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An ultraviolet device for the destruction of bacteria on contaminated dental handpiece surfaces
Endodontia AN
ULTRAVIOLET DEVICE ON CONTAMINATED
FOR THE DESTRUCTION OF BACTERIA DENTAL HANDPIECE SURFACES*
VICTOR H. DIETZ, D.D.S., PH.D.,
1. Preliminary
ANN ARBOR, MICH.
Report
T
HE dentist, as a public health mentor, is surely not unaware of the potential danger of direct and cross-infection which may be carried by the medium of a contaminated handpiece or contra-angle. It has been stated, ‘ ‘ . . . the one instrument that is used most often, the handpiece, is cleansed the least. Burs and mandrels, disks and stones are sterilized thoroughly before use. However, the chuck, which holds them and which also enters the mouth, may be indifferently cleansed. All too frequently it may be contaminated and may carry contamination from one patient to another. “I Knighton demonstrated an average colony count of 61,000 on ten handpieces, with contra-angle and right angle attachments, immediately after use, with a decrease to approximately half this count two hours after dental operations. Eighteen to twenty-four hours after the use of the handpieces and attachments, the average colony count was about 500 which he partially attributed to dehydration. In subsequent investigations he found, also by viable plate counting procedures, that “cold sterilization” was partially but not completely effective. The dental handpiece and its attachments, as insidious inoculating devices, no doub,t constitute an important public health problem. “Unsterilized handpieces are dangerous, and their use cannot be condoned. It would appear that the handpiece is the sole surviving source for the transmission of infection in many dental offices. ’ ‘3 The need for a simple chairside procedure for substantially suppressing surface contaminants or maintaining the sterility of handpieces was sought by the use of ultraviolet energy. A device of eaely design (Fig. 1)) attached to the dental unit and permitting the simple insertion of the handpiece and contra-angle, was constructed and tested. Preliminary bacteriologic experiments, conducted by the immersion of sterile contra-angles into two inches of saliva and exposed to the radiation for five minutes, evidenced almost a 50 per cent reduction in the numbers of bacteria as determined by the viable plate counting method. This degree of reduction was rather consistent in all of five instances as compared with five similarly treated controls not subjected to radiation. A great variation, however, versity
*The W. K. Kellogg of Michigan.
Foundation
Institute
of Graduat
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e and
Postgraduate
Dentistry,
Uni-
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seemed to exist in the number of bacteria with which the contra-angles were cornaminated by this method. Early in the process of experimentation it hecame evident that a more powerful unit embracing other important practical features would be most desirable. To realize these advantages a second device (Fig. 2) was constructed. This unit possessesthe distinct advantage of permitting the aseptic insertion and withdrawal of the handpiece. In addition, all of the knurled portion of the straight handpiece receives the full impact of ultraviolet radiat.ion.
Fig. Fig. l.-An disinfectlon of Fig. Z.-A of the handpiece
1.
early design of an ultraviolet apparatus intended the contaminated dental handpiece. later type of ultraviolet device permitting the aseptic by the expedient of a pedal-controlled door.
Fig.
2.
for
the insertion
simple and
chairside removal
The improved device utilizes t,he small, yet powerful, 4-watt, U-type, ultraviolet lamp and, for reasons of utmost efficiency and economy, is continuous in operation. Haynes* demonstrated that practical maximum efficiency is attained after two minutes of continuous operation from the start with an output of 100 per cent of the ultraviolet energy in the 2,537 B band. This was computed in still air at an ambient temperature of 75O F. The lamp is strategically placed in order to afford ultraviolet impact upon all surfaces of the handpiece-contraangle assembly. To accomplish this, the radiation chamber is completely lined with Alzak aluminum (anodized surface) having a coefficient of reflectivity 70 per cent of the incident energy. Luckiesh and Taylor5 demonstrated that “the
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reflectances of chromium and stainless steel, for example, are low compared with clean aluminum surf aces. ’ ’ Reflection is both diffuse and specular, and advantage is taken of the linear sources where the maximum intensities are in the direction perpendicular to the surface of the source. Hence, the Lucite door should not constitute a “blind spot” as the rays striking this area are of great obliquity and decrease with the cosine of the angle of emission. The radiation chamber is designed to take advantage of most reflecting surfaces, and as a result of the small cubic volume of the chamber the handpiece is bombarded with incident, reflected, and re-reflected rays. The chromiumplated surfaces of the handpiece and contra-angle reflect rays with a 40-50 per cent efficiency, according to the coefficient of reflectivity of chromium. A Brief /R&urn6 of the Theory and Activity of Germicidal Ultraviolet Light Ultraviolet rays of 3,287 and 2,265 B wave lengths have, since the original observations of Barnard and Morgan ,G been confirmed by numerous investigators as probably the most bactericidal. Hence, the concept, “the shorter the ultraviolet wave length the greater the b.actericidal action,” is wholly erroneous. Porter’ mentioned that the hydrogen-ion concentration has no effect on the bactericidal action of the light between the limits of pH 4.5 and 7.5. This is particularly important for our consideration as we shall deal in part with bacteria in the saliva, the latter which is invariably within the range of neutrality. Numerous investigators have demonstrated ultraviolet light of specific wave lengths to be lethal for all bacteria. There is, nevertheless, marked variation in resistance between various species but the common mouth organisms, particularly streptococci, are readily destroyed. Duggar and HollaendeF observed very little difference in resistance between vegetative cells and spores of Bacillus subtilis and Bacillus megatherium when exposed t,o ultraviolet light (2,650A). Other investigators have found spores only slightly more resistant. Hence, it is of profound interest to bacteriologists that there is a complete absence of parallelism between heat resistance and ultraviolet resistance of vegetative cells and spores. The extensive investigations of Sharps using 2,537 A attest to its broad bactericidal effect on a variety of bacteria. Smithburn and Lavin,lO also working within the 2,537 ii band, killed the resistant tubercle bacillus in a very heavy suspension (1 mg. per mm.) although such radiation required ten minutes’ study made its appearance in the pubexposure. A most precise quantitative lished investigations of Rentschler, Nagy, and Mouromseff,‘l who delicately controlled the dispersion factor when inoculating agar plates and rigidly controlled the specific ultraviolet exposure photometrically. Of considerable interest is the fact that they were able to demonstrate, among various bacterial species, a decidedly different resistance to ultraviolet radiation at different stages of the population cycle. All viruses that have been examined in purified or semipurified preparations are readily inactivated by ultraviolet light. Porter” “Although sufficient data are not available to draw any definite constated, clusions, it seems that viruses require about the same energy for inactivation as bacteria.”
