Abstract
Objectives
Composite resin restorations present high survival rates and when a failure occurs repair is often possible. The aim of this study was to assess the effect of various repair techniques on indirect restorations.
Methods
LAVA Ultimate (3M), and Clearfil Estenia blocks (Kuraray) were repaired with our without surface roughness treatments, silane application and artificial ageing. Micro-shear bond stress tests were performed, while cohesive strength served as positive control. ANOVA was used for cohesive strength and effect of ageing, and linear mixed models to evaluate the effect of treatment variables on repair strength.
Results
Both materials reacted differently on surface treatments. Untreated (no treatment, no silane) repair strength was 16.3 ± 6.3 MPa for LAVA Ultimate and 19.0 ± 4.3 MPa for Estenia. Thermal cycling resulted in a 14–58% reduction of cohesive strength. Without cycling, all treatments resulted in a significant increase of bond strength in LAVA Ultimate (p < 0.003). After cycling use of air-abrasion showed a positive trend for both substrates, significantly effective for LAVA Ultimate (p < 0.04), and silane and CoJet for Estenia (p < 0.024). The positive effect of HF treatment disappeared after cycling.
Conclusion
It may be concluded that (1) the effect of surface treatment procedures on the repair bond strength of indirect composites is depended on the substrate and ageing. (2) Silane did not have a clear overall positive effect on bond strength and (3) artificial ageing had a strong negative influence on the stability of the adhesive interface and on the cohesive strength of one indirect composite resin material, but not the other.
1
Introduction
Improvements in quality of materials and placement techniques made the clinical application of resin-based composites feasible and predictable even in complex clinical situations such as cusp replacing restorations or rehabilitation of severely worn dentitions . Even though the annual survival rates of composites are satisfactory, the restorations may also present failures that can be inherent to the materials, (e.g. material fracture) , to the operator (e.g. improper placement technique and individual criteria for failure assessment) , or to the individual risk factors of the patient (caries risk or bruxism) . Overall, secondary caries and fracture are the predominant failure reasons of composite restorations . Repairing failed restorations may be more advantageous and less invasive than replacement . However, when repairing a restoration, one must often obtain adhesion to different substrates such as composite resins, metals, ceramics and tooth materials at the same time. Therefore, it is important to understand the possibilities of restoration repair, where only the missing or defect part is replaced .
Numerous in vitro studies have reported on the effect of different surface treatments on repair strength of composite restorations . Unfortunately, no conclusion could be drawn on which (universal) repair technique was the best, as the used materials and methods of all these studies varied strongly. Overall, these studies confirmed a positive role of air abrasion, but still only scarce information of repair on indirect restorations is available.
Therefore, the aim of this in vitro study was to investigate the effect of different surface roughening treatments, silane application and artificial ageing on the repair bond strength of two indirect composite resin-based systems. The hypotheses of this study were: (i) different surface treatment techniques will result in different repair strengths, (ii) application of a separate silane layer will enhance the repair strength and (iii) artificial ageing will decrease the stability of the repair adhesive interface.
2
Materials and methods
2.1
Production of samples
To obtain standardized samples of indirect composite resin, industrial pre-polymerized blocks of LAVA Ultimate for CAD-CAM use (color A3-LT, 3M ESPE Dental Products, St. Paul, Minnesota, USA) were cut with a diamond blade (Buehler Ltd., Lake Bluff, IL, USA) of 0.4 mm thick, resulting in 96 cubical samples of 6 × 6 mm in width and 4 mm in height. Additionally, using a custom Teflon mold, 96 similar sized cubical samples were obtained of Clearfil Estenia C&B (color DA3, Kuraray, Okayama, Japan). This composite was applied in two layers of 2 mm thick and each layer was separately photocured for 20 s with a Bluephase 16i LED polymerization unit (Ivoclar Vivadent, Liechtenstein; light intensity >1200 mW/cm 2 ), then blocks were complementary cured with Palatray CU (wavelength 400–500 nm; Heraeus Kulzer, Hanau, Germany) for 12 min. Finally, samples were covered with glycerin-based Air Barrier paste (Kuraray) and exposed to thermal curing in a heat curing oven (Multimat Mach 3, Dentsply De Trey, Hanau-Wolfgang, Germany) at 110 °C for 15 min according to the manufacturers’ instruction. All blocks of LAVA Ultimate and Clearfil Estenia were immersed in 70% ethanol for 5 min for cleaning and then air-dried. To obtain a standardized surface roughness, similar to a rough dental diamond bur, samples were grinded by hand for 10 s with a dry 150-grit silicon carbide grinding paper (Siawat, Frauenfeld, Switzerland). Finally, samples were cleaned ultrasonically for 15 min in distilled water and stored dry at room temperature.
