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Surface characteristics of polyether and addition silicone impression materials after long-term disinfection
S E C T I O N EDITOR
Surface characteristics of polyether and addition silicone impression materials after long-term disinfection X a v i e r L e p e , D D S , MS, a G l e n H. J o h n s o n , D D S , MS, b a n d J o h n C. B e r g , P h D c
School of Dentistry, University of Washington, Seattle, Wash. It has been demonstrated that short-term disinfection can affect the surface properties of impression materials. This study evaluated advancing contact angle, receding contact angle, imbibition and m a s s loss of a polyether impression material, and two different viscosities of an addition silicone impression material after long-term i m m e r s i o n disinfection (18 hours). The brand n a m e s of the impression materials tested w e r e I m p r e g u m F, Extrude Extra, and Extrude Wash, and all w e r e tested by use of the Wilhelmy technique; first, for the nondisinfected state, w h i c h served as controls, and t h e n after 1 and 18 hours of disinfection in a full-strength solution of acid glutaraldehyde. Weight changes before and after the disinfection process w e r e also measured to detect w e i g h t loss and mass change over time. All materials exhibited some degree of imbibition. Polyether lost 0.4% m a s s in air, w h i c h indicated loss of a volatile component. Polyether and addition silicone were both relatively hydrophobic and could be disinfected w i t h acid glutaraldehyde for up to 18 hours without affecting wettahility. (J PROSTHETDENT 1995;74:181-6.)
A l t h o u g h
spray atomization disinfection of impressions has demonstrated effectiveness, 1 immersion disinfection is a more popular method. It is believed that longer-than-recommended immersion disinfection times 2, 3 are used by dentists and dental laboratories. Dentists often leave impressions in the disinfectant solution while treating patients. Some commercial laboratories routinely disinfect all impressions they receive, regardless of whether they have been previously disinfected by the dentist. Other times, they may leave the impressions in the disinfectant solution overnight. Surface roughness and line-detail reproduction of casts made from polyether and addition silicone impressions after recommended times of immersion disinfection in a 2% acid gluteraldehyde solution have demonstrated better reproduction quality than impressions immersed in alkaline gluteraldehyde or phenylphenol. 4 Pratten et al. 5 reported that short-term disinfection can affect impression materials by increasing or decreasing their wettability and that the newer hydrophilic addition silicone materials have wettability properties similar to that of polyether. 6
Supported in part by Kerr Manufacturing Company, Romulus, Mich. aAssistant Professor, Department of Restorative Dentistry. bprofessor, Department of Restorative Dentistry. CProfessor, Department of Chemical Engineering. Copyright 9 1995 by The Editorial Council of THE JOURNALOF PROSTHETIC DENTISTRY.
0022-3913/95/$3.00 + 0. 10/1/65112
AUGUST 1995
If short-term disinfection can affect impression materials, then it seems possible that longer-than-recommended times of immersion disinfection may change the chemical composition and surface characteristics of impression materials, thereby changing the wettability of these materials. This study evaluated wetting properties of three elastomeric impression materials by use of longer-than-recommended immersion disinfection times in a full-strength solution of acid glutaraldehyde. In addition, imbibition and mass change in air of these materials were tested. MATERIAL AND METHODS Cylindrical-shaped specimens of impression materials were prepared for wetting and weight change measurements. The three impression materials evaluated in this study were a polyether (Impregum-F [PE]) and two viscosities of an addition silicone material (Extrude Extra [PVS] and Extrude Wash [PVS-W]). A 2% solution of acid glutaraldehyde (Banicide [AC]) was used as the disinfectant (Table I). Ultradent I cc plastic syringes (Ultradent Products, Inc., South Jordan, Utah) were sectioned at the tip to create an open cylindrical-shaped mold. The syringe and plunger were then cleaned with cotton swabs moistened with acetone and were allowed to dry. The polyether material was weighed, mixed according to the manufacturer's recommendations, and placed in the syringe. The plunger was inserted to the i c c marker. The addition silicone materials were automixed and placed directly in the Ultradent syringe.
THE JOURNAL OF PROSTHETIC DENTISTRY
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THE JOURNAL OF PROSTHETIC DENTISTRY
LEPE, J O H N S O N , AND B E R G
sample
voor ! / CO.triTeR
F F i g . 1. Sample suspended in wetting liquid.
T a b l e I. M a t e r i a l s used Brand
Lot No.
Polyether Impregum-F (PE) Catalyst Base Addition silicone Extrude Extra (PVS) Extrude Wash (PVS-W) 2% Acid glutaraldehyde Banicide (AC)
Manufacturer
Espe Seefeld, Germany
F i g . 2. Schematic d i a g r a m of microtensiometer apparatus used in Wilhelmy technique.
sulfate was used as the w e t t i n g liquid to simulate the pouring of a n impression with stone. The m e a s u r e d downw a r d force, relative to the weight of the cylinder in air, is the wetting force minus a buoyancy correction. The wetting force (F) is the downward component of the surface tension force acting a r o u n d the p e r i m e t e r of the cylinder:
~LPCOSO
605 2296 Kerr Manufacturing Co. Romulus, Mich. 3-2042 3-1021 Pascal Bellevue, Wash. 040695
where ~L is the surface tension of the liquid, P is the wetted perimeter of the cylinder and O is the contact angle of the liquid against the solid. The buoyancy correction is due to the weight of the displaced liquid:
p~fiAh where PLis the density of the liquid,g is the gravitational constant, A is the cross-sectional area of the cylinder, and h is the depth of the cylinder's immersion.
