Hydrostatic intrapulpal pressure and bond strength of bonding systems C. Prati 1 D.H. Pashley2 G. MonlanarP
1Department of Conservative Dentistry School of Dentistry University of Bologna Bologna, Italy 2Department of Oral Biology School of Dentistry Medical College of Georgia Augusta, Georgia 30912-1129 Received February 12, 1990 Accepted September 5, 1990 This investigation was supported, in part, by grant DE 06427 from the National Institute of Dental Research to David H. Pashley.
Dent Mater 7:54-58, January, 1991 Abstract-The purpose of this study was to evaluate the effect of intra-pulpal pressure on shear bond strength of three light-cured glass-ionomer cements (GC lining cement, Vitrabond, and Zionomer) and four dentin bonding agents [Gluma/ Scotchbond, Scotchbond 2, MBL, and Clearfil Photo Bond]. Buccal dentin surfaces were prepared just below the DEJ by means of a diamond bur. Dentin treatments were made for Zionomer (Zionomer conditioner), Scotchbond 2 (Scotchprep), MBL (10-3 solution), Clearfil PB (H3P04), GC lining cement (Polyacrylic acid), and Gluma]Scotchbond (EDTA). Resin composites were inserted into tubes, positioned on dentin, cured, tested after five rain or 24 h, and compared with samples bonded and stored under an intra-pulpal pressure of 36 cm of saline. After 24 h in superficial dentin, intrapulpal pressure reduced the bond strength only in MBL, Scotchbond 2, and Zionomer. Clearfil PB bond strength was increased, while Vitrabond, GC lining cement, and Gluma/Scotchbond were unaffected by the presence of pulpal pressure. However, in deep dentin, Scotchbond 2 and Clearfil PB shear bond strengths were significantly reduced by storage in the presence of 36-cm H20 pulpal pressure. Only Vitrabond remained unaffected by pulpal pressure in deep dentin.
umerous studies have evaluated the adhesion of dentin bonding agents (DBA) with flattened and dried extracted teeth used without the presence of pulpal fluid and hydrostatic pressure (Causton, 1984; Komatsu and Finger, 1986; Retief et al., 1988). Depth of dentin (Suzuki and Finger, 1988; Tagami eta/,, 1990) and storage time of bond samples (Retief et aL, 1988) seem to be the most important variables in bond strength tests. However, the presence of pulpal fluid under pressure in vital dentin suggests that this additional variable may influence dentin bonding, and that this variable should be evaluated in vitro so that its possible influence on the bonding of glass-ionomer cements (GIC) and DBA can be determined. Recent in vitro studies suggested that the presence of fluid inside dentinal tubules with or without hydrostatic pressure may reduce bond strength with respect to tests performed without palpal fluid (Mitchem et al., 1988; Andreaus et al., 1989; Tao and Pashley, 1989). These studies concluded that pulpal pressure can play an important role in reducing the adhesion of bonding systems that require smear-layer removal. Since these early studies were done with older GIC and DBA, it is important for the effects of pulpal pressure on the bond strengths of the newest generation of these materials to be evaluated in both superficial and deep dentin and at various storage times. The aim of this study was to evaluate the effect of intrapulpal pressure on four DBA and three GIC and to clarify the importance of dentin thickness and storage time on the shear bond strength of these materials to human dentin.
