a period. of not less than one half hour between patients, and often an hour or much longer. The reason for
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this variation is simply that the ultraviolet device is turned on the “first thing” in the morning and turned off as the “last thing ” after the day’s work is done. However, there is no objection to irradiating the handpiece through the night. Obviously, however, the burning of the lamp about sixteen hours additionally every day would abbreviate the lamp-life on the basis of its burning expectancy. 5. luring a six-month period the full brunt of responsibility for disinfecting; the handpiece was thrown upon the ult,raviolet device. During this period thirty-five patients were attended and teeth were entered sixty-three times. These cases were especially selected, and in forty-two primary entrances into teeth, only sixteen demonst,rated the presence of viable bacteria. In no instance was t,here any evidence of bacterial cont,amination from one patient to the next on the basis of a negative culture or according to the type or species of bacteria previously encountered. The random sequence in the bacteriologic cultures was entirely fortuitous and would not have been possible if, in this special series of cases, a high percentage of the initial cultures had not been negative. Had the sequence of patients been such as to encounter, e.g., XtreptoCOCCUS z’iridans two or three times successively from consecutive patients, even then proof of contamination would not have been absolute. However, had such been the case, the evidence would have been strongly suggestive of contamination. Staphylococci, occasionally demonstrable on the operator’s hands, were never encountered in the initial cultures.
Discussion The ultraviolet device herein described is not to be construed as an absolute method of sterilization. That it is a distinct aid in suppressing the bacteria with which a handpiece has been contaminated has been adequately demonstrated. There are, oftentimes, minor or relatively imperceptible breaks in the technique of manipulating a sterile handpiece. When these breaches occur the handpiece should be immediately replaced in the ultraviolet device for a few minutes. Evidence is not yet complete but the few bacteria that may be transferred b,y a contra-angle ‘ ‘ clicking ’ ’ against an instrument handle appear to succumb in a matter of seconds. This difference may be due to an absence of the apparently protective salivary mucin and the few or very superficially disposed bacteria. The simplicity of using the ultraviolet device for operative (Fig. 10) and surgical procedures (Fig. 11) is shown. In the experimental method of contaminating the handpiece with whole saliva, mucin, food debris, and other extraneous substances may easily shield bacteria. In addition bacteria are demonst,rably deposited in clumps and, as pointed out by Duggar,“’ “. . . it is possible that when bacteria are present in clumps some of them may escape the bactericidal effect of the lamps.” Porter” further elucidated the significance of the bacterial population in his statement: “The relation between the amount of ultraviolet radiation and the percentage of bacteria killed in a given culture is determined by the distribution of bacteria of varying resistance to the radiation and is not due to the probability of hitting a vital spot in a given organism by a photon.” Nevertheless, this experiment was designed to determine the actual effectiveness of the ultraviolet device herein
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This was attempted under condescribed under the least artificial conditions. ditions which embodied certain features which may be encountered in the various clinical applications other than in endodontic procedures where it is apparently quite effective. It seems especially desirable to employ the device immedia.tely after silicone or oil sterilization as these fluids persist in creeping over the surfaces of the handpiece as a thin film and easily pick up dust and air-borne bacteria, if unprotected. During the intermittent use of the handpiece, on the same patient, it should repeatedly be inserted in the device. In surgical procedures the straight handpiece is most commonly employed; however, with the aid of an The dentist holds the assistant the changing of burs constitutes no problem. handpiece and inserts the bur while the assistant stabilizes the pulley wheel and secures the bur. The assistant may present the surgeon with the handpiece, removing it by the pulley wheel, and may similarly receive and reinsert it.
Fig.
10.
Fig.
11.
Fig. lO.-This demonstrates the simple removal of the handpiece by the pedal elevation of the plastic door during an operative procedure. Fig. Il.-The use of the device in oral surgery demonstrates the operator’s ability to maintain lip retraction while removing the handpiece by a single deft movement.
