Bond strength of restorative materials to human dentin: influence of post-extraction time D.R. Beech1 M.J. Tyas1,2. A. Solomon3
1Australian Dental Standards Laboratory 240 Langridge Street Abbotsford Victoria 3067 Australia 2Present address: School of Dental Science University of Melbourne 711 Elizabeth St Melbourne 3000 Australia 3Private practitioner Melbourne, Australia Received November 11, 1989 Accepted September 6, 1990 *To whom correspondence and reprint requests should be addressed
Dent Mater 7:15-17, January, 1991
Abstract-This study was undertaken to determine if the time after which teeth are extracted influences the tensile bond strength of a glass ionomer (Fuji II; GC) and a dentin bonding agent (Scotchbond Self Cure; 3M) to dentin. Within 20 min of extraction, 14 teeth were bonded with glass ionomer and 13 teeth with Scotchbond Self Cure plus a composite material (Clearfil; Kuraray), by attachment of orthodontic brackets to prepared dentin surfaces. The bonds were fractured in tension, and yielded values of 3.7 MPa for glass ionomer and 1.08 MPa for Scotchbond Self Cure + Clearfil. These data were significantly different (P < 0.002) from data previously obtained from the use of old teeth, from which values of 2.20 MPa and 1.82 MPa for glass ionomer and Clearfil + Scotchbond Self Cure, respectively, were obtained. It was concluded that the time after extraction can significantly change bond strengths to dentin, but that the direction and magnitude of these changes depend on the adhesive system used.
~
t has been reported (Causton and Johnson, 1979) that the shear bond strength of a polycarboxylate cement (Durelon; Espe GmbH, Germany) to human dentin is influenced by the time between the extraction of the teeth and the preparation of the specimen. Subsequent authors (Peddey, 1981; Aboush and Jenkins, 1983; Nakamichi et al., 1983; Kimura et at., 1985; Williams et aL, 1985; Mitchem and Gronas, 1986; Pashley et al., 1988) have used a variety of materials, test methods, and teeth with various post-extraction times in order to explore this phenomenon further. The results of these later studies have been variable, with no consistent pattern emerging. Much stress in scientific and product literature is placed on gauging the performance of adhesive materials by comparison of bond strengths. If the bonding behavior of dentin changes significantly postextraction, then there is little clinical validity in r e p o r t e d bond strengths. The present work was undertaken to assess the effect of post-extraction time on the tensile bond strength to dentin of a composite/dentin bonding agent combination and a glass-ionomer cement. MATERIALS AND METHODS
Human teeth were obtained immediately after extraction under local anesthetic and placed in tap water at room temperature. Within 15 rain of extraction, the teeth were embedded in plaster blocks, and a dentin surface (usually lingual or buccal) was prepared by abrasion on silicon-carbide paper under flowing water, and finished with 600-grade. Serf-adhesive PVC tape containing a hole was applied over the dentin. Glass-ionomer cement (Fuji II; G-C, Japan) or a dentin bonding agent (Scotchbond Self Cure, 3M, USA), followed by resin composite (Clearfil; Ku-
raray, Japan), was placed on the exposed dentin, followed by a 3.2-ramdiameter stainless steel pad with wire loop for glass ionomer, or a 3.5-mmdiameter mesh-backed orthodontic bracket with wire loop for composite. The hole in the tape corresponded exactly to the size of the bracket. Glass-ionomer powder and liquid were weighed to give a powder:liquid ratio of 1.5:1. For composite bonding, two coats of dentin bonding agent were applied in accordance with the manufacturers instructions. The glass-ionomer cement specimens were stored in a closed container over water at 37°C for 24 h, and the composite specimens were immersed in water at 37°C for 24 h. The bond strengths were measured in tension by use of a universal testing machine (Shimadzu, Japan) at a cross-head speed of 1 mm/min. The details of the method have been described previously (Beech et aL, 1985; Solomon and Beech, 1985). Six glass-ionomer and seven composite specimens were tested initially, and the experiment was repeated three months later with 14 additional fresh teeth-eight with glass ionomer and six with composite. These data were compared with those previously reported (Beech et al., 1985; Solomon and Beech, 1985) from use of teeth which had been stored in tap water at 4°C for several months (15 Clearffl + Scotchbond Self Cure, 19 Fuji II glass ionomer), and in which an identical method was followed. RESULTS
