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The effect of tray material and surface condition on the shear bond strength of impression materials
The effect of tray material and surface c o n d i t i o n on the shear b o n d strength of i m p r e s s i o n materials Russell R. Wang, DDS, MSD, a Thuy Nguyen, Ann M. Boyle, DMD, MA c
DDS, b and
School of Dentistry, Case Western Reserve University, Cleveland, Ohio, and School of Dental Medicine, Southern Illinois University, Alton, Ill. This study compared the adhesive shear bond strength of three selected impression m a t e r i a l s w i t h t h a t o f t h e r m o p l a s t i c a n d a c r y l i c r e s i n t r a y m a t e r i a l s as a f u n c t i o n o f s u r f a c e p r e p a r a t i o n . P o l y e t h e r ( I m p r e g u m ) , p o l y v i n y l s i l o x a n e (Reprosil), a n d p o l y s u l fide (Permlastic) impression materials were evaluated on smooth, rough, and contamin a t e d t r a y s u r f a c e s . S m o o t h s u r f a c e s a m p l e s w e r e f o r m e d a g a i n s t g l a s s a n d s e r v e d as the control groups. Experimental groups consisted of samples contaminated with a r t i f i c i a l s a l i v a a n d r o u g h s u r f a c e s a m p l e s t h a t w e r e a b r a d e d w i t h 110 Dm o f A1203. A t o t a l o f 126 s a m p l e s w e r e s u b d i v i d e d i n t o 18 g r o u p s o f s e v e n s p e c i m e n s each. E a c h s a m p l e c o n s i s t e d o f a I i n c h square, 3 m m t h i c k m a s s o f a n i m p r e s s i o n m a t e r i a l sandwiched between the prepared surfaces of a pair of resin plates. Each specimen w a s t e s t e d in a u n i v e r s a l t e s t i n g m a c h i n e for a d h e s i v e s h e a r b o n d s t r e n g t h . D a t a w e r e a n a l y z e d w i t h t h r e e - w a y a n a l y s i s o f v a r i a n c e a n d S c h e f f e ' s test. T h e r e s u l t s i n d i c a t e d that the thermoplastic resin material had better adhesive properties than the acrylic resin. F o r b o t h t r a y m a t e r i a l s m e a n a d h e s i v e s h e a r b o n d s t r e n g t h s f o r I m p r e g u m a n d Reprosil were significantly greater than those of Permlastic. Tray surface contamin a t e d w i t h s a l i v a d e c r e a s e d t h e a d h e s i v e s h e a r s t r e n g t h at t h e t r a y a d h e s i v e i m p r e s s i o n i n t e r f a c e . (J PROSTHET DENT 1995;74:449-54.)
T r a y design and impression technique are import a n t p a r a m e t e r s for a n accurate impression.l-5 Stock t r a y s are useful for some procedures, but t h e i r flexibility a n d construction vary. In addition, t h e v a r y i n g thickness of impression m a t e r i a l in a stock t r a y m a y cause dimensional changes and inaccuracies in the cast. A custom tray, which provides rigidity a n d allows more uniform thickness of impression material, results in more accurate casts because of even contraction d u r i n g polymerization of the impression material. 6, 7 Additionally, an i m p o r t a n t but often undiscussed factor in the accuracy of impression m a t e r i a l s is the complete adhesion of the elastomer to the t r a y as the impression is removed from undercuts during the impression procedure. Tjan and W h a n g 4 compared the accuracy of die casts from impressions m a d e with adhesive-coated trays and t r a y s without adhesives and concluded t h a t impression adheaAssistant Professor, Department of Restorative Dentistry, and Head, Section of Fixed Prosthodontics, Case Western Reserve University. bDental Resident, Department of Dentistry, MetroHealth Medical Center of Cleveland. CAssociate Professor, Department of Restorative Dentistry, Southern Illinois University. Copyright 9 1995 by THE EDITORIALCOUNCIL OF THE JOURNAL OF PROSTHETIC DENTISTRY,
0022-3913/95/$5.00 + 0. 10/1167361
NOVEMBER 1995
Pulling direction
Shear stress
Tray Adhesive Impression material
F i g . 1. Schematic r e p r e s e n t a t i o n of adhesive bond stress at e l a s t o m e r / t r a y interface.
sires should be used, p a r t i c u l a r l y when r e p e a t pours are required. Ciesco et al. s found t h a t the i m m e d i a t e accuracy and dimensional stability of five impression m a t e r i a l s was improved when a custom tray/adhesive system was used. F o r elastomeric impressions clinical custom trays are usually m a d e of autopolymerizing acrylic resin. Monomer in the acrylic resin is considered to be the p r i m a r y i r r i t a n t and contact-sensitizing agent. 9 Direct contact and inhalation of the monomer d u r i n g fabrication of acrylic resin
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Pulling direction ~
Resin plate
~ ~ . ~ [ ~
Impression material, 1 square inch, with adhesive
Resin plate
F i g . 2. Shear specimen geometry.
Table I. Impression materials, batch numbers, and adhesives Impression material
Polyvinylsiloxane (medium body) Polysulfide (regular body)
Polyether
Manufacturer
Reprosil Caulk Dentsply Milford, Del Permlastic Kerr/Sybron Dental Romulus, Mich. Impregum Premier Dental Norristown, Pen.
Batch no.