As previously indicated, the all-day operation of the lamp is not generally advised from the standpoint of lamp economy. However, the cost for operating a lamp continuously over an eight-hour period does not exceed one cent a day. It should be remembered that the suppression of the bacteria by the use of ultraviolet light is only exerting its effect on the surface. A grossly contaminated handpiece is best sterilized by the method of Crowley and OstrandeP and its sterility maintained before and durin g any operation by the use of the
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ultraviolet device. The use of subsequent dry heat sterilization, as described herein, was merely a requisite experimental procedure. Once saturated with liquid silicone, dry heat sterilization for approximately ten subsequent times has not been found injurious. This at,tests to the maintenance of high viscosity by silicone at 160-170° C. for a period of two hours. This contrasts sharply with the findings of Harvey, LeMay, and Shuttlewort,hGO who, in reference to the dry heat sterilization of handpieces, lubricated with ordinary oil or grease, stated : “Relubrication is then necessary. ” The opening and closing of the door of the ultraviolet device is of no consequence as to the possibility of bacterial contamination from the air. Air-borne bacteria are quite dry and unprotected, and as such are immediately destroyed upon being wafted into an ultraviolet stream. The intensity of the lamp “is sufficient for almost instantaneous destruction of bacteria introduced by the opening and closing of the cabinet, door. . . ,” therefore, “a 4-watt germicidal lamp provides ultraviolet intensities on the instrument surfaces ranging from 0.5 to 1.0 watt per square foot.“6’ The Ba.cillus subtilis and its allied species are ubiquitous air inhabitants and it is of interest that Schreiber,62 as early as 1896, demonstrated t,hat the B. subtilis was unable to form spores when exposed to direct sunlight for one hour. This early work marks one of the first experiments with ultraviolet light in the guise of sunlight. His procedure was very good for his time as he eliminated the infra-red and other heat wave effects by placing cultures in the active stage of growth in tubes that were partially immersed in running water. In respect to the vegetative forms he found that, their content became granular, the protoplasm contracted, and involution forms appeared. Modern investigators have substantiated t,hese findings while working with ultraviolet light. The Bacillus subtilis is one of the most resistant of the air-borne bacteria to ultraviolet radiation and yet it readily succumbs at intensities not much greater than those required for Escherichia coli which is the organism considered as most representative of average resistance. Wherever there is considerable human traffic there is a profound increase in the transient air flora from the human source. Generally, it may be said that these bacteria are more readily destroyed than is the representative Escherichia coli. BurketG3 using a commercial ultraviolet cabinet designed for destroying bact,eria upon dental instruments and burs, found, under the conditions of his experiment, that the apparatus was ‘I. . . bactericidal for the usual oral flora (saliva), and pure cultures of beta streptococcus, Staphylococcus aureus and albus, Escherichia co&i, and Ba~cillus subtilis including spore forms. Radiation for thirty minutes of blood agar plates streaked with eighteen-hour cultures of these organisms prevented growth.” Burket concluded that “improvements in design of the ultraviolet generator, the sterilizing cabinet, and the burr holder may result in a more efficient instrument which would be practical for the sterilization of dental burrs.” In the author’s experience, ultraviolet light is quite inadequate for the In fact. sterilization of ‘ ‘ clogged ’ ’ burs and certain other dental instruments.
