- Email: [email protected]
Control of microbial contamination with commercially available cleaning solutions
f microbial contamination cleaning solutions Mansour Assery, Gerald N. Graser, Eastman
Dental
Center,
BDS,a P. Colm Sugrue, DDS, MS,b and Arthur Rochester,
with
BDS,a D. Eisenberg,
commercia
PhDC
N.Y.
The elimination of cross-contamination from operatory to laboratory is required for effective infection control. This study determined whether microbial crosscontamination occurs during cleaning of dental prostheses with an ultrasonicator and examined ways to reduce or eliminate the contamination that might occur. The antimicrobial activities of a temporary cement remover and tartar and st: :n remover were compared with deionized water and a known strong antimicrobial agent. All solutions were assessed without and with ultrasonication. The microbitidal strains were cultured in brain-heart infusion broth, with and without acrylic resin slabs, and the organisms were killed either without or with sonication and without or with acrylic resin slabs. Further testing with natural plaque-contaminated denture materials is warranted. (J PROSTHET DENT 1992;67:275-7.)
I
n the light of current concerns regarding the spread of infectious diseases, we have become more aware of various routes of cross-contamination outside the dental operatory, facilitated by the dentist and dental auxillary personne1.l It is known that prostheses may become contaminated by microorganisms at various stages of fabrication,2-5 and that these contaminated prostheses can spread microorganisms to other materials, equipment, and personnel.6-g Possible mechanisms of prevention of such spread have also been investigated.lO-l2 Transfer of oral flora to the dental laboratory and its laboratory personnel has been widely reported.2-4, 7, I33l4 0 ne investigator identified a contaminated prosthesis as the source of an outbreak of mycoplasmal pneumonia in a dental laboratory.15 These data underlie the importance of proper infection control practices in the dental laboratory. Some of the solutions used in the fabrication and/or repair of prostheses would be anticipated to be highly toxic to bacteria and might be effective disinfecting agents on their own. These solutions can be acidic or basic detergents containing sodium hydroxide, tetrasodium ethylene diamine, sulfuric acid, alkyl ammonium chloride, or isopropyl alcohol. The purpose of this investigation was to assess the antimicrobial activities of two commonly used solutions against important oral pathogens.
aFormer postdoctoral student, Department of Prosthodontics. bChairman, Department of Prosthodontics; Senior Clinician, Senior Research Associate, Eastman Dental Center; Associate Professor, Department of Dental Research, University of Rochester. ‘Former Head, Microbiology Section, Department of Oral Biology, currently Associate Research Director, The Council for Tobacco Research-U.S.A., Inc., New York, N.Y. 10/1/31364
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
I.
support
Ability of test solution/BHI mixtures growth of S. mutans or C. albicans Organisms
Test solution Deionized
Concentration water
No added cells
S. mutans
to added eT7.albicam
1 ml nl
cl*
4
4
FS 10% 1%
0 0 0
0 0
0 0
4
4
0.1%
0
4
4
0.01% FS
0
4
4
DM
DM 0 0
0.1%
0 0 0
DM 0
0.01%
0
4
4
FS 10% 1% 0.1% 0.01%
PPT 0 0 0 0
PPT 0 0
PPT 0 0
(control)
TCR
SPOR
10% 1%
TSR
0
4 4
4
4
4
4
One ml of test solution at indicated concentration was added to 9 ml of BHI with 0.01 ml of culture inoculum. FS, full strength; DM, denatured media (media turned dark brown); PPT, precipitated or coagulated media components; 1 ml nl, 1 ml test/total ml. *Number of tubes showing cell growth out of total of four tubes for each test.
MATERIAL Organisms
AND
METHODS
and growth
conditions
Candida albicans (ATCC 44505) and Streptococcus mutans GS-5 were selected for the study-C. albicans because of its relationship to denture-induced stomatitis and S. mutans because of its role in the etiology of dental caries. S. mutans and C. albicans were cultured anaerobically
275
ASSERY
Table
Effect of lo-minute
II.