Adhesive
Hydroplastic
921130
Caulk
Formatray
011693
Kerr
2 2 9 7 W 1 8 1 Premier
trays can cause problems for both the dentist and for dental personnel. In addition, the acrylic resin dust from tray adjustment procedures is a biohazard to the patient and the practitioner. Because of these problems other types of custom tray material such as thermopolymerizing and light-cured resins are receiving more attention. Dixon et al. 1~ 11 evaluated the tensile bond strength of one type of impression material adhesive to an autopolymerizing tray resin and two light-polymerizingresins and concluded that no significant difference existed in tensile bonding strength for the three tray materials as the result of variations in the surface treatment. Hogan and Agar 12 evaluated the tensile bond strength of impression materials to a thermoplastic tray material as a function of drying time of the adhesive. Their study suggested that drying time variance of 15 minutes to 24 hours would not significantly affect tray adhesive strength. 12 Other studies of adhesive properties of impression materials to tray resins have used the tensile test13-19; however, tensile stress is not the only stress t h a t occurs at the elastomer/tray interface as the impression tray is removed from the dental arch (Fig. 1). Shear stress will also occur at the elastomer/tray interface. In principle, critical shear stress values are usually lower than tensile stress values for a single material or for a multilayered material system during mechanical
450
Table II. Tray materials Traymaterial Manufacturer
Batchno.
Tak Systems Inc. Wareham, Mass. Kerr/Sybron Dental Romulus, Mich.
511-2225 121-492-686
loadings of the material. Therefore it may be more relevant to examine the adhesive shear bond strength for impression/tray systems. This study characterized and determined the adhesive shear bond strength of three types of impression materials to a thermoplastic tray resin and to a conventional acrylic tray resin as a function of surface conditions. The null hypothesis for this study was that no differences existed in the shear bond strength at the tray-impression interface for the two tray resins, three impression materials, and tray surface conditions tested. MATERIAL AND METHODS Three impression materials (polysulfide, polyether, and polyvinylsiloxane) and two tray materials (thermoplastic and acrylic resin) were used in this study (Table I and Table II). Each sample consisted of a fixed volume of impression material sandwiched between the ends of a pair of acrylic plates (Fig. 2). In all, 126 pairs of plates with the dimensions 3 inch • I inch • ~iGinch were formed with Teflon molds (Du Pont, Wilmington, Del.). Once a Teflon mold was full of acrylic resin, a glass slab was placed over the open side of the mold to create a uniformly smooth surface for each of the plates. Sixty-three pairs of plates were made of autopolymerizing acrylic resin, which was mixed at a 2:1 liquid/powder ratio by volume to standardize sample fabrication. The other 63 pairs of plates were made of the thermoplastic resin. The thermoplastic beads were placed in a water bath at 160 ~ C for 2 minutes until they were soft and moldable. All samples were retrieved from the molds after 20 minutes and were stored at room temperature for 24 hours before surface preparation was performed.
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[ Resin Plate ~~__.._]~Screw hole ~ ~ ~ ~ ~ ~ ~ ~ m m m l l ~ ~ T e f l o n mold v
I "
ression material
Fig. 3. Schematic representation of jig assembly for specimen fabrication.
Three types of surface preparation were used for the experiment. For each kind of tray material 21 pairs of plates were abraded with 110 ~m alumina by use of a microetcher (Danville Engineering, Inc., Danville, Calif.) to create a micromechanical roughened surface. The samples were ultrasonically cleaned and air-dried, and a layer of tray adhesive was applied. Another 21 pairs of plates were contaminated with synthetic saliva (Moi-stir, Kingwood Laboratories Inc., Carmel, Ind.). The artificial saliva was applied with cotton tips on the testing surface of designated groups. The contaminated surface was allowed to air dry for 10 minutes; then a layer of tray adhesive was painted on the surface. For the final set of 21 sample pairs, the control surface was formed by polymerization against the clean glass slab as described earlier. These surfaces also received a layer of tray adhesive. Consequently the 126 pairs of resin plates formed 18 distinct test groups with seven pairs in each group. Matching pairs of prepared resin plates were fit back into the Teflon molds, and a two-piece metal spacer was inserted between two Teflon molds with each pair of plates in place to ensure parallelism. The two-piece spacer apparatus provided a 1 inch square area to be filled with impression material, which would be bonded to one end of each resin plate. The spacer apparatus aided in retaining the impression material and maintaining an even thickness of 3 mm of impression material. The two Teflon molds and the two-piece spacer apparatus were precisely aligned and tightened with screws during specimen fabrication. A schematic representation of the jig assembly is illustrated in Fig. 3. The three impression materials were prepared either by hand mix or automixing according to the manufacturer's recommendations. Each impression material was loaded
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into a plastic syringe and injected into the jig. Each material contacted the adhesive-coated resin surfaces and was confined by the second part of the spacer apparatus to form a uniform volume of impression material that was 1 inch square and 3 mm thick. The jig was disassembled after 20 minutes, and the samples were retrieved and stored at room temperature for 24 hours before shear testing was performed. Excess material was trimmed with a sharp scalpel. Each specimen was then attached to a universal testing machine with a 500 N load cell and separated at a crosshead speed of 0.5 mm/minute until failure occurred. Stress-strain curves as a function of loading time and fracture strength were recorded and calculated. A three-way analysis of variance (ANOVA) was used to evaluate main effects and two- and three-factor interactions of tray materials, impression materials, and tray surface conditions. Scheffee's sequential range test was performed for multiple comparison to identify the location of statistical differences among the three variables. All hypothesis testing was conducted at the 95% level of confidence. RESULTS The mean and standard deviation of adhesive shear bond strength for each tray material are presented in Tables III and IV. The thermoplastic tray material had higher mean shear bond strength values than the acrylic tray resin for all groups. For thermoplastic resin the highest mean shear bond strength was 7.23 MPa for samples abraded with 110 Mm aluminum oxide and adhered to Impregum impression material. The lowest mean shear bond strength of the thermoplastic group was 0.48 MPa for material contaminated with saliva and adhered to Permlastic material. For acrylic resin the greatest mean shear bond strength was 3.01 MPa for samples abraded with 110 lam
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T a b l e IH. M e a n and SD of shear bond strength (MPa)
T a b l e IV. Shear bond s t r e n g t h (MPa) for acrylic resin
for thermoplastic resin as a function of impression materials and surface conditions.