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Numerous theories have been proposed as to the mechanism of action of ultraviolet light, and t,o date the issue is not conclusively settled. The theory, once avidly maintained by early investigators, that some oxidizing substance such as ozone is formed during irradiation and that this substance was the immediate b,actericidal agent, has been substantially disproved. The investigations of Thiele and Wolf,13 and many more recent workers, have proved ultraviolet rays to be lethal under anaerobic conditions; hence, the originally postulated oxidizing agent is nonexistent. Similarly, hardly can it be hydrogen peroxide, as EhrismannX4 demonstrated that it wo~~ld have to attain a concentration of 30 per cent in order to equal the rapid and positive bactericidal action of ultra.violet light. Incidentall-, neither has so much as a trace of hydrogen peroxide been demonstrated as a concomitant of ultraviolet activity on bacteria. Quite recently, however, Wyss et, a1.l” demonstrated a marked similarity between certain biological effects produced by ultraviolet radiation of nutrient broth and by the addition of hydrogen peroxide to the broth. It is especially noteworthy that the effects of both agents can be negated by catalase. They believe that the results are due to the direct or indirect interference of an organic peroxide in some metabolic function. An analysis of the work of Gates,lG Ehrismann and Noethling,17 and Hollaender and Claus’* indicates that bacterial death follows in the wake of a disturbance of certain molecular groupings in the cell having high specific absorption spectra for ultraviolet light. Further experimental proof of denaturation and microscopic evidence of cellular coagulation lends credence to the probabilit,y of a direct ultraviolet effect. However, whether this is immediately due to a change in the permeability of the cell wall, an enzymatic alteration, alteration of the cytoplasmic colloids, or in the nucleic acid substance remains highly debatable. Nevertheless, it is probably safe to assume that the lethal action of ultraviolet rays is probably direct and most certainly quite complex. A few of the newer concepts of the mechanism of the bactericidal action of ultraviolet rays are possibly of more theoretical than practical concern, but are of considerable interest. In this connection, the investigations of Bucholz and Jenev’” suggest. a photoelectric action. These workers pointed out that the highiv Y lethal waves 2,650 and 2,530 A correspond respectively to energy values of 4.6 and 4.8 volts, and concluded that this amount of energy is required to displace sufficient electrons from the bacterial protoplasm to give rise to irreversible photochemical alterations and t,hus bring about death of the cell. Wyckoff,zo on the other hand, studied this aspect of the problem in the light of the quantum theory and found that about four million quanta of energy are required to kill a single .coliform bacillus, showing that death is not due to the cathode rays (a single quantum absorption), but to some more generalized effect, on the bacterial prot’oplasm. Emmons and Hollaender*’ speculated upon the molecular groupings responsible for the lethality of ultraviolet radiation and maintained that : “As in bacteria and yeasts the wave lengths most toxic are 2,537 to 2,650 B-the wave lengths most highly absorbed by nucleic acids rather than by proteins.” Fol-
DEVICE
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lowing this concept, Mackinnon and Artagaveytia-Allendez2 believe that “it is possible that the different aspects of Emmons and Hollaender’s mutants may be due to changes in the nutritional requirements, perhaps to losses in the ability to synthesize growth factors. ’ ’ Along this line of reasoning one may assume that the lethal ultraviolet dose in any given instance may b.e the result of nutritional derangement or impairA critical ment to a degree as to be inhibitory to growth and reproduction. appraisal of the actual lethal mechanism, just how, when, and where it strikes, is indeed quite susceptible to conjecture.
Physical This discussion
Aspects of the Ultraviolet
Light
will be essentially confined to the ultraviolet system of light as shown (Fig. 2). The most important single element is the ultraviolet lamp (G-4T-4), for which the following data23 obtain. The rated wattage of this bulb is 4 watts, and has an over-all length of 5yL inches with a tubular diameter of 1,s inch. The bent tube construction makes the lamp approximately 1 inch in width. This feature is especially important a.s it enables the incident rays to converge around either side of the handpiece to be reflected effectively. This lamp may be operated on a circuit of 110-125 volts with an approximate amperage of 0.08. The approximate glass temperature is 100° F. and the lamp life, under specified test conditions of three-hour or longer operating periods, is rated at 2,500 hours. The “effective length” of the ultraviolet source is 6 inches and the ultraviolet output watts (2,537 .K) is 0.5. The wattage per square foot at 37 inches is 0.007, whereas at 8 inches it is 0.06 and at 4 inches it is 0.43. In the device shown we are especially concerned with the intensity at 4 inches for the incident light. from above, and the intensity at 8 inches for the reflected light that strikes all other surfaces. It may be noted that the intensities vary, from bare lamps, practically inversely as the distance, rather than the usual designation, “inversely as the square of the distance. ” Hence, ultraviolet light is simply like ot,her radiant energy but is incapable of being apprehended to any appreciable extent by the human retina as is the case with luminous energy. Ultraviolet rays obey the laws of visible light with which we are all familiar. Thus, it, too, according to modern theory, consists of quanta of energy which move as if guided by waves, The emission of extraneous visible rays (blue band) and the type of glass used in the construction of the ultraviolet lamp cause it to burn with a soft blue light. This coexistent visible light readily demonstrates such common phenomena as reflection, refraction, and dispersion. These phenomena apply to the ultraviolet light as well as the visible light. Jordan and Burrowsz4 pointed out that the ultraviolet spectrum is by far the most bactericidal but that even visible light is slightly active, particularly blue. The dentist can easily understand the position of ultraviolet light when comparing it with x-rays as both are at the short end of the spectrum. However, whereas x-rays have wave lengths of only 0.1 to almost 0.2 A, the rays of
used in the refined apparatus
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ultraviolet cover that part of the spectrum just below visible light or at wave lengths less than 3,800 A. The use of ultraviolet at the 2,537 ,I line is in realit! a short wave ultraviolet light. The 2,53i .i ultraviolet, lamp burns “cold” because it is removed from the thermal range of the spec*trum beginning above 3,800 d which, of’ caourse, proceeds to the intense and penetrating infra-red rays at the other end of the spectrum.
Fundamental
Principles
of Mercury
Arc Lamps
In the new low prcssur~ mercury are lamps there is generated an electron How between the electrodes which is tarried by ionized mercury vapor. Weitz and Amick2” liken each lamp to a radio broadcasting station but “generating about a dozen principal wave lengths instead of one. These along with other minor lines and some continuous radiation are known as the mercury spectrum. The power or energy emitted is usually different, for each wave length, some quite powerful, others relatively weak. ’ ’ The germicidal ultraviolet lamp operates on the principle of the fluorescent lamps. However,, the ultraviolet lamps are provided with a special glass that permits 95 per cent of the energy that is emitted to be in the region of 2,537 B. The fluorescent phosphors are, of course, omitted in ultraviolet lamps. Luckiesh, Holladay, and Taylor,“” of the Lighting Research Laboratory of the General Electric Company, conclusively proved that 2,537 1% ultraviolet energy is the most lethal zone for virtually all bacteria and viruses. Pathogenic organisms and viruses succumb most readily to ultraviolet energy, and highly resistant spores fare but little better under its impact. In view of the fact, that Escherichicb coli most nearly represents an average in its resistance to germicidal energy among t,he bacterial galaxy, it is commonly used as a standard to measure the intensity of ultraviolet energy required to kill bacteria. Dr. Max B. Lurie of the Phipps Institute demonstrated that with an intensity of 0.23 watts per square foot, 95 per cent of these bacteria are killed in three seconds.”
Ozone Production In the process of operating with the ultraviolet device, the odor of ozone is detectable upon opening the door. This is due to the fact that the 2,537 .& energy is accompanied by minute traces of 1,850 A energy which ionizes the atmospheric oxygen to produce ozone. The ozone exerts an oxidizing or “masking effect, ’ ’ upon the oil or grease used in lubricating the handpiece and is The device is equipped with a door brake rendered completely nonodorous. knob in order to deodorize the office by leaving the door open, The room must not be occupied during this time as the primary purpose of the door is for the Just looking at a bare ultraviolet protection of t,he dentist and the patient. lamp for a period of thirty seconds is sufficient to produce a severe conjunctivitis in some persons at a distance of three to six feet from the light source. The device may be used for deodorizing purposes when a patient has become ill and vomited, also for sweetening the atmosphere after using such a pungent pervasive drug as amyl nitrite. Some air circulation should be effected by opening
DEVICE
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the windows first, locking the door in the up position, and immediately leaving the office. Gentle circulation wafts the ozonized atmosphere from the radiation chamber. Relative to odor correction, the eff’ectiveness is quite immeasurable ; however, the generation of ozone is easily demonstrated in the device by wetting a strip of KI-Starch paper and placing it over the handpiece sheath. In a short interval a blue color denotes the presence of ozone descending upon the handpiece. Deodorization is probably in part oxidative, either directly or by decomposition of ozone into molecular and atomic oxygen. Its masking effect may be due to its reputed desensitization of the nasal mucosa. Odor suppression occurs despite the presence of barely detectable ozone. The dentist wearing ordinary spectacles need have no fear of looking directly at the lamp for a matter of a few minutes. Spectacle lenses will completely filter out the ultraviolet energy. Ultraviolet radiation of any wave length has no penetration for the human body comparable to x-radiation and, hence, Buttolph2* stated that : “Experience indino deep-seated physiological effects. cates it to be inevitable that experimenters with germicidal energy learn respect, for it only by painful experience, which usually takes the form of a reddening of the face and a smarting sensation in the eyes appearing two or three hours after exposure and varying in intensity with the length of exposure. While this effect is often called an erythema, it is very much more superficial in nature than that produced by ultraviolet energy of a longer wave length, the penetration of the skin being so slight, for example, that it seems to be almost impossible to produce the blistering easily resulting from long exposure to ultraviolet in the sun-tan range. The skin irritation disappears in a day or two leaving little pigmentation. ’ ’ The A. M. A. Council on Physical Medicine permits not over 0.5 microwatt per square cm. or 0.0005 watts per square foot exposure on the face. The likelihood of attaining this intensity is, under conditions of normal use of this device, impossible for both patient and operator. Overexposure to the ultraviolet energy responds by superficial erythema, not tanning, as the most efficient sun tanning energy band embraces the 2,976 A zone.
