A d h e s i v e p r o p e r t i e s of s e v e r a l i m p r e s s i o n m a t e r i a l s y s t e m s : Part I J o h n n y Y. C h a i , B D S , M S , a L e e M. J a m e s o n , D D S , M S , b J o h n B. M o s e r , P h D , c a n d R i c h a r d A. H e s b y , D D S , M S D d
Northwestern University, Dental School, Chicago, Ill. The tensile a d h e s i v e bond strength of five impression a d h e s i v e s y s t e m s w a s studied: polysulfide, polyether, p o l y v i n y l s i l o x a n e , condensation silicone impression, and p o l y v i n y l s i l o x a n e putty a d h e s i v e s y s t e m s . R e s u l t s s h o w e d no s i g n i f c a n t difference in a d h e s i v e bond strength to a u t o p o l y m e r i z i n g acrylic resin b e t w e e n the former four impression m a t e r i a l s studied. P o l y e t h e r and m e d i u m - v i s c o s i t y polyvin y l s i l o x a n e demonstrated significantly higher a d h e s i v e bond strength to polystyrene than e i t h e r polysulfide or condensation silicone. The m e d i u m - v i s c o s i t y p o l y v i n y l s i l o x a n e impression m a t e r i a l s h o w e d significantly higher a d h e s i v e bond strength to p o l y s t y r e n e than a u t o p o l y m e r i z i n g acrylic resin w h e r e a s polysulfide and condensation silicone impression m a t e r i a l s adhered significantly better to a u t o p o l y m e r i z i n g acrylic resin than polystyrene. The p o l y v i n y l s i l o x a n e putty did not adhere to its impression adhesive. V a r i a t i o n of the speed of tensile t e s t i n g b e t w e e n 5 to 20 inches per minutes did not affect the a d h e s i v e bond strength of a polysulfide impression material. (J PROSTHET DENT 1991;66:201-9.)
C o n t r o v e r s y has existed over the rationale for the use of stock trays in making elastomeric impressions. A survey in 1980 revealed that almost 75% of the sampled dentists used stock trays in making impressions for cast restorations. Less than 20% of the sampled dentists used a putty-wash system with stock trays. 1 Another study showed 70 % of the dentists used stock trays instead of customs trays and approximately 40% of them used a putty-wash system. 2 The common practice of using stock trays had been attributed to cost and convenience.3 The differences between stock trays and custom trays are thought to be (1) the provision of a uniform thickness of impression material, (2) the dimensional stability of tray material, (3) their rigidity and wall thickness, and (4) the ability of the tray material to retain an impression adhesive and hence the impression material. Common stock trays are made of polystyrene. To provide adequate strength to a tray, medium-impact polystyrene is commonly used. Medium-impact polystyrene products are molded by use of portions of regular polystyrene with high-impact polystyrene (acrylonitrile-butadiene-styrene)
Presented at the American Prosthodontic Society meeting, Chicago, Ill. aAssistant Professor, Division of Fixed Prosthodontics, Department of Restorative Dentistry. bprofessor and Director, Advanced Education Prosthodontics. cProfessor, Division of Biological Materials, Department of Basic Science. dprofessor and Director, Division of Fixed Prosthodontics, Department of Restorative Dentistry. 10/1/26187
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and vacuum-injection. The exact proportion of these two raw materials in a stock tray has not been released by manufacturers. The importance of an even and correct thickness of impression material (2 to 3 mm) within custom trays has been emphasized. 47 A recent study also showed that increasing the thickness of impression material from 1 to 4 mm resulted in increasingly inaccurate dies. s However a community study showed that the difference in thickness of impression material around prepared or unprepared teeth was less than 1 mm between stock and custom trays. 2 Distortion of an impression due to dimensional change of the tray material is only applicable to custom tray material, autopolymerizing poly(methylmethacrylate). Studies of dimensional shrinkage of acrylic resin tray material reported 24-hour shrinkage values from 0.08 % to 0.38 % .9-12 Some authors believed that small values of this magnitude were unlikely to cause significant distortion in the subsequent impression. 9 Some believed that impressions should not be made sooner than 9 hours after making a custom tray or that placing the tray in boiling water for 5 minutes allowed it to be used soon after it was made. 1° Most investigators recommended that no impression should be made within 24 hours after the tray was made. 11,12 However, controversy existed about the effect of a shrinking custom tray on the size of the resulting die. 12,13 Rigid trays have been shown to induce more stress during removal according to a photoelastic study. 14 However the use of polymeric impression trays of insufficient wall thickness to provide flexibility is discouraged because polysulfide and polyether impression adhesives can dissolve polymeric tray material. Too much flexion of an
201
CHAI ET AL.
Batch numbers Impression materials
Brands
Polyether Potyvinylsiloxane regular body Polysulfide regular body
Impregum-F* Mirror-3? Permlastic¢
Condensation silicone
Denture Elasticon¢
Polyvinylsiloxane putty
Mirror-3?
Base
Catalyst
Adhesive
473 71268 30387 1012 12388 1334 71268
130 71268 30387 1012 12388 1334 71268
0036/2 12688 71387 111887 12688
*ESPE-Premier, Norristown, Pa. ¢Kerr Manufacturing Co., Romulus, Mich.
impression tray can itself induce error in the impression, 15 Although the adhesive bond strengths of impression materials to different tray materials were intensely studied, 1517 those to a common stock tray material, polystyrene. have not been investigated. Comparison of adhesive bond strength of other impression materials has often been made with polysutfide since it is probably the first elastomeric impression material used clinically. Generally, polyether systems showed the highest adhesive bond strength, followed by polysulfide systems and then the condensation silicone systems. 15, is, 19 Although PhiUips 2° indicated that silicone systems do not provide enough adhesion, some addition silicone systems showed greater bond strength than polysulfide systems and sometimes were comparable to polyether systemsY" 22 When the mode of rupture at the junction of the impression material and adhesive-tray material is examined, polyetber fails cohesively within the impression material. It is reasonable to assume that the actual adhesive bond strength is higher than what has been observed. The mode of failure of silicone impression systems is commonly adhesive in nature except for one type of condensation silicone studied by Davis et al. 19 Nicholson et al. 21 emphasized that the rupture of addition silicone material occurred at the adhesive-resin interface, indicating the poor adhesion of adhesive to acrylic resin tray material. There is no common mode of failure for the polysutfide impression systems. It seemed that variations in tray material and thickness of impression material all influenced the mode of failure. When the material failed adhesively, adhesive usually remained on the tray material. 15, 19.21,23 Comparison of results of different bond strength studies has been particularly difficult because of the lack of standardization of technique. The most striking observation is the vast difference in crosshead speed. Speeds as low as 2 mm per minute 17and as high as 20 inches per minute have been used. 19 Only one study attempted to compare the effect on bond strength of varying the crosshead speed. It was
Z()~
discovered that increasing the crosshead speed from 2 inches per minute to 20 inches per minute generally increased the bond strength, especially the shear bond strength. 16 This research (1) compared the bond strength of different elastomeric impression adhesive systems, (2) compared the bond strength of different tray materials, and (3) examined the effect on adhesive bond strength of varying the rate of separation.