as a function of impression materials and surface conditions. Acrylic t r a y r e s i n
T h e r m o p l a s t i c tray resin
Permlastic Impregum Reprosil
Control Group
Surface contaminated
Surface abraded
0.91 (0.14) 4.76 (0.39) 3.88 (0.20)
0.48 (0.08) 4.16 (0.16) 2.85 (0.16)
1.44 (0.12) 7.23 (0.32) 5.14 (0.13)
Permlastic Impregum Reprosil
Control Group
Surface contaminated
Surface abraded
0.43 (0.03) 1.38 (0.05) 2.45 (0.08)
0.31 (0.04) 0.82 (0.07) 2.08 (0.04)
0.55 (0.04) 2.36 (0.15) 3.01 (0.11)
T a b l e V. S u m m a r y of three-way analysis of variance Source
S u m of squares
DF
Mean square
F ratio
p Value
Tray IM Surface Tray + IM Tray + surface Surface + IM Tray + IM + surface Error
118.96 198.91 48.88 62.75 8.22 11.84 1.39 2.86
1 2 2 2 2 4 4 108
118.96 99.45 24.44 31.38 4.11 2.96 0.35 0.03
4500.049 3762.090 924.549 1186.841 155.448 111.977 13.121
0.001 0.001 0.001 0.001 0.001 0.001 0.001
IM, Impressionmaterial.
T a b l e VI. S u m m a r y of Scheffe's test for tray materials T h e r m o p l a s t i c tray
Acrylic tray
Impression material
l
Impregum Reprosil Permlastic
]Reprosil [Impregum Permlastic
Abraded IControl Contaminated
Abraded IC~176 [Contaminated
Surface conditon
Shear bond strengths are listed as a decreasing order. Groups connected with vertical line are not statisticallydifferentat p -<0.05.
a l u m i n u m oxide a n d adhered to Reprosil impression material. The lowest m e a n shear bond strength of the acrylic group was 0.31MPa for m a t e r i a l contaminated with saliva a n d adhered to Permlastic impression material. Reprosil impression material exhibited a greater m e a n bond strength across all surface conditions with acrylic resin tray material, whereas I m p r e g u m impression material demonstrated better adhesive shear results with thermoplastic tray materials across all surface conditions. Tables III and IV present the r a n k of values of adhesive shear bond strength from the greatest to the least: surface
452
abraded groups, control groups, and surface contaminated groups. This t r e n d was consistent throughout the groups for each selected impression material. Table V summarizes the A_NOVA for the three-factor analysis. Interaction effects among tray resins, impression materials, and tray surface conditions were significant. All the m a i n effects and the two-way and three-way interactions were significant at p <- 0.001 level. Because of the confounding effects of the three-way interaction, simple contrasts were calculated to determine significant difference among tray materials, tray surface conditions, a n d impression materials. Table VI is the s u m m a r y of Scheffe's multiple range test . Groups connected with vertical lines are not statistically different at p -< 0.05. For impression materials significant differences were found between Permlastic and either I m p r e g u m or Reprosil regardless of tray resins used. However, no significant difference of adhesive shear bond strength was seen between I m p r e g u m and Reprosil impression materials. The Scheffe test also indicated that a n abraded surface demonstrated significantly greater shear bond s t r e n g t h t h a n either contaminated or control surfaces for both tray materials used. Adhesive m e a n shear bond strengths of the control groups were similar to the m e a n shear bond strengths of the contaminated surface groups.
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I ~.~
9
Acrylic resin
eL
2
Control
Contaminated
Abraded
Surface condition
Fig. 4. Mean adhesive bond strength as function of impression material and tray material.
Fig. 5. Mean adhesive shear bond strength as function of surface condition and tray material.
All Permlastic samples exhibited adhesive failures that occurred either between the adhesive and the tray material or between the adhesive and the Permlastic impression material. More than 50% of the tested samples of Impregum and Reprosil impression materials exhibited some degree of cohesive failure inside the layer of the impression material and left some impression material on the tray surface. Fig. 4 illustrates the mean bond strengths as a function of impression materials and tray materials, and Fig. 5 depicts the mean shear bond strength as a function of surface conditions and tray materials.
