Effect of curing mode on the hardness of dual-cured composite resin core build-up materials

Shear bond strengths of two newly marketed self-adhesive resin cements to different substrates: A light and scanning electron microscopy evaluation

The purpose of this in vitro study was to compare the shear bond strengths (SBSs) of two newly marketed self-adhesive resin cements (RCs) to enamel, dentin, and lithium disilicate (LiSi) glass ceramic block. Forty-eight enamel and 48 dentin substrates were obtained from sound human molars. Additionally, 6 × 7 × 5 -mm- sized 24 specimens were produced from LiSi glass ceramic blocks. The tooth specimens were randomly assigned into four groups (n = 12) according to the surface treatments: (1) G-CEM ONE (GCO), (2) G-CEM ONE Adhesive Enhancing Primer (GCO-AEP) + GCO, (3) RelyX Universal (RXU), and (4) Scotchbond Universal Plus (SUP) + RXU. LiSi specimens were randomly divided into two groups (n = 12): (1) G-MultiPrimer (GMP) + GCO and (2) SUP + RXU. Following the RC applications, all specimens were kept in 100% humidity at 37°C for 24 hr and then submitted for SBS testing in a universal testing machine (1 mm/min). Data were analyzed by Welch's, one-way analysis of variance and two independent samples t tests. The nature of failures was examined under a light microscope, and scanning electron microscopy analyses were also performed for interfaces. GCO and RXU showed similar SBS to enamel (p > .05), and the use of adhesives resulted in improved SBS (p < .05). No difference was detected between GCO-AEP + GCO and SUP + RXU. The GCO-AEP + GCO exhibited the highest SBS to dentin (p < .05), followed by GCO ≥ SUP + RXU > RXU (p < .05). There was no significant difference between SBSs of two RCs to LiSi blocks (p > .05). No cohesive failure was determined for the tested groups by light microscope. The use of adhesives prior to the application of self-adhesive RCs improved their bonding to tooth tissues. GCO demonstrated superior SBS to dentin, whereas both self-adhesive RCs generated similar SBS to enamel and LiSi glass ceramic surfaces.

The Effect of Touch-Cure Polymerization on the Conversion and Hardness of Core Build-Up Resin Composites: A Laboratory Study

To improve the self-curing capacity and interfacial strength with dentine of dual-cured composite materials, touch-cure activators have been introduced. The aim of the study was to evaluate the effect of these activators on the hardness and conversion of dual-cured resin composite core build-up restoratives. The materials tested were Clearfil DC Core Plus (CF) and Gradia Core (GC) with the corresponding adhesives Clearfil S³ Bond Plus (for CF) and G-Premio Bond/G-Premio DCA activator (for GC). Disk-shaped specimens (n = 6/group) were prepared for the following groups: dual-cured, self-cured and self-cured in contact with the adhesive activators at the bottom surface. After a 3-week storage period (dark/dry/37 °C) the Martens hardness (HM) and degree of conversion (DC%) were determined for the previously mentioned groups and the top surfaces of groups in contact with the adhesives. A statistical analysis was performed by a one-way ANOVA and Holm–Sidak test per material and a Pearson’s correlation analysis (HM vs. DC%) at an α = 0.05. The self-cured specimens resulted in significantly lower HM and DC% values from the dual-cured group, as expected. However, in the presence of the adhesives with touch-cure activators, the conversion of the self-cured groups showed insignificant differences in HM and DC% from the dual-cured in both composite materials. The improvements on the bottom composite surfaces in contact with the adhesives did not extend to the entire specimen length. Nevertheless, improved interfacial curing may improve interfacial durability.

Effect of curing mode on the conversion and IIT-derived mechanical properties of core build-up resin composites

The aim of the study was to evaluate the degree of conversion and the mechanical properties of five composite core build-up materials polymerized in dual-curing and self-curing modes. The materials tested were: Clearfil DC Core Plus (CF), Gradia Core (GC), Luxacore-Z Dual Smartmix (LX), Multicore Flow (MC) and Paracore (PC). Disk-shaped specimens were prepared from each material; half the specimens were light-cured, whereas the rest were only self-cured. After a 3-week storage period (dark/dry/37 °C) the Martens Hardness, Indentation Modulus, and Elastic Index were determined by instrumented indentation testing (IIT), while the degree of conversion was assessed by ATR-FTIR spectroscopy. Statistical analysis was performed by 2-way ANOVA and post-hoc testing (α = 0.05). The dual-curing mode resulted in statistically higher Martens Hardness and Elastic Index than the self-curing mode in most materials but showed insignificant differences in Indentation Modulus. MC and PC demonstrated significantly higher degree of conversion in both curing modes. Overall, the self-curing mode was inferior to the dual-curing in conversion and mechanical properties for most products, despite their differences in monomer composition and filler loading.

Influence of polymerization methods and priming agents on the bond strength between resin luting agents and gold alloy

PURPOSE

To evaluate the influence of polymerization methods and a metal priming agent on the bond strength between gold alloy for metal ceramic restorations and dual-cure-type resin luting agents, and on the strength and hardness of the luting agents.