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the utilization of bactericidal rays has nothing to recommend them for those instruments that we are able to sterilize by comparatively simple, rapid, and absolutely positive methods. The handpiece alone remains an exception, and the auxiliary use of ultraviolet light is especially desirable. Numerous workers have reported sensational results with similar intensities of ultraviolet light when applied to a great number of variable procedures. Such reports maintain the complete destruction of bacteria, or, at least, a SOcalled 99 per cent kill, in a matter of seconds rather than minutes or even an hour. Unfortunately, no such spectacular results can as yet be reported with the present device. However, the data herein reported are relentlessly factual for just one thing, the survival of .some bacteria. The streptococci and staphylococci are readily destroyed, and these are of chief concern in pulp infections and also in mixed infections involving the dental apparatus. Public health officers of glassware in public recommending ultraviolet cabinets for the “sterilization” dining establishments realize that ultraviolet intensities must be of considerable magnitude to ‘ ‘burn through” lipstick smudges occasionally remaining after the otherwise thorough mechanical washing of cups and glasses. Similarly, this device must be potentiated to such an extent that the apparent protective effect of saliva is immediately annihilated and that the initial stimulatory effect upon bacteria is reduced to only a few seconds. Summary 1. An ultraviolet device, attached to the dental unit, has been described for the destruction of bacteria upon the contaminated dental handpiece. 2. The device serves a secondary function by deodorizing oils and greases used for the lubrication of handpieces. It may also be used as an aid in deodorizing the dental office. 3. After two years’ clinical trial, during which time the device was frequently used all day, there has been no harm to the operator, or any of the patients, due to the escape of the ultraviolet rays incident to opening and closing the door. 4. Grossly contaminated handpieces showed a 99 per cent reduction of the surface bacteria in approximately one hour of irradiation. 5. A new method is described for experimentally contaminating dental handpieces which affords greater consistency in the distribution and density of organisms. This method also enables a control handpiece to be used in each instance. 6. It has been demonstrated that periods of irradiation of thirty seconds or less may not only stimulate the proliferation of bacteria b,ut also are apparently capable of inhibiting some bactericidal factor in the saliva. . 7. A six months’ clinical trial indicated that this device was quite efficient in a. series of endodontic procedures in which instance the rubber dam was always applied. 8. After the use of a positive method of sterilizing the handpiece, the device may be used in operative and surgical procedures for the purpose of suppressing contamination before and during use on a patient.
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9. From a practical standpoint, this device is very simple to use in any dental procedure and constitutes not the slightest encumbrance thereto. 10. All mechanical features are now completely satisfactory and a new extremely powerful device is contemplated which should afford a 99 per cent kill of surface bacteria in not more than one or two minutes.
References 1. Editorial. 2. Knighton.
