Abstract
Objectives
The aim of the study was to test whether or not the shear bond strengths of six self-adhesive resin cements to dentin and to glass-ceramic, 24 h and long-term-aged, are similar to the one of a conventional resin cement.
Methods
Human molars ( N = 168, n = 12 per group) and silicabased glass-ceramic specimens ( N = 168, n = 12 per group) were embedded in acrylic resin and randomly divided into 28 groups. The following resin cements were luted according to the manufacturers’ instructions: Clearfil SA (CSA), G-Cem (GCM), SmartCem2 (SMC), SpeedCEM (SPC), RelyX Unicem (RXU), RelyX Unicem2 (RXU2) and Panavia21 (control group, PAN). Shear bond strength was measured initially (24 h of water storage 37 °C) and after aging (24,000 thermal cycles, 5/55 °C). The failure types (adhesive, and cohesive) were evaluated after debonding. The shear bond strength values were analyzed using three-way and one-way ANOVA, followed by a post hoc Scheffé and two-sample Student’s t -tests.
Results
RXU, RXU2 and GCM showed similar after 24 h and aged shear bond strength to dentin as the control group. CSA, SMC and SPC exhibited significantly lower values. Before aging, none of the bond strength values to glass-ceramic differed significantly from the other. After thermocycling, GCM showed higher results to glass-ceramic than CSA, SMC, RXU2 and the control group. Analyzing failure types after spontaneous debonding and shear bond test at dentin, solely adhesive failures were found, while at glass-ceramic only cohesive failures occurred.
Conclusion
Not all self-adhesive resin cements can be a valid alternative to conventional resin cements in order to bond silica-based glass-ceramics to human dentin.
1
Introduction
The available cements in dentistry can be classified into water-based and resin-based polymerizing cements . Water-based cements include glass-ionomer and zinc phosphate cements, whereas polymerizing cements comprise resin composites, adhesive cements and resin-modified glass-ionomer cements. Chemical bonding of water-based cements to tooth tissues or restoration materials is only low (for glass-ionomer cements) or not existent (for zinc phosphate cement) . In contrast, polymerizing cements constitute some chemical and mechanical connection to the tooth and to the restoration .
The type of cementation may influence the outcome of the reconstruction depending upon restorative material the reconstruction is made out of, i.e. glass-ceramic, oxide ceramics and composites . Several studies showed that silica-based glass-ceramic restorations exhibit better clinical long-term stability when luted with polymerizing resin-based cements instead of water-based cements . When polymerizing resin-based cements were applied, the fracture resistance of silica-based glass-ceramic crowns increased significantly . Hence, this restorative materials require to be reinforced by adhesive cementation .
In order to achieve a good bonding between the polymerizing resin-based cement and the substrates, i.e. the restorative material and the tooth substance, several pre-treatment bonding steps are required. These pre-treatment steps are technique sensitive and, therefore, prone to handling errors. It has been shown that polymerizing cements are very technique sensitive. Handling problems like, e.g. contamination of the substrate with saliva or blood significantly reduce the bond strength of the respective polymerizing cement .
To facilitate the pretreatment procedures of the tooth tissue, self-adhesive resin cements were recently developed. Self-adhesive resin cements are polymerizing cements, which bond to the substrate, more specifically to dentin, without the pre-treatment with bonding solutions. The first introduced and well documented self-adhesive resin cement is RelyX Unicem (3M ESPE, Germany). In order to achieve a self-adhesive reaction of this cement to the tooth structure, new methacrylate monomers with phosphoric acid groups were implemented. This results in a low pH value and hydrophilic properties in the beginning of the setting. Subsequently, the negatively charged groups of the monomer bind to Ca 2+ ions of the tooth and in combination with the alkaline part of the fillers a neutralization reaction follows . Several in vitro and clinical studies showed promising results of RelyX Unicem with respect to bond strength . The chemical reaction of most of the other self-adhesive cements have not been clearly announced yet by the manufacturers.
