Curing potential of dual-polymerizable resin cements in simulated clinical situations

Effects of a relined fiberglass post with conventional and self-adhesive resin cement

Objectives

This study was conducted to evaluate the mechanical properties of relined and non-relined fiberglass posts when cemented to root canal dentin using a conventional dual-cure resin cement or a self-adhesive resin cement.

Materials and Methods

Two types of resin cements were utilized: conventional and self-adhesive. Additionally, 2 cementation protocols were employed, involving relined and non-relined fiberglass posts. In total, 72 bovine incisors were cemented and subjected to push-out bond strength testing (n = 10) followed by failure mode analysis. The cross-sectional microhardness (n = 5) was assessed along the root canal, and interface analyses (n = 3) were conducted using scanning electron microscopy (SEM). Data from the push-out bond strength and cross-sectional microhardness tests were analyzed via 3-way analysis of variance and the Bonferroni post-hoc test (α = 0.05).

Results

For non-relined fiberglass posts, conventional resin cement exhibited higher push-out bond strength than self-adhesive cement. Relined fiberglass posts yielded comparable results between the resin cements. Type II failure was the most common failure mode for both resin cements, regardless of cementation protocol. The use of relined fiberglass posts improved the cross-sectional microhardness values for both cements. SEM images revealed voids and bubbles in the incisors with non-relined fiberglass posts.

Conclusions

Mechanical properties were impacted by the cementation protocol. Relined fiberglass posts presented the highest push-out bond strength and cross-sectional microhardness values, regardless of the resin cement used (conventional dual-cure or self-adhesive). Conversely, for non-relined fiberglass posts, the conventional dual-cure resin cement yielded superior results to the self-adhesive resin cement.

How the translucency of direct anatomic fiber posts affects the bond strength and microhardness of a self-adhesive luting agent in flared roots

OBJECTIVES

To evaluate the influence of the composite resin translucency used in direct anatomic fiber posts on the bond strength (BS) and microhardness (VHN) of a luting agent into flared roots.

MATERIALS AND METHODS

The root canals of 70 single-rooted premolars were endodontically treated and prepared to simulate an oversized root canal. Prior to post cementation, composite resins with varying translucency (high translucent, HT; medium translucent, MT; high opacity, HO) were placed around the fiber posts to create anatomic fiber posts. The attenuation profile (%) of light passing either through the post or through the anatomic posts (n = 8) was obtained prior to the cementing procedures. A positive control group (PC) in which a prefabricated fiber post (PFP) with the diameter compatible with the root canal was cemented and a poorly adapted fiber post (negative control group, NC) were also evaluated. For both tests, the data were subjected to 2-way ANOVA and Bonferroni tests (α = 0.05).

RESULTS

A more severe light attenuation through the post at the cervical (P < .001) and medium (P < 0.001) thirds was noted when less translucent composite resin surrounded the anatomic post. HO groups showed lower BS (P = .009) and VHN (P < .001) values than the other groups, regardless of root third. No significant difference in BS values was noted between PC and HT groups.

CONCLUSION

The use of a more translucent composite resin in anatomic fiber posts increased the microhardness and bond strength of a dual polymerization self-adhesive RLA compared to the use of MT and HO composite. A well-adapted PFP showed the highest adhesive and mechanical behavior.

CLINICAL RELEVANCE

Clinicians should choose more translucent composite resins to create direct anatomic fiber posts to be cemented in flared root canals. That choice may allow improved mechanical properties of self-adhesive RLA and higher bond strength to the root canal as a consequence.

Light Transmission of Various Aesthetic Posts at Different Depths and Its Effect on Push-Out Bond Strength, Microhardness of Luting Cement

Background and Objectives: One requirement for the cemented post is the light transmittance on its entire length up to the deepest portion of a root canal to ensure the complete polymerization of resin cement. This study aimed to determine the light transmission ability in different aesthetic posts at different depths and its effect on the push-out bond strength and microhardness of luting cement at the corresponding interface. Materials and Methods: Twenty endodontic posts from glass fiber posts (GFP), zirconia ceramic posts (ZCP), and highly translucent zirconium oxide posts (HTZP) were sequentially sectioned into 12.8 and 4 mm lengths after recording the light intensity using a dental radiometer. Sixty single rooted premolar teeth root canals were treated and implanted vertically in a resin block. The post space was prepared and cemented with GFP, ZCP, and HTZP posts with twenty samples each. The root portion of teeth samples were sectioned into cervical, middle, and apical portion. A universal testing machine was utilized for the push-out bond strength test for the first ten samples from each group. The remaining ten samples from each group were used for the microhardness test using a micro-indenter instrument. The data were statistically analyzed using one-way Analysis of variance and Tukey HSD tests at p < 0.05. Results: The GFP endodontic postpresented with significant highest light translucency compared to HTZP, which was significantly higher than ZCP. GFP posts showed significantly higher bond strength per unit area compared to ZCP at analogous cross sections. The hardness of luting cement was also significantly higher amongst all tested endodontic posts. Conclusions: GFP high light translucency enhanced the curing of the luting resin cement that resulted in harder cement and a stronger bond supported by hardness and push-out tests. These findings suggest that GFP is preferred to be used with light-cured luting cements for restoration of endodontically treated teeth.