Miscellaneous
Facts Relating
to the Ultraviolet
Devices
The early experimental device shown (Fig. 1) also employed the 2,537 B band but with a 31/s watt bulb as the energy source. The physical design and the use of tin as a reflector surface were probably the main reasons for low efficiency. The average distance of the bulb from the contra-angle was less than one inch. This design was objectionable as it required double handling to manipulate the handpiece and did not afford complete radiation of the handpiece sheath. In addition, removal of the handpiece, aseptically, was not conveniently possible. The original principle in this early device, an automatic mercury arc switch actuating the light upon the insertion of the handpiece, was incorporated in the hope of minimizing excessive reflective radiation from the insertion slot. Frequently turning an ultraviolet lamp on and off greatly minimizes the lamp life more than do long periods of use. This, in addition to a lower efficiency during the first minute “warm-up” period, caused this feature to be abandoned.
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The present device (Fig. 3) was found equally efficient when the handpiece is inserted in a “sagittal * ’ position or crosswise as shown. However, a effectively- disinfected as the differences are surface in any position is almost indeed minimal. The rctmt)ive mechanism at the pulley end of the sheath permits the handpiece to be retained in secure cantilever posit,ion. As such, all surfaces are liberally and unobstructively struck with ultraviolet energy. This overcomes the objections raised by CrowleyZ9 who stated, “There are some instrument cabinets on the market which are supposed to disinfect instruments by means of ultraviolet rays. Kane of these cabinets is effective, since the rays do not hit all surfaces of t,he instrumenm in the cabinets.” The killing effect of ultraviolet energy, it should be emphasized, is entirely additive irrespective of the direction from which a particular bacterium is struck. Xi
Fig.
3.-A
“close-up”
view
of
the
device may
be
shown readily
in
Fig. 2, in observed.
which
the
details
of
CollSbYlCtiOn
The ultraviolet lamp is ordinarily rated at its output after one hundred hours of continuous operation. Butt.olph30 recommended replacing lamps “that depreciate below 70% of the 100-hour rating, as indicated by simple available germicidal output meters. ’ ’ The bulb and reflecting surfaces should be cleansed every four to six weeks with 70% alcohol applied with a clean towel. Maximal efficiency is obtained if these surfaces are absolutely free of dust.
DEVICE
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The reflecting surfaces of the radiation chamber are strategically convergent and thoroughly “bathe” the handpiece-contra-angle assembly. The present Spatial distribution factors contour is quite effective in its output distribution. and isointensity radiation have been carefully studied. Physical
and Bacteriological Aspects of the Use of 2,537 A Ultraviolet Energy
The new low-pressure mercury-vapor lamps have demonstrated a bactericidal efficiency at least five times greater than the older t,ypes of quartz mercury arcs which operate at much higher vapor pressures. (Luckiesh, Kerr, and Knowles) 31 Other than when a rubber dam is used for dental operations, saliva contaminating the handpiece is of chief concern. As saliva contains about 99.5 per cent of water,32 and as it is the suspending medium for the b,acteria of the oral cavity, it should prove to be no insurmountable obstacle to the penetration of the ultraviolet rays. In fact, Luckiesh and Holladay33 found that it required a 115 inch depth of distilled water to absorb 90 per cent of the incident energy of 2,537 ii ultraviolet rays, Although the Escherichia coli is generally assumed to be representative of pathogenic bacteria in susceptibility to ultraviolet energy, this assumption is not absolutely infallible as it does not hold true for many fungi and their spores. Fortunately, however, the latter organisms are of little concern to the dent.ist and only infrequently obfuscate bacteriological procedures. Luckiesh, Kerr, and Knowles34 demonstrated, in a series of precision experiments, that the “time t as well as the intensity E of germicidal energy is required to kill a micro-organism. The dosage is expressed as Et. When E is measured in microwatts per square eentimeter and t in minutes, the dosage is expressed in microwatt-minutes per square centimeter. (One microwatt per square centiIt has been shown that the effecmeter equals 0.929 milliwatt per square foot.) tiveness of the dosage Et in killing micro-organisms is reasonably constant over an extensive practical range. For example 50 microwatts per square centimeter operating for one minute result in approximately the same degree of kill as one microwatt per square centimeter operating for 50 minutes.” Hence, from these principles it is readily deduced that for any given species of organism there is an exponential decrease in the percentage of survivors as the Et is increased. Buttolph,3s in reference to the short wave 2,537 li radiation, stated: “The availability of this new source and the simplicity of use portend much as another advancement in control of infectious diseases and as a new tool in public health work. The only logical basis for utilizing this new device for the full benefit to individuals and to the public in general lies in medical and other scientific researches which establish its benefits, its limitations and its proven domain of effectiveness. Such studies are slow and painstaking, but these alone build the firm foundation for appraisal and specification of germicidal equipment and application. ” The admonitions of Buttolph have been heeded in the unique application of ultraviolet energy to the dental handpiece. How effective the use of this
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device actually would be in the prevention of communicable oral and systemic diseases, if diligently and conscientiously used by all dentists, is at present wholly a matter of conjecture. However, LeedeF tactfully justified the use of ultraviolet cabinets on the basis of their simplicity, the human element, not unprevalent among dentists, “of skipping the immersion t.ype of sterilization, ” and the fact that, “we would at least. get some disinfectant effect.”
