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Microleakage and bond strength of resin restorations with various bonding agents
Microleakage and bond strength of resin restorations with various bonding agents
P. D. Hammesfahr, C. T. Huang, S. E. Shaffer The L. D. Caulk Divisionof Dentsply International, Milford, Delaware, U.S.A.
Hammesfahr PD, Huang C-T, Shaffer SE. Microleakage and bond strength of resin restorations with various bonding agents. Dent Mater 1987: 3: 194-199. Abstract - Shear bond strengths and microleakage of 7 dentin adhesives were evaluated by in vitro test procedures. The relative microleakage of the 7 systems was determined in modified Class V cavity preparations having margins in both dentin and enamal. The degree of microleakage was determined using a scoring system that ranked penetration along Jche gingival wall, and the degree of diffusion into the dentin. The 7 dentin adhesive systems were clearly distinguishable by both test procedures, with PRISMA | UNIVERSAL BOND T M having the highest dentin bond strengths and lowest microleakage results.
Key words: Dentin adhesive, microleakage, bond strengths, polymerizable resins, Class V cavity preparation.
In the last decade, there has been a wide-spread increase in the use of polymerizable composite materials for restorations providing strength, esthetics, and durability. However, these polymeric materials and their respective inorganic fillers were not particularly adhesive to enamel or dentin, and thus, the need for suitable adhesion between the restorative material and tooth structure was clearly evident. Therefore, retention via physical (mechanical) or chemical means was pursued. In the case with the polymeric materials, suitable mechanical means were first developed to create the necessary retention between the restorative materials and enamel. For example, Buonocore introduced an acid-conditioning technique in 1955(1) that created micro-mechanical retention in enamel. This practice is now well established, provides exceptionally strong retention of polymeric materials to enamel, and has been shown to be clinically successful. However, this simple and convenient acid-conditioning technique is not widely recommended for use on dentin. This is due partly to the different chemical structure of dentin, being comprised mostly of organic material including extension of living cells within the dentinal tubules (2). The use of acids on freshly cut dentin has been suggested as being a potential causative
involving polymerizable adhesive materials are of interest for numerous reasons. Many publications (7-15) concerning polymerizable or polymer containing dentin adhesives have resulted in widely differing results which are often contradictory (9-12). Consequently, the purpose of this research was to provide a comprehensive in vitro evaluation of the adhesive and microleakage properties of the major dentin adhe-
agent for sensitivity noted by patients after composite restorative procedures. Therefore, it is generally considered contraindicated to expose dentin to acids. In fact, it is this very problem that led to the development of nonfluid, acid gels to control placement techniques for the enamel etchant. Thus, much research has been conducted into finding a suitable alternative to enamel conditioning and mechanical retention through the use of chemical adhesion (3-5). While it was known for some time that certain cements and glass ionomers provided adhesion to tooth structure (6), systems
P. D. Hammesfahr, Director of Technical Research, CAULK/DENTSPLY, Lakeview & Clarke Avenues, P. O. Box 359, Milford, DE 19963, U.S.A. Received April 2, 1986; accepted for publication November 10, 1986.
* Caulk/Dentsply Division of Dentsply International, Inc. Milford, Delaware 19963
Table 1. Materials Adhesive
Restorative
Code
Manufacturer
BondliteTM
Herculite T M Syringeable Herculite T M Condensable Visar-FilTM Marathon TM
HS HC VF M
Kerr/Sybron
Heliosit Heliomolar AurafilrM
H HM A
Vivadent
PF PM FF S P-10 P-30
Caulk/Dentsply
Creation TM Bond Dentin-Adhesit
VLC Dentin Bonding Agent Prisma| Univeral BondT M Prisma-Fil| Prisma| Micro-Fine Ful-Fil| ScotchbondvM(S. C. and Silux| VLC) P-10| P-30T M SinterbondTM
SinterFilT M
SF
DenMat Corp.
J&J Dental Products Co.
3M Dental Products
Teledyne Getz
195
Resins: microleakage & bond strength Table 2. Shear bond strength to dentin Adhesive
ENAMEL~
Composite
COMPOSITE-- ~1.0 1-"~,,,,..LEAKAGE DENTIN~ ~1~
Fig. 1. Scoring system: penetration along the gingival wall. sives, and a new, one-component, visible light-cured dentin adhesive resin, PRISMA | U N I V E R S A L BOND TM.*
Material and methods In this study, 7 dentin adhesives were evaluated by in vitro bond tests and microleakage studies. Each dentin adhesive was used with a corresponding composite restorative material sold by the dentin adhesive manufacturer (Table 1). PRISMA | UNIVERSAL BOND TM is a one-component, visible light-cured dentin and enamel adhesive. It is comprised of polymerizable elastomeric oligomers, monomers, a visible light photo-initiator/accelerator system, and a polymerizable phosphoric acid ester adhesion promoter (U.S. Patent #4,514,342). The adhesion promoter contains a fully hydrolyzed phosphoric acid ester that does not contain any hydrolyzible halogen functions. The phosphoric acid ester is chemically
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
Prisma Universal Bond Prisma Universal Bond Prisma Universal Bond VLC Dentin Bonding Agent Dentin-Adhesit VLC Scotchbond Sinterbond S. C. Scotchbond VLC Scotchbond S. C. Scotchbond Bondlite Bondlite Dentin-Adhesit Creation Bond Creation Bond
PM PF FF A HM S SF S P-30 P-10 HS HC H VF M
~,~._
~'~
1080 (438) 1060 (570) 961 (578) 880 (511) 733 (347) 620 (270) 540 (290) 530 (290) 500 (240) 470 (380) 380 (270) 360 (240) 310 (200) 240 (160) 80 (60)
J
*Standard deviation is shown in parentheses. bonded to a molecule containing numerous polymerizable acrylate groups that co-polymerize with the main resin component upon curing. PRISMA U N I V E R S A L BOND is non-acidic, with essentially a neutral pH.
Bondstrengthprocedure Extracted human teeth obtained from local clinics were used for the in vitro testing. The teeth were treated with 1% sodium hypochlorite for 18-24 h to dissolve any attached tissue, then rinsed with water and stored (in water) at 4~ until needed. A flat bonding surface was prepared on each tooth by wetsanding a caries-free and crack-free area with carbide abrasive paper. Sanding was accomplished on a low-speed rotating wheel with carbide grit size !20, 320, and 600.
