Denial Research Factors affecting the stability of sodium hypochlorite solutions used to disinfect dental impressions Donald E. Gerhardt* / Henry N. Williams** Increased concern over the transmission of acquired immunodeficiency syndrome, hepa- titis B. herpes, and other diseases has prompted research into the disinfection of dental impressions. Among the factors to be considered when dental impressions are disinfected is the stability of the disinfectant .solutions during storage and use. This study is con- cerned with the effect on disinfectant solutions of repeated immersion of alginate dental impressions taken in metal trays. The effects of the impression materials, metal trays, and dilution were evaluated, and the impact of light, heat, and storage were also addressed. The findings indicated that in the test solutions, although considerable chlorine was consumed during the disinfection procedures, bactericidal activity was maintained, while in the control solution both chlorine content and bactericidal activity were remarkably stable. (Quintessence lnt, 1991:22:587-591.) Introduction Increased concern over the transmission of infectious diseases in the dental office, especially hepatitis B, acquired immunodeficiency syndrome, and herpes, has prompted the dental profession tc investigate aU possible routes of infection. One area of interest is the transmission of diseases to dental and laboratory per- sonnel via dental impressions and the stone casts made from these impressions. The effectiveness of this mode of transmission has been shown by Leung and Schon- feld,' and the matter of disinfecting dental impressions is now being addressed by the profession. Three important factors must be considered when dental impressions are disinfected: (!) how are the impression material and resultant cast affected, (2) how stable are the disinfectant solutions, and (3) how Assistant Professor, Department of Fixed Restorative Dentistry. Baltimore College of Dental Surgery, Dental School. University of Maryland, 656 West Baltimore Street. Baltimore, Maryland 21201. Associale Professor, Deparlmenl of Microbiology, Baltimore College of Dental Surgery, Dental School, University of Mary- land. effective are the disinfection procedures? The first con- sideration has been addressed by several studies that assessed the accuracy of stone casts made from algin- ate dental impressions disinfected in sodium hypo- chlorite (NaOCl) solutions." All studies concluded that the dimensional changes after disinfection are either insignificant or at least acceptable for most clin- ical applications. Assuming that immersing alginate impressions in NaOCl disinfecting solutions is clini- cally acceptable, the next question is how are these solutions affected hy the disinfecting procedures, and how long are they ahle to maintain their effectiveness (ie, how stable are the solutions)? Various internal and external factors that act on a disinfectant solution may alter the effectiveness of the disinfectant and influence the stability of the solution. The hterature suggests that chlorine solutions are inherently unstable and if used for disinfecting should be made fresh daily.^ However, other reports indicate that chlorine solutions are stable over long periods of time under varying conditions of storage and use.'"" Since studies have not addressed the stability of chlor- ine solutions as used in a clinical environment, many questions remain to be answered about the proper use of chlorine disinfectants. For example, can they be used indefinitely, or must they be discarded after a specific period of time? Quintessence Internationai Volume 22, Number 7/1991 587
Transcript
Denial Research
Factors affecting the stability of sodium hypochlorite solutions used todisinfect dental impressionsDonald E. Gerhardt* / Henry N. Williams**
Increased concern over the transmission of acquired immunodeficiency syndrome, hepa-titis B. herpes, and other diseases has prompted research into the disinfection of dentalimpressions. Among the factors to be considered when dental impressions are disinfectedis the stability of the disinfectant .solutions during storage and use. This study is con-cerned with the effect on disinfectant solutions of repeated immersion of alginate dentalimpressions taken in metal trays. The effects of the impression materials, metal trays,and dilution were evaluated, and the impact of light, heat, and storage were alsoaddressed. The findings indicated that in the test solutions, although considerablechlorine was consumed during the disinfection procedures, bactericidal activity wasmaintained, while in the control solution both chlorine content and bactericidal activitywere remarkably stable. (Quintessence lnt, 1991:22:587-591.)
