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Bonding of resin dentin adhesives under simulated physiological conditions
Bonding of resin dentin adhesives under simulated physiological conditions
J.C. Mitchem 1, L.G. Terkla 1, D. G. Gronas 2 1oregon Health Sciences University,Schoolof Dentistry, Portland, Oregon, 2U.S. Veterans Hospital, Vancouver,Washington, USA
Mitchem JC, Terkla LG, Gronas DG. Bonding of resin dentin adhesives under simulated physiological conditions. Dent Mater 1988: 4: 351-353. Abstract - Three resin dentin adhesive materials (Seotchbond, Tenure and Gluma) were evaluated for adhesion to dentin in 3 types of tests. The dentin in 2 of these tests was maintained under simulated physiological conditions. The adhesive bond strength to dentin maintained under physiological conditions is significantly lower when compared with a standard laboratory test. One of the adhesives (Gluma) failed to bond in 8 out of 10 tests.
Reported incidents o f postoperative sensitivity, marginal discoloration and complete loss of material in Class V composite restorations (1-4) raise serious questions about the ability of present-day dentin adhesives to bond to dentin under clinical conditions. In vivo work by Van Dijken & Per Horstedt (5) substantiates this concern. They demonstrated concentration gaps under a variety of conditions for a number of resin dentin adhesives. In addition, they reported the presence of voids in the resin surface overlying dentin in which the tubules were cut in cross-section and etched. Tubular fluid was cited as the cause. Bream et al. (6) pointed out the significant contribution that moisture plays in inhibiting in vivo adhesion. Qvist & Qvist (7, 8) have demonstrated the morphological differences between adhesives applied to dentin in vitro and in vivo. The latter show reduced replication of the dentin surface, presumably because of the presence of outward fluid flow. Numerous in vitro studies have tested the efficacy of resin dentin adhesives on flattened dentin surfaces of extracted teeth without the presence of pulpal fluid acting under physiological pressure. The purpose of this study was to evaluate the bond of resin dentin adhesives to dentin that was maintained under simulated physiological conditions. Material and methods
Terkla et al. (9) described a monitored physiological testing system that uti-
lized teeth whose pulp chambers were filled with an artificial dental pulp fluid and maintained under normal intrapulpal pressure (25 mmHg) and 37~ The initial phase of this bonding study utilized teeth that had been restored in that monitored system (Fig. 1). A mechanical wet grinder, utilizing 300-grit paper, was used to remove the occlusal enamel and resin restoration until the pulpal wall of the cavity was reached. The final surface just below the pulpal wall was finished by hand on 600-grit carbide paper under water. The pulp chambers were filled with phosphate
Key words: resins, dentin adhesive, dental materials. John C. Mitchem, 611 SW Campus Drive, Portland, OR 97201, USA.
Received July 21; accepted November 2, 1987.
buffer solution and reconnected to the apparatus in order to establish physiological pressure. Scotchbond (light-activated) was applied to the dentin following the manufacturers directions. A split Teflon ring (2.5 mm thick) contained in an acrylic cylinder was used to form a cylindrical mold 3.2 mm in diameter into which the restorative resin (P30) was injected. Following polymerization (40 s with a Heliomat light), the tooth was disconnected from the apparatus, the Teflon mold removed and the sample stored in water at 37~ for 24 h. The shear bond strength was deter-
fluid reservoir
dial gauge micrometer
valve ~ 1
microsyringe C-1
valve#4
v a l v e #3 #2
tooth bellowsoad :ell
,tO,, Brush recorder
filter
bridge k~ amplifier --
37~:: w a t e r
Fig. 1. Schematic view of monitored physiological testing apparatus.
bath
pressure reference
352
M i t c h e m et al.
