pH neutralization and influence on mechanical strength in self-adhesive resin luting agents

Degree of conversion of dual-cured composite luting agents: The effect of transition metal-based touch-cure activators

PURPOSE

The aim of the study was (a) to assess the effect of universal adhesives and tooth primers with novel touch-cure activators on the conversion of dual-cured resin composite luting agents (RLAs) polymerized under the self-curing mode, and (b) to investigate the source of the catalytic effect exerted by the activators.

MATERIALS AND METHODS

The materials selected were the adhesive RLAs Panavia V5/Tooth Primer (PV5/TP5), Variolink Esthetic DC/Adhese Universal DC (VLE/ADC), and the self-adhesive RLAs GCem ONE/AE Primer (GCO/AEP), RelyX Universal/Scotchbond Universal Plus (RXU/SUP) and Panavia SA Universal/Clearfil Universal Bond Quick (PSU/CUQ), the later serving as a control with an aryl-sulfinate activator. Coronal dentin specimens were prepared (n = 5/material), treated with the corresponding primers/adhesives (non-irradiated) and covered with a 100 μm-thick RLA layer (SC+A group). Three specimen series were additionally prepared (n = 3 × 5/material): A self-cured without the primers/adhesives (SC group), a dual-cured (20 s irradiation) with the corresponding primers/adhesives (DC+A group) and a dual-cured without primers/adhesives (DC group). All specimens were stored for 15 min (37 °C/dark/60 %RH). After demolding the degree of C = C conversion (DC%, top RLA surfaces) was measured by ATR-FTIR spectroscopy. The primer/adhesive liquids were further analyzed by ICP-MS and the microbrush tips of ADC by SEM-EDS.

RESULTS

The touch-cure activators increased the DC% in all self-cured RLAs but failed to reach the values of the corresponding dual-cured RLAs. The effect of the activators in dual-cured specimens was negligible. The ICP-MS analysis showed the presence of V (AEP, TP5, ADC) and Cu (SUP) transitional metals in the activators, with V been located at the free ends of ADC tip bristles. The V activators demonstrated the highest DC% improvement in self-cured specimens.

CONCLUSION

The new touch-cure activators significantly increased the conversion of the self-cured RLAs. Therefore, this step should be considered as universally applicable and not selective, as currently proposed for the self-adhesive luting agents by the manufacturers.

Effect of Luting Materials on the Accuracy of Fit of Zirconia Copings: A Non-Destructive Digital Analysis Method

The marginal accuracy of fit between prosthetic restorations and abutment teeth represents an essential aspect with regard to long-term clinical success. Since the final gap is also influenced by the luting techniques and materials applied, this study analyzed the accuracy of the fit of single-tooth zirconia copings before and after cementation using different luting materials. Forty plaster dies with a corresponding zirconia coping were manufactured based on a single tooth chamfer preparation. The copings were luted on the plaster dies (n = 10 per luting material) with a zinc phosphate (A), glass-ionomer (B), self-adhesive resin (C), or resin-modified glass-ionomer cement (D). The accuracy of fit for each coping was assessed using a non-destructive digital method. Intragroup statistical analysis was conducted using Wilcoxon signed rank tests and intergroup analysis by Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). Accuracy of fit was significantly different before/after cementation within A (0.033/0.110 µm) and B (0.035/0.118 µm; p = 0.002). A had a significantly increased marginal gap compared to C and D, and B compared to C and D (p ≤ 0.001). Significantly increased vertical discrepancies between A and B versus C and D (p < 0.001) were assessed. Of the materials under investigation, the zinc phosphate cement led to increased vertical marginal discrepancies, whereas the self-adhesive resin cement did not influence the restoration fit.

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.

Comparing Various Resin Luting Cement Systems in Different Etching Modes Through Bond Durability and Morphological Features

OBJECTIVES

This study aimed to investigate bond performance of various resin luting cement (RLC) systems on enamel and dentin in different etching modes and to compare the RLC-tooth interface morphology using scanning electron microscopy (SEM).