Dentin
The sanded teeth were dried with compressed air immediately prior to use. A l a y e r of an enamel/dentin adhesive (PRISMA | U N I V E R S A L BOND TM*) was applied to the dentin and thinned by blowing with compressed air. The layer was light-cured for ten seconds a visible light polymerization unit COMPOSITE with (PRISMA-LITE| Optionally, a second layer of PRISMA UNIVERSAL BOND could be added in the same LEAKAGE manner without affecting results. Next, composite was placed in a cylindrical plastic matrix with a 3.68 mm inside diameter, and positioned onto the bonding site. A cellophane matrix was placed over the top of the composite post, followed by application of slight Fig. 2. Scoring system: penetration toward pressure (ca. 225 g) with the light guide the pulp. to the top of the post to ensure proper 13'
Mean bond strength*, psi
~
seating. Immediately afterwards, the composite was cured for 30 s under slight pressure (ca. 225 g) which was applied in the manner previously described. The specimens were placed in distilled water for approximately 24 h at 37~ prior to debonding. Alternatively, specimens were also thermocycled (described under microleakage section) to determine the effect of thermal stress and hydrolytic stability. An Instron Universal Testing Machine t was used to apply a shear force to remove the bonded composite cylinders from the teeth. Each specimen was mounted vertically in a plastic bottle cap (one inch diameter) with self-cure polymethyl methacrylate resin so that the force from the Instron's crosshead was applied parallel to the flat tooth surface. The Instron's needle attachment was positioned on the post close to or touching the flat tooth surface to minimize variables due to leverage effects during de-bonding. The composite cylinder was placed under a continual load rate of 5 mm/min until the composite cylinder was fractured from the dentin. The shear strength was calculated in either MPa or psi. When evaluating competitive dentin or enamel bonding agents, the manufacturer's recommended procedure for bonding was uti* Instron, Model 1123 Canton, Massachusetts Table 3. T-test comparison of shear bond strengths to dentin (Table 2) Pairs XI ~ _X6 X_l @ _!13 X3 # _X9 X3 =~ X12
P 0.01 0.01 0.05 0.01
196
Hammesfahr et al.
Table 4. Shear bond strength to etched enamel Adhesive VLC Scotchbond Prisma Universal Bond Prisma Universal Bond VLC Dentin Bonding Agent Prisma Universal Bond Sinterbond Bondlite S. C. Scotchbond Bond[ite S. C. Scotchbond VLC Scotchbond Dentin-Adhesit
Composite
Mean bond strength*, psi
P-30 PF FF A PM SF HC P-t0 HS S S H
3270 (564) 3220 (990) 2970 (1300) 2900 (761) 2700 (925) 2470 (806) 2230 (447) 2180 (973) 2050 (361) 1770 (592) 1710 (695) 1530 (1090)
*Standard deviation is shown in parentheses. Table 5. Shear bond strengths to dentin - hydrolytic stability Adhesive A.
B.
Composite
Mean bond strength*, psi
Thermocycled between 10~ and 48~ for 540 Cycles Prisma Universal Bond PF VLC Scotchbond S Sinterbond SF
1,290 (732) 521 (265) 483 (306)
24-h boil in water Prisma Universal Bond VLC Scotchbond Sinterbond
PF S SF
720 (381) 106 (89) 340 (180)
*Standard deviation is shown in parentheses.
lized in the same m a n n e r as described above. The test specimens were then stored and d e b o n d e d as described above. Etched enamel
The sanded teeth were dried with compressed air immediately prior to use. Acid etching was p e r f o r m e d with either a 50% phosphoric acid liquid ( C A U L K TOOTH CONDITIONER LIQUID*) or a 37% phosphoric acid gel ( C A U L K TOOTH CONDITIONER GEL*). The acid etchant was placed onto the bonding site with a small brush and either left undisturbed if using the gel or agitated periodically if using the liquid, for a total of 60 s. Afterwards, the acid etchant was rinsed from the enamel with an air-water mist for 15 s, then dried with compressed air. A t this point, one coat of the bonding agent was applied as described previously for dentin. The composite cylinder was also bonded as discussed previously. De-bonding with the Instron p r o d u c e d the data which allowed the calculation of the shear strength in MPa or psi. Microleakage procedure
Extracted human
molar teeth
were
cleaned and disinfected with a sodium hypochlorite solution (1% in water) as described above. The teeth were then stored in water until needed. Two nonretentive V-shaped, Class V cavities were prepared on opposite sides of each tooth, e.g., buccal and lingual surfaces, or mesial and distal surfaces, to provide a control as well as a test system. A No. 58 carbide bur at high speed with water cooling was used to cut the preparation at the junction of the enamel and c e m e n t u m so that half of the cavosurface margins w e r e in enamel and half were in c e m e n t u m (dentin). A new No. 58 bur was used after 5 cavity preparations were cut. Approxi-
mate dimensions of the preparations were 4 m m mesiodistally, 3 m m occluso-gingivally, and 2 m m pulpal. Each cavity was rinsed with water, then dried with compressed air with no additional treatment to the dentin surface prior to bonding unless specified by the manufacturer. A group of at least 5 teeth were used for each experiment. Multiple replications of each experiment w e r e necessary to ensure sufficient sample size for evaluation. The enamel wall only of the preparation was conditioned for 60 s with an acid gel ( C A U L K T O O T H C O N D I T I O N E R G E L * ) which was applied with a small brush and left undisturbed for the prescribed time, followed by a 15-s rinse with an air-water mist. The preparations were then airdried with a compressed, oil-free air stream for 10 s. The following represent an e x a m p l e of the technique employed: T h e conditioned enamel and freshly cut dentin surface were coated with a uniform thin layer of an enamel/dentin adhesive, ( P R I S M A | U N I V E R S A L BONDTM*). A small brush was used to place the adhesive and an air blast from a dental syringe was used to further thin the application and r e m o v e any excess adhesive. The adhesive was then cured for 10 s with a dental visible light polymerization unit ( P R I S M A - L I T E | A second application of the P R I S M A U N I V E R S A L B O N D adhesive was placed with a small brush and thinned with an air blast. The second adhesive coat was also light polymerized for 10 s. A light-cured composite ( P R I S M A FIL| FUL-FIL | or light-cured microfilled resin ( P R I S M A | M I C R O F I N E * ) was placed in the preparation in one increment. Following bulk placement, a clear cervical matrix was pressed into place with locking college pliers and held under slight pressure
Table 6. Microleakage - penetration along gingival wall Adhesive 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Prisma Universal Bond Prisma Universal Bond Dentin Bonding Agent Prisma Universal Bond Bondlite VLC Scotchbond Bondlite S. C. Scotchbond VLC Scotchbond Dentin-Adhesit Dentin-Adhesit Sinterbond
Composite PM FF A PF HS S HC S P-30 HM H SF
*Standard deviation is shown in parentheses.