Table 1 shows the results of tensile bond strengths for the initial and repeat experiments with the two materials. When Student's t test was used, there was no significant difference between the mean tensile bond strengths in the initial and repeat experiments for either dentin bonding agent (P = 0.78) or glass ion-
Dental Materials~January 1991 15
TABLE 1 TENSILE BOND STRENGTHSTO DENTIN OF FRESHLYEXTRACTEDTEETH, MPa
Scotchbond Self Cure/Clearfil
Fuji II glass ionomer
Initial run Second run
n 7 7
Mean 1.00 1.11
S.D. 0.84 0.63
Pooled data Initial run Second run
14 6 8
1.05 3.54 3.83
0.72 0.97 0.66
Pooled data
14
3.70
0.79
TABLE 2 COMPARISON OF TENSILE BOND STRENGTHS(MPa) TO DENTIN OF FRESHLYEXTRACTEDAND 'OLD'* TEETH
Freshly extracted Scotchbond Self Cure/Clearfil Fuji II glass ionomer
'Old'
n
Mean
S.D.
n
Mean
S.D.
14 14
1.08 3.70
0.72 0.79
15 19
1.82 2.13
0.37 1.02
*Beech et aL, 1985; Solomon and Beech, 1985.
omer (P = 0.53). The results from the two series were therefore pooled (Table 1). Table 2 compares these pooled fresh-teeth data with the previous data from use of old teeth. One-way analysis of variance indicated that there was a significant difference among the four groups, which (on further analysis by t tests) was shown to be between that of the two glassionomer groups (P < 0.001) and that of the two Scotchbond Self Cure groups (P < 0.001). All specimens failed at the material/dentin interface, as observed by careful visual examination, sometimes with the aid of a low-power microscope (x 25). DISCUSSION
The methods used in the experiment with 'fresh' teeth were identical to those used previously for 'old' teeth. Plain-backed buttons were used for glass ionomer, since the material adheres strongly to stainless steel, and mesh-backed buttons were used for composite, since mechanical attachment is required. The dilemma presented by an experiment which tests the effect of substrate age on adhesion is either to use the same batch of adhesive each time (the results therefore being subject to age changes in the adhesive), or to use a fresh batch of adhesive each time (the results therefore being subject to possible batch variations in the adhesive). In
16 BEECH et aL/BONDING TO DENTIN
these experiments, fresh adhesive was used each time, since there is no evidence that significant batch-tobatch variations occur with the glassionomer and dentin bonding agents used in the study. Causton and Johnson (1979) reported that the shear bond strength of a polycarboxylate cement (Durelon; Espe GmbH, Germany) to dentin decreased from 6.3 MPa at 15 min to 4.5 MPa at six mo postextraction. This is consistent with the decrease we have observed between immediately post-extraction and after long-term storage for glass-ionomer cement, although our test method was tensile rather than shear. They speculated that bond strengths may be affected by the changes in the "relationship" between mineral and organic phases of dentin which occur with age involving breakdown of cells and protein, and which presumably alter the number of bonding sites. Another factor may be a greater tendency of newly-cut dentin from freshly extracted teeth to exude fluid from the dentin tubules, compared with old teeth (Kimura et aL, 1985). Scotchbond Self Cure is essentially an organic, hydrophobic material, which would need to compete with dentinal fluid exudate in order to wet the dentin surface. However, dentinal fluid would probably assist in the wetting of dentin by water-based cements such as glass ionomer and polycarboxylate.