MATERIAL AND METHODS Acrylic resin (Formatray, Kerr Manufacturing Co., Romulus, Mich.) blocks of 1-inch square testing surface were made from an aluminum mold (Figs. 1 and 2). Acrylic resin testing surfaces were allowed to polymerize against a piece of aluminum foil to simulate the practice of burnishing aluminum foil over wax spacers when making a custom tray. Liquid/powder ratio according to mold consistency was used. Before the resin became rubbery, the thread portion of a screw hook (Screw Hook No. 6, Zhe Jiang, China) was set into the resin. After the rubbery stage, the mold was placed into a water bath (Lab-line Imperial III Water Bath, Lab-line Instruments, Inc., Melrose Park, Ill.) at 50 ° C _+ 1° C for 8 to 10 minutes to complete polymerization. The completed sample was finished with a sharp scalpel to the correct dimension. The samples were stored at room temperature for at least 24 hours before the experiment. Samples were chosen randomly for each part of the experiment.
Part 1: Comparison of different i m p r e s s i o n material systems The five impression material systems chosen were polysulfide, condensation silicone, medium-viscosity (regular) polyvinylsiloxane, polyether impression material, and polyvinylsiloxane putty (Table I). Each acrylic resin block was scrubbed with soap and tap water for 15 seconds, dried with a clean paper towel, and allowed to air dry for at least 15 minutes. One layer of the specified adhesive was painted onto the surface of the resin
AUGUST 1991 VOLUME S6 NUMBER 2
IMPRESSION ADHESIVE: PART I
Table II. M e a n adhesive bond strength of all materials tested Mean adhesive bond strength/psi Acrylic 5"/rain
Polystyrene 5"/min
Impression materials
X
SD
Polysulfide Polyether Polyvinylsiloxane regular Condensation silicone Polyvinylsiloxane putty
58.90 72.62 66.72 60.48 0.30
2.6 9.3 14.8 5.7 0.4
block and allowed to air dry at room temperature (25 ° _+ 3 ° C) for 15 minutes. A perforated metal plate with a thickness of I m m was used to retain the impression material mechanically (Fig. 3). The metal plate was bent at the corners to provide a I/8 inch thickness of impression material between the perforations and the surface of the resin block. A hook at the other side of the metal plate allowed attachment to the Instron Universal Load testing machine (Instron Corporation, Canton, Mass.). Adhesive of the corresponding type is painted on the metal plate to increase retention. The impression material was mixed according to the manufacturer's recommendation. Each specimen was allowed to set in a water bath at 37 ° C for 15 minutes. Material covering the resin block other than the testing surface was trimmed off with a sharp scapel blade. Hooks on the metal plate and resin blocks were attached to the Instron Universal Load testing machine with a metal chain. Each specimen was tested under tensile loads at a crosshead speed of 5 inches per minute until separation of the metal plate from the resin block was observed. The chart speed was set at 2 inches per minute. Five samples of each impression material were tested.
Part 2: Comparison of different tray material Autopolymerizing acrylic resin was compared with polystyrene (stock tray material). Polystyrene plates were cut into 1-inch squares and attached to resin blocks by first wetting the polystyrene plate with monomer before adding the resin dough. The same aluminum mold was used and a resin block with a polystyrene testing surface was made (Fig. 4). To standardize the surface roughness of all of the polystyrene plates, each sample was polished with white diamond on a felt wheel. The same five impression materiai systems were used.
Part 3: Variation in crosshead speed Five samples each of the impression materials except the putty material were tested with autopolymerizing acrylic resin as the tray material. The crosshead speed was set at
THE JOURNAL OF PROSTHETIC DENTISTRY
51.84 78.32 85.66 45.22 0.94
Acrylic 20"/rain SD
X
SD
5.2 18.6 8.4 12.9 0.66
59.38 59.98 71.85 55.94
7.0 17.8 10.0 12.3 Not tested
20 inches per minute and results were compared with those tested at 5 inches per minute (Part 1). Data obtained were analyzed with Student's t-test (unpaired), analysis of variance (ANOVA), and Scheffe's multiple comparison. RESULTS
Part 1: Comparison of different impression material s y s t e m s Data obtained with autopolymerizing acrylic resin as tray material and crosshead speed of the tensile testing machine set at 5 inches per minute are shown in Fig. 5 and Table II. A significant difference was found between the polyvinylsiloxane putty material and all other impression materials (p < 0.05). No statistically significant difference (p > 0.05) was found among polyether, medium-viscosity (regular) polyvinlysiloxane, condensation silicone, and polysulfide impression materials. The mode of failure of each impression adhesive material was determined as the most common interface where failure occurred. For polyether impression material, below one tenth of the testing surfaces were covered by impression adhesive and no impression material remained (Fig. 6). Adhesive failure of the polyether impression material occurred between its adhesive and the acrylic resin. For medium-viscosity polyvinylsiloxane impression material, more than three quarters of its adhesive remained on the acrylic resin block with less than one tenth of its impression material left (Fig. 7), indicating that its mode of failure was primarily adhesive in nature and was between the impression material and adhesive. Acrylic resin blocks used for polysulfide impression material had approximately half to seven eighths of their surfaces covered by adhesive after testing, with less than a tenth of the impression material remaining (Fig. 8). Approximately one eighth to one third of the total area of testing surface was covered by condensation silicone impression material, with all adhesive remaining on the acrylicresin after testing (Fig. 9). There w a s no sign of any adhesion of polyvinylsiloxane putty material to its adhesive. All impression adhesive stayed on the testing surface after the testing (Fig. 10).
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CHAI ET AL.
P a r t 2: ComlH~rison o f d i f f e r e n t t r a y mater'mls Mean tensile bond strengths of impression materials tested with polystyrene as tray material are shown in Fig. 5 and Table II. Statistically significant difference (p < 0.05) was found between polyvinytsiloxane putty material and each of the other materials. No significant difference (p > 0.05) was found between medium-viscosity polyvinylsiloxane and polyether or between polysulfide and condensation silicone impression material. However, significant difference (p < 0.05) was found with medium-viscosity polyvinylsiloxane and polyether when compared with polysulfide and condensation silicone impression material. When the tensile bond strength of each material to autopolymerizing acrylic resin was compared with that to polystyrene, medium-viscosity polyvinylsiloxane showed statistically significantly higher bond strength to polystyrene than acrylic resin (p < 0.05) (Fig. 11, Table II). Polysulfide and condensation silicone adhered significantly better to autopolymerizing acrylic resin than to polystyrene (p < 0.05). No statistically significant difference was found in bond strength between the tray materials for polyether and polyvinylsiloxane putty material (p > 0.05). The modes of failure of polyether, medium-viscosity polyvinylsiloxane, and polyvinylsiloxane putty impression material were similar to those observed for acrylic resin. Failure occurred between polyether impression adhesive and polystyrene, primarily between medium-viscosity polyvinylsiloxane impression material and its adhesive, and between polyvinylsiloxane putty material and its adhesive. For both polysu]fide and condensation silicone impression material, almost all adhesive with little or no impression material remained on polystyrene (Figs. 5 through 9).
P a r t 3: V a r i a t i o n in c r o s s h e a d s p e e d ANOVA revealed no significant difference (p > 0.05) in bond strength among the four impression materials investigated by use of a rate of separation of 20 inches per minute and acrylic resin (Fig. 5, Table II). When the tensile bond strength of each material in this group was compared with those tested at a speed of 5 inches per minute, no statistically significant difference was found ~)r any of these materials (p > 0.05) (Fig. 12). The mode of failure of sample tested at a speed of 20 inches per minute did not seem to be different from those tested at 5 inches per minute.