Mean penetration value* 0.36 0.41 0.45 0.56 0.57 0.64 0.68 0.93 1.08 1.13 1.13 1.28
(0.33) 7 (0.39) (0.44) (0.41) (0.42) (0.43) (0.36) (0.32) (0.28) (0.15) (0.37) (0.25)
AJ J
7
Resins: microleakage & bond strength Table 7. T-test comparison of microleakage penetration data (Table 6) Pairs X1 4= ~6 X2:7(z _X9 X44= X8
P
0.01 0.01 0.01
during a 10-s light-cure exposure. The matrix was removed, and the composite was cured for an additional 20 s. The restorations were immediately finished with abrasive discs, (SOF-LEX) -+ coarse, medium, and fine. Following the finishing procedure the specimens were stored in water (distilled or tap) at 37~ for 16-48 h. Other restorative systems were also evaluated using the manufacturer's directions and the technique described above. The teeth in each group were then thermocycled between a water bath of 48~ + 2~ and 10~ + 2~ for 24 h (540 cycles). Immersion time was approximately one minute in each bath with transfer time of 13 s in air between baths. Following the thermocycling period, the t e e t h were evaluated for marginal microleakage by modification of a silver nitrate staining technique described by Wu et al. (16). Dental compound was placed in the intra-radicular areas, and the teeth were coated with fingernail polish up to within 2 m m of the restoration to prevent silver nitrate penetration into the teeth from areas other than the cavity preparation. In a darkened room, the teeth were placed in 50% (by wt.) silver nitrate aqueous solution, and stored in total darkness for 2 h. The teeth were removed from the silver nitrate solution and rinsed in
tap water. Following rinsing, the teeth were sectioned ~ longitudinally with a diamond blade through the center of the restorations. The development process consisted of exposure of each sectioned specimen to a photoflood lamp for 5 min. Areas of silver nitrate penetration (microleakage) turned black due to the light exposure. The degree of marginal microleakage along the gingival wall (dentin) was determined by the degree of penetration of silver nitrate stain as measured by the scoring criteria described below. In scoring the microleakage results, it was felt that there was no single system available that would accurately reflect the leakage patterns observed. That is, leakage was observed to occur both along the gingival wall as well as into the dentin toward the pulp. Using various scoring methods, superficial leakage a short distance along the gingival wall could also have a large degree of penetration toward the pulp and yet receive a low score. Therefore, it was decided to use a separate score for each form of leakage observed; leakage along the gingival wall and leakage into the dentin toward the pulp. Leakage along the gingival wall of the cavity was reported as the ratio of the depth of penetration along the wall to the total length of the wall from the cementum to the apex. For example, stain penetration one-half of the distance to the apex is 0.5, while leakage to the bottom (apex) of the cavity yields 1.0 as the leakage value (Fig. 1). In the cases when penetration continues past the apex and is observed on the occlusal wall, the ratio is calculated
w Isomet Low-Speed Saw Buehler Ltd. Evanston, Illinois 60204
* Dental Products/3M 3M Center St. Paul, Minnesota 55144
Table 8. Microleakage - diffusion toward the pulp Adhesive 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Prisma Universal Bond Prisma Universal Bond VLC Dentin Bonding Agent Bondlite Bondlite Prisma Universal Bond VLC Scotchbond VLC Scotchbond Sinterbond S. C. Scotchbond Dentin-Adhesit Dentin-Adhesit
Composite
Mean diffusion value*
FF PM A HS HC PF S P-30 SF S H HM
0.27 (0.19) 7 0.28 (0.24) 0.30 (0.35) 0.31 (0.23) -1 0.35 (0.24) 0.36 (0.30) 0.45 (0.33) 0.51 (0.27) 0.56 (0.31) 7 0.60 (0.31) 0.71 (0.22) 0.77 (0.21)
*Standard deviation is shown in parentheses.
J A
197
Table 9. T-test comparison of microleakage - diffusion data (table 8) Pairs _X~4= _X8 X7 5d=_X12 iR8 4= X12
p
0.01 0.05 0.05
in a similar manner to yield penetration values between 1.0 and 2.0 (Fig. 1). The procedure used to calculate these ratios was to project a 35 mm color transparency of each tooth onto a screen and measure the distances with a metric ruler. During the microleakage process the silver nitrate solution may penetrate or diffuse into the dentin, and a method to quantify the depth of this diffusion was also developed. The technique was similar to the previous discussion where a ratio was calculated: the depth of diffusion is the ratio of the maximum distance the stain penetrated the dentin to the distance between the gingival wall and the pulp chamber. As an example (Fig. 2), penetration one-half of the distance to the pulp chamber yields 0.5, and penetration to the pulp chamber yields 1.0. The procedure used to measure these distances was identical to that described above.
Results Bond strength
Table 2 presents the bond strengths to dentin for the various dentin adhesive/ composite systems examined. Analysis of variance and t-tests (17, 18) were analyzed for the dentin bonding results (Table 2). The brackets shown in Table 2 indicate that the average bond strengths in each group are not significantly different at P > 0.05. However, Table 3 illustrates the pairs of mean bond strength which are Significantly different. Thus, PRISMA | UNIVERSAL BOND TM* with PRISMA | MICRO-FINE* and FUL-FIL| were significantly better (P < 0.05) than VLC Scotchbond with Silux*, Dentin-Adhesit with HeliositII and Bondlite with Herculite Syringeable~. II Vivadent Schaan, Liechtenstein Kerr/Sybron Romulus, Michigan 48174 **Amalgamated Dental International Weybridge, England tt j&j Dental Products East Windsor, NJ 08520
198
Hammesfahr et al.
Table 4 presents the representative bond strengths to enamel of the systems evaluated. In the systems tested, the enamel often failed cohesively, fracturing within the enamel. Therefore, an analysis of variance and t-test for enamel adhesion are invalid and were not preformed. Table 5 presents the bond strengths for several systems using adverse conditions to evaluate the hydrolytic stability of the dentin adhesives. As can be seen PRISMA | UNIVERSAL BOND ~* maintains acceptable adhesion even with numerous thermocycles or severe testing in boiling water for 24 h. Microleakage
Table 6 presents the results of the in vitro microleakage study in terms of the average penetration of stain along the gingival wall. Table 8 shows the results of the diffusion of stain toward the pulp. Analysis of variance (ANOVA) was applied to the penetration data (Table 6) and indicates no significant differences within the three bracketed groups (P > 0.05). The t-test was utilized in Table 7 to show differences between individual adhesive systems. For example, P R I S M A | U N I V E R S A L BOND TM* with P R I S M A | M I C R O FINE* and F U L - F I L | were significantly better (P < 0.01) than VLC Scotchbond with Silux and P-30', respectively. Comparison of the diffusion ratio of the dentin adhesive systems (Table 8) by A N O V A shows that there is no significant difference in leakage of the systems within each bracket. The t-test indicates that significant differences do exist between the l e a k a g e results of several of the individual adhesives (Table 9). The Prisma system (PRISMA | U N I V E R S A L B O N D TM and FUL-FIL | showed significantly less diffusion into the dentin than Scotchbond and P-30* (P < 0.01). Discussion The search for a suitable adhesive bond between tooth structure and polymerizable materials has lead to the exploration of numerous chemical systems. For example, adhesion was claimed using carboxylic acid monomers such as 4-methacryloxyethyltrimellitic anhydride (4-META) (19) or pyromellitic acid dihydroxyethyl methacrylate (PMDM) used in conjunction with N-
PENETRATION VALUES ZERO LEAKAGE
,.1r
I
PRISMA UNIVERSAL BOND/
PRISMA MICRO.FINE
I
0.0 . 0.25 0.25-
0.50
0.50-
0.75
0.75-
1.0
PRISMA UNIVERSAL BOND/ FUL FIE
>1.0
VLC SCOTCHBOND/ SILUX
VLC SCOTCHBOND/ P-30
Fig. 3. Population percentages of microleakage samples.