2.2
Surface treatment procedure and groups of treatment
Samples of LAVA Ultimate and Clearfil Estenia were assigned to six surface treatment protocols (n = 16): (1) no treatment, serving as negative control, (2) air-abrasion with CoJet (30 μm Al 2 O 3 -particles coated with SiO 2 , 3M ESPE) for 10 s at a distance of 10 mm in a circular motion with a pressure of 3 bar (MicroEtcher II, Danville Materials, San Ramon, CA, USA), (3) air-abrasion with SilJet (30 μm Al 2 O 3 -particles coated with SiO 2 , Danville Materials) with the identical procedure, (4) air-abrasion with SilJet Plus (silanized silica-coated 30 μm Al 2 O 3 -particles, Danville Materials) with the identical procedure, (5) air-abrasion with Aluminum Oxide particles (50 μm, Rønvig Dental, Daugaard, Denmark) with the identical procedure and (6) etching with hydrofluoric acid (Porcelain Etch Gel, 9.6% (Pulpdent Co., Watertown, MA, USA)) for 10 s. All materials used in this study are listed in Table 1 . After the surface treatment, all blocks were assigned into different subgroups, identified with a waterproof mark and stored dry at 37 °C ( Fig. 1 a).
| Materials | Category | Manufacturer | Origin | Lot code(s) | Composition |
|---|---|---|---|---|---|
| LAVA Ultimate CAD/CAM Restorative | indirect resin composite | 3M ESPE | St. Paul, USA | N490227 A3-LT Shade | Hybrid composite with nanoceramic compounds (ZrO 2 /SiO 2 nanoparticles) embedded in highly cross-linked polymer matrix |
| Estenia C&B | Indirect resin composite | Kuraray Noritake Dental Inc. | Okayama, Japan | Lot n. BS0007; DA3 Shade | UTMA, aromatic dimethacrylate, aliphatic dimethacrylate, di-comphorquinone. Alumina microfiller, silanized glass filler, pigments, 92% colloidal silica spheres, 16 wt% microfillers, grain size 0.02 μm, 76% wt microfillers, grain size 2 μm |
| Air-barrier paste | Insulating | Kuraray Noritake Dental Inc. | Okayama, Japan | 6A0001 | Glycerin paste |
| CoJet Sand | Air abrasion | 3M ESPE | Seefeld, Germany | 520953 | 30 μm Al 2 O 3 particles coated with SiO 2 |
| Siljet | Air abrasion | Danville Materials | San Ramon, USA | 31624 | 30 μm Al 2 O 3 particles coated with SiO 2 |
| Siljet Plus | Air abrasion | Danville Materials | San Ramon, USA | 116-168B | Pre-silanized 30 μm Al 2 O 3 particles coated with SiO 2 |
| Aluminium oxide | Air abrasion | Rønvig Dental | Daugaard, Denmark | Not informed | 50 μm Al 2 O 3 |
| Porcelain etch gel | Etchant | Pulpdent Co. | Watertown, USA | 100825 | Hydrofluoric (3 ppm) 9.6% |
| RelyX Ceramic primer | Silane | 3M ESPE | St. Paul, USA | N417664 | Silane stabilized alcohol solution |
| Adper Scotchbond Multipurpose Plus | Adhesive (bonding) | 3M ESPE | St. Paul, USA | N421442 | Bis-GMA, HEMA, tertiary amines (light-cure and self-cure initiators), photo-initiator |
| Filtek Supreme XTE | Nanofiller resin composite | 3M ESPE | St. Paul, USA | N272867; N433402; N437301; N4522993; A1D Shade | Combination of aggregated ZrO 2 /SiO 2 cluster filler with primary particle size and a SiO 2 filler (nano agglomerated/nano aggregated), BisGMA, Bis-EMA, UDMA, TEGDMA, hydrophilic dimethacrylate, di-camphorquinone, N , N -Diethanol- p -toluidine, water |
2.3
Repair procedure
Half the number of samples per group (n = 8) received a separate silane application (Relyx Ceramic Primer, 3M ESPE) before application of adhesive resin Scotchbond Multipurpose (3M ESPE) without using the primer. The other half of the samples (n = 8) was only treated with adhesive resin without silane. The adhesive was gently air-dried and photopolymerized for 10 s using the LED-polymerization unit ( Fig. 1 b and c). Using a silicone mold, ‘fresh’ direct composite resin (Filtek Supreme XTE, color A1D, 3M ESPE) was placed in 2 layers of 2 mm thick and each layer was photopolymerized for 20 s to obtain standardized samples of 6 × 6 mm in width and 8 mm in height. After removing from the mold, samples were post photocured for 10 s per site. Gross marginal overhang was removed with a 400-grit paper under water irrigation, exposing completely the adhesive interface ( Fig. 1 d).