Epidemiologic
Considerations
The literatures7 is abundantly replete with reports of spectacular results by the use of ultraviolet energy in the steriliza,tion of contaminated air, the effect of ultraviolet radiation of air on the incidence of infections in infant hospitals, and in the control and reduction of respiratory cross infections. A number of reports regarding the sensitivity to ultraviolet rays of various pathogenic and nonpathogenic organisms has been published.38 A critical analysis of the more recent and accurately controlled experiments indicates that most investigators have found pathogens more readily killed by ultraviolet energy. A few have found little, if any difference, and one investigator39 “ found Bacillus diphtheriae harder to kill than B. prodigiosus, although the other pathogens that he used were more easily destroyed.” The assumption may be reasonably made that the pathogens, with one possible exception, are at least just as readily killed as the Bncillus prodigiosus. These findings are presented under this section as a prelude to an important feature to be considered later under the experimental section. Other than the saliva-borne bacteria, those which may inadvertently be carried on the dentist’s hands are a secondary consideration in any clinicoepidemiologic study. That the hand transmission of disease or at least bacteria is probably not infrequent may be predicated best upon the investigations of Sauer, Minsk, and Rosenstern, who stated that: “The adoption of the Dick aseptic nursery technic at The Cradle in 1929 practically eliminated &n&borne cross infections, such as enteritis and impetigo . . . 3,132 infants have been admitted . . .” and, “the total mortality rate before the introduction of the aseptic technic was 5.8 per cent and after its introduction 0.8 per cent.” As the dentist operates at the oral portal of the respiratory tract it is not inconceivable that bacteria or viruses, causing the great variety of respiratory diseases, may occasionally be manually or instrumentally transferred. Indigenous or transient organisms on the hands, which contaminate the contra-angle or handpiece, should be suppressed to the fullest extent. In the course of man! dental operations, gingival capillaries are cut or traumatized creating an ideal site for the proliferation of bacteria thereupon. What the possibility is for transferring viruses to the oral cavity with their ultimate causation of some respiratory disease is, of course, not known; but Wells et a1.4’ and Greene et al.*2 described epidemics of virus diseases which were controlled by the ultraviolet radiation of the air. Buttolph43 pointed out that “every person is at times a carrier of pathogenic organisms awaiting only an opportunity, provided by mechanical lesions or the invasion of other sources of infection to make their own characteristic entrance into the underlying tissues as an active infection
DEVICE
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which may be diagnosed generally as streptococcic or virus, or specifically, as bronchitis or scarlet fever or measles or mumps, depending upon the organisms involved and the location of lesions.” Almost a half million patients are attended in a single day in dental offices and clinics throughout the United States. Probably in more instances than not, the dental handpiece is employed among this number of patients. Hence, the handpiece, as an insidious inoculating device, cannot be underestimated as a great potential hazard despite the fact that cause and effect from this source are not readily demonstrable.
Experimental
Procedure
It. is not intended to present the variety of experimental approaches undertaken to determine the effectiveness of ultraviolet energy on the disinfection of the handpiece. Some preliminary investigations showed a great inconsistency inherent to the method; others, though quite exact, a great degree of artificiality. All findings henceforth appertain only to the use of the newer device as pictured in Fig. 3. TABLE
*Viable
I.
VARIATIONS
IP; VIABLE
COUNTS
BY THE
IMMERSION
TECHNIQIT
Test
1
Handpiece Handpiece Handpiece
1 2 3
146 bacteria 239 bacteria 73 bacteria
in 0.1 of the in 0.1 of the in 0.1 of the
washed washed washed
off dilution* off dilution off dilution
Test
2
Handpiece Handpiece Handpiece
4 5 6
140 bacteria 55 bacteria 97 bacteria
in 0.1 of the washed in 0.1 of the washed in 0.1 of the washed
off dilution off dilution off dilution
Test
3
Handpiece Handpiece Handpiece
7 8 9
48 bacteria I63 bacteria 211 bacteria
in 0.1 of the in 0.1 of the in 0.1 of the
off dilution off dilution off dilution
counts
made
after
forty-eight
hours’
washed washed washed
incubation.
Three new handpiece sheaths with contra-angles attached, all of identical manufacture, were used in the investigations. These assemblies were initially After the use of this sterilized by the method of Crowley and Ostrander.44 method of sterilization it was found necessary to eliminate all the silicone from the surface by wiping the handpieces thoroughly with a towel and then dry heat sterilizing them at 160-170° C. for one and one-half hours. The latter treatment of the handpieces (with contra-angles attached to be understood) which were wrapped in a towel, substantially eliminated the invariable oozing of the silicone from the interior of the mechanism with its propensity to creep as a thin film over the surface. These handpieces, so treated, and again wiped thoroughly with the sterile towel, possessed a dry clean surface bereft of any substance that may contribute to oil-water immiscibilities when inoculated with bacteria. Unless this treatment had been thoroughly observed there would be a great inconsistency in the inoculum, as ordinarily effected, by immersing the handpiece in a large test tube filled with freshly,secreted saliva. After preliminary tests were found grossly inaccurate something inherent to the method was obviously wrong. Although every precaution had been observed for consistency, it was quite apparent that the dispersion of droplets
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upon the handpieces varied considerably in number and size. A 50 ml. test tube with a rubber stopper was autoclaved, cooled, and filled to the 40 ml. level with fresh paraffin-stimulated saliva. The stopper was replaced and the saliva thoroughly agitated. Each ha,ndpiece was momentarily dipped into the saliva to the level of the end of the knurling on t,he sheath at the pulley end. T’pon withdrawing the handpiece the saliva showed a variable distribution over the surface. Occasionally a large globule of saliva would develop under the bur lock, within the bur opening, and would run to the undersurface of the handpiece if held horizontall-. This inoculum was wa,shed off in a 50 ml. tube eont,aining 35 ml. of sterile PSS; 0.1 ml. was inoculated into a Petri dish, and a pour plate was made using 5 per cent defibrinated rabbit’s blood. Running a series of three handpieces, three times each with t,he same salivary sample, the nine viable plate counts showed rariations, within any single test, as great as 400 per cent (Table I).
Fig. 4.-The rotating appamtus for the controlled experimental This device is motor driven to identical handpieces simultaneously. A microscopic slide part of the synchronously revolving handpieces. shown in order to determine the distribution and dispersion of salivary
contamination effect 44 r.p.m. was originally droplets.
of
on used
three the as
It was thought, perhaps, impossible to use saliva for this purpose despite the fact that in any dental operation not employing the rubber dam, saliva is the primary medium for carrying bacteria to the handpiece. From a practical point of view, the tests would probably be more naturally representative of the
DEVICE
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problem of the contaminated handpiece if saliva with its mu&, heterogenous bacteria, and other extraneous substances could be utilized. The intrinsic and extrinsic protein substances in saliva undoubtedly absorb someultraviolet light. Along this line of investigation Spizizen, .Hampil, and Carte? demonstrated that: “Viruses in brain tissue when suspended in saline are readily inactivated, but longer exposure times are required for complete inactivation when the infected brain suspension is diluted in human plasma, since plasma itself absorbs considerable 2,537 A ultraviolet.” Dreyer and Hanssen46worked with solutions of various albumins and globulins, exposed in very thin layers, and found ultraviolet rays to cause a true coagulation of the proteins. This denaturation was assumed as the proteins were no longer soluble in weak acids or alkalis. Untitered suspensionsof Streptococcus viridans in PSS gave a poorer distribution over the handpiece due to the low viscosity. At this time it was thought feasible to add approximately 0.05 per cent agar to the PSS to simulate the viscosity of saliva. This procedure was abandoned in favor of a method designed to nebulize saliva in the air similar to the method of Wells4’ who atomized Esche&hia coli into the air “to permit an accuracy in air sampling difficult to secure when working only with naturally occurring bacterial contamination. ’ ’ An apparatus was constructed for the purpose of uniformly inoculating the surfaces of the handpieces by the gravitation of the finely dispersed salivary droplets in the air. This rotating apparatus (Fig. 4) permits the three sterile handpieces to rotate synchronously at approximately 44 r.p.m. It was found that air convection in the vicinity of the contra-angle head was negligible if held below 50 r.p.m. This rotating apparatus is motor-driven and the handpieces are easily inserted and removed aseptically with the exception of one inch at the pulley end which is well above the critical area necessarily subjected to the radiation chamber. A series of preliminary tests indicated a remarkable consistency in the number of bacteria that may b.e deposited on each handpiece by this method. Although this was evident for each test, time, quantitative, and technical features were altered until maximum reproducibility was inherent to the total procedure. These tests, and all succeeding procedures, were performed without a bur or other cutting instrument inserted. (This
article
will be pdlished
will
be concluded
in that issue.)
in the December
issue.
References
for the
entire
article
ULTRAVIOLET DEVICE ON CONTAMINATED
FOR THE DESTRUCTION OF BACTERIA DENTAL HANDPIECE SURFACES*
VICTOR H. DIETZ, D.D.S., PH.D.,
1. Preliminary
ANN ARBOR, MICH.