phenylglycine glycidylmethacrylate (NPG-GMA) (20). The adhesive qualities of cyanoacrylates (21) or isocyahates (9) (such as the isocyanate terminated prepolymer to toluenediisocyanate and trimethylol propane used in Dentin-Adhesit II) were also explored. Recently, the use of glutaraldehyde and hydroxyethyl methacrylate ( H E M A ) is reported to provide acceptable adhesion to dentin treated with ethylenediaminetetraacetic acid, sodium salt (EDTA) (22). One of the earliest chemical systems evaluated for adhesion were phosphates such as glycerophosphoric acid dimethacrylate (Sevriton**) (23). These early efforts with glycerophosphoric acid dimethacrylate provided a bond to dentin of about 3 MPa according to Buonocore (24); however, longterm adhesion was poor due to hydrolytic instability. Since then much research effort has been expended to develop a hydrolytically stable adhesive bond with related phosphates (7, 25, 26) (PRISMA | U N I V E R S A L BOND vM*) and chlorophosphates (7) (Scotchbond t and Dentin Bonding Agent~). Unlike the halophosphates, PRISM A | U N I V E R S A L BOND TM* contains the fully hydrolyzed phosphoric acid ester function. It was believed that the hydrolysis of the extremely labile halogen-phosphorous bond (P-C1) would lead to the formation of the strong acid, hydrogen chloride (HC1), which may weaken the adhesion to cavity wall due to the hydrolysis of P-O bond; moreover, as mentioned earlier,
application of acid on dentin is thought to be contrainedicated. The adhesion promoter in P R I S M A | U N I V E R A L BOND TM* contains no such unstable bond (i.e., highly reactive P-C1 bond) and, as Table 5 indicates, is stable to even vigorous hydrolytic conditions and is neutral when applied. Relative microleakage scores of different dentin adhesives must consider the numerical distribution of the results, i.e., the relative frequency of the penetration values over a large population of samples. This is illustrated in Fig. 3 for several systems. Thus, in comparing P R I S M A | U N I V E R S A L BOND vM* with P R I S M A | M I C R O FINE to VLC Scotchbond*, it can be seen that 49% of the P R I S M A system had leakage of only one-fourth the distance along the gingival wall toward the apex of the restoration (penetration value = 0.25), while the Scotchbond system had only 32% of the samples in this region. Perhaps more importantly, the P R I S M A system only had 2% of the samples with leakage to the apex of the restoration (penetration value = 1.0), while 21% of the Scotchbond system leaked to the apex or beyond. While neither system totally eliminated the microleakage, the distribution of more acceptable results were shifted in the favor of the P R I S M A system. The values of diffusion toward the pulp as presented in Table 8, show a general trend corresponding approximately to the relative amount of penetration along the gingival wall. In other words, as the penetration along the gingival wall increased, so did the
Resins: microleakage & bond strength
relative a m o u n t of diffusion t o w a r d t h e pulp. T h e significance of this finding is unclear.
Conclusion T h e m e t h o d p r e s e n t e d for e v a l u a t i o n of a d h e s i v e s h e a r b o n d testing b e t w e e n d e n t i n or e n a m e l a n d a d h e s i v e b o n d i n g a g e n t / c o m p o s i t e systems was s h o w n to clearly distinguish b e t w e e n materials. In addition, t h e m e t h o d p r e s e n t e d for e v a l u a t i o n of m i c r o l e a k a g e in vitro similarly distinguishes a m o n g m a t e rials. E a c h system requires relatively large n u m b e r s of samples a n d careful analysis of t h e i n f o r m a t i o n o b t a i n e d . Further, correlations between these two classes of d a t a essentially do n o t exist.
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7. Eliades GC, Caputo AA, Vougiouklakis GJ. Composition, wetting properties, and bond strength with dentin of six new dentin adhesives. J Dent Mater 1985: 1: 170-6. 8. Chan D e N , Reinhardt JW, Schulein TM. Bond strengths of restorative materials to dentin. Gen Dent 1985: 3(3): 236-8. 9. Chan D e N , Reinhardt JW, Jensen ME. Shear bond strength of a new dentinal adhesive. J Dent Res 1984: 63: Abstact No. 1341. 10. Share J, Bodkin J. Shear strength of composite to enamel and dentin with conventional and dentin bonding agents. J Dent Res 1984: 63: Abstract No. 261. 11. Wang S, Goldman M, Nathanson D. Bond strength of four dentin bondingsystems. J Dent Res 1984: 63: Abstract No. 262. 12. Lorey RE, Nykamp TL, Myers GE. Bonding internally etched complete crown castings to dentin. J Dent Res 1984: 63: Abstract No. 1032. 13. Neo J, Ch~ilkley Y, Jensen M. Composite resin microleakage: effects of bonding agents and polishing times. J Dent Res 1984: 63: Abstract No. 74. 14. Gillette KE, Robinson BE, Blank LW, Hargrave JW, Pelleu GB. A dentin bonding agent and microleakage below the cemento enamel junction. J Dent Res 1984.63: Abstract No. 73. 15. Crim GA, Esposito CJ, Chapman KW. Microleakage with a dentin-bonding agent. Gen Dent 1985: 3(3): 232-4. 16. Wu N, Cobb E. A silver staining technique for investigating wear of restorative dental composites. J Biomed Mater Res 1981: 15: 343-8. 17. Weinberg R, Cheuk SL. Introduction to
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dental statistics. Park Ridge, New Jersey: Noyes Medical, 1980: 49-82. Snedecor GW, Cochran WG. Statistical methods. Ames, Iowa: The Iowa State University Press, 1980: 215-33. Nakabayashi N, Kojima K, Masuhara, E. The promotion of adhesion by the infiltration of monomers into tooth substrates. J B i o m e d Mater Res 1982: 16: 265-73. Bowen RL, Cobb EN. Method for obtaining strong adhesive bonding of composites to dentin. J Dent Res 1982: 61: Abstract 463. Causton BE, Johnson NW. The influence of mineralizing solutions on the bonding of composite restorations to dentin. Cyanoacrylate pretreatment. J Dent Res 1981: 60(7): 1315-20. Munksguard EC, Asmussen E. B o n d strength between dentin and restorative resins mediated by mixtures of HEMA and glutaraldehyde. J Dent Res 1984:63 (8): 1087-9. Haggar D. Utilization of the energy of swelling for the acceleration of sulfinic acid-controlled polymerization of methyl methacrylate at room temperature. Helvetica Clinica Acta 1951: 34: 1872-6. Buonocore MG, Wileman W, Brudevoid F. A report on a resin composition capable of bonding to human dentin surfaces. J Dent Res 1956: 35: 846-51. Anbar M, Farley EP: Potential use of organic polyphosphonates as adhesives in the restoration of teeth. J Dent Res 1974: 53: 879-88. Farley EP, Jones RL, Anbar M. Improved adhesion of acrylic restorative materials to dental enamel by precoating with monomers containing phosphonate groups. J Dent Res 1977: 56: 943-52.