N
MATERIALS AND METHODS Tooth Preparation.-Erupted human third molars were extracted from
54 PRATI et al./EFFECTS OF PULPAL PRESSURE ON ADHESIVE BONDING
young patients (ages 20-35 yr), then were stored for no more than 24 h at room temperature in saline solution, and their crowns were divided from the roots by means of a high-speed diamond bur, 1 mm apical to the cementum-enamel junction. A second section parallel to the long axis of the tooth divided the crown into two equal halves. The pulp tissue was removed by use of a stainless-steel hand instrument. The cut dentin was etched with 37% orthophosphoric acid (3M Co., St. Louis, MO, USA) for 10 s for removal of debris, then washed and dried. An adaptable plastic tube (Saniplast SPA, Italy) was positioned on the cut dentin surface with L o c t i t e s e a l a n t ( H e n k e l , Germany). Teeth were then mounted with self-curing acrylic resin (Palavit 55, Kulzer, Germany) in stainless-steel molds (Fig.). After 15 min, saline solution was injected into the plastic tube. The tube was then connected with a saline column used to apply a positive hydrostatic pressure of 36-cm H~O to superficial or deep dentin as a simulation of pulpal pressure (Fig.). The buccal surface of each half of the crown was ground with a highspeed, water-cooled medium diamond bur (Comet, Switzerland) for removal of all enamel and so that a dentin surface about 4 mm in diameter would be obtained just below the dentin-enamel junction. The dentin surface was inspected with a stereomicroscope (magnification 10 x) so that the presence of enamel areas or fractures could be evaluated. All traces of enamel were removed from the bonding area. This dentin was defined as superficial dentin. Some specimens were re-used for preparation of deep dentin samples by the sinking of 2-mm-deep guide holes and reduction of dentin until the holes disappeared. This was defined as deep dentin, which was
between 0.5 and 0.9 mm from the pulp chamber. SALINE I
Adhesive Materia/s.-The bonding systems were then applied according to manufacturers' directions (Tables t, 2). Clearfil Photo-Bond: Phosphoric acid gel (3M, St. Louis, MO) was applied to the dentin surface for 30 s and then washed and dried with oilfree compressed air. Clearfil PhotoBond was then mixed according to instructions, applied with a small brush to the dentin, and photo-cured for 20 s with a light-curing unit (Visilux II, 3M Co., St. Louis, MO). Resin composite (Clearfil Ray Post, Kuraray) was then placed in a cylindrical Teflon tube (4 mm height, 4 mm internal diameter), then applied to the dentin surface and photo-cured. No composite increments were made. GC lining cement: Polyacrylic acid gel (10%) was applied for 10 s, washed, and air-dried. After 30 s, the powder and liquid phases were mixed according to manufacturer's directions and placed in cylindrical samples, which were then applied to the dentin surface. The specimens were stored for 24 h in 100% humidity at 25°C prior to being tested. Gluma Bond primer/Scotchbond DC: The dentin surface was treated with EDTA pH 7.4 (Gluma cleanser, Bayer, Germany) for 60 s with a small brush, washed with water, and dried with oil-free compressed air. A layer of Gluma primer was then applied to the dentin, brushed for 60 s, gently air-dried so that a reflective, dry surface would be obtained, and then coated with a layer of Scotchbond DC (3M, St. Louis, MO) and photo-cured for 20 s. A resin composite (Silux, 3M) was inserted into cylindrical tubes, placed on the dentin surface, and photo-cured. MBL (Metafil Bonding Liner, a 4META-containing bonding agent, Sun Medical, Kyoto, Japan): Dentin surfaces were treated with 10-3 solution (10% citric acid, 3% ferric chloride) for 30 s, washed with water for 10 s, and dried with oil-free compressed air. Primer solution was then applied on the dentin for 30 s and gently blown dry. Bonding agents (solution C and Catalyst) were mixed according to manufacturer's directions and applied to the dentin with
4mm Sample I I CYLINDRICAL ~
COMPOSITE""~~ \\\\~////// ~
36 cm
Plastic Tube Connected to Pressure Bottle
RESIN
I
• !
PLEXIGLAS
Fig. Schematicof the toothpreparationand apparatususedfor applicationof hydrostaticpressure. a small brush. The cylinder filled with resin composite (Silux, 3M) was then applied to the treated dentin surface and light-cured as previously described. Scotchbond 2: Scotchprep primer was applied to the dentin surface, continuously agitated with a small brush for 60 s, and gently dried with oil-free compressed air for 10 s so that a reflective surface would be obtained. Scotchbond 2 resin was then applied and photo-cured for 30 s. Finally, Silux resin composite was applied as previously described. Vitrabond: The powder and liquid were mixed according to manufacturer's directions, placed in the Teflon tube, and then applied to the dentin. The material was then photocured for 60 s. No pre-treatment of the dentin surface was made. Zionomer: Zionomer conditioner was applied and gently agitated with a small brush on the dentin for 30 s, washed with water, and dried with oil-free compressed air. Zionomer powder and liquid were mixed according to manufacturer's directions and applied in cylindrical tubes to the dentin surface. The material was photo-cured for 60 s.