tray material when the selected impression materials were used on various surface conditions. The effect of artificial saliva contamination on the adhesive shear bond strength of impression/adhesive/tray system has been demonstrated in this study regardless of the impression and tray materials used. When contaminated surface of thermoplastic trays was compared with control surface of thermoplastic trays, the adhesive shear bond strength decreased 13% for Impregum, 27% for Reprosil, and 45% for Permlastic impression materials. Similarly, acrylic tray bond strength for the contaminated surface decreased 15% for Reprosil, 41% for Impregum, and 48% for Permlastic impression materials when compared with bond stength of the control surfaces. The effect of saliva contamination on the modes of failures did not differ greatly from what was expected. Contamination of tray surfaces prevented adhesion to the tray material; therefore failure occurred at the tray-adhesive interface for most samples in the Permlastic and Reprosil impression material groups. Conversely, surface abraded groups had significant increases in adhesive bond strengths with all the experimental groups regardless of the type of tray impression material used. The findings from this study imply that after try-in and clinical adjustment are performed, a custom tray should be properly rinsed, air-dried, and abraded either at chairside or in the laboratory to create with
DISCUSSION The minimum adhesive shear bond strengths for the impression/adhesive/tray system required in clinical applications have not been established. The force needed to remove a completed impression from the oral cavity can vary depending on the number and severity of the undercuts. Undercuts can be created by interproximal embrasures, soft and hard tissues, and pontics, andminimal adhesive shear bond strengths must exceed the amount of force required to dislodge a tray from undercuts; otherwise, distortion and displacement of the impression may occur. From the available data it would appear that the thermoplastic tray material exhibited greater adhesive shear bond strength values than those observed for acrylic resin
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mechanical roughening on the tray surface before tray adhesive is placed.
6.
CONCLUSIONS
7.
This study determined the adhesive shear bond strength of different impression materials to thermoplastic resin and to conventional acrylic resin tray materials as a function of surface condition. Within the parameters of this study, the following conclusions were drawn. 1. Thermoplastic tray material demonstrated greater adhesive shear bond strengths than those of the acrylic tray resin for all groups. 2. Greater strength at the adhesive/tray interface occurred when the tray surface was abraded by aluminum oxide before the tray adhesive was applied regardless of the tray adhesive and impression material used. 3. Tray surface contamination by artificial saliva decreased the adhesive shear bond strength at tray/adhesive/ impression interface regardless of the tray impression material used. 4. Impregum and Reprosil impression materials had significantly greater shear bond strength values than Permlastic impression material to both types of tray material. REFERENCES 1. Saunders WP, Sarkey SW, Smith GM, Taylor WG. Effect ofimpression tray design and impression technique upon the accuracy of stone casts produced from a puttywash polyvinyl siIoxane impression material, J Dent 1991;19:283-9. 2. Waiters RA, Spurrier S. Aa effect of tray design and material retention on the linear dimensional changes in polysulfide impressions. J PROSTHETDENT 1990;63:277-81. 3. MacSween R, Price RB. Peel bond strengths of five impression material tray adhesives. J Can Dent &ssoc 1991;57:654-7. 4. Tjan AH, Whang SB. Effect of contaminants on the adhesion of lightbodied silicones to putty silicones in putty-wash impression technique. J PROSTh~TDENT 1988;59:562-7. 5. Luebke RJ, Scaudrett FR, Kerber PE. The effect of delayed and second
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8.
9. 10.
11.
12.
13.
14. 15. 16. 17.
18.
I9.
pours on elastomeric impression material accuracy. J PROSTItETDENT 1979;41:517-21. McCabe J, Storer R. Elastomeric materials: the measurement of some properties relevant to clinical practice. Br Dent J 1980;149:73-9. Dykema RW, Goodacre CJ, Philips RW. Johnston's modern practice in fixed prosthodontics. Philadelphia: WB Saunders Co, 1986:115-20. Ciesce JN, Malone WFP, Sandrik JL, Mazur B. Comparison ofelastomeric impression materials used in fixed prosthodontics. J PROSTHET DENT 1981;45:89-94. Mjor IA. Dental materials: biological properties and clinical evaluations. Boca Rato: CRC Press, ][nc, 1985:193-204. Dixon DL, Breeding LC, Bosser MJ, NaEso AJ. The effect ofcustom tray material type and surface treatment on the tensile bond strength of an impression material/adhesive system. Int J Prosthodont 1993;6:303-6. Dixon DL, Breeding LC, Brown JS. The effect of custom tray material type and adhesive drying time on the tensile bond strength of an impression material/adhesive system. Int J Prosthodont 1994;67:129-34. Hogan WR, Agar JR. The bond strength of elastomer tray adhesives to thermoplastic and acrylic resin tray materials. J PROSTt-mTDENT1992; 67:541-3. Sulong MZ, Setchell DJ. Properties of the tray adhesive of an addition polymerizing silicone to impression tray materials. J PROSTHETDENT 1991;66:743-7. Tjan AHL, Whang SB. Comparing effects of tray treatment on the accuracy of dies. J Prosthet Dent 1987;58:175-8. Davis GB, Moser JB, Brinsden GI. The bonding properties of elastomer tray adhesives. J PROSTHETDENT 1976;36:278-85. Grant BE, Tjan AHL. Tensile and peel bond strengths of tray adhesives. J PROSTHETDENT 1988;59:165-8. Chai J, Jameson LM, Moser JB, Hesby RA. Adhesive properties of several impression material systems. Part I. J PROSTHET DENT 1991; 65:201-9. Chai J, Jameson LM, Moser JB, Hesby RA. Adhesive properties of several impression material systems. Part II. J PROSTHET DENT 1991; 66:287-92. Shigeto N, Kawazoe Y, Hamada T, Yamada S. Adhesive between copper-plated acrylic tray resin and a polysutfide rubber impression material J PROSTHETDENT 1979;42:228-30.