ET AL
exposure to test solution followed by inoculation into nutrient media that permitted
growth No sonication Control
1% TCR 0.1% TSR
Table
of positive
III.
C. albicans
mutans
0 0 0 0 0
1% SPOR 0.01% SPOR DDW Numbers
s.
Sonication
0 0 0 10
tubes out of possible
Effect of acrylic resin samples on cell No sonication TCR
TSR
0 0
0
0
0
0
S. mutans C. albicans Numbers
indicate
positive
SPOR
cell growth
Sonication DDW
TCR
TSR
10 10
0 0
0 0
from total of
SPOR 0 0
DDW 10 10
10.
(by useof Gas Pak jars; BBL, Cockeysville, MD.) or aerobically, at 37” C in brain-heart infusion broth (BHI) (Difco Laboratories, Detroit, Mich.). Determination of test solution compatibility with BHI culture medium. Because temporary cement remover (TCR), tartar and stain remover (TSR) (Healthco International, Boston, Mass.), or Sporicidin (SPOR) (Sporicidin International, Rockville, Md.) might denature culture media or otherwise render BHI broth nonsupportive of cell growth, the compatibility of each test solution wasdetermined with BHI broth. Serial dilutions wereused of each test solution, TCR and TSR, and of the positive control, SPOR. Full-strength, 10% , 1% , 0.1%, and 0.01% dilutions in water of each test solution were prepared. These solutions were diluted again 1:lO into BHI. To determine the strongest TCR, TSR, and SPOR concentrations that would allow S. mutans and C. albicans to grow, 1 ml of each dilution of each test solution, control, and 0.01 ml of an overnight culture of S. mutans or C. albicans were incubated for 48 hours. Test solutions and controls. The TCR test solution contains sodium hydroxide and the TSR test solution contains sulfamic acid, alkyl dimethyl benzyl ammonium chloride, and isopropyl alcohol. Sporicidin is an alkaline preparation of 2% glutaraldehyde with phenolic buffer. Deionized water (DDW) acted as a control. Preparation of acrylic resin samples. Acrylic resin samples15 X 6 X 2 mm were prepared with a heat-cured acrylic resin (Ch Lucitone, Dentsply, York, Pa.) and sterilized by autoclaving for 20 minutes in an autoclave (Ritter, Sybron Corporation, Rochester, N.Y.). Determination of survival of test organisms after exposure to test solutions. Ziplock plastic bags (Dow 276
C. albicans
0 0 0 0 10
0 0 0 0 10
10 are shown.
survival
Organism
S. mutam
0 0 0 0 0
0 0 0 0 10
0
Control
ConsumerProducts, Inc., Indianapolis, Ind.) were sterilized in an ethylene oxide sterilizer. Forty-five milliliters of either test or control solution was added to each sterile Ziplock bag. These were inoculated with 5 ml of an early stationary-phase culture of S. mutans (~-10’ CFU) or C. albicans (>108 CFU). The test solution/inoculum mixture wasthen either sonicated (L and R Ultrasonicator model LU, Kearny, N.J.) or not sonicated for 10 minutes. An inoculum from each test solution (1 ml) was added to BHI culture broth in concentrations that did not denature or form precipitate in the growth medium and would allow growth of the organisms,aspreviously determined. Sterile water-treated controls always formed turbid cultures. Determination of the effect of acrylic resin samples on cell survival. To determine the effect of denture materials on the antimicrobial activity of test solutions, 10 sterile acrylic resin sampleswere addedto eachZiplock bag containing test/control solution and inoculum. These were either sonicatedfor 10 minutes or not sonicated,as previously described. Each acrylic resin samplewas removed, rinsed with sterile water, placed in BHI, and incubated as described. RESULTS Undiluted SPOR and TSR, but not TCR, denatured or precipitated culture medium componentswhen added to BHI. Cells of S. mutans or 6. albicans formed turbid cultures signifying growth when TCR, SPOR, or TSR solutions were present in the growth medium at 0.1% or less, Media used to test for the presenceof living cells always contained concentrations of TCR, SPOR, or TSR that would support growth. Addition to BHI broth of 1% or 0.1% solutions of TCR and TSR, respectively, permitted. growth of C. albicans and S. mutans. Only the 0.01% solution of SPOR permitted growth of both strains (Table I). Thus, S. mutans wasmore sensitive to SPOR than TCR or TSR and C. albicans wasmore sensitiveto TSR than TCR or SPOR. The lo-minute test period resulted in completekilling of S. mutans and C. albicans whether or not sonication was used (Table II). The results in Table III indicate that the acrylic resin samplescontaminated by the test organisms and subsequentlytreated with TCR, TSR, and SPOR harbored no live cells. This finding indicated that both organFEBRUARY
1992
VOLUME
67
NUMBER
2
CONTROL
isms were negative slabs. All each test
OF MICROBIAL
CONTAMINATION
killed by the test solutions TCR and TSR and the control, SPOR, in the presence of acrylic resin water-treated samples contained viable cells of species.