P. D. Hammesfahr, C. T. Huang, S. E. Shaffer The L. D. Caulk Divisionof Dentsply International, Milford, Delaware, U.S.A.
Hammesfahr PD, Huang C-T, Shaffer SE. Microleakage and bond strength of resin restorations with various bonding agents. Dent Mater 1987: 3: 194-199. Abstract - Shear bond strengths and microleakage of 7 dentin adhesives were evaluated by in vitro test procedures. The relative microleakage of the 7 systems was determined in modified Class V cavity preparations having margins in both dentin and enamal. The degree of microleakage was determined using a scoring system that ranked penetration along Jche gingival wall, and the degree of diffusion into the dentin. The 7 dentin adhesive systems were clearly distinguishable by both test procedures, with PRISMA | UNIVERSAL BOND T M having the highest dentin bond strengths and lowest microleakage results.
Key words: Dentin adhesive, microleakage, bond strengths, polymerizable resins, Class V cavity preparation.
In the last decade, there has been a wide-spread increase in the use of polymerizable composite materials for restorations providing strength, esthetics, and durability. However, these polymeric materials and their respective inorganic fillers were not particularly adhesive to enamel or dentin, and thus, the need for suitable adhesion between the restorative material and tooth structure was clearly evident. Therefore, retention via physical (mechanical) or chemical means was pursued. In the case with the polymeric materials, suitable mechanical means were first developed to create the necessary retention between the restorative materials and enamel. For example, Buonocore introduced an acid-conditioning technique in 1955(1) that created micro-mechanical retention in enamel. This practice is now well established, provides exceptionally strong retention of polymeric materials to enamel, and has been shown to be clinically successful. However, this simple and convenient acid-conditioning technique is not widely recommended for use on dentin. This is due partly to the different chemical structure of dentin, being comprised mostly of organic material including extension of living cells within the dentinal tubules (2). The use of acids on freshly cut dentin has been suggested as being a potential causative
involving polymerizable adhesive materials are of interest for numerous reasons. Many publications (7-15) concerning polymerizable or polymer containing dentin adhesives have resulted in widely differing results which are often contradictory (9-12). Consequently, the purpose of this research was to provide a comprehensive in vitro evaluation of the adhesive and microleakage properties of the major dentin adhe-
agent for sensitivity noted by patients after composite restorative procedures. Therefore, it is generally considered contraindicated to expose dentin to acids. In fact, it is this very problem that led to the development of nonfluid, acid gels to control placement techniques for the enamel etchant. Thus, much research has been conducted into finding a suitable alternative to enamel conditioning and mechanical retention through the use of chemical adhesion (3-5). While it was known for some time that certain cements and glass ionomers provided adhesion to tooth structure (6), systems
P. D. Hammesfahr, Director of Technical Research, CAULK/DENTSPLY, Lakeview & Clarke Avenues, P. O. Box 359, Milford, DE 19963, U.S.A. Received April 2, 1986; accepted for publication November 10, 1986.
* Caulk/Dentsply Division of Dentsply International, Inc. Milford, Delaware 19963
Table 1. Materials Adhesive
Restorative
Code
Manufacturer
BondliteTM
Herculite T M Syringeable Herculite T M Condensable Visar-FilTM Marathon TM
HS HC VF M
Kerr/Sybron
Heliosit Heliomolar AurafilrM
H HM A
Vivadent
PF PM FF S P-10 P-30
Caulk/Dentsply
Creation TM Bond Dentin-Adhesit
VLC Dentin Bonding Agent Prisma| Univeral BondT M Prisma-Fil| Prisma| Micro-Fine Ful-Fil| ScotchbondvM(S. C. and Silux| VLC) P-10| P-30T M SinterbondTM
SinterFilT M
SF
DenMat Corp.
J&J Dental Products Co.
3M Dental Products
Teledyne Getz
195
Resins: microleakage & bond strength Table 2. Shear bond strength to dentin Adhesive
ENAMEL~
Composite
COMPOSITE-- ~1.0 1-"~,,,,..LEAKAGE DENTIN~ ~1~
Fig. 1. Scoring system: penetration along the gingival wall. sives, and a new, one-component, visible light-cured dentin adhesive resin, PRISMA | U N I V E R S A L BOND TM.*
Material and methods In this study, 7 dentin adhesives were evaluated by in vitro bond tests and microleakage studies. Each dentin adhesive was used with a corresponding composite restorative material sold by the dentin adhesive manufacturer (Table 1). PRISMA | UNIVERSAL BOND TM is a one-component, visible light-cured dentin and enamel adhesive. It is comprised of polymerizable elastomeric oligomers, monomers, a visible light photo-initiator/accelerator system, and a polymerizable phosphoric acid ester adhesion promoter (U.S. Patent #4,514,342). The adhesion promoter contains a fully hydrolyzed phosphoric acid ester that does not contain any hydrolyzible halogen functions. The phosphoric acid ester is chemically
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
Prisma Universal Bond Prisma Universal Bond Prisma Universal Bond VLC Dentin Bonding Agent Dentin-Adhesit VLC Scotchbond Sinterbond S. C. Scotchbond VLC Scotchbond S. C. Scotchbond Bondlite Bondlite Dentin-Adhesit Creation Bond Creation Bond
PM PF FF A HM S SF S P-30 P-10 HS HC H VF M
~,~._
~'~
1080 (438) 1060 (570) 961 (578) 880 (511) 733 (347) 620 (270) 540 (290) 530 (290) 500 (240) 470 (380) 380 (270) 360 (240) 310 (200) 240 (160) 80 (60)
J
*Standard deviation is shown in parentheses. bonded to a molecule containing numerous polymerizable acrylate groups that co-polymerize with the main resin component upon curing. PRISMA U N I V E R S A L BOND is non-acidic, with essentially a neutral pH.
