Influence of Polymerization Mode on Degree of Conversion and Micropush-out Bond Strength of Resin Core Systems Using Different Adhesive Systems

Chemical and mechanical properties of dual-polymerizing core build-up materials

OBJECTIVES

To investigate the chemical (degree of conversion (DC)) and mechanical properties (Martens hardness (HM), elastic indentation modulus (E_IT), and biaxial flexural strength (BFS)) of four dual-polymerizing resin composite core build-up materials after light- and self-polymerization.

MATERIALS AND METHODS

Round specimens with a diameter of 12 mm and a thickness of 1.5 mm were manufactured from CLEARFIL DC CORE PLUS (CLE; Kuraray), core·X flow (COR; Dentsply Sirona), MultiCore Flow (MUL; Ivoclar Vivadent), and Rebilda DC (REB; VOCO) (N = 96, n = 24/material). Half of the specimens were light-polymerized (Elipar DeepCure-S, 3 M), while the other half cured by self-polymerization (n = 12/group). Immediately after fabrication, the DC, HM, E_IT, and BFS were determined. Data was analyzed using Kolmogorov-Smirnov, Mann-Whitney U, and Kruskal-Wallis tests, Spearman's correlation, and Weibull statistics (p < 0.05).

RESULTS

Light-polymerization either led to similar E_IT (MUL; p = 0.119) and BFS (MUL and REB; p = 0.094-0.326) values or higher DC, HM, E_IT, and BFS results (all other groups; p < 0.001-0.009). When compared with the other materials, COR showed a high DC (p < 0.001) and HM (p < 0.001) after self-polymerization and the highest BFS (p = 0.020) and Weibull modulus after light-polymerization. Positive correlations between all four tested parameters (R = 0.527-0.963, p < 0.001) were found.

CONCLUSIONS

For the tested resin composite core build-up materials, light-polymerization led to similar or superior values for the degree of conversion, Martens hardness, elastic indentation modulus, and biaxial flexural strength than observed after self-polymerization. Among the tested materials, COR should represent the resin composite core build-up material of choice due to its high chemical (degree of conversion) and mechanical (Martens hardness, elastic indentation modulus, and biaxial flexural strength) properties and its high reliability after light-polymerization. The examined chemical and mechanical properties showed a positive correlation.

CLINICAL RELEVANCE

The chemical and mechanical performance of dual-polymerizing resin composite core build-up materials is significantly affected by the chosen polymerization mode.

Could light-curing time, post-space region and cyclic fatigue affect the nanomechanical behavior of a dual-curing cement for fiber post luting?

OBJECTIVE

To evaluate the effects of curing time, post-space region and cyclic fatigue on the micromechanical properties of a fiber-post luting cement. The null hypotheses were that (1) curing time, (2) fatigue and (3) post-space region does not affect the nanoindentation modulus and hardness of the dual-curing cement.

MATERIALS AND METHODS

48 premolars were endodontically treated and a class I cavity and 8 mm deep post space was prepared. Fiber posts were luted with a universal, dualized adhesive system and a dual-curing cement following manufacturer's instructions. Specimens were divided into three groups (16 specimens for each group) according to light-curing time (no light-curing, 20 s light-curing and 120 s light-curing), which was performed with a LED lamp at 1000 mW/cm 2. The coronal part of the cavity was restored using a nano-filled resin composite. After 24 h, 8 specimens for each group were randomly extract in order to undergo to fatigue test in wet condition through a chewing simulator, while the other specimens were kept in distilled water as benchmark. All the restored teeth were then sectioned in 1 mm thick slices perpendicularly to the fiber post axis. Specimen slices were classified in coronal and apical to be tested through a nanoindenter. Data were analyzed through Kruskal-Wallis test with a significance level of 1%, in order to evaluate the influence of treatments (i.e., curing time and cyclic loading) on the micromechanical properties of the tested luting cement.

RESULTS

Both fatigue and curing time significantly influenced nanoindentation modulus and hardness of dual-curing cement (p < 0.01). No significant differences were reported for post space region. A significant interaction was found among the analyzed factors (p < 0.01).

SIGNIFICANCE

120 s light-curing time is recommended in order to achieve optimal mechanical proprieties, independently from post space region and cyclic fatigue. As matter of fact, 120 s light-curing allowed to prevent strain hardening induced by the fatigue simulation.