Table 1. Remaining dentin thickness of test samples. Test
~2+SD in mm
Standard lab Physiological static Physiological monitored
1.8+0.3 2.3+0.6 2.1+0.5
mined in an fnstron testing machine at a cross-head rate of 1.3 mm/min. The apparatus is illustrated in Ref. 10. In addition, a static physiological system was developed that would allow the testing of adhesives in the presence of physiological pressure, but under more simplified laboratory conditions. Recently extracted and relatively young teeth (impacted or recently erupted third molars) were prepared by removing the roots to expose the pulp chamber. The pulp was removed and the chamber sealed with an acrylic plate retained by cyanoacrylate cement. The buccal surface was ground flat to the dentin and the lingual surface was drilled into the pulp chamber to receive a threaded stainless steel tube, which was sealed in place with cyanoacrylate cement. The flattened buccal surface was surrounded with a piece of base plate wax and placed face down on a glass plate. A 12.7 mm I.D. acrylic cylinder was then placed around the tooth and on the wax and filled with acrylic. The level of the test surface extended slightly beyond the mounting ring when the base plate wax was removed. Each tooth was then tested for seal of the pulp chamber and patency of the dentinal tubules by filling the pulp chamber with water and placing the system under approximately 70 psi pressure. All test surfaces were prepared by hand on 600-grit carbide paper under water.
Physiological pressure was produced by filling the pulp chamber with water and connecting the mounted tooth to an I.V. bottle containing water. The column height was adjusted to 34 cm to provide 25 mmHg pressure. Three resin dentin adhesive systems were evaluated: Scotchbond (light-activated) (3M), Tenure (DenMat, batch nos. 114001 and 012687-1), and Gluma (Bayer, batch no. 073386). Bonding procedures were as outlined above and manufacturers' instructions were followed throughout. The prepared samples were stored for 24 h at 37~ prior to shear testing on an Instron testing machine at a cross-head rate of 1.3 mm/min. The same 3 adhesive systems were also evaluated by bonding them according to a standard laboratory adhesive test. This test was reported by Mitchem & Gronas (10), and utilized flattened buccal surfaces of recently extracted teeth that had been stored in room temperature water. The age of these teeth since extraction was approximately one year. The remaining dentin thickness (RDT) was measured directly by sectioning the teeth after adhesive testing or indirectly by x-ray evaluation using a 1 mm Fixott-Everett grid. Table 1 lists the R D T for the 3 tests. The effect of differences in R D T was minimized by using the same teeth for all 3 adhesives in 2 of the tests.
Results Table 2 contains the results of the 3 evaluation techniques. Also included are the physical differences between the 2 types of tests that maintained physiological pressure on the dentin (static and monitored). The data was
Table 2. Results of in vitro tests for shear bond strength. Material
Physiological
Standard lab
Scotchbond Tenure Gluma
8.6-+2.3 7.4+4.9 5.3+3.5
Static
Monitored
6.1 + 1.0 3.9+2.6 0.4_+0.9
3.7_+0.9
J~_+SD in MPa n = 10 Differences between physiological tests
Test Monitored Static
Temperature
Dentin surface
Pulp fluid
37~ 22~
Occlusal Buccal
Sorensen's phosphate buffer Water
analyzed by ANOVA with differences determined by Tukey's contrasts at the 95% level. Statistically equal values are connected by lines.
Discussion It is evident that the bond strength of resin dentin adhesives is affected when the dentin is maintained at physiological conditions. The significant differences between the values generated in the 2 physiological tests for Scotchbond may be explained by temperature, the pulpal fluid used or the surface of dentin prepared for bonding. It is likely that the latter is the main contributor. The R D T of occlusal dentin varies considerably on a given surface due to the presence of the pulp horns. This variance probably leads to more moisture on the surface as the RDT becomes smaller. Both the Tenure and Gluma systems recommend removal of the smear layer prior to bonding. This removal should open dentinal tubules and increase the moisture on the surface. As pointed out by Stevenson in 1956 (11), the presence of a smear layer significantly reduces dentin permeability. The high variance seen with these 2 systems in both tests can be explained partially by the relatively extensive restorative technique involved (this is especially true for Tenure). The value of 0.4 MPa for Gluma was derived from 10 samples, 8 of which were 0. The relatively low values for the Tenure system are in agreement with Fagen et al. (12) It is becoming increasingly evident, both from this study and in vivo observations, that researchers and manufacturers must pay closer attention to the clinical conditions under which their products will be used. In the case of dentin adhesives, extracted teeth stored and tested under "standard" laboratory conditions can lead to inappropriate conclusions.