Influence of curing modes on conversion and shrinkage of dual-cure resin-cements

OBJECTIVE

To explore the effect of curing modes of dual-cure resin cements on their degree of conversion (DC) and polymerization shrinkage (PS) over specific post-activation periods.

METHODS

Five self-adhesive (PANAVIA SA, RelyX Universal Resin, RelyX Unicem 2, Bifix SE, and SpeedCEM Plus) and three conventional (PANAVIA V5, Nexus Third Generation, and RelyX Ultimate Universal) dual-cure resin cements were studied. Four specimens (n = 4) were made per curing mode (light/self-cure) to measure either DC or PS. FTIR was utilized to measure real-time DC (%) over 24 h. The Bonded Disk method was used to measure shrinkage at 23 °C over 1 h. The data were analyzed using one-way ANOVA, Tukey post-hoc tests and independent/ paired sample t-tests (a = 0.05).

RESULTS

After 1 h post-activation, the DC of light-cured (LC) specimens ranged between 66.6% and 77.4%, whereas for self-cured (SC) specimens DC ranged between 44.4% and 73.2%. After 24 h, the DC of LC specimens ranged between 74.8% and 82.4% and between 62.7% and 81.7% for SC specimens. After 24 h, the DC of three cements (BSE, PV5, and RXU) were comparable between their curing modes (p > 0.05), whereas five cements (CEM, NX3, PSA, RXU2, RXL) had significantly lower DC for SC compared to LC specimens (p < 0.05). After 1 h post-activation, shrinkage ranged between 5.9% and 8.5% for LC and between 4.9% and 8.3% for SC specimens. Most cements were not significantly different between curing modes. However, light-cured PAS, RXL and RXU2 had significantly higher shrinkage (p < 0.05). After 1 h post-activation, a strong positive correlation existed between conversion and shrinkage (LC: r² = 0.95 and SC: r² = 0.93).

SIGNIFICANCE

Whenever light access is possible, light-curing of resin-cements remains beneficial to the overall efficacy of their conversion and thus all factors that depend on that. Conversion and shrinkage behavior are intrinsically important factors in clinical selection of resin-cement products.

Influence of Ambient Temperature and Light-curing Moment on Polymerization Shrinkage and Strength of Resin Composite Cements

Objective:

The purpose of this study was to establish a clinically appropriate light-curing moment for resin composite cements while achieving the highest indirect tensile strength and lowest polymerization shrinkage.

Methods and Materials:

Polymerization shrinkage of seven resin composite cements (Multilink Automix, Multilink Speed Cem, RelyX Ultimate, RelyX Unicem 2 Automix, Panavia V5, Panavia SA plus, VITA Adiva F-Cem) was measured at ambient temperatures of 23°C and 37°C. Testing was done for autopolymerized and light-cured specimens after light application at either 1, 5, or 10 minutes after mixing. Indirect tensile strength of all cements was measured after 24 hours of storage at temperatures of 23°C and 37°C, for autopolymerized and light-cured specimens after light application 1, 5, or 10 minutes after mixing. To illustrate filler size and microstructures, SEM images of all cements were captured. Statistical analysis was performed with one-way ANOVA followed by post hoc Fisher LSD test (α=0.05).

Results:

Final polymerization shrinkage of the resin composite cements ranged from 3.2% to 7.0%. An increase in temperature from 23°C to 37°C as well as the light-curing moment resulted in material dependent effects on the polymerization shrinkage and indirect tensile strength of the cements. Polymerization shrinkage of the cements did not correlate with the indirect tensile strength of the cement in the respective groups. Highest indirect tensile strengths were observed for the materials containing a homogeneous distribution of fillers with a size of about 1 μm (Multilink Automix, Panavia V5, VITA Adiva F-Cem).

Conclusion:

The magnitude of the effect of light-curing moment and temperature increase on polymerization shrinkage and indirect tensile strength of resin composite cements is material dependent and cannot be generalized.