Further work is necessary to determine the extent to which dentin prepared for bonding (as in the present study) will become moist from tubular exudate, since it will depend on the presence and characteristics of the smear layer (Tao and Pashley, 1989). However, Tao and Pashley (1989) have shown the detrimental effect on the bond s t r e n g t h of Scotchbond Light Cure to dentin, when the dentin surface is wetted by artificial perfusion fluid after removal of smear layer. In another study (Pashley et aL, 1988), the shear bond strength of composite to dentin mediated by Scotchbond Light Cure was measured in dog teeth in vivo and in the same teeth in vitro after extraction. Dentin surface preparation resulted in the formation of a smear layer, and no difference between in vivo and "n vitro results was found. In a similar study ( ~ w ~ r t et aL, 1990), human dentin car. es were prepared and bonded either immediately before or immediately after extraction. When Scotchbond Dual Cure (Light Cure) was used, there was an approximately eight-fold increase in tensile bond strength for cavities prepared and bonded immediately after extraction. Again, this may be because teeth in vivo had fluid exudate on the dentin surface; however, more work is required for this explanation to be assessed. Mitchem and Gronas (1986) did not find any effect of post-extraction age up to 26 days with Scotchbond Self Cure (3M, USA); however, a shear method was used which may not reflect changes found by tensile methods, and it was not clear what storage medium had been used. ICunura et aL (1985) found that the tensile bond strength of a dentin bonding agent (Clearfil; Kuraray, Japan) for composites increased with post-extraction time from 15 rain to one week and did not change thereafter, although they treated the dentin with 30% phosphoric acid. Interestingly, by far the best result was found after Clearffl was soaked in formalin for six too, which suggests that post-extraction changes in protein may play a significant role for this material. Comparison of bond strengths to 10% citric acid/3% fer-
ric chloride-treated dentin, 15 min and one mo post-extraction, also revealed a substantial increase with post-extraction time. Nakamichi et al. (1983) found the bond strength of a resin composite bonded by dentin primer (Clearfil Bond System F; Kuraray, Japan) to be significantly higher to old dentin than to dentin from freshly extracted human teeth. Their results, however, are not comparable with those reported here, since Nakamichi et al. (1983) acid-etched the dentin, and also their shortest postextraction time was in the order of days. They considered, however, that in old teeth, odontoblast process degeneration allowed the resin tags to penetrate dentin more deeply, resulting in stronger bonding. Resin penetration may have been facilitated by the 'funneling' of the dentin tubular openings that occurs as a result of acid treatment. With respect to glass-ionomer cement, there is limited work on the influence of post-extraction time on adhesion to dentin. Aboush and Jenkins (1983) found an increase in bond strength between 60 min and 30 days, and between 60 min and 120 days, but did not use teeth sooner than 60 min post-extraction. Tyler et al. (1987) reported a significantly higher bond strength to dentin in extracted monkey teeth than in the same teeth prior to extraction. In all cases, the failure was cohesive, which they attributed to the effect of dentinal fluid on the physical properties of the cement. In our study, f r e s h l y extracted teeth may have had less dentinal fluid on the surface than would be present clinically, but cohesive failure leaving a thin, visually undetectable, layer of cement could not be ruled out in our study. Smearlayer effects are, again, probably important. It would appear from the results presented here that different materials are affected to different extents by the post-extraction age of the tooth. Our findings and those of Causton and Johnson (1979) agree
that there is a decrease in the bond strength of polyacrylic-acid-based cements with increasing time after extraction. Further, our findings and those of Nakamichi et al. (1983) and Kimura et al. (1985) with respect to polymeric dentin bonding agents all show an increase in bond strength with increasing time after extraction. It may be argued that laboratory bond strength measurements should always be carried out on fresh teeth to simulate clinical conditions more closely. However, there are considerable logistical problems in the acquisition of fresh t e e t h and the immediate preparation of bonded specimens, and there are also other variables associated with d e n t i n for example, patient age, tooth type and r e g i o n of d e n t i n s e l e c t e d (Aboush and Jenkins, 1984), and depth into the dentin from the dentin-enamel junction (Causton, 1984). Because of the large influence of these and other experimental variables on the results, it is not possible f o r b o n d s t r e n g t h s to be compared among researchers. Labo r a t o r y bond s t r e n g t h m e a s u r e m e n t s are essentially screening tests and do not predict clinical performance, and thus the ideal of using f r e s h l y e x t r a c t e d t e e t h is probably unnecessary. In any case, the significance of bond strength is overemphasized, when, clinically, the reliability of achieving a bond every time, the durability of the bond in the oral environment, and the sensitivity of the placement technique in non-ideal conditions are more important.