Excess m a t e r i a l from t h e tip of the syringe was sectioned off a n d t h e sample was removed from the b a r r e l of the syringe. The samples were t h e n cut to size (approximately 25 mm) and tested by use of the Wilhelmy technique. 7 The average sample p e r i m e t e r was 1.9665 cm, a n d a sample size of two was used for each test. The Wilhelmy technique used for wetting measurem e n t s is illustrated systematically in Fig. 1. The cylindrical specimen is suspended in the wetting liquid from the a r m of a Cahn Model RG 2000 electrobalance a p p a r a t u s (Cahn I n s t r u m e n t s , Cerritos, Calif.) by m e a n s of a suspended wire. I n this study, a n aqueous solution of calcium
182
W h e n t h e surface tension of the liquid and the cylinder per i m e t e r are known, the m e a s u r e d downward force yields the value of t h e contact angle. Fig. 2 is a schematic d i a g r a m of the complete a p p a r a t u s used. 8 In a given test, the cylinder remains in a fixed position while the liquid, contained in a small plastic cup, is m a d e to rise or fall by m e a n s of an electronic translator, in this case the Inchworm t r a n s l a t o r (Burleigh Instruments, Fishers, N. Y.). The signals for t h e force, from the electrobalance, a n d the liquid level position from the t r a n s l a tor, are simultaneously fed to a computer while the liquid surface is cycled up and t h e n down over the cylinder surface. The r e s u l t i n g force trace is analyzed via software
VOLIfME 74 N U M B E R 2
LEPE, JOHNSON, AND BERG
THE JOURNAL OF PROSTHETIC DENTISTRY
PE
dry 1 hrAC 18 hr AC
PVS
dry 1 hrAC 18 hr AC
PVSwash
61"4~(2'69) ~
{""""i" "'""i'"'" i !"" i" i "'"-f'"" i "fi......... i
dry lhrAC
............................................................................................................................................................
i.-.-...i-....-+.----.!......
18 hr AC ~o
~o
~0
~o
1~o
advancing contact angle
Fig. 3. Mean advancing contact angles of polyether and addition silicone after 1 and 18 hours of disinfection in Banicide disinfection solution (AC).
produced in one of the author's (JCB) laboratory to yield the advancing and receding contact angles. Advancing contact angles (ACAs) are produced as the liquid is made to advance over the solid surface, and receding contact angles (RCAs) are obtained when the liquid interline is made to retreat across the surface. The difference between the advancing and receding angles (contact angle hysteresis) is a consequence of a solid surface roughness and solid surface energetic heterogeneity. For smooth surfaces, ACAs are believed to reflect the low surface energy portions of the surface, and receding angles are thought to reflect the higher energy portions. 9 The high sensitivity of both the electrobalance (-+0.2 tag force) and the translator (-+ 10 nanometers) assures high precision so that any measured differences between successive cycles or different specimens were indicative of systematic differences instead of random error. The liquid surface tension of the saturated aqueous solution of calcium sulfate was measured independently with a roughened platinum wire (of known perimeter) as the test cylinder, because it is known that, for this solid both, the advancing and receding contact angles are zero. Specimens were immersed in a full strength 2% solution of acid glutaraldehyde disinfectant (Banicide) for 1 and 18 hours. Nondisinfected dry specimens served as controls as did the specimens for 1 and 18 hour immersion in an aqueous solution of calcium sulfate. An aqueous solution of calcium sulfate was used for the control specimens because it is known to be a good surfactant. 6 Before disinfecting and/or testing, the control and the disinfected specimens were rinsed with distilled water for 10 seconds. This was done to simulate rinsing the impression after removal from the oral cavity and also after removal from the disinfectant solution. The data were analyzed with a two-factor analysis of
AUGUST 1~5
variance model (ANOVA). Where cross product interactions were not significant, paired comparisons of factor level means were made by use of the Student NewmanKeul's procedure. All hypothesis testing was conducted at the 95% level of confidence. It was also speculated that contact with the test solutions might alter the wetting characteristics, and because the sample specimens were quite smooth, the differences noted might be because of changes in the surface chemistry. In addition, it was thought that the age of the specimens might affect their surface properties. Thus in addition to wetting measurements, the solid specimens were weighed after preparation to detect any weight changes due to age (up to 18 hours) of the specimens. Weight losses would be indicative of desorption of volatile constituents. Last, weight changes were determined after the specimens were soaked in the different solutions over periods of time up to 5 hours. RESULTS
Advancing contact angle The mean values for all three testing times are illustrated in Fig. 3. The two-factor ANOVA results for ACAs are presented in Table II. Results indicated that for each material no differences in contact angles were evident for all testing times. However, there were differences among the three impression materials. Because cross-product interactions were not significant, facter-level means (for example, means for the three times combined) were analyzed and compared with rank impression materials. The factor level means for PE, PVS, PVS-W were 69.8, 64.5, and 75.3 degrees, respectively, and all means differed at ~ )0.05. In comparison to PE, the PVS heavy viscosity tray material demonstrated a lower advancing contact angle and the
183
THE J O U R N A L OF PROSTHETIC DENTISTRY
PE
LEPE, JOHNSON, AND BERG
dry 1 hrAC 18hr AC
PVS
dry 1 htAC 18 hr AC
~ ~ ~
. . . . . . . . . 0~
iiiiiiiiiiiiiiiiiiiiiiiiiiii
~
40o
60~
80~
100o
receding contact angle
F i g . 4. M e a n receding contact angles of polyether and addition silicone after i and 18 hours of disinfection in Banicide solution (AC).