Within the last years, several new self-adhesive resin cements have been introduced . At present, no scientific literature is available of the newly introduced self-adhesive resin cements and their bond strength after long-term aging. Whereas studies show that aging can have a negative impact on the shear bond strength of conventional resin cements , the bond strength of the newly introduced self-adhesive resin cements after long-term aging has not been investigated yet . Good long-term bonding capacity, however, is desired for clinical long-term success. As mentioned before, reconstructions made out of weak silica-based ceramics need to be reinforced by the adhesive cementation. Consequently, the self-adhesive resin cements should be to establish good long-term bonding not only to the tooth substance, but also to the ceramic. Hence, laboratory studies of the new self-adhesive resin cements are needed, which simulate the oral conditions and age the adhesive interfaces to measure the long-term bonding capacity to tooth and to the reconstruction material .
Therefore, the aim of this study was to test whether or not various self-adhesive resin cements exhibit similar shear bond strength to the substrates dentin and glass-ceramic as a conventional resin cement.
The null-hypothesis was that the shear bond strength of self-adhesive resin cements to both substrates is similar to the conventional cement both initially, and after long-term aging.
2
Material and methods
Six self-adhesive resin test cements were included in the study. One conventional resin cement acted as control group. Table 1 gives detailed information of all tested cements. 168 teeth were divided into 14 groups of twelve each. Additionally 168 ceramic specimens were divided into 14 further experimental groups of twelve each ( Fig. 1 ).
| Cement and bonding agents | Abbreviation | Manufacturers | Batch | Composition |
|---|---|---|---|---|
| Panavia21 | PAN | Kuraray Dental Co. Ltd., Osaka, Japan | 408CA | MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, fillers, BPO, hydrophilic liphatic dimethacrylate, hydrophilic dimethacrylate, DEPT, sodium aromatic sulfonate |
| +ED Primer A/B | 00283A/00143E | HEMA, MDP, 5-NMSA, water, accelerator, ethanol, 3-methacryloxypropyl tris(trimethylsiloxy)silane MPTS, initiator | ||
| +Clearfil Ceramic Primer | 00009C | MDP, ethanol, MPTS | ||
| Clearfil SA | CSA | Kuraray Dental Co. Ltd., Osaka, Japan | 033BBA | MDP, Bis-GMA, TEGDMA, other methacrylate monomers, silanated barium glass filler, silanated colloidal silica, dl-camphorquinone, benzoyl peroxide, initiator, surface treated sodium fluoride, accelerators, pigments |
| +Clearfil Ceramic Primer | 00009C | MDP, ethanol, MPTS | ||
| G-Cem | GCM | GC, Leuven, Belgium | 810241 | Fluoro-alumino-silicate glass, initiator, pigments, 4-META, phosphoric acid ester monomer, water, UDMA, dimethacrylate, silica powder, initiator, stabilizer |
| +GC Ceramic Primer | 901272 | Ethanol, methyl methacrylate, 2-HEMA | ||
| SmartCem2 | SMC | Dentsply DeTrey GmbH, Konstanz, Germany | 809231 | PENTA, UDMA, EBPADMA, di- and trifunctional diluents, photoinitiating system, self-cure initiating system |
| +Calibra Silane Coupling Agent | 812051 | Acetone, Ethyl Alcohol, Organo Silane | ||
| SpeedCEM | SPC | Ivoclar VIvadent, Schaan, Liechtenstein | 627590 | Acidic monomers, dimethacrylates, barium glass, ytterbium trifluoride, co-polymer, silicon dioxodes, catalysts, stabilizers, pigments |
| +Monobund Plus | 626221 | Ethanol, water, 3-methacryloxy propyl-trimethoxysilane | ||
| RelyX Unicem (Aplicap) | RXU | 3M ESPE, Seefeld, Germany | 363991 | Methacrylate monomers containing phosphoric acid groups, alkaline fillers, silanated fillers, initiator components, pigments, methacrylate monomers, initiator components, stabilizers |
| +RelyX Ceramic Primer | 7XY | Ethanol, water, methacrylacid-3-trimethoxysilylpropylester | ||
| RelyX Unicem2 (Automix) | RXU2 | 3M ESPE, Seefeld, Germany | 421455 | Methacrylate monomers containing phosphoric acid groups, methacrylate monomers, silanated fillers, initiator components, stabilizer components, rheologic additives, alkaline fillers, pigments, rheologic additives |
| +RelyX Ceramic Primer | 7XY | Ethanol, water, methacrylacid-3-trimethoxysilylpropylester | ||
2.1
Preparation of human dentin specimens
For this study 168 caries-free human molars were used. The teeth were cleaned from remnant soft tissue and stored in 0.5% chloramine T at room temperature during the first 7 days after extraction and thereafter stored in distilled water at 5 °C for a maximum of 6 months. They were ground flat with silicon carbide polishing paper P80 (Labo-Pol-21; Struers, Ballerup, Denmark) under water-cooling and subsequently embedded in a cylindrical form by acrylic resin (ScandiQuick, ScanDia, Hagen, Germany). The teeth were ground with SiC P500 until a dentin surface area of at least 5 mm 2 was exposed. Immediately prior to the luting procedure, the dentin specimens of the control group were pretreated according to the respective manufacturer’s recommendations ( Table 2 ).
