Correlation among dentin depth, permeability, and bond strength of adhesive resins J. Tagami ~ L. Tagz D.H. Pashley2.
1Department of Operative Dentistry Tokyo Medical and Dental University 1-5-45 Bunkyoku, Yushima Tokyo 113, Japan 2Department of Oral Biology/Physiology School of Dentistry Medical College of Georgia Augusta, Georgia 30912-1129 Received April 14, 1989 Accepted July 28, 1989 *Corresponding author
This investigation was supported, in part, by DE06427 from the National Institute of Dental Research. Dent Mater 6:45-50, January, 1990
Abstract-Correlations among dentin permeability, dentin depth, and dentin bonding of Scotchbond, Clearfil New Bond, and Superbond C&B were studied in bovine incisor crown segments. Since the dentin surface was prepared on deeper dentin, the permeability of the dentin increased both in the presence of, and especially after removal of, the smear layer. In general, the deeper the dentin, the lower the bond strengths of Scotchbond, Clearfil New Bond, and Superbond C&B. The higher the dentin permeability, the lower the bond strength of Superbond C&B, but there was no simple relationship in the case of either Scotchbond or Ciearfil New Bond. The bond strength of Superbond C&B was much higher than those of Scotchbond or Clearfil New Bond at any depth of dentin. Superbond C&B should be considered as both an enamel- and dentin-bonding agent.
ith improvements in oral health care, fewer teeth are being e x t r a c t e d . A l t h o u g h extracted human molars have been the preferred substrate for dentin bonding studies, an alternative substrate is the use of bovine incisor dentin (Nakamichi et al., 1983). However, since the shapes of incisors are so different from those of molars, there may be structural differences in tubule densities or diameters in superficial or deep dentin that may modify dentin bonding. Further, these differences may alter the water content of dentin at different depths, which would alter the wetness of prepared dentin surfaces. Recently, Tag and Pashley (1989) reported that there was an inverse correlation between dentin permeability and the shear bond strengths of Scotchbond in human molar dentin after acid removal of smear layers. Many commercially available dentin-bonding systems advocate removal of the smear layer as a method of improving bond strengths (Retief et al., 1988). Several reports indicate that bond strengths of adhesive resins are highest on superficial dentin and lowest on deep dentin (Nakamichi et al., 1983; Causton, 1984; Mitchem and Gronas, 1986; Suzuki and Finger, 1988). This may be due either to differences in chemical composition or to regional differences in wetness (i.e., dentin permeability). Thus, there are several factors that may contribute to the high coefficient of variation that is often reported in dentin-bonding studies. The purpose of this study was to investigate, with use of bovine incisors, the correlations among dentin permeability, dentin depth, and the bond strength of several adhesive resin materials.
w
MATERIALS AND METHODS
Toad Preparation.-Thirty-six intact bovine lower incisors were surgically removed from young animals at a local abattoir. The procedure involved the use of elevators and forceps applied only to root surfaces. The teeth were placed in 4°C isotonic saline containing 0.2% (w/v) sodium azide as a preservative. The teeth were used within one month of extraction. Crown segments were prepared by removal of the distal two-thirds of the roots by use of a low-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL). The pulp tissue was removed with a broach, avoiding contact of the walls of the coronal pulp chamber. The resulting crown segments (Fig. 1) were glued with cyanoacrylate (Histacryl blue, B. Melsungen AG, West Germany) to 2 x 2 x 0.7-cm pieces of Plexiglas containing 2-cm lengths of 18-gauge s t a i n l e s s steel t u b i n g through their centers. This served to connect the pulp chamber with the device used to m e a s u r e dentin permeability (Pashley et al., 1988) and ensured that the pulp chamber and dentin were always full of a physiologic salt solution (Dulbecco's phosphate-buffered saline, Gibco Laboratories, Grand Island, NY).
Dentin Depth. - A groove was prepared in the enamel of the cingulum to serve as a reference mark for measuring the labiolingual thickness of the crown segments by use of a digital micrometer (Sylvae Ultra-Cal II, Fowler Co., Inc., Newton, MA). The crown segment was positioned in a s a n d i n g machine (Ecomet, Buehler, Ltd., Lake Bluff, IL) so that the enamel could be removed from
Dental Materials~January 1990 45
Kyoto, Japan) group was pre-treated with the 10-3 solution (10% citric acid, 3% ferric chloride) included in the kit for 30 s, followed by a water rinse for five s.