Effect of aging and curing mode on the compressive and indirect tensile strength of resin composite cements

BACKGROUND

Resin composite cements are used in dentistry to bond ceramic restorations to the tooth structure. In the oral cavity these cements are subjected to aging induced by masticatory and thermal stresses. Thermal cycling between 5 and 55 °C simulates the effect of varying temperatures in vitro. Purpose of this study was to compare indirect tensile to compressive strength of different cements before and after thermal cycling. The effect of the curing mode was additionally assessed.

METHODS

Indirect tensile strength and compressive strength of 7 dual-curing resin composite cements (Multilink Automix, Multilink SpeedCem, RelyX Ultimate, RelyX Unicem 2 Automix, Panavia V5, Panavia SA Plus, Harvard Implant semi-permanent) was measured. The specimens were either autopolymerized or light-cured (n = 10). The mechanical properties were assessed after 24 h water storage at 37 °C and after aging (20,000 thermo cycles) with previous 24 h water storage at 37 °C.

RESULTS

Indirect tensile strength ranged from 5.2 ± 0.8 to 55.3 ± 4.2 MPa, compressive strength from 35.8 ± 1.8 MPa to 343.8 ± 19.6 MPa.

CONCLUSIONS

Thermocyclic aging of 20,000 cycles can be considered a suitable method to simulate the degradation of indirect tensile strength but not compressive strength of resin composite cements. The effect of thermocycling and the curing mode on the resin composite cements is material dependent and cannot be generalized.

Effect of activation modes on the compressive strength, diametral tensile strength and microhardness of dual-cured self-adhesive resin cements

The purpose of this study was to compare the compressive strength, diametral tensile strength and microhardnss of several selfadhesive resin cements (Rely-X U200, Clearfill SA Luting, G-CEM LinkAce, Maxcem Elite, PermaCem 2.0, and Zirconite) using different activation modes (self-cured, light-cured) and testing time (immediately, 24 h, thermocycling). Specimens were prepared for the compressive strength (Ø 4×6 mm) and diametral tensile strength and microhardness (Ø 6×3 mm) according to ISO standards. The strength after 24 h was higher than immediately after. In addition, G-CEM showed the highest values. In terms of the activation modes, Rely-X U200, PermaCem 2.0 had higher values in the light-curing than the self-curing. In conclusion, all cements demonstrated clinically available strength values and revealed differences in strength according to their composition, testing time and activation mode. Furthermore, correlation was found between the microhardness (degree of conversion) and mechanical strengths of the cements tested.

Universal cements: dual activated and chemically activated

Objective: The aim of the present study was to assess the bond strength of universal cements cured either dually or chemically only.

Methods: Three cements were assessed using different types of application: dual activated (DA) or chemically activated (CA). In total 80 dentin blocks were used, obtained through the enamel wear of the lingual and buccal surfaces of bovine incisors. Standard cone-shaped cavity preparations were created using diamond burs. Subsequently, indirect restoration blocks were designed with Filtek Z350 (3M ESPE) composite resin. The teeth were divided into two groups (DA and CA) and then subdivided into four subgroups (n = 10) prior to cementation with the respective products: Duo-Link (Bisco); RelyX Ultimate (3M ESPE); Nexus 3 (Kerr) and conventional RelyX ARC (3M ESPE) as the control. The cementation in the PA group was applied following the manufacturer’s instructions. The CA group was cemented in a darkroom to avoid exposure to light. They were stored in distilled water at 37 °C for 24 h and submitted to the push-out test. Data were analyzed by two-way ANOVA and Tukey’s post-hoc test (p < .05).

Results: The greatest bond strength results were obtained for photoactivated universal cements.

Conclusion: Chemical activation is not sufficient to ensure acceptable bond strength.

Influence of luting agent translucency on fiber post retention

The aim was to assess the influence of cement translucency on the retentive strength of luted fiber posts. Twenty extracted human premolars were randomly divided into four equal groups, based on the combinations of materials to be tested. Two post types of the same size, shape, and chemical composition, but different light-transmission properties [Translucent post (TP) and Opaque post (OP)] were selected. The two post types were luted using the etch-and-rinse, light-curing adhesive in combination with two shades of the same resin cement of markedly different light-transmitting ability [Transparent shade (TS) and Opaque shade (OS)]. Early post retention was assessed using the thin-slice push-out test. Post type did not significantly influence post retention; however, cement translucency emerged as a relevant factor in intraradicular cementation, with the TS achieving higher push-out strengths. The between-factor interaction was also statistically significant; specifically, OP-OS yielded significantly lower retentive strengths than all the other groups. Post translucency did not influence post retention, provided that a highly translucent cement was utilized for luting.

