Abstract
Objectives
To compare in-vitro micro-shear bond strengths (μSBS) of resin composite to calcium silicate cement (Biodentine™) vs. glass ionomer cement vs. resin modified glass ionomer cement (RM-GIC) using an adhesive in self-etch (SE)/total etch (TE) mode after aging three substrates and bond and characterizing their failure modes.
Methods
Resin composite was SE/TE bonded to 920 standardized disks of Biodentine™, GIC & RM-GIC. Dividing samples into two groups, the first underwent early ( t = 0 min, 5 min, 20 min, 24 h) or delayed ( t = 2 wk, 1 month, 3 months, 6 months) substrate aging before bonding and μSBS ( t = 24 h) testing. In the second, adhesive was applied after either early ( t = 5 min) or delayed ( t = 2 wk) substrate aging and then tested after bond aging ( t = 2 wk, 1 month, 3 months, 6 months). The failure modes were identified using stereomicroscope. SEM images of selected samples were analyzed.
Results
No significant differences were observed between (SE)/(TE) bonding modes ( P = 0.42). With substrate aging, a significant reduction in μSBS occurred between early and delayed time intervals for Biodentine™ ( P = 0.001), but none for the GIC/RM-GIC ( P = 0.465, P = 0.512 respectively). With bond aging, there was no significant difference between time intervals for all groups, except at 6 months for the GIC ( P < 0.05). Modes of failure were primarily cohesive within all the substrates (68.82%) followed by adhesive failure at the resin–substrate interface (21.71%).
Significance
Biodentine™ is a weak restorative material in its early setting phase. Placing the overlying resin composite as part of the laminate/layered definitive restoration is best delayed for >2 wk to allow sufficient intrinsic maturation to withstand contraction forces from the resin composite. A total-etch or self-etch adhesive may be used.
1
Introduction
The operative treatment of deep carious lesions approaching the pulp and the related histopathological dentin–pulp complex changes pose a significant challenge as an increased risk of pulp exposure reduces the overall predictability and long term success . Treatment modalities must aim to maintain pulp vitality using a minimally invasive, tooth preserving approach. With the introduction of a calcium silicate material Biodentine™ (Septodont, St Maure des Fosses, France) to the market, the clinical procedure has been somewhat simplified by combining its therapeutic pulp capping capabilities with its ability to be used simultaneously as a provisional bulk restorative material. However, because Biodentine™ is exposed to wear under load with time and its relatively poor esthetics, a second, overlaid restoration of resin composite is required to provide mechanical strength, wear resistance, and improved esthetics of the definitive restoration .
The quality and durability of the adhesive bond between Biodentine™ and the resin composite is of clinical significance with regards to the longevity and predictability of the final laminate restoration. The durability of this bond may be affected by the type of adhesive used (self-etch vs. etch and rinse adhesives). To date, there is no published information on the effect of the bonding technique on the bond strength of Biodentine™ to resin composite. As Biodentine™ has a similar chemical composition to MTA, hydration of Biodentine™ should resemble that of MTA. Therefore, it is assumed that when Biodentine™ is exposed to a low pH such as that of phosphoric acid etch, this could affect the chemical setting of Biodentine™ by disrupting the hydration of tricalcium silicates resulting in weakening of the setting material’s microstructure . Milder etching for a shorter time period may cause selective loss of matrix around the crystalline structures with minimal loss of cement, exposing these crystalline structures and hence encouraging successful adhesion through micro-mechanical retention .
Currently, placing the veneering restoration is a 2-stage clinical procedure, completed ideally within 6 months of placing the initial Biodentine™ bulk restoration, as per manufacturer’s recommendations. However, investigating the potential for bonding the veneering restoration at the same visit as placing the Biodentine™ is worthwhile as this would be easier and less time consuming, eliminating the need to bring the patient back for a second visit.
There are many methods used to assess interfacial bond strength between dissimilar restorative materials. Statically, they can be measured using a macro- or micro-test depending on the area of the tested interface . The micro-shear test was used in this investigation allowing simpler specimen preparation with a reduced risk of specimen preparation damage. It eliminates the need to section specimens to obtain sticks or hour-glass specimens which is required for other tests such as the micro-tensile test . Indeed this is necessary with Biodentine™ which is brittle in thin cross section and must be used in bulk to avoid damage to the Biodentine™ samples.
The aim of this in-vitro study was to determine the micro-shear bond strength (μSBS) of a resin composite (N’Durance, Septodont, Louisville, USA) to Biodentine™ using a self-etch adhesive (Scotchbond™ Universal, 3M ESPE, USA) compared to glass ionomer cement (GIC) (Fuji IX™ GP, GC Corporation, Tokyo, Japan) and resin modified glass ionomer cement (RM-GIC) (Fuji II LC, GC corporation, Tokyo, Japan), which are materials that have similar clinical applications to Biodentine™ in terms of being used as provisional bulk restorative materials in deep cavities. The study also aimed to compare the use of the self-etch adhesive in a self-etch mode (SE) and a total-etch (TE) mode while aging the substrates and aging the bond at different time intervals and to identify the specific modes of failure. The null hypothesis was that there is no difference in the μSBS within each substrate (Biodentine™, GIC, and RM-GIC) and when comparing between them using the self-etch and total etch techniques at the different time intervals.
