Dent Mater 8:296-298, September, 1992
A new light-activated adhesive cavity liner: an in vitro bond strength and microleakage study M. Tsunekawa, 1'3Y. Usami, 2 M. Iwaku, 2 J.C. Setcos, ~ S.J. Marshall x
1Departmentof Restorative Dentistry, School of Dentistry, Unwers~tyof California, San Francisco, CA, USA 2Department of Operative Dentistry and Endodontics, School of Dentistry, Nugata University, Niigata, Japan 3Nowat Nippon Shika Yakuhzn Co. Ltd, Shimonoseki, Japan
Abstract. A new formulation of a light-activated calcium hydroxidebased cavity liner was developed for this study. Its shear bond strength and marginal microleakage in a Class V cavity preparation were compared to those of commercially available lightactivated liners and conventional glass ionomer liners: GC Lining Cement (GC), Ketac-Bond (ESPE), Time Line (Caulk), Vitrabond (3M), XR Ionomer (Kerr), and Zlonomer (DenMat). The new formulation had significantly higher shear bond strength to dentin than the commercially available materials. Its microleakage along gingival (cemento-dentin) walls was statistically equivalent to one of the other materials and significantly better than all the others.
INTRODUCTION Prevention ofmicroleakage around restorations has long been a goal of dentistry. Microleakage has been associated with probable bacterial contamination (Br/~nnstrom, 1984; 1987), leading to pulpal sensitivity and possible secondary caries (Bullard et al., 1988). There are various dentin adhesive systems commercially available that claim to mediate a bond between composite and dentin. However, the bonding of resin to dentin has not been as successful as to acid-etched enamel. So for those situations when the seal is not perfect, there needs to be some mechanism to help control possible damage caused to sensitive tissues by bacterial activity. Some promise has been suggested by antibacterial properties of products with an initial high pH, such as calcium hydroxide. Some of these characteristics need to be further tested. Calcium hydroxide has been widely used as the basis of many cavity liners for at least the past four decades. The presence of calcium hydroxide stimulates the formation of reparative dentin at the base of deep tooth cavities, thus aiding the natural healing process. Calcium hydroxide-based liners are intended to serve as a protective barrier for pulpal tissue against any leachable constituent of dental filling materials. However, calcium hydroxide liners have problems of dissolution and leakage (Derand, 1990). Currently there is a trend to substitute glass ionomer cements for calcium hydroxide liners. Aglass ionomer is less soluble than calcium hydroxide and has the beneficial effects of fluoride ion release. Thus, calcium hydroxide is used only in areas of deep excavation and small "pin-point" exposures. The purpose of this study was to develop an effective 296 Tsunekawa et al /New adhesive cavity hner
formulation of a light-activated calcium hydroxide-based cavity liner for adhesion to dentin and to evaluate its bond strength and effectivenessin reducing marginal microleakage in Class V cavities. For comparison, two conventional and four light-activated liners were chosen.