REFERENCES ABOUSH, Y.E.Y. and JENKINS, C.B.G. (1983): The Effect of Post-extraction Storage on the Adhesion of Glass Ionomers to Dentine, J Dent Res 62: 441, Abstr. No. 237. ABOUSH, Y.E.Y. and JENKINS, C.B.G. (1984): Factors Affecting the Tensile Bond Strength of a Glass Ionomer Restorative to Dentine, J Dent Res 63: 511, Abstr. No. 194.
BEECH, D.R.; SOLOMON, A.; and BERNIER,R. (1985): Bond Strength of Polycarboxylic Acid Cements to Treated Dentin, Dent Mater 1: 154157. CAUSTON, B.E. (1984): Improved Bonding of a Composite Commercial Halogenated Phosphate Ester, Br Dent J 156: 93-95. CAUSTON, B.E. and JOHNSON, N.W. (1979): Changes in the Dentin of Human Teeth Following Extraction and their Implications for in vitro Studies of Adhesion to Tooth Substance, Arch Oral Biol 24: 229-232. KIMURA~S.; SHIMIZU,T.; and FuJII, B. (1985): Influence of Dentin and Storing Conditions, Dent Mater J 4: 6880. MITCHEM, J.C. and GRONAS,D. (1986); Effect of Time after Extraction and Depth of Dentin on Resin Dentin Adhesives, J A m Dent Assoc 113: 285287. NAKAMICHI, I.; IWAKU, M.; and FUSAYAMA,T. (1983): Bovine Teeth as Possible Substitute in the Adhesion Test, J Dent Res 62: 1076--1081. PASHLEY, F.L.; TAO, L.; MACKERT, J.R.; ~nd PASHLEY, D.H. (1988): Comparison of in vivo vs. in vitro Bonding of Composite Resin to the Dentin of Canine Teeth, J Dent Res 67: 467-470. PEDDEY, M. (1981): The Bond Strength of Polycarboxylic Acid Cements to Dentine: Effect of Surface Modification and Time after Extraction, AuNt Dent J 26: 178-180. SOLOMON, A. and BEECH, D.R. (1985): Bonding of Composites to Dentin Using Primers, Dent Mater 1: 79-82. STEWART, B.L.; HARCOURT,J.K.; and TYAS, M.J. (1990): Comparison of Bond Strengths to Dentine in Cavities Restored Before and After Extraction, J Dent Res 69: 945, Abst. No. 99. TAO, L. and PASHLEY, D.H. (1989): Dentin Perfusion Effects on the Shear Bond Strengths of Bonding Agents to Dentin, Dent Mater 5: 181-184. TYLER, M.; CHARBENEAU, G.; DENNISON, J.; HEYS, D.; and FITZGERALD,M. (1987): In vivo and in vitro Tensile Bond Strengths of Glass Ionomer Cement, J Dent Res 66: 112, Abstr. No. 48. WILLIAMS, V.D.; SVARE, C.W.; and AQUILINO, S.A. (1985): Duration of Tooth Storage vs. Potential for Adhesive Bonding, J Dent Res 64: 276, Abstr. No. 911.