METHODS

A total of 154 disks cast by a gold alloy were treated with or without a metal priming agent. One of the three luting agents was applied on the disk. The luting agent was either chemically or dual-polymerized. The shear bond strength was measured both before and after thermocycling. In addition, scanning electron microscope (SEM) observation, flexural strength test, and Knoop hardness test were performed.

RESULTS

Significant differences among the luting agents were observed in terms of bond strength and flexural strength. Significant differences between chemically and dual-polymerized luting agents were observed regarding shear bond strength, flexural strength, and Knoop hardness before thermocycling. The application of the priming agent was effective only for a luting agent.

CONCLUSION

Both bond strength and flexural strength differed among three luting agents. The effect of the priming agent on bond strength differed among the luting agents. Both the bond and flexural strength of a chemically polymerized luting agent differed before or after thermocycling.

Hardness Development in Resin Composite Core Materials

PURPOSE

To investigate the hardness characteristics of 13 contemporary resin core materials.

MATERIALS AND METHODS

Specimens (n = 12) were fabricated using stainless steel molds with top surfaces of dual-cure products photopolymerized while additional groups were allowed to self-cure. Twelve Knoop hardness indentations 500 microns apart were obtained of photopolymerized top and bottom sample surfaces as well as the self-cured sample surface with the mean recorded as the representative sample hardness. Testing was completed at 10 minutes, 1 hour, and 24 hours. In addition, hardness values were compared to that obtained from polished coronal dentin samples. Mean data between groups were analyzed with Kruskal-Wallis/Dunn's, within groups with repeated measures ANOVA/Tukey's.

RESULTS

Hardness results were material dependent. All but two products demonstrated a 0.8 bottom/top Knoop hardness ratio at 10 minutes. Product's self-cure cure reaction did not attain hardness similarity with any photopolymerized top surfaces and while some materials were found to have similar dentin hardness to resin top surface ratio similarity, only one product had hardness equal to or greater than that of dentin during any time period.

CONCLUSIONS

Under this study's conditions, hardness development was material dependent and all but two products demonstrated adequate hardness-derived degree of cure assessment at 10 minutes after preparation. Self-cured samples demonstrated hardness increase; however, no self-cured material achieved hardness similarity to photopolymerized top surfaces. None of the materials achieved hardness similarity to dentin and only one product demonstrated hardness greater than that of dentin.

Evaluation of physical-mechanical properties of self-adhesive versus conventional resin cements

Aim: The purpose of this study was to compare the microhardness, diametral tensile strength, compressive strength and the rheological properties of self-adhesive versus conventional resin cements. Methods: Specimens of a conventional (RelyX ARC) and 3 self-adhesive (RelyX U200, Maxcem Elite, Bifix SE) types of resin cements were prepared. The Knoop test was used to assess the microhardness, using a Microhardness Tester FM 700. For the diametral tensile strength test, a tensile strength was applied at a speed of 0.6 mm/minute. A universal testing machine was used for the analysis of compressive strength and a thermo-controlled oscillating rheometer was used for the Rheology test. One-way ANOVA and Tukey’s test (α=0.05) were used for data analysis. Results: According to microhardness analysis, all the cements were statistically similar (p>0.05), except for Maxcem that presented lower hardness compared with the other cements in relation to the top surface (p<0.05). In the diametral tensile strength test, Relyx U200 and RelyX ARC cements were statistically similar (p>0.05), presented higher value when compared to the Maxcem and Bifix cements (p<0.05). The compressive strength of RelyX ARC and Maxcem Elite cements was statistically higher than RelyX U200 and Bifix cements (p<0.05). Regarding the rheology test, Maxcem Elite and RelyX ARC cements showed a high modulus of elasticity. Conclusions: The self-adhesive cements presented poorer mechanical properties than conventional resin cement. Chemical structure and types of monomers employed interfere directly in the mechanical properties of resin cements.

Effect of Exclusive Primer and Adhesive on Microtensile Bond Strength of Self-Adhesive Resin Cement to Dentin

The aim of this study was to investigate the effect of G-CEM One Primer (GCOP) and self-etching adhesive on the microtensile bond strength (µTBS) between self-adhesive resin cement G-CEM One (GCO) and dentin. Teeth were sectioned to expose the flat dentin surface and randomly assigned into five groups (n = 15) according to the dentin surface treatment: 1) no surface treatment, 2) GCOP, 3) All-Bond Universal (ABU), 4) GCOP followed by ABU (GCOP/ABU), 5) ABU followed by GCOP (ABU/GCOP). The composite resin blocks were bonded to the dentin surface using GCO. The specimens were stored in distilled water at 37 °C for 24 h, then sectioned into sticks (1 mm × 10 mm). The μTBS values were statistically analyzed using 1-way analysis of variance (ANOVA) and Tukey’s honestly significant difference (HSD) test (α = 0.05) and failure mode was examined under a stereomicroscope. The bonding interface of each specimen was evaluated using confocal laser scanning microscopy. The GCOP group exhibited the highest µTBS value and there were no significant differences observed between GCOP, GCOP/ABU, ABU/GCOP groups (p > 0.05). The use of GCOP with GCO results in the improved µTBS between GCO and dentin. In conclusion, using only GCOP with GCO for bonding of indirect restoration is extremely simple and increasing bond strength.