Evaluation of removal forces of implant-supported zirconia copings depending on abutment geometry, luting agent and cleaning method during re-cementation

PURPOSE

To evaluate the effects of different abutment geometries in combination with varying luting agents and the effectiveness of different cleaning methods (prior to re-cementation) regarding the retentiveness of zirconia copings on implants.

MATERIALS AND METHODS

Implants were embedded in resin blocks. Three groups of titanium abutments (pre-fabricated, height: 7.5 mm, taper: 5.7°; customized-long, height: 6.79 mm, taper: 4.8°; customized-short, height: 4.31 mm, taper: 4.8°) were used for luting of CAD/CAM-fabricated zirconia copings with a semi-permanent (Telio CS) and a provisional cement (TempBond NE). Retention forces were evaluated using a universal testing machine. Furthermore, the influence of cleaning methods (manually, manually in combination with ultrasonic bath or sandblasting) prior to re-cementation with a provisional cement (TempBond NE) was investigated with the pre-fabricated titanium abutments (height: 7.5 mm, taper: 5.7°) and SEM-analysis of inner surfaces of the copings was performed. Significant differences were determined via two-way ANOVA.

RESULTS

Significant interactions between abutment geometry and luting agent were observed. TempBond NE showed the highest level of retentiveness on customized-long abutments, but was negatively affected by other abutment geometries. In contrast, luting with Telio CS demonstrated consistent results irrespective of the varying abutment geometries. Manual cleaning in combination with an ultrasonic bath was the only cleaning method tested prior to re-cementation that revealed retentiveness levels not inferior to primary cementation.

CONCLUSION

No superiority for one of the two cements could be demonstrated because their influences on retentive strength are also depending on abutment geometry. Only manual cleaning in combination with an ultrasonic bath offers retentiveness levels after re-cementation comparable to those of primary luting.

Microhardness of dual-polymerized resin cement around a translucent fiber post in the intraradicular environment

Aim:

In this study, we evaluated the effect of photopolymerization on Vickers microhardness of dual-polymerized resin cement at three locations when a translucent quartz fiber post was used.

Materials and Methods:

Single-rooted bovine teeth received quartz fiber post systems (length: 12 mm) using a dual-polymerized resin cement. In Group 1, the posts were cemented but not photopolymerized, and in Group 2, the posts were both cemented and photopolymerized. After cementation, approximately 1.5-mm thick sections were obtained (two cervical, two middle, and two apical) for regional microhardness evaluations.

Statistical Analysis:

Statistical analyses were performed using the SPSS software (ver. 11.0 for Windows; SPSS, Inc., Chicago, IL, USA). Microhardness (kg/mm²) data were submitted to two-way analysis of variance (two-way ANOVA) and repeated measures with microhardness values as the dependent variable and polymerization status (two levels: with and without) and root region (three levels: cervical, middle, and apical) as independent variables. Multiple comparisons were made using Dunnett's T3 post-hoc test. P values of <0.05 were considered to indicate statistical significance in all tests.

Results:

Photopolymerization did not significantly change the microhardness values when compared with no photopolymerization. Microhardness values also showed no significant difference between the three regions in the root canals in both groups.

Conclusions:

The mode of polymerization of the cement tested in combination with the translucent quartz fiber post system did not affect the microhardness of the cement at the cervical, middle, or apical regions of the root.

Current perspectives on post systems: a literature review

This literature review summarizes the most recent and reliable evidence on post systems. A search was limited to review articles published over the last 10 years in dental journals with an impact factor. Papers cited in the initially retrieved review articles were also included if significant. Preservation of tooth tissue, presence of a ferrule effect, and adhesion are regarded as the most effective conditions for long-term success of post-endodontic restorations. Adhesively luted fibre-reinforced composite post restorations have demonstrated satisfactory survival rates over relatively long follow-up periods. The clinical effectiveness of such restorations has been mainly ascribed to the more biomimetic behaviour of fibre-reinforced composite posts that reduces the risk of vertical root fractures. The most common type of failure when using fibre posts is post debonding and it is generally agreed that achieving stable adhesion to intraradicular dentine is more challenging than to coronal dentine. Several factors related to endodontic treatment, root canal shape, post space preparation, post translucency, adhesive cement handling and curing may have an influence on the outcome of the luting procedure. The most reliable results in fibre post cementation are obtained by etch-and-rinse adhesives in combination with dual-cure resin cements. The use of self-adhesive resin cements has also been proposed. Simplification is an obvious advantage of these new materials. However, the durability of their bond still needs to be verified with long-term clinical studies. Several techniques for pre-treating the fibre-reinforced composite post surface have been tested with the aim of improving the bond strength at the post-core and post-cement interfaces. Silicoating followed by silanization currently appears to be the most effective and convenient method for this purpose. In conclusion, the available evidence validates the use of fibre posts as an alternative to metal posts and preferably to other tooth-coloured posts, such as zirconia dowels, in the restoration of endodontically treated teeth. Longer term clinical trials are expected to further strengthen this evidence.