Dental Materials~January 1991 17
1Australian Dental Standards Laboratory 240 Langridge Street Abbotsford Victoria 3067 Australia 2Present address: School of Dental Science University of Melbourne 711 Elizabeth St Melbourne 3000 Australia 3Private practitioner Melbourne, Australia Received November 11, 1989 Accepted September 6, 1990 *To whom correspondence and reprint requests should be addressed
Dent Mater 7:15-17, January, 1991
Abstract-This study was undertaken to determine if the time after which teeth are extracted influences the tensile bond strength of a glass ionomer (Fuji II; GC) and a dentin bonding agent (Scotchbond Self Cure; 3M) to dentin. Within 20 min of extraction, 14 teeth were bonded with glass ionomer and 13 teeth with Scotchbond Self Cure plus a composite material (Clearfil; Kuraray), by attachment of orthodontic brackets to prepared dentin surfaces. The bonds were fractured in tension, and yielded values of 3.7 MPa for glass ionomer and 1.08 MPa for Scotchbond Self Cure + Clearfil. These data were significantly different (P < 0.002) from data previously obtained from the use of old teeth, from which values of 2.20 MPa and 1.82 MPa for glass ionomer and Clearfil + Scotchbond Self Cure, respectively, were obtained. It was concluded that the time after extraction can significantly change bond strengths to dentin, but that the direction and magnitude of these changes depend on the adhesive system used.
~
t has been reported (Causton and Johnson, 1979) that the shear bond strength of a polycarboxylate cement (Durelon; Espe GmbH, Germany) to human dentin is influenced by the time between the extraction of the teeth and the preparation of the specimen. Subsequent authors (Peddey, 1981; Aboush and Jenkins, 1983; Nakamichi et al., 1983; Kimura et at., 1985; Williams et aL, 1985; Mitchem and Gronas, 1986; Pashley et al., 1988) have used a variety of materials, test methods, and teeth with various post-extraction times in order to explore this phenomenon further. The results of these later studies have been variable, with no consistent pattern emerging. Much stress in scientific and product literature is placed on gauging the performance of adhesive materials by comparison of bond strengths. If the bonding behavior of dentin changes significantly postextraction, then there is little clinical validity in r e p o r t e d bond strengths. The present work was undertaken to assess the effect of post-extraction time on the tensile bond strength to dentin of a composite/dentin bonding agent combination and a glass-ionomer cement. MATERIALS AND METHODS
Human teeth were obtained immediately after extraction under local anesthetic and placed in tap water at room temperature. Within 15 rain of extraction, the teeth were embedded in plaster blocks, and a dentin surface (usually lingual or buccal) was prepared by abrasion on silicon-carbide paper under flowing water, and finished with 600-grade. Serf-adhesive PVC tape containing a hole was applied over the dentin. Glass-ionomer cement (Fuji II; G-C, Japan) or a dentin bonding agent (Scotchbond Self Cure, 3M, USA), followed by resin composite (Clearfil; Ku-
raray, Japan), was placed on the exposed dentin, followed by a 3.2-ramdiameter stainless steel pad with wire loop for glass ionomer, or a 3.5-mmdiameter mesh-backed orthodontic bracket with wire loop for composite. The hole in the tape corresponded exactly to the size of the bracket. Glass-ionomer powder and liquid were weighed to give a powder:liquid ratio of 1.5:1. For composite bonding, two coats of dentin bonding agent were applied in accordance with the manufacturers instructions. The glass-ionomer cement specimens were stored in a closed container over water at 37°C for 24 h, and the composite specimens were immersed in water at 37°C for 24 h. The bond strengths were measured in tension by use of a universal testing machine (Shimadzu, Japan) at a cross-head speed of 1 mm/min. The details of the method have been described previously (Beech et aL, 1985; Solomon and Beech, 1985). Six glass-ionomer and seven composite specimens were tested initially, and the experiment was repeated three months later with 14 additional fresh teeth-eight with glass ionomer and six with composite. These data were compared with those previously reported (Beech et al., 1985; Solomon and Beech, 1985) from use of teeth which had been stored in tap water at 4°C for several months (15 Clearffl + Scotchbond Self Cure, 19 Fuji II glass ionomer), and in which an identical method was followed. RESULTS
