Effects of laboratory disinfecting denture acrylic resins

agents on color stability


Stanley J. McNeme, DDS,* Ann S. von Gonten, DDS,b and Gerald D. Woolsey, DDS, MSC Fort Hood, Tex.

This study determined the effects of chemical disinfecting agents on denture acrylic resins. Tested resins included the products CH Lucitone, Triad VLC, and Truliner. The disinfecting agents were sodium hypochlorite, Exspor, Cidex, and WescodyneD. Acrylic resin samples were placed in the various disinfecting agents and then evaluated for color changes at time intervals ranging from 15 minutes to 72 hours. No observable color change of any acrylic resin was seen before 2 hours. Both 1% sodium hypochlorite and 2% Cidex disinfectants produced the least discoloration of the acrylic resins, and Wescodyne-D disinfectant produced the most acrylic resin discoloration. Truliner resin discolored more than Triad VLC resin, and both underwent more color change than CH Lucitone resin. If manufacturers’ recommended disinfecting times are followed, clinical and laboratory disinfection of acrylic resin dentures should cause no observable color change. (J PROSTHET DENT 1991;66:132-6.)


nfectious diseases have become a major concern in the health care field. Infection control in dentistry is currently undergoing dramatic changes.l Dental and laboratory personnel are continually exposed to infectious microorganisms. Concern about transmission of these organisms between the office and laboratory has produced renewed interest in sterilization and asepsis. Sterilization is defined as a physical or chemical procedure that destroys all microbial life. Disinfection is defined as a less lethal process than sterilization and one that inactivates most recognized pathogens, but not necessarily all microorganisms, with bacterial endospores being the most resistant to destruction.3 Exclusive of spores, Mycobacterium tuberculosis presents the most severe challenge to a liquid germicidal chemical. Next in descending order of resistance are small nonlipid viruses (common oral and respiratory viruses), fungi, medium-size lipid viruses (polio virus), and vegetative bacteria. Spaulding3 proposed a classification system to categorize chemical disinfectants according to their activity levels

The viewsexpressedin this article are thoseof the authors and do not reflect,the official policy or position of the Department of Defenseor the United States Government aMajor, U.S. Army, D.C.; Resident, Advanced Educational Program in General Dentistry. bMajor, U.S. Army, D.C.; Mentor, Removable Prosthodontics, Advanced Educational Program in General Dentistry. cColonel,U.S. Army, D.C.; Chief, Fixed Prosthodontics,and Mentor, Advanced Educational Program in General Dentistry. 10/l/22666


against a spectrum of microbial groups. The high-level disinfectants will kill all groups except the spores and could sterilize if given enough contact time. Intermediate-level disinfectants are not sporicidal, but will kill M. tuberculosis and the remaining groups of microorganisms, including the human immunodeficiency virus (HIV). Low-level disinfectants will not kill M. tuberculosis or certain of the nonlipid viruses or fungi. The Environmental Protection Agency (EPA) does not allow any chemical disinfectant to make any disinfection claims for hepatitis B virus. No laboratory method exists for testing disinfection efficacy against the virus. The Centers for Disease Control (CDC) does say that if a product kills M. tuberculosis, it will certainly kill hepatitis B and HIV.4 Specific sources and pathways of cross contamination within the dental laboratory have been identified.5,6 Laboratory bacterial cross contamination from denture to denture has been demonstrated.7-10 Williams et al.‘l have shown that dental laboratory pumice continues to be a major reservoir of bacterial contamination in prosthetic dentistry. Recommendations to replace pumice in the pumice pan and autoclave the polishing wheel after each use have been made.8ylo, l2 Various methods of decontaminating removable prostheses have been investigated. In one study, denture-soaking solution was found to be a growth medium for pathogenic bacteria that colonize dentures.13 Gas sterilization or soaking of dentures for at least 15 minutes in a glutaraldehyde or sodium hypochlorite solution has been suggested.2 McGowen et a1.14demonstrated the effective use of sodium hypochlorite as a short-term sterilizing agent.









Fig. 1. Dentures on left soaked nightly year,&. New dc,ntures on right immediately

in undiluted sodium hypochlorite before insertion

for qevt-ral

Fig. 2. Truliner resin sample after placement in Exspor disinfectant for 72 hours. Top half of disk was not placed in Exspor disinfectant and serI,ed as control.

Fig. 3. Truliner resin sample display discoloration after immersion of bottom half of disk in !Yesccldyne-D disinfectant for ‘ip hours.