DISCUSSION Polyether and medium-viscosity polyvinylsiloxane demonstrated better adhesive bond strength to autopolymerizing acrylic resin than polysulfide or condensation silicone impression material although they did not differ statisti-
-~,y~
cally. Previous studies that compared different impression materials seemed to favor the former two materials but statistical analysis was not performed. The highest mean adhesive bond strength achieved by polyether impression material was approximately 73 psi. This result compared closely with those reported by Samman and Fletcher, 15 and Davis et al., 19 which were in the range of 70 to 85 psi. However, values as high as those reported by Grant and Tjan 22 (approximately 110 psi) and Nicholson et al. 21 (approximately 440 psi) were never achieved. The modified type of the common polyether impression material (Impregum-F) investigated in this study only partly explains the vast differences reported. The adhesive strength of polyether impression material bonded to polystyrene (78.32 psi) was higher than that to acrylic resin but not statistically significant. The adhesive strengths of medium-viscosity polyvinylsiloxane bonded to different tray materials demonstrated values statistically similar to those of polyether impression material. This finding was supported by recent studies that found polyvinylsiloxane impression material as a group at least as strong as polysulfide and sometimes comparable to polyether impression material. 21,22 Polyether and medium-viscosity polyvinylsiloxane showed stronger adhesion to polystyrene than either polysulfide or condensation silicone. The better bond strength of medium-viscosity polyvinylsiloxane to polystyrene than acrylic resin may be due to a difference in the solubility of tray materials in the solvent of the impression adhesive and a difference between their surface finish. The same rationale may be used to explain the significant differences in bond strength of polysulfide and condensation silicone impression materials to the two tray materials. However, the exact nature of this variation has yet to be investigated. The polysulfide impression material tested in this study showed a result similar (approximately 60 psi/acrylic resin) to most of those reported, 17,19.22 except that of Nicholson et al. 21 (approximately 170 psi). This material was also the most consistent material tested (smallest standard deviation). Its adhesive bond to polystyrene was approximately 8 to 9 psi lower than that to acrylic resin. The strength of condensation silicone bonded to acrylic resin was comparable to that of the polysulfide impression material (about 60 psi). This is the highest reported adhesive bond strength of a condensation silicone impression material. Previous studies had not shown condensation silicone material to exceed a bond value of 30 psi. 19,22 Its bond strength to polystyrene was approximately 15 psi lower than that to acrylic resin, indicating that additional mechanical retention is needed (extra holes) when this material is used with polystyrene stock trays. This study showed little or no adhesion of polyvinylsiloxane putty material to its adhesive. When this material is used, adequate mechanical retention is therefore man-
At~GtJST 1991
VOLUME 66
NUMBER 2
IMPRESSION ADHESIVE: PART I
Fig. Fig. Fig. Fig.
1. 2. 3. 4.
Acrylic resin block. Aluminum mold. Perforated metal plate. Acrylic resin block with polystyrene testing surface.
datory. Because of the extremely viscous consistency of the putty, retention holes should have enough sizeto allow this material to flow through them easily. Classifying the mode of failureof an impression material/adhesive/tray material system for an impression materialis of academic interestunless its bond strength is unacceptably low. For instance, because polyvinylsiloxane putty material failed at the impression material-adhesive junction, attempts to increase itsadhesive strength should therefore aim primarily at improving the adhesion between the impression material and its adhesive. The term adhesivefailurehas been used to describe failureeitherbetween the tray material and impression adhesive or between the impression adhesive and impression material. The term cohesive failure has been used loosely.Davis et al.,I9and S a m m a n and Fletcher15 described cohesive failureas one that occurred within the body of the impression material itself,usually referring to polyether impression material.
THE JOURNAL OF PROSTHETIC DENTISTRY
However, adhesive failure between adhesive and acrylic resin was observed for the polyether impression material used in the present study. Nicholson et al. 21 described the mode of failure of polyether impression material as cohesive when they referred to "pieces of fractured Impregum bonded to the acrylic blocks." The same phenomenon was described by Kawamura is as mixed failure. Pure cohesive failures were not observed in this study. However, mixed adhesive-cohesive failures were found for some materials tested. Pure adhesive failures were seen for polyether and polyvinylsiloxane putty. When the amount of adhesive or impression material left on a testing surface versus its bond strength was compared with different impression materials, no correlation was found between these two variables. The amount of an impression material left on the tray material does not indicate its ability to adhere to it. When individual impression materials that showed differences in bond strength to differ-
205
CHAI E T AL.
1M
~olyether ~olwinytsiloxane regular :'olysuff'zle 3ondommtion silicone
t03
=olyvinylstoxanePutty
=
20"/rain Acrylic Resin
5"/min Acrylic Resin
5*/rain
Polystyrene
Fig. 5. Tensile adhesive bond strength of all impression material systems.
ent tray materials were examined, only the condensation siliconeshowed more impression material remaining on the acrylic resin than on the polystyrene. Although the condensation silicone impression material showed significantly better adhesion to acrylic resin, no correlation between the amount of impression material left on a tray material and its bond strength should be suggested. Variation of crosshead speed of the tensile load testing machine between 20 and 5 inches per minute did not cause a change in bond strength of four impression materials investigated. This finding is contrary to those of Ellam and Smith Is who demonstrated an increase in adhesive bond strength when the crosshead speed was raised from 2 inches to 20 inches per minute.
Clinical implications One would question the clinical significance of the observed difference between impression adhesive systems and the critical adhesive bond strength. Polysulfide is the elastomeric impression material that seems to have proved adequate adhesive bond strength clinically, and compari~,t~ of adhesive bond strength to it has often been made. It appears that if the adhesive bond strength of an impression ~y~tem is below 50 psi (under the same experimental conditions as the present study), which is achieved by polysul~de with polystyrene as tray material, one should question ~he efficacy of this adhesive system. However, whether the ~c~ce needed to remove an impression tray from a mouth +'+~Ltldreach this level is unknown.
The results of the present study suggest that the speed of removal of an impression tray from the mouth does not seem to affectthe adhesive bond strength of these impression materials. However, removal of elastomeric impression from the mouth with a quick snap is stilladvisable to minimize viscous deformation of elastomeric impression materials.
CONCLUSIONS AND SUMMARY The tensile adhesive bond strength of five impression material systems was investigated: polyether, medium-viscosity polyvinylsiloxane, polysulfide, condensation silicone, and polyvinylsiloxane putty impression materials. Autopolymerizing acrylic resin and polystyrene were used as tray materials. The effect of variation in the speed of tensile testing was also studied. Results showed no significant difference in the strength of adhesive bond to autopolymerizing acrylic resin between the former four impression materials studied. As a group, the polyether and medium-viscosity polyvinylsiloxane demonstrated significantly higher adhesive bond strength to polystyrene than polysulfide and condensation silicone impression materials as a group. The medium-viscosity polyvinylsiloxane impression material showed significantly higher adhesive bond strength to polystyrene than autopolymerizing acrylic resin, whereas polysulfide and condensation silicone impression materials adhered significantly better to autopolymerizing acrylic resin than to polystyrene. The polyvinylsiloxane putty material did not adhere to its impression
IMPRESSION ADHESIVE: PART I
Fig. 6. Polyether samples after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 7. Medium-viscosity polyvinylsiloxane after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 8. Polysulfide samples after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 9. Condensation silicone samples after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 10. Polyvinylsiloxane putty samples after testing. Right, acrylic resin; left, polystyrene.
THE JOURNAL OF PROSTHETIC DENTISTRY
207
C H A I E T AL.
Polyvinytsilc
Conden,sati
Potwirry~Ioxl
O
20
40
60
80
100
Tensile Adhesive Bond Strength / psi
Fig.
11. Comparison
O
of adhesion between acrylic resin and polystyrene.