T a b l e II. ANOVA for advancing contact angle Source
SS
Main effects Product Time Interactions Product • time Explained Residual Total
377.282 347.324 29.958 72.021 449.303 51.384 500.686
MSE
F
p Value
4 2 2
94.321 173.662 14.979
16.521 30.417 2.624
0.000 0.000 0.127
4 8 9 17
18.005 56.163 5.709 29.452
3.154 9.837
0.070 0.001
DF
PVS-W low viscosity impression m a t e r i a l h a d a higher ACA. Receding
contact
angle
The m e a n values for all t h r e e testing times are shown in Fig. 4. The two-factor ANOVA results for RCAs are shown in Table III. Results a g a i n revealed t h a t for each m a t e r i a l no differences were evident for all testing times. There were differences among the three impression m a t e r i a l s as was seen for advancing contact angles. Because crossproduct interactions were again not significant, factorlevel m e a n s were compared. The factor-level means for PE, PVS, PVS-W were 44.9, 61.2, and 75.8 degrees, respectively, and all m e a n s differed at a )0.05. In comparison to PE, both PVS h e a v y viscosity t r a y m a t e r i a l and PVS-W low viscosity impression m a t e r i a l h a d significantly higher RCAs. Weight
loss and mass
change
Polyether exhibited significantly g r e a t e r m a s s loss (0.4%) over 18 hours compared with the two addition silicone m a t e r i a l s (0.02% to 0.04%) (Fig. 5). A small a m o u n t
184
of imbibition, ranging from 0.1% for t h e PVS-W m a t e r i a l to 0.3% for t h e P E material, w a s present. No significant differences were found among t h e three m a t e r i a l s for imbibition. Mean values from 0 to 4 hours a r e reported in Fig. 6. DISCUSSION The newer hydrophilic impression m a t e r i a l s are popular, and t h e i r hydrophilicity could conceivably m a k e impression-making procedures a n d pouring g y p s u m casts easier. Because of their hydrophilicity, however, the possibility exists t h a t they could distort during the disinfection process if left in contact with t h e disinfectant for too long. W e t t i n g is m e a s u r e d b y the contact angle degree. Advancing a n d receding contact angles are used to m e a s u r e wettability. Advancing contact angle is m e a s u r e d when a liquid is s p r e a d on a solid surface, similar to w h a t happens when the stone is poured onto the surface of an impression material. RCA is m e a s u r e d w h e n a solid is removed from a liquid surface, such as w h e n the set impression is removed from the wet i n t r a o r a l tissues. Although the mean ACAs were shown to differ statisti-
VOLL~V~ 74 NIYM~ER 2
LEPE,
JOHNSON,
AND BERG
THE JOURNAL
0.60%
Banicide
OF PROSTHETIC
DENTISTRY
solution
0.350% 0.50% 0.300% 0.40%
PE
f
0.30%
0.250%
PE
0.200% .s 0.20%
~
~~~
PVS
PE (wet tested) 0.150%
0.10% PVS
0.100%
wash
.
/ ..... ~
0.00%
r"
o
o
o f
PVS I
-0,10% 0.0
4.5
I
0.050%
~" ~
J
/
PVS
wash
/
.%
I
9.0
13.5
18.0
0.000% 0.0
~ ,
,
,
I
1.0
. . . .
i
. . . .
2.0
I
3.0
. . . .
I
,
,
4.0
.
,
5.0
drying time in air (hours) soaking time (hours)
Fig. 5. Mass loss of polyether and addition silicone over 18-hour period of drying time in air.