| Pretreatment of dentin | Pretreatment of glass-ceramic | |
|---|---|---|
| Control group | Dispense one drop of ED Primer liquids A and B, stir for 5 s, apply to dentin with a sponge pledget, leave for 60 s, dry gently by oil-free air | Etching with 5% hydrofluoric acid 60 s, rinse off with water spray, drying with alcohol 98%, apllication of the silane (Clearfil Ceramic Primer) |
| Test groups | No pretreament | Etching with 5% hydrofluoric acid 60 s, rinse off with water spray, drying with alcohol 98%, application of the silane recommended by the manufacturer of the cement |
2.2
Preparation of glass-ceramic specimens
Glass-ceramic ingots (VITA Mark II, VITA Zahnfabrik, Bad Säckingen, Germany) were embedded in acrylic resin ScandiQuick (ScanDia, Hagen, Germany) and cut from cylindrical rods into slices of 5 mm thickness by a cutting machine (Accutom 50, Struers, Ballerup, Danemark). The specimens were flattened with a polishing machine with P2400 silicon carbide polishing paper (SCAN DIA, Hagen, Germany). The surfaces of the glass-ceramic specimens were etched with 5% hydrofluoric acid for 60 s (VITA Ceramics Etch; VITA Zahnfabrik, Bad Säckingen, Germany, LOT 12150), rinsed with water, cleaned with alcohol, dried with oil-free air, and silanized according to the respective manufacturer’s recommendations ( Table 2 ).
2.3
Resin cement luting
The embedded specimens (human teeth and glass-ceramic) were randomly divided in the test- or control groups. In order to apply the different cements to the bonding area, the specimens were fixed in a special holding device to retain the surface parallel to the bench. An acrylic cylinder with an inner diameter of 2.9 mm (D+R Tec, Birmensdorf, Switzerland) was fixed on the specimen surface by means of a custom-made device. Therefore the procedure for the preparation of the specimens will only be briefly summarized. The cements were mixed according to the manufacturers’ recommendations and applied into the opening of the cylinders. A steel screw with an inner diameter matching to the acrylic cylinders was inserted parallel to the axis of the cylinders and loaded with 1 N. The excess cement was removed with foam pellets. By using this device it could be ensured to attain a thickness of the cement of 1 mm evenly. The specimens were light polymerized by an LED polymerization light with a light intensity of 1200 mW/cm 2 (Bluephase G2; Ivoclar Vivadent GmbH, Schaan, Liechtenstein) according to the manufacturers’ recommendations. To achieve a constant light polymerization, the output tip has been kept in contact to the acrylic cylinder from two opposed sites for 30 s each per side. All specimens were carefully removed and stored in distilled water at 37 °C for 24 h. Subsequently, half of all specimens was subjected to long-term thermocycling during 24,000 cycles at 5 and 55 °C with a dwelling time of 20 s.
2.4
Shear bond strength measurements
The shear bond strength was measured in a Universal Testing Machine (Z 010; Zwick, Ulm, Germany). The specimens were positioned in the sample holder with the bonding surface parallel to the loading piston. The loading piston had a chisel configuration and the load was applied with a crosshead speed of 1 mm/min. The load was applied at the outer surface of the cylinder in a distance of 300 μm to the specimen surface. The maximal load was measured before de-bonding occurred. The shear bond strength values were calculated with the following formula: fracture load/bond area = N/mm 2 = MPa.