In the past, soaking dentures in sodium hypochlorite was discouraged because of its possible bleaching effect on the denture material (IFig. 1). Bleaching of an acrylic resin denture by sodium hypochlorite has been observed by the authors. Moore et a1.‘5 investigated the use of denture cleansers, one of which was a sodium hypochlorite/Calgon mixture, to steriliz? dentures. Rudd et al.‘” demonstrated that soaking dentu.:es in full-strength sodium hypochlorite for 15 hours did not cause any color change. However, no studies have investigated the effects of other medium- and high-level disinfect.ants on the color of acrylic resin. This investigation evaluated the effects that certain medium- and high-level chemical disinfecting agents have on heat-activated, light-activat,?d, and autopolymerizing acrylic denture res ns.

sion). and Truliner Denture Corrective Relining Material Vein (autopolymerized) acrylic resin (Harry .J. Bosworth Co.. Skokie, Ill.) were made. Each material was manipulated according to the manufacturers’ instructions. The samples were formed in disks in a stone mold (X6 mm diameter by :3 mm thick) to maintain uniform thickness. Lucitonr resins samples were packed and processed at 165’ F. for 9 hours. The samples were polished wit,h 600grit sandpaper followed by pumice. The Triad material was pressed into disks, activated for 1 minute in the Triad VLC Curing Unit, (Dentsply/York Division). painted with the Triad Air-Barrier coating (Dentsply/York Division) on one side, and polymerized for an additional 10 minutes. The Truliner resin was poured into the disk and, after it attained a heavy rubber consistency, placed m a pressure cooker at 140” F for 10 minutes at 15 psi. .A 1 mm diameter hole was placed in each sample. Stainless steel wire placed in the hole of each sample permitted suspension of the sample halfway into a selected disinfection solution. Four disinfecting solutions were used: Sodium hypochlorite diluted 1~5with distilled water to make a I ‘, solution,




Twelve samples each of Triad Reline VLC Resin Regular Pink Fibered ms terial (light-activated) (Dentsply/York Division, York, Pa.), CH Lucitone characterized denture base resin, light. (hear-activatc,d) (Dentsply/York Divi-







Table I. Products used in this study Product

Triad VLC resin regular pink fibered material Truliner Vein CH Lucitone characterized denture base resin, light Exspor Sodium hypochlorite Clorox brand Wescodyne-D Cidex



II. Results of acrylic resin immersion times in chemical disinfectants

Table Company

Dentsply/York Division York, Pa. Harry J. Bosworth Co. Skokie, Ill. Dentsply/York Division Alcide Corp. Norwalk, Conn. Clorox Corp. Oakland, Calif. West Chemical Products, Inc. New York, N.Y. Johnson & Johnson East Windsor, N.J.

Exspor, 2% Cidex, and Wescodyne-D diluted 1:213 in distilled water (Table I). The solutions were placed in containers in which the acrylic resin samples were suspended halfway into the solution; the top half of each disk exposed to the atmosphere served as its own standard. Samples were in contact with disinfecting solutions for 15 minutes, 30 minutes, 45 minutes, 60 minutes, 2 hours, 4 hours, 8 hours, 16 hours, 24 hours, 46 hours, and 72 hours. After each sample had been immersed for the specified time, it was rinsed with water and dried. A single acrylic resin sample of CH Lucitone resin was immersed in full-strength, 5.25%, sodium hypochlorite for 72 hours. The acrylic resin samples were evaluated for color change by two independent standardized observers. Each observer was standardized to 80 % agreement before the evaluation of the acrylic resin disks. The disks were placed on a white background as recommended by Powers and Lepeak.17 Samples were graded for the amount of discoloration on a scale of slight, moderate, and severe. Because each sample was half immersed in the disinfecting solution, it served as its own control. All samples were placed in a humidifier after completion of each immersion phase.

RESULTS The results of the color comparisons of the sets of samples are recorded in Table II. Other than a slight change of Truliner resin in Exspor disinfectant at 45 minutes, no color changes were observed until contact for 2 hours. At that time Truliner resin was graded as severely discolored and Triad VLC acrylic resin moderately discolored in Wescodyne-D disinfectant. Truliner resin also became slightly discolored in Exspor disinfectant. By hour 4, Triad VLC acrylic resin was slightly discolored in sodium hypochlorite and continued to discolor in Wescodyne-D disinfectant. Lucitone CH acrylic resin exhibited slight discoloration in Exspor and Wescodyne-D disinfectants. Triad VLC resin continued to discolor in Exspor and Wescodyne-D disinfectants. 134


Sodium hypochlorite Time 15







Cidex ABC

Wescodyne-D A




30 minutes 45 minutes 1 hour 2 hours 4 hours 8 hours 16 hours 24 hours 48 hours 72 hours

S S S S/M s s/M s s s s sss SSM








A, Lucitone CH; B, Triad VLC; C, Truliner. S, Slight discoloration; M, moderate discoloration; B, severe discoloration.