Table
III. ANOVA for receding contact angle DF
MSE
F
p Value
2874.25 2874.84 2.41
4 2 2
718.56 1435.92 1.20
65.74 131.38 0.11
0.000 0.000 0.897
114.57 2988.82 98.37 3087.19
4 8 9 17
28.64 373.60 10.93 181.60
2.62 34.18
0.106 0.000
Source
S8
Main effects Product Time Interactions Product x time Explained Residual Total
cally for the three impression materials, the difference of the highest value versus the lowest was only 16.8 degrees. The highest mean value for ACA was 78.2 degrees for PVS-W and the lowest was 61.4 degrees for PVS. Hydrophilic materials have a contact angle that is significantly less than 90 degrees, and the lower the angle for the material the better wettability properties the material will display. Values above 90 degrees indicate poor wetting of the liquid to the solid. In other words, all of these materials can be considered relatively hydrophobic because their values are near 90 degrees. The mean values of all three materials for RCAs also differed statistically. The highest value was 79.2 degrees for PVS-W and the lowest was 43.3 degrees for PE. These differences may be clinically significant because of the large differences in magnitude. The highest mean values for both advancing and receding contact angles were for the light body addition silicone. This was contrary to what was expected. Most disinfectants and impression materials have a surfactant incorporated in their products and some of the low-viscosity materials have a greater amount of the surfactant to improve their wetting characteristics. Because they would be in closer contact with the oral tissues during the impression making process and the stone
AUGUST
Fig. 6. Imbibition of polyether and addition silicone over 5-hour period of soaking in Banicide (AC) disinfectant solution.
1~5
during the pouring process, it seems logical that they should have the lowest values, but this did not occur. The difference in surfactant concentration between PVS and PVS-W base materials is 0.25%. PVS base material has 1.0% surfactant compared with PVS-W, which has 1.25% by weight incorporated in the base material. Immersion disinfection is the most popular way of disinfecting impressions, most likely because it is guaranteed that all surfaces of the impression and the tray will be contacted by the disinfectant. It has been found that short-term immersion disinfection can alter impression materials by making them more or less wettable. 5 It is suggested that the surface characteristics and chemical composition may be affected during the disinfecting procedure by diluting or absorbing the surfactant present in the impression material and by increasing the surface roughness. It was thought that long-term disinfection would produce more dramatic changes in wettability, but no significant changes were present for each material for ACA or RCA after I and 18 hours of disinfection compared with the nondisinfected state. However, weight loss in air was significant for PE. It is evident that a volatile product is lost from the impression material over time.
185
THE
JOURNAL OF PROSTHETIC DENTISTRY
LEPE, JOHNSON, AND B E R G
Imbibition of disinfectant was evident in all three materials but was largest in Impregum-F impression material. This is the only impression material in this study t h a t was hand mixed. Impregum-F impression material is considered of medium viscosity, but its mixing characteristics resemble a heavy- viscosity material, which m a k e s it difficult to mix. Hand mixing and the viscosity may contribute to the trapping of air bubbles in the mix. These voids are most likely filled with the disinfectant during immersion and may be the cause for the imbibition results. Drying a polyether impression and letting it remain undisturbed for 30 to 45 minutes after immersion disinfection and before pouring may be enough to allow the disinfectant to evaporate from the voids. An improved mixing technique is highly desirable to avoid air bubbles. The combination of air bubbles and a low RCA, together with the stiffness of Impregum-F impression material, may be the reason why impressions made with this material are difficult to remove from the mouth. CLINICAL IMPLICATIONS Polyether and addition silicone impression materials can be disinfected with an acid glutaraldehyde disinfectant longer than 18 hours without altering the inherent wettability of the impression material. CONCLUSIONS 1. All products differed statistically for advancing contact angle (ACA) and receding contact angle (RCA). There was low RCA for polyether impression material, which may contribute to resistance to removal of an impression. 2. There was a large hysteresis between ACA and RCA for polyether impression material, which may indicate a chemically heterogeneous surface. 3. No significant differences were shown for either ACA or RCA for each material after disinfection of 1 hour and 18 hours, compared with the nondisinfected state.
4. All three materials demonstrated a degree (0.1% to 0.3%) of imbibition of disinfectant. 5. Polyether lost 0.4% mass with drying in air over 18 hours, which indicates a loss of a volatile component. 6. All three materials were relatively hydrophobic. The laboratory assistance of Mr. Derek Campbell, graduate student in chemical engineering at the University of Washington, is greatly appreciated.
REFERENCES 1. Drennon DG, Johnson GH, PowellGL. The accuracyand efficacyof disinfectionby spray atomizationon elastomericimpressions.J PRosTHET DENT 1989;62:468-75. 2. Council on Dental Materials, Instruments, and Equipment. Vinyl polysiloxane impression materials: a status report. J Am Dent Assoc 1990;120:595-60. 3. Council on Dental Materials, Instruments, and Equipment; Council on Dental Practice; Council on Dental Therapeutics. Infection control recommendations for the dental office and the dental laboratory. J Am Dent Assoc 1988;116:241-8. 4. Drennon DG, Johnson GH. The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts. J PROSTHET DENT 1990;63:233-41. 5. Pratten DH, Covey DA, Sheats RD. Effect of disinfectant solutions on the wettability of elastomeric impression materials. J PROSTHETDENT 1990;63:223-7. 6. Pratten DH, Craig RG. Wettabilityofhydrophilic addition silicone impression material. J PROSTHETDENT 1989;61:197-202. 7. Hodgson KT, Berg JC. Dynamic wettability properties of single wood pulp fibers and their relationship to absorbency. Wood and Fiber Science 1988;20:3-17. 8. Schuchardt DR, Berg JC. Liquid transport in composite cellulosesuperabsorbent fiber networks. Wood and Fiber Science 1991;23:34257. 9. Johnson RD Jr, Dettre RH. Surface and colloid science, vol 2. Matijevic E, ed. New York: Wiley-Interscience, 1969. 10. O'Brien WJ. Dental materials: properties and selection. 1st ed. Chicago: Quintessence Publ Co, 1989:73.