Effect of the Degree of Conversion on Mechanical Properties and Monomer Elution from Self-, Dual- and Light-Cured Core Composites

The objective of this work was to measure and correlate the degree of conversion (DC), mechanical properties and monomer elution from self-, dual- and light-cured core composites. Five samples of each of the following materials were prepared for each test: Clearfil (Core, Photo Core, Automix), Bisco (Core-Flo, Light-Core and Bis-Core). DC was determined using FTIR, compressive and flexural strength and modulus of elasticity using a universal testing machine and microhardness using Vickers hardness. Elution was measured using HPLC. One-way ANOVA with Tukey's post-test and Pearson's correlation were used to statistically analyze the data. DC of Clearfil-Dual (70.1%) and Clerafil-Photo (66.8%) were higher than Clearfil-Self (55.4%) and all Bisco materials (51.4-55.3%). Flexural strength of Clearfilwas higher than that of Bisco composites. The Microhardness of Clearfil-Dual (119.8VHN) and Clearfil-Photo (118.0VHN) were higher compared to other materials. The greatest elution was detected from self-cured materials. DC positively correlated to microhardness and compressive/flexural strength and negatively to BisGMA elution. Clearfil-Photo and Automix showed higher conversion, lower monomer elution and, generally, better mechanical properties. Self-cured composites should not be recommended for routine clinical use as their performance was inferior to dual- and light-cured composites. Microhardness may be used as an indicator of elution.

Influence of different curing modes on flexural properties, fracture toughness, and wear behavior of dual-cure provisional resin-based composites

We investigated the influence of different curing modes on the mechanical properties and wear behavior of dual-cure provisional resin-based composites (DCPRs). Three DCPRs and a self-curing bis-acryl provisional resin-based composite were used. Flexural strength (σ_F), elastic modulus (E), resilience (R), and fracture toughness (K_IC) were measured. The specimens were fabricated with and without light irradiation, stored in distilled water at 37°C for 24 h, and subjected to 5,000 or 10,000 thermal cycles. For sliding impact wear testing, 12 specimens were prepared with and without light irradiation. The maximum facet depth and volume loss were determined using a noncontact profilometer. Some of the mechanical properties and wear behavior of DCPRs are affected by light irradiation. This study indicated that proper light irradiation is important in polymerization process of the DCPRs to enhance the wear resistance and some mechanical properties.

Influence of the depth of intraradicular dentin on the pushout bond strength of resin materials

AIM

The aim of the present study was to evaluate the pushout bond strength between glass-fiber posts to different regions of intraradicular dentin with different materials for adhesive cementation.

METHODS

After endodontic filling, 40 teeth were divided into five groups according to adhesive cementation: Adper Single Bond 2 + RelyX ARC, Excite DSC + RelyX ARC (EXC), Adper SE Plus + RelyX ARC (SEP), RelyX Unicem, and Set. After the bonding process, roots were sectioned obtaining slices to be analyzed from each third. The bond strength was measured using the pushout test in a universal testing machine (Emic DL 3000) at a cross-head speed of .5 mm/minutes in different areas of the post space (cervical, middle, and apical). Data were subjected to analysis of variance and Fisher's test (α = .05).

RESULTS

The highest values for the pushout bond strength were found for the SEP group in all experimental conditions, without a significant difference for the EXC group in the middle and apical regions. There was a decrease in pushout bond strength in the cervical-apical direction for all groups, except the EXC group, which did not show a difference among the different regions.

CONCLUSIONS

The different interactions of the resin materials and the intraradicular depth influenced the bond strength of adhesives materials to dentin substrate.

Incremental and Bulk-fill Techniques With Bulk-fill Resin Composite in Different Cavity Configurations

PURPOSE:

To compare the microtensile bond strengths of incremental and bulk-fill techniques under different C-factor and compliance conditions.

METHODS AND MATERIALS:

Extracted human third molars were divided into three experimental groups. For group I, Class I cavities were prepared. For group II, MOD cavities of the same size were prepared. For group III, the cavities were prepared the same way as group II only with high compliance cavity walls. The cavity wall compliance of the specimens was evaluated. Each of these groups was divided into four subgroups. The teeth were restored using two different materials: TB (Tetric N-Ceram Bulk Fill; Ivoclar Vivadent, Hanau, Germany) and VB (Venus Bulk Fill; Heraeus Kulzer, Armonk, NY, USA), and two methods, either an incremental or bulk-fill technique. Then, the microtensile bond strengths (μ-TBSs) were measured and compared. The polymerization stresses of the composites were calculated using a custom-made device. The results were statistically analyzed using the Kruskal-Wallis test and Weibull analysis.