20
40
60
•
5"lmin Act 4i¢ Resin
•
20"/rain Acl lic Resin
80
Tensile Adhesive Bond Strength t psi
Fig. 12. Comparison of adhesion with crosshead speeds of 5 inches per minute and 20 inches per minute. ,~dhesive. Retention of this material on an impression tray :.~ therefore entirely mechanical. Variation of the speed of ~e~sile testing between 5 to 20 inches per minutes did not Mfect the adhesive bond strength of the impression mate~i:.l tested. R EFERENCES Shillingburg HT, Hatch RA, Keenan MP, Hemphill MW. Impression materials and techniques used fur cast restorations in eight states. J Am Dent Ass0c 1980;100:696-9.
2. Bomberg TJ, Hatch RA, Hoffman W Jr. Impression material thickness in stock and custom trays. J PROSTHET DENT 1985;54:170-2. 3. Bomberg TJ, Hatch RA, Hoffman W Jr. Impression trays, their selection, and associated costs. New Mexico Dent J 1983;34:10. 4. Hnsoda J, Fusayama T. Distortion of irreversible hydrocolloid and mercaptan rubber-base impressions. J PROSTHETDENT 1961;11:318-33. 5. Myers GE, Stockman DG. Factors that affect the accuracy and dimensional stability of the mercaptan rubber-base impression materials. J PROSTHET DENT 1961;10:525-35. 6. Tylman SD, Malone WFP. Tylman's theory and practice of fixed prosthodontics. 7th ed. St Louis: CV Mosby Co, 1978. 7. Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed
IMPRESSION ADHESIVE:PARTI
prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, Inc, 1981. 8. de AraujoPA, Jorgsnsen KD. Effect of material bulk and undercuts on the accuracyof impressionmaterials. J PROSTHETDENT1985;54:791-4. 9. StackhouseJA. Dimensionalchange of custom acrylicimpressiontrays. J New Jersey Dent Assoc 1976;47:28-9. 10. Pagniano RP, Scheid RC, ClowsonRL, Daagefoerde RO, Zardiackas LD. Linear dimensional change of acylicresins used in fabrication of custom trays. J PROSTHETDENT1982;47:279-83. 11. GoldfogelM, HarveyWL, WinterD. Dimensionalchangeof acrylicresin tray materials. J PROSTHETDENT1985;54:284-6. 12. Eames WB, SiewekeJC. Seven acrylicresins for custom trays and five putty-wash systems compared. Oper Dent 1980;5:162-7. 13. FehiingAW, Hesby RA, Pelleu GB Jr. Dimensionalstability of autopolymerizing acrylic resin impression trays. J PEOSTHETDENT 1986; 55:592-7. 14. Collard EW, Caputo AA, Standlee JP, Trabert KC. Dynamicstresses encountered in impressionremoval.J PROSTHETDENT1973;29:498-506. 15. Samman JM, Fletcher AM. A study of impression tray adhesives. Quintessence Intl 1985;4:305-9. 16. Ellam AH, Smith DC. The relative effectiveness of adhesives for polysulphide impression materials. Br Dent J 1966;120:135-8.
17. Shigeto N, Kawazoe Y, Hamada T, Yamada S. Adhesion between copper-plated acrylictray resin and a polysulfiderubber impression material.J PROSTHET DF~r 1979;42:228-30. 18. Kawamura M. The bonding of rubber impression materials to tray mater/als.J Osaka Odontol Soc 1970;33:359. 19. Davis GB, Moser JB, Brinsden GI. The bonding propertiesof elastomer tray adhesives. J PROSTHET DENT 1976;36:278-87. 20. PhillipsRW. Elements of dental material. 4th ed. Philadelphia: W B Saunders, 1984:121. 21. Nicholson JW, Porter KH, Dolan T. Strength of tray adhesives for
elastomeric impression materials. Oper Dent 1985;10:12-6. 22. Grant BE, Tjan AHL.Tensileand peal bond strengths oftray adhesives. J PROSTHETDENT1988;59:165-8. 23. PhillipsRW. Skinner'sscienceof dental materials. 8th ed. Philadelphia: WB Saundars, 1982:150. Reprint requests to:
DR. JOHNNYY. CHAI DENTALSCHOOL NORTHWESTERN UNIVERSITY 240 E. HURON ST. CHICAGO, IL 60611
Effect of p o r c e l a i n c r o w n s u b s t r u c t u r e s on v i s u a l l y perceivable Value B. J. C r i s p i n , D D S , M S , a S. K. O k a m o t o , D D S , b a n d H. G l o b e c University of California, Los Angeles, School of Dentistry, Los Angeles, Calif. F a c t o r s t h a t will affect the p o t e n t i a l color of c e r a m i c r e s t o r a t i o n s m u s t be u n d e r stood to co n t r o l v a r i a b l e s t h a t exist. Clinical o b s e r v a t i o n s o f p o r c e l a i n r e s t o r a t i o n s l e a d to the h y p o t h e s i s t h a t c e r t a i n s u b s t r u c t u r e s tend to p r o d u c e c r o w n s w i t h a l o w e r t h a n e x p e c t e d V a l u e (brightness). This study w a s done to d e t e r m i n e w h e t h e r a v i s u a l l y p e r c e i v a b l e difference could be d e t e c t e d b e t w e e n g r o u p s of c e r a m i c c r o w n s w i t h different s u b s t r u c t u r e s . T w o t e s t g r o u p s of c r o w n t y p e s w i t h f o u r different p o r c e l a i n s u b s t r u c t u r e s w e r e c o m p a r e d . In the first group, m e t a l c e r a m i c c r o w n s m a d e w i t h e i t h e r G a l a x y o r R e x il l i u m I I I alloys w e r e co m p ar ed . In the second group, aluminous p o r c e l a i n j a c k e t c r o w n s w i t h and w i t h o u t a tin-plated, bonded p l a t i n u m foil i n t e r n a l l y w e r e c o m p a r e d . Visual a n a l y s i s s h o w e d t h a t (1) in the m e t a l c e r a m i c group, the c r o w n s with the Rex i l l i u m I I I s u b s t r u c t u r e w e r e s c o r e d as m o r e o f te n h a v i n g a l o w e r significant Value, and (2) in the aluminous p o r c e l a i n j a c k e t g r o u p t h e c r o w n s w i t h t h e tin-plated, bonded p l a t i n u m s u b s t r u c t u r e s w e r e s c o r e d as m o r e o f te n h a v i n g a l o w e r significant Value. (J PROSTHET DENT 1991;66:209-12.)