METHODS AND MATERIALS

The self-adhesive RLC systems used in combination with universal adhesives were as follows: Scotchbond Universal Adhesive Plus + RelyX Universal (3M Oral Care) and Clearfil Universal Bond Quick ER + SA Luting Multi (Kuraray Noritake Dental). These RLC systems were also used alone as self-adhesive RLC systems without universal adhesives (self-adhesive mode). The conventional RLC systems for comparison materials were as follows: BeautiBond Xtream + ResiCem EX (Shofu) and Tooth Primer + Panavia V5 (Kuraray Noritake Dental). Twelve specimens were prepared for each group to measure shear bond strength (SBS) in different etching modes. A stainless-steel rod was used as a substitute for indirect restorations. Bonded specimens were allocated to baseline (stored for 24 hours) and artificially aged (thermocycling [TC] for 10,000 cycles) groups. Representative treated tooth surfaces and RLC-tooth interfaces were observed using SEM.

RESULTS

Three-way analysis of variance (ANOVA) revealed that all the factors (etching mode, storage period, and RLC system) had a significant influence on the enamel SBS values (p<0.05). Enamel SBS was significantly higher in etch-&-rinse (ER) mode than in self-etch (SE) mode, regardless of RLC system or storage period. Three-way ANOVA showed that all the factors had a significant influence on the dentin SBS values (p<0.001). Most RLC systems showed significantly higher dentin SBS in SE mode than in ER mode, regardless of storage period. However, the combination with Scotchbond Universal Adhesive Plus and RelyX Universal showed no significant difference in SBS values between etching modes at the baseline and showed a significantly higher SBS value in ER mode than in SE mode after TC.

CONCLUSIONS

The self-adhesive RLC systems with universal adhesives tended to show higher enamel and dentin bond performance than the self-adhesive RLC systems alone. The morphology of treated tooth surfaces and resin cement-tooth interfaces were dependent on the RLC system and etching mode used. The RLC systems with primer application showed a thin, high-density layer above the intact dentin in both etching modes, suggesting chemical interaction.

In vitro evaluation of a silane containing self-adhesive resin luting agent

OBJECTIVES

To investigate the setting characteristics, wettability and bonding capacity with a lithium disilicate ceramic of a silane containing self-adhesive resin luting agent (Panavia SA Universal-PU).

METHODS

The degree of conversion (DC %) and extent of acid neutralization (SY %) of PU were measured on dual- (DC) and self-cured (SC) specimens after 10, 30 and 60 min storage by ATR-FTIR spectroscopy, whereas the presence of silanols was traced by curve-fitting the 60 min spectra, using the silane-free analog (Panavia SA Plus-PS) as a control. The role of a dedicated adhesive (Clearfil Universal Bond Quick-CU) in assisting the early DC % in PU-SC was investigated on 10 min-stored specimens. The water contact angles on polished and HF acid-etched lithium disilicate surfaces (IPS e.max Press), were assessed before and after silanization by unset PU or a silane primer (Ultradent Silane-SL). Finally, the shear strength of PU-DC specimens bonded to the acid-etched ceramic surfaces was determined before and after SL treatment.

RESULTS

The DC % was higher in DC than SC (PU, PS; all time intervals), in PU-SC than PS-SC (30, 60 min) and in the CU assisted PU-SC group. The SY % was lower in DC than SC (PU, PS) and higher in PS-SC than PU-SC groups. Silanols were found only in unset PU and PU-DC groups. SL treatment provided higher water contact angles on polished and acid-etched ceramic surfaces and higher shear bond strength on acid-etched ceramic surfaces than PU (p < 0.05 for all comparisons).

SIGNIFICANCE

Although the degree of conversion of the silane containing luting agent was improved in the self-curing mode, especially in the adhesive assisted group, it was still inferior to light-curing. Acid-neutralization and presence of silanols were affected by the setting modes. The use of a silane primer enhanced the hydrophobicity and bond strength of the silane containing luting agent with the etched ceramic substrate.

Comparison of the Mechanical Properties and Push-out Bond Strength of Self-adhesive and Conventional Resin Cements on Fiber Post Cementation

OBJECTIVES

The purpose of this study was to compare the mechanical properties and push-out bond strength of self-adhesive resin cements (SACs) and a conventional resin cement (CRC).

