Dent Mater8:21-26,January1992
Effects of dentin surface treatments on the shear bond strength of Vitrabond C. Prati ~, G. MontanarP, G. Biagini 2, F. Fava 3, D.H. Pashley 4 IDepartment of Conservative Dentistry, School of Dentistry, Medical College of GeorgiaAugusta GA, USA 2Department of Chemical and Material Sciences, University of Bologna, Bologna, Italy 3Department of Anatomy, University of Ancona, Ancona, Italy 4Department of Oral Biology, School of Dentistry, Medical College of Georgia, Augusta, GA
Abstract. The influences of nine dentin surface treatments were evaluated on the shear bond strength of a new light-cured glassionomer cement (GIC) and on the SEM morphology of the treated dentin surfaces. The following treatments were performed: saline solution (control), NaOCI, acidic glycine, EDTA, malic acid, malic acid plus glycine, polyacrylic acid, tannic acid, and neutral + acidic oxalate solutions. Buccal dentin surfaces were polished with #320grit abrasive paper, treated with one of the chemicals, washed, and air-dried. Cylindrical GIC samples were then applied to the dentin surface, stored in 100% humidity, and tested after 24 h. SEM observations demonstrated no effect of saline or NaOCI treatment on the smear layer but its complete removal with exposure of collagen fibrils after malic or malic acid plus glycine treatment. Partial removal of the smear layer occurred following glycine treatment and with tannic or polyacrylic acids. Complete removal of the smear layer was seen after EDTA or pyruvic acid treatment. Oxalate treatment produced a layer of crystals, which completely covered the dentin surface. Shear bond strength of GIC was significantlyincreased only by treatment with the oxalate solutions. Cut dentin surfaces are covered with a thin layer of grinding debris called the smear layer (Eick et al., 1970; Pashley, 1984). Most dental materials are placed directly onto the smear layer, since it cannot easily be removed by being rinsed or scrubbed with water. The forces responsible for the internal adhesion of superficial smear layer particles to each other and to the underlying dentin matrix are unknown but have been estimated to be 5-6 MPa in magnitude (Tao and Pashley, 1988). Many materials bonded to smear layers have a functional strength that is limited by the intrinsic weakness ofthe smearlayer. Someinvestigators (Welsh and Hembree, 1985; McLean et al., 1985; Merlo et al., 1987; Mathis et al., 1988; Prati et al., 1989) have advocated either removal of the smear layers or their modification prior to the placement of glass-ionomer cements (GIC). Powis et al. (1982) reported that the bond strengths of GIC to dentin could be significantly improved by pre-treatment of the smear layers with acids, chelators, or ferric chloride. The strength of the dentin/GIC bonds in the study by Powis et al. (1982) was limited to 7 MPa by the cohesive strength of the ASPA cement that they used. They suggested that such studies be repeated when new materials were developed that had higher cohesive strengths that would permit true testing of dentin/GIC bond strengths. The newest generation of glass-ionomer-like materials such as Vitrabond (3M Dental Products, St. Paul, MN) has higher cohesive strengths (ca. 10-12 MPa) and chemistry somewhat
different from that of previously marketed GICs. The purpose of this study was to compare the effects of nine different dentin treatments on the SEM appearance and bond strength of Vitrabond to human dentin in vitro in an attempt to discover which pre-treatments produced the highest dentin/Vitrabond shear bond strengths.
MATERIALSAND METHODS The chemical compositions of the dentin treatment solutions, their concentrations, pH, and times of application are listed in Table 1. Shear Bond Test Procedure.--The human third molars extracted from young patients (ages, from 20 to 31 yr) used in the study were stored in isotonic saline solution at room temperature for no more than one month. The teeth were examined under a dissecting microscope to make certain that they were free of cracks, defects, and caries. The teeth were mounted with self-curing acrylic resin (Palavit 55, Kulzer, Germany) in uniform molds. Buccal surfaces were ground flat with a water-cooled high-speed diamond bur #206 (Intensive, Switzerland) and then polished with abrasive discs (Sof-Lex, 3M Dental Products, St. Paul, MN) just below the dentin-enamel junction (i.e., into superficial dentin). Each treatment solution was placed on the dentin surface and actively agitated by means of a small brush, for the time indicated in Table 1, washed with water for 10 s, and dried with compressed oil-free air for 10 s. No samples were usedmore than once. No samples received more than one surface treatment. Vitrabond, a light-cured glassionomer cement, was prepared as suggested by the manufacturer's directions and applied in cylindrical Teflon tubes (4.0 mm in diameter and 4.0 mm in height) and then positioned on the dentin surface and photocured with a light-curing unit (Visilux II, 3M) for 120 s. The light-curing unit was positioned around the specimens with an inclination of from 25 to 30 degrees. The cylinder was not removed during storage or bond- strength testing. No bonding was observed between material and cylindrical tube. Some samples were tested after five min so that the early bond strength could be determined. The rest of the samples were stored at 37°C in a container which produced 100% humidity for 24 h prior to being tested. Samples were mounted in a universal testing machine, and the cylinders were subjected to shear stress at their bases with a 0.5-mm-diameter stainless steel loop at the level of the dentin surface (Fig. 1) at a cross-head speed of 0.5 cm/min.