Bond performance of "Touch and Cure" adhesives on resin core systems

The purpose of this study was to compare the micro-tensile bond strength (µTBS) of three resin core composites to dentin and to examine the bonded interface of the composites. One experimental TDK-03(TD) and, two commercial, DC core Automix One (DC) and Unifil core EM(UN) were used. Flat dentin surfaces of human molars were exposed using #600 SiC paper and bonded with the respective adhesive of each system. After bonding, the composites were built up on the surfaces and cured under two conditions: "light condition" or "dark condition". µTBSs (MPa) in the light condition were: TD; 60.02±17.08, DC; 38.21±13.70, and UN; 29.50±9.71; in the dark condition: TD; 54.62±17.11, DC; 8.40±4.81, and UN; 9.47±6.56. Dark curing negatively affected the bond strength of the two commercial resin-core materials. The experimental material was not affected by the curing conditions.

Microhardness of dual-polymerizing resin cements and foundation composite resins for luting fiber-reinforced posts

STATEMENT OF PROBLEM

The optimal luting material for fiber-reinforced posts to ensure the longevity of foundation restorations remains undetermined.

PURPOSE

The purpose of this study was to evaluate the suitability of 3 dual-polymerizing resin cements and 2 dual-polymerizing foundation composite resins for luting fiber-reinforced posts by assessing their Knoop hardness number.

MATERIAL AND METHODS

Five specimens of dual-polymerizing resin cements (SA Cement Automix, G-Cem LincAce, and Panavia F2.0) and 5 specimens of dual-polymerizing foundation composite resins (Clearfil DC Core Plus and Unifil Core EM) were polymerized from the top by irradiation for 40 seconds. Knoop hardness numbers were measured at depths of 0.5, 2.0, 4.0, 6.0, 8.0, and 10.0 mm at 0.5 hours and 7 days after irradiation. Data were statistically analyzed by repeated measures ANOVA, 1-way ANOVA, and the Tukey compromise post hoc test (α=.05).

RESULTS

At both times after irradiation, the 5 resins materials showed the highest Knoop hardness numbers at the 0.5-mm depth. At 7 days after irradiation, the Knoop hardness numbers of the resin materials did not differ significantly between the 8.0-mm and 10.0-mm depths (P>.05). For all materials, the Knoop hardness numbers at 7 days after irradiation were significantly higher than those at 0.5 hours after irradiation at all depths (P<.05). At 7 days after irradiation, the Knoop hardness numbers of the 5 resin materials were found to decrease in the following order: DC Core Plus, Unifil Core EM, Panavia F2.0, SA Cement Automix, and G-Cem LincAce (P<.05).

CONCLUSIONS

The Knoop hardness number depends on the depth of the cavity, the length of time after irradiation, and the material brand. Although the Knoop hardness numbers of the 2 dual-polymerizing foundation composite resins were higher than those of the 3 dual-polymerizing resin cements, notable differences were seen among the 5 materials at all depths and at both times after irradiation.

Comparative evaluation of compressive strength and flexural strength of conventional core materials with nanohybrid composite resin core material an in vitro study

Several dental materials have been used for core build-up procedures. Most of these materials were not specifically developed for this purpose, but as a consequence of their properties, have found application in core build-up procedures. Improvements in composites and the development of nanocomposites have led to their use as a core build up material due to their superior mechanical properties, optical properties and ease of handling. However it is not clear if they have better mechanical properties than the conventional core build up materials like amalgam, GIC and dual cure composite core build up material. The strength of the core material is very important and this study was undertaken to compare the mechanical properties of materials used for direct core foundations. The differences between the compressive strength and flexural strength of Filtek Z350 nanocomposite with conventional core build up materials like Amalgam, Vitremer GIC and Fluorocore were tested. Cylindrical plexi glass split molds of dimension 6 ± 1 mm [height] x4 ± 1 mm [diameter] were used to fabricate 15 samples of each core material for testing the compressive strength and rectangular plexi glass split molds of dimension 25 ± 1 mm [length] x 2 ± 1 mm[height] x2 ± 1 mm [width] used for fabricating samples for flexural strength. The samples were stored a water bath at 250 °C for 24 h before testing. The samples were tested using a Universal Instron testing machine. The results of the study showed that Fluorocore had the highest compressive strength and flexural strength followed by Filtek Z350 [nanocomposite] Amalgam had the least flexural strength and Vitremer GIC had the least compressive strength. Thus flurocore and nanocomposite are stronger than other core build up materials and hence should be preferred over other conventional core build up materials in extensively damaged teeth.