N 2 From Pressure Tank
Fluid Flow
Pressurized Buffer Reservoir
1
Microsyringe
Fig. 1. Schematic of the apparatus used to measure dentin permeability via fluid flow from the pressurized reservoir through a micropipette to the crown segment. The progress of a tiny air bubble (insert) in the micropipette was proportional to permeability,
the facial surface of the cervical third of the crown segment by use of 320-grit SiC abrasive paper under flowing water. When all the enamel was removed, the labiolingual thickness of the crown segment was recorded by digital micrometer. Then, the facial enamel and dentin were ground further so that sufficient dentin surface area for bonding could be obtained (e.g., an area 4.5 mm in diameter). The labiolingual thickness was then recorded, and measurements of dentin permeability and dentin bond strengths were taken. This was followed by additional grinding of about 0.5 mm of the labial surface, and re-measurement of thickness, dentin p e r m e a b i l i t y , and bond strength. These procedures were repeated until the pulp chamber was exposed. At each step, the labiolingual thickness was recorded. Total dentin thickness was determined from the initial dentin exposure and the pulp exposure. The dentin depth of each sequential step was then calculated and expressed in both millimeters and as a percent of the total dentin thickness.
46
Dentin Permeability. - D e n t i n permeability was measured as hydraulic conductance (Reeder et al., 1978; Fogel et al., 1988) and expressed in ~L cm -2 min -1 cm H20 -1. The fluid pressure was 0.7 kg/cm 2. The surface area of the bonded surface was controlled by a nylon cylinder (Small Parts, Inc., Miami, F L 33138; part # RSN-4/2) with an ID of 3 mm and height of 3 mm. The dentin studied was always in the center of the cervical third of the labial dentin. After the nylon cylinder was positioned, the remaining dentin surface was sealed with two layers of nail polish so that the measured permeability of the dentin would be identical to the bonded surface area. Dentin permeability measurements always preceded dentin bonding. Smear layers were left intact on dentin used for bonding with original Scotchbond (3M, St. Paul, MN). Specimens in the Clearfil New Bond group (Clearfil F II, Kuraray, Osaka, Japan) were treated with the 37% phosphoric acid supplied with the kit, for 60 s prior to measurement of dentin permeability. Dentin to be used in the Superbond C&B (Sun Medical Co.,
TAGAMI et aUDENTIN DEPTH, PERMEABILITY, AND BOND STRENGTH
Dentin Bending. - A f t e r the permeability of the dentin was measured, the dentin surfaces were rinsed and air-dried, respectively, for ten s. The nylon matrix was placed on the dentin, and original light-cured Scotchbond (3M, St. Paul, MN) was painted on the dentin surface by use of a fine brush. The excess alcohol was evaporated with an air stream for 10 s, and the surface was light-cured for 10 s in a Visilux-2 unit (3M). The Scotchbond was then covered with Silux universal shade composite (3M) in two 1.5-mm increments, with 30 s of light-curing at each step. The second bonding group was treated with Clearfil New Bond selfcured dentin bonding agent. After one drop each of catalyst and universal were mixed, it was brushed on by use of the applicators included in the kit and was spread with a gentle stream of air for 10 s. It was covered with Clearfil F II resin composite (self-cured) in one increment. The third b o n d i n g g r o u p was treated with Superbond C&B resin by the brush-on technique described in the manufacturer's instructions. Approximately 0.5-1.0 mm of Superbond C&B resin was applied to the dentin. The remaining height of the nylon matrix was filled in one increment with Clearfil F II resin composite (chemically-cured). The specimens were all stored in distilled water at 37°C for 24 h. No fluid pressure was applied to the dentin during bonding or during storage. Shear bond strength was measured on an Instron machine with a fine wire loop used around the base of the nylon cylinder. The bond strengths were expressed in MPa. Statistics. - T h e relationships among dentin depth, dentin permeability, and bond strengths were evaluated by regression analysis. Curve-fitting with least-squares equations was attempted with linear, exponential, and power functions. Dentin depths were also stratified into four groups: 0-10% from the D E J (superficial
0.07 -
0.004 - -
0.003 - -
0.06 -
NO Treatment y=l.1×10-5x+2.7x10 r=0.55
4
--e-37%
p = < 0.001
H3PO 4
y= 1.2x
10-4x
- 1.4×
10 -3
r = 0.55
A
r
0 -1-
p = < 0.001
0.05-
0.002 - -
:
•
•i
o.oo1
0.04 -
O
•
10-3
Solution
y-- 2 . 4 x 1 0 - 4 X r = 0.68 p = < 0.0001
.
