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Control of cross-infection risks in the dental operatory: prevention of water retraction by bur cooling spray systems
JÂD)A RESEARCH
REPORTS
A new dental u n it control system w as fo u n d to overcome the p o ssib ility o f m echanically retracting bacteria fro m the m o u th into the w ater lin e used to provide a spray o f w ater to cool high-speed burs during treatm ents. T h is was dem onstrated by results obtained after clinical use and after use in sim ulated, worst case test conditions u sin g a red tem pera indicator solution a nd indicator bacteria.
Control of cross-infection risks in the dental operatory: prevention of water retraction by bur cooling spray systems James J. Crawford, MA, PhD Cindy Broderius, ASCP
" ith o u t adequate aseptic pre cautions, various routes can transfer infections between the dental operatory. H ands, instrum entation, a n d eq u ip m en t routinely become soiled w ith saliva and blood, and they are used repeatedly in the m ouths of 20 to 40 or m ore persons each day. Intrao ral treat m ents are perform ed w ith in strum entation th at routinely penetrates oral tissues, and w ith com plex eq u ip m en t that is difficult to clean and sterilize. Blood and saliva persist beneath fingernails of ungloved operators, and saliva-borne m icroorga nism s adhere to dental u n it eq u ip m en t th a t is handled d u rin g treatm ent.1”3 Infection risks for dental personnel are adm ittedly h ig h .4-6 T he im portance of p ro tec tin g p atien ts, as w ell as dental personnel, has been addressed by the US P ublic H ealth Service in the guidelines on infection control and elsewhere.5 8 T h is report discusses another possible m e c h a n ism of cross c o n ta m in a tio n addressed in the C enters for D isease C o n tro l (C D C ) g u id e lin e s a n d e ls e w h ere.3,5,6 It describes the in a d v erten t asp iratio n of saliva, blood, or debris by a w ater spray retraction device b u ilt into a d e n ta l u n it. U n less th e system is adequately flushed between treatm ents, it is possible for oral debris collected from
W
a p atient to be expelled into the m outh of the next patient. T h e CDC guidelines recom m end correcting this problem w ith a check v alv e.5 T h is m ay p ro v id e a tem porary solution th at requires interm it tent testing to verify proper function. T h is article provides test data on the effectiveness of a new com m ercial dental u n it to prevent asp iratio n of oral fluids by the water spray system used to cool high-speed burs, using a m ethod that elim inates water retraction an d aspiration. W hen handpieces were developed to drive burs for cu ttin g teeth at h ig h speeds, an opening was placed in the handpiece near the bu r from w hich a spray of water and air was delivered to cool the b u r and to p ro tec t the u n d e rly in g p u lp from therm al dam age. T h e plastic tu b in g first used in the handpiece hoses apparently expanded under the pressure involved in delivering the water spray. W hen the bur and spray were stopped, w ater pressure dropped, tubin g gradually contracted, and w ater continued to d rip from the h a n d piece as it was removed from the p a tie n t’s m o u th , p o ssib ly s p o ttin g a p a tie n t’s clothing. T he prevailing m ethod initially used by m ost m anufacturers to prevent d rip p in g was to provide a sm all, pistona ctiv ated , neg ativ e p ressu re (su ctio n ) device w ithin the u n it th at was activated
each tim e the b u r an d spray were stopped. T h is device w ould in stan tly draw w ater back u p from the o p en in g adjacent to the bur, plus u p to 10 m L of air an d any spattered saliva or blood. T h is process has been referred to as w ater retraction, and the result as asp iratio n , or m ore g ra p h i cally as “suckback.” Abel an d others9 were the first to detect oral bacteria in co o lin g spray w ater from high-speed handpieces after dental treat m ents (Streptococcus m itis was detected in 26%, S salivarius in 16%, enterococci in 40%). W ith a m arker dye, cultures of m arker b a c te ria w ere p la c e d in a tr e a tm e n t m an ik in to detect asp iratio n . C linical tests of asp iratio n of p atien ts’ oral bacteria were perform ed in private offices. It was also docum ented th at five m ajo r brands of dental units m anufactured before 1978 show ed asp iratio n (Craw ford, J., u n p u b lished data, 1978). Based p artly on this u n p u b lish ed data, reported to the A m er ican D ental A ssociation (ADA), recom m endations to correct this p o ten tial for cross co n tam in atio n were p ublished by the ADA in 1978, an d were later confirm ed an d published by Bagga an d o th ers.10,11 T h e re w ere tw o o b je ctiv es in th is investigation: to evaluate the ability of the test dental u n it co n tro l system (Spirit JA D A , V o l. 116, M ay 1988 ■ 685
RESEARCH
REPORTS