Table 1 shows the results of tensile bond strengths for the initial and repeat experiments with the two materials. When Student's t test was used, there was no significant difference between the mean tensile bond strengths in the initial and repeat experiments for either dentin bonding agent (P = 0.78) or glass ion-
Dental Materials~January 1991 15
TABLE 1 TENSILE BOND STRENGTHSTO DENTIN OF FRESHLYEXTRACTEDTEETH, MPa
Scotchbond Self Cure/Clearfil
Fuji II glass ionomer
Initial run Second run
n 7 7
Mean 1.00 1.11
S.D. 0.84 0.63
Pooled data Initial run Second run
14 6 8
1.05 3.54 3.83
0.72 0.97 0.66
Pooled data
14
3.70
0.79
TABLE 2 COMPARISON OF TENSILE BOND STRENGTHS(MPa) TO DENTIN OF FRESHLYEXTRACTEDAND 'OLD'* TEETH
Freshly extracted Scotchbond Self Cure/Clearfil Fuji II glass ionomer
'Old'
n
Mean
S.D.
n
Mean
S.D.
14 14
1.08 3.70
0.72 0.79
15 19
1.82 2.13
0.37 1.02
*Beech et aL, 1985; Solomon and Beech, 1985.
omer (P = 0.53). The results from the two series were therefore pooled (Table 1). Table 2 compares these pooled fresh-teeth data with the previous data from use of old teeth. One-way analysis of variance indicated that there was a significant difference among the four groups, which (on further analysis by t tests) was shown to be between that of the two glassionomer groups (P < 0.001) and that of the two Scotchbond Self Cure groups (P < 0.001). All specimens failed at the material/dentin interface, as observed by careful visual examination, sometimes with the aid of a low-power microscope (x 25). DISCUSSION
The methods used in the experiment with 'fresh' teeth were identical to those used previously for 'old' teeth. Plain-backed buttons were used for glass ionomer, since the material adheres strongly to stainless steel, and mesh-backed buttons were used for composite, since mechanical attachment is required. The dilemma presented by an experiment which tests the effect of substrate age on adhesion is either to use the same batch of adhesive each time (the results therefore being subject to age changes in the adhesive), or to use a fresh batch of adhesive each time (the results therefore being subject to possible batch variations in the adhesive). In
16 BEECH et aL/BONDING TO DENTIN
these experiments, fresh adhesive was used each time, since there is no evidence that significant batch-tobatch variations occur with the glassionomer and dentin bonding agents used in the study. Causton and Johnson (1979) reported that the shear bond strength of a polycarboxylate cement (Durelon; Espe GmbH, Germany) to dentin decreased from 6.3 MPa at 15 min to 4.5 MPa at six mo postextraction. This is consistent with the decrease we have observed between immediately post-extraction and after long-term storage for glass-ionomer cement, although our test method was tensile rather than shear. They speculated that bond strengths may be affected by the changes in the "relationship" between mineral and organic phases of dentin which occur with age involving breakdown of cells and protein, and which presumably alter the number of bonding sites. Another factor may be a greater tendency of newly-cut dentin from freshly extracted teeth to exude fluid from the dentin tubules, compared with old teeth (Kimura et aL, 1985). Scotchbond Self Cure is essentially an organic, hydrophobic material, which would need to compete with dentinal fluid exudate in order to wet the dentin surface. However, dentinal fluid would probably assist in the wetting of dentin by water-based cements such as glass ionomer and polycarboxylate.