Report
T
HE dentist, as a public health mentor, is surely not unaware of the potential danger of direct and cross-infection which may be carried by the medium of a contaminated handpiece or contra-angle. It has been stated, ‘ ‘ . . . the one instrument that is used most often, the handpiece, is cleansed the least. Burs and mandrels, disks and stones are sterilized thoroughly before use. However, the chuck, which holds them and which also enters the mouth, may be indifferently cleansed. All too frequently it may be contaminated and may carry contamination from one patient to another. “I Knighton demonstrated an average colony count of 61,000 on ten handpieces, with contra-angle and right angle attachments, immediately after use, with a decrease to approximately half this count two hours after dental operations. Eighteen to twenty-four hours after the use of the handpieces and attachments, the average colony count was about 500 which he partially attributed to dehydration. In subsequent investigations he found, also by viable plate counting procedures, that “cold sterilization” was partially but not completely effective. The dental handpiece and its attachments, as insidious inoculating devices, no doub,t constitute an important public health problem. “Unsterilized handpieces are dangerous, and their use cannot be condoned. It would appear that the handpiece is the sole surviving source for the transmission of infection in many dental offices. ’ ‘3 The need for a simple chairside procedure for substantially suppressing surface contaminants or maintaining the sterility of handpieces was sought by the use of ultraviolet energy. A device of eaely design (Fig. 1)) attached to the dental unit and permitting the simple insertion of the handpiece and contra-angle, was constructed and tested. Preliminary bacteriologic experiments, conducted by the immersion of sterile contra-angles into two inches of saliva and exposed to the radiation for five minutes, evidenced almost a 50 per cent reduction in the numbers of bacteria as determined by the viable plate counting method. This degree of reduction was rather consistent in all of five instances as compared with five similarly treated controls not subjected to radiation. A great variation, however, versity
*The W. K. Kellogg of Michigan.
Foundation
Institute
of Graduat
1455
e and
Postgraduate
Dentistry,
Uni-
1456
VICTOR
H.
DIETZ
seemed to exist in the number of bacteria with which the contra-angles were cornaminated by this method. Early in the process of experimentation it hecame evident that a more powerful unit embracing other important practical features would be most desirable. To realize these advantages a second device (Fig. 2) was constructed. This unit possessesthe distinct advantage of permitting the aseptic insertion and withdrawal of the handpiece. In addition, all of the knurled portion of the straight handpiece receives the full impact of ultraviolet radiat.ion.
Fig. Fig. l.-An disinfectlon of Fig. Z.-A of the handpiece
1.
early design of an ultraviolet apparatus intended the contaminated dental handpiece. later type of ultraviolet device permitting the aseptic by the expedient of a pedal-controlled door.
Fig.
2.
for
the insertion
simple and
chairside removal
The improved device utilizes t,he small, yet powerful, 4-watt, U-type, ultraviolet lamp and, for reasons of utmost efficiency and economy, is continuous in operation. Haynes* demonstrated that practical maximum efficiency is attained after two minutes of continuous operation from the start with an output of 100 per cent of the ultraviolet energy in the 2,537 B band. This was computed in still air at an ambient temperature of 75O F. The lamp is strategically placed in order to afford ultraviolet impact upon all surfaces of the handpiece-contraangle assembly. To accomplish this, the radiation chamber is completely lined with Alzak aluminum (anodized surface) having a coefficient of reflectivity 70 per cent of the incident energy. Luckiesh and Taylor5 demonstrated that “the
DEVICE
FOR
DESTRUCTION
OF
BACTERIA
1457
reflectances of chromium and stainless steel, for example, are low compared with clean aluminum surf aces. ’ ’ Reflection is both diffuse and specular, and advantage is taken of the linear sources where the maximum intensities are in the direction perpendicular to the surface of the source. Hence, the Lucite door should not constitute a “blind spot” as the rays striking this area are of great obliquity and decrease with the cosine of the angle of emission. The radiation chamber is designed to take advantage of most reflecting surfaces, and as a result of the small cubic volume of the chamber the handpiece is bombarded with incident, reflected, and re-reflected rays. The chromiumplated surfaces of the handpiece and contra-angle reflect rays with a 40-50 per cent efficiency, according to the coefficient of reflectivity of chromium. A Brief /R&urn6 of the Theory and Activity of Germicidal Ultraviolet Light Ultraviolet rays of 3,287 and 2,265 B wave lengths have, since the original observations of Barnard and Morgan ,G been confirmed by numerous investigators as probably the most bactericidal. Hence, the concept, “the shorter the ultraviolet wave length the greater the b.actericidal action,” is wholly erroneous. Porter’ mentioned that the hydrogen-ion concentration has no effect on the bactericidal action of the light between the limits of pH 4.5 and 7.5. This is particularly important for our consideration as we shall deal in part with bacteria in the saliva, the latter which is invariably within the range of neutrality. Numerous investigators have demonstrated ultraviolet light of specific wave lengths to be lethal for all bacteria. There is, nevertheless, marked variation in resistance between various species but the common mouth organisms, particularly streptococci, are readily destroyed. Duggar and HollaendeF observed very little difference in resistance between vegetative cells and spores of Bacillus subtilis and Bacillus megatherium when exposed t,o ultraviolet light (2,650A). Other investigators have found spores only slightly more resistant. Hence, it is of profound interest to bacteriologists that there is a complete absence of parallelism between heat resistance and ultraviolet resistance of vegetative cells and spores. The extensive investigations of Sharps using 2,537 A attest to its broad bactericidal effect on a variety of bacteria. Smithburn and Lavin,lO also working within the 2,537 ii band, killed the resistant tubercle bacillus in a very heavy suspension (1 mg. per mm.) although such radiation required ten minutes’ study made its appearance in the pubexposure. A most precise quantitative lished investigations of Rentschler, Nagy, and Mouromseff,‘l who delicately controlled the dispersion factor when inoculating agar plates and rigidly controlled the specific ultraviolet exposure photometrically. Of considerable interest is the fact that they were able to demonstrate, among various bacterial species, a decidedly different resistance to ultraviolet radiation at different stages of the population cycle. All viruses that have been examined in purified or semipurified preparations are readily inactivated by ultraviolet light. Porter” “Although sufficient data are not available to draw any definite constated, clusions, it seems that viruses require about the same energy for inactivation as bacteria.”