D ental U n it Controls, P elton 8c Crane Co) to reliably prevent extensive retraction of oral bacteria in to the handpiece under conditions of clinical use, an d retraction of indicator dye and bacterial test solutions in to the handpiece and hose line under the “w orst possible” experim ental in vitro test situations; and to determ ine if the test system could help overcome the contam in a tio n p ro b le m of passive ca p illary asp iratio n of oral fluids back into the handpiece. It is im p o r ta n t to u n d e rs ta n d the difference between this possible, passive capillary asp iratio n of oral fluids, and their retraction by the high-speed h a n d piece co o lin g spray retraction system. C apillary asp iratio n can result whenever the o p en in g of any sm all-diam eter, “wettable” tu b in g contacts a liquid. Forces of surface tension spontaneously cause low surface tension fluid to enter such an opening. In this m anner, sm all am ounts of flu id can be im bibed into any w ater/ air coo lin g spray openings (or into any o th e r o p enings) on the handpiece by capillary action. T h is is not caused by any m echanical activity of the handpiece or un it. T h o ro u g h cleaning and disinfecting of the outside of the handpiece may clean an d decontam inate these openings and help control this source of contam ination. Sterilization of the handpiece by heat or gas is preferred an d is the only reliable m ethod to assure control of contam ination associated w ith this capillary action.5 Methods and materials
W ater sam ples were collected from the high-speed handpiece cooling w ater spray system an d handpiece tub in g before and a fte r th re e types of te st o p e r a tio n procedures: —T u rn in g the handpiece and w ater spray on a n d off repeatedly for 10 seconds w ith the head of the handpiece subm erged in “ test dye” solution (red tem pera dye, Palm er Co, d iluted in water). —T u rn in g a sterilized handpiece and water spray on an d off three times w hile keeping the head of the handpiece sub m erged in broth suspension containing m ore th a n 100,000 colony form ing units of Bacillus subtilis var niger per m illiliter. —T reatm ents of dental patients. These consisted of p rep arin g teeth for crowns and o th e r restorative treatm ents perform ed w ith o u t a rubber dam. In each type of test, handpieces were tightly attached to hose end fittings. For tests of B subtilis aspiration, a sterile test tube was used to aseptically collect a 10686 ■ JADA, Vol. 116, May 1988
m L spray-w ater sam ple from the h a n d piece before the test procedure. After the procedure, 10 m L of water was collected from the end of the disconnected hose an d cultured to detect any aspiration back into the hose. T h e w ater spray was th en operated for 1 m inute to clear the line. T h e handpiece was reattached to the hose and only the surface of the handpiece was cleaned and disinfected for 2 m inutes w ith 70% isopropyl alcohol. T h is procedure was a d e q u a te to e lim in a te co u n ts of the vegetative test bacteria of concern on the surfaces of handpieces to zero, 20 of 20 times. T h en 2 m L of w ater was collected from the handpiece spray o p en in g to detect bacteria aspirated just in to the handpiece. S im ilar procedures were used to detect asp ira tio n of oral streptococci d u rin g clinical treatments. However, after treat m ents, the outside of the handpiece was disinfected an d removed from the hose an d 1 m L of sterile water was flushed th ro u g h the handpiece spray tube w ith a tuberculin syringe to co llect an y a sp ira te d o ral streptococci. For detection of dye asp iratio n , the handpiece was operated in the test dye solution, the outside of the handpiece was cleaned, and the handpiece was removed from its hose. A pproxim ately 0.5 m L of w ater was collected from the hose end an d exam ined on w hite paper to detect any dye aspirated in to the hose line; the line was flushed for a m inute, and the handpiece was replaced. From the handpiece, 0.5 m L of water was collected to detect aspiration of dye lim ited to the handpiece. T h irty dental u nits were tested in dental school clinics. These were equip p ed w ith a positive closure valve to cut off water flow w hen the rheostat is released an d no form of retraction. T hey are also equip p ed w ith a chip air feature in the air supply to the handpiece th at can be activated independently to blow a stream of air over the bur through an op en in g it shares w ith the w ater spray. It continues to blow for a m om ent after the foot control is released. W hen activated along w ith the w ater spray, and the water and b u r are stopped, the chip air continues to blow, blow ing away the last drop of the spray water. T w o units were used as positive test co n tro ls; these were n o t corrected to prevent aspiration of oral debris, were m anufactured by a m ajor dental m anufac turer before 1983, and were equip p ed w ith functio n in g water spray retraction valves typical of many brands of units made in recent years. T est dye so lu tio n was p rep ared by d ilu tin g fluorescent red tem pera water-
soluble poster p ain t, 1:50 in tap water. B acillus subtilis var niger cultures used in bacterial asp iratio n tests were vegetative cultures grow n for 24 hours in trypticase soy broth for 24 hours a t 37 C an d adjusted to a concentration of approxim ately 106 colony-form ing u nits (CFU). Sam ples for cu ltu re from treatm en t procedures were vortexed at h ig h speed for 30 seconds, a n d d ilu tio n s were prepared. From the o rig in al an d each d ilu tio n , 0.1 m L was spread on separate agar plates, incubated w ith 5% carbon dioxide for 24 h r at 37 C, and colonies were counted. C olum bia-N alidixic Acid agar (BectonD ickinson Co), in addition to sheep blood agar, was used to culture clinical samples to help detect oral streptococci and restrict colony grow th of nonoral, aq u atic bacteria th at could obscure oral species. Sam ples to detect B subtilis were inoculated on b lood agar plates and incubated in air at 37 C. T h e capillary effect was tested by in se rtin g 1-mm diam eter polyethylene can n u latio n tu b in g in to the air an d water ports in the hose line in place of the handpiece.