Dental Materials~January 1992 21
TABLE 1: DENTINTREATMENTSUSED IN THE STUDY Materials
pH
Saline Solution
Application T i m e
Manufacturer
7.4
2 min
Baxter Co., Trieste, Italy
10.1
1 min
Ogna, Milan, Italy
Pyruvic Acid 10% w/w
1.0
1 min
Sigma, St. Louis, MO
Polyacrylic Acid Gel, 10%
2.6
Malic Acid 10% w/w + Glycine 10% w/w
1.0
1 min
Sigma, St. Louis, MO
Glycine, 10% w/w
3.9
1 min
Sigma, St. Louis, MO
Malic Acid 10% w/w
2.0
1 min
Sigma, St. Louis, MO
Tannic Acid 25% w/w
3.9
1 min
Carlo Erba, Milan, Italy
EDTA Dipotassium Oxalate, 30% Monopotassium-mono-hydrogen oxalate, 3% "
7.4 9.0
1 min 2 min
Bayer GmbH, Leverkusen, Germany OP Lab., Augusta, GA, DDS#1
1.9
2 min
OP Lab., Augusta, GA, DDS#2
Sodium Hypochlorite 3%
TABLE 2: SHEAR BOND STRENGTH(MPa) OF VlTRABOND AFTER DENTIN TREATMENTS Dentin Treatment
5 min
ttest
24 hr
Sodium Hypochlorite
2.96 +0.8 (6)
Pyruvic Acid
4.18 + 1.4 (7)
Polyacrylic
4.40 +1.7 (9)
Saline (control)
4.36 + 1.7(10)
NS
5.94 +2.6(10)
Malic Acid + Glycine
6.71 +2.4(12)
Glycine
6.94 +1.7 (8)
Malic Acid
7.12 +3.5 (7)
Tannic Acid EDTA
6.21 + 1.41(6)
NS
8.02 +2.6 (9) 8.46 +3.1 (9)
Oxalate Solutions 7.11 +0.13(6) p
Effects of dentin surface treatments on the shear bond strength of Vitrabond C. Prati ~, G. MontanarP, G. Biagini 2, F. Fava 3, D.H. Pashley 4 IDepartment of Conservative Dentistry, School of Dentistry, Medical College of GeorgiaAugusta GA, USA 2Department of Chemical and Material Sciences, University of Bologna, Bologna, Italy 3Department of Anatomy, University of Ancona, Ancona, Italy 4Department of Oral Biology, School of Dentistry, Medical College of Georgia, Augusta, GA
Abstract. The influences of nine dentin surface treatments were evaluated on the shear bond strength of a new light-cured glassionomer cement (GIC) and on the SEM morphology of the treated dentin surfaces. The following treatments were performed: saline solution (control), NaOCI, acidic glycine, EDTA, malic acid, malic acid plus glycine, polyacrylic acid, tannic acid, and neutral + acidic oxalate solutions. Buccal dentin surfaces were polished with #320grit abrasive paper, treated with one of the chemicals, washed, and air-dried. Cylindrical GIC samples were then applied to the dentin surface, stored in 100% humidity, and tested after 24 h. SEM observations demonstrated no effect of saline or NaOCI treatment on the smear layer but its complete removal with exposure of collagen fibrils after malic or malic acid plus glycine treatment. Partial removal of the smear layer occurred following glycine treatment and with tannic or polyacrylic acids. Complete removal of the smear layer was seen after EDTA or pyruvic acid treatment. Oxalate treatment produced a layer of crystals, which completely covered the dentin surface. Shear bond strength of GIC was significantlyincreased only by treatment with the oxalate solutions. Cut dentin surfaces are covered with a thin layer of grinding debris called the smear layer (Eick et al., 1970; Pashley, 1984). Most dental materials are placed directly onto the smear layer, since it cannot easily be removed by being rinsed or scrubbed with water. The forces responsible for the internal adhesion of superficial smear layer particles to each other and to the underlying dentin matrix are unknown but have been estimated to be 5-6 MPa in magnitude (Tao and Pashley, 1988). Many materials bonded to smear layers have a functional strength that is limited by the intrinsic weakness ofthe smearlayer. Someinvestigators (Welsh and Hembree, 1985; McLean et al., 1985; Merlo et al., 1987; Mathis et al., 1988; Prati et al., 1989) have advocated either removal of the smear layers or their modification prior to the placement of glass-ionomer cements (GIC). Powis et al. (1982) reported that the bond strengths of GIC to dentin could be significantly improved by pre-treatment of the smear layers with acids, chelators, or ferric chloride. The strength of the dentin/GIC bonds in the study by Powis et al. (1982) was limited to 7 MPa by the cohesive strength of the ASPA cement that they used. They suggested that such studies be repeated when new materials were developed that had higher cohesive strengths that would permit true testing of dentin/GIC bond strengths. The newest generation of glass-ionomer-like materials such as Vitrabond (3M Dental Products, St. Paul, MN) has higher cohesive strengths (ca. 10-12 MPa) and chemistry somewhat
different from that of previously marketed GICs. The purpose of this study was to compare the effects of nine different dentin treatments on the SEM appearance and bond strength of Vitrabond to human dentin in vitro in an attempt to discover which pre-treatments produced the highest dentin/Vitrabond shear bond strengths.