Further work is necessary to determine the extent to which dentin prepared for bonding (as in the present study) will become moist from tubular exudate, since it will depend on the presence and characteristics of the smear layer (Tao and Pashley, 1989). However, Tao and Pashley (1989) have shown the detrimental effect on the bond s t r e n g t h of Scotchbond Light Cure to dentin, when the dentin surface is wetted by artificial perfusion fluid after removal of smear layer. In another study (Pashley et aL, 1988), the shear bond strength of composite to dentin mediated by Scotchbond Light Cure was measured in dog teeth in vivo and in the same teeth in vitro after extraction. Dentin surface preparation resulted in the formation of a smear layer, and no difference between in vivo and "n vitro results was found. In a similar study ( ~ w ~ r t et aL, 1990), human dentin car. es were prepared and bonded either immediately before or immediately after extraction. When Scotchbond Dual Cure (Light Cure) was used, there was an approximately eight-fold increase in tensile bond strength for cavities prepared and bonded immediately after extraction. Again, this may be because teeth in vivo had fluid exudate on the dentin surface; however, more work is required for this explanation to be assessed. Mitchem and Gronas (1986) did not find any effect of post-extraction age up to 26 days with Scotchbond Self Cure (3M, USA); however, a shear method was used which may not reflect changes found by tensile methods, and it was not clear what storage medium had been used. ICunura et aL (1985) found that the tensile bond strength of a dentin bonding agent (Clearfil; Kuraray, Japan) for composites increased with post-extraction time from 15 rain to one week and did not change thereafter, although they treated the dentin with 30% phosphoric acid. Interestingly, by far the best result was found after Clearffl was soaked in formalin for six too, which suggests that post-extraction changes in protein may play a significant role for this material. Comparison of bond strengths to 10% citric acid/3% fer-
ric chloride-treated dentin, 15 min and one mo post-extraction, also revealed a substantial increase with post-extraction time. Nakamichi et al. (1983) found the bond strength of a resin composite bonded by dentin primer (Clearfil Bond System F; Kuraray, Japan) to be significantly higher to old dentin than to dentin from freshly extracted human teeth. Their results, however, are not comparable with those reported here, since Nakamichi et al. (1983) acid-etched the dentin, and also their shortest postextraction time was in the order of days. They considered, however, that in old teeth, odontoblast process degeneration allowed the resin tags to penetrate dentin more deeply, resulting in stronger bonding. Resin penetration may have been facilitated by the 'funneling' of the dentin tubular openings that occurs as a result of acid treatment. With respect to glass-ionomer cement, there is limited work on the influence of post-extraction time on adhesion to dentin. Aboush and Jenkins (1983) found an increase in bond strength between 60 min and 30 days, and between 60 min and 120 days, but did not use teeth sooner than 60 min post-extraction. Tyler et al. (1987) reported a significantly higher bond strength to dentin in extracted monkey teeth than in the same teeth prior to extraction. In all cases, the failure was cohesive, which they attributed to the effect of dentinal fluid on the physical properties of the cement. In our study, f r e s h l y extracted teeth may have had less dentinal fluid on the surface than would be present clinically, but cohesive failure leaving a thin, visually undetectable, layer of cement could not be ruled out in our study. Smearlayer effects are, again, probably important. It would appear from the results presented here that different materials are affected to different extents by the post-extraction age of the tooth. Our findings and those of Causton and Johnson (1979) agree
that there is a decrease in the bond strength of polyacrylic-acid-based cements with increasing time after extraction. Further, our findings and those of Nakamichi et al. (1983) and Kimura et al. (1985) with respect to polymeric dentin bonding agents all show an increase in bond strength with increasing time after extraction. It may be argued that laboratory bond strength measurements should always be carried out on fresh teeth to simulate clinical conditions more closely. However, there are considerable logistical problems in the acquisition of fresh t e e t h and the immediate preparation of bonded specimens, and there are also other variables associated with d e n t i n for example, patient age, tooth type and r e g i o n of d e n t i n s e l e c t e d (Aboush and Jenkins, 1984), and depth into the dentin from the dentin-enamel junction (Causton, 1984). Because of the large influence of these and other experimental variables on the results, it is not possible f o r b o n d s t r e n g t h s to be compared among researchers. Labo r a t o r y bond s t r e n g t h m e a s u r e m e n t s are essentially screening tests and do not predict clinical performance, and thus the ideal of using f r e s h l y e x t r a c t e d t e e t h is probably unnecessary. In any case, the significance of bond strength is overemphasized, when, clinically, the reliability of achieving a bond every time, the durability of the bond in the oral environment, and the sensitivity of the placement technique in non-ideal conditions are more important.