2.5
Failure types analysis
The de-bonding surface was examined by two operators under a binocular microscope (Wild M3B, Heerbrugg, Switzerland) and the failure was classified into the following three different failure types: (i) adhesive (no cement remnants on the polished specimen surface), (ii) cohesive (fracture totally into the ceramic/dentin), and (iii) mixed (cement remnants and polished specimen surface exposed).
2.6
Statistical analysis
The statistical package for Social Science Version 19 (SPSS Inc., Chicago, IL, U.S.) was used for the statistical analysis. After a first screening of the results, the values for dentin showed a normal distribution of 71% and for glass-ceramic 86%. Hence, the shear bond strength values were analyzed based on the assumption of normal distribution. Three-way ANOVA between resin cement vs. aging type vs. bond area and one-way ANOVA testing the impact of resin cement and the impact of aging level on bond strength has been performed followed by a post hoc Scheffé test. In addition, a two-sample Student’s t -test was computed. All results from the statistical analysis with a p -value < 5% were considered as statistically significant.
2
Material and methods
Six self-adhesive resin test cements were included in the study. One conventional resin cement acted as control group. Table 1 gives detailed information of all tested cements. 168 teeth were divided into 14 groups of twelve each. Additionally 168 ceramic specimens were divided into 14 further experimental groups of twelve each ( Fig. 1 ).
| Cement and bonding agents | Abbreviation | Manufacturers | Batch | Composition |
|---|---|---|---|---|
| Panavia21 | PAN | Kuraray Dental Co. Ltd., Osaka, Japan | 408CA | MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, fillers, BPO, hydrophilic liphatic dimethacrylate, hydrophilic dimethacrylate, DEPT, sodium aromatic sulfonate |
| +ED Primer A/B | 00283A/00143E | HEMA, MDP, 5-NMSA, water, accelerator, ethanol, 3-methacryloxypropyl tris(trimethylsiloxy)silane MPTS, initiator | ||
| +Clearfil Ceramic Primer | 00009C | MDP, ethanol, MPTS | ||
| Clearfil SA | CSA | Kuraray Dental Co. Ltd., Osaka, Japan | 033BBA | MDP, Bis-GMA, TEGDMA, other methacrylate monomers, silanated barium glass filler, silanated colloidal silica, dl-camphorquinone, benzoyl peroxide, initiator, surface treated sodium fluoride, accelerators, pigments |
| +Clearfil Ceramic Primer | 00009C | MDP, ethanol, MPTS | ||
| G-Cem | GCM | GC, Leuven, Belgium | 810241 | Fluoro-alumino-silicate glass, initiator, pigments, 4-META, phosphoric acid ester monomer, water, UDMA, dimethacrylate, silica powder, initiator, stabilizer |
| +GC Ceramic Primer | 901272 | Ethanol, methyl methacrylate, 2-HEMA | ||
| SmartCem2 | SMC | Dentsply DeTrey GmbH, Konstanz, Germany | 809231 | PENTA, UDMA, EBPADMA, di- and trifunctional diluents, photoinitiating system, self-cure initiating system |
| +Calibra Silane Coupling Agent | 812051 | Acetone, Ethyl Alcohol, Organo Silane | ||
| SpeedCEM | SPC | Ivoclar VIvadent, Schaan, Liechtenstein | 627590 | Acidic monomers, dimethacrylates, barium glass, ytterbium trifluoride, co-polymer, silicon dioxodes, catalysts, stabilizers, pigments |
| +Monobund Plus | 626221 | Ethanol, water, 3-methacryloxy propyl-trimethoxysilane | ||
| RelyX Unicem (Aplicap) | RXU | 3M ESPE, Seefeld, Germany | 363991 | Methacrylate monomers containing phosphoric acid groups, alkaline fillers, silanated fillers, initiator components, pigments, methacrylate monomers, initiator components, stabilizers |
| +RelyX Ceramic Primer | 7XY | Ethanol, water, methacrylacid-3-trimethoxysilylpropylester | ||
| RelyX Unicem2 (Automix) | RXU2 | 3M ESPE, Seefeld, Germany | 421455 | Methacrylate monomers containing phosphoric acid groups, methacrylate monomers, silanated fillers, initiator components, stabilizer components, rheologic additives, alkaline fillers, pigments, rheologic additives |
| +RelyX Ceramic Primer | 7XY | Ethanol, water, methacrylacid-3-trimethoxysilylpropylester | ||
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