2
Materials and methods
The materials used are summarized in Table 1 . Nine hundred and twenty disks of Biodentine™ ( n = 320), Fuji IX™ (control) ( n = 320), and Fuji II LC™ (control) ( n = 280) were fabricated by mixing each material according to the manufacturer’s instructions and condensing them into a standardized 3 × 4 mm cylindrical plastic polymer mold. A glass slab was placed on top of the mold so that all the materials set against a smooth surface to ensure standardization of the sample surface. The samples were divided into two main groups. In the first group, the effect of aging the substrate (Biodentine™, GIC and RM-GIC) on the micro-shear bond strength (μSBS) was investigated. In the second group, the effect of aging the bond on the μSBS was investigated.
| Material | Manufacturer | Material composition | LOT Number |
|---|---|---|---|
| Tricalcium silicate cement | Biodentine™, Septodont, St Maure des Fosses, France | Powder: Tri-calcium silicate, di-calcium silicate, calcium carbonate and oxide filler, iron oxide, zirconium oxide radiopacifierLiquid: calcium chloride acceleratorhydrosoluble polymer water reducing agent. | B03916 |
| GIC | Fuji IX™ GP, GC corporation, Tokyo, Japan | Powder: fluoro-alumino-silicate glass, polyacrylic acid powderLiquid: polyacrylic acid, Polybasic carboxylic acid | 1202221 |
| RMGIC | Fuji II LC, GC corporation, Tokyo, Japan | Powder: Fluoro-alumino-silicate glass Liquid: poly-acrylic acid, 2-hydroxyethyl methacrylate (HEMA) dimethacrylate, camphorquinone, water | 1203161 |
| Composite | N’Durance ® , Septodont, Louisville, USA | The resin based matrix contains approximately 19 wt % of ethoxylated BisGMA, UDMA and the new dicarbamate dimethacrylate dimer acid. The filler system contains approx. 80 wt% (65 vol%) silanated 40 nm ytterbium fluoride, silanated 500 nm barium glass and 10 nm silica. There is approximately 1 wt% of catalyst, inhibitors and pigments. | 121710A |
| Self-etch adhesive | Scotchbond™ Universal, 3M, ESPE, USA | MDP phosphate monomer, Dimethacrylate resins, HEMA, Vitrebond™ Copolymer, filler, ethanol, water initiators, silane | 455500 |
| Etchant | Scotchbond™ Universal, 3M, ESPE, USA | 34% phosphoric acid by weight | 455500 |
The first group ( n = 440) which investigated the effect of aging the substrate on the μSBS was subdivided into the following:
- 1.
Aging each substrate for “early” time intervals ( t = 0 min, t = 5 min, t = 20 min, t = 24 h) following which the same adhesive was applied in either SE or TE mode. The first time interval represents the application of the adhesive immediately after setting of each material as stated in the manufacturer’s instructions, from the start of mixing. For RM-GIC there were only two time intervals ( t = 0 min, and t = 24 h) as the material was photo-cured on command.
- 2.
Aging the substrate for a “delayed” time interval ( t = 2 wk, t = 1 month, t = 3 months, t = 6 months) following which the same adhesive was applied in either SE or TE mode.
The bonded samples in both groups were stored in distilled water for 24 h before being subjected to μSBS testing.
The second group ( n = 480) which investigated the effect of aging the adhesive bond on the μSBS was subdivided into the following:
- 1.
Aging the substrate for 5 min following which the same adhesive was applied in either SE or TE mode and the bond then aged in distilled water before testing ( t = 2 wk, t = 1 month, t = 3 months, t = 6 months).
- 2.
Aging the substrate for 2 wk following which the adhesive was applied in either SE or TE mode and the bond aged for the same time intervals as the previous group ( t = 2 wk, t = 1 month, t = 3 months, t = 6 months) before being subjected to μSBS testing.