Bondstrengthprocedure Extracted human teeth obtained from local clinics were used for the in vitro testing. The teeth were treated with 1% sodium hypochlorite for 18-24 h to dissolve any attached tissue, then rinsed with water and stored (in water) at 4~ until needed. A flat bonding surface was prepared on each tooth by wetsanding a caries-free and crack-free area with carbide abrasive paper. Sanding was accomplished on a low-speed rotating wheel with carbide grit size !20, 320, and 600.
Dentin
The sanded teeth were dried with compressed air immediately prior to use. A l a y e r of an enamel/dentin adhesive (PRISMA | U N I V E R S A L BOND TM*) was applied to the dentin and thinned by blowing with compressed air. The layer was light-cured for ten seconds a visible light polymerization unit COMPOSITE with (PRISMA-LITE| Optionally, a second layer of PRISMA UNIVERSAL BOND could be added in the same LEAKAGE manner without affecting results. Next, composite was placed in a cylindrical plastic matrix with a 3.68 mm inside diameter, and positioned onto the bonding site. A cellophane matrix was placed over the top of the composite post, followed by application of slight Fig. 2. Scoring system: penetration toward pressure (ca. 225 g) with the light guide the pulp. to the top of the post to ensure proper 13'
Mean bond strength*, psi
~
seating. Immediately afterwards, the composite was cured for 30 s under slight pressure (ca. 225 g) which was applied in the manner previously described. The specimens were placed in distilled water for approximately 24 h at 37~ prior to debonding. Alternatively, specimens were also thermocycled (described under microleakage section) to determine the effect of thermal stress and hydrolytic stability. An Instron Universal Testing Machine t was used to apply a shear force to remove the bonded composite cylinders from the teeth. Each specimen was mounted vertically in a plastic bottle cap (one inch diameter) with self-cure polymethyl methacrylate resin so that the force from the Instron's crosshead was applied parallel to the flat tooth surface. The Instron's needle attachment was positioned on the post close to or touching the flat tooth surface to minimize variables due to leverage effects during de-bonding. The composite cylinder was placed under a continual load rate of 5 mm/min until the composite cylinder was fractured from the dentin. The shear strength was calculated in either MPa or psi. When evaluating competitive dentin or enamel bonding agents, the manufacturer's recommended procedure for bonding was uti* Instron, Model 1123 Canton, Massachusetts Table 3. T-test comparison of shear bond strengths to dentin (Table 2) Pairs XI ~ _X6 X_l @ _!13 X3 # _X9 X3 =~ X12
P 0.01 0.01 0.05 0.01
196
Hammesfahr et al.
Table 4. Shear bond strength to etched enamel Adhesive VLC Scotchbond Prisma Universal Bond Prisma Universal Bond VLC Dentin Bonding Agent Prisma Universal Bond Sinterbond Bondlite S. C. Scotchbond Bond[ite S. C. Scotchbond VLC Scotchbond Dentin-Adhesit
Composite
Mean bond strength*, psi
P-30 PF FF A PM SF HC P-t0 HS S S H
3270 (564) 3220 (990) 2970 (1300) 2900 (761) 2700 (925) 2470 (806) 2230 (447) 2180 (973) 2050 (361) 1770 (592) 1710 (695) 1530 (1090)
*Standard deviation is shown in parentheses. Table 5. Shear bond strengths to dentin - hydrolytic stability Adhesive A.
B.
Composite
Mean bond strength*, psi
Thermocycled between 10~ and 48~ for 540 Cycles Prisma Universal Bond PF VLC Scotchbond S Sinterbond SF
1,290 (732) 521 (265) 483 (306)
24-h boil in water Prisma Universal Bond VLC Scotchbond Sinterbond
PF S SF
720 (381) 106 (89) 340 (180)
*Standard deviation is shown in parentheses.
lized in the same m a n n e r as described above. The test specimens were then stored and d e b o n d e d as described above. Etched enamel
The sanded teeth were dried with compressed air immediately prior to use. Acid etching was p e r f o r m e d with either a 50% phosphoric acid liquid ( C A U L K TOOTH CONDITIONER LIQUID*) or a 37% phosphoric acid gel ( C A U L K TOOTH CONDITIONER GEL*). The acid etchant was placed onto the bonding site with a small brush and either left undisturbed if using the gel or agitated periodically if using the liquid, for a total of 60 s. Afterwards, the acid etchant was rinsed from the enamel with an air-water mist for 15 s, then dried with compressed air. A t this point, one coat of the bonding agent was applied as described previously for dentin. The composite cylinder was also bonded as discussed previously. De-bonding with the Instron p r o d u c e d the data which allowed the calculation of the shear strength in MPa or psi. Microleakage procedure
Extracted human
molar teeth
were
cleaned and disinfected with a sodium hypochlorite solution (1% in water) as described above. The teeth were then stored in water until needed. Two nonretentive V-shaped, Class V cavities were prepared on opposite sides of each tooth, e.g., buccal and lingual surfaces, or mesial and distal surfaces, to provide a control as well as a test system. A No. 58 carbide bur at high speed with water cooling was used to cut the preparation at the junction of the enamel and c e m e n t u m so that half of the cavosurface margins w e r e in enamel and half were in c e m e n t u m (dentin). A new No. 58 bur was used after 5 cavity preparations were cut. Approxi-
mate dimensions of the preparations were 4 m m mesiodistally, 3 m m occluso-gingivally, and 2 m m pulpal. Each cavity was rinsed with water, then dried with compressed air with no additional treatment to the dentin surface prior to bonding unless specified by the manufacturer. A group of at least 5 teeth were used for each experiment. Multiple replications of each experiment w e r e necessary to ensure sufficient sample size for evaluation. The enamel wall only of the preparation was conditioned for 60 s with an acid gel ( C A U L K T O O T H C O N D I T I O N E R G E L * ) which was applied with a small brush and left undisturbed for the prescribed time, followed by a 15-s rinse with an air-water mist. The preparations were then airdried with a compressed, oil-free air stream for 10 s. The following represent an e x a m p l e of the technique employed: T h e conditioned enamel and freshly cut dentin surface were coated with a uniform thin layer of an enamel/dentin adhesive, ( P R I S M A | U N I V E R S A L BONDTM*). A small brush was used to place the adhesive and an air blast from a dental syringe was used to further thin the application and r e m o v e any excess adhesive. The adhesive was then cured for 10 s with a dental visible light polymerization unit ( P R I S M A - L I T E | A second application of the P R I S M A U N I V E R S A L B O N D adhesive was placed with a small brush and thinned with an air blast. The second adhesive coat was also light polymerized for 10 s. A light-cured composite ( P R I S M A FIL| FUL-FIL | or light-cured microfilled resin ( P R I S M A | M I C R O F I N E * ) was placed in the preparation in one increment. Following bulk placement, a clear cervical matrix was pressed into place with locking college pliers and held under slight pressure
Table 6. Microleakage - penetration along gingival wall Adhesive 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Prisma Universal Bond Prisma Universal Bond Dentin Bonding Agent Prisma Universal Bond Bondlite VLC Scotchbond Bondlite S. C. Scotchbond VLC Scotchbond Dentin-Adhesit Dentin-Adhesit Sinterbond
Composite PM FF A PF HS S HC S P-30 HM H SF
*Standard deviation is shown in parentheses.