REFERENCES ABOUSH, Y.E.Y. and JENKINS, C.B.G. (1983): The Effect of Post-extraction Storage on the Adhesion of Glass Ionomers to Dentine, J Dent Res 62: 441, Abstr. No. 237. ABOUSH, Y.E.Y. and JENKINS, C.B.G. (1984): Factors Affecting the Tensile Bond Strength of a Glass Ionomer Restorative to Dentine, J Dent Res 63: 511, Abstr. No. 194.
BEECH, D.R.; SOLOMON, A.; and BERNIER,R. (1985): Bond Strength of Polycarboxylic Acid Cements to Treated Dentin, Dent Mater 1: 154157. CAUSTON, B.E. (1984): Improved Bonding of a Composite Commercial Halogenated Phosphate Ester, Br Dent J 156: 93-95. CAUSTON, B.E. and JOHNSON, N.W. (1979): Changes in the Dentin of Human Teeth Following Extraction and their Implications for in vitro Studies of Adhesion to Tooth Substance, Arch Oral Biol 24: 229-232. KIMURA~S.; SHIMIZU,T.; and FuJII, B. (1985): Influence of Dentin and Storing Conditions, Dent Mater J 4: 6880. MITCHEM, J.C. and GRONAS,D. (1986); Effect of Time after Extraction and Depth of Dentin on Resin Dentin Adhesives, J A m Dent Assoc 113: 285287. NAKAMICHI, I.; IWAKU, M.; and FUSAYAMA,T. (1983): Bovine Teeth as Possible Substitute in the Adhesion Test, J Dent Res 62: 1076--1081. PASHLEY, F.L.; TAO, L.; MACKERT, J.R.; ~nd PASHLEY, D.H. (1988): Comparison of in vivo vs. in vitro Bonding of Composite Resin to the Dentin of Canine Teeth, J Dent Res 67: 467-470. PEDDEY, M. (1981): The Bond Strength of Polycarboxylic Acid Cements to Dentine: Effect of Surface Modification and Time after Extraction, AuNt Dent J 26: 178-180. SOLOMON, A. and BEECH, D.R. (1985): Bonding of Composites to Dentin Using Primers, Dent Mater 1: 79-82. STEWART, B.L.; HARCOURT,J.K.; and TYAS, M.J. (1990): Comparison of Bond Strengths to Dentine in Cavities Restored Before and After Extraction, J Dent Res 69: 945, Abst. No. 99. TAO, L. and PASHLEY, D.H. (1989): Dentin Perfusion Effects on the Shear Bond Strengths of Bonding Agents to Dentin, Dent Mater 5: 181-184. TYLER, M.; CHARBENEAU, G.; DENNISON, J.; HEYS, D.; and FITZGERALD,M. (1987): In vivo and in vitro Tensile Bond Strengths of Glass Ionomer Cement, J Dent Res 66: 112, Abstr. No. 48. WILLIAMS, V.D.; SVARE, C.W.; and AQUILINO, S.A. (1985): Duration of Tooth Storage vs. Potential for Adhesive Bonding, J Dent Res 64: 276, Abstr. No. 911.
Dental Materials~January 1991 17