References 1. Dennison JB, Ziemicki TL, Charbeneau GT. Retention of unprepared cervical restorations utilizing a dentin bonding agent. J Dent Res 1986: 65: 173, Abstr 35. 2. Doering JV, Jenson ME. Clinical evaluation of dentin bonding materials on cervical abrasion lesions. J Dent Res 1986: 65: 173, Abstr 36.
Resin b o n d i n g u n d e r s i m u l a t e d clinical conditions
3. Vanherle G, Verschueren M, Lambrechts P, et al. Clinical investigation of dental adhesive systems. I. An in vivo study. J Prosthet Dent 1986: 55: 157-63. 4. Tyas MJ, Burns GA, Byrne PF, et al. Clinical evaluation of scotchbond: one year results. Aust Dent J 1986: 31: 159-64. 5. Van Dijken JW, Per Horstedt MA. In vivo adaptation of restorative materials to dentin. J Prosthet Dent 1986: 56: 677-81. 6. Braem M, Lambrechts P, Vanherle G. Clinical evaluation of dental adhesive
systems. II. A scanning eleiztron microscopy study. J Prosthet Dent 1986: 55: 551-60. 7. Qvist V, Qvist J. Replica patterns on composite restorations performed in vivo with different acid-etch restorative procedures. Scand J Dent Res 1985: 93: 360-70. 8. Qvist V, Qvist J. Replica patterns on composite restorations performed in vitro with different acid-etch procedures and dentin adhesives. Scand J Dent Res 1987: 95: 87-93. 9. Terkla LG, Brown AC, Hainisch AP,
353
Mitchem JC. Testing sealing properties of restorative materials against moist dentin. J Dent Res 1987: 66: 1758-64. 10. Mitchem JC, Gronas DG. Effects of time after extraction and depth of dentin on resin dentin adhesives. J A m Dent Assoc 1986: 113: 285-7. 11. Stevenson TS. Fluid movement in human dentin. Arch Oral Biol 1965: 10: 93544. 12. Fagen TR, Crall JJ, Jensen ME, et al. A comparison of two dentin bonding agents in primary and permanent teeth. Pediatr Dent 1986: 8: 144-6.
J.C. Mitchem 1, L.G. Terkla 1, D. G. Gronas 2 1oregon Health Sciences University,Schoolof Dentistry, Portland, Oregon, 2U.S. Veterans Hospital, Vancouver,Washington, USA
Mitchem JC, Terkla LG, Gronas DG. Bonding of resin dentin adhesives under simulated physiological conditions. Dent Mater 1988: 4: 351-353. Abstract - Three resin dentin adhesive materials (Seotchbond, Tenure and Gluma) were evaluated for adhesion to dentin in 3 types of tests. The dentin in 2 of these tests was maintained under simulated physiological conditions. The adhesive bond strength to dentin maintained under physiological conditions is significantly lower when compared with a standard laboratory test. One of the adhesives (Gluma) failed to bond in 8 out of 10 tests.
Reported incidents o f postoperative sensitivity, marginal discoloration and complete loss of material in Class V composite restorations (1-4) raise serious questions about the ability of present-day dentin adhesives to bond to dentin under clinical conditions. In vivo work by Van Dijken & Per Horstedt (5) substantiates this concern. They demonstrated concentration gaps under a variety of conditions for a number of resin dentin adhesives. In addition, they reported the presence of voids in the resin surface overlying dentin in which the tubules were cut in cross-section and etched. Tubular fluid was cited as the cause. Bream et al. (6) pointed out the significant contribution that moisture plays in inhibiting in vivo adhesion. Qvist & Qvist (7, 8) have demonstrated the morphological differences between adhesives applied to dentin in vitro and in vivo. The latter show reduced replication of the dentin surface, presumably because of the presence of outward fluid flow. Numerous in vitro studies have tested the efficacy of resin dentin adhesives on flattened dentin surfaces of extracted teeth without the presence of pulpal fluid acting under physiological pressure. The purpose of this study was to evaluate the bond of resin dentin adhesives to dentin that was maintained under simulated physiological conditions. Material and methods
Terkla et al. (9) described a monitored physiological testing system that uti-
lized teeth whose pulp chambers were filled with an artificial dental pulp fluid and maintained under normal intrapulpal pressure (25 mmHg) and 37~ The initial phase of this bonding study utilized teeth that had been restored in that monitored system (Fig. 1). A mechanical wet grinder, utilizing 300-grit paper, was used to remove the occlusal enamel and resin restoration until the pulpal wall of the cavity was reached. The final surface just below the pulpal wall was finished by hand on 600-grit carbide paper under water. The pulp chambers were filled with phosphate
Key words: resins, dentin adhesive, dental materials. John C. Mitchem, 611 SW Campus Drive, Portland, OR 97201, USA.