Mean penetration value* 0.36 0.41 0.45 0.56 0.57 0.64 0.68 0.93 1.08 1.13 1.13 1.28
(0.33) 7 (0.39) (0.44) (0.41) (0.42) (0.43) (0.36) (0.32) (0.28) (0.15) (0.37) (0.25)
AJ J
7
Resins: microleakage & bond strength Table 7. T-test comparison of microleakage penetration data (Table 6) Pairs X1 4= ~6 X2:7(z _X9 X44= X8
P
0.01 0.01 0.01
during a 10-s light-cure exposure. The matrix was removed, and the composite was cured for an additional 20 s. The restorations were immediately finished with abrasive discs, (SOF-LEX) -+ coarse, medium, and fine. Following the finishing procedure the specimens were stored in water (distilled or tap) at 37~ for 16-48 h. Other restorative systems were also evaluated using the manufacturer's directions and the technique described above. The teeth in each group were then thermocycled between a water bath of 48~ + 2~ and 10~ + 2~ for 24 h (540 cycles). Immersion time was approximately one minute in each bath with transfer time of 13 s in air between baths. Following the thermocycling period, the t e e t h were evaluated for marginal microleakage by modification of a silver nitrate staining technique described by Wu et al. (16). Dental compound was placed in the intra-radicular areas, and the teeth were coated with fingernail polish up to within 2 m m of the restoration to prevent silver nitrate penetration into the teeth from areas other than the cavity preparation. In a darkened room, the teeth were placed in 50% (by wt.) silver nitrate aqueous solution, and stored in total darkness for 2 h. The teeth were removed from the silver nitrate solution and rinsed in
tap water. Following rinsing, the teeth were sectioned ~ longitudinally with a diamond blade through the center of the restorations. The development process consisted of exposure of each sectioned specimen to a photoflood lamp for 5 min. Areas of silver nitrate penetration (microleakage) turned black due to the light exposure. The degree of marginal microleakage along the gingival wall (dentin) was determined by the degree of penetration of silver nitrate stain as measured by the scoring criteria described below. In scoring the microleakage results, it was felt that there was no single system available that would accurately reflect the leakage patterns observed. That is, leakage was observed to occur both along the gingival wall as well as into the dentin toward the pulp. Using various scoring methods, superficial leakage a short distance along the gingival wall could also have a large degree of penetration toward the pulp and yet receive a low score. Therefore, it was decided to use a separate score for each form of leakage observed; leakage along the gingival wall and leakage into the dentin toward the pulp. Leakage along the gingival wall of the cavity was reported as the ratio of the depth of penetration along the wall to the total length of the wall from the cementum to the apex. For example, stain penetration one-half of the distance to the apex is 0.5, while leakage to the bottom (apex) of the cavity yields 1.0 as the leakage value (Fig. 1). In the cases when penetration continues past the apex and is observed on the occlusal wall, the ratio is calculated
w Isomet Low-Speed Saw Buehler Ltd. Evanston, Illinois 60204
* Dental Products/3M 3M Center St. Paul, Minnesota 55144
Table 8. Microleakage - diffusion toward the pulp Adhesive 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Prisma Universal Bond Prisma Universal Bond VLC Dentin Bonding Agent Bondlite Bondlite Prisma Universal Bond VLC Scotchbond VLC Scotchbond Sinterbond S. C. Scotchbond Dentin-Adhesit Dentin-Adhesit
Composite
Mean diffusion value*
FF PM A HS HC PF S P-30 SF S H HM
0.27 (0.19) 7 0.28 (0.24) 0.30 (0.35) 0.31 (0.23) -1 0.35 (0.24) 0.36 (0.30) 0.45 (0.33) 0.51 (0.27) 0.56 (0.31) 7 0.60 (0.31) 0.71 (0.22) 0.77 (0.21)
*Standard deviation is shown in parentheses.
J A
197
Table 9. T-test comparison of microleakage - diffusion data (table 8) Pairs _X~4= _X8 X7 5d=_X12 iR8 4= X12
p
0.01 0.05 0.05
in a similar manner to yield penetration values between 1.0 and 2.0 (Fig. 1). The procedure used to calculate these ratios was to project a 35 mm color transparency of each tooth onto a screen and measure the distances with a metric ruler. During the microleakage process the silver nitrate solution may penetrate or diffuse into the dentin, and a method to quantify the depth of this diffusion was also developed. The technique was similar to the previous discussion where a ratio was calculated: the depth of diffusion is the ratio of the maximum distance the stain penetrated the dentin to the distance between the gingival wall and the pulp chamber. As an example (Fig. 2), penetration one-half of the distance to the pulp chamber yields 0.5, and penetration to the pulp chamber yields 1.0. The procedure used to measure these distances was identical to that described above.
Results Bond strength
Table 2 presents the bond strengths to dentin for the various dentin adhesive/ composite systems examined. Analysis of variance and t-tests (17, 18) were analyzed for the dentin bonding results (Table 2). The brackets shown in Table 2 indicate that the average bond strengths in each group are not significantly different at P > 0.05. However, Table 3 illustrates the pairs of mean bond strength which are Significantly different. Thus, PRISMA | UNIVERSAL BOND TM* with PRISMA | MICRO-FINE* and FUL-FIL| were significantly better (P < 0.05) than VLC Scotchbond with Silux*, Dentin-Adhesit with HeliositII and Bondlite with Herculite Syringeable~. II Vivadent Schaan, Liechtenstein Kerr/Sybron Romulus, Michigan 48174 **Amalgamated Dental International Weybridge, England tt j&j Dental Products East Windsor, NJ 08520
198
Hammesfahr et al.