Introduction
Increased concern over the transmission of infectiousdiseases in the dental office, especially hepatitis B,acquired immunodeficiency syndrome, and herpes,has prompted the dental profession tc investigate aUpossible routes of infection. One area of interest is thetransmission of diseases to dental and laboratory per-sonnel via dental impressions and the stone casts madefrom these impressions. The effectiveness of this modeof transmission has been shown by Leung and Schon-feld,' and the matter of disinfecting dental impressionsis now being addressed by the profession.
Three important factors must be considered whendental impressions are disinfected: (!) how are theimpression material and resultant cast affected, (2)how stable are the disinfectant solutions, and (3) how
Assistant Professor, Department of Fixed Restorative Dentistry.Baltimore College of Dental Surgery, Dental School. Universityof Maryland, 656 West Baltimore Street. Baltimore, Maryland21201.Associale Professor, Deparlmenl of Microbiology, BaltimoreCollege of Dental Surgery, Dental School, University of Mary-land.
effective are the disinfection procedures? The first con-sideration has been addressed by several studies thatassessed the accuracy of stone casts made from algin-ate dental impressions disinfected in sodium hypo-chlorite (NaOCl) solutions." All studies concludedthat the dimensional changes after disinfection areeither insignificant or at least acceptable for most clin-ical applications. Assuming that immersing alginateimpressions in NaOCl disinfecting solutions is clini-cally acceptable, the next question is how are thesesolutions affected hy the disinfecting procedures, andhow long are they ahle to maintain their effectiveness(ie, how stable are the solutions)? Various internal andexternal factors that act on a disinfectant solution mayalter the effectiveness of the disinfectant and influencethe stability of the solution.
The hterature suggests that chlorine solutions areinherently unstable and if used for disinfecting shouldbe made fresh daily.̂ However, other reports indicatethat chlorine solutions are stable over long periods oftime under varying conditions of storage and use.'""Since studies have not addressed the stability of chlor-ine solutions as used in a clinical environment, manyquestions remain to be answered about the proper useof chlorine disinfectants. For example, can they beused indefinitely, or must they be discarded after aspecific period of time?
Quintessence Internationai Volume 22, Number 7/1991 587
Dental Research
Assuming that chlorine disinfectants do lose theireffectiveness during a period of elinical use, what isthe critical factor: time, conditions of storage, or use?The answer to this question is extremely importantand could strongly infiuence disinfecting procedures.This study evaluates the effects of time, storage, anduse on the stability of chlorine solutions prepared todisinfect dental impressions,
iVIethod and materials
Clorox bleach (The Clorox Co), diluted 1:10 in chlo-rine-demand-free water, was used to prepare experi-mental and control solutions of sodium hypoehlorite.This dilution has been used in previous studies in-volving both surface and dental impression disinfec-tion.-'- Prior to testing, and after each set of 16 impres-sions was immersed in the experimental solution, de-terminations were made of the bactericidal activityand the amount of both total and free chlorine.
The experimental protocol consisted of makingimpressions of dentoform models using irreversiblehydroeolloid (alginate) impression material (Jeltrate,type 1, LD Caulk Co), The impressions were made inchrome-plated brass trays with soldered rims, washedin running tap water, and then '"disinfected" by im-mersion for 10 minutes in a 1-L volume of the 0.6%solution of NaOCl, A second liter of the solution waskept as a eontrol. Both solutions were stored at roomtemperature in opaque, covered containers exeept forthe testing periods, when both solutions were uncov-ered. A total of 80 impressions. 16 per day. were madeand immersed over a 5-day period.
Chlorine determinations were made using the DPD(n,n diethyl-p-phenylenediamine) eolormetric method(Spectrokit Reagent Systems, Milton Roy Co) priorto the start of testing and each day after 16 impressionshad been immersed. Measurements of absorbancewere obtained in a Spectronic 20 photometer (Bausch& Lomh, Inc), Absorbance readings obtained fromthe photometer were converted to milligrams per literof chlorine using conversion tables supplied with thechlorine testmg kit. The percentage of chlorine andthe parts per milhon of chlorine in each of the solu-tions were derived from these figures. Freshly dilutedsolutions used in this study contained 0,60% totalchlorine (6,000 ppm) and 0,45% free chlorine (4,500ppm).