Testing.- After five min or 24 h of storage in 100% humidity at room temperature, the samples were disconnected from the h y d r o s t a t i c pressure apparatus and the shear bond strengths tested in a universal testing machine. The samples were loaded with a stainless-steel loop placed around the base of the cylinder with a cross-head speed of 0.5 cm/min. After the bond strength test, both sides of the samples were inspected under an optical stereomicroscope so
that the type of failure (cohesive, adhesive, or both) could be evaluated.
Statistical Ana/ysis.-The means and variances of bond strength were ranked by Duncan's multiple range test set at p < 0.05. Comparisons between bond strength samples with or without pulpal pressure or between five min and 24 h of storage were done by Student's t test. RESULTS The effects of the presence or absence of pulpal pressure on the early (five-minute) and 24-hour shear bond strengths of several glass-ionomer cements (GIC) and dentin bonding agents (DBA) made to superficial dentin are shown in Table 3. The materials are listed in order of increasing bond strength. There was no effect of pulpal pressure on GC lining cement after 24 h of storage, although the bond strengths of this true GIC were rather low. The shear bond strength of Z i o n o m e r - a new hybrid, light-cured " G I C " - w a s statistically significantly higher than that of GC lining cement, both at five min and 24 h. However, unlike the true GIC, Zionomer shear bond strengths were lower in the presence of a pulpal pressure at five min (p < 0.02). Vitrabond, another lightactivated GIC hybrid, produced shear bond strengths that were not statistically different from those of Zionomer, but which were unaffected by placement or storage under a positive pulpal pressure. There was no significant difference between the five-minute and the 24-hour shear bond strengths of Vitrabond. The combined use of Gluma dentin conditioner/primer and Scotchbond DC/Silux gave 24-hour shear bond
Dental Materials/January 1991
55
TABLE 1
MATERIALS TESTED Material
Manufacturer
GC lining cement
G-C Dental Industrial Corporation, Tokyo, Japan DenMat, Santa Maria, CA Bayer Dental, Germany 3M Dental Products Company, St. Paul, MN 3M Dental Products Company, St. Paul, MN 3M Dental Products Company, St. Paul, MN 3M Dental Products Company, St. Paul, MN Kuraray, Osaka, Japan Kuraray, Osaka, Japan Sun Medical Company, Kyoto, Japan
Zionomer Gluma Scotchbond DO Scotchbond 2 Silux Plus Vitrabond Clearfil Photo Bond Clearfil Ray Post MBL (Metafil Bonding Liner)
TABLE 2
COMBINATION OF DENTIN TREATMENTS, BONDING SYSTEMS, AND RESINS Dentin Treatment
Primer
Phosphoric acid EDTA Polyacrylic acid 10-3 solution -
Gluma bond MBL primer Scotchprep -
-
Zionomer conditioner
Bonding System
Resin Composite
Clearfil Photo Bond Scotchbond DO GC lining cement MBL bond Scotchbond 2 Vitrabond Zionomer
Clearfil Ray Post Silux Silux Silux -
TABLE 3
SHEAR BOND STRENGTH AT DENTIN-ENAMEL JUNCTION Shear Bond Strength (MPa), ~ ± S.D. (N) Material GC lining Zionomer Gluma/Scotchbond Vitrabond Clearfil PB Scotchbond 2 MBL
Storage Time
No Pulpal Pressure
Sig.