Results Tests with test indicator dye. N o test dye was
detected in w ater from hoses or handpieces from any of 30 test u nits after repeated activation of the handpieces w ith their w ater spray orifice subm erged in the dye solution. Tests with bacteria. N o test bacteria were
detected in water from the hoses of any test u n its after op eratin g the handpiece w ith the head subm erged in a solution of test bacteria w ith the cooling spray, or b oth the cooling spray an d chip air activated. N o test bacteria were detected in water sam ples collected from the disinfected handpieces removed from 24 of 25 test units. T w enty CFU of test bacteria were detected in the w ater spray from one handpiece removed from a unit. Tests after patient treatment. N o oral bac
teria were detected in 2 m L of sterile water flushed w ith a needle an d syringe th ro u g h 25 handpieces after their use to treat patients at 25 of the separate test units. Visual tests. Plastic capillary tu b in g was
fitted tightly into the openings of the a ir / w ater supply lines in the hose ends of eight test units. Ends of the tubes were sub merged in red tem pera solution, w hile the rheostat was pressed on an d off three times. No retraction of red solution could be
RESEARCH
o b serv ed . H ow ever, a p p ro x im a te ly a m icroliter (a barely visible am ount) of dye could be seen in the last 1 to 2 m m of the tip in each capillary. T h is was washed away d u rin g thorough cleaning, by the m eth o d described to clean an d disinfect used handpieces. T h e several m illiliters of dye aspirated by two uncorrected positive control u nits were not noticeably reduced by the cleaning procedure. Positive control tests. O ther lim ited tests
were also p erform ed w ith tw o older, uncorrected dental units m ade by another d en tal m a n u fa c tu re r before 1983 th a t served as positive study controls. T h e tests, perform ed w ith the red dye an d B subtilis b acterial test suspension in the same m an n er as reported here, serve as positive controls. A pproxim ately 5 or more m L of red tem pera test solution was aspirated by each u n it, in ten of ten trials w ith each unit. T est counts of B subtilis bacteria retracted into the hose lines ranged from 240 to 7,400 CFU per m L; counts of the test bacteria aspirated into the disinfected handpieces ranged from 370 to 880 per mL. A spiration tests of oral bacteria during clinical use were not done as the units were n ot considered safe to use u n til they had been corrected, w hich made them u nsat isfactory for positive controls. Conclusions
T h e first approach used in dentistry to control the potential risk of aspirating spatter in to w ater lines of high-speed handpieces was to try to remove aspirated microbes by operating the cooling spray after treatm ents. T he second was to insert a check valve in the water line in the dental u n it between the retraction valve and the h andpiece.10,11 T h is w ould let water flow o u t b u t n ot back into the line (for example, the com m only used check valve from the T ip le r Co). However, this valve is designed as an air check valve and can be clogged by debris or by grow th of aquatic bacteria from the w ater line. In another dental school in w hich check valves were installed several years before, m ost were found to be obstructed. Because the check valve is used to check negative pressure in a line, w hen it becomes clogged and leaks, saliva an d co n tam in atio n can once again be aspirated in to the handpiece and tubing leading to the dental unit. U nits in w hich asp iratio n has been corrected w ith this type of valve should be tested w ith red dye s o lu tio n p e rh a p s m o n th ly , to verify continued correction. An alternative m echanism to prevent
aspiration of m aterial from the m outh is a positive w ater shutoff system such as th at b u ilt into the new dental u n it system tested. T h is system sim ply stops the flow of w ater from the line. It cannot fail w ith o u t detection as spray w ater w ill ju st continue to flow u n til the u n it is shut off. An additional stream of ch ip air can aid in e x p e llin g c o n ta m in a tio n from the handpiece w hen cu ttin g is stopped. T h e new dental u n its tested appear to be capable of preventing oral contam ina tion of the w ater spray system inside the handpiece th a t could otherw ise be caused by asp ira tio n 11; it appeared to be com pletely capable of preventing retraction of any test fluid back in to the water spray line housed in the high-speed handpiece hose. In 25 of 25 u nits tested clinically, any bacteria im bibed in the handpiece cooling spray orifices were uniform ly removed or killed by the scrubbing and disinfection. O nly a sm all am o u n t of test bacilli (ten CFU) was detected