The bactericidal activity of the disinfectant wasevaluated each day, after 16 impressions had heen im-mersed, A sterile, blank, round disk, measuring 10 mm
in diameter, was held with forceps and momentarilyimmersed in the disinfectant solution. The disk wasremoved and drained by pressing it to the sides of thevessel containing the disinfectant and placed on thesurface of a tryptiease soy agar plate that had justbeen inoeulated with a culture of Slaphylococcus au-reus, P.'^eudomonas aeruginosa, or Bacillus subtitis. Theplates were incubated for 24 hours and examined forzones of inhibition surrounding the disinfectant disk,Tbe diameter of any observed zone was measured.This procedure was repeated on both the test and ex-perimental solutions daily for the duration of thestudy.
Results
Both total chlorine and free chlorine levels in the ex-perimental solution fell steadily throughout the testperiod (Fig 1), Total chlorine of 6,000 ppm in the freshsolution dropped to 2,000 ppm after 80 impressionshad been immersed. The free chlorine component de-creased from 4,500 ppm to 1,500 ppm, and the com-bined chlorine from 1,500 to 500 ppm. The controlsolution remained constant at 6,000 ppm total chlo-rine and 4,500 ppm free chlorine.
The results of the bactericidal evaluation showed thesodium hypoohlorite disinfectant produced zones ofinhibition against the three bacterial species each dayover the duration of the study. On the first day, im-mediately following preparation and prior to use, thezones of inhibition measured approximately 40 nunon the S aureus plates, 35 mm on the P aeruginosaplates, and 30 mm on the B subtilis plates. The i:onesizes remained virtually unchanged during the courseof the study, revealing that there was little change inthe bactericidal activity of the solutions (Table 1).
Discussion
The results indicated that, within the parameters ofthis study, hypoehlorite solutions lost chlorine withuse, but not over time or under conditions of storage.However, the loss of chlorine did not correlate with aloss of bactericidal aetivity of the disinfectant solu-tion.
Once hypoehlorite solufions are prepared, their sta-bility is affected by organic contaminants, heavy metalions, dilufion, time, light, and temperature. The majorfactor contributing to the loss of chlorine in this studywas most likely the alginate impression material, Al-ginate contains large amounts of sodium, potassium,
588 Quintessence international Volume 22, Number 7/1991
Dental Research
Fig 1 Changes in lotai and treeavailable chlorine resulting fromthe immersion of 16 impressionsper day over a 5-day period.
1000
TOTAL a FREE AVAILABLE CHLORINE
total CI
tree CI
40 60
number of impressions
100
and calcium, all of which react readily with chlorineatid could be expected to reduce the amount of chlo-tine available for disinfecting. Organic material inchlorine solutions consumes chlorine and reduces itscapacity for bactericidal activity. The alginate impres-sion material itself, an organic compound, may havebeen responsible for consuming large amounts of theavailable chlorine.
The second factor responsible for the loss of chlo-rine was the reaction between the hypochlorite solu-tion and the metal trays. Because of its electronic con-figuration, chlorine has a tendency to acquire extraelectrons. Chlorine in water reacts quickly witb inor-ganic reducing substances, such as copper, nickel, andcobalt, which are powerful catalysts of decomposition,changing the solution from chlorine to inorganic chlo-ride ions. The chlorine thus reduced to chloride is lostas a disinfectant. The reactivity with metals in thisstudy was evident from the appearance of the metalimpression trays after a 10-niinute immersion in thehypochlorite solution (Fig 2). The primary point ofattack was the solder used to attach the rims. Thisreaction between chlorine and metal undoubtedly con-sumed considerable amounts of free chlorine.