Pulpal Pressure
24 h 5 m]n 24 h 5 min 24 h 5 mJn 24 h 5 mln 24 h 5 m~n 24 h 5 mln 24 h
3.2 _ 0.6 (7) 5.2 __ 1.5 (9) 7.2 __ 3.3 (9)
NS p
1Department of Conservative Dentistry School of Dentistry University of Bologna Bologna, Italy 2Department of Oral Biology School of Dentistry Medical College of Georgia Augusta, Georgia 30912-1129 Received February 12, 1990 Accepted September 5, 1990 This investigation was supported, in part, by grant DE 06427 from the National Institute of Dental Research to David H. Pashley.
Dent Mater 7:54-58, January, 1991 Abstract-The purpose of this study was to evaluate the effect of intra-pulpal pressure on shear bond strength of three light-cured glass-ionomer cements (GC lining cement, Vitrabond, and Zionomer) and four dentin bonding agents [Gluma/ Scotchbond, Scotchbond 2, MBL, and Clearfil Photo Bond]. Buccal dentin surfaces were prepared just below the DEJ by means of a diamond bur. Dentin treatments were made for Zionomer (Zionomer conditioner), Scotchbond 2 (Scotchprep), MBL (10-3 solution), Clearfil PB (H3P04), GC lining cement (Polyacrylic acid), and Gluma]Scotchbond (EDTA). Resin composites were inserted into tubes, positioned on dentin, cured, tested after five rain or 24 h, and compared with samples bonded and stored under an intra-pulpal pressure of 36 cm of saline. After 24 h in superficial dentin, intrapulpal pressure reduced the bond strength only in MBL, Scotchbond 2, and Zionomer. Clearfil PB bond strength was increased, while Vitrabond, GC lining cement, and Gluma/Scotchbond were unaffected by the presence of pulpal pressure. However, in deep dentin, Scotchbond 2 and Clearfil PB shear bond strengths were significantly reduced by storage in the presence of 36-cm H20 pulpal pressure. Only Vitrabond remained unaffected by pulpal pressure in deep dentin.
umerous studies have evaluated the adhesion of dentin bonding agents (DBA) with flattened and dried extracted teeth used without the presence of pulpal fluid and hydrostatic pressure (Causton, 1984; Komatsu and Finger, 1986; Retief et al., 1988). Depth of dentin (Suzuki and Finger, 1988; Tagami eta/,, 1990) and storage time of bond samples (Retief et aL, 1988) seem to be the most important variables in bond strength tests. However, the presence of pulpal fluid under pressure in vital dentin suggests that this additional variable may influence dentin bonding, and that this variable should be evaluated in vitro so that its possible influence on the bonding of glass-ionomer cements (GIC) and DBA can be determined. Recent in vitro studies suggested that the presence of fluid inside dentinal tubules with or without hydrostatic pressure may reduce bond strength with respect to tests performed without palpal fluid (Mitchem et al., 1988; Andreaus et al., 1989; Tao and Pashley, 1989). These studies concluded that pulpal pressure can play an important role in reducing the adhesion of bonding systems that require smear-layer removal. Since these early studies were done with older GIC and DBA, it is important for the effects of pulpal pressure on the bond strengths of the newest generation of these materials to be evaluated in both superficial and deep dentin and at various storage times. The aim of this study was to evaluate the effect of intrapulpal pressure on four DBA and three GIC and to clarify the importance of dentin thickness and storage time on the shear bond strength of these materials to human dentin.