Reprint requests to: RUSSEL R. WANG,DDS, MSD DEPARTMENTOF RESTORATIVEDENTISTRY SCHOOLOF DENTISTRY CASE WESTERNRESERVEUNIVERSITY 10900 EUCLIDAVE. CLEVELAND,OH 44143
VOLUME 74 NUMBER5
DDS, b and
School of Dentistry, Case Western Reserve University, Cleveland, Ohio, and School of Dental Medicine, Southern Illinois University, Alton, Ill. This study compared the adhesive shear bond strength of three selected impression m a t e r i a l s w i t h t h a t o f t h e r m o p l a s t i c a n d a c r y l i c r e s i n t r a y m a t e r i a l s as a f u n c t i o n o f s u r f a c e p r e p a r a t i o n . P o l y e t h e r ( I m p r e g u m ) , p o l y v i n y l s i l o x a n e (Reprosil), a n d p o l y s u l fide (Permlastic) impression materials were evaluated on smooth, rough, and contamin a t e d t r a y s u r f a c e s . S m o o t h s u r f a c e s a m p l e s w e r e f o r m e d a g a i n s t g l a s s a n d s e r v e d as the control groups. Experimental groups consisted of samples contaminated with a r t i f i c i a l s a l i v a a n d r o u g h s u r f a c e s a m p l e s t h a t w e r e a b r a d e d w i t h 110 Dm o f A1203. A t o t a l o f 126 s a m p l e s w e r e s u b d i v i d e d i n t o 18 g r o u p s o f s e v e n s p e c i m e n s each. E a c h s a m p l e c o n s i s t e d o f a I i n c h square, 3 m m t h i c k m a s s o f a n i m p r e s s i o n m a t e r i a l sandwiched between the prepared surfaces of a pair of resin plates. Each specimen w a s t e s t e d in a u n i v e r s a l t e s t i n g m a c h i n e for a d h e s i v e s h e a r b o n d s t r e n g t h . D a t a w e r e a n a l y z e d w i t h t h r e e - w a y a n a l y s i s o f v a r i a n c e a n d S c h e f f e ' s test. T h e r e s u l t s i n d i c a t e d that the thermoplastic resin material had better adhesive properties than the acrylic resin. F o r b o t h t r a y m a t e r i a l s m e a n a d h e s i v e s h e a r b o n d s t r e n g t h s f o r I m p r e g u m a n d Reprosil were significantly greater than those of Permlastic. Tray surface contamin a t e d w i t h s a l i v a d e c r e a s e d t h e a d h e s i v e s h e a r s t r e n g t h at t h e t r a y a d h e s i v e i m p r e s s i o n i n t e r f a c e . (J PROSTHET DENT 1995;74:449-54.)
T r a y design and impression technique are import a n t p a r a m e t e r s for a n accurate impression.l-5 Stock t r a y s are useful for some procedures, but t h e i r flexibility a n d construction vary. In addition, t h e v a r y i n g thickness of impression m a t e r i a l in a stock t r a y m a y cause dimensional changes and inaccuracies in the cast. A custom tray, which provides rigidity a n d allows more uniform thickness of impression material, results in more accurate casts because of even contraction d u r i n g polymerization of the impression material. 6, 7 Additionally, an i m p o r t a n t but often undiscussed factor in the accuracy of impression m a t e r i a l s is the complete adhesion of the elastomer to the t r a y as the impression is removed from undercuts during the impression procedure. Tjan and W h a n g 4 compared the accuracy of die casts from impressions m a d e with adhesive-coated trays and t r a y s without adhesives and concluded t h a t impression adheaAssistant Professor, Department of Restorative Dentistry, and Head, Section of Fixed Prosthodontics, Case Western Reserve University. bDental Resident, Department of Dentistry, MetroHealth Medical Center of Cleveland. CAssociate Professor, Department of Restorative Dentistry, Southern Illinois University. Copyright 9 1995 by THE EDITORIALCOUNCIL OF THE JOURNAL OF PROSTHETIC DENTISTRY,
0022-3913/95/$5.00 + 0. 10/1167361
NOVEMBER 1995
Pulling direction
Shear stress
Tray Adhesive Impression material
F i g . 1. Schematic r e p r e s e n t a t i o n of adhesive bond stress at e l a s t o m e r / t r a y interface.
sires should be used, p a r t i c u l a r l y when r e p e a t pours are required. Ciesco et al. s found t h a t the i m m e d i a t e accuracy and dimensional stability of five impression m a t e r i a l s was improved when a custom tray/adhesive system was used. F o r elastomeric impressions clinical custom trays are usually m a d e of autopolymerizing acrylic resin. Monomer in the acrylic resin is considered to be the p r i m a r y i r r i t a n t and contact-sensitizing agent. 9 Direct contact and inhalation of the monomer d u r i n g fabrication of acrylic resin
THE JOURNAL OF PROSTHETIC DENTISTRY
449
THE JOURNAL OF PROSTHETIC DENTISTRY
WANG, NGUYEN, AND BOYLE
Pulling direction ~
Resin plate
~ ~ . ~ [ ~
Impression material, 1 square inch, with adhesive
Resin plate
F i g . 2. Shear specimen geometry.
Table I. Impression materials, batch numbers, and adhesives Impression material
Polyvinylsiloxane (medium body) Polysulfide (regular body)
Polyether
Manufacturer
Reprosil Caulk Dentsply Milford, Del Permlastic Kerr/Sybron Dental Romulus, Mich. Impregum Premier Dental Norristown, Pen.
Batch no.