DISCUSSION The results of the experiments clearly indicated that TCR, TSR, and SPOR were effective, in the lo-minute test period, in killing viable cells of each test organism whether or not sonication was used. However, this finding cannot be construed to mean that sonication would not have an effect in vivo. Disinfecting ability is reduced in the presence of organic material or layers of microorganisms.16 For effective disinfection, an item must first be cleaned mechanically.17 Moreover, disaggregation of microorganisms due to sonication may play a significant role in disinfection.ls Disinfectants may be harmful to denture base resin, whether heat-cured or autocured. Some disinfectants are not suitable for use with denture base material and have been shown to have a permanent deleterious effect on resin surface morphology and to decrease rigidity.lQ Alternative disinfectants such as chlorine dioxide or sodium hypochlorite may be appropriate. l6 Further experimentation with natural plaque adherent to acrylic resin is warranted.
S. mutans and C. albicans cells alike were killed in 10 minutes, with or without sonication, by TCR and TSR as they were with a known disinfectant, SPOR. Cells on acrylic resin slabs were also killed by TCR, TSR, and SPOR. In the dental laboratory, TCR and TSR may kill oral bacteria that contaminate denture materials. REFERENCES 1. Runnells RR. An overview PROSTHETDENT~~S&~S:~~~-9.
I
THE
JOURNAL
of infection
control
in dental
Availability
practice.
2. Posti JJ. Bacterial contamination between dental surgery and dental lab. Suom Hammaslaak Toim 1970;66:49. 3. Posti JJ. Bacterial contamination between the dental surgery and dental lab. Zahntechnik 1970;28:358-9. 4. Wakefield CW. Laboratory contamination of dental prostheses. J PROSTHETDENT~S~~;~~:~~~-~. 5. Henderson C. Evaluation of the barrier system, an infection control system for the dental laboratory. J PROSTHET DENT 1987;58:517-21. 6. Fisher WT. Reducing laboratory contamination. J PROSTHET DBNT 1972;27:221. 7. Lorato DC. Disinfection of pumice. J PROSTHET DENT 1967;18:534-5. 8. Eames W. A comparison of eight ultrasonic cleaners. Oper Dent 1980;5:118-24. 9. Perkulis B, Engelhard WE, Kramer WA. Ultrasonic and benzalkonium chloride as a method of sterilizing dental instruments. J Dent Child 1970;37:69-78. 10. Moore TC, Smith DE, Kenny GE. Sanitization of dentures by severai denture hveiene methods.J P~o~~~~~D~~~1984;52:158-63. 11. Rudd RW. Sterilization of complete dentures with sodium hypochlorite. J PROSTHET DENT 1984;51:318-21. 12. Dills SS, Olshan AM, Goldner S, Brogdon C. Comparison of the antimicrobial capability of an abrasive paste and chemical-soak denture c1eaners.J PROSTHET DENT 1988;60:467-70. 13. Khan RC. The microbiologic cross-contamination of dental prostheses. J PROSTHETDENT 1982;47:556-9. 14. Miller RL. Aerosols produced by dental instrumentation. First International Symposium on Aerobiology. Naval Biological Laboratory (ed). Berkeley: University of California, 1963. 15. Sanda MA. Point source epidemic of mycoplasma pneumoniae infection in a prosthodontic laboratory. Am Rev Respir Dis 1975;112:213-7. 16. Bell SA, Brockmann SL, Sackuvich DA. The effectiveness of two disinfectants on denture base acrylic resin with an organic load. J PROSTHET DENT 1989;61:580-3. 17. Guidelines for infection control in the dental office and the commercial dental laboratory. J Am Dent Assoc 1985;110:969-72. 18. Sierra G, Boucher RM. Ultrasonic synergistic effects in liquid-phase chemical sterilization. Appl Microbial 1971;22:160-4. 19. Shen C, Savid NS, Colaizzi FA. The effect of glutaraldehyde disinfectants on denture base acrylic resins. J PROSTHET DENT 1989;61:583-9. Reprint