2.1
Micro-shear bond strength test
Prior to adhesive resin polymerization, a 1-mm thick slice of Tygon tubing (Saint-Gobain, USA) with a 0.75-mm internal diameter was placed on the bonded area (see Fig. 1 ) . The adhesive resin was bonded to the disks of Biodentine™/GIC/RM-GIC according to the manufacturer’s instructions. Resin composite was condensed into the tube and polymerized for 40 s. All specimens were stored in distilled water at 37 °C for either 24 h or longer depending on the experimental group, before testing. After the storage period, the Tygon tubes were removed carefully from all specimens using a sharp scalpel (Swann-Morton, Sheffield, England). Pre-test failures were recorded. The specimens were attached to the micro-shear testing device using a fast-setting adhesive (Everbuild Ltd, Leeds, UK). The testing device was attached to a SMAC LAL300 linear actuator (SMAC Ltd., West Sussex, UK). Wire (diameter of 0.2 mm) was looped around the resin-composite cylinder and positioned as close as possible to the resin–Biodentine™/GIC/RM-GIC interface . A shear force was applied at a crosshead speed of 1.0 mm/min until debonding occurred. The micro-shear shear bond strength ( t ) was calculated in MPa using the equation t = F /( πR 2 ), where F was the applied load at failure and R was the radius of the resin composite cylinder ( Fig. 1 ).
2.2
Interface examination
After debonding, the fractured surfaces were evaluated using a stereomicroscope (Kyowa Optical Co. Ltd., Tokyo, Japan) with a 60 × 0.75 NA objective to classify the failure modes into one of the following categories: (A) adhesive failure at the interface between resin and Biodentine™/GIC/RM-GIC; (B) adhesive failure at the interface between resin and composite; (C) cohesive failure within resin; (D) cohesive failure within Biodentine™/GIC/RM-GIC; (E) cohesive failure within composite. Representative specimens ( n = 7) chosen randomly from each group were examined additionally using a scanning electron microscope (SEM) (Hitachi S3500, Japan). Prior to SEM observations, the specimens were air dried and gold sputter-coated at 45 mA current for 2 min (Emitech K550, Kent, England).
2.3
Statistical analysis
Descriptive statistics were used to summarize the study characteristics and bond strength for various materials. Percentages were used to present the failure modes for different substrates. The bond strength for the three substrates, namely Biodentine™, GIC and RM-GIC, at different time intervals (both for aging the substrate and aging the bond) were analyzed using parametric analysis as the data followed normal distribution. Linear regression models were used to test the significance of various predictors. Significance was predetermined at α = 0.05. If there was evidence of an interaction effect, the temporal changes were assessed separately for the substrates in the post-hoc analysis which was adjusted for multiple comparisons using the Bonferroni correction. Also, the main effect of substrate and time were tested by including them in the model for its overall significance. All analyses were carried out using Stata/SE 11.2 for windows (Statacorp LP, USA).
2
Materials and methods
The materials used are summarized in Table 1 . Nine hundred and twenty disks of Biodentine™ ( n = 320), Fuji IX™ (control) ( n = 320), and Fuji II LC™ (control) ( n = 280) were fabricated by mixing each material according to the manufacturer’s instructions and condensing them into a standardized 3 × 4 mm cylindrical plastic polymer mold. A glass slab was placed on top of the mold so that all the materials set against a smooth surface to ensure standardization of the sample surface. The samples were divided into two main groups. In the first group, the effect of aging the substrate (Biodentine™, GIC and RM-GIC) on the micro-shear bond strength (μSBS) was investigated. In the second group, the effect of aging the bond on the μSBS was investigated.
| Material | Manufacturer | Material composition | LOT Number |
|---|---|---|---|
| Tricalcium silicate cement | Biodentine™, Septodont, St Maure des Fosses, France | Powder: Tri-calcium silicate, di-calcium silicate, calcium carbonate and oxide filler, iron oxide, zirconium oxide radiopacifierLiquid: calcium chloride acceleratorhydrosoluble polymer water reducing agent. | B03916 |
| GIC | Fuji IX™ GP, GC corporation, Tokyo, Japan | Powder: fluoro-alumino-silicate glass, polyacrylic acid powderLiquid: polyacrylic acid, Polybasic carboxylic acid | 1202221 |
| RMGIC | Fuji II LC, GC corporation, Tokyo, Japan | Powder: Fluoro-alumino-silicate glass Liquid: poly-acrylic acid, 2-hydroxyethyl methacrylate (HEMA) dimethacrylate, camphorquinone, water | 1203161 |
| Composite | N’Durance ® , Septodont, Louisville, USA | The resin based matrix contains approximately 19 wt % of ethoxylated BisGMA, UDMA and the new dicarbamate dimethacrylate dimer acid. The filler system contains approx. 80 wt% (65 vol%) silanated 40 nm ytterbium fluoride, silanated 500 nm barium glass and 10 nm silica. There is approximately 1 wt% of catalyst, inhibitors and pigments. | 121710A |
| Self-etch adhesive | Scotchbond™ Universal, 3M, ESPE, USA | MDP phosphate monomer, Dimethacrylate resins, HEMA, Vitrebond™ Copolymer, filler, ethanol, water initiators, silane | 455500 |
| Etchant | Scotchbond™ Universal, 3M, ESPE, USA | 34% phosphoric acid by weight | 455500 |
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