RESULTS:

In group I, the μ-TBS obtained using the incremental technique was significantly higher than that obtained by the bulk-fill technique ( p<0.05). In contrast, no difference of the μ-TBS value was observed between the two techniques in groups II and III. The μ-TBS value of group I was significantly lower than those of groups II and III ( p<0.05). No statistical difference in the μ-TBS was observed when the cavities were filled with either TB or VB ( p>0.05).

CONCLUSIONS:

The incremental technique showed higher bond strength than did the bulk-fill technique in high C-factor cavities. However, no difference was found between the two techniques in the low C-factor cavities. The bond strength in the high C-factor cavities was significantly lower than that of the low C-factor cavities.

In vitro fracture strength and patterns in root-filled teeth restored with different base materials

BACKGROUND

There is little research on the effects of an intermediate base on the fracture strength of root-filled teeth. This study compared the fracture strengths and patterns of root-filled teeth restored with intermediate bases of glass-ionomer cement (GIC), zinc polycarboxylate cement (ZPC), dual-cured resin composite (DCRC) and Biodentine^® under resin composite.

METHODS

Standardized cavities were prepared in 100 extracted human maxillary and mandibular premolars, and root canal treatment was performed. The teeth were stratified and randomly allocated to five groups (n = 20): (i) GIC; (ii) ZPC; (iii) DCRC; (iv) Biodentine; and (v) prepared but unrestored (control). The teeth were subjected to an oblique, ramped load until fracture. The fracture loads, level, mode and location were recorded.

RESULTS

Mean fracture strengths of all restored groups were not significantly different amongst the groups. There were significant overall effects on mean fracture strength for tooth type (P = 0.002) and buccolingual width of the crown (P = 0.001).

CONCLUSIONS

The four materials were appropriate intermediate bases. The laminate restorative technique promoted fracture strengths that are likely to withstand normal and maximum masticatory function. The base material can influence failure mode, which may have implications for the clinical presentation of fractures of root-filled teeth.

Influence of Different Curing Modes on Polymerization Behavior and Mechanical Properties of Dual-Cured Provisional Resins

This study determined the influence of curing mode on polymerization behavior and mechanical properties of dual-cured provisional resins. Three dual-cured bisacryl-based provisional resins were used: Tempsmart (TS; GC Corp), Luxatemp Automix Solar (LX; DMG Chemisch Pharmazeutishe Fabrik GmbH), and Integrity Multi·Cure (IG; Dentsply Caulk). A self-cured bisacryl-based provisional resin, Protemp Plus (PP; 3M ESPE) and a conventional poly(methyl methacrylate) (PMMA) provisional resin, Unifast III (UF; GC Corp) were used as controls. The inorganic filler content and coefficients of linear thermal expansion of the test materials were measured. Six specimens of each material were used to determine the flexural strength, elastic modulus, and resilience. The changes in ultrasound velocity during polymerization were measured. The average inorganic filler contents of the provisional resins, apart from UF, ranged from 24.4 to 39.3 wt%. The highest inorganic filler content was determined for LX, whereas TS showed the lowest value among the tested materials. The average coefficients of thermal expansion of the tested provisional resins ranged from 77.3 to 107.7 (×10^-6/°C). TS and IG showed significantly lower thermal expansions than the other tested provisional resins. The mean flexural strengths of the provisional resins ranged from 70.4 to 122.6 MPa, the mean elastic moduli ranged from 1.8 to 3.7 GPa, and the mean resilience of the provisional resins ranged from 1.1 to 2.3 MJ/mm³, respectively. Dual-cured provisional resins showed significantly higher flexural strengths than the PMMA resin. However, in all cases, the light-curing mode showed significantly higher flexural strengths than the self-curing mode. In the initial polymerization phase, dual-cured resins in the light-curing mode showed a rapid increase in the speed of sound (V) during light irradiation, followed by a slower increase. Conversely, the dual-cured resins in the self-curing mode showed a slower initial increase, followed by a rapid increase. Although no significant difference in V was observed between 10 and 15 minutes in the light-curing mode of all tested dual-cured resins, a significantly higher V value was obtained at 15 minutes than at 10 minutes in the self-curing modes for LX and IG. Regardless of the curing mode, tested dual-cured provisional resins showed superior mechanical properties than the conventional PMMA provisional resin. However, dual-cured provisional resin flexural properties and polymerization behavior were affected by the curing mode. This study indicated that the light-curing mode might be recommended for all dual-cured provisional resins because of the enhancement of their mechanical properties and reduction of chair time.