METHODS AND MATERIALS

Eighty bovine incisors were divided into four groups for cementation of a fiberglass post (Whitepost - FGM Dental Group, Coral Springs, FL) with different resin cements: three SACs (Maxcem Elite, MAX - Kerr; Calibra Universal, CAL - Dentsply; and RelyX Unicem 2, RUN - 3M Oral Care) and one CRC (RelyX Ultimate, RXU - 3M Oral Care). The groups were subdivided into two groups each (n=10) for evaluation of the push-out bond strength test (POBS) after 24 hours of water storage or after thermal aging (5000 cycles), following 24 hours of storage. The failure modes were evaluated using a stereomicroscope. Flexural strength (FS) and modulus of elasticity (EM) were determined using a three-point bending. Also, pH of the cements was measured over 48 hours and filler morphology was observed by scanning electron microscopy. Appropriate statistical analyses were performed by SPSS 21.0 (SPSS Inc., Chicago, IL, USA), with a significance level set at 5%. Results: RXU presented the highest POBS at both evaluation times. Among the SACs, RUN and CAL presented significantly lower POBS than MAX in cervical and middle-thirds at the 24-hour evaluation, and in all root regions after thermocycling. Adhesive failure between the cement and dentin were the most prevalent fractures at both times evaluated. MAX presented the lowest FS and RUN showed the highest EM. The pH reached the minimal point at the 30-minute evaluation for RXU and MAX. For RUN and CAL, the minimal pH was observed at the 60-minute evaluation. RXU and RUN presented spherical and regular filler particles, while MAX and CAL presented irregularly shaped and sized filler particles.

CONCLUSIONS

The mechanical behavior of SACs is not superior to CRC; however, among all the SACs evaluated, MAX presented the highest POBS and stability after thermocycling evaluation. MAX also reached the closest neutral pH after 48 hours. Therefore, SACs with low initial pH and strong neutralization reactions are recommended, because these characteristics may lead to better mechanical properties and stability.

Physical, Mechanical, and Adhesive Properties of Novel Self-Adhesive Resin Cement

Objective

To evaluate a newly developed self-adhesive resin cement on physical, mechanical, and adhesive properties and compare it with other commercial self-adhesive resin cements.

Materials and Methods

Experimental self-adhesive resin cement (SARC) was formulated by our proprietary adhesive resin and filler technology. Maxcem Elite, RelyX Unicem 2, SpeedCem Plus, SmartCEM 2, and Calibra Universal 2 were selected for comparison. Working and setting times, film thickness, water sorption and solubility, flexural strength, and modulus were measured in accordance with ISO-4049. Consistency was tested according to modified ISO 4823. Shear bond strengths were conducted according to ISO 29022. The data were analyzed by one-way ANOVA and post hoc Tukey's tests (p ≤ 0.05).

Results

All cements showed about 2–4 min working time and about 3–6 min setting time except that RelyX Unicem 2 has a longer working time (9'58”) and setting time (10'18”). All cements meet ISO standards for film thickness (≤50 µm), water sorption (≤40 µg/mm³) except Maxcem Elite (46.19 µg/mm³), and water solubility (≤7.5 µg/mm³) except SmartCEM 2 (11.35 µg/mm³) and Calibra Universal (9.87 µg/mm³). Experimental SARC showed significantly higher flexural strength and modulus than other cements (p < 0.001). For self-curing, Experimental SARC has statistically higher bond strength than other cements (p < 0.001) except statistically the same as RelyX Unicem 2 (p > 0.05). For light-curing, Experimental SARC showed significantly higher bond strength than other cements (p < 0.001) except statistically the same as Maxcem Elite and RelyX Unicem 2 (p > 0.05). For dual-curing, the bond strength of Experimental SARC is significantly higher than that of other cements (p < 0.001).

Conclusion

The newly developed self-adhesive resin cement exhibited favorable bonding capability and physical and mechanical properties compared to other commercial self-adhesive resin cements and is a good option for cementation of indirect restorations with potential long-term clinical success.

Varying 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) level improves polymerisation kinetics and flexural strength in self-adhesive, remineralising composites

OBJECTIVES

To assess the influence of systematically varying concentrations of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) versus 3% 4-META on the polymerisation kinetics and shrinkage, biaxial flexural strength (BFS) and modulus of remineralising composites.

METHODS

Composites were prepared by adding poly(propylene glycol) dimethacrylate (24 wt%), camphorquinone (1 wt%) and MDP (0%, 5%, 10%, 15% and 20 wt%) or 4-META (3%) to urethane dimethacrylate. These were mixed with glass fillers containing 8 wt% monocalcium phosphate and 4 wt% polylysine (powder-liquid ratio of 3:1). Continuous spectral changes, following 20 s light exposure (37 °C), were assessed with an ATR-FTIR to monitor polymerisation kinetics (n = 3). Final extrapolated conversions (D_C,max) were employed to calculate polymerisation shrinkage. BFS and modulus of 24-h dry stored disc specimens (10 × 1 mm; n = 10) were determined using a ball-on-ring jig setup.