1458
VICTOR
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Numerous theories have been proposed as to the mechanism of action of ultraviolet light, and t,o date the issue is not conclusively settled. The theory, once avidly maintained by early investigators, that some oxidizing substance such as ozone is formed during irradiation and that this substance was the immediate b,actericidal agent, has been substantially disproved. The investigations of Thiele and Wolf,13 and many more recent workers, have proved ultraviolet rays to be lethal under anaerobic conditions; hence, the originally postulated oxidizing agent is nonexistent. Similarly, hardly can it be hydrogen peroxide, as EhrismannX4 demonstrated that it wo~~ld have to attain a concentration of 30 per cent in order to equal the rapid and positive bactericidal action of ultra.violet light. Incidentall-, neither has so much as a trace of hydrogen peroxide been demonstrated as a concomitant of ultraviolet activity on bacteria. Quite recently, however, Wyss et, a1.l” demonstrated a marked similarity between certain biological effects produced by ultraviolet radiation of nutrient broth and by the addition of hydrogen peroxide to the broth. It is especially noteworthy that the effects of both agents can be negated by catalase. They believe that the results are due to the direct or indirect interference of an organic peroxide in some metabolic function. An analysis of the work of Gates,lG Ehrismann and Noethling,17 and Hollaender and Claus’* indicates that bacterial death follows in the wake of a disturbance of certain molecular groupings in the cell having high specific absorption spectra for ultraviolet light. Further experimental proof of denaturation and microscopic evidence of cellular coagulation lends credence to the probabilit,y of a direct ultraviolet effect. However, whether this is immediately due to a change in the permeability of the cell wall, an enzymatic alteration, alteration of the cytoplasmic colloids, or in the nucleic acid substance remains highly debatable. Nevertheless, it is probably safe to assume that the lethal action of ultraviolet rays is probably direct and most certainly quite complex. A few of the newer concepts of the mechanism of the bactericidal action of ultraviolet rays are possibly of more theoretical than practical concern, but are of considerable interest. In this connection, the investigations of Bucholz and Jenev’” suggest. a photoelectric action. These workers pointed out that the highiv Y lethal waves 2,650 and 2,530 A correspond respectively to energy values of 4.6 and 4.8 volts, and concluded that this amount of energy is required to displace sufficient electrons from the bacterial protoplasm to give rise to irreversible photochemical alterations and t,hus bring about death of the cell. Wyckoff,zo on the other hand, studied this aspect of the problem in the light of the quantum theory and found that about four million quanta of energy are required to kill a single .coliform bacillus, showing that death is not due to the cathode rays (a single quantum absorption), but to some more generalized effect, on the bacterial prot’oplasm. Emmons and Hollaender*’ speculated upon the molecular groupings responsible for the lethality of ultraviolet radiation and maintained that : “As in bacteria and yeasts the wave lengths most toxic are 2,537 to 2,650 B-the wave lengths most highly absorbed by nucleic acids rather than by proteins.” Fol-
DEVICE
FOR
DESTRUCTION
OF
BACTERIA
1459
lowing this concept, Mackinnon and Artagaveytia-Allendez2 believe that “it is possible that the different aspects of Emmons and Hollaender’s mutants may be due to changes in the nutritional requirements, perhaps to losses in the ability to synthesize growth factors. ’ ’ Along this line of reasoning one may assume that the lethal ultraviolet dose in any given instance may b.e the result of nutritional derangement or impairA critical ment to a degree as to be inhibitory to growth and reproduction. appraisal of the actual lethal mechanism, just how, when, and where it strikes, is indeed quite susceptible to conjecture.
Physical This discussion
Aspects of the Ultraviolet
Light
will be essentially confined to the ultraviolet system of light as shown (Fig. 2). The most important single element is the ultraviolet lamp (G-4T-4), for which the following data23 obtain. The rated wattage of this bulb is 4 watts, and has an over-all length of 5yL inches with a tubular diameter of 1,s inch. The bent tube construction makes the lamp approximately 1 inch in width. This feature is especially important a.s it enables the incident rays to converge around either side of the handpiece to be reflected effectively. This lamp may be operated on a circuit of 110-125 volts with an approximate amperage of 0.08. The approximate glass temperature is 100° F. and the lamp life, under specified test conditions of three-hour or longer operating periods, is rated at 2,500 hours. The “effective length” of the ultraviolet source is 6 inches and the ultraviolet output watts (2,537 .K) is 0.5. The wattage per square foot at 37 inches is 0.007, whereas at 8 inches it is 0.06 and at 4 inches it is 0.43. In the device shown we are especially concerned with the intensity at 4 inches for the incident light. from above, and the intensity at 8 inches for the reflected light that strikes all other surfaces. It may be noted that the intensities vary, from bare lamps, practically inversely as the distance, rather than the usual designation, “inversely as the square of the distance. ” Hence, ultraviolet light is simply like ot,her radiant energy but is incapable of being apprehended to any appreciable extent by the human retina as is the case with luminous energy. Ultraviolet rays obey the laws of visible light with which we are all familiar. Thus, it, too, according to modern theory, consists of quanta of energy which move as if guided by waves, The emission of extraneous visible rays (blue band) and the type of glass used in the construction of the ultraviolet lamp cause it to burn with a soft blue light. This coexistent visible light readily demonstrates such common phenomena as reflection, refraction, and dispersion. These phenomena apply to the ultraviolet light as well as the visible light. Jordan and Burrowsz4 pointed out that the ultraviolet spectrum is by far the most bactericidal but that even visible light is slightly active, particularly blue. The dentist can easily understand the position of ultraviolet light when comparing it with x-rays as both are at the short end of the spectrum. However, whereas x-rays have wave lengths of only 0.1 to almost 0.2 A, the rays of
used in the refined apparatus
1460
VICTOR
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ultraviolet cover that part of the spectrum just below visible light or at wave lengths less than 3,800 A. The use of ultraviolet at the 2,537 ,I line is in realit! a short wave ultraviolet light. The 2,53i .i ultraviolet, lamp burns “cold” because it is removed from the thermal range of the spec*trum beginning above 3,800 d which, of’ caourse, proceeds to the intense and penetrating infra-red rays at the other end of the spectrum.
Fundamental
Principles
of Mercury
Arc Lamps
In the new low prcssur~ mercury are lamps there is generated an electron How between the electrodes which is tarried by ionized mercury vapor. Weitz and Amick2” liken each lamp to a radio broadcasting station but “generating about a dozen principal wave lengths instead of one. These along with other minor lines and some continuous radiation are known as the mercury spectrum. The power or energy emitted is usually different, for each wave length, some quite powerful, others relatively weak. ’ ’ The germicidal ultraviolet lamp operates on the principle of the fluorescent lamps. However,, the ultraviolet lamps are provided with a special glass that permits 95 per cent of the energy that is emitted to be in the region of 2,537 B. The fluorescent phosphors are, of course, omitted in ultraviolet lamps. Luckiesh, Holladay, and Taylor,“” of the Lighting Research Laboratory of the General Electric Company, conclusively proved that 2,537 1% ultraviolet energy is the most lethal zone for virtually all bacteria and viruses. Pathogenic organisms and viruses succumb most readily to ultraviolet energy, and highly resistant spores fare but little better under its impact. In view of the fact, that Escherichicb coli most nearly represents an average in its resistance to germicidal energy among t,he bacterial galaxy, it is commonly used as a standard to measure the intensity of ultraviolet energy required to kill bacteria. Dr. Max B. Lurie of the Phipps Institute demonstrated that with an intensity of 0.23 watts per square foot, 95 per cent of these bacteria are killed in three seconds.”
Ozone Production In the process of operating with the ultraviolet device, the odor of ozone is detectable upon opening the door. This is due to the fact that the 2,537 .& energy is accompanied by minute traces of 1,850 A energy which ionizes the atmospheric oxygen to produce ozone. The ozone exerts an oxidizing or “masking effect, ’ ’ upon the oil or grease used in lubricating the handpiece and is The device is equipped with a door brake rendered completely nonodorous. knob in order to deodorize the office by leaving the door open, The room must not be occupied during this time as the primary purpose of the door is for the Just looking at a bare ultraviolet protection of t,he dentist and the patient. lamp for a period of thirty seconds is sufficient to produce a severe conjunctivitis in some persons at a distance of three to six feet from the light source. The device may be used for deodorizing purposes when a patient has become ill and vomited, also for sweetening the atmosphere after using such a pungent pervasive drug as amyl nitrite. Some air circulation should be effected by opening
DEVICE
FOR
DESTRUCTION
OF
1461
BACTERIA
the windows first, locking the door in the up position, and immediately leaving the office. Gentle circulation wafts the ozonized atmosphere from the radiation chamber. Relative to odor correction, the eff’ectiveness is quite immeasurable ; however, the generation of ozone is easily demonstrated in the device by wetting a strip of KI-Starch paper and placing it over the handpiece sheath. In a short interval a blue color denotes the presence of ozone descending upon the handpiece. Deodorization is probably in part oxidative, either directly or by decomposition of ozone into molecular and atomic oxygen. Its masking effect may be due to its reputed desensitization of the nasal mucosa. Odor suppression occurs despite the presence of barely detectable ozone. The dentist wearing ordinary spectacles need have no fear of looking directly at the lamp for a matter of a few minutes. Spectacle lenses will completely filter out the ultraviolet energy. Ultraviolet radiation of any wave length has no penetration for the human body comparable to x-radiation and, hence, Buttolph2* stated that : “Experience indino deep-seated physiological effects. cates it to be inevitable that experimenters with germicidal energy learn respect, for it only by painful experience, which usually takes the form of a reddening of the face and a smarting sensation in the eyes appearing two or three hours after exposure and varying in intensity with the length of exposure. While this effect is often called an erythema, it is very much more superficial in nature than that produced by ultraviolet energy of a longer wave length, the penetration of the skin being so slight, for example, that it seems to be almost impossible to produce the blistering easily resulting from long exposure to ultraviolet in the sun-tan range. The skin irritation disappears in a day or two leaving little pigmentation. ’ ’ The A. M. A. Council on Physical Medicine permits not over 0.5 microwatt per square cm. or 0.0005 watts per square foot exposure on the face. The likelihood of attaining this intensity is, under conditions of normal use of this device, impossible for both patient and operator. Overexposure to the ultraviolet energy responds by superficial erythema, not tanning, as the most efficient sun tanning energy band embraces the 2,976 A zone.