requests
to:
DR.GERALD N.GRASER EASTMAN DENTAL CENTER 625E~~woonA1.x ROCHESTER,NY 14620
J
of JOURNAL back
issues,
1986-1991
Back issues of THE JOURNAL OF PROSTHETIC DENTISTRY are available for purchase from the publisher, Mosby-Year Book, Inc., at a cost of $7.00 per issue. (Foreign postage is not included.) The following quantity discounts are available: 25 % off on quantities of 12 to 23, and one third off on quantities of 24 or more. Please write to Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, or call (800)325-4177, ext. 4351, or (314)453-4351 for information on availability of particular issues for that period from 1980 to 1991. If unavailable from the publisher, photocopies of complete issues are available from University Microforms International, 300 N. Zeeb Rd., Ann Arbor, MI 48106, (313)761-4700.
OF
PROSTHETIC
DENTISTRY
Dental
Center,
BDS,a P. Colm Sugrue, DDS, MS,b and Arthur Rochester,
with
BDS,a D. Eisenberg,
commercia
PhDC
N.Y.
The elimination of cross-contamination from operatory to laboratory is required for effective infection control. This study determined whether microbial crosscontamination occurs during cleaning of dental prostheses with an ultrasonicator and examined ways to reduce or eliminate the contamination that might occur. The antimicrobial activities of a temporary cement remover and tartar and st: :n remover were compared with deionized water and a known strong antimicrobial agent. All solutions were assessed without and with ultrasonication. The microbitidal strains were cultured in brain-heart infusion broth, with and without acrylic resin slabs, and the organisms were killed either without or with sonication and without or with acrylic resin slabs. Further testing with natural plaque-contaminated denture materials is warranted. (J PROSTHET DENT 1992;67:275-7.)
I
n the light of current concerns regarding the spread of infectious diseases, we have become more aware of various routes of cross-contamination outside the dental operatory, facilitated by the dentist and dental auxillary personne1.l It is known that prostheses may become contaminated by microorganisms at various stages of fabrication,2-5 and that these contaminated prostheses can spread microorganisms to other materials, equipment, and personnel.6-g Possible mechanisms of prevention of such spread have also been investigated.lO-l2 Transfer of oral flora to the dental laboratory and its laboratory personnel has been widely reported.2-4, 7, I33l4 0 ne investigator identified a contaminated prosthesis as the source of an outbreak of mycoplasmal pneumonia in a dental laboratory.15 These data underlie the importance of proper infection control practices in the dental laboratory. Some of the solutions used in the fabrication and/or repair of prostheses would be anticipated to be highly toxic to bacteria and might be effective disinfecting agents on their own. These solutions can be acidic or basic detergents containing sodium hydroxide, tetrasodium ethylene diamine, sulfuric acid, alkyl ammonium chloride, or isopropyl alcohol. The purpose of this investigation was to assess the antimicrobial activities of two commonly used solutions against important oral pathogens.