Influence of light irradiation on Vickers hardness of dual-cure cement polymerized under restorations

This study evaluated, by measuring Vickers hardness (Hv), the effects of these factors on the degree of polymerization of dual-cure cement (Panavia F2.0) placed under a restoration: light transmission property of restoratives materials, distance from the directly irradiated surface, and elapsed time after light irradiation. Two materials were used for the restoration: silver-palladium-copper-gold alloy (Alloy) versus zirconia (ZR). Restorations were cemented on bovine enamel by dual-cure cement. At 30 min, 2 h, 6 h, 1 day, and 1 week after definitive irradiation, Hv values at the enamel side of cement were evaluated at three measuring points: two points at the left and right margins and one point at the center. Data were analyzed by two-way ANOVA with Bonferroni correction (α=0.05). With the Alloy restoration, Hv value at the center was significantly lower than those at the margins at 30 min after irradiation. For both Alloy and ZR restorations, Hv value at each measuring point continued to increase significantly up to 6 h.

Bond strength to radicular dentin and sealing ability of AH Plus in combination with a bonding agent

OBJECTIVE

To evaluate the sealing ability and bond strength of AH Plus sealer associated with the hybridization protocol of radicular dentin with Scotchbond Multi Purpose (SB).

MATERIALS AND METHODS

Ninety palatal roots of maxillary molars were selected and divided into three groups (n = 30) according to filling protocol (G1, AH Plus/Resilon; G2, SB/AH Plus/Resilon; and G3, AH Plus/Gutta-Percha). In groups in which AH Plus + resin cones were used, dentin was hybridized before applying sealing material. For the bond strength test, 60 roots of bovine teeth were selected. Six holes were made in each root, two in the cervical, middle and apical third of the root. The roles were filled with AH Plus sealer with or without an adhesive system and submitted to push out test and the fracture mode was examined using a stereomicroscope (×32).

RESULTS

Statistical analysis showed that ScotchBond Multi Purpose (SB) + Resilon cone + AH Plus group promoted higher sealing ability than the gutta-percha + AH Plus group (p < 0.05). Bond strength was lower with SB application than without it (p < 0.05). A reverse correlation was found between bond strength and sealing ability. The fracture mode methodology revealed 22.77% of adhesive, 11.67% of cohesive and 65.55% of mixture fractures for SBMP/AH Plus protocol, whereas the AH Plus protocol indicated 86.11% of cohesive and 13.89% of mixed fractures.

CONCLUSION

It was concluded that the use of the adhesive system Scotchbond Multi Purpose improved coronal sealing ability of AH Plus, but bond strength of sealer was reduced when adhesive was applied.

Degree of conversion of two dentin bonding agents with and without a desensitizing agent using fourier transform infrared spectroscopy: An in vitro study

Objective:

This in vitro study investigated the effect of a desensitizer on the degree of conversion of two bonding resins using Fourier transform infrared (FTIR) spectroscopy.

Materials and Methods:

An etch-and-rise bonding resin and a self-etching adhesive resin were selected for the study. Vivasens (Ivoclar Vivadent) was used as a desensitizing agent. Grouping was done as follows: Group I: Adper Single Bond (n=10), Group II: Adper Single Bond + Vivasens (n=10), Group III: AdheSE One (n=10), Group IV: AdheSE One + Vivasens (n=10). The bonding resin alone was light cured for 20 seconds in groups I and III. For groups II and IV, 1 ml each of the bonding resin and the desensitizer was mixed in a vial and light cured for 20 seconds. The specimens were analysed using FTIR spectroscopy.

Results:

Group II (Adper Single Bond + Vivasens) showed a significantly higher degree of conversion compared to Group I (Adper Single Bond). Comparing Groups III and IV, Group IV (AdheSE One + Vivasens) showed a significantly higher degree of conversion compared to Group III (AdheSE One).

Conclusions:

The degree of conversion is increased when a dentin bonding agent is used along with a desensitizer. Hence, this combination can be recommended to effectively control postoperative sensitivity.