Reprint requests to: DR. XAVIERLEPE DEPARTMENT OF RESTORATIVEDENTISTRY, SM-56 SCHOOL OF DENTISTRY UNIVERSITYOF WASHINGTON SEATTLe, WA 98195
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186
VOLUME 74 NUMBER 2
Surface characteristics of polyether and addition silicone impression materials after long-term disinfection X a v i e r L e p e , D D S , MS, a G l e n H. J o h n s o n , D D S , MS, b a n d J o h n C. B e r g , P h D c
School of Dentistry, University of Washington, Seattle, Wash. It has been demonstrated that short-term disinfection can affect the surface properties of impression materials. This study evaluated advancing contact angle, receding contact angle, imbibition and m a s s loss of a polyether impression material, and two different viscosities of an addition silicone impression material after long-term i m m e r s i o n disinfection (18 hours). The brand n a m e s of the impression materials tested w e r e I m p r e g u m F, Extrude Extra, and Extrude Wash, and all w e r e tested by use of the Wilhelmy technique; first, for the nondisinfected state, w h i c h served as controls, and t h e n after 1 and 18 hours of disinfection in a full-strength solution of acid glutaraldehyde. Weight changes before and after the disinfection process w e r e also measured to detect w e i g h t loss and mass change over time. All materials exhibited some degree of imbibition. Polyether lost 0.4% m a s s in air, w h i c h indicated loss of a volatile component. Polyether and addition silicone were both relatively hydrophobic and could be disinfected w i t h acid glutaraldehyde for up to 18 hours without affecting wettahility. (J PROSTHETDENT 1995;74:181-6.)
A l t h o u g h
spray atomization disinfection of impressions has demonstrated effectiveness, 1 immersion disinfection is a more popular method. It is believed that longer-than-recommended immersion disinfection times 2, 3 are used by dentists and dental laboratories. Dentists often leave impressions in the disinfectant solution while treating patients. Some commercial laboratories routinely disinfect all impressions they receive, regardless of whether they have been previously disinfected by the dentist. Other times, they may leave the impressions in the disinfectant solution overnight. Surface roughness and line-detail reproduction of casts made from polyether and addition silicone impressions after recommended times of immersion disinfection in a 2% acid gluteraldehyde solution have demonstrated better reproduction quality than impressions immersed in alkaline gluteraldehyde or phenylphenol. 4 Pratten et al. 5 reported that short-term disinfection can affect impression materials by increasing or decreasing their wettability and that the newer hydrophilic addition silicone materials have wettability properties similar to that of polyether. 6
Supported in part by Kerr Manufacturing Company, Romulus, Mich. aAssistant Professor, Department of Restorative Dentistry. bprofessor, Department of Restorative Dentistry. CProfessor, Department of Chemical Engineering. Copyright 9 1995 by The Editorial Council of THE JOURNALOF PROSTHETIC DENTISTRY.
0022-3913/95/$3.00 + 0. 10/1/65112
AUGUST 1995
If short-term disinfection can affect impression materials, then it seems possible that longer-than-recommended times of immersion disinfection may change the chemical composition and surface characteristics of impression materials, thereby changing the wettability of these materials. This study evaluated wetting properties of three elastomeric impression materials by use of longer-than-recommended immersion disinfection times in a full-strength solution of acid glutaraldehyde. In addition, imbibition and mass change in air of these materials were tested. MATERIAL AND METHODS Cylindrical-shaped specimens of impression materials were prepared for wetting and weight change measurements. The three impression materials evaluated in this study were a polyether (Impregum-F [PE]) and two viscosities of an addition silicone material (Extrude Extra [PVS] and Extrude Wash [PVS-W]). A 2% solution of acid glutaraldehyde (Banicide [AC]) was used as the disinfectant (Table I). Ultradent I cc plastic syringes (Ultradent Products, Inc., South Jordan, Utah) were sectioned at the tip to create an open cylindrical-shaped mold. The syringe and plunger were then cleaned with cotton swabs moistened with acetone and were allowed to dry. The polyether material was weighed, mixed according to the manufacturer's recommendations, and placed in the syringe. The plunger was inserted to the i c c marker. The addition silicone materials were automixed and placed directly in the Ultradent syringe.
THE JOURNAL OF PROSTHETIC DENTISTRY
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THE JOURNAL OF PROSTHETIC DENTISTRY
LEPE, J O H N S O N , AND B E R G
sample
voor ! / CO.triTeR
F F i g . 1. Sample suspended in wetting liquid.
T a b l e I. M a t e r i a l s used Brand
Lot No.