aFormer postdoctoral student, Department of Prosthodontics. bChairman, Department of Prosthodontics; Senior Clinician, Senior Research Associate, Eastman Dental Center; Associate Professor, Department of Dental Research, University of Rochester. ‘Former Head, Microbiology Section, Department of Oral Biology, currently Associate Research Director, The Council for Tobacco Research-U.S.A., Inc., New York, N.Y. 10/1/31364
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
I.
support
Ability of test solution/BHI mixtures growth of S. mutans or C. albicans Organisms
Test solution Deionized
Concentration water
No added cells
S. mutans
to added eT7.albicam
1 ml nl
cl*
4
4
FS 10% 1%
0 0 0
0 0
0 0
4
4
0.1%
0
4
4
0.01% FS
0
4
4
DM
DM 0 0
0.1%
0 0 0
DM 0
0.01%
0
4
4
FS 10% 1% 0.1% 0.01%
PPT 0 0 0 0
PPT 0 0
PPT 0 0
(control)
TCR
SPOR
10% 1%
TSR
0
4 4
4
4
4
4
One ml of test solution at indicated concentration was added to 9 ml of BHI with 0.01 ml of culture inoculum. FS, full strength; DM, denatured media (media turned dark brown); PPT, precipitated or coagulated media components; 1 ml nl, 1 ml test/total ml. *Number of tubes showing cell growth out of total of four tubes for each test.
MATERIAL Organisms
AND
METHODS
and growth
conditions
Candida albicans (ATCC 44505) and Streptococcus mutans GS-5 were selected for the study-C. albicans because of its relationship to denture-induced stomatitis and S. mutans because of its role in the etiology of dental caries. S. mutans and C. albicans were cultured anaerobically
275
ASSERY
Table
Effect of lo-minute
II.
ET AL
exposure to test solution followed by inoculation into nutrient media that permitted
growth No sonication Control
1% TCR 0.1% TSR
Table
of positive
III.
C. albicans
mutans
0 0 0 0 0
1% SPOR 0.01% SPOR DDW Numbers
s.
Sonication
0 0 0 10
tubes out of possible
Effect of acrylic resin samples on cell No sonication TCR
TSR
0 0
0
0
0
0
S. mutans C. albicans Numbers
indicate
positive
SPOR
cell growth
Sonication DDW
TCR
TSR
10 10
0 0
0 0
from total of
SPOR 0 0
DDW 10 10
10.
(by useof Gas Pak jars; BBL, Cockeysville, MD.) or aerobically, at 37” C in brain-heart infusion broth (BHI) (Difco Laboratories, Detroit, Mich.). Determination of test solution compatibility with BHI culture medium. Because temporary cement remover (TCR), tartar and stain remover (TSR) (Healthco International, Boston, Mass.), or Sporicidin (SPOR) (Sporicidin International, Rockville, Md.) might denature culture media or otherwise render BHI broth nonsupportive of cell growth, the compatibility of each test solution wasdetermined with BHI broth. Serial dilutions wereused of each test solution, TCR and TSR, and of the positive control, SPOR. Full-strength, 10% , 1% , 0.1%, and 0.01% dilutions in water of each test solution were prepared. These solutions were diluted again 1:lO into BHI. To determine the strongest TCR, TSR, and SPOR concentrations that would allow S. mutans and C. albicans to grow, 1 ml of each dilution of each test solution, control, and 0.01 ml of an overnight culture of S. mutans or C. albicans were incubated for 48 hours. Test solutions and controls. The TCR test solution contains sodium hydroxide and the TSR test solution contains sulfamic acid, alkyl dimethyl benzyl ammonium chloride, and isopropyl alcohol. Sporicidin is an alkaline preparation of 2% glutaraldehyde with phenolic buffer. Deionized water (DDW) acted as a control. Preparation of acrylic resin samples. Acrylic resin samples15 X 6 X 2 mm were prepared with a heat-cured acrylic resin (Ch Lucitone, Dentsply, York, Pa.) and sterilized by autoclaving for 20 minutes in an autoclave (Ritter, Sybron Corporation, Rochester, N.Y.). Determination of survival of test organisms after exposure to test solutions. Ziplock plastic bags (Dow 276
C. albicans
0 0 0 0 10
0 0 0 0 10
10 are shown.