Effect of different light curing methods on mechanical and physical properties of resin-cements polymerized through ceramic discs

OBJECTIVE

The aim of this study was to compare the polimerization ability of three different light-curing units (quartz tungsten halogen, light-emitting diodes and plasma arc) and their exposure modes (high-intensity and soft-start) by determination of microhardness, water sorption and solubility, and diametral tensile strength of 5 dual-curing resin cements.

MATERIAL AND METHODS

A total of 720 disc-shaped samples (1 mm height and 5 mm diameter) were prepared from different dual-curing resin cements (Duolink, Nexus, Bifix-QM, Panavia F and RelyX Unicem). Photoactivation was performed by using quartz tungsten halogen (high-power and soft-up modes), light-emitting diode (standard and exponential modes) and plasma arc (normal and ramp-curing modes) curing units through ceramic discs. Then the samples (n=8/per group) were stored dry in the dark at 37°C for 24 h. The Vickers hardness test was performed on the resin cement layer with a microhardness tester (Shimadzu HMV). For sorption and solubility tests; the samples were stored in a desiccator at 37°C and weighed to a constant mass. The samples were weighed both before and after being immersed in deionized water for different periods of time (24 h and 7 days) and being desiccated. The diametral tensile strength of the samples was tested in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by nonparametric Kruskal Wallis and Mann-Whitney U tests at 5% significance level.

RESULTS

Resin cement and light-curing unit had significant effects (p<0.05) on microhardness, diametral tensile strength, water solubility and sorption. However, no significant differences (p>0.05) were obtained with different modes of LCUs.

CONCLUSION

The study indicates that polymerization of resin cements with different light-curing units may result in various polymer structures, and consequently different mechanical and physical properties.

Influence of the interaction of light- and self-polymerization on subsurface hardening of a dual-cured core build-up resin composite

OBJECTIVE

To investigate the influence of time delay and duration of photo-activation on subsurface microhardness of a dual-cured resin composite.

MATERIAL AND METHODS

A commercially available dual-cured core build-up resin composite (Rebilda DC) was filled in cavities (diameter: 4.0 mm; height: 6.0 mm) of polystyrene molds and light-cured for 20 or 60 s either immediately after the filling procedure (time delay 0 s) or after a time delay of 30, 90, 180 or 300 s. Non-irradiated self-cured specimens served as a control group (n = 15). Specimens were stored in complete darkness and at 100% relative humidity at 37°C for 2 weeks and cross-sectioned. Knoop Hardness Numbers (KHNs) were measured six times per depth and averaged at distances of 0.25, 0.50, 1.00, 2.00, 3.50 and 5.50 mm from the light-exposed surface. Data were statistically analyzed using one- and two-way ANOVA followed by Scheffé's post-hoc test at a level of significance of 0.05.

RESULTS

Mean hardness values in all experimental groups ranged between 54.3 ± 2.1 and 58.1 ± 2.3 KHN. Light-curing did not significantly increase composite KHN at any depth measured. Delaying light exposure had no influence on KHN, irrespective of depth. A longer light-exposure time (60 versus 20 s) resulted in significantly higher KHN only at depths of 3.50 and 5.50 mm.

CONCLUSION

Photo-activation of the tested dual-cured resin composite provided no clinically relevant benefit compared to self-curing regarding the degree of hardening.

Monomer Conversion in Dual-cured Core Buildup Materials

Some dual-cured core buildup materials demonstrate a very slow chemical initiation mechanism that leads to low conversion at areas distal to the activating light, providing a weak core structure during the early setting stages.

Effect of reinforcement with resin composite on fracture strength of structurally compromised roots

This study was aimed at evaluating the fracture resistance of structurally compromised roots restored with four different post and core systems. Thirty-two bovine roots were uniformly shaped to simulate human mandibular premolar roots. The roots were divided into four groups based on the type of restoration: cemented cast post and core (Group MC), resin composite build-up (Group CR), resin composite and prefabricated glass fiber post build-up (Group FRC), and thick-layer dual-cured resin composite-reinforced small-diameter tapered cast post and core (Group CRM). After a static loading test, the failure mode and fracture resistance were recorded. Group CRM (719.38+/-196.73 N) exhibited a significantly high fracture resistance compared with the other groups (Group MC: 429.56+/-82.43 N; Group CR: 349.56+/-66.21 N; Group FRC: 398.94+/-112.71 N; p<0.05). In conclusion, Group CRM exhibited better mechanical properties for structurally compromised roots with no ferrules, although all types of restorations showed non-restorable fracture modes.