in one water sam ple from one of 25 handpiece heads subm erged and operated in the test solution that contained more th an 100,000 CFU bacilli per mL. T h e absence of bacteria in water collected from the hose line of th at u n it im m ediately after operating the handpiece in the bacterial suspension suggests that the sm all num ber of bacteria detected in the handpiece sam ple escaped the process of externally cleaning an d disinfecting the handpiece. P ositive co n tro l tests p e r form ed w ith an older, uncorrected dental u n it agreed w ith unreported data collected several years ago an d w ith findings of Bagga and oth ers,11 w hich showed exten sive a s p ira tio n of saliv a b a c te ria by retraction valves in uncorrected cooling spray systems m anufactured by five m ajor dental u n it m anufacturers. Iso p ro p y l alco h o l was fo u n d to be effective in k illin g the vegetative test bacteria and saliva streptococci on the handpiece in this an d previous studies, w hen it was ap p lied as a double wet-scrub, allo w in g ap p ro x im ately 2 m in u tes of contact tim e w ith the well cleaned item. A lthough isopropyl alcohol used in this way can be effective in k illin g some sim ple vegetative bacteria, it is n o t recommended as a ro u tin e c lin ic a l d isin fe cta n t for handpieces. It dries quickly an d is not considered adequate to inactivate hepatitis B an d other serious h y d ro p h ilic viral pathogens encountered in dentistry in a brief period of contact. T h e new dental u n it system tested was n ot intended to elim inate the need for sterilization of used handpieces, or a t least
REPORTS
their th o ro u g h cleaning an d disinfection, according to current CDC guidelines.5 But the results indicate that the new u n it c o n tro l system tested is effectiv e in protecting the u n it w ater from contam i n atio n w ith oral m icroorganism s, an d can protect p atien ts from risks of cross co n tam in atio n if handpieces are adequately prepared for reuse. Evidence collected by Bagga an d o th ers11 show th at the retraction of handpiece w ater spray is a p o ten tial problem w ith m any dental units th at may n o t have been corrected an d are still in wide use in the U nited States.
-----------------JÜOA ----------------T h is sludy was supp o rted by Pelton & C rane Co, C harlotte, NC. In f o r m a tio n a b o u t th e m a n u fa c tu re rs o f the products m en tioned in this article may be available from the authors. N either the au th o rs n o r the A m erican D ental A ssociation has any com m ercial interests in the products m entioned. Dr. C raw ford is professor, an d director, clinical oral m icrobiology laboratory, an d Ms. B roderius is a bacteriologist, d epartm ent of endodontics, U niversity of N o rth C arolina, School of D entistry, C hapel H ill, N C 27514. A ddress req u ests for re p rin ts to Dr. Crawford. 1. A llen, A.Z., a n d B ryan, R .J. O c cu lt b lo o d accu m u latio n u n d er fingernails: a m echanism for the spread of blood-borne infection. JADA 105(3):455-459, 1982. 2. A u tio , K .L ., a n d o th ers. S tu d ies o n c ro ss c o n tam in atio n in the dental clinic. JADA 100(3):358361, 1980. 3. C raw ford, J.J . Sterilization, disin fectio n an d asepsis in dentistry. In Block, S.S., ed. D isinfection, sterilization a n d preservation, ed 3. P h ilad elp h ia, Lea 8c Febiger, 1983, p p 505-523. 4. C raw ford, J. State-of-the-art: practical infection control in dentistry. JAD A 110(4):629-633, 1985. 5. C enters for Disease C o ntrol, US D epartm ent of H ealth and H u m a n Services, Pu b lic H ealth Service. R ecom m ended infection-control practices for den tist ry. M MW R 35(14):237-242, 1986. 6. C otto n e, J.A. In fection co n tro l in dentistry. Proceedings: N atio n al conference on infection control in dentistry, C hicago, 1986. A tlanta, US D epartm ent of H ealth an d H u m a n Services, Pu b lic H ealth Service, Centers for Disease C ontrol, 1986, p p 36-43. 7. C raw ford, J.J. C linical asepsis in dentistry, ed 3. M esquite, T X , R. A. Kolstad, 1987. 8. C enters for Disease C ontrol, US D epartm ent of H ealth an d H u m a n Services, Pu b lic H ealth Service. H ep atitis surveillance, 1982-1983. M M W R 34:1SS10SS, 1985. 9. A bel, L .C ., a n d o th e rs. S tu d ies o n d e n ta l aerobiology: bacterial c o n tam in atio n of w ater used by dental handpieces. J D ent Res 50:1567-1569, 1971. 10. A m erican D e n tal A sso ciatio n , C o u n c il o n D ental T h erapeutics, and C ouncil o n D ental M aterials a n d Devices. Infection control in the dental office. JADA 97(4):673-677, 1978. 11. B agga, B.S., a n d others. C o n ta m in atio n of dental u n it co o lin g w ater w ith oral m icroorganism s a n d its prevention. JADA 109(5):712-716, 1984.