survival
Organism
S. mutam
0 0 0 0 0
0 0 0 0 10
0
Control
ConsumerProducts, Inc., Indianapolis, Ind.) were sterilized in an ethylene oxide sterilizer. Forty-five milliliters of either test or control solution was added to each sterile Ziplock bag. These were inoculated with 5 ml of an early stationary-phase culture of S. mutans (~-10’ CFU) or C. albicans (>108 CFU). The test solution/inoculum mixture wasthen either sonicated (L and R Ultrasonicator model LU, Kearny, N.J.) or not sonicated for 10 minutes. An inoculum from each test solution (1 ml) was added to BHI culture broth in concentrations that did not denature or form precipitate in the growth medium and would allow growth of the organisms,aspreviously determined. Sterile water-treated controls always formed turbid cultures. Determination of the effect of acrylic resin samples on cell survival. To determine the effect of denture materials on the antimicrobial activity of test solutions, 10 sterile acrylic resin sampleswere addedto eachZiplock bag containing test/control solution and inoculum. These were either sonicatedfor 10 minutes or not sonicated,as previously described. Each acrylic resin samplewas removed, rinsed with sterile water, placed in BHI, and incubated as described. RESULTS Undiluted SPOR and TSR, but not TCR, denatured or precipitated culture medium componentswhen added to BHI. Cells of S. mutans or 6. albicans formed turbid cultures signifying growth when TCR, SPOR, or TSR solutions were present in the growth medium at 0.1% or less, Media used to test for the presenceof living cells always contained concentrations of TCR, SPOR, or TSR that would support growth. Addition to BHI broth of 1% or 0.1% solutions of TCR and TSR, respectively, permitted. growth of C. albicans and S. mutans. Only the 0.01% solution of SPOR permitted growth of both strains (Table I). Thus, S. mutans wasmore sensitive to SPOR than TCR or TSR and C. albicans wasmore sensitiveto TSR than TCR or SPOR. The lo-minute test period resulted in completekilling of S. mutans and C. albicans whether or not sonication was used (Table II). The results in Table III indicate that the acrylic resin samplescontaminated by the test organisms and subsequentlytreated with TCR, TSR, and SPOR harbored no live cells. This finding indicated that both organFEBRUARY
1992
VOLUME
67
NUMBER
2
CONTROL
isms were negative slabs. All each test
OF MICROBIAL
CONTAMINATION
killed by the test solutions TCR and TSR and the control, SPOR, in the presence of acrylic resin water-treated samples contained viable cells of species.
DISCUSSION The results of the experiments clearly indicated that TCR, TSR, and SPOR were effective, in the lo-minute test period, in killing viable cells of each test organism whether or not sonication was used. However, this finding cannot be construed to mean that sonication would not have an effect in vivo. Disinfecting ability is reduced in the presence of organic material or layers of microorganisms.16 For effective disinfection, an item must first be cleaned mechanically.17 Moreover, disaggregation of microorganisms due to sonication may play a significant role in disinfection.ls Disinfectants may be harmful to denture base resin, whether heat-cured or autocured. Some disinfectants are not suitable for use with denture base material and have been shown to have a permanent deleterious effect on resin surface morphology and to decrease rigidity.lQ Alternative disinfectants such as chlorine dioxide or sodium hypochlorite may be appropriate. l6 Further experimentation with natural plaque adherent to acrylic resin is warranted.