2.4
Preparation of specimens and ageing procedure
All samples were sectioned into four rectangular stick-shaped specimens of approximately 2.8 × 2.8 mm in width and 8 mm in length (n = 32 specimens per group) using a low speed diamond blade under abundant water-cooling ( Fig. 1 e). Half the number of stick-shaped specimens (n = 16) were subjected to artificial ageing using 10,000 thermal cycles (SD Mechatronik, Feldkirchen, Germany), with water baths at temperatures ranging from 5 to 55 °C, dwell time of 22 s, corresponding to a 1 year of temperature changes in the oral environment . After ageing, the specimens were stored dry at room temperature until the shear bond strength test. The other half of specimens was not subjected to thermal cycling.
2.5
Micro-shear bond strength test (μSBS)
Previously to the micro-shear bond strength test (μSBS) the exact dimensions of each specimen were measured with a digital micrometer (Magnescale Ly-101, Sony Inc., Tokyo, Japan). Each specimen was held in a customized metallic/acrylic griping device to align and maintain the adhesive interface in the same position ( Fig. 1 f). The specimens were loaded using a rectangular stylus positioned perpendicularly to the adhesive interface (Lloyd 1000N load cell), at a crosshead speed of 1 mm/min until failure, using an universal testing machine (Lloyd LS1,1 KN NEXYGEN Plus Materials Testing and Data Analysis Software, Lloyd instruments Ltd., UK). μSBS data were registered and converted into MPa (σ) according to the formula σ = F/A, where F = load for specimen failure (N) and A = bonded area (mm 2 ). The specimens that were lost during cutting (n = 5) and those that debonded during griping for the test (n = 13) were excluded from the datasheet. For specimens that were lost during gripping, they were given the lowest measured bond strength value for that group.
2.6
Cohesive strength serving as positive control
To test the cohesive strength of the composite resin materials (LAVA Ultimate, Clearfil Estenia, and Filtek Supreme XTE) 8 samples per material were additionally fabricated with the same dimensions of 6 × 6 mm in width and 8 mm in height. Samples were also sectioned into four rectangular stick-shaped specimens and half the number of the specimens was subjected to thermal cycling before measuring, whereas the other half was tested without ageing. The μSBS testing conditions were the same as described above.
2.7
Fracture analysis
After testing, a stereomicroscope (Leica M50, equipped with a digital camera CANON 50D) was used for fracture analysis at a magnification of 10×. Fractures were scored and classified as cohesive in the indirect substrate, adhesive at the interface, cohesive in the direct composite or mixed. In samples with mixed failures the distribution (%) of the different materials was scored.
2.8
Statistical analysis
To test the differences between the cohesive strength of the materials, Analysis of variance with Tukey’s post hoc test was used (p < 0.05). Linear mixed models were used to determine the effect of different surface treatment techniques, use of silane, and artificial ageing on the repair bond strength of both indirect composite resin materials. These contained a random intercept for sample to correct for the fact that multiple specimens were made from one sample. For this, the nlme library within the statistical program R (R Foundation, Vienna, Austria) was used .
2
Materials and methods
2.1
Production of samples
To obtain standardized samples of indirect composite resin, industrial pre-polymerized blocks of LAVA Ultimate for CAD-CAM use (color A3-LT, 3M ESPE Dental Products, St. Paul, Minnesota, USA) were cut with a diamond blade (Buehler Ltd., Lake Bluff, IL, USA) of 0.4 mm thick, resulting in 96 cubical samples of 6 × 6 mm in width and 4 mm in height. Additionally, using a custom Teflon mold, 96 similar sized cubical samples were obtained of Clearfil Estenia C&B (color DA3, Kuraray, Okayama, Japan). This composite was applied in two layers of 2 mm thick and each layer was separately photocured for 20 s with a Bluephase 16i LED polymerization unit (Ivoclar Vivadent, Liechtenstein; light intensity >1200 mW/cm 2 ), then blocks were complementary cured with Palatray CU (wavelength 400–500 nm; Heraeus Kulzer, Hanau, Germany) for 12 min. Finally, samples were covered with glycerin-based Air Barrier paste (Kuraray) and exposed to thermal curing in a heat curing oven (Multimat Mach 3, Dentsply De Trey, Hanau-Wolfgang, Germany) at 110 °C for 15 min according to the manufacturers’ instruction. All blocks of LAVA Ultimate and Clearfil Estenia were immersed in 70% ethanol for 5 min for cleaning and then air-dried. To obtain a standardized surface roughness, similar to a rough dental diamond bur, samples were grinded by hand for 10 s with a dry 150-grit silicon carbide grinding paper (Siawat, Frauenfeld, Switzerland). Finally, samples were cleaned ultrasonically for 15 min in distilled water and stored dry at room temperature.