Received July 21; accepted November 2, 1987.
buffer solution and reconnected to the apparatus in order to establish physiological pressure. Scotchbond (light-activated) was applied to the dentin following the manufacturers directions. A split Teflon ring (2.5 mm thick) contained in an acrylic cylinder was used to form a cylindrical mold 3.2 mm in diameter into which the restorative resin (P30) was injected. Following polymerization (40 s with a Heliomat light), the tooth was disconnected from the apparatus, the Teflon mold removed and the sample stored in water at 37~ for 24 h. The shear bond strength was deter-
fluid reservoir
dial gauge micrometer
valve ~ 1
microsyringe C-1
valve#4
v a l v e #3 #2
tooth bellowsoad :ell
,tO,, Brush recorder
filter
bridge k~ amplifier --
37~:: w a t e r
Fig. 1. Schematic view of monitored physiological testing apparatus.
bath
pressure reference
352
M i t c h e m et al.
Table 1. Remaining dentin thickness of test samples. Test
~2+SD in mm
Standard lab Physiological static Physiological monitored
1.8+0.3 2.3+0.6 2.1+0.5
mined in an fnstron testing machine at a cross-head rate of 1.3 mm/min. The apparatus is illustrated in Ref. 10. In addition, a static physiological system was developed that would allow the testing of adhesives in the presence of physiological pressure, but under more simplified laboratory conditions. Recently extracted and relatively young teeth (impacted or recently erupted third molars) were prepared by removing the roots to expose the pulp chamber. The pulp was removed and the chamber sealed with an acrylic plate retained by cyanoacrylate cement. The buccal surface was ground flat to the dentin and the lingual surface was drilled into the pulp chamber to receive a threaded stainless steel tube, which was sealed in place with cyanoacrylate cement. The flattened buccal surface was surrounded with a piece of base plate wax and placed face down on a glass plate. A 12.7 mm I.D. acrylic cylinder was then placed around the tooth and on the wax and filled with acrylic. The level of the test surface extended slightly beyond the mounting ring when the base plate wax was removed. Each tooth was then tested for seal of the pulp chamber and patency of the dentinal tubules by filling the pulp chamber with water and placing the system under approximately 70 psi pressure. All test surfaces were prepared by hand on 600-grit carbide paper under water.
Physiological pressure was produced by filling the pulp chamber with water and connecting the mounted tooth to an I.V. bottle containing water. The column height was adjusted to 34 cm to provide 25 mmHg pressure. Three resin dentin adhesive systems were evaluated: Scotchbond (light-activated) (3M), Tenure (DenMat, batch nos. 114001 and 012687-1), and Gluma (Bayer, batch no. 073386). Bonding procedures were as outlined above and manufacturers' instructions were followed throughout. The prepared samples were stored for 24 h at 37~ prior to shear testing on an Instron testing machine at a cross-head rate of 1.3 mm/min. The same 3 adhesive systems were also evaluated by bonding them according to a standard laboratory adhesive test. This test was reported by Mitchem & Gronas (10), and utilized flattened buccal surfaces of recently extracted teeth that had been stored in room temperature water. The age of these teeth since extraction was approximately one year. The remaining dentin thickness (RDT) was measured directly by sectioning the teeth after adhesive testing or indirectly by x-ray evaluation using a 1 mm Fixott-Everett grid. Table 1 lists the R D T for the 3 tests. The effect of differences in R D T was minimized by using the same teeth for all 3 adhesives in 2 of the tests.