Polyether Impregum-F (PE) Catalyst Base Addition silicone Extrude Extra (PVS) Extrude Wash (PVS-W) 2% Acid glutaraldehyde Banicide (AC)
Manufacturer
Espe Seefeld, Germany
F i g . 2. Schematic d i a g r a m of microtensiometer apparatus used in Wilhelmy technique.
sulfate was used as the w e t t i n g liquid to simulate the pouring of a n impression with stone. The m e a s u r e d downw a r d force, relative to the weight of the cylinder in air, is the wetting force minus a buoyancy correction. The wetting force (F) is the downward component of the surface tension force acting a r o u n d the p e r i m e t e r of the cylinder:
~LPCOSO
605 2296 Kerr Manufacturing Co. Romulus, Mich. 3-2042 3-1021 Pascal Bellevue, Wash. 040695
where ~L is the surface tension of the liquid, P is the wetted perimeter of the cylinder and O is the contact angle of the liquid against the solid. The buoyancy correction is due to the weight of the displaced liquid:
p~fiAh where PLis the density of the liquid,g is the gravitational constant, A is the cross-sectional area of the cylinder, and h is the depth of the cylinder's immersion.
Excess m a t e r i a l from t h e tip of the syringe was sectioned off a n d t h e sample was removed from the b a r r e l of the syringe. The samples were t h e n cut to size (approximately 25 mm) and tested by use of the Wilhelmy technique. 7 The average sample p e r i m e t e r was 1.9665 cm, a n d a sample size of two was used for each test. The Wilhelmy technique used for wetting measurem e n t s is illustrated systematically in Fig. 1. The cylindrical specimen is suspended in the wetting liquid from the a r m of a Cahn Model RG 2000 electrobalance a p p a r a t u s (Cahn I n s t r u m e n t s , Cerritos, Calif.) by m e a n s of a suspended wire. I n this study, a n aqueous solution of calcium
182
W h e n t h e surface tension of the liquid and the cylinder per i m e t e r are known, the m e a s u r e d downward force yields the value of t h e contact angle. Fig. 2 is a schematic d i a g r a m of the complete a p p a r a t u s used. 8 In a given test, the cylinder remains in a fixed position while the liquid, contained in a small plastic cup, is m a d e to rise or fall by m e a n s of an electronic translator, in this case the Inchworm t r a n s l a t o r (Burleigh Instruments, Fishers, N. Y.). The signals for t h e force, from the electrobalance, a n d the liquid level position from the t r a n s l a tor, are simultaneously fed to a computer while the liquid surface is cycled up and t h e n down over the cylinder surface. The r e s u l t i n g force trace is analyzed via software
VOLIfME 74 N U M B E R 2
LEPE, JOHNSON, AND BERG
THE JOURNAL OF PROSTHETIC DENTISTRY
PE
dry 1 hrAC 18 hr AC
PVS
dry 1 hrAC 18 hr AC
PVSwash
61"4~(2'69) ~
{""""i" "'""i'"'" i !"" i" i "'"-f'"" i "fi......... i
dry lhrAC
............................................................................................................................................................
i.-.-...i-....-+.----.!......
18 hr AC ~o
~o
~0
~o
1~o
advancing contact angle
Fig. 3. Mean advancing contact angles of polyether and addition silicone after 1 and 18 hours of disinfection in Banicide disinfection solution (AC).
produced in one of the author's (JCB) laboratory to yield the advancing and receding contact angles. Advancing contact angles (ACAs) are produced as the liquid is made to advance over the solid surface, and receding contact angles (RCAs) are obtained when the liquid interline is made to retreat across the surface. The difference between the advancing and receding angles (contact angle hysteresis) is a consequence of a solid surface roughness and solid surface energetic heterogeneity. For smooth surfaces, ACAs are believed to reflect the low surface energy portions of the surface, and receding angles are thought to reflect the higher energy portions. 9 The high sensitivity of both the electrobalance (-+0.2 tag force) and the translator (-+ 10 nanometers) assures high precision so that any measured differences between successive cycles or different specimens were indicative of systematic differences instead of random error. The liquid surface tension of the saturated aqueous solution of calcium sulfate was measured independently with a roughened platinum wire (of known perimeter) as the test cylinder, because it is known that, for this solid both, the advancing and receding contact angles are zero. Specimens were immersed in a full strength 2% solution of acid glutaraldehyde disinfectant (Banicide) for 1 and 18 hours. Nondisinfected dry specimens served as controls as did the specimens for 1 and 18 hour immersion in an aqueous solution of calcium sulfate. An aqueous solution of calcium sulfate was used for the control specimens because it is known to be a good surfactant. 6 Before disinfecting and/or testing, the control and the disinfected specimens were rinsed with distilled water for 10 seconds. This was done to simulate rinsing the impression after removal from the oral cavity and also after removal from the disinfectant solution. The data were analyzed with a two-factor analysis of
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variance model (ANOVA). Where cross product interactions were not significant, paired comparisons of factor level means were made by use of the Student NewmanKeul's procedure. All hypothesis testing was conducted at the 95% level of confidence. It was also speculated that contact with the test solutions might alter the wetting characteristics, and because the sample specimens were quite smooth, the differences noted might be because of changes in the surface chemistry. In addition, it was thought that the age of the specimens might affect their surface properties. Thus in addition to wetting measurements, the solid specimens were weighed after preparation to detect any weight changes due to age (up to 18 hours) of the specimens. Weight losses would be indicative of desorption of volatile constituents. Last, weight changes were determined after the specimens were soaked in the different solutions over periods of time up to 5 hours. RESULTS
Advancing contact angle The mean values for all three testing times are illustrated in Fig. 3. The two-factor ANOVA results for ACAs are presented in Table II. Results indicated that for each material no differences in contact angles were evident for all testing times. However, there were differences among the three impression materials. Because cross-product interactions were not significant, facter-level means (for example, means for the three times combined) were analyzed and compared with rank impression materials. The factor level means for PE, PVS, PVS-W were 69.8, 64.5, and 75.3 degrees, respectively, and all means differed at ~ )0.05. In comparison to PE, the PVS heavy viscosity tray material demonstrated a lower advancing contact angle and the
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THE J O U R N A L OF PROSTHETIC DENTISTRY
PE
LEPE, JOHNSON, AND BERG
dry 1 hrAC 18hr AC
PVS
dry 1 htAC 18 hr AC
~ ~ ~
. . . . . . . . . 0~
iiiiiiiiiiiiiiiiiiiiiiiiiiii
~
40o
60~
80~
100o
receding contact angle
F i g . 4. M e a n receding contact angles of polyether and addition silicone after i and 18 hours of disinfection in Banicide solution (AC).