C raw ford-B roderius : C R O SS-IN FE C TIO N RISKS: PR E V E N T IO N O F W A T ER R E T R A C T IO N ■ 687
REPORTS
A new dental u n it control system w as fo u n d to overcome the p o ssib ility o f m echanically retracting bacteria fro m the m o u th into the w ater lin e used to provide a spray o f w ater to cool high-speed burs during treatm ents. T h is was dem onstrated by results obtained after clinical use and after use in sim ulated, worst case test conditions u sin g a red tem pera indicator solution a nd indicator bacteria.
Control of cross-infection risks in the dental operatory: prevention of water retraction by bur cooling spray systems James J. Crawford, MA, PhD Cindy Broderius, ASCP
" ith o u t adequate aseptic pre cautions, various routes can transfer infections between the dental operatory. H ands, instrum entation, a n d eq u ip m en t routinely become soiled w ith saliva and blood, and they are used repeatedly in the m ouths of 20 to 40 or m ore persons each day. Intrao ral treat m ents are perform ed w ith in strum entation th at routinely penetrates oral tissues, and w ith com plex eq u ip m en t that is difficult to clean and sterilize. Blood and saliva persist beneath fingernails of ungloved operators, and saliva-borne m icroorga nism s adhere to dental u n it eq u ip m en t th a t is handled d u rin g treatm ent.1”3 Infection risks for dental personnel are adm ittedly h ig h .4-6 T he im portance of p ro tec tin g p atien ts, as w ell as dental personnel, has been addressed by the US P ublic H ealth Service in the guidelines on infection control and elsewhere.5 8 T h is report discusses another possible m e c h a n ism of cross c o n ta m in a tio n addressed in the C enters for D isease C o n tro l (C D C ) g u id e lin e s a n d e ls e w h ere.3,5,6 It describes the in a d v erten t asp iratio n of saliva, blood, or debris by a w ater spray retraction device b u ilt into a d e n ta l u n it. U n less th e system is adequately flushed between treatm ents, it is possible for oral debris collected from
W
a p atient to be expelled into the m outh of the next patient. T h e CDC guidelines recom m end correcting this problem w ith a check v alv e.5 T h is m ay p ro v id e a tem porary solution th at requires interm it tent testing to verify proper function. T h is article provides test data on the effectiveness of a new com m ercial dental u n it to prevent asp iratio n of oral fluids by the water spray system used to cool high-speed burs, using a m ethod that elim inates water retraction an d aspiration. W hen handpieces were developed to drive burs for cu ttin g teeth at h ig h speeds, an opening was placed in the handpiece near the bu r from w hich a spray of water and air was delivered to cool the b u r and to p ro tec t the u n d e rly in g p u lp from therm al dam age. T h e plastic tu b in g first used in the handpiece hoses apparently expanded under the pressure involved in delivering the water spray. W hen the bur and spray were stopped, w ater pressure dropped, tubin g gradually contracted, and w ater continued to d rip from the h a n d piece as it was removed from the p a tie n t’s m o u th , p o ssib ly s p o ttin g a p a tie n t’s clothing. T he prevailing m ethod initially used by m ost m anufacturers to prevent d rip p in g was to provide a sm all, pistona ctiv ated , neg ativ e p ressu re (su ctio n ) device w ithin the u n it th at was activated
each tim e the b u r an d spray were stopped. T h is device w ould in stan tly draw w ater back u p from the o p en in g adjacent to the bur, plus u p to 10 m L of air an d any spattered saliva or blood. T h is process has been referred to as w ater retraction, and the result as asp iratio n , or m ore g ra p h i cally as “suckback.” Abel an d others9 were the first to detect oral bacteria in co o lin g spray w ater from high-speed handpieces after dental treat m ents (Streptococcus m itis was detected in 26%, S salivarius in 16%, enterococci in 40%). W ith a m arker dye, cultures of m arker b a c te ria w ere p la c e d in a tr e a tm e n t m an ik in to detect asp iratio n . C linical tests of asp iratio n of p atien ts’ oral bacteria were perform ed in private offices. It was also docum ented th at five m ajo r brands of dental units m anufactured before 1978 show ed asp iratio n (Craw ford, J., u n p u b lished data, 1978). Based p artly on this u n p u b lish ed data, reported to the A m er ican D ental A ssociation (ADA), recom m endations to correct this p o ten tial for cross co n tam in atio n were p ublished by the ADA in 1978, an d were later confirm ed an d published by Bagga an d o th ers.10,11 T h e re w ere tw o o b je ctiv es in th is investigation: to evaluate the ability of the test dental u n it co n tro l system (Spirit JA D A , V o l. 116, M ay 1988 ■ 685
RESEARCH
REPORTS