S. mutans and C. albicans cells alike were killed in 10 minutes, with or without sonication, by TCR and TSR as they were with a known disinfectant, SPOR. Cells on acrylic resin slabs were also killed by TCR, TSR, and SPOR. In the dental laboratory, TCR and TSR may kill oral bacteria that contaminate denture materials. REFERENCES 1. Runnells RR. An overview PROSTHETDENT~~S&~S:~~~-9.
I
THE
JOURNAL
of infection
control
in dental
Availability
practice.
2. Posti JJ. Bacterial contamination between dental surgery and dental lab. Suom Hammaslaak Toim 1970;66:49. 3. Posti JJ. Bacterial contamination between the dental surgery and dental lab. Zahntechnik 1970;28:358-9. 4. Wakefield CW. Laboratory contamination of dental prostheses. J PROSTHETDENT~S~~;~~:~~~-~. 5. Henderson C. Evaluation of the barrier system, an infection control system for the dental laboratory. J PROSTHET DENT 1987;58:517-21. 6. Fisher WT. Reducing laboratory contamination. J PROSTHET DBNT 1972;27:221. 7. Lorato DC. Disinfection of pumice. J PROSTHET DENT 1967;18:534-5. 8. Eames W. A comparison of eight ultrasonic cleaners. Oper Dent 1980;5:118-24. 9. Perkulis B, Engelhard WE, Kramer WA. Ultrasonic and benzalkonium chloride as a method of sterilizing dental instruments. J Dent Child 1970;37:69-78. 10. Moore TC, Smith DE, Kenny GE. Sanitization of dentures by severai denture hveiene methods.J P~o~~~~~D~~~1984;52:158-63. 11. Rudd RW. Sterilization of complete dentures with sodium hypochlorite. J PROSTHET DENT 1984;51:318-21. 12. Dills SS, Olshan AM, Goldner S, Brogdon C. Comparison of the antimicrobial capability of an abrasive paste and chemical-soak denture c1eaners.J PROSTHET DENT 1988;60:467-70. 13. Khan RC. The microbiologic cross-contamination of dental prostheses. J PROSTHETDENT 1982;47:556-9. 14. Miller RL. Aerosols produced by dental instrumentation. First International Symposium on Aerobiology. Naval Biological Laboratory (ed). Berkeley: University of California, 1963. 15. Sanda MA. Point source epidemic of mycoplasma pneumoniae infection in a prosthodontic laboratory. Am Rev Respir Dis 1975;112:213-7. 16. Bell SA, Brockmann SL, Sackuvich DA. The effectiveness of two disinfectants on denture base acrylic resin with an organic load. J PROSTHET DENT 1989;61:580-3. 17. Guidelines for infection control in the dental office and the commercial dental laboratory. J Am Dent Assoc 1985;110:969-72. 18. Sierra G, Boucher RM. Ultrasonic synergistic effects in liquid-phase chemical sterilization. Appl Microbial 1971;22:160-4. 19. Shen C, Savid NS, Colaizzi FA. The effect of glutaraldehyde disinfectants on denture base acrylic resins. J PROSTHET DENT 1989;61:583-9. Reprint
requests
to:
DR.GERALD N.GRASER EASTMAN DENTAL CENTER 625E~~woonA1.x ROCHESTER,NY 14620
J
of JOURNAL back
issues,
1986-1991
Back issues of THE JOURNAL OF PROSTHETIC DENTISTRY are available for purchase from the publisher, Mosby-Year Book, Inc., at a cost of $7.00 per issue. (Foreign postage is not included.) The following quantity discounts are available: 25 % off on quantities of 12 to 23, and one third off on quantities of 24 or more. Please write to Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, or call (800)325-4177, ext. 4351, or (314)453-4351 for information on availability of particular issues for that period from 1980 to 1991. If unavailable from the publisher, photocopies of complete issues are available from University Microforms International, 300 N. Zeeb Rd., Ann Arbor, MI 48106, (313)761-4700.
OF
PROSTHETIC
DENTISTRY