The Sterilization of the Dental Handpiece, J-. Am. Dent. A. 36: 325, 1948. Holmes T.: Unnublished data. (Professor of Bacteriolaev. -” , Washington .I -University School of D&tistry, St. Louis, ‘MO.) ibid., p. 327. 3. Editorial, Howard: (Engineering Department, General Elec4. Haynes, Personal communication. tric Co., Nela Park, Cleveland.) 5. Luckiesh, M., and Taylor, A. H.: Transmittance and Reflectance of Germicidal (h2537) Energy, J. Optic. Sac. America S6: 227, 1946. Barnard, J. E., and Morgan, H. deR.: Proe. Roy. Soe., London, B, 72: 126, 1903. 7h: Porter, J. R.: Bacterial Chemistry and Physiology, New York, 1946, John Wiley & Sons, Inc., p. 154. 8. Duggar, B. M., and Hollaender, Irradiation of Plant Viruses and of Micro-organA.: isms With Monochromatic Light, J. Bact. 27: 219 and 241, 1934. 9. SharD. D. G.: Lethal Bction of Short IJltraviolet Ravs Y on Several Common Patho genie Bacteria, J. Bact. 37: 447, 1939. Radiation on Tubercle BaK. C.. and Lavin. G. I.: Effects of Ultraviolet 10. Smithburn, cilli, km. Re;. Tuberc. 36: 782, 1939. Effect of Ultraviolet H. C., Nagy, R., and Mouromseff, G. J.: Bactericidal 11. Rentschler, Radiation, J. Bact. 4.1: 745, 1941. 12. Porter, J. R.: Ibid., p. 159. Ueber die Abtiitung von Bakterien durch Licht, Arch. f. 13. Thiele, H., and Wolf, K.: Hvp. 60: 29. 1907. 0.: ’ Ueber den hiechanismus 14. Ehri&a>n, der bactericiden Wirkung ultravioletter Strahlen, Ztschr. f. Hyg. u. Infektionskr. 111: 618, 1930. 15. Wyss, O., Clark, J. B., Haas, F., and Stone, W. S.: The Role of Peroxide in the Biological Effects of Irradiated Broth, J. Bact. 56: 51, 1948. Action of Ultraviolet Light; Absorption of Ultra16. Gates, F. L.: Studv of Bactericidal violet Light bi Bacteria., J. Gen. Physiol. 14: 31, 1930. ” Wirkung monochromatischen O., and Noethling, W.: Ueber die bactericide 17. Ehrismann, Lichtes, Ztschr. f. Hyg. u. Infektionskr. 113: 597, 1932. Effect of Ultraviolet Radiation on 18. Hollaender, 9., and Claus, W. D.: ‘Bactericidal Escherichia coli in Liquid Suspensions, J. Gen. Physiol. 19: 7.53, 1936. 19. Bucholz, J., and Jeney, A. V.: Ueber das Wesen der bakteriziden Wirkung van monochromatischen ultravioletten Strahlen, Zentralbl. f. Bakt. 133: 299, 1935. 20. Wyckoff, R. W. G.: Killing of Colon Bacilli by Ultraviolet Light, J. Gen. Physiol. 15: 351, 1932. 21. Emmons,. C. W., and Hollaender, A.: The Influence of Monochromatic Ultraviolet Radiation on the Rate of Variant Production in Trichophpton Mentagrophytes, Genetics 24: 70, 1939. (Abst.) 22. Mackinnon, R. (:.: Vitamin Deficiencies of Seven J. I;:., and Artagaveytia-Allende, Strains of Ectothrix, Large-Spored Trichophgtons Isolated From Man and Cattle, J. Bact. 56: 91, 194% L. J.: Germicidal Protection and Disinfection. General EXectrie Co.. Enrrineer23. Buttolah. ing ‘Division, Lamp Department, Cleveland, Ohio, ‘November, 1947, p. 4. .’ 24. Jordan, E. O., and Burrows, W.: Textbook of Bacteriology, ed. 14. Philadelphia, 1947, W. B. Saunders Company, p. 62. Mercurv Lamos. General Electric Co.. Engineering 25. Weitz. C. E.. and Amick. C. L.: division: Lamp Department, Clevelan& Ohio; August, 1947. (Preface.) y I’ of Germicidal, Erythemal, and Infrared Energy, qew M. : Applications 26. Luckiesh, York, 7946, D. Van Nostrand Company, Inc. +>7 Lurie, M. B.: G-E Germicidal Lamps, General Quoted from the brochure (Y690): Electric (‘o., Nela Park, Cleveland, Ohio? p. 10. 28. Buttolph, I,. .T.: Germicidal Ajr Disinfection, General Electric (‘o., Engineering Dvision, Lamp Department, Cleveland, Ohio, February, 1947, p. 8. of Dental Instruments: Questions and Answers. .J. Am. 29. Crowley, M. C.: Disinfection WI.
Dent.
30. Buttolph,
A. 37:
T,. .T.:
243,
Zbicl.
1948.