MATERIALSAND METHODS The raw materials and the formulation of a new light-activated fluoride-releasing filling material are shown in Table 1. The light-activated filling material developed in this study was identified as Mas #7. Calcium hydroxide was silanated in a tumble mixer by charging 100 parts by weight of calcium hydroxide powder with 4 parts by weight of r-methacryloxypropyltrimethoxy silane in 200 parts by weight of ethanol solution. The tumbling was continued for 2 h. Ethanol was evaporated and air-dried at room temperature, and then at 60°C overnight. The powder was heated to 115°C for 2.5 h. After crushing and sieving, microcapsuled calcium hydroxide was obtained and formulated into the powder of the experimental material (Table 1). The powder/liquid mixing ratio was 1.00/0.88 by weight. Four commercially available light-activated liners and two conventional glass ionomer liners were used for comparison as shown in Table 2: Time Line, Vitrabond, XR Ionomer, Zionomer, GC Lining Cement, and Ketac Bond. Shear bond strength test. Seventy extracted human molars which had been stored in a 1% chloramine solution at room temperature were used as test specimens. These specimens were embedded with fast-curing acrylic resin (Sample-Kwick, Buehler, Lake Bluff, IL, USA) in a cylindrical plastic mold (h=30 mm, d=15 mm). The occlusal one-third of the tooth crown was removed with a low speed saw (Isomet, Buehler, Lake Bluff, IL, USA). The exposed occlusal part of the dentin surface ofthe test specimens was ground wet on 800 grit silicon carbide paper on a polishing machine (DAP-V, Struers, Copenhagen, Denmark). The embedded teeth were washed in running fluoride-free water and dried with an oil-free air syringe. Each of the light-activated liners was applied to the dentin surfaces in accordance with its manufacturer's instructions. Smear layers were left intact except for Zionomer, GC Lining Cement, and Ketac-Bond. Zionomer's dentin conditioner and Ketac-Conditioner (ESPE) had been applied for
TABLE 2: LINERSUSED FOR COMPARISON
TABLE 1: FORMULATIONOF NEW LIGHT-ACTIVATEDFLUORIDE
RELEASING LINER MATERIAL Raw Materials Manufacturer BatchNumber Parts(w/w)
L,ner
Manufacturer
Batch Number
T,me Line
L D. Caulk, M,Iford, DE, USA
Paste 092388
Vttrabond
3M Dental Products, Mnneapohs,MN, USA
Powder' 6w2 Liquid. 8yl
XR Ionomer
Kerr Manufactur,ng Co, Romulus,MI, USA
Powder91017 Liquid' 8434
Ztonomer
DenMat Corporation, Santa Maria,CA, USA
Conditioner 291017 Powder498005 L~qu~d499002
GC Lin,ngCement
GC Co, Tokyo, Japan
Powder 120661 LJquld 300561
Ketac-BondApphcap
ESPE 0001 Seefeld/Oberbay,Germany
POWDER Strontiumalumtnofluoro s,hcateglass
SanklnKogyoK.K, Tokyo, Japan
K-92
90
P-Toluenesulfintcacrd salt. d,hydrate
J T Baker Chemical Co, Ph,lhpsberg,NJ, USA
013357
4
Sankln KogyoK K,
09112
Methacryloxyethyl-p-(N,Nd,methyl)am,nobenzoate Calc,um hydroxide r-Methacryloxypropyl tnmethoxystlane
SpectrumChem,calCo, Gardena, CA, USA
EH227
Un,on CarbideCo, Danbury,CT, USA
UCC3163
3
10
LIQUID Tetra-methacryloxyethyl pyrophosphate
SanklnKogyoK K. Tokyo, Japan
SK-301
40
Methacryloxyethyl phosphate
KyoelshaO,I Chemical Co, Osaka, Japan
1070272
30
Ethoxylatedbts-phenolA dJmethacrylate
SartomerCo, Westchester, PA, USA
GUK 0220
30
Camphorqulnone
Eastman KodakCo. Rochester, NY, USA
807410A
0 26
10 s (Zionomer) and 30 s (conventional glass ionomer liners) to remove the smear layer prior to adhesion. The adhesion area was defined by using an adhesive water-repellant tape with a 3 mm diameter circular hole in its center. A cylindrical plastic tube (d=5 mm, h=2-3 ram) was placed over the 3 mm opening and fixed with dental wax. Each material was mixed according to the manufacturer's instructions. The lightactivated liner was placed onto the dentin surface to a thickness of 1-2 ram, then exposed for 20 s with a visible light unit (Optilux 400, Demetron Research Corp., Danbury, CT, USA). Composite (Silux, 3M) was then placed onto the liner surface and light-cured for 40 s. The test specimens were immersed m distilled water at 37°C. After 24 h, the test specimens were clamped horizontally into the shear adhesion apparatus and loaded with a knife edge parallel to the vertical plane of the material-dentin interface. Bond strengths were measured in an Instron universal testing machine (Model 1011, Instron Corp., Canton, MA, USA) at a cross-head speed of 1 mm/min. Ten specimens were tested for each variable. Results were compared using one-way ANOVA and Student-NewmanKeuls critical difference tests (p
A new light-activated adhesive cavity liner: an in vitro bond strength and microleakage study M. Tsunekawa, 1'3Y. Usami, 2 M. Iwaku, 2 J.C. Setcos, ~ S.J. Marshall x
1Departmentof Restorative Dentistry, School of Dentistry, Unwers~tyof California, San Francisco, CA, USA 2Department of Operative Dentistry and Endodontics, School of Dentistry, Nugata University, Niigata, Japan 3Nowat Nippon Shika Yakuhzn Co. Ltd, Shimonoseki, Japan
Abstract. A new formulation of a light-activated calcium hydroxidebased cavity liner was developed for this study. Its shear bond strength and marginal microleakage in a Class V cavity preparation were compared to those of commercially available lightactivated liners and conventional glass ionomer liners: GC Lining Cement (GC), Ketac-Bond (ESPE), Time Line (Caulk), Vitrabond (3M), XR Ionomer (Kerr), and Zlonomer (DenMat). The new formulation had significantly higher shear bond strength to dentin than the commercially available materials. Its microleakage along gingival (cemento-dentin) walls was statistically equivalent to one of the other materials and significantly better than all the others.