Bond strength durability of self-etching adhesives and resin cements to dentin

OBJECTIVES

To evaluate the microtensile bond strength (microTBS) of one- (Xeno III, Dentsply) and two-step (Tyrian-One Step Plus, Bisco) self-etching adhesive systems bonded to dentin and cemented to chemically cured (C&B Metabond) or light-cured paste of a dual-cure resin cement (Variolink II, Ivoclar) within a short (24 h) and long period of evaluation (90 days).

MATERIAL AND METHODS

Forty recently extracted human molars had their roots removed and their occlusal dentin exposed and ground wet with 600-grit SiC paper. After application of one of the adhesives, the resin cement was applied to the bonded surface and a composite resin block was incrementally built up to a height of 5 mm (n=10). The restored teeth were stored in distilled water at 37 degrees C for 7 days. The teeth were then cut along two axes (x and y), producing beam-shaped specimens with 0.8 mm(2) cross-sectional area, which were subjected to microTBS testing at a crosshead speed of 0.05 mm/min and stressed to failure after 24 h or 90 days of storage in water. The microTBS data in MPa were subjected to three-way analysis of variance and Tukey's test (alpha= 0.05).

RESULTS

The interaction effect for all three factors was statistically significant (three-way ANOVA, p<0.001). All eight experimental means (MPa) were compared by the Tukey's test (p<0.05) and the following results were obtained: Tyrian-One Step Plus /C&B/24 h (22.4+/-7.3); Tyrian-One Step Plus /Variolink II/24 h (39.4+/-11.6); Xeno III/C&B/24 h (40.3+/-12.9); Xeno III/Variolink II/24 h (25.8+/-10.5); Tyrian-One Step Plus /C&B/90 d (22.1+/-12.8) Tyrian-One Step Plus/VariolinkII/90 d (24.2+/-14.2); Xeno III/C&B/90 d (27.0+/-13.5); Xeno III/Variolink II/90 d (33.0+/-8.9).

CONCLUSIONS

Xeno III/Variolink II was the luting agent/adhesive combination that provided the most promising bond strength after 90 days of storage in water.

Microhardness of resin cements in the intraradicular environment: effects of water storage and softening treament

OBJECTIVES

To analyze the microhardness of four dual-cure resin cements used for cementing fiber-reinforced posts under the following conditions: after 7 days of storage in water, after additional 24h of immersion in 75% ethanol, and after 3 months of storage in water. Hardness measurements were taken at the cervical, middle and apical thirds along the cement line.

METHODS

Root canals of 40 bovine incisors were prepared for post space. Fibrekor glass fiber-reinforced posts (Jeneric/Pentron) of 1mm in diameter were cemented using Panavia F 2.0 (Kuraray), Variolink (Ivoclar-Vivadent), Rely X Unicem (3M ESPE) or Duolink (Bisco) (N=10). After 7 days of water storage at 37 degrees C, half the sample (N=5) was longitudinally sectioned and the initial microhardness measured along the cement line from cervical to apex. These same samples were further immersed in 75% ethanol for 24h and reassessed. The remaining half (N=5) was kept unsectioned in deionized water at 37 degrees C for 3 months, followed by sectioning and measuring. Data were analyzed by a series of two-way ANOVA and Tukey tests at alpha=5%.

RESULTS

Statistically significant differences were identified among the cements, thirds and conditions. Significant interactions were also observed between cements and thirds and between cements and conditions. Panavia F exhibited significantly higher initial microhardness than the other three cements, which showed no statistical difference among themselves. Variolink and Duolink showed significantly higher microhardness values in the cervical third, without significant difference among the thirds for the other cements. Immersion in ethanol significantly reduced the hardness values for all cements, regardless of the thirds. Storage in water for 3 months had no influence on the hardness of most of the cements, with the exception of Unicem that showed a significant increase in the hardness values after this period.

SIGNIFICANCE

Results showed heterogeneity in the microhardness of the cements inside the canal. All cements presented some degree of softening after ethanol treatment, which suggests instability of the polymer. The quality of curing of resin cements in the root canal environment seems unpredictable and highly material dependent.