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Bacteria in Water Under Pressure, 31. Luckiesh, M., Kerr, J. P., and Knowles, T.: Killing G. E. Review 50: 16, 1947. Textbook of Biochemistry, ed. 4, Philadelphia, 1946, W. B. Saun32. Harrow, Benjamin: ders Company, p. 213. Water by Means of Germicidal Lamps, 33. Luckiesh, M., and Holladay, L. L:: Disinfecting G. E. Review 47: 45, 1944. 34. Luckiesh, M., Kerr, J. P., and Knowles, T.: Ibid., u. 3. Germicidal Radiatidn-Medical-Research Reports (Reprint G. S. l), 35. Buttolph; L.‘J.: General Electric Co., Engineering Division, Cleveland, Ohio, January, ” 1945. (Preface.) Director, Bureau of Disease Control, Michigan 36. Leeder, F. S.: Personal communication. Department of Health, Lansing. 37. Germicidal Radiation-Medical Research Reports (Reprint G. 8. l), General Electric Co., Engineering Division, Cleveland, Ohio, January, 1945. 38. Duggar, B. M.: Biological Effects of Radiation, New York, 1936, McGraw-Hill Book Company, Inc. Air Contamination and Air Sterilization, Am. J. 39. Quoted by Robertson, C. E., et al.: Dis. Child. 58: 1023, 1939. Control of Cross Infections of the 40. Sauer, L. W., Minsk, L. L., and Rosenstern, I.: Respiratory Tract, J. A. M. A. 118: 1271, 1942. Control of Epi41. Wells, W. F., Wells, M. W., and Wilder, T. 8.: The Environmental demic Contagion. I. An Epidemiologic Study of Radiant Disinfection of Air in Day Schools, Am. J. Hyg. 35: 97, 1942. 42. Greene, D., Barenberg, L. H., and Greenberg, B.: Effect of Irradiation of the Air in a Ward on the Incidence of Infections of the Respiratory Tract With a Note on Varicella, Am. J. Dis. Child. 61: 273, 1941. Principles of Ultraviolet D&infection of Enclosed Spaces. From a 43. Buttolph, L. J.: paper presented at the Annual Meeting of the American Public Health Association, New York City, Oct. 3, 1944. 44. Crowlev. M. C.. and Ostrander. F. D.: Silicone Fluid for Sterilization of Dental Handpieces, Science 12: 542, lQ48. 45. Spizizen, J., Hampil, B., and Carter, J. E.: The Inactivation of Viruses in Human Plasma by Uitravioiet Irradiation, Proc. Sot. Am. Bact. 1: 77, 1948. Sur la loi de la vitease d’hemolyse des hkmaties sous 46. Dreyer, G., and Hanssen, 0.: l’action de la lumihre. de la chaleur et de auelaues cores Comet. I hemolvtiaues. LIL, 1 rend. Aead. d. SC. 145: ‘234, 1907. of Air, Arch. Phvs. Theranv_I 23: 143. 1942. 47. Wells, W. F.: Radiant Disinfection 48. Knighton, Holmes T.: Unpublished data. ’ Germicidal Protection and Disinfection, General Electric Co., En49. Buttolph, L. J.: gineering Division, Lamp Dept., Cleveland, Ohio! November, 1947, p. 4. 50. Buttolph, L. J.: Principles of Ultraviolet Disinfectron of Enclosed Spaces. From a paper presented at the Annual Meeting of the American Public Health Association, New York City, Oct. 3, 1944. 51. Claugh, 0. W.: Inhibitory Effect of Saliva on L. acidophilus, J. D. Res. 15: 213, 1935. 52. Hine, M. K.: Daily Observations of Bacterial Inhibition by Saliva, J. D. Res. 15: 305, 1936. Action of Human Saliva, 53. Bibby, B. G., Hine, M. K., and Clough, 0. W.: Antibacterial J. Am. Dent. A. 25: 1290, 1938. Salivarv Factor Which Influences Growth of L. acidoohilus and Is Ex54. Hill. T. J.: ‘pression of Susceptibility or Resistance to Dental Caries, J. km. Dent. A. 26: 239, 1939. 55. Novak, M., and Lacy, A. M.: Quantitative Method for Determining Bacterial Count of Restaurant Glassware, Am. J. Hyg. 36: 316, 1942. 56. Crowley, M. C., and Ostrander, F. D.: Ibid. 57. Duggar, B. M.: Ibid. 58. Porter, J. R.: Ihid., p. 156. 59. Crowley, M. C., and Ostrander, F. D.: Zbicl. 60. Harvey, W., LeMay, C. H., and Shuttleworth, C. W.: Sterilization of Dental Handpieces, Proc. Roy. Sot. Med. 40: 507, 1947. 61. Buttolph, L. J.: Germicidal Protection and Disinfection, General Electric Co., Engineering Division, Lamp Department, Cleveland, Ohio, November, 1947, p. 5. 62. Schreiber, 0.: Ueber die physiologischen Bedingungen der endogenen Sporenbildung bei Bacillus anthracis, subtilis, und tumescence, Zentralbl. f. Bakt. P. Abt. I, original, 20: 353, 1896. The Bactericidal Action of Ultraviolet Radiation on the Oral Flora 63. Burket, L. W.: and Its Effectiveness for Dental Burr Sterilization, Am. J. Orthodontics and Oral Surg. (Oral Surg. Sect.) 30: 533-538, 1944. CLUB BLDG., GRAND AND WASHINGTON, ST. LOUIS 3, MO. PRESENT ADDRESS : UNIVERSITY I
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