D ental U n it Controls, P elton 8c Crane Co) to reliably prevent extensive retraction of oral bacteria in to the handpiece under conditions of clinical use, an d retraction of indicator dye and bacterial test solutions in to the handpiece and hose line under the “w orst possible” experim ental in vitro test situations; and to determ ine if the test system could help overcome the contam in a tio n p ro b le m of passive ca p illary asp iratio n of oral fluids back into the handpiece. It is im p o r ta n t to u n d e rs ta n d the difference between this possible, passive capillary asp iratio n of oral fluids, and their retraction by the high-speed h a n d piece co o lin g spray retraction system. C apillary asp iratio n can result whenever the o p en in g of any sm all-diam eter, “wettable” tu b in g contacts a liquid. Forces of surface tension spontaneously cause low surface tension fluid to enter such an opening. In this m anner, sm all am ounts of flu id can be im bibed into any w ater/ air coo lin g spray openings (or into any o th e r o p enings) on the handpiece by capillary action. T h is is not caused by any m echanical activity of the handpiece or un it. T h o ro u g h cleaning and disinfecting of the outside of the handpiece may clean an d decontam inate these openings and help control this source of contam ination. Sterilization of the handpiece by heat or gas is preferred an d is the only reliable m ethod to assure control of contam ination associated w ith this capillary action.5 Methods and materials
W ater sam ples were collected from the high-speed handpiece cooling w ater spray system an d handpiece tub in g before and a fte r th re e types of te st o p e r a tio n procedures: —T u rn in g the handpiece and w ater spray on a n d off repeatedly for 10 seconds w ith the head of the handpiece subm erged in “ test dye” solution (red tem pera dye, Palm er Co, d iluted in water). —T u rn in g a sterilized handpiece and water spray on an d off three times w hile keeping the head of the handpiece sub m erged in broth suspension containing m ore th a n 100,000 colony form ing units of Bacillus subtilis var niger per m illiliter. —T reatm ents of dental patients. These consisted of p rep arin g teeth for crowns and o th e r restorative treatm ents perform ed w ith o u t a rubber dam. In each type of test, handpieces were tightly attached to hose end fittings. For tests of B subtilis aspiration, a sterile test tube was used to aseptically collect a 10686 ■ JADA, Vol. 116, May 1988
m L spray-w ater sam ple from the h a n d piece before the test procedure. After the procedure, 10 m L of water was collected from the end of the disconnected hose an d cultured to detect any aspiration back into the hose. T h e w ater spray was th en operated for 1 m inute to clear the line. T h e handpiece was reattached to the hose and only the surface of the handpiece was cleaned and disinfected for 2 m inutes w ith 70% isopropyl alcohol. T h is procedure was a d e q u a te to e lim in a te co u n ts of the vegetative test bacteria of concern on the surfaces of handpieces to zero, 20 of 20 times. T h en 2 m L of w ater was collected from the handpiece spray o p en in g to detect bacteria aspirated just in to the handpiece. S im ilar procedures were used to detect asp ira tio n of oral streptococci d u rin g clinical treatments. However, after treat m ents, the outside of the handpiece was disinfected an d removed from the hose an d 1 m L of sterile water was flushed th ro u g h the handpiece spray tube w ith a tuberculin syringe to co llect an y a sp ira te d o ral streptococci. For detection of dye asp iratio n , the handpiece was operated in the test dye solution, the outside of the handpiece was cleaned, and the handpiece was removed from its hose. A pproxim ately 0.5 m L of w ater was collected from the hose end an d exam ined on w hite paper to detect any dye aspirated in to the hose line; the line was flushed for a m inute, and the handpiece was replaced. From the handpiece, 0.5 m L of water was collected to detect aspiration of dye lim ited to the handpiece. T h irty dental u nits were tested in dental school clinics. These were equip p ed w ith a positive closure valve to cut off water flow w hen the rheostat is released an d no form of retraction. T hey are also equip p ed w ith a chip air feature in the air supply to the handpiece th at can be activated independently to blow a stream of air over the bur through an op en in g it shares w ith the w ater spray. It continues to blow for a m om ent after the foot control is released. W hen activated along w ith the w ater spray, and the water and b u r are stopped, the chip air continues to blow, blow ing away the last drop of the spray water. T w o units were used as positive test co n tro ls; these were n o t corrected to prevent aspiration of oral debris, were m anufactured by a m ajor dental m anufac turer before 1983, and were equip p ed w ith functio n in g water spray retraction valves typical of many brands of units made in recent years. T est dye so lu tio n was p rep ared by d ilu tin g fluorescent red tem pera water-
soluble poster p ain t, 1:50 in tap water. B acillus subtilis var niger cultures used in bacterial asp iratio n tests were vegetative cultures grow n for 24 hours in trypticase soy broth for 24 hours a t 37 C an d adjusted to a concentration of approxim ately 106 colony-form ing u nits (CFU). Sam ples for cu ltu re from treatm en t procedures were vortexed at h ig h speed for 30 seconds, a n d d ilu tio n s were prepared. From the o rig in al an d each d ilu tio n , 0.1 m L was spread on separate agar plates, incubated w ith 5% carbon dioxide for 24 h r at 37 C, and colonies were counted. C olum bia-N alidixic Acid agar (BectonD ickinson Co), in addition to sheep blood agar, was used to culture clinical samples to help detect oral streptococci and restrict colony grow th of nonoral, aq u atic bacteria th at could obscure oral species. Sam ples to detect B subtilis were inoculated on b lood agar plates and incubated in air at 37 C. T h e capillary effect was tested by in se rtin g 1-mm diam eter polyethylene can n u latio n tu b in g in to the air an d water ports in the hose line in place of the handpiece.