Adhesive
Hydroplastic
921130
Caulk
Formatray
011693
Kerr
2 2 9 7 W 1 8 1 Premier
trays can cause problems for both the dentist and for dental personnel. In addition, the acrylic resin dust from tray adjustment procedures is a biohazard to the patient and the practitioner. Because of these problems other types of custom tray material such as thermopolymerizing and light-cured resins are receiving more attention. Dixon et al. 1~ 11 evaluated the tensile bond strength of one type of impression material adhesive to an autopolymerizing tray resin and two light-polymerizingresins and concluded that no significant difference existed in tensile bonding strength for the three tray materials as the result of variations in the surface treatment. Hogan and Agar 12 evaluated the tensile bond strength of impression materials to a thermoplastic tray material as a function of drying time of the adhesive. Their study suggested that drying time variance of 15 minutes to 24 hours would not significantly affect tray adhesive strength. 12 Other studies of adhesive properties of impression materials to tray resins have used the tensile test13-19; however, tensile stress is not the only stress t h a t occurs at the elastomer/tray interface as the impression tray is removed from the dental arch (Fig. 1). Shear stress will also occur at the elastomer/tray interface. In principle, critical shear stress values are usually lower than tensile stress values for a single material or for a multilayered material system during mechanical
450
Table II. Tray materials Traymaterial Manufacturer
Batchno.
Tak Systems Inc. Wareham, Mass. Kerr/Sybron Dental Romulus, Mich.
511-2225 121-492-686
loadings of the material. Therefore it may be more relevant to examine the adhesive shear bond strength for impression/tray systems. This study characterized and determined the adhesive shear bond strength of three types of impression materials to a thermoplastic tray resin and to a conventional acrylic tray resin as a function of surface conditions. The null hypothesis for this study was that no differences existed in the shear bond strength at the tray-impression interface for the two tray resins, three impression materials, and tray surface conditions tested. MATERIAL AND METHODS Three impression materials (polysulfide, polyether, and polyvinylsiloxane) and two tray materials (thermoplastic and acrylic resin) were used in this study (Table I and Table II). Each sample consisted of a fixed volume of impression material sandwiched between the ends of a pair of acrylic plates (Fig. 2). In all, 126 pairs of plates with the dimensions 3 inch • I inch • ~iGinch were formed with Teflon molds (Du Pont, Wilmington, Del.). Once a Teflon mold was full of acrylic resin, a glass slab was placed over the open side of the mold to create a uniformly smooth surface for each of the plates. Sixty-three pairs of plates were made of autopolymerizing acrylic resin, which was mixed at a 2:1 liquid/powder ratio by volume to standardize sample fabrication. The other 63 pairs of plates were made of the thermoplastic resin. The thermoplastic beads were placed in a water bath at 160 ~ C for 2 minutes until they were soft and moldable. All samples were retrieved from the molds after 20 minutes and were stored at room temperature for 24 hours before surface preparation was performed.
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[ Resin Plate ~~__.._]~Screw hole ~ ~ ~ ~ ~ ~ ~ ~ m m m l l ~ ~ T e f l o n mold v
I "
ression material
Fig. 3. Schematic representation of jig assembly for specimen fabrication.
Three types of surface preparation were used for the experiment. For each kind of tray material 21 pairs of plates were abraded with 110 ~m alumina by use of a microetcher (Danville Engineering, Inc., Danville, Calif.) to create a micromechanical roughened surface. The samples were ultrasonically cleaned and air-dried, and a layer of tray adhesive was applied. Another 21 pairs of plates were contaminated with synthetic saliva (Moi-stir, Kingwood Laboratories Inc., Carmel, Ind.). The artificial saliva was applied with cotton tips on the testing surface of designated groups. The contaminated surface was allowed to air dry for 10 minutes; then a layer of tray adhesive was painted on the surface. For the final set of 21 sample pairs, the control surface was formed by polymerization against the clean glass slab as described earlier. These surfaces also received a layer of tray adhesive. Consequently the 126 pairs of resin plates formed 18 distinct test groups with seven pairs in each group. Matching pairs of prepared resin plates were fit back into the Teflon molds, and a two-piece metal spacer was inserted between two Teflon molds with each pair of plates in place to ensure parallelism. The two-piece spacer apparatus provided a 1 inch square area to be filled with impression material, which would be bonded to one end of each resin plate. The spacer apparatus aided in retaining the impression material and maintaining an even thickness of 3 mm of impression material. The two Teflon molds and the two-piece spacer apparatus were precisely aligned and tightened with screws during specimen fabrication. A schematic representation of the jig assembly is illustrated in Fig. 3. The three impression materials were prepared either by hand mix or automixing according to the manufacturer's recommendations. Each impression material was loaded
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into a plastic syringe and injected into the jig. Each material contacted the adhesive-coated resin surfaces and was confined by the second part of the spacer apparatus to form a uniform volume of impression material that was 1 inch square and 3 mm thick. The jig was disassembled after 20 minutes, and the samples were retrieved and stored at room temperature for 24 hours before shear testing was performed. Excess material was trimmed with a sharp scalpel. Each specimen was then attached to a universal testing machine with a 500 N load cell and separated at a crosshead speed of 0.5 mm/minute until failure occurred. Stress-strain curves as a function of loading time and fracture strength were recorded and calculated. A three-way analysis of variance (ANOVA) was used to evaluate main effects and two- and three-factor interactions of tray materials, impression materials, and tray surface conditions. Scheffee's sequential range test was performed for multiple comparison to identify the location of statistical differences among the three variables. All hypothesis testing was conducted at the 95% level of confidence. RESULTS The mean and standard deviation of adhesive shear bond strength for each tray material are presented in Tables III and IV. The thermoplastic tray material had higher mean shear bond strength values than the acrylic tray resin for all groups. For thermoplastic resin the highest mean shear bond strength was 7.23 MPa for samples abraded with 110 Mm aluminum oxide and adhered to Impregum impression material. The lowest mean shear bond strength of the thermoplastic group was 0.48 MPa for material contaminated with saliva and adhered to Permlastic material. For acrylic resin the greatest mean shear bond strength was 3.01 MPa for samples abraded with 110 lam
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T a b l e IH. M e a n and SD of shear bond strength (MPa)
T a b l e IV. Shear bond s t r e n g t h (MPa) for acrylic resin
for thermoplastic resin as a function of impression materials and surface conditions.