T a b l e II. ANOVA for advancing contact angle Source
SS
Main effects Product Time Interactions Product • time Explained Residual Total
377.282 347.324 29.958 72.021 449.303 51.384 500.686
MSE
F
p Value
4 2 2
94.321 173.662 14.979
16.521 30.417 2.624
0.000 0.000 0.127
4 8 9 17
18.005 56.163 5.709 29.452
3.154 9.837
0.070 0.001
DF
PVS-W low viscosity impression m a t e r i a l h a d a higher ACA. Receding
contact
angle
The m e a n values for all t h r e e testing times are shown in Fig. 4. The two-factor ANOVA results for RCAs are shown in Table III. Results a g a i n revealed t h a t for each m a t e r i a l no differences were evident for all testing times. There were differences among the three impression m a t e r i a l s as was seen for advancing contact angles. Because crossproduct interactions were again not significant, factorlevel m e a n s were compared. The factor-level means for PE, PVS, PVS-W were 44.9, 61.2, and 75.8 degrees, respectively, and all m e a n s differed at a )0.05. In comparison to PE, both PVS h e a v y viscosity t r a y m a t e r i a l and PVS-W low viscosity impression m a t e r i a l h a d significantly higher RCAs. Weight
loss and mass
change
Polyether exhibited significantly g r e a t e r m a s s loss (0.4%) over 18 hours compared with the two addition silicone m a t e r i a l s (0.02% to 0.04%) (Fig. 5). A small a m o u n t
184
of imbibition, ranging from 0.1% for t h e PVS-W m a t e r i a l to 0.3% for t h e P E material, w a s present. No significant differences were found among t h e three m a t e r i a l s for imbibition. Mean values from 0 to 4 hours a r e reported in Fig. 6. DISCUSSION The newer hydrophilic impression m a t e r i a l s are popular, and t h e i r hydrophilicity could conceivably m a k e impression-making procedures a n d pouring g y p s u m casts easier. Because of their hydrophilicity, however, the possibility exists t h a t they could distort during the disinfection process if left in contact with t h e disinfectant for too long. W e t t i n g is m e a s u r e d b y the contact angle degree. Advancing a n d receding contact angles are used to m e a s u r e wettability. Advancing contact angle is m e a s u r e d when a liquid is s p r e a d on a solid surface, similar to w h a t happens when the stone is poured onto the surface of an impression material. RCA is m e a s u r e d w h e n a solid is removed from a liquid surface, such as w h e n the set impression is removed from the wet i n t r a o r a l tissues. Although the mean ACAs were shown to differ statisti-
VOLL~V~ 74 NIYM~ER 2
LEPE,
JOHNSON,
AND BERG
THE JOURNAL
0.60%
Banicide
OF PROSTHETIC
DENTISTRY
solution
0.350% 0.50% 0.300% 0.40%
PE
f
0.30%
0.250%
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PVS
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o
o
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I
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I
,
,
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.
,
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drying time in air (hours) soaking time (hours)
Fig. 5. Mass loss of polyether and addition silicone over 18-hour period of drying time in air.
Table
III. ANOVA for receding contact angle DF
MSE
F
p Value
2874.25 2874.84 2.41
4 2 2
718.56 1435.92 1.20
65.74 131.38 0.11
0.000 0.000 0.897
114.57 2988.82 98.37 3087.19
4 8 9 17
28.64 373.60 10.93 181.60
2.62 34.18
0.106 0.000
Source
S8
Main effects Product Time Interactions Product x time Explained Residual Total
cally for the three impression materials, the difference of the highest value versus the lowest was only 16.8 degrees. The highest mean value for ACA was 78.2 degrees for PVS-W and the lowest was 61.4 degrees for PVS. Hydrophilic materials have a contact angle that is significantly less than 90 degrees, and the lower the angle for the material the better wettability properties the material will display. Values above 90 degrees indicate poor wetting of the liquid to the solid. In other words, all of these materials can be considered relatively hydrophobic because their values are near 90 degrees. The mean values of all three materials for RCAs also differed statistically. The highest value was 79.2 degrees for PVS-W and the lowest was 43.3 degrees for PE. These differences may be clinically significant because of the large differences in magnitude. The highest mean values for both advancing and receding contact angles were for the light body addition silicone. This was contrary to what was expected. Most disinfectants and impression materials have a surfactant incorporated in their products and some of the low-viscosity materials have a greater amount of the surfactant to improve their wetting characteristics. Because they would be in closer contact with the oral tissues during the impression making process and the stone
AUGUST
Fig. 6. Imbibition of polyether and addition silicone over 5-hour period of soaking in Banicide (AC) disinfectant solution.