At hour 8, Triad VLC acrylic resin developed a white residue in Exspor disinfectant, which made the color of the samples appear darker. Truliner resin continued to change in color in Exspor disinfectant. Generally, the samples in Wescodyne-D disinfectant continued to show the most discoloration. By 72 hours, the Truliner resin had discolored a moderate amount in both Exspor (Fig. 2) and Cidex disinfectants and severely in Wescodyne-D disinfectant (Fig. 3). Lucitone CH resin underwent moderate discoloration in Wescodyne-D disinfectant. Triad VLC resin discolored slightly in Exspor and severely in Wescodyne-D disinfectants.

DISCUSSION In earlier works, denture base resins have been shown to undergo color changes from the use of denture cleansers, and the color stability of autopolymerizing resins was inferior to that of heat-polymerized materials.18, lg Kahn et a1.20found that Triad VLC denture material showed greater staining than acrylic resin material because of the differences in water sorption of the two materials. The data from this investigation support these findings. Wescodyne-D disinfectant caused the most severe discoloration, followed by Exspor disinfectant. Truliner resin exhibited more discoloration than Triad VLC acrylic resin, and Lucitone CH resin discolored the least in WescodyneD disinfectant. Neither 1% sodium hypochlorite nor 2 % Cidex disinfectant caused any discoloration until 72 hours when 2 % Cidex disinfectant produced a moderate discoloration in Truliner resin. Because it is imperative that laboratory bacterial cross contamination among denture patients be avoided,lO disinfection of dentures before and after laboratory procedures is necessary.21The Council on Dental Therapeutics of the American Dental Association currently recognizes












more than 30 conmercial products as effective for use in dentistry as sterilizing or disinfecting agents.2P All of the disinfectants tested, 2 !5 Cidex, Exspor, Wescodyne-D, and 1 “C sodium bypochlorite are classified as intermediate-level disinfectants. Intermediate levels of disinfection can be achieved in Cidex 2% alkaline glutaraldehyde after 10 minutes. Wescodyne-D 1.6% iodine disinfects in 10 to 30 minutes. Exspor chlorine dioxide disinfects in 2 minutes, and 1% sodium hypochlorite achieves intermediate levels ot’disinfec tion in 30 minutes.2a Sodium hypochlorite at a level of 5.25cc will sterilize after % minutes.14, Ifi We;;codyne-D disinfectant is no longer commercially available. An assumption is made that other iodopores will perform in a similar manner. No change was noled for arty of the samples until after 30 minutes. The :First observable color changes were noted at 2 hours except for Truliner resin. Even if an acrylic resin complete denture were immersed for the recommended 30 minutes in ‘Wescodyne-D iEisinfectant both before and after laboratory maniptilation, no color change would be anticipated. However, gf the denture required disinfection d.uring later adjustments or repairs, Wescodyne-D disinfectant could discolor the resin and the discoloration might worsen with repestea exposure to the chemical. The effect of prolonged exposure of acrylic resin to chemical disinfectants has been evaluated. If a denture were left by an oversight in Exspor or Wescodyne-D disinfectants for several hours or overnight, discoloration could be expected. The heat-activated acrylic resin did not dis color noticeably until after 16 l.ours of contact with Exspor or Wescodyne-D disinfect.ants, but the autopolymerizing acrylic resin and Triad VLC resin were observed to discolor in Wescodyne-D after only 2 hours. Since a variety of ADA-approved intermediate disinfectants are available. this study suggests that the choice of disinfection of a prosthesis with acrylic, resin components should be limited to non iodine--containing solut;ons to preclude potentially esthetic alterations ir the pros,thesis. One pararneter not investigated in this study was variation of the concentration of sodium hypochlorite. The Centers for Disease Control recommends a dilution of between 1:lO and l::.OO ~)f a 5.25”; solution, resulting in 500 to 5000 ppm of hypochlorite. 24 Schaeferz5 recommended a 1:5 dilution (I “c solution). -4bbot Laboratories and Traveno1 Laborat’ories recc*mmend a 2.5% (1:2) dilution.*“, x Rudd et al.‘” soaked all acrylic resin dentures in fullstrength sodium hypochlorite for 15 hours and found no discoloration. We j’ound no observable color changes in any of the samples after 7:! hours in the 1% sodium hypochlorite solution. To further test the hypothesis that sodium hypochlorite can bleach a denture, a sample of CH Lucitone resin was soaked for 72 hours iri full-strength sodium hypochlorite. No discoloration was observed by either of the prosthodontists using the grading methods outlined. It is unlikely that occasional use of f~.ill-strength sodium hypochlorite for all






acrylic resin denture decontamination ation.

will cause discolor-

CONCLUSIONS A study was undertaken to measure the color stability of a number of brands of acrylic resins immersed in various disinfecting solutions. Within the limitations of this study, we conclude that: 1. Truliner denture corrective relining material, Vein, will discolor more than Triad VLC resin regular pink fibered material, and both discolor more than CH Lucitone characterized denture base resin, light, when immersed in Wescodyne-D or Exspor disinfectants. 2. No observable color change of any of the samples was seen before 2 hours except for Truline resin. 3. If manufacturers’ recommended disinfecting times are followed, no color change of a denture should be noted. 4. Wescodyne-I) disinfectant produced the most noticeable discoloration. 5. On the basis of the results from this study, both I”;, sodium hypochlorite and 2 “; Cidex disinfectant produced the least color change in the samples tested.



19. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985. 20. Khan Z, van Fraunhofer JA, Razavi R. The staining characteristics, transverse strength, and microhardness of a visible light-cured denture base material. J PROSTHETDENT 1987;57:384-6. 21. Centers for Disease Control: Recommended infection-control practices for dentistry. MMWR 1986;35:237-42. 22. Facts about AIDS for the dental team. Chicago: ADA Council on Dental Therapeutics, 2nd ed. October 1988;lO. 23. Dental items of significance: USAF Dental Service Infection Control Program (Special Issue). United States Air Force Dental Investigation Service 1986;22:23-6. 24. Centers for Disease Control. Acquired immunodeficiency syndrome (AIDS) precautions for health care workers and allied professionals. MMWR 1983:32:450-l.


of one-piece

Ashok Jhanji, Northwestern


25. Schaefer ME. Infection control in dental laboratory procedures. CDAJ 1985;13:81-4. 26. Abbott Laboratories. Antibody to hepatitis B surface antigen I (Human), Ausralia 11-12. Radioimmunoassay for the detection of hepatitis B surface antigen. North Chicago, Ilk Abbott Laboratories, Diagnostic Division, October 1977. 27. Travenol Laboratories, Inc. Solid phase radioimmunoassay kit for detection of hepatitis B surface antigen. Deerfield, 111:Travenol Laboratories, Inc, September 1977. Reprint




DDS, MS,* and Steve T. Stevensb



School, Chicago, Ill.

This technique is a controlled process in which the thickness of the obturator can be easily modified by adding to or shaving off the dimensionally stable silicone putty. All phases of the obturator fabrication are heat-cured and not autopolymerized, thus negating the disavantages of other techniques. The technique provides more predictable results in obturator fabrication as it uses silicone putty as the obturating material as opposed to sugar, asbestos, or other silicone rubber foams that can be messy, dangerous, and unstable. This technique can also be used for patients with atrophic maxillae where the hollow denture can significantly reduce the weight of the restoration. (J PROSTHET DENT 1991;66:136-8.)


arious techniques for making hollow obturators have been suggested and different materials for obturation of the defect have been tried. Pare1 and La Fuentel used cellophane and sugar to make hollow obturators. Elliott2 used clay and cellophane paper, while El Mahdy3 and Guelde4 made the hollow obturator using two flasks with interchangeable parts. Silicone rubber foams and polyurethane foam bases have also demonstrated encouraging results as obturating agents. Radcliffe et a1.,5Tanaka et a1.,6 and Holt7 cured the two halves of the obturator with autopolymerizing resin. Schneider8 favored crushed ice while asbestos was used for the obturation by Worley and Kniejski.g Chalian and Barnett’O and Fattore et al.ll used a double flask technique to make the hollow obturator. These techniques have the following disadvantages: (1) they are complex procedures; (2) autopolymerizing resin is required to repair the obturator; (3) seepage of saliva can occur into the obturator when it is not completely sealed; and (4) uneven thickness of the obturator occurs as the obBAssistant Professor, Department of Restorative bCertified Dental Technician, Senior Technician, Restorative Dentistry.



Dentistry. Department


turating materials deform under the pressure of flask closure. This article presents a simple technique to make a onepiece obturator to overcome most of these disadvantages using silicone putty. Silicone putty has these advantages: (1) it remains stable after it sets, (2) it can be carved or shaved easily to control the thickness of the obturator, (3) it is easy and clean to use, and (4) it does not stick to the acrylic resin.

PROCEDURE 1. After the master casts are mounted, set up the teeth, shape the obturator as desired, examine it in the mouth, and make any necessary corrections. 2. Flask the wax prosthesis, eliminate the wax with clean boiling water, and remove any residual wax with lowsudsing detergent. 3. Adapt baseplate wax to the defect in the cast in the lower half of the flask to create a uniform thickness for the tissue surface on the superior and lateral surfaces of the obturator (Fig. 1). 4. Mix silicone putty (Accoe, Coe Laboratories, Inc., Chicago, Ill.) with the accelerator in a quantity sufficient to fill the defect (Fig. 2).




Effects of laboratory disinfecting agents on color stability of denture acrylic resins.

This study determined the effects of chemical disinfecting agents on denture acrylic resins. Tested resins included the products CH Lucitone, Triad VL...
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