RESULTS

Maximum rate of polymerisation and D_C,max increased linearly from 2.5 to 3.5% s^-1 and 67 to 83%, respectively, upon increasing MDP from 0 to 20 wt%. Values with 3% 4-META were 2.6% s^-1 and 78%. Shrinkage was 3.8 ± 0.3% for all formulations. Raising 4-META or MDP from 0 to 3 versus 5%, respectively, increased strength from 106 to 145 versus 136 MPa. A decreasing trend with higher MDP concentrations was noted. Elastic modulus showed no specific trend upon MDP increase.

SIGNIFICANCE

Whilst final conversion levels were enhanced by 3% 4-META or >5% MDP, trends did not correlate with strength. Peak strengths with 3% 4-META or 5% MDP may therefore be due to acidic monomers providing linkage between the hydrophilic, non-silane treated particles and the polymer matrix.

Modelling ATR-FTIR Spectra of Dental Bonding Systems to Investigate Composition and Polymerisation Kinetics

Component ratios and kinetics are key to understanding and optimising novel formulations. This warrants investigation of valid methods. Attenuated Total Reflectance Fourier Transform Infra-Red (ATR)-FTIR spectra of separate primers/adhesives were modelled using summed spectra of solvents (water, ethanol), methacrylate monomers (HEMA (hydroxyethyl methacrylate), Bis-GMA (bisphenol A glycidyl methacrylate), and 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate)), and fillers, multiplied by varying fractions. Filler loads were obtained following their separation from the adhesives, by analysing three repetitions (n = 3). Spectral changes during light exposure at 37 °C (20 s, LED 1100-1330 mW/cm2) were used to determine polymerisation kinetics (n = 3). Independent samples T-test was used for statistical analysis (significance level of 5%). FTIR modelling suggested a primer solvent percentage of OBFL (Optibond FL) (30%) was half that of CFSE (Clearfil SE 2) (60%). OBFL included ethanol and water, while CFSE included only water. Monomer peaks were largely those of HEMA with lower levels of phosphate monomers. OBFL/CFSE adhesive model spectra suggested that both contained equal volumes of Bis-GMA/HEMA, with CFSE having 10-MDP. Filler levels and spectra from OBFL (48 wt.%) and CFSE (5 wt.%) were different. Both systems reached a 50% conversion rate within seconds of light exposure. The final conversion for OBFL (74 ± 1%) was lower compared to CFSE (79 ± 2%) (p < 0.05). ATR-FTIR is a useful method to investigate relative levels of main components in bonding systems and their polymerisation kinetics. Such information is valuable to understanding such behaviour.

The effects of different surface treatments on the shear bond strengths of two dual-cure resin cements to CAD/CAM restorative materials

PURPOSE

The aim of the present study was to investigate the effects of surface treatments on the bond strengths between polymer-containing restorative materials and two dual-cure resin cements.

MATERIALS AND METHODS

In the present study, rectangular samples prepared from Lava Ultimate (LU) and Vita Enamic (VE) blocks were used. The specimen surfaces were treated using CoJet sandblasting, 50 µm Al₂O₃ sandblasting, % 9 HF (hydrofluoric) acid, ER,Cr:YSGG laser treatment, and Z-Prime. Dual-cure resin cements (TheraCem and 3M RelyX U 200) were applied on each specimen's treated surface. A micro-tensile device was used to evaluate shear bond strength. Statistical analysis was performed using the SAS 9.4v3.

RESULTS

While the bond strength using TheraCem with LU or VE was not statistically significant (P=.164), the bond strength using U200 with VE was statistically significant (P=.006). In the TheraCem applied VE groups, Z-Prime and HF acid were statistically different from CoJet, Laser, and Sandblast groups. In comparison of TheraCem used LU group, there was a statistically significant difference between HF acid and other surface treatments.

CONCLUSION

The bonding performance between the restorative materials and cements were material type-dependent and surface treatment had a large effect on the bond strength. Within the limitations of the study, the use of both U200 and TheraCem may be suggested if Z-prime was applied to intaglio surfaces of VE. The cementation of LU using TheraCem is suitable after HF acid conditioning of the restoration surfaces.

Is Conventional Resin Cement Adhesive Performance to Dentin Better Than Self-adhesive? A Systematic Review and Meta-Analysis of Laboratory Studies

CLINICAL RELEVANCE

Conventional multistep resin cements presented higher adhesive performance to dentin than simplified self-adhesive cements, which is an important criterion for indirect