Results Table 2 contains the results of the 3 evaluation techniques. Also included are the physical differences between the 2 types of tests that maintained physiological pressure on the dentin (static and monitored). The data was
Table 2. Results of in vitro tests for shear bond strength. Material
Physiological
Standard lab
Scotchbond Tenure Gluma
8.6-+2.3 7.4+4.9 5.3+3.5
Static
Monitored
6.1 + 1.0 3.9+2.6 0.4_+0.9
3.7_+0.9
J~_+SD in MPa n = 10 Differences between physiological tests
Test Monitored Static
Temperature
Dentin surface
Pulp fluid
37~ 22~
Occlusal Buccal
Sorensen's phosphate buffer Water
analyzed by ANOVA with differences determined by Tukey's contrasts at the 95% level. Statistically equal values are connected by lines.
Discussion It is evident that the bond strength of resin dentin adhesives is affected when the dentin is maintained at physiological conditions. The significant differences between the values generated in the 2 physiological tests for Scotchbond may be explained by temperature, the pulpal fluid used or the surface of dentin prepared for bonding. It is likely that the latter is the main contributor. The R D T of occlusal dentin varies considerably on a given surface due to the presence of the pulp horns. This variance probably leads to more moisture on the surface as the RDT becomes smaller. Both the Tenure and Gluma systems recommend removal of the smear layer prior to bonding. This removal should open dentinal tubules and increase the moisture on the surface. As pointed out by Stevenson in 1956 (11), the presence of a smear layer significantly reduces dentin permeability. The high variance seen with these 2 systems in both tests can be explained partially by the relatively extensive restorative technique involved (this is especially true for Tenure). The value of 0.4 MPa for Gluma was derived from 10 samples, 8 of which were 0. The relatively low values for the Tenure system are in agreement with Fagen et al. (12) It is becoming increasingly evident, both from this study and in vivo observations, that researchers and manufacturers must pay closer attention to the clinical conditions under which their products will be used. In the case of dentin adhesives, extracted teeth stored and tested under "standard" laboratory conditions can lead to inappropriate conclusions.
References 1. Dennison JB, Ziemicki TL, Charbeneau GT. Retention of unprepared cervical restorations utilizing a dentin bonding agent. J Dent Res 1986: 65: 173, Abstr 35. 2. Doering JV, Jenson ME. Clinical evaluation of dentin bonding materials on cervical abrasion lesions. J Dent Res 1986: 65: 173, Abstr 36.
Resin b o n d i n g u n d e r s i m u l a t e d clinical conditions
3. Vanherle G, Verschueren M, Lambrechts P, et al. Clinical investigation of dental adhesive systems. I. An in vivo study. J Prosthet Dent 1986: 55: 157-63. 4. Tyas MJ, Burns GA, Byrne PF, et al. Clinical evaluation of scotchbond: one year results. Aust Dent J 1986: 31: 159-64. 5. Van Dijken JW, Per Horstedt MA. In vivo adaptation of restorative materials to dentin. J Prosthet Dent 1986: 56: 677-81. 6. Braem M, Lambrechts P, Vanherle G. Clinical evaluation of dental adhesive
systems. II. A scanning eleiztron microscopy study. J Prosthet Dent 1986: 55: 551-60. 7. Qvist V, Qvist J. Replica patterns on composite restorations performed in vivo with different acid-etch restorative procedures. Scand J Dent Res 1985: 93: 360-70. 8. Qvist V, Qvist J. Replica patterns on composite restorations performed in vitro with different acid-etch procedures and dentin adhesives. Scand J Dent Res 1987: 95: 87-93. 9. Terkla LG, Brown AC, Hainisch AP,
353
Mitchem JC. Testing sealing properties of restorative materials against moist dentin. J Dent Res 1987: 66: 1758-64. 10. Mitchem JC, Gronas DG. Effects of time after extraction and depth of dentin on resin dentin adhesives. J A m Dent Assoc 1986: 113: 285-7. 11. Stevenson TS. Fluid movement in human dentin. Arch Oral Biol 1965: 10: 93544. 12. Fagen TR, Crall JJ, Jensen ME, et al. A comparison of two dentin bonding agents in primary and permanent teeth. Pediatr Dent 1986: 8: 144-6.