Cements for use in esthetic dentistry

Dental cements are designed to retain restorations, appliances, and post and cores in a stable and, presumably, long-lasting position in the oral environment. Conventional glass ionomer and zinc phosphate cements are among the most popular materials for luting metallic restorations and posts, whereas resin-based cements are preferred for esthetic applications. Successful cementation of esthetic restorations is largely dependent on the appropriate treatment and silane application to the internal surface of the restoration. Clinicians are frequently advised to use three-step total-etch or two-step self-etch adhesive for luting purposes to avoid problems of incompatibility between adhesives and chemical- or dual-cure cements. A reliable cementation procedure can only be achieved if the operator is aware of the mechanisms involved and the material limitations.

Effect of different bonding procedures on micro-tensile bond strength between a fiber post and resin-based luting agents

The purpose of this study was to evaluate the effect of silanization and light-irradiation on bonding between a fiber post and different resin-based luting agents. Sixty silicium fiber posts (Easy Post) were divided into 10 groups according to the type of resin-based luting agent employed, whether the post surface was silanized, whether the adhesive was light-irradiated, and whether Calibra luting agent was used. The micro-tensile bond strength and bonded interface of specimens in each group were evaluated. Specimens luted with Calibra or FluoroCore 2 resin-based luting agent systems were superior to those treated with Multilink or Variolink II, in terms of both bond strength and interfacial integrity. Application of silane, light-irradiation of the adhesive, or light-irradiation of the Calibra resin-based luting agent did not significantly increase the bond strength further. It can be concluded that Calibra or FluoroCore 2 resin-based luting agent systems are more suitable for luting prefabricated Easy Post in a clinical situation, while pre-silanization of the post surface and light-irradiation of XP Bond/SCA adhesive or resin-based luting agent may not be as important as hitherto considered.

Bonding of lithium-disilicate ceramic to enamel and dentin using orthotropic fiber-reinforced composite at the interface

OBJECTIVE

To evaluate the effect of orthotropic fiber-reinforced composite (FRC) at the interface on bonding of lithium-disilicate ceramic to dentin and enamel using different adhesive systems.

MATERIAL AND METHODS

Dentin and enamel surfaces were ground occlusally on human molar teeth. Ceramic blocks of IPS Empress 2 (Ivoclar-Vivadent) were fabricated. Following acid etching and silane treatment of the ceramics, the teeth were divided into two groups (dentin and enamel). Ceramic blocks were bonded to the tooth substance with or without a layer of FRC and dual-polymerizing composite cement (Duolink). Total-etching (etchant (Etch 37) with adhesive (One Step Plus)) and self-etching (self-priming etchant (Tyrian SPE) with adhesive (One Step Plus)) systems were used, with five test specimens in each group. The cement was polymerized with a LED curing unit (Elipar Freelight LED 2) with standard mode of 40 s. The specimens were thermocycled for 6000 cycles and tested with the microtensile tester at a rate of 5 mm/min. Fracture mode analyses were done by light microscope and with SEM. The data were analyzed using three-way analysis of variance (ANOVA).

RESULTS

ANOVA showed that enamel had statistically significant (p<0.001) higher bond strength values than dentin. Bond strength values were significantly higher (p=0.012) with the total-etching system than with the self-etching system. The existence of FRC also had a minor effect on bond strength values (p=0.013).

CONCLUSIONS

The enamel and total-etching system provided more reliable bonding than dentin and the self-etching system. Use of an FRC layer at the interface did not improve bond strength values, but instead changed fracture pattern behavior.

Hardness Development of Dual-cured Resin Cements through Different Thicknesses of Ceramics

This study investigated the Knoop hardness of a thin layer in three dual-cured resin cements (Linkmax HV, Nexus 2, and Variolink II HV) irradiated through or not through different thicknesses (1 through 5 mm) of a machinable ceramic. Hardness was recorded at a series of time intervals up to five days, starting from the end of a light irradiation period. Increase in hardness was more rapid over the first 0.5 hour; thereafter it continued at a low rate until maximum hardness was attained. Ceramic thickness had a significant influence on hardness in all dual-cured resin cements, especially when ceramic thickness was more than 4 mm. In addition, it was noted that the polymerization of Nexus 2 seemed to be more dependent on light exposure compared with the other two materials. Variolink II HV and Linkmax HV, on the other hand, seemed to indicate the potential of being compensated by chemical curing to some degree.