-
4.6x 10- 3
o
~"r-
0.03
0
I 0
-~
50
100
0.02
0.01
A
DEJ
00
"_O'o.....
nil igll ~
" U
A
¢Z)O
0 0
10
20
30
40 Dentin
50 Depth
............
pu,p
•
I)o
•
•
1
1
l
1
1
60
70
80
90
100
(%
)
Fig. 2, Relationships between dentin permeability (Lp) and dentin depth. 37% H3PO~; dentin treated with phosphoric acid for 60 s; 10-3, dentin treated with 10-3 solution for 30 s; Insert-No treatment (dentin without any surface treatment).
dentin), 11-40% from the DEJ (upper middle dentin), 41-70% from the DEJ (lower middle dentin), and 71100% from the D E J (deep dentin). A two-way analysis of variance was performed for identification of statistically significant differences in bond strength as a function of dentin depth within a bonding system and, within any given dentin depth, among the three bonding systems. RESULTS
The relationship between dentin permeability and dentin depth depended on whether the smear layer was present or absent. In the group of specimens treated with Scotchbond, the smear layer created with 320-grit SiC abrasive paper was left u n d i s t u r b e d . This r e d u c e d the permeability of the dentin so much that reductions in dentin thickness led to relatively small changes in dentin permeability (Fig. 2, insert)
compared with those seen in the Clearfil New Bond and Superbond groups. In the latter two groups, the smear layer was removed by use of 37% phosphoric acid and the 10-3 solution, respectively. Both groups exhibited a statistically significant (p
1Department of Operative Dentistry Tokyo Medical and Dental University 1-5-45 Bunkyoku, Yushima Tokyo 113, Japan 2Department of Oral Biology/Physiology School of Dentistry Medical College of Georgia Augusta, Georgia 30912-1129 Received April 14, 1989 Accepted July 28, 1989 *Corresponding author
This investigation was supported, in part, by DE06427 from the National Institute of Dental Research. Dent Mater 6:45-50, January, 1990
Abstract-Correlations among dentin permeability, dentin depth, and dentin bonding of Scotchbond, Clearfil New Bond, and Superbond C&B were studied in bovine incisor crown segments. Since the dentin surface was prepared on deeper dentin, the permeability of the dentin increased both in the presence of, and especially after removal of, the smear layer. In general, the deeper the dentin, the lower the bond strengths of Scotchbond, Clearfil New Bond, and Superbond C&B. The higher the dentin permeability, the lower the bond strength of Superbond C&B, but there was no simple relationship in the case of either Scotchbond or Ciearfil New Bond. The bond strength of Superbond C&B was much higher than those of Scotchbond or Clearfil New Bond at any depth of dentin. Superbond C&B should be considered as both an enamel- and dentin-bonding agent.
ith improvements in oral health care, fewer teeth are being e x t r a c t e d . A l t h o u g h extracted human molars have been the preferred substrate for dentin bonding studies, an alternative substrate is the use of bovine incisor dentin (Nakamichi et al., 1983). However, since the shapes of incisors are so different from those of molars, there may be structural differences in tubule densities or diameters in superficial or deep dentin that may modify dentin bonding. Further, these differences may alter the water content of dentin at different depths, which would alter the wetness of prepared dentin surfaces. Recently, Tag and Pashley (1989) reported that there was an inverse correlation between dentin permeability and the shear bond strengths of Scotchbond in human molar dentin after acid removal of smear layers. Many commercially available dentin-bonding systems advocate removal of the smear layer as a method of improving bond strengths (Retief et al., 1988). Several reports indicate that bond strengths of adhesive resins are highest on superficial dentin and lowest on deep dentin (Nakamichi et al., 1983; Causton, 1984; Mitchem and Gronas, 1986; Suzuki and Finger, 1988). This may be due either to differences in chemical composition or to regional differences in wetness (i.e., dentin permeability). Thus, there are several factors that may contribute to the high coefficient of variation that is often reported in dentin-bonding studies. The purpose of this study was to investigate, with use of bovine incisors, the correlations among dentin permeability, dentin depth, and the bond strength of several adhesive resin materials.