Table 4 presents the representative bond strengths to enamel of the systems evaluated. In the systems tested, the enamel often failed cohesively, fracturing within the enamel. Therefore, an analysis of variance and t-test for enamel adhesion are invalid and were not preformed. Table 5 presents the bond strengths for several systems using adverse conditions to evaluate the hydrolytic stability of the dentin adhesives. As can be seen PRISMA | UNIVERSAL BOND ~* maintains acceptable adhesion even with numerous thermocycles or severe testing in boiling water for 24 h. Microleakage
Table 6 presents the results of the in vitro microleakage study in terms of the average penetration of stain along the gingival wall. Table 8 shows the results of the diffusion of stain toward the pulp. Analysis of variance (ANOVA) was applied to the penetration data (Table 6) and indicates no significant differences within the three bracketed groups (P > 0.05). The t-test was utilized in Table 7 to show differences between individual adhesive systems. For example, P R I S M A | U N I V E R S A L BOND TM* with P R I S M A | M I C R O FINE* and F U L - F I L | were significantly better (P < 0.01) than VLC Scotchbond with Silux and P-30', respectively. Comparison of the diffusion ratio of the dentin adhesive systems (Table 8) by A N O V A shows that there is no significant difference in leakage of the systems within each bracket. The t-test indicates that significant differences do exist between the l e a k a g e results of several of the individual adhesives (Table 9). The Prisma system (PRISMA | U N I V E R S A L B O N D TM and FUL-FIL | showed significantly less diffusion into the dentin than Scotchbond and P-30* (P < 0.01). Discussion The search for a suitable adhesive bond between tooth structure and polymerizable materials has lead to the exploration of numerous chemical systems. For example, adhesion was claimed using carboxylic acid monomers such as 4-methacryloxyethyltrimellitic anhydride (4-META) (19) or pyromellitic acid dihydroxyethyl methacrylate (PMDM) used in conjunction with N-
PENETRATION VALUES ZERO LEAKAGE
,.1r
I
PRISMA UNIVERSAL BOND/
PRISMA MICRO.FINE
I
0.0 . 0.25 0.25-
0.50
0.50-
0.75
0.75-
1.0
PRISMA UNIVERSAL BOND/ FUL FIE
>1.0
VLC SCOTCHBOND/ SILUX
VLC SCOTCHBOND/ P-30
Fig. 3. Population percentages of microleakage samples.
phenylglycine glycidylmethacrylate (NPG-GMA) (20). The adhesive qualities of cyanoacrylates (21) or isocyahates (9) (such as the isocyanate terminated prepolymer to toluenediisocyanate and trimethylol propane used in Dentin-Adhesit II) were also explored. Recently, the use of glutaraldehyde and hydroxyethyl methacrylate ( H E M A ) is reported to provide acceptable adhesion to dentin treated with ethylenediaminetetraacetic acid, sodium salt (EDTA) (22). One of the earliest chemical systems evaluated for adhesion were phosphates such as glycerophosphoric acid dimethacrylate (Sevriton**) (23). These early efforts with glycerophosphoric acid dimethacrylate provided a bond to dentin of about 3 MPa according to Buonocore (24); however, longterm adhesion was poor due to hydrolytic instability. Since then much research effort has been expended to develop a hydrolytically stable adhesive bond with related phosphates (7, 25, 26) (PRISMA | U N I V E R S A L BOND vM*) and chlorophosphates (7) (Scotchbond t and Dentin Bonding Agent~). Unlike the halophosphates, PRISM A | U N I V E R S A L BOND TM* contains the fully hydrolyzed phosphoric acid ester function. It was believed that the hydrolysis of the extremely labile halogen-phosphorous bond (P-C1) would lead to the formation of the strong acid, hydrogen chloride (HC1), which may weaken the adhesion to cavity wall due to the hydrolysis of P-O bond; moreover, as mentioned earlier,
application of acid on dentin is thought to be contrainedicated. The adhesion promoter in P R I S M A | U N I V E R A L BOND TM* contains no such unstable bond (i.e., highly reactive P-C1 bond) and, as Table 5 indicates, is stable to even vigorous hydrolytic conditions and is neutral when applied. Relative microleakage scores of different dentin adhesives must consider the numerical distribution of the results, i.e., the relative frequency of the penetration values over a large population of samples. This is illustrated in Fig. 3 for several systems. Thus, in comparing P R I S M A | U N I V E R S A L BOND vM* with P R I S M A | M I C R O FINE to VLC Scotchbond*, it can be seen that 49% of the P R I S M A system had leakage of only one-fourth the distance along the gingival wall toward the apex of the restoration (penetration value = 0.25), while the Scotchbond system had only 32% of the samples in this region. Perhaps more importantly, the P R I S M A system only had 2% of the samples with leakage to the apex of the restoration (penetration value = 1.0), while 21% of the Scotchbond system leaked to the apex or beyond. While neither system totally eliminated the microleakage, the distribution of more acceptable results were shifted in the favor of the P R I S M A system. The values of diffusion toward the pulp as presented in Table 8, show a general trend corresponding approximately to the relative amount of penetration along the gingival wall. In other words, as the penetration along the gingival wall increased, so did the
Resins: microleakage & bond strength
relative a m o u n t of diffusion t o w a r d t h e pulp. T h e significance of this finding is unclear.
Conclusion T h e m e t h o d p r e s e n t e d for e v a l u a t i o n of a d h e s i v e s h e a r b o n d testing b e t w e e n d e n t i n or e n a m e l a n d a d h e s i v e b o n d i n g a g e n t / c o m p o s i t e systems was s h o w n to clearly distinguish b e t w e e n materials. In addition, t h e m e t h o d p r e s e n t e d for e v a l u a t i o n of m i c r o l e a k a g e in vitro similarly distinguishes a m o n g m a t e rials. E a c h system requires relatively large n u m b e r s of samples a n d careful analysis of t h e i n f o r m a t i o n o b t a i n e d . Further, correlations between these two classes of d a t a essentially do n o t exist.
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dental statistics. Park Ridge, New Jersey: Noyes Medical, 1980: 49-82. Snedecor GW, Cochran WG. Statistical methods. Ames, Iowa: The Iowa State University Press, 1980: 215-33. Nakabayashi N, Kojima K, Masuhara, E. The promotion of adhesion by the infiltration of monomers into tooth substrates. J B i o m e d Mater Res 1982: 16: 265-73. Bowen RL, Cobb EN. Method for obtaining strong adhesive bonding of composites to dentin. J Dent Res 1982: 61: Abstract 463. Causton BE, Johnson NW. The influence of mineralizing solutions on the bonding of composite restorations to dentin. Cyanoacrylate pretreatment. J Dent Res 1981: 60(7): 1315-20. Munksguard EC, Asmussen E. B o n d strength between dentin and restorative resins mediated by mixtures of HEMA and glutaraldehyde. J Dent Res 1984:63 (8): 1087-9. Haggar D. Utilization of the energy of swelling for the acceleration of sulfinic acid-controlled polymerization of methyl methacrylate at room temperature. Helvetica Clinica Acta 1951: 34: 1872-6. Buonocore MG, Wileman W, Brudevoid F. A report on a resin composition capable of bonding to human dentin surfaces. J Dent Res 1956: 35: 846-51. Anbar M, Farley EP: Potential use of organic polyphosphonates as adhesives in the restoration of teeth. J Dent Res 1974: 53: 879-88. Farley EP, Jones RL, Anbar M. Improved adhesion of acrylic restorative materials to dental enamel by precoating with monomers containing phosphonate groups. J Dent Res 1977: 56: 943-52.