Influence of activation modes on diametral tensile strength of dual-curing resin cements

In metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. The effect of the lack of photoactivation on the strength of these cements has been rarely studied. This study evaluated the influence of activation modes on the diametral tensile strength (DTS) of dual-curing resin cements. Base and catalyst pastes of Panavia F, Variolink II, Scotchbond Resin Cement, Rely X and Enforce were mixed and inserted into cylindrical metal moulds (4 x 2 mm). Cements were either: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated through mylar strips (chemical and photo-activation = dual-cured groups) (n = 10). After a 24 h storage in 37ºC distilled water, specimens were subjected to compressive load in a testing machine. A self-curing resin cement (Cement-It) and a zinc phosphate cement served as controls. Comparative analyses were performed: 1) between the activation modes for each dual-curing resin cement, using Student’s t test; 2) among the self-cured groups of the dual-curing resin cements and the control groups, using one-way ANOVA and Tukey’s test (alpha = 0.05). The dual-cured groups of Scotchbond Resin Cement (53.3 MPa), Variolink II (48.4 MPa) and Rely X (51.6 MPa) showed higher DTS than that of self-cured groups (44.6, 40.4 and 44.5 MPa respectively) (p < 0.05). For Enforce (48.5 and 47.8 MPa) and Panavia F (44.0 and 43.3 MPa), no significant difference was found between the activation modes (p > 0.05). The self-cured groups of all the dual-curing resin cements presented statistically the same DTS as that of Cement-It (44.1 MPa) (p > 0.05), and higher DTS than that of zinc phosphate (4.2 MPa). Scotchbond Resin Cement, Variolink II and Rely X depended on photoactivation to achieve maximum DTS. In the absence of light, all the dual-curing resin cements presented higher DTS than that of zinc phosphate and statistically the same as that of Cement-It (p > 0.05).

Influence of ceramic thickness and polymerization mode of a resin luting agent on early bond strength and durability with a lithium disilicate–based ceramic system

STATEMENT OF PROBLEM

Attenuation of polymerization light energy by translucent all-ceramic materials may result in insufficient polymerization of underlying resin luting agents and inadequate early bond strength and durability. There is little information regarding the selection of an appropriate polymerization mode for cementing translucent all-ceramic restorations.

PURPOSE

The purpose of this study was to evaluate the influence of ceramic thickness and polymerization mode on the early bond strength and bond durability of a lithium disilicate-based ceramic system.

MATERIAL AND METHODS

The occlusal surfaces of 120 extracted, intact, human third molars were sectioned to expose a flattened area of dentin. The surface was etched with 32% phosphoric acid, and a single-step adhesive (One-Step) was applied to the etched dentin surfaces. Ceramic specimens (Empress 2), 6 mm in diameter and 1 mm, 1.5 mm, or 2 mm thick (n=40 per group), were fabricated using fluoropolymer resin matrixes. Each specimen was ground flat. Following hydrofluoric acid etching and silane treatment, ceramic discs of each thickness were further divided into 2 groups (n=20 per group) and bonded to the dentin surfaces with a dual-polymerized resin luting agent (Illusion), either with a catalyst (dual polymerization) or without a catalyst (light polymerization). A shear bond test was performed after 10 minutes (n=10) or after 24 hours following 1000 thermal cycles between 5 degrees C and 55 degrees C and a dwell time of 30 seconds (n=10). Debonded dentin surfaces were examined with SEM. The data were analyzed with 3-way analysis of variance (ANOVA) (alpha=.05).

RESULTS

The shear bond strengths ranged between 13.2 +/- 4.1 MPa and 15.9 +/- 2.0 MPa. Three-way ANOVA revealed that ceramic thickness, polymerization mode, storage time, or combinations of these parameters did not influence shear bond strength. The location of failure for all specimens was adhesive, between the dentin surface and bonding agent.

CONCLUSION

Both light polymerization and dual polymerization provided similar early shear bond strengths for the lithium disilicate-based ceramic system (Empress 2). The bond strength was not dependent on the thickness of the ceramic material tested. Durability of the bond was similar for both of the polymerization modes.

The influence of chemical activation on hardness of dual-curing resin cements

During the cementation of metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. This study evaluated the influence of chemical activation compared with dual-curing (chemical and light activation), on the hardness of four dual-curing resin cements. In a darkened environment, equal weight proportions of base and catalyst pastes of the cements Scotchbond Resin Cement, Variolink II, Enforce and Panavia F were mixed and inserted into moulds with cavities of 4 mm in diameter and 2 mm in height. Subsequently, the cements were: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated (dual-curing = dual-cured groups). The Vickers hardness number was measured at 1 hour, 24 hours and 7 days after the start time of cements' spatulation. For all the cements, the hardness values of self-cured groups were lower than those of the respective dual-cured groups at 1 hour and 24 hours. At 7 days, this behavior continued for Variolink II and Panavia F, whilst for Scotchbond Resin Cement and Enforce there was no statistical difference between the two activation modes. All cements showed a significant increase in their hardness values from 1 hour to 7 days for both activation modes. Of the self-cured groups, Scotchbond Resin Cement and Variolink II presented the highest and the lowest hardness values, respectively, for all three times tested. Within the limitations of this study, up to the time of 24 h, chemical activation alone was unable to promote similar hardness as to that obtained with dual-curing.