A third reason for the loss of chlorine is simply thedilution of the test solution with water. In this study,as is common in clinical practice, the impressions wererinsed in running water and merely shaken to remove
exee.ss water. Water on the impression introduced intothe solution and hypochlorite removed during the re-trival of 80 impression trays may have been a signifi-cant factor in the overall loss of chlorine.
Ultraviolet light and temperature probably bad littleeffect on these results. Both solutions, test and control,were stored in opaque plastic containers with coversso that light would not be a decomposing factor. Allsolutions were stored at room temperature (approxi-
Quintessence International Volume 22, Number 7/1991 589
Denial Research
Fig 2 Corrosion precipitate (arrows) resulting from the im-mersion ol metal trays in the NaOCi disinfecting solution.
mately 24 °C) over the span of the study. No loss ofchlorine was found in the control solution over theperiod of t week. Although, under the experimentalconditions used, light and temperature were observedto have minimal effect on the results, these factors havethe potential to affect prepared solutions and aretherefore variables that must be considered in any clin-ical situation.
Chlorines are selective in their attacks on varioustypes of organic material, and not all organic materialslows the gcmiicidal effectiveness of hypochloritesolutions. However, other organic material, such asmicrobes and blood, will consume chlorine until thedemand is satisfied. Consequently, hypochlorite so-lutions tend to lose effectiveness rapidly in the pres-ence of blood and saliva. This will have a substantialimpact on the disinfection of dental impressionsshould they be heavily covered with blood or sahvawhen placed into the solutions. The effect would beespecially critical in solutions with lower levels ofchlorine, which could rapidly lose their effectivenessunless the chlorine dosage is adjusted to overcome thedemand.
Both the test and control solutions retained theirbiocidal activity throughout the study. This reflectsthe fact that chlorine solutions are effective even atlow concentrations of free chlorine. Dychdala'^ hasreported that a chlorine solution at pH 7.2 and 25 °Cand containing on average 0.8 ppm chlorine requiresonly 30 seconds to accomplish a 100% biocidal resultagainst S aureus. The solutions used in this study in-itially contained free chlorine concentrations of 4.500ppm and at the conclusion of testing still contained
1,500 ppm of free chlorine. This concentration wasmore than sufficient to maintain a biocidal effective-ness against the three strains of organisms used.
Conclusions
Three factors affecting the stability of chlorine solu-tions, time, conditions of storage, and use, were eval-uated to ascertain whether chlorine solutions must bechanged daily or can be retained for extended use.The results indicated that chlorine disinfecting solu-tions of sufficient concentration can be retained forperiods up to 1 week and still maintain their effec-tiveness.
The critical factor of those tested was use. The wayin which a chlorine disinfecting solution is used willdetermine how frequently it must be replaced or re-plenished. In the present study, three elements, algin-ate impression material, metal trays, and dilution,were responsible for reducing the total available chlo-rine in the disinfectant solution by two thirds. Timeand conditions of storage were of secondary impor-tance. Properly stored, and unused, a dilute chlorinesolution was observed to remain stable over a 1-weekperiod.
After 5 days, during which time 80 impressions wereimmersed in the chlorine solution, the residual un-reaeted chlorine was sutFicicnt to maintain bacteri-cidal activity against selected organisms.
References
1. Leung RL, Schonfeld SE: Gypsum casis as a potential sourceof microbial cross contamination, J Prosthet Dent 19S3 49'21O-211.
2. Herrera SP, Merchant VA: Dimensional stability of dentalimpressions after immersion disinfection. / Am Dent Assoc1986;113:419^22.
3. Durr DP, Novak EV: Dimensional stability of alginaie impres-sions immersed in disinfecting solutions. / Dem Child
4. Setcos JC, Peng L, Palenik CJ: The effect of disinfection pro-cedures on an alginate impression material. J Dent Res1984;63:235 (abstr No. 582).