W
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i
l
e
the esthetic demands of patients have never been greater, factors affecting the color of ceramic restorations must be understood to control the variables t h a t exist. 1"7 Clinical observations of porcelain restorations made at the University of California, Los Angeles (UCLA), School of Dentistry with various substructures indicated t h a t certain trends existed. When esthetically demanding single-unit all-ceramic restorations were made by use of the
aAssociate Professor, Director, Center for Esthetic Dentistry. bAdjunct Professor, Section of Removable Prosthodontics. CResearch Associate; Certified Dental Technician. 10/1/14819 THE JOURNALOF PROSTHETICDENTISTRY
twin foil technique (tin-plated, platinum-bonded aluminous porcelain jacket), they appeared lower in Value than aluminous porcelain jacket crowns made without the bonded platinum foil. In addition, follow-up of a population treated with etched-metal bonded fixed partial dentures made with a nickle-chrome alloy indicated t h a t the pontics were routinely lower in Value t h a n conventional fixed partial dentures made with a gold-palladium alloy. Hue and Chroma discrepancies in a ceramic restoration appear less significant and are easier to modify than increasing the Value when it is too low. 1 Any factor t h a t may reduce the Value of a ceramic restoration must be understood in order to be controlled. This preliminary study visually compared two groups of 209
Northwestern University, Dental School, Chicago, Ill. The tensile a d h e s i v e bond strength of five impression a d h e s i v e s y s t e m s w a s studied: polysulfide, polyether, p o l y v i n y l s i l o x a n e , condensation silicone impression, and p o l y v i n y l s i l o x a n e putty a d h e s i v e s y s t e m s . R e s u l t s s h o w e d no s i g n i f c a n t difference in a d h e s i v e bond strength to a u t o p o l y m e r i z i n g acrylic resin b e t w e e n the former four impression m a t e r i a l s studied. P o l y e t h e r and m e d i u m - v i s c o s i t y polyvin y l s i l o x a n e demonstrated significantly higher a d h e s i v e bond strength to polystyrene than e i t h e r polysulfide or condensation silicone. The m e d i u m - v i s c o s i t y p o l y v i n y l s i l o x a n e impression m a t e r i a l s h o w e d significantly higher a d h e s i v e bond strength to p o l y s t y r e n e than a u t o p o l y m e r i z i n g acrylic resin w h e r e a s polysulfide and condensation silicone impression m a t e r i a l s adhered significantly better to a u t o p o l y m e r i z i n g acrylic resin than polystyrene. The p o l y v i n y l s i l o x a n e putty did not adhere to its impression adhesive. V a r i a t i o n of the speed of tensile t e s t i n g b e t w e e n 5 to 20 inches per minutes did not affect the a d h e s i v e bond strength of a polysulfide impression material. (J PROSTHET DENT 1991;66:201-9.)
C o n t r o v e r s y has existed over the rationale for the use of stock trays in making elastomeric impressions. A survey in 1980 revealed that almost 75% of the sampled dentists used stock trays in making impressions for cast restorations. Less than 20% of the sampled dentists used a putty-wash system with stock trays. 1 Another study showed 70 % of the dentists used stock trays instead of customs trays and approximately 40% of them used a putty-wash system. 2 The common practice of using stock trays had been attributed to cost and convenience.3 The differences between stock trays and custom trays are thought to be (1) the provision of a uniform thickness of impression material, (2) the dimensional stability of tray material, (3) their rigidity and wall thickness, and (4) the ability of the tray material to retain an impression adhesive and hence the impression material. Common stock trays are made of polystyrene. To provide adequate strength to a tray, medium-impact polystyrene is commonly used. Medium-impact polystyrene products are molded by use of portions of regular polystyrene with high-impact polystyrene (acrylonitrile-butadiene-styrene)
Presented at the American Prosthodontic Society meeting, Chicago, Ill. aAssistant Professor, Division of Fixed Prosthodontics, Department of Restorative Dentistry. bprofessor and Director, Advanced Education Prosthodontics. cProfessor, Division of Biological Materials, Department of Basic Science. dprofessor and Director, Division of Fixed Prosthodontics, Department of Restorative Dentistry. 10/1/26187
THE JOURNAL OF PROSTHETIC DENTISTRY
and vacuum-injection. The exact proportion of these two raw materials in a stock tray has not been released by manufacturers. The importance of an even and correct thickness of impression material (2 to 3 mm) within custom trays has been emphasized. 47 A recent study also showed that increasing the thickness of impression material from 1 to 4 mm resulted in increasingly inaccurate dies. s However a community study showed that the difference in thickness of impression material around prepared or unprepared teeth was less than 1 mm between stock and custom trays. 2 Distortion of an impression due to dimensional change of the tray material is only applicable to custom tray material, autopolymerizing poly(methylmethacrylate). Studies of dimensional shrinkage of acrylic resin tray material reported 24-hour shrinkage values from 0.08 % to 0.38 % .9-12 Some authors believed that small values of this magnitude were unlikely to cause significant distortion in the subsequent impression. 9 Some believed that impressions should not be made sooner than 9 hours after making a custom tray or that placing the tray in boiling water for 5 minutes allowed it to be used soon after it was made. 1° Most investigators recommended that no impression should be made within 24 hours after the tray was made. 11,12 However, controversy existed about the effect of a shrinking custom tray on the size of the resulting die. 12,13 Rigid trays have been shown to induce more stress during removal according to a photoelastic study. 14 However the use of polymeric impression trays of insufficient wall thickness to provide flexibility is discouraged because polysulfide and polyether impression adhesives can dissolve polymeric tray material. Too much flexion of an
201
CHAI ET AL.
Batch numbers Impression materials
Brands
Polyether Potyvinylsiloxane regular body Polysulfide regular body
Impregum-F* Mirror-3? Permlastic¢
Condensation silicone
Denture Elasticon¢
Polyvinylsiloxane putty
Mirror-3?
Base
Catalyst
Adhesive
473 71268 30387 1012 12388 1334 71268
130 71268 30387 1012 12388 1334 71268
0036/2 12688 71387 111887 12688
*ESPE-Premier, Norristown, Pa. ¢Kerr Manufacturing Co., Romulus, Mich.
impression tray can itself induce error in the impression, 15 Although the adhesive bond strengths of impression materials to different tray materials were intensely studied, 1517 those to a common stock tray material, polystyrene. have not been investigated. Comparison of adhesive bond strength of other impression materials has often been made with polysutfide since it is probably the first elastomeric impression material used clinically. Generally, polyether systems showed the highest adhesive bond strength, followed by polysulfide systems and then the condensation silicone systems. 15, is, 19 Although PhiUips 2° indicated that silicone systems do not provide enough adhesion, some addition silicone systems showed greater bond strength than polysulfide systems and sometimes were comparable to polyether systemsY" 22 When the mode of rupture at the junction of the impression material and adhesive-tray material is examined, polyetber fails cohesively within the impression material. It is reasonable to assume that the actual adhesive bond strength is higher than what has been observed. The mode of failure of silicone impression systems is commonly adhesive in nature except for one type of condensation silicone studied by Davis et al. 19 Nicholson et al. 21 emphasized that the rupture of addition silicone material occurred at the adhesive-resin interface, indicating the poor adhesion of adhesive to acrylic resin tray material. There is no common mode of failure for the polysutfide impression systems. It seemed that variations in tray material and thickness of impression material all influenced the mode of failure. When the material failed adhesively, adhesive usually remained on the tray material. 15, 19.21,23 Comparison of results of different bond strength studies has been particularly difficult because of the lack of standardization of technique. The most striking observation is the vast difference in crosshead speed. Speeds as low as 2 mm per minute 17and as high as 20 inches per minute have been used. 19 Only one study attempted to compare the effect on bond strength of varying the crosshead speed. It was
Z()~
discovered that increasing the crosshead speed from 2 inches per minute to 20 inches per minute generally increased the bond strength, especially the shear bond strength. 16 This research (1) compared the bond strength of different elastomeric impression adhesive systems, (2) compared the bond strength of different tray materials, and (3) examined the effect on adhesive bond strength of varying the rate of separation.
MATERIAL AND METHODS Acrylic resin (Formatray, Kerr Manufacturing Co., Romulus, Mich.) blocks of 1-inch square testing surface were made from an aluminum mold (Figs. 1 and 2). Acrylic resin testing surfaces were allowed to polymerize against a piece of aluminum foil to simulate the practice of burnishing aluminum foil over wax spacers when making a custom tray. Liquid/powder ratio according to mold consistency was used. Before the resin became rubbery, the thread portion of a screw hook (Screw Hook No. 6, Zhe Jiang, China) was set into the resin. After the rubbery stage, the mold was placed into a water bath (Lab-line Imperial III Water Bath, Lab-line Instruments, Inc., Melrose Park, Ill.) at 50 ° C _+ 1° C for 8 to 10 minutes to complete polymerization. The completed sample was finished with a sharp scalpel to the correct dimension. The samples were stored at room temperature for at least 24 hours before the experiment. Samples were chosen randomly for each part of the experiment.