as a function of impression materials and surface conditions. Acrylic t r a y r e s i n
T h e r m o p l a s t i c tray resin
Permlastic Impregum Reprosil
Control Group
Surface contaminated
Surface abraded
0.91 (0.14) 4.76 (0.39) 3.88 (0.20)
0.48 (0.08) 4.16 (0.16) 2.85 (0.16)
1.44 (0.12) 7.23 (0.32) 5.14 (0.13)
Permlastic Impregum Reprosil
Control Group
Surface contaminated
Surface abraded
0.43 (0.03) 1.38 (0.05) 2.45 (0.08)
0.31 (0.04) 0.82 (0.07) 2.08 (0.04)
0.55 (0.04) 2.36 (0.15) 3.01 (0.11)
T a b l e V. S u m m a r y of three-way analysis of variance Source
S u m of squares
DF
Mean square
F ratio
p Value
Tray IM Surface Tray + IM Tray + surface Surface + IM Tray + IM + surface Error
118.96 198.91 48.88 62.75 8.22 11.84 1.39 2.86
1 2 2 2 2 4 4 108
118.96 99.45 24.44 31.38 4.11 2.96 0.35 0.03
4500.049 3762.090 924.549 1186.841 155.448 111.977 13.121
0.001 0.001 0.001 0.001 0.001 0.001 0.001
IM, Impressionmaterial.
T a b l e VI. S u m m a r y of Scheffe's test for tray materials T h e r m o p l a s t i c tray
Acrylic tray
Impression material
l
Impregum Reprosil Permlastic
]Reprosil [Impregum Permlastic
Abraded IControl Contaminated
Abraded IC~176 [Contaminated
Surface conditon
Shear bond strengths are listed as a decreasing order. Groups connected with vertical line are not statisticallydifferentat p -<0.05.
a l u m i n u m oxide a n d adhered to Reprosil impression material. The lowest m e a n shear bond strength of the acrylic group was 0.31MPa for m a t e r i a l contaminated with saliva a n d adhered to Permlastic impression material. Reprosil impression material exhibited a greater m e a n bond strength across all surface conditions with acrylic resin tray material, whereas I m p r e g u m impression material demonstrated better adhesive shear results with thermoplastic tray materials across all surface conditions. Tables III and IV present the r a n k of values of adhesive shear bond strength from the greatest to the least: surface
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abraded groups, control groups, and surface contaminated groups. This t r e n d was consistent throughout the groups for each selected impression material. Table V summarizes the A_NOVA for the three-factor analysis. Interaction effects among tray resins, impression materials, and tray surface conditions were significant. All the m a i n effects and the two-way and three-way interactions were significant at p <- 0.001 level. Because of the confounding effects of the three-way interaction, simple contrasts were calculated to determine significant difference among tray materials, tray surface conditions, a n d impression materials. Table VI is the s u m m a r y of Scheffe's multiple range test . Groups connected with vertical lines are not statistically different at p -< 0.05. For impression materials significant differences were found between Permlastic and either I m p r e g u m or Reprosil regardless of tray resins used. However, no significant difference of adhesive shear bond strength was seen between I m p r e g u m and Reprosil impression materials. The Scheffe test also indicated that a n abraded surface demonstrated significantly greater shear bond s t r e n g t h t h a n either contaminated or control surfaces for both tray materials used. Adhesive m e a n shear bond strengths of the control groups were similar to the m e a n shear bond strengths of the contaminated surface groups.
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I ~.~
9
Acrylic resin
eL
2
Control
Contaminated
Abraded
Surface condition
Fig. 4. Mean adhesive bond strength as function of impression material and tray material.
Fig. 5. Mean adhesive shear bond strength as function of surface condition and tray material.
All Permlastic samples exhibited adhesive failures that occurred either between the adhesive and the tray material or between the adhesive and the Permlastic impression material. More than 50% of the tested samples of Impregum and Reprosil impression materials exhibited some degree of cohesive failure inside the layer of the impression material and left some impression material on the tray surface. Fig. 4 illustrates the mean bond strengths as a function of impression materials and tray materials, and Fig. 5 depicts the mean shear bond strength as a function of surface conditions and tray materials.