INTRODUCTION Prevention ofmicroleakage around restorations has long been a goal of dentistry. Microleakage has been associated with probable bacterial contamination (Br/~nnstrom, 1984; 1987), leading to pulpal sensitivity and possible secondary caries (Bullard et al., 1988). There are various dentin adhesive systems commercially available that claim to mediate a bond between composite and dentin. However, the bonding of resin to dentin has not been as successful as to acid-etched enamel. So for those situations when the seal is not perfect, there needs to be some mechanism to help control possible damage caused to sensitive tissues by bacterial activity. Some promise has been suggested by antibacterial properties of products with an initial high pH, such as calcium hydroxide. Some of these characteristics need to be further tested. Calcium hydroxide has been widely used as the basis of many cavity liners for at least the past four decades. The presence of calcium hydroxide stimulates the formation of reparative dentin at the base of deep tooth cavities, thus aiding the natural healing process. Calcium hydroxide-based liners are intended to serve as a protective barrier for pulpal tissue against any leachable constituent of dental filling materials. However, calcium hydroxide liners have problems of dissolution and leakage (Derand, 1990). Currently there is a trend to substitute glass ionomer cements for calcium hydroxide liners. Aglass ionomer is less soluble than calcium hydroxide and has the beneficial effects of fluoride ion release. Thus, calcium hydroxide is used only in areas of deep excavation and small "pin-point" exposures. The purpose of this study was to develop an effective 296 Tsunekawa et al /New adhesive cavity hner
formulation of a light-activated calcium hydroxide-based cavity liner for adhesion to dentin and to evaluate its bond strength and effectivenessin reducing marginal microleakage in Class V cavities. For comparison, two conventional and four light-activated liners were chosen.