5. Trevelyan MR: The prosthetic treatment of hepatitis B antigenpositive patients. Br Dem J 1974; 137:63-64.
6. Bergman B, Bergman M, Olsson S: Alginate impression mate-rials, dimensional stability and surface detail sharpness follow-ing treatment with disinfectant solutions. Swed Dent J1985;9:25 5-262.
7. Minagi S. Fukushima K. Maeda N. et al: Disinfection methodfor impression materials: freedom from fear of hepatitis B andacquired immunodeHciency syndrome. J Pro.sthet Dent1986;56:451-454.
590 Quintessence International Volume 22, Number 7/1991
Dental Research
8, Cottone JA, Molinari JA: Selection fot dental practice of chem-ical disinfectants and sterilants for hepatitis and AIDS, Au.\tDenlJ t987;32;368-374,
10. Pappakrdo G. Tanner F, Roussianos D, et al: Efficacy andstability of two chlorine eontaining antiseptics, Drjig,v E.xp ClinRes 1986:12:905-909
11, Hoffman PN, Death JE, CoLiles D: The stability of sodium
hypochloriie solutions, in Collins CH, Allwood MC, BloomfieldSF, et al (eds): Disinfectanls: Their Use und Evaiualitm of Effec-tiveness. London. Academic Press, 1981, pp 77-83,
12. Molinari JA, et al: Cleaning and disinfectant properties of dentalsurface disinfectants, J Am Dent As.toc 1988;]17:t79-182.
13. Dychdala G: Chlorine and chlorine compounds, in Blcx:k SS(ed): Dixinfeclion. Slerilization and Pre.servation, ed 3, Philadel-phia, Lea & Febiger, 19S3, pp 157-182. D
Books on
Orthodontics
lurrent Controversies inOrthodonticsedited by B. Meisen
"Much needed information on how controversieswithin the field of orthodontics are shaping thefuture of orthodontics.'*
Orthodontics as a science is still very young, anda majorpart of the development of this profession has beenbased on "trial-and-erroT" approaches rather than deductive research. Controversies have thus sprung upwithin the field of orthodontics.
This book brings together contributors who are experts in their fields, and who evaluate selected topics ofcontroversy in an attempt to differentiate between untried "traditions" and fact supported through scientific tests.
Contents: l. Esthetic Need ior Orthodontic Treatment; 2, Prediction in Ihe Planning and Conduct of Orthodontic Treatment; 3. DentofacialMorphology and Breathing: A Century ot Controversy; 4, Occlusion, Malocclusion, and Craniomandibniar Function: 5, FunctionalAppliances: 6. The Biomechanical Rationale of Orthodontic Therapy; 7, Limitations in Adult Orthodontics; 8, Rigid Fixation forOrthognathie Surgery: Current Perspectives and Controversies; 9, Lingual Orthodontics in Adults: 10, Orthodontie Controversies: TheirOrigins, Consequences, and Resolution,
Presents a series of practical "design cards" forfunctional appliances. The cards give detailed noteson clinical selection of appliances and technicalconstruction. An invaluable tool for communication,
Contenls include: The Fránkel System; Expansion and LabialSegment Alignment Appliances (ELSAAs); and more.
103 pp/184 ilius (48 in color)/US S68/Code; 2184
Bench-Top OrthodonticsH. Lawson/J. L. Blazucki
Superb self-teaching book for the laboratory phasesof orthodontics. Dental students, technicians, andauxiliaries will appreciate the atlas format of clearpictures—no mere guessing as to what the finishedproduct should look like! Proper sequence of stepsis clearly laid out and illustrated.
Contents include: Orthodontic Wire: Apphance Components:Hawley Retainer: Repairs: Bruxism Appliance; Fixed TranspalatalArch: Habit Appliance, Orthodontic Study Models: and more,
143 PP/32Ü illus/US $38/Code: 2338
To order Quintessence Books, use the order card bound in this issue.
Quintessence International Volume 22, Number 7/1991 591