1~5
during the pouring process, it seems logical that they should have the lowest values, but this did not occur. The difference in surfactant concentration between PVS and PVS-W base materials is 0.25%. PVS base material has 1.0% surfactant compared with PVS-W, which has 1.25% by weight incorporated in the base material. Immersion disinfection is the most popular way of disinfecting impressions, most likely because it is guaranteed that all surfaces of the impression and the tray will be contacted by the disinfectant. It has been found that short-term immersion disinfection can alter impression materials by making them more or less wettable. 5 It is suggested that the surface characteristics and chemical composition may be affected during the disinfecting procedure by diluting or absorbing the surfactant present in the impression material and by increasing the surface roughness. It was thought that long-term disinfection would produce more dramatic changes in wettability, but no significant changes were present for each material for ACA or RCA after I and 18 hours of disinfection compared with the nondisinfected state. However, weight loss in air was significant for PE. It is evident that a volatile product is lost from the impression material over time.
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LEPE, JOHNSON, AND B E R G
Imbibition of disinfectant was evident in all three materials but was largest in Impregum-F impression material. This is the only impression material in this study t h a t was hand mixed. Impregum-F impression material is considered of medium viscosity, but its mixing characteristics resemble a heavy- viscosity material, which m a k e s it difficult to mix. Hand mixing and the viscosity may contribute to the trapping of air bubbles in the mix. These voids are most likely filled with the disinfectant during immersion and may be the cause for the imbibition results. Drying a polyether impression and letting it remain undisturbed for 30 to 45 minutes after immersion disinfection and before pouring may be enough to allow the disinfectant to evaporate from the voids. An improved mixing technique is highly desirable to avoid air bubbles. The combination of air bubbles and a low RCA, together with the stiffness of Impregum-F impression material, may be the reason why impressions made with this material are difficult to remove from the mouth. CLINICAL IMPLICATIONS Polyether and addition silicone impression materials can be disinfected with an acid glutaraldehyde disinfectant longer than 18 hours without altering the inherent wettability of the impression material. CONCLUSIONS 1. All products differed statistically for advancing contact angle (ACA) and receding contact angle (RCA). There was low RCA for polyether impression material, which may contribute to resistance to removal of an impression. 2. There was a large hysteresis between ACA and RCA for polyether impression material, which may indicate a chemically heterogeneous surface. 3. No significant differences were shown for either ACA or RCA for each material after disinfection of 1 hour and 18 hours, compared with the nondisinfected state.
4. All three materials demonstrated a degree (0.1% to 0.3%) of imbibition of disinfectant. 5. Polyether lost 0.4% mass with drying in air over 18 hours, which indicates a loss of a volatile component. 6. All three materials were relatively hydrophobic. The laboratory assistance of Mr. Derek Campbell, graduate student in chemical engineering at the University of Washington, is greatly appreciated.
REFERENCES 1. Drennon DG, Johnson GH, PowellGL. The accuracyand efficacyof disinfectionby spray atomizationon elastomericimpressions.J PRosTHET DENT 1989;62:468-75. 2. Council on Dental Materials, Instruments, and Equipment. Vinyl polysiloxane impression materials: a status report. J Am Dent Assoc 1990;120:595-60. 3. Council on Dental Materials, Instruments, and Equipment; Council on Dental Practice; Council on Dental Therapeutics. Infection control recommendations for the dental office and the dental laboratory. J Am Dent Assoc 1988;116:241-8. 4. Drennon DG, Johnson GH. The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts. J PROSTHET DENT 1990;63:233-41. 5. Pratten DH, Covey DA, Sheats RD. Effect of disinfectant solutions on the wettability of elastomeric impression materials. J PROSTHETDENT 1990;63:223-7. 6. Pratten DH, Craig RG. Wettabilityofhydrophilic addition silicone impression material. J PROSTHETDENT 1989;61:197-202. 7. Hodgson KT, Berg JC. Dynamic wettability properties of single wood pulp fibers and their relationship to absorbency. Wood and Fiber Science 1988;20:3-17. 8. Schuchardt DR, Berg JC. Liquid transport in composite cellulosesuperabsorbent fiber networks. Wood and Fiber Science 1991;23:34257. 9. Johnson RD Jr, Dettre RH. Surface and colloid science, vol 2. Matijevic E, ed. New York: Wiley-Interscience, 1969. 10. O'Brien WJ. Dental materials: properties and selection. 1st ed. Chicago: Quintessence Publ Co, 1989:73.
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