MATERIALSAND METHODS The chemical compositions of the dentin treatment solutions, their concentrations, pH, and times of application are listed in Table 1. Shear Bond Test Procedure.--The human third molars extracted from young patients (ages, from 20 to 31 yr) used in the study were stored in isotonic saline solution at room temperature for no more than one month. The teeth were examined under a dissecting microscope to make certain that they were free of cracks, defects, and caries. The teeth were mounted with self-curing acrylic resin (Palavit 55, Kulzer, Germany) in uniform molds. Buccal surfaces were ground flat with a water-cooled high-speed diamond bur #206 (Intensive, Switzerland) and then polished with abrasive discs (Sof-Lex, 3M Dental Products, St. Paul, MN) just below the dentin-enamel junction (i.e., into superficial dentin). Each treatment solution was placed on the dentin surface and actively agitated by means of a small brush, for the time indicated in Table 1, washed with water for 10 s, and dried with compressed oil-free air for 10 s. No samples were usedmore than once. No samples received more than one surface treatment. Vitrabond, a light-cured glassionomer cement, was prepared as suggested by the manufacturer's directions and applied in cylindrical Teflon tubes (4.0 mm in diameter and 4.0 mm in height) and then positioned on the dentin surface and photocured with a light-curing unit (Visilux II, 3M) for 120 s. The light-curing unit was positioned around the specimens with an inclination of from 25 to 30 degrees. The cylinder was not removed during storage or bond- strength testing. No bonding was observed between material and cylindrical tube. Some samples were tested after five min so that the early bond strength could be determined. The rest of the samples were stored at 37°C in a container which produced 100% humidity for 24 h prior to being tested. Samples were mounted in a universal testing machine, and the cylinders were subjected to shear stress at their bases with a 0.5-mm-diameter stainless steel loop at the level of the dentin surface (Fig. 1) at a cross-head speed of 0.5 cm/min.
Dental Materials~January 1992 21
TABLE 1: DENTINTREATMENTSUSED IN THE STUDY Materials
pH
Saline Solution
Application T i m e
Manufacturer
7.4
2 min
Baxter Co., Trieste, Italy
10.1
1 min
Ogna, Milan, Italy
Pyruvic Acid 10% w/w
1.0
1 min
Sigma, St. Louis, MO
Polyacrylic Acid Gel, 10%
2.6
Malic Acid 10% w/w + Glycine 10% w/w
1.0
1 min
Sigma, St. Louis, MO
Glycine, 10% w/w
3.9
1 min
Sigma, St. Louis, MO
Malic Acid 10% w/w
2.0
1 min
Sigma, St. Louis, MO
Tannic Acid 25% w/w
3.9
1 min
Carlo Erba, Milan, Italy
EDTA Dipotassium Oxalate, 30% Monopotassium-mono-hydrogen oxalate, 3% "
7.4 9.0
1 min 2 min
Bayer GmbH, Leverkusen, Germany OP Lab., Augusta, GA, DDS#1
1.9
2 min
OP Lab., Augusta, GA, DDS#2
Sodium Hypochlorite 3%
TABLE 2: SHEAR BOND STRENGTH(MPa) OF VlTRABOND AFTER DENTIN TREATMENTS Dentin Treatment
5 min
ttest
24 hr
Sodium Hypochlorite
2.96 +0.8 (6)
Pyruvic Acid
4.18 + 1.4 (7)
Polyacrylic
4.40 +1.7 (9)
Saline (control)
4.36 + 1.7(10)
NS
5.94 +2.6(10)
Malic Acid + Glycine
6.71 +2.4(12)
Glycine
6.94 +1.7 (8)
Malic Acid
7.12 +3.5 (7)
Tannic Acid EDTA
6.21 + 1.41(6)
NS
8.02 +2.6 (9) 8.46 +3.1 (9)
Oxalate Solutions 7.11 +0.13(6) p