Results Tests with test indicator dye. N o test dye was
detected in w ater from hoses or handpieces from any of 30 test u nits after repeated activation of the handpieces w ith their w ater spray orifice subm erged in the dye solution. Tests with bacteria. N o test bacteria were
detected in water from the hoses of any test u n its after op eratin g the handpiece w ith the head subm erged in a solution of test bacteria w ith the cooling spray, or b oth the cooling spray an d chip air activated. N o test bacteria were detected in water sam ples collected from the disinfected handpieces removed from 24 of 25 test units. T w enty CFU of test bacteria were detected in the w ater spray from one handpiece removed from a unit. Tests after patient treatment. N o oral bac
teria were detected in 2 m L of sterile water flushed w ith a needle an d syringe th ro u g h 25 handpieces after their use to treat patients at 25 of the separate test units. Visual tests. Plastic capillary tu b in g was
fitted tightly into the openings of the a ir / w ater supply lines in the hose ends of eight test units. Ends of the tubes were sub merged in red tem pera solution, w hile the rheostat was pressed on an d off three times. No retraction of red solution could be
RESEARCH
o b serv ed . H ow ever, a p p ro x im a te ly a m icroliter (a barely visible am ount) of dye could be seen in the last 1 to 2 m m of the tip in each capillary. T h is was washed away d u rin g thorough cleaning, by the m eth o d described to clean an d disinfect used handpieces. T h e several m illiliters of dye aspirated by two uncorrected positive control u nits were not noticeably reduced by the cleaning procedure. Positive control tests. O ther lim ited tests
were also p erform ed w ith tw o older, uncorrected dental units m ade by another d en tal m a n u fa c tu re r before 1983 th a t served as positive study controls. T h e tests, perform ed w ith the red dye an d B subtilis b acterial test suspension in the same m an n er as reported here, serve as positive controls. A pproxim ately 5 or more m L of red tem pera test solution was aspirated by each u n it, in ten of ten trials w ith each unit. T est counts of B subtilis bacteria retracted into the hose lines ranged from 240 to 7,400 CFU per m L; counts of the test bacteria aspirated into the disinfected handpieces ranged from 370 to 880 per mL. A spiration tests of oral bacteria during clinical use were not done as the units were n ot considered safe to use u n til they had been corrected, w hich made them u nsat isfactory for positive controls. Conclusions
T h e first approach used in dentistry to control the potential risk of aspirating spatter in to w ater lines of high-speed handpieces was to try to remove aspirated microbes by operating the cooling spray after treatm ents. T he second was to insert a check valve in the water line in the dental u n it between the retraction valve and the h andpiece.10,11 T h is w ould let water flow o u t b u t n ot back into the line (for example, the com m only used check valve from the T ip le r Co). However, this valve is designed as an air check valve and can be clogged by debris or by grow th of aquatic bacteria from the w ater line. In another dental school in w hich check valves were installed several years before, m ost were found to be obstructed. Because the check valve is used to check negative pressure in a line, w hen it becomes clogged and leaks, saliva an d co n tam in atio n can once again be aspirated in to the handpiece and tubing leading to the dental unit. U nits in w hich asp iratio n has been corrected w ith this type of valve should be tested w ith red dye s o lu tio n p e rh a p s m o n th ly , to verify continued correction. An alternative m echanism to prevent
aspiration of m aterial from the m outh is a positive w ater shutoff system such as th at b u ilt into the new dental u n it system tested. T h is system sim ply stops the flow of w ater from the line. It cannot fail w ith o u t detection as spray w ater w ill ju st continue to flow u n til the u n it is shut off. An additional stream of ch ip air can aid in e x p e llin g c o n ta m in a tio n from the handpiece w hen cu ttin g is stopped. T h e new dental u n its tested appear to be capable of preventing oral contam ina tion of the w ater spray system inside the handpiece th a t could otherw ise be caused by asp ira tio n 11; it appeared to be com pletely capable of preventing retraction of any test fluid back in to the water spray line housed in the high-speed handpiece hose. In 25 of 25 u nits tested clinically, any bacteria im bibed in the handpiece cooling spray orifices were uniform ly removed or killed by the scrubbing and disinfection. O nly a sm all am o u n t of test bacilli (ten CFU) was detected in one water sam ple