MATERIALSAND METHODS The raw materials and the formulation of a new light-activated fluoride-releasing filling material are shown in Table 1. The light-activated filling material developed in this study was identified as Mas #7. Calcium hydroxide was silanated in a tumble mixer by charging 100 parts by weight of calcium hydroxide powder with 4 parts by weight of r-methacryloxypropyltrimethoxy silane in 200 parts by weight of ethanol solution. The tumbling was continued for 2 h. Ethanol was evaporated and air-dried at room temperature, and then at 60°C overnight. The powder was heated to 115°C for 2.5 h. After crushing and sieving, microcapsuled calcium hydroxide was obtained and formulated into the powder of the experimental material (Table 1). The powder/liquid mixing ratio was 1.00/0.88 by weight. Four commercially available light-activated liners and two conventional glass ionomer liners were used for comparison as shown in Table 2: Time Line, Vitrabond, XR Ionomer, Zionomer, GC Lining Cement, and Ketac Bond. Shear bond strength test. Seventy extracted human molars which had been stored in a 1% chloramine solution at room temperature were used as test specimens. These specimens were embedded with fast-curing acrylic resin (Sample-Kwick, Buehler, Lake Bluff, IL, USA) in a cylindrical plastic mold (h=30 mm, d=15 mm). The occlusal one-third of the tooth crown was removed with a low speed saw (Isomet, Buehler, Lake Bluff, IL, USA). The exposed occlusal part of the dentin surface ofthe test specimens was ground wet on 800 grit silicon carbide paper on a polishing machine (DAP-V, Struers, Copenhagen, Denmark). The embedded teeth were washed in running fluoride-free water and dried with an oil-free air syringe. Each of the light-activated liners was applied to the dentin surfaces in accordance with its manufacturer's instructions. Smear layers were left intact except for Zionomer, GC Lining Cement, and Ketac-Bond. Zionomer's dentin conditioner and Ketac-Conditioner (ESPE) had been applied for
TABLE 2: LINERSUSED FOR COMPARISON
TABLE 1: FORMULATIONOF NEW LIGHT-ACTIVATEDFLUORIDE
RELEASING LINER MATERIAL Raw Materials Manufacturer BatchNumber Parts(w/w)
L,ner
Manufacturer
Batch Number
T,me Line
L D. Caulk, M,Iford, DE, USA
Paste 092388
Vttrabond
3M Dental Products, Mnneapohs,MN, USA
Powder' 6w2 Liquid. 8yl
XR Ionomer
Kerr Manufactur,ng Co, Romulus,MI, USA
Powder91017 Liquid' 8434
Ztonomer
DenMat Corporation, Santa Maria,CA, USA
Conditioner 291017 Powder498005 L~qu~d499002
GC Lin,ngCement
GC Co, Tokyo, Japan
Powder 120661 LJquld 300561
Ketac-BondApphcap
ESPE 0001 Seefeld/Oberbay,Germany
POWDER Strontiumalumtnofluoro s,hcateglass
SanklnKogyoK.K, Tokyo, Japan
K-92
90
P-Toluenesulfintcacrd salt. d,hydrate
J T Baker Chemical Co, Ph,lhpsberg,NJ, USA
013357
4
Sankln KogyoK K,
09112
Methacryloxyethyl-p-(N,Nd,methyl)am,nobenzoate Calc,um hydroxide r-Methacryloxypropyl tnmethoxystlane
SpectrumChem,calCo, Gardena, CA, USA
EH227
Un,on CarbideCo, Danbury,CT, USA
UCC3163
3
10
LIQUID Tetra-methacryloxyethyl pyrophosphate
SanklnKogyoK K. Tokyo, Japan
SK-301
40
Methacryloxyethyl phosphate
KyoelshaO,I Chemical Co, Osaka, Japan
1070272
30
Ethoxylatedbts-phenolA dJmethacrylate
SartomerCo, Westchester, PA, USA
GUK 0220
30
Camphorqulnone
Eastman KodakCo. Rochester, NY, USA
807410A
0 26
10 s (Zionomer) and 30 s (conventional glass ionomer liners) to remove the smear layer prior to adhesion. The adhesion area was defined by using an adhesive water-repellant tape with a 3 mm diameter circular hole in its center. A cylindrical plastic tube (d=5 mm, h=2-3 ram) was placed over the 3 mm opening and fixed with dental wax. Each material was mixed according to the manufacturer's instructions. The lightactivated liner was placed onto the dentin surface to a thickness of 1-2 ram, then exposed for 20 s with a visible light unit (Optilux 400, Demetron Research Corp., Danbury, CT, USA). Composite (Silux, 3M) was then placed onto the liner surface and light-cured for 40 s. The test specimens were immersed m distilled water at 37°C. After 24 h, the test specimens were clamped horizontally into the shear adhesion apparatus and loaded with a knife edge parallel to the vertical plane of the material-dentin interface. Bond strengths were measured in an Instron universal testing machine (Model 1011, Instron Corp., Canton, MA, USA) at a cross-head speed of 1 mm/min. Ten specimens were tested for each variable. Results were compared using one-way ANOVA and Student-NewmanKeuls critical difference tests (p