2.2
Surface treatment procedure and groups of treatment
Samples of LAVA Ultimate and Clearfil Estenia were assigned to six surface treatment protocols (n = 16): (1) no treatment, serving as negative control, (2) air-abrasion with CoJet (30 μm Al 2 O 3 -particles coated with SiO 2 , 3M ESPE) for 10 s at a distance of 10 mm in a circular motion with a pressure of 3 bar (MicroEtcher II, Danville Materials, San Ramon, CA, USA), (3) air-abrasion with SilJet (30 μm Al 2 O 3 -particles coated with SiO 2 , Danville Materials) with the identical procedure, (4) air-abrasion with SilJet Plus (silanized silica-coated 30 μm Al 2 O 3 -particles, Danville Materials) with the identical procedure, (5) air-abrasion with Aluminum Oxide particles (50 μm, Rønvig Dental, Daugaard, Denmark) with the identical procedure and (6) etching with hydrofluoric acid (Porcelain Etch Gel, 9.6% (Pulpdent Co., Watertown, MA, USA)) for 10 s. All materials used in this study are listed in Table 1 . After the surface treatment, all blocks were assigned into different subgroups, identified with a waterproof mark and stored dry at 37 °C ( Fig. 1 a).
| Materials | Category | Manufacturer | Origin | Lot code(s) | Composition |
|---|---|---|---|---|---|
| LAVA Ultimate CAD/CAM Restorative | indirect resin composite | 3M ESPE | St. Paul, USA | N490227 A3-LT Shade | Hybrid composite with nanoceramic compounds (ZrO 2 /SiO 2 nanoparticles) embedded in highly cross-linked polymer matrix |
| Estenia C&B | Indirect resin composite | Kuraray Noritake Dental Inc. | Okayama, Japan | Lot n. BS0007; DA3 Shade | UTMA, aromatic dimethacrylate, aliphatic dimethacrylate, di-comphorquinone. Alumina microfiller, silanized glass filler, pigments, 92% colloidal silica spheres, 16 wt% microfillers, grain size 0.02 μm, 76% wt microfillers, grain size 2 μm |
| Air-barrier paste | Insulating | Kuraray Noritake Dental Inc. | Okayama, Japan | 6A0001 | Glycerin paste |
| CoJet Sand | Air abrasion | 3M ESPE | Seefeld, Germany | 520953 | 30 μm Al 2 O 3 particles coated with SiO 2 |
| Siljet | Air abrasion | Danville Materials | San Ramon, USA | 31624 | 30 μm Al 2 O 3 particles coated with SiO 2 |
| Siljet Plus | Air abrasion | Danville Materials | San Ramon, USA | 116-168B | Pre-silanized 30 μm Al 2 O 3 particles coated with SiO 2 |
| Aluminium oxide | Air abrasion | Rønvig Dental | Daugaard, Denmark | Not informed | 50 μm Al 2 O 3 |
| Porcelain etch gel | Etchant | Pulpdent Co. | Watertown, USA | 100825 | Hydrofluoric (3 ppm) 9.6% |
| RelyX Ceramic primer | Silane | 3M ESPE | St. Paul, USA | N417664 | Silane stabilized alcohol solution |
| Adper Scotchbond Multipurpose Plus | Adhesive (bonding) | 3M ESPE | St. Paul, USA | N421442 | Bis-GMA, HEMA, tertiary amines (light-cure and self-cure initiators), photo-initiator |
| Filtek Supreme XTE | Nanofiller resin composite | 3M ESPE | St. Paul, USA | N272867; N433402; N437301; N4522993; A1D Shade | Combination of aggregated ZrO 2 /SiO 2 cluster filler with primary particle size and a SiO 2 filler (nano agglomerated/nano aggregated), BisGMA, Bis-EMA, UDMA, TEGDMA, hydrophilic dimethacrylate, di-camphorquinone, N , N -Diethanol- p -toluidine, water |
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