N
MATERIALS AND METHODS Tooth Preparation.-Erupted human third molars were extracted from
54 PRATI et al./EFFECTS OF PULPAL PRESSURE ON ADHESIVE BONDING
young patients (ages 20-35 yr), then were stored for no more than 24 h at room temperature in saline solution, and their crowns were divided from the roots by means of a high-speed diamond bur, 1 mm apical to the cementum-enamel junction. A second section parallel to the long axis of the tooth divided the crown into two equal halves. The pulp tissue was removed by use of a stainless-steel hand instrument. The cut dentin was etched with 37% orthophosphoric acid (3M Co., St. Louis, MO, USA) for 10 s for removal of debris, then washed and dried. An adaptable plastic tube (Saniplast SPA, Italy) was positioned on the cut dentin surface with L o c t i t e s e a l a n t ( H e n k e l , Germany). Teeth were then mounted with self-curing acrylic resin (Palavit 55, Kulzer, Germany) in stainless-steel molds (Fig.). After 15 min, saline solution was injected into the plastic tube. The tube was then connected with a saline column used to apply a positive hydrostatic pressure of 36-cm H~O to superficial or deep dentin as a simulation of pulpal pressure (Fig.). The buccal surface of each half of the crown was ground with a highspeed, water-cooled medium diamond bur (Comet, Switzerland) for removal of all enamel and so that a dentin surface about 4 mm in diameter would be obtained just below the dentin-enamel junction. The dentin surface was inspected with a stereomicroscope (magnification 10 x) so that the presence of enamel areas or fractures could be evaluated. All traces of enamel were removed from the bonding area. This dentin was defined as superficial dentin. Some specimens were re-used for preparation of deep dentin samples by the sinking of 2-mm-deep guide holes and reduction of dentin until the holes disappeared. This was defined as deep dentin, which was
between 0.5 and 0.9 mm from the pulp chamber. SALINE I
Adhesive Materia/s.-The bonding systems were then applied according to manufacturers' directions (Tables t, 2). Clearfil Photo-Bond: Phosphoric acid gel (3M, St. Louis, MO) was applied to the dentin surface for 30 s and then washed and dried with oilfree compressed air. Clearfil PhotoBond was then mixed according to instructions, applied with a small brush to the dentin, and photo-cured for 20 s with a light-curing unit (Visilux II, 3M Co., St. Louis, MO). Resin composite (Clearfil Ray Post, Kuraray) was then placed in a cylindrical Teflon tube (4 mm height, 4 mm internal diameter), then applied to the dentin surface and photo-cured. No composite increments were made. GC lining cement: Polyacrylic acid gel (10%) was applied for 10 s, washed, and air-dried. After 30 s, the powder and liquid phases were mixed according to manufacturer's directions and placed in cylindrical samples, which were then applied to the dentin surface. The specimens were stored for 24 h in 100% humidity at 25°C prior to being tested. Gluma Bond primer/Scotchbond DC: The dentin surface was treated with EDTA pH 7.4 (Gluma cleanser, Bayer, Germany) for 60 s with a small brush, washed with water, and dried with oil-free compressed air. A layer of Gluma primer was then applied to the dentin, brushed for 60 s, gently air-dried so that a reflective, dry surface would be obtained, and then coated with a layer of Scotchbond DC (3M, St. Louis, MO) and photo-cured for 20 s. A resin composite (Silux, 3M) was inserted into cylindrical tubes, placed on the dentin surface, and photo-cured. MBL (Metafil Bonding Liner, a 4META-containing bonding agent, Sun Medical, Kyoto, Japan): Dentin surfaces were treated with 10-3 solution (10% citric acid, 3% ferric chloride) for 30 s, washed with water for 10 s, and dried with oil-free compressed air. Primer solution was then applied on the dentin for 30 s and gently blown dry. Bonding agents (solution C and Catalyst) were mixed according to manufacturer's directions and applied to the dentin with
4mm Sample I I CYLINDRICAL ~
COMPOSITE""~~ \\\\~////// ~
36 cm
Plastic Tube Connected to Pressure Bottle
RESIN
I
• !
PLEXIGLAS
Fig. Schematicof the toothpreparationand apparatususedfor applicationof hydrostaticpressure. a small brush. The cylinder filled with resin composite (Silux, 3M) was then applied to the treated dentin surface and light-cured as previously described. Scotchbond 2: Scotchprep primer was applied to the dentin surface, continuously agitated with a small brush for 60 s, and gently dried with oil-free compressed air for 10 s so that a reflective surface would be obtained. Scotchbond 2 resin was then applied and photo-cured for 30 s. Finally, Silux resin composite was applied as previously described. Vitrabond: The powder and liquid were mixed according to manufacturer's directions, placed in the Teflon tube, and then applied to the dentin. The material was then photocured for 60 s. No pre-treatment of the dentin surface was made. Zionomer: Zionomer conditioner was applied and gently agitated with a small brush on the dentin for 30 s, washed with water, and dried with oil-free compressed air. Zionomer powder and liquid were mixed according to manufacturer's directions and applied in cylindrical tubes to the dentin surface. The material was photo-cured for 60 s.