tray material when the selected impression materials were used on various surface conditions. The effect of artificial saliva contamination on the adhesive shear bond strength of impression/adhesive/tray system has been demonstrated in this study regardless of the impression and tray materials used. When contaminated surface of thermoplastic trays was compared with control surface of thermoplastic trays, the adhesive shear bond strength decreased 13% for Impregum, 27% for Reprosil, and 45% for Permlastic impression materials. Similarly, acrylic tray bond strength for the contaminated surface decreased 15% for Reprosil, 41% for Impregum, and 48% for Permlastic impression materials when compared with bond stength of the control surfaces. The effect of saliva contamination on the modes of failures did not differ greatly from what was expected. Contamination of tray surfaces prevented adhesion to the tray material; therefore failure occurred at the tray-adhesive interface for most samples in the Permlastic and Reprosil impression material groups. Conversely, surface abraded groups had significant increases in adhesive bond strengths with all the experimental groups regardless of the type of tray impression material used. The findings from this study imply that after try-in and clinical adjustment are performed, a custom tray should be properly rinsed, air-dried, and abraded either at chairside or in the laboratory to create with
DISCUSSION The minimum adhesive shear bond strengths for the impression/adhesive/tray system required in clinical applications have not been established. The force needed to remove a completed impression from the oral cavity can vary depending on the number and severity of the undercuts. Undercuts can be created by interproximal embrasures, soft and hard tissues, and pontics, andminimal adhesive shear bond strengths must exceed the amount of force required to dislodge a tray from undercuts; otherwise, distortion and displacement of the impression may occur. From the available data it would appear that the thermoplastic tray material exhibited greater adhesive shear bond strength values than those observed for acrylic resin
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WANG,NGUYEN,AND BOYLE
mechanical roughening on the tray surface before tray adhesive is placed.
6.
CONCLUSIONS
7.
This study determined the adhesive shear bond strength of different impression materials to thermoplastic resin and to conventional acrylic resin tray materials as a function of surface condition. Within the parameters of this study, the following conclusions were drawn. 1. Thermoplastic tray material demonstrated greater adhesive shear bond strengths than those of the acrylic tray resin for all groups. 2. Greater strength at the adhesive/tray interface occurred when the tray surface was abraded by aluminum oxide before the tray adhesive was applied regardless of the tray adhesive and impression material used. 3. Tray surface contamination by artificial saliva decreased the adhesive shear bond strength at tray/adhesive/ impression interface regardless of the tray impression material used. 4. Impregum and Reprosil impression materials had significantly greater shear bond strength values than Permlastic impression material to both types of tray material. REFERENCES 1. Saunders WP, Sarkey SW, Smith GM, Taylor WG. Effect ofimpression tray design and impression technique upon the accuracy of stone casts produced from a puttywash polyvinyl siIoxane impression material, J Dent 1991;19:283-9. 2. Waiters RA, Spurrier S. Aa effect of tray design and material retention on the linear dimensional changes in polysulfide impressions. J PROSTHETDENT 1990;63:277-81. 3. MacSween R, Price RB. Peel bond strengths of five impression material tray adhesives. J Can Dent &ssoc 1991;57:654-7. 4. Tjan AH, Whang SB. Effect of contaminants on the adhesion of lightbodied silicones to putty silicones in putty-wash impression technique. J PROSTh~TDENT 1988;59:562-7. 5. Luebke RJ, Scaudrett FR, Kerber PE. The effect of delayed and second
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pours on elastomeric impression material accuracy. J PROSTItETDENT 1979;41:517-21. McCabe J, Storer R. Elastomeric materials: the measurement of some properties relevant to clinical practice. Br Dent J 1980;149:73-9. Dykema RW, Goodacre CJ, Philips RW. Johnston's modern practice in fixed prosthodontics. Philadelphia: WB Saunders Co, 1986:115-20. Ciesce JN, Malone WFP, Sandrik JL, Mazur B. Comparison ofelastomeric impression materials used in fixed prosthodontics. J PROSTHET DENT 1981;45:89-94. Mjor IA. Dental materials: biological properties and clinical evaluations. Boca Rato: CRC Press, ][nc, 1985:193-204. Dixon DL, Breeding LC, Bosser MJ, NaEso AJ. The effect ofcustom tray material type and surface treatment on the tensile bond strength of an impression material/adhesive system. Int J Prosthodont 1993;6:303-6. Dixon DL, Breeding LC, Brown JS. The effect of custom tray material type and adhesive drying time on the tensile bond strength of an impression material/adhesive system. Int J Prosthodont 1994;67:129-34. Hogan WR, Agar JR. The bond strength of elastomer tray adhesives to thermoplastic and acrylic resin tray materials. J PROSTt-mTDENT1992; 67:541-3. Sulong MZ, Setchell DJ. Properties of the tray adhesive of an addition polymerizing silicone to impression tray materials. J PROSTHETDENT 1991;66:743-7. Tjan AHL, Whang SB. Comparing effects of tray treatment on the accuracy of dies. J Prosthet Dent 1987;58:175-8. Davis GB, Moser JB, Brinsden GI. The bonding properties of elastomer tray adhesives. J PROSTHETDENT 1976;36:278-85. Grant BE, Tjan AHL. Tensile and peel bond strengths of tray adhesives. J PROSTHETDENT 1988;59:165-8. Chai J, Jameson LM, Moser JB, Hesby RA. Adhesive properties of several impression material systems. Part I. J PROSTHET DENT 1991; 65:201-9. Chai J, Jameson LM, Moser JB, Hesby RA. Adhesive properties of several impression material systems. Part II. J PROSTHET DENT 1991; 66:287-92. Shigeto N, Kawazoe Y, Hamada T, Yamada S. Adhesive between copper-plated acrylic tray resin and a polysutfide rubber impression material J PROSTHETDENT 1979;42:228-30.
Reprint requests to: RUSSEL R. WANG,DDS, MSD DEPARTMENTOF RESTORATIVEDENTISTRY SCHOOLOF DENTISTRY CASE WESTERNRESERVEUNIVERSITY 10900 EUCLIDAVE. CLEVELAND,OH 44143
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