Miscellaneous
Facts Relating
to the Ultraviolet
Devices
The early experimental device shown (Fig. 1) also employed the 2,537 B band but with a 31/s watt bulb as the energy source. The physical design and the use of tin as a reflector surface were probably the main reasons for low efficiency. The average distance of the bulb from the contra-angle was less than one inch. This design was objectionable as it required double handling to manipulate the handpiece and did not afford complete radiation of the handpiece sheath. In addition, removal of the handpiece, aseptically, was not conveniently possible. The original principle in this early device, an automatic mercury arc switch actuating the light upon the insertion of the handpiece, was incorporated in the hope of minimizing excessive reflective radiation from the insertion slot. Frequently turning an ultraviolet lamp on and off greatly minimizes the lamp life more than do long periods of use. This, in addition to a lower efficiency during the first minute “warm-up” period, caused this feature to be abandoned.
1462
VICTOR
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The present device (Fig. 3) was found equally efficient when the handpiece is inserted in a “sagittal * ’ position or crosswise as shown. However, a effectively- disinfected as the differences are surface in any position is almost indeed minimal. The rctmt)ive mechanism at the pulley end of the sheath permits the handpiece to be retained in secure cantilever posit,ion. As such, all surfaces are liberally and unobstructively struck with ultraviolet energy. This overcomes the objections raised by CrowleyZ9 who stated, “There are some instrument cabinets on the market which are supposed to disinfect instruments by means of ultraviolet rays. Kane of these cabinets is effective, since the rays do not hit all surfaces of t,he instrumenm in the cabinets.” The killing effect of ultraviolet energy, it should be emphasized, is entirely additive irrespective of the direction from which a particular bacterium is struck. Xi
Fig.
3.-A
“close-up”
view
of
the
device may
be
shown readily
in
Fig. 2, in observed.
which
the
details
of
CollSbYlCtiOn
The ultraviolet lamp is ordinarily rated at its output after one hundred hours of continuous operation. Butt.olph30 recommended replacing lamps “that depreciate below 70% of the 100-hour rating, as indicated by simple available germicidal output meters. ’ ’ The bulb and reflecting surfaces should be cleansed every four to six weeks with 70% alcohol applied with a clean towel. Maximal efficiency is obtained if these surfaces are absolutely free of dust.
DEVICE
FOR
DESTRUCTION
OF
BACTERIA
1463
The reflecting surfaces of the radiation chamber are strategically convergent and thoroughly “bathe” the handpiece-contra-angle assembly. The present Spatial distribution factors contour is quite effective in its output distribution. and isointensity radiation have been carefully studied. Physical
and Bacteriological Aspects of the Use of 2,537 A Ultraviolet Energy
The new low-pressure mercury-vapor lamps have demonstrated a bactericidal efficiency at least five times greater than the older t,ypes of quartz mercury arcs which operate at much higher vapor pressures. (Luckiesh, Kerr, and Knowles) 31 Other than when a rubber dam is used for dental operations, saliva contaminating the handpiece is of chief concern. As saliva contains about 99.5 per cent of water,32 and as it is the suspending medium for the b,acteria of the oral cavity, it should prove to be no insurmountable obstacle to the penetration of the ultraviolet rays. In fact, Luckiesh and Holladay33 found that it required a 115 inch depth of distilled water to absorb 90 per cent of the incident energy of 2,537 ii ultraviolet rays, Although the Escherichia coli is generally assumed to be representative of pathogenic bacteria in susceptibility to ultraviolet energy, this assumption is not absolutely infallible as it does not hold true for many fungi and their spores. Fortunately, however, the latter organisms are of little concern to the dent.ist and only infrequently obfuscate bacteriological procedures. Luckiesh, Kerr, and Knowles34 demonstrated, in a series of precision experiments, that the “time t as well as the intensity E of germicidal energy is required to kill a micro-organism. The dosage is expressed as Et. When E is measured in microwatts per square eentimeter and t in minutes, the dosage is expressed in microwatt-minutes per square centimeter. (One microwatt per square centiIt has been shown that the effecmeter equals 0.929 milliwatt per square foot.) tiveness of the dosage Et in killing micro-organisms is reasonably constant over an extensive practical range. For example 50 microwatts per square centimeter operating for one minute result in approximately the same degree of kill as one microwatt per square centimeter operating for 50 minutes.” Hence, from these principles it is readily deduced that for any given species of organism there is an exponential decrease in the percentage of survivors as the Et is increased. Buttolph,3s in reference to the short wave 2,537 li radiation, stated: “The availability of this new source and the simplicity of use portend much as another advancement in control of infectious diseases and as a new tool in public health work. The only logical basis for utilizing this new device for the full benefit to individuals and to the public in general lies in medical and other scientific researches which establish its benefits, its limitations and its proven domain of effectiveness. Such studies are slow and painstaking, but these alone build the firm foundation for appraisal and specification of germicidal equipment and application. ” The admonitions of Buttolph have been heeded in the unique application of ultraviolet energy to the dental handpiece. How effective the use of this
1464
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device actually would be in the prevention of communicable oral and systemic diseases, if diligently and conscientiously used by all dentists, is at present wholly a matter of conjecture. However, LeedeF tactfully justified the use of ultraviolet cabinets on the basis of their simplicity, the human element, not unprevalent among dentists, “of skipping the immersion t.ype of sterilization, ” and the fact that, “we would at least. get some disinfectant effect.”