Part 1: Comparison of different i m p r e s s i o n material systems The five impression material systems chosen were polysulfide, condensation silicone, medium-viscosity (regular) polyvinylsiloxane, polyether impression material, and polyvinylsiloxane putty (Table I). Each acrylic resin block was scrubbed with soap and tap water for 15 seconds, dried with a clean paper towel, and allowed to air dry for at least 15 minutes. One layer of the specified adhesive was painted onto the surface of the resin
AUGUST 1991 VOLUME S6 NUMBER 2
IMPRESSION ADHESIVE: PART I
Table II. M e a n adhesive bond strength of all materials tested Mean adhesive bond strength/psi Acrylic 5"/rain
Polystyrene 5"/min
Impression materials
X
SD
Polysulfide Polyether Polyvinylsiloxane regular Condensation silicone Polyvinylsiloxane putty
58.90 72.62 66.72 60.48 0.30
2.6 9.3 14.8 5.7 0.4
block and allowed to air dry at room temperature (25 ° _+ 3 ° C) for 15 minutes. A perforated metal plate with a thickness of I m m was used to retain the impression material mechanically (Fig. 3). The metal plate was bent at the corners to provide a I/8 inch thickness of impression material between the perforations and the surface of the resin block. A hook at the other side of the metal plate allowed attachment to the Instron Universal Load testing machine (Instron Corporation, Canton, Mass.). Adhesive of the corresponding type is painted on the metal plate to increase retention. The impression material was mixed according to the manufacturer's recommendation. Each specimen was allowed to set in a water bath at 37 ° C for 15 minutes. Material covering the resin block other than the testing surface was trimmed off with a sharp scapel blade. Hooks on the metal plate and resin blocks were attached to the Instron Universal Load testing machine with a metal chain. Each specimen was tested under tensile loads at a crosshead speed of 5 inches per minute until separation of the metal plate from the resin block was observed. The chart speed was set at 2 inches per minute. Five samples of each impression material were tested.
Part 2: Comparison of different tray material Autopolymerizing acrylic resin was compared with polystyrene (stock tray material). Polystyrene plates were cut into 1-inch squares and attached to resin blocks by first wetting the polystyrene plate with monomer before adding the resin dough. The same aluminum mold was used and a resin block with a polystyrene testing surface was made (Fig. 4). To standardize the surface roughness of all of the polystyrene plates, each sample was polished with white diamond on a felt wheel. The same five impression materiai systems were used.
Part 3: Variation in crosshead speed Five samples each of the impression materials except the putty material were tested with autopolymerizing acrylic resin as the tray material. The crosshead speed was set at
THE JOURNAL OF PROSTHETIC DENTISTRY
51.84 78.32 85.66 45.22 0.94
Acrylic 20"/rain SD
X
SD
5.2 18.6 8.4 12.9 0.66
59.38 59.98 71.85 55.94
7.0 17.8 10.0 12.3 Not tested
20 inches per minute and results were compared with those tested at 5 inches per minute (Part 1). Data obtained were analyzed with Student's t-test (unpaired), analysis of variance (ANOVA), and Scheffe's multiple comparison. RESULTS
Part 1: Comparison of different impression material s y s t e m s Data obtained with autopolymerizing acrylic resin as tray material and crosshead speed of the tensile testing machine set at 5 inches per minute are shown in Fig. 5 and Table II. A significant difference was found between the polyvinylsiloxane putty material and all other impression materials (p < 0.05). No statistically significant difference (p > 0.05) was found among polyether, medium-viscosity (regular) polyvinlysiloxane, condensation silicone, and polysulfide impression materials. The mode of failure of each impression adhesive material was determined as the most common interface where failure occurred. For polyether impression material, below one tenth of the testing surfaces were covered by impression adhesive and no impression material remained (Fig. 6). Adhesive failure of the polyether impression material occurred between its adhesive and the acrylic resin. For medium-viscosity polyvinylsiloxane impression material, more than three quarters of its adhesive remained on the acrylic resin block with less than one tenth of its impression material left (Fig. 7), indicating that its mode of failure was primarily adhesive in nature and was between the impression material and adhesive. Acrylic resin blocks used for polysulfide impression material had approximately half to seven eighths of their surfaces covered by adhesive after testing, with less than a tenth of the impression material remaining (Fig. 8). Approximately one eighth to one third of the total area of testing surface was covered by condensation silicone impression material, with all adhesive remaining on the acrylicresin after testing (Fig. 9). There w a s no sign of any adhesion of polyvinylsiloxane putty material to its adhesive. All impression adhesive stayed on the testing surface after the testing (Fig. 10).
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CHAI ET AL.
P a r t 2: ComlH~rison o f d i f f e r e n t t r a y mater'mls Mean tensile bond strengths of impression materials tested with polystyrene as tray material are shown in Fig. 5 and Table II. Statistically significant difference (p < 0.05) was found between polyvinytsiloxane putty material and each of the other materials. No significant difference (p > 0.05) was found between medium-viscosity polyvinylsiloxane and polyether or between polysulfide and condensation silicone impression material. However, significant difference (p < 0.05) was found with medium-viscosity polyvinylsiloxane and polyether when compared with polysulfide and condensation silicone impression material. When the tensile bond strength of each material to autopolymerizing acrylic resin was compared with that to polystyrene, medium-viscosity polyvinylsiloxane showed statistically significantly higher bond strength to polystyrene than acrylic resin (p < 0.05) (Fig. 11, Table II). Polysulfide and condensation silicone adhered significantly better to autopolymerizing acrylic resin than to polystyrene (p < 0.05). No statistically significant difference was found in bond strength between the tray materials for polyether and polyvinylsiloxane putty material (p > 0.05). The modes of failure of polyether, medium-viscosity polyvinylsiloxane, and polyvinylsiloxane putty impression material were similar to those observed for acrylic resin. Failure occurred between polyether impression adhesive and polystyrene, primarily between medium-viscosity polyvinylsiloxane impression material and its adhesive, and between polyvinylsiloxane putty material and its adhesive. For both polysu]fide and condensation silicone impression material, almost all adhesive with little or no impression material remained on polystyrene (Figs. 5 through 9).
P a r t 3: V a r i a t i o n in c r o s s h e a d s p e e d ANOVA revealed no significant difference (p > 0.05) in bond strength among the four impression materials investigated by use of a rate of separation of 20 inches per minute and acrylic resin (Fig. 5, Table II). When the tensile bond strength of each material in this group was compared with those tested at a speed of 5 inches per minute, no statistically significant difference was found ~)r any of these materials (p > 0.05) (Fig. 12). The mode of failure of sample tested at a speed of 20 inches per minute did not seem to be different from those tested at 5 inches per minute.