from one of 25 handpiece heads subm erged and operated in the test solution that contained more th an 100,000 CFU bacilli per mL. T h e absence of bacteria in water collected from the hose line of th at u n it im m ediately after operating the handpiece in the bacterial suspension suggests that the sm all num ber of bacteria detected in the handpiece sam ple escaped the process of externally cleaning an d disinfecting the handpiece. P ositive co n tro l tests p e r form ed w ith an older, uncorrected dental u n it agreed w ith unreported data collected several years ago an d w ith findings of Bagga and oth ers,11 w hich showed exten sive a s p ira tio n of saliv a b a c te ria by retraction valves in uncorrected cooling spray systems m anufactured by five m ajor dental u n it m anufacturers. Iso p ro p y l alco h o l was fo u n d to be effective in k illin g the vegetative test bacteria and saliva streptococci on the handpiece in this an d previous studies, w hen it was ap p lied as a double wet-scrub, allo w in g ap p ro x im ately 2 m in u tes of contact tim e w ith the well cleaned item. A lthough isopropyl alcohol used in this way can be effective in k illin g some sim ple vegetative bacteria, it is n o t recommended as a ro u tin e c lin ic a l d isin fe cta n t for handpieces. It dries quickly an d is not considered adequate to inactivate hepatitis B an d other serious h y d ro p h ilic viral pathogens encountered in dentistry in a brief period of contact. T h e new dental u n it system tested was n ot intended to elim inate the need for sterilization of used handpieces, or a t least
REPORTS
their th o ro u g h cleaning an d disinfection, according to current CDC guidelines.5 But the results indicate that the new u n it c o n tro l system tested is effectiv e in protecting the u n it w ater from contam i n atio n w ith oral m icroorganism s, an d can protect p atien ts from risks of cross co n tam in atio n if handpieces are adequately prepared for reuse. Evidence collected by Bagga an d o th ers11 show th at the retraction of handpiece w ater spray is a p o ten tial problem w ith m any dental units th at may n o t have been corrected an d are still in wide use in the U nited States.
-----------------JÜOA ----------------T h is sludy was supp o rted by Pelton & C rane Co, C harlotte, NC. In f o r m a tio n a b o u t th e m a n u fa c tu re rs o f the products m en tioned in this article may be available from the authors. N either the au th o rs n o r the A m erican D ental A ssociation has any com m ercial interests in the products m entioned. Dr. C raw ford is professor, an d director, clinical oral m icrobiology laboratory, an d Ms. B roderius is a bacteriologist, d epartm ent of endodontics, U niversity of N o rth C arolina, School of D entistry, C hapel H ill, N C 27514. A ddress req u ests for re p rin ts to Dr. Crawford. 1. A llen, A.Z., a n d B ryan, R .J. O c cu lt b lo o d accu m u latio n u n d er fingernails: a m echanism for the spread of blood-borne infection. JADA 105(3):455-459, 1982. 2. A u tio , K .L ., a n d o th ers. S tu d ies o n c ro ss c o n tam in atio n in the dental clinic. JADA 100(3):358361, 1980. 3. C raw ford, J.J . Sterilization, disin fectio n an d asepsis in dentistry. In Block, S.S., ed. D isinfection, sterilization a n d preservation, ed 3. P h ilad elp h ia, Lea 8c Febiger, 1983, p p 505-523. 4. C raw ford, J. State-of-the-art: practical infection control in dentistry. JAD A 110(4):629-633, 1985. 5. C enters for Disease C o ntrol, US D epartm ent of H ealth and H u m a n Services, Pu b lic H ealth Service. R ecom m ended infection-control practices for den tist ry. M MW R 35(14):237-242, 1986. 6. C otto n e, J.A. In fection co n tro l in dentistry. Proceedings: N atio n al conference on infection control in dentistry, C hicago, 1986. A tlanta, US D epartm ent of H ealth an d H u m a n Services, Pu b lic H ealth Service, Centers for Disease C ontrol, 1986, p p 36-43. 7. C raw ford, J.J. C linical asepsis in dentistry, ed 3. M esquite, T X , R. A. Kolstad, 1987. 8. C enters for Disease C ontrol, US D epartm ent of H ealth an d H u m a n Services, Pu b lic H ealth Service. H ep atitis surveillance, 1982-1983. M M W R 34:1SS10SS, 1985. 9. A bel, L .C ., a n d o th e rs. S tu d ies o n d e n ta l aerobiology: bacterial c o n tam in atio n of w ater used by dental handpieces. J D ent Res 50:1567-1569, 1971. 10. A m erican D e n tal A sso ciatio n , C o u n c il o n D ental T h erapeutics, and C ouncil o n D ental M aterials a n d Devices. Infection control in the dental office. JADA 97(4):673-677, 1978. 11. B agga, B.S., a n d others. C o n ta m in atio n of dental u n it co o lin g w ater w ith oral m icroorganism s a n d its prevention. JADA 109(5):712-716, 1984.
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