Epidemiologic
Considerations
The literatures7 is abundantly replete with reports of spectacular results by the use of ultraviolet energy in the steriliza,tion of contaminated air, the effect of ultraviolet radiation of air on the incidence of infections in infant hospitals, and in the control and reduction of respiratory cross infections. A number of reports regarding the sensitivity to ultraviolet rays of various pathogenic and nonpathogenic organisms has been published.38 A critical analysis of the more recent and accurately controlled experiments indicates that most investigators have found pathogens more readily killed by ultraviolet energy. A few have found little, if any difference, and one investigator39 “ found Bacillus diphtheriae harder to kill than B. prodigiosus, although the other pathogens that he used were more easily destroyed.” The assumption may be reasonably made that the pathogens, with one possible exception, are at least just as readily killed as the Bncillus prodigiosus. These findings are presented under this section as a prelude to an important feature to be considered later under the experimental section. Other than the saliva-borne bacteria, those which may inadvertently be carried on the dentist’s hands are a secondary consideration in any clinicoepidemiologic study. That the hand transmission of disease or at least bacteria is probably not infrequent may be predicated best upon the investigations of Sauer, Minsk, and Rosenstern, who stated that: “The adoption of the Dick aseptic nursery technic at The Cradle in 1929 practically eliminated &n&borne cross infections, such as enteritis and impetigo . . . 3,132 infants have been admitted . . .” and, “the total mortality rate before the introduction of the aseptic technic was 5.8 per cent and after its introduction 0.8 per cent.” As the dentist operates at the oral portal of the respiratory tract it is not inconceivable that bacteria or viruses, causing the great variety of respiratory diseases, may occasionally be manually or instrumentally transferred. Indigenous or transient organisms on the hands, which contaminate the contra-angle or handpiece, should be suppressed to the fullest extent. In the course of man! dental operations, gingival capillaries are cut or traumatized creating an ideal site for the proliferation of bacteria thereupon. What the possibility is for transferring viruses to the oral cavity with their ultimate causation of some respiratory disease is, of course, not known; but Wells et a1.4’ and Greene et al.*2 described epidemics of virus diseases which were controlled by the ultraviolet radiation of the air. Buttolph43 pointed out that “every person is at times a carrier of pathogenic organisms awaiting only an opportunity, provided by mechanical lesions or the invasion of other sources of infection to make their own characteristic entrance into the underlying tissues as an active infection
DEVICE
FOR
DESTRUCTION
OF
1465
BACTERIA
which may be diagnosed generally as streptococcic or virus, or specifically, as bronchitis or scarlet fever or measles or mumps, depending upon the organisms involved and the location of lesions.” Almost a half million patients are attended in a single day in dental offices and clinics throughout the United States. Probably in more instances than not, the dental handpiece is employed among this number of patients. Hence, the handpiece, as an insidious inoculating device, cannot be underestimated as a great potential hazard despite the fact that cause and effect from this source are not readily demonstrable.
Experimental
Procedure
It. is not intended to present the variety of experimental approaches undertaken to determine the effectiveness of ultraviolet energy on the disinfection of the handpiece. Some preliminary investigations showed a great inconsistency inherent to the method; others, though quite exact, a great degree of artificiality. All findings henceforth appertain only to the use of the newer device as pictured in Fig. 3. TABLE
*Viable
I.
VARIATIONS
IP; VIABLE
COUNTS
BY THE
IMMERSION
TECHNIQIT
Test
1
Handpiece Handpiece Handpiece
1 2 3
146 bacteria 239 bacteria 73 bacteria
in 0.1 of the in 0.1 of the in 0.1 of the
washed washed washed
off dilution* off dilution off dilution
Test
2
Handpiece Handpiece Handpiece
4 5 6
140 bacteria 55 bacteria 97 bacteria
in 0.1 of the washed in 0.1 of the washed in 0.1 of the washed
off dilution off dilution off dilution
Test
3
Handpiece Handpiece Handpiece
7 8 9
48 bacteria I63 bacteria 211 bacteria
in 0.1 of the in 0.1 of the in 0.1 of the
off dilution off dilution off dilution
counts
made
after
forty-eight
hours’
washed washed washed
incubation.
Three new handpiece sheaths with contra-angles attached, all of identical manufacture, were used in the investigations. These assemblies were initially After the use of this sterilized by the method of Crowley and Ostrander.44 method of sterilization it was found necessary to eliminate all the silicone from the surface by wiping the handpieces thoroughly with a towel and then dry heat sterilizing them at 160-170° C. for one and one-half hours. The latter treatment of the handpieces (with contra-angles attached to be understood) which were wrapped in a towel, substantially eliminated the invariable oozing of the silicone from the interior of the mechanism with its propensity to creep as a thin film over the surface. These handpieces, so treated, and again wiped thoroughly with the sterile towel, possessed a dry clean surface bereft of any substance that may contribute to oil-water immiscibilities when inoculated with bacteria. Unless this treatment had been thoroughly observed there would be a great inconsistency in the inoculum, as ordinarily effected, by immersing the handpiece in a large test tube filled with freshly,secreted saliva. After preliminary tests were found grossly inaccurate something inherent to the method was obviously wrong. Although every precaution had been observed for consistency, it was quite apparent that the dispersion of droplets
1466
VICTOR
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upon the handpieces varied considerably in number and size. A 50 ml. test tube with a rubber stopper was autoclaved, cooled, and filled to the 40 ml. level with fresh paraffin-stimulated saliva. The stopper was replaced and the saliva thoroughly agitated. Each ha,ndpiece was momentarily dipped into the saliva to the level of the end of the knurling on t,he sheath at the pulley end. T’pon withdrawing the handpiece the saliva showed a variable distribution over the surface. Occasionally a large globule of saliva would develop under the bur lock, within the bur opening, and would run to the undersurface of the handpiece if held horizontall-. This inoculum was wa,shed off in a 50 ml. tube eont,aining 35 ml. of sterile PSS; 0.1 ml. was inoculated into a Petri dish, and a pour plate was made using 5 per cent defibrinated rabbit’s blood. Running a series of three handpieces, three times each with t,he same salivary sample, the nine viable plate counts showed rariations, within any single test, as great as 400 per cent (Table I).
Fig. 4.-The rotating appamtus for the controlled experimental This device is motor driven to identical handpieces simultaneously. A microscopic slide part of the synchronously revolving handpieces. shown in order to determine the distribution and dispersion of salivary
contamination effect 44 r.p.m. was originally droplets.
of
on used
three the as
It was thought, perhaps, impossible to use saliva for this purpose despite the fact that in any dental operation not employing the rubber dam, saliva is the primary medium for carrying bacteria to the handpiece. From a practical point of view, the tests would probably be more naturally representative of the
DEVICE
FOR
DESTRUCTION
OF
1467
BACTERIA
problem of the contaminated handpiece if saliva with its mu&, heterogenous bacteria, and other extraneous substances could be utilized. The intrinsic and extrinsic protein substances in saliva undoubtedly absorb someultraviolet light. Along this line of investigation Spizizen, .Hampil, and Carte? demonstrated that: “Viruses in brain tissue when suspended in saline are readily inactivated, but longer exposure times are required for complete inactivation when the infected brain suspension is diluted in human plasma, since plasma itself absorbs considerable 2,537 A ultraviolet.” Dreyer and Hanssen46worked with solutions of various albumins and globulins, exposed in very thin layers, and found ultraviolet rays to cause a true coagulation of the proteins. This denaturation was assumed as the proteins were no longer soluble in weak acids or alkalis. Untitered suspensionsof Streptococcus viridans in PSS gave a poorer distribution over the handpiece due to the low viscosity. At this time it was thought feasible to add approximately 0.05 per cent agar to the PSS to simulate the viscosity of saliva. This procedure was abandoned in favor of a method designed to nebulize saliva in the air similar to the method of Wells4’ who atomized Esche&hia coli into the air “to permit an accuracy in air sampling difficult to secure when working only with naturally occurring bacterial contamination. ’ ’ An apparatus was constructed for the purpose of uniformly inoculating the surfaces of the handpieces by the gravitation of the finely dispersed salivary droplets in the air. This rotating apparatus (Fig. 4) permits the three sterile handpieces to rotate synchronously at approximately 44 r.p.m. It was found that air convection in the vicinity of the contra-angle head was negligible if held below 50 r.p.m. This rotating apparatus is motor-driven and the handpieces are easily inserted and removed aseptically with the exception of one inch at the pulley end which is well above the critical area necessarily subjected to the radiation chamber. A series of preliminary tests indicated a remarkable consistency in the number of bacteria that may b.e deposited on each handpiece by this method. Although this was evident for each test, time, quantitative, and technical features were altered until maximum reproducibility was inherent to the total procedure. These tests, and all succeeding procedures, were performed without a bur or other cutting instrument inserted. (This
article
will be pdlished
will
be concluded
in that issue.)
in the December
issue.
References
for the
entire
article