DISCUSSION Polyether and medium-viscosity polyvinylsiloxane demonstrated better adhesive bond strength to autopolymerizing acrylic resin than polysulfide or condensation silicone impression material although they did not differ statisti-
-~,y~
cally. Previous studies that compared different impression materials seemed to favor the former two materials but statistical analysis was not performed. The highest mean adhesive bond strength achieved by polyether impression material was approximately 73 psi. This result compared closely with those reported by Samman and Fletcher, 15 and Davis et al., 19 which were in the range of 70 to 85 psi. However, values as high as those reported by Grant and Tjan 22 (approximately 110 psi) and Nicholson et al. 21 (approximately 440 psi) were never achieved. The modified type of the common polyether impression material (Impregum-F) investigated in this study only partly explains the vast differences reported. The adhesive strength of polyether impression material bonded to polystyrene (78.32 psi) was higher than that to acrylic resin but not statistically significant. The adhesive strengths of medium-viscosity polyvinylsiloxane bonded to different tray materials demonstrated values statistically similar to those of polyether impression material. This finding was supported by recent studies that found polyvinylsiloxane impression material as a group at least as strong as polysulfide and sometimes comparable to polyether impression material. 21,22 Polyether and medium-viscosity polyvinylsiloxane showed stronger adhesion to polystyrene than either polysulfide or condensation silicone. The better bond strength of medium-viscosity polyvinylsiloxane to polystyrene than acrylic resin may be due to a difference in the solubility of tray materials in the solvent of the impression adhesive and a difference between their surface finish. The same rationale may be used to explain the significant differences in bond strength of polysulfide and condensation silicone impression materials to the two tray materials. However, the exact nature of this variation has yet to be investigated. The polysulfide impression material tested in this study showed a result similar (approximately 60 psi/acrylic resin) to most of those reported, 17,19.22 except that of Nicholson et al. 21 (approximately 170 psi). This material was also the most consistent material tested (smallest standard deviation). Its adhesive bond to polystyrene was approximately 8 to 9 psi lower than that to acrylic resin. The strength of condensation silicone bonded to acrylic resin was comparable to that of the polysulfide impression material (about 60 psi). This is the highest reported adhesive bond strength of a condensation silicone impression material. Previous studies had not shown condensation silicone material to exceed a bond value of 30 psi. 19,22 Its bond strength to polystyrene was approximately 15 psi lower than that to acrylic resin, indicating that additional mechanical retention is needed (extra holes) when this material is used with polystyrene stock trays. This study showed little or no adhesion of polyvinylsiloxane putty material to its adhesive. When this material is used, adequate mechanical retention is therefore man-
At~GtJST 1991
VOLUME 66
NUMBER 2
IMPRESSION ADHESIVE: PART I
Fig. Fig. Fig. Fig.
1. 2. 3. 4.
Acrylic resin block. Aluminum mold. Perforated metal plate. Acrylic resin block with polystyrene testing surface.
datory. Because of the extremely viscous consistency of the putty, retention holes should have enough sizeto allow this material to flow through them easily. Classifying the mode of failureof an impression material/adhesive/tray material system for an impression materialis of academic interestunless its bond strength is unacceptably low. For instance, because polyvinylsiloxane putty material failed at the impression material-adhesive junction, attempts to increase itsadhesive strength should therefore aim primarily at improving the adhesion between the impression material and its adhesive. The term adhesivefailurehas been used to describe failureeitherbetween the tray material and impression adhesive or between the impression adhesive and impression material. The term cohesive failure has been used loosely.Davis et al.,I9and S a m m a n and Fletcher15 described cohesive failureas one that occurred within the body of the impression material itself,usually referring to polyether impression material.
THE JOURNAL OF PROSTHETIC DENTISTRY
However, adhesive failure between adhesive and acrylic resin was observed for the polyether impression material used in the present study. Nicholson et al. 21 described the mode of failure of polyether impression material as cohesive when they referred to "pieces of fractured Impregum bonded to the acrylic blocks." The same phenomenon was described by Kawamura is as mixed failure. Pure cohesive failures were not observed in this study. However, mixed adhesive-cohesive failures were found for some materials tested. Pure adhesive failures were seen for polyether and polyvinylsiloxane putty. When the amount of adhesive or impression material left on a testing surface versus its bond strength was compared with different impression materials, no correlation was found between these two variables. The amount of an impression material left on the tray material does not indicate its ability to adhere to it. When individual impression materials that showed differences in bond strength to differ-
205
CHAI E T AL.
1M
~olyether ~olwinytsiloxane regular :'olysuff'zle 3ondommtion silicone
t03
=olyvinylstoxanePutty
=
20"/rain Acrylic Resin
5"/min Acrylic Resin
5*/rain
Polystyrene
Fig. 5. Tensile adhesive bond strength of all impression material systems.
ent tray materials were examined, only the condensation siliconeshowed more impression material remaining on the acrylic resin than on the polystyrene. Although the condensation silicone impression material showed significantly better adhesion to acrylic resin, no correlation between the amount of impression material left on a tray material and its bond strength should be suggested. Variation of crosshead speed of the tensile load testing machine between 20 and 5 inches per minute did not cause a change in bond strength of four impression materials investigated. This finding is contrary to those of Ellam and Smith Is who demonstrated an increase in adhesive bond strength when the crosshead speed was raised from 2 inches to 20 inches per minute.
Clinical implications One would question the clinical significance of the observed difference between impression adhesive systems and the critical adhesive bond strength. Polysulfide is the elastomeric impression material that seems to have proved adequate adhesive bond strength clinically, and compari~,t~ of adhesive bond strength to it has often been made. It appears that if the adhesive bond strength of an impression ~y~tem is below 50 psi (under the same experimental conditions as the present study), which is achieved by polysul~de with polystyrene as tray material, one should question ~he efficacy of this adhesive system. However, whether the ~c~ce needed to remove an impression tray from a mouth +'+~Ltldreach this level is unknown.
The results of the present study suggest that the speed of removal of an impression tray from the mouth does not seem to affectthe adhesive bond strength of these impression materials. However, removal of elastomeric impression from the mouth with a quick snap is stilladvisable to minimize viscous deformation of elastomeric impression materials.
CONCLUSIONS AND SUMMARY The tensile adhesive bond strength of five impression material systems was investigated: polyether, medium-viscosity polyvinylsiloxane, polysulfide, condensation silicone, and polyvinylsiloxane putty impression materials. Autopolymerizing acrylic resin and polystyrene were used as tray materials. The effect of variation in the speed of tensile testing was also studied. Results showed no significant difference in the strength of adhesive bond to autopolymerizing acrylic resin between the former four impression materials studied. As a group, the polyether and medium-viscosity polyvinylsiloxane demonstrated significantly higher adhesive bond strength to polystyrene than polysulfide and condensation silicone impression materials as a group. The medium-viscosity polyvinylsiloxane impression material showed significantly higher adhesive bond strength to polystyrene than autopolymerizing acrylic resin, whereas polysulfide and condensation silicone impression materials adhered significantly better to autopolymerizing acrylic resin than to polystyrene. The polyvinylsiloxane putty material did not adhere to its impression
IMPRESSION ADHESIVE: PART I
Fig. 6. Polyether samples after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 7. Medium-viscosity polyvinylsiloxane after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 8. Polysulfide samples after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 9. Condensation silicone samples after testing. Top row, acrylic resin; bottom row, polystyrene. Fig. 10. Polyvinylsiloxane putty samples after testing. Right, acrylic resin; left, polystyrene.
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207
C H A I E T AL.
Polyvinytsilc
Conden,sati
Potwirry~Ioxl
O
20
40
60
80
100
Tensile Adhesive Bond Strength / psi
Fig.
11. Comparison
O
of adhesion between acrylic resin and polystyrene.
20
40
60
•
5"lmin Act 4i¢ Resin
•
20"/rain Acl lic Resin
80
Tensile Adhesive Bond Strength t psi
Fig. 12. Comparison of adhesion with crosshead speeds of 5 inches per minute and 20 inches per minute. ,~dhesive. Retention of this material on an impression tray :.~ therefore entirely mechanical. Variation of the speed of ~e~sile testing between 5 to 20 inches per minutes did not Mfect the adhesive bond strength of the impression mate~i:.l tested. R EFERENCES Shillingburg HT, Hatch RA, Keenan MP, Hemphill MW. Impression materials and techniques used fur cast restorations in eight states. J Am Dent Ass0c 1980;100:696-9.
2. Bomberg TJ, Hatch RA, Hoffman W Jr. Impression material thickness in stock and custom trays. J PROSTHET DENT 1985;54:170-2. 3. Bomberg TJ, Hatch RA, Hoffman W Jr. Impression trays, their selection, and associated costs. New Mexico Dent J 1983;34:10. 4. Hnsoda J, Fusayama T. Distortion of irreversible hydrocolloid and mercaptan rubber-base impressions. J PROSTHETDENT 1961;11:318-33. 5. Myers GE, Stockman DG. Factors that affect the accuracy and dimensional stability of the mercaptan rubber-base impression materials. J PROSTHET DENT 1961;10:525-35. 6. Tylman SD, Malone WFP. Tylman's theory and practice of fixed prosthodontics. 7th ed. St Louis: CV Mosby Co, 1978. 7. Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed
IMPRESSION ADHESIVE:PARTI
prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, Inc, 1981. 8. de AraujoPA, Jorgsnsen KD. Effect of material bulk and undercuts on the accuracyof impressionmaterials. J PROSTHETDENT1985;54:791-4. 9. StackhouseJA. Dimensionalchange of custom acrylicimpressiontrays. J New Jersey Dent Assoc 1976;47:28-9. 10. Pagniano RP, Scheid RC, ClowsonRL, Daagefoerde RO, Zardiackas LD. Linear dimensional change of acylicresins used in fabrication of custom trays. J PROSTHETDENT1982;47:279-83. 11. GoldfogelM, HarveyWL, WinterD. Dimensionalchangeof acrylicresin tray materials. J PROSTHETDENT1985;54:284-6. 12. Eames WB, SiewekeJC. Seven acrylicresins for custom trays and five putty-wash systems compared. Oper Dent 1980;5:162-7. 13. FehiingAW, Hesby RA, Pelleu GB Jr. Dimensionalstability of autopolymerizing acrylic resin impression trays. J PEOSTHETDENT 1986; 55:592-7. 14. Collard EW, Caputo AA, Standlee JP, Trabert KC. Dynamicstresses encountered in impressionremoval.J PROSTHETDENT1973;29:498-506. 15. Samman JM, Fletcher AM. A study of impression tray adhesives. Quintessence Intl 1985;4:305-9. 16. Ellam AH, Smith DC. The relative effectiveness of adhesives for polysulphide impression materials. Br Dent J 1966;120:135-8.
17. Shigeto N, Kawazoe Y, Hamada T, Yamada S. Adhesion between copper-plated acrylictray resin and a polysulfiderubber impression material.J PROSTHET DF~r 1979;42:228-30. 18. Kawamura M. The bonding of rubber impression materials to tray mater/als.J Osaka Odontol Soc 1970;33:359. 19. Davis GB, Moser JB, Brinsden GI. The bonding propertiesof elastomer tray adhesives. J PROSTHET DENT 1976;36:278-87. 20. PhillipsRW. Elements of dental material. 4th ed. Philadelphia: W B Saunders, 1984:121. 21. Nicholson JW, Porter KH, Dolan T. Strength of tray adhesives for
elastomeric impression materials. Oper Dent 1985;10:12-6. 22. Grant BE, Tjan AHL.Tensileand peal bond strengths oftray adhesives. J PROSTHETDENT1988;59:165-8. 23. PhillipsRW. Skinner'sscienceof dental materials. 8th ed. Philadelphia: WB Saundars, 1982:150. Reprint requests to:
DR. JOHNNYY. CHAI DENTALSCHOOL NORTHWESTERN UNIVERSITY 240 E. HURON ST. CHICAGO, IL 60611
Effect of p o r c e l a i n c r o w n s u b s t r u c t u r e s on v i s u a l l y perceivable Value B. J. C r i s p i n , D D S , M S , a S. K. O k a m o t o , D D S , b a n d H. G l o b e c University of California, Los Angeles, School of Dentistry, Los Angeles, Calif. F a c t o r s t h a t will affect the p o t e n t i a l color of c e r a m i c r e s t o r a t i o n s m u s t be u n d e r stood to co n t r o l v a r i a b l e s t h a t exist. Clinical o b s e r v a t i o n s o f p o r c e l a i n r e s t o r a t i o n s l e a d to the h y p o t h e s i s t h a t c e r t a i n s u b s t r u c t u r e s tend to p r o d u c e c r o w n s w i t h a l o w e r t h a n e x p e c t e d V a l u e (brightness). This study w a s done to d e t e r m i n e w h e t h e r a v i s u a l l y p e r c e i v a b l e difference could be d e t e c t e d b e t w e e n g r o u p s of c e r a m i c c r o w n s w i t h different s u b s t r u c t u r e s . T w o t e s t g r o u p s of c r o w n t y p e s w i t h f o u r different p o r c e l a i n s u b s t r u c t u r e s w e r e c o m p a r e d . In the first group, m e t a l c e r a m i c c r o w n s m a d e w i t h e i t h e r G a l a x y o r R e x il l i u m I I I alloys w e r e co m p ar ed . In the second group, aluminous p o r c e l a i n j a c k e t c r o w n s w i t h and w i t h o u t a tin-plated, bonded p l a t i n u m foil i n t e r n a l l y w e r e c o m p a r e d . Visual a n a l y s i s s h o w e d t h a t (1) in the m e t a l c e r a m i c group, the c r o w n s with the Rex i l l i u m I I I s u b s t r u c t u r e w e r e s c o r e d as m o r e o f te n h a v i n g a l o w e r significant Value, and (2) in the aluminous p o r c e l a i n j a c k e t g r o u p t h e c r o w n s w i t h t h e tin-plated, bonded p l a t i n u m s u b s t r u c t u r e s w e r e s c o r e d as m o r e o f te n h a v i n g a l o w e r significant Value. (J PROSTHET DENT 1991;66:209-12.)
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the esthetic demands of patients have never been greater, factors affecting the color of ceramic restorations must be understood to control the variables t h a t exist. 1"7 Clinical observations of porcelain restorations made at the University of California, Los Angeles (UCLA), School of Dentistry with various substructures indicated t h a t certain trends existed. When esthetically demanding single-unit all-ceramic restorations were made by use of the
aAssociate Professor, Director, Center for Esthetic Dentistry. bAdjunct Professor, Section of Removable Prosthodontics. CResearch Associate; Certified Dental Technician. 10/1/14819 THE JOURNALOF PROSTHETICDENTISTRY
twin foil technique (tin-plated, platinum-bonded aluminous porcelain jacket), they appeared lower in Value than aluminous porcelain jacket crowns made without the bonded platinum foil. In addition, follow-up of a population treated with etched-metal bonded fixed partial dentures made with a nickle-chrome alloy indicated t h a t the pontics were routinely lower in Value t h a n conventional fixed partial dentures made with a gold-palladium alloy. Hue and Chroma discrepancies in a ceramic restoration appear less significant and are easier to modify than increasing the Value when it is too low. 1 Any factor t h a t may reduce the Value of a ceramic restoration must be understood in order to be controlled. This preliminary study visually compared two groups of 209