Testing.- After five min or 24 h of storage in 100% humidity at room temperature, the samples were disconnected from the h y d r o s t a t i c pressure apparatus and the shear bond strengths tested in a universal testing machine. The samples were loaded with a stainless-steel loop placed around the base of the cylinder with a cross-head speed of 0.5 cm/min. After the bond strength test, both sides of the samples were inspected under an optical stereomicroscope so
that the type of failure (cohesive, adhesive, or both) could be evaluated.
Statistical Ana/ysis.-The means and variances of bond strength were ranked by Duncan's multiple range test set at p < 0.05. Comparisons between bond strength samples with or without pulpal pressure or between five min and 24 h of storage were done by Student's t test. RESULTS The effects of the presence or absence of pulpal pressure on the early (five-minute) and 24-hour shear bond strengths of several glass-ionomer cements (GIC) and dentin bonding agents (DBA) made to superficial dentin are shown in Table 3. The materials are listed in order of increasing bond strength. There was no effect of pulpal pressure on GC lining cement after 24 h of storage, although the bond strengths of this true GIC were rather low. The shear bond strength of Z i o n o m e r - a new hybrid, light-cured " G I C " - w a s statistically significantly higher than that of GC lining cement, both at five min and 24 h. However, unlike the true GIC, Zionomer shear bond strengths were lower in the presence of a pulpal pressure at five min (p < 0.02). Vitrabond, another lightactivated GIC hybrid, produced shear bond strengths that were not statistically different from those of Zionomer, but which were unaffected by placement or storage under a positive pulpal pressure. There was no significant difference between the five-minute and the 24-hour shear bond strengths of Vitrabond. The combined use of Gluma dentin conditioner/primer and Scotchbond DC/Silux gave 24-hour shear bond
Dental Materials/January 1991
55
TABLE 1
MATERIALS TESTED Material
Manufacturer
GC lining cement
G-C Dental Industrial Corporation, Tokyo, Japan DenMat, Santa Maria, CA Bayer Dental, Germany 3M Dental Products Company, St. Paul, MN 3M Dental Products Company, St. Paul, MN 3M Dental Products Company, St. Paul, MN 3M Dental Products Company, St. Paul, MN Kuraray, Osaka, Japan Kuraray, Osaka, Japan Sun Medical Company, Kyoto, Japan
Zionomer Gluma Scotchbond DO Scotchbond 2 Silux Plus Vitrabond Clearfil Photo Bond Clearfil Ray Post MBL (Metafil Bonding Liner)
TABLE 2
COMBINATION OF DENTIN TREATMENTS, BONDING SYSTEMS, AND RESINS Dentin Treatment
Primer
Phosphoric acid EDTA Polyacrylic acid 10-3 solution -
Gluma bond MBL primer Scotchprep -
-
Zionomer conditioner
Bonding System
Resin Composite
Clearfil Photo Bond Scotchbond DO GC lining cement MBL bond Scotchbond 2 Vitrabond Zionomer
Clearfil Ray Post Silux Silux Silux -
TABLE 3
SHEAR BOND STRENGTH AT DENTIN-ENAMEL JUNCTION Shear Bond Strength (MPa), ~ ± S.D. (N) Material GC lining Zionomer Gluma/Scotchbond Vitrabond Clearfil PB Scotchbond 2 MBL
Storage Time
No Pulpal Pressure
Sig.
Pulpal Pressure
24 h 5 m]n 24 h 5 min 24 h 5 mJn 24 h 5 mln 24 h 5 m~n 24 h 5 mln 24 h
3.2 _ 0.6 (7) 5.2 __ 1.5 (9) 7.2 __ 3.3 (9)
NS p