Properties of dual-curable luting composites polymerized with single and dual curing modes

The purpose of this study was to evaluate the influence of visible-light exposure on water absorption, solubility and colour stability of dual-curable luting composites. Using eight dual-curable luting composites (2bond2, Bistite II, G-CERA Cosmotech II, Imperva Dual, Linkmax, Lute-It, Panavia Fluoro Cement and Variolink II), disk specimens were prepared by the following two methods: (i) dual-cured specimens; exposed with visible-light from a light-curing unit, and (ii) chemical-cured specimens; chemically polymerized without exposure. Five specimens were produced for each material and curing mode. Water absorption and solubility were determined according to standardized testing methods, and the data were compared using analysis of variance (ANOVA) and contrasts. With regard to colour stability, the colour difference (DeltaE*) values between 24 h and the other immersion periods (1, 2, 3, 4, 8, 12, 16, 20 and 24 weeks) were calculated and then analysed by repeated measure ANOVA. The dual-cured specimens exhibited significantly lower solubility values than the chemical-cured specimens except for the Lute-It material. The dual-cured Linkmax material exhibited the lowest solubility (0.51 +/- 0.01 microg mm(-3)) and the lowest DeltaE* value after 24 weeks (2.64 +/- 0.39). The dual-curable luting composites should be light-exposed after seating of restorations in order to reduce water absorption and solubility, and to improve colour stability.

In vitro wear simulation measurements of composite versus resin-modified glass ionomer luting cements for all-ceramic restorations

BACKGROUND

Although composite cements are generally indicated for cementation of all-ceramic restorations, some manufacturers of dental cements propose that resin-modified glass ionomers (RMGIs) may be used for cementation of high-strength ceramic restorations.

PURPOSE

This study was undertaken to compare the in vitro abrasion and attrition wear of two dual-cure cements (in dual-cure and self-cure modes) and two RMGI cements when placed between ceramic and enamel to simulate the margin of a restoration.

METHODS

Rectangular fragments of pressed ceramic (Empress 2) were cemented between the halves of bovine incisors sectioned mesiodistally, using one of the following materials: RelyX ARC, Variolink II, RelyX Luting, or ProTec CEM. The two resin cements were tested in dual-cure and self-cure modes. A three-body wear test was performed in the new Oregon Health Sciences University (OHSU) oral wear simulator (100,000 cycles; abrasion load: 20 N; attrition load: 90 N). Degree of conversion of resin cements was determined by Fourier transform infrared spectroscopy. Results were analyzed by analysis of variance and Tukey's test (p = .05). Epoxy replicas of wear specimens were observed in the scanning electron microscope.

RESULTS

No significant differences in abrasion wear (RelyX ARC dual-cure: 11 +/- 4.4 microm; RelyX ARC self-cure: 17 +/- 7.0 microm; Variolink dual-cure: 14 +/- 8.6 microm; Variolink self-cure: 23 +/- 10.7 microm) or attrition wear (RelyX ARC dual-cure: 18 +/- 6.4 microm; RelyX ARC self-cure: 31 +/- 4.5 microm; Variolink dual-cure: 32 +/- 6.8 microm; Variolink self-cure: 39 +/- 15.9 microm) were found between activation modes of the resin cements. ProTec CEM (32 +/- 8.7 microm) showed abrasion similar to that of Variolink II and RelyX ARC self-cure. Resin-modified glass ionomers showed more attrition wear than the resin cements (ProTec CEM: 62 +/- 13.0 microm; RelyX Luting: 69 +/- 7.1 microm). RelyX ARC showed a similar degree of conversion for both activation modes (dual-cure: 70 +/- 4.3%; self-cure: 68 +/- 1.2%), but Variolink II had a higher degree of conversion in dual-cure mode (67 +/- 0.5% vs 60 +/- 1.0%). Cement wear was accompanied by marginal breakdown and increased surface roughness of enamel and ceramic.

CONCLUSIONS

The activation mode of resin cements did not influence their wear resistance. The RMGIs underwent higher attrition wear than the resin cements.

CLINICAL SIGNIFICANCE

Increased submargination associated with marginal breakdown and increased roughness of the surrounding structures may be expected when ceramic inlays are cemented with resin-modified glass ionomers.