w
MATERIALS AND METHODS
Toad Preparation.-Thirty-six intact bovine lower incisors were surgically removed from young animals at a local abattoir. The procedure involved the use of elevators and forceps applied only to root surfaces. The teeth were placed in 4°C isotonic saline containing 0.2% (w/v) sodium azide as a preservative. The teeth were used within one month of extraction. Crown segments were prepared by removal of the distal two-thirds of the roots by use of a low-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL). The pulp tissue was removed with a broach, avoiding contact of the walls of the coronal pulp chamber. The resulting crown segments (Fig. 1) were glued with cyanoacrylate (Histacryl blue, B. Melsungen AG, West Germany) to 2 x 2 x 0.7-cm pieces of Plexiglas containing 2-cm lengths of 18-gauge s t a i n l e s s steel t u b i n g through their centers. This served to connect the pulp chamber with the device used to m e a s u r e dentin permeability (Pashley et al., 1988) and ensured that the pulp chamber and dentin were always full of a physiologic salt solution (Dulbecco's phosphate-buffered saline, Gibco Laboratories, Grand Island, NY).
Dentin Depth. - A groove was prepared in the enamel of the cingulum to serve as a reference mark for measuring the labiolingual thickness of the crown segments by use of a digital micrometer (Sylvae Ultra-Cal II, Fowler Co., Inc., Newton, MA). The crown segment was positioned in a s a n d i n g machine (Ecomet, Buehler, Ltd., Lake Bluff, IL) so that the enamel could be removed from
Dental Materials~January 1990 45
Kyoto, Japan) group was pre-treated with the 10-3 solution (10% citric acid, 3% ferric chloride) included in the kit for 30 s, followed by a water rinse for five s.
N 2 From Pressure Tank
Fluid Flow
Pressurized Buffer Reservoir
1
Microsyringe
Fig. 1. Schematic of the apparatus used to measure dentin permeability via fluid flow from the pressurized reservoir through a micropipette to the crown segment. The progress of a tiny air bubble (insert) in the micropipette was proportional to permeability,
the facial surface of the cervical third of the crown segment by use of 320-grit SiC abrasive paper under flowing water. When all the enamel was removed, the labiolingual thickness of the crown segment was recorded by digital micrometer. Then, the facial enamel and dentin were ground further so that sufficient dentin surface area for bonding could be obtained (e.g., an area 4.5 mm in diameter). The labiolingual thickness was then recorded, and measurements of dentin permeability and dentin bond strengths were taken. This was followed by additional grinding of about 0.5 mm of the labial surface, and re-measurement of thickness, dentin p e r m e a b i l i t y , and bond strength. These procedures were repeated until the pulp chamber was exposed. At each step, the labiolingual thickness was recorded. Total dentin thickness was determined from the initial dentin exposure and the pulp exposure. The dentin depth of each sequential step was then calculated and expressed in both millimeters and as a percent of the total dentin thickness.
46
Dentin Permeability. - D e n t i n permeability was measured as hydraulic conductance (Reeder et al., 1978; Fogel et al., 1988) and expressed in ~L cm -2 min -1 cm H20 -1. The fluid pressure was 0.7 kg/cm 2. The surface area of the bonded surface was controlled by a nylon cylinder (Small Parts, Inc., Miami, F L 33138; part # RSN-4/2) with an ID of 3 mm and height of 3 mm. The dentin studied was always in the center of the cervical third of the labial dentin. After the nylon cylinder was positioned, the remaining dentin surface was sealed with two layers of nail polish so that the measured permeability of the dentin would be identical to the bonded surface area. Dentin permeability measurements always preceded dentin bonding. Smear layers were left intact on dentin used for bonding with original Scotchbond (3M, St. Paul, MN). Specimens in the Clearfil New Bond group (Clearfil F II, Kuraray, Osaka, Japan) were treated with the 37% phosphoric acid supplied with the kit, for 60 s prior to measurement of dentin permeability. Dentin to be used in the Superbond C&B (Sun Medical Co.,
TAGAMI et aUDENTIN DEPTH, PERMEABILITY, AND BOND STRENGTH
Dentin Bending. - A f t e r the permeability of the dentin was measured, the dentin surfaces were rinsed and air-dried, respectively, for ten s. The nylon matrix was placed on the dentin, and original light-cured Scotchbond (3M, St. Paul, MN) was painted on the dentin surface by use of a fine brush. The excess alcohol was evaporated with an air stream for 10 s, and the surface was light-cured for 10 s in a Visilux-2 unit (3M). The Scotchbond was then covered with Silux universal shade composite (3M) in two 1.5-mm increments, with 30 s of light-curing at each step. The second bonding group was treated with Clearfil New Bond selfcured dentin bonding agent. After one drop each of catalyst and universal were mixed, it was brushed on by use of the applicators included in the kit and was spread with a gentle stream of air for 10 s. It was covered with Clearfil F II resin composite (self-cured) in one increment. The third b o n d i n g g r o u p was treated with Superbond C&B resin by the brush-on technique described in the manufacturer's instructions. Approximately 0.5-1.0 mm of Superbond C&B resin was applied to the dentin. The remaining height of the nylon matrix was filled in one increment with Clearfil F II resin composite (chemically-cured). The specimens were all stored in distilled water at 37°C for 24 h. No fluid pressure was applied to the dentin during bonding or during storage. Shear bond strength was measured on an Instron machine with a fine wire loop used around the base of the nylon cylinder. The bond strengths were expressed in MPa. Statistics. - T h e relationships among dentin depth, dentin permeability, and bond strengths were evaluated by regression analysis. Curve-fitting with least-squares equations was attempted with linear, exponential, and power functions. Dentin depths were also stratified into four groups: 0-10% from the D E J (superficial
0.07 -
0.004 - -
0.003 - -
0.06 -
NO Treatment y=l.1×10-5x+2.7x10 r=0.55
4
--e-37%
p = < 0.001
H3PO 4
y= 1.2x
10-4x
- 1.4×
10 -3
r = 0.55
A
r
0 -1-
p = < 0.001
0.05-
0.002 - -
:
•
•i
o.oo1
0.04 -
O
•
10-3
Solution
y-- 2 . 4 x 1 0 - 4 X r = 0.68 p = < 0.0001
.
-
4.6x 10- 3
o
~"r-
0.03
0
I 0
-~
50
100
0.02
0.01
A
DEJ
00
"_O'o.....
nil igll ~
" U
A
¢Z)O
0 0
10
20
30
40 Dentin
50 Depth
............
pu,p
•
I)o
•
•
1
1
l
1
1
60
70
80
90
100
(%
)
Fig. 2, Relationships between dentin permeability (Lp) and dentin depth. 37% H3PO~; dentin treated with phosphoric acid for 60 s; 10-3, dentin treated with 10-3 solution for 30 s; Insert-No treatment (dentin without any surface treatment).
dentin), 11-40% from the DEJ (upper middle dentin), 41-70% from the DEJ (lower middle dentin), and 71100% from the D E J (deep dentin). A two-way analysis of variance was performed for identification of statistically significant differences in bond strength as a function of dentin depth within a bonding system and, within any given dentin depth, among the three bonding systems. RESULTS
The relationship between dentin permeability and dentin depth depended on whether the smear layer was present or absent. In the group of specimens treated with Scotchbond, the smear layer created with 320-grit SiC abrasive paper was left u n d i s t u r b e d . This r e d u c e d the permeability of the dentin so much that reductions in dentin thickness led to relatively small changes in dentin permeability (Fig. 2, insert)
compared with those seen in the Clearfil New Bond and Superbond groups. In the latter two groups, the smear layer was removed by use of 37% phosphoric acid and the 10-3 solution, respectively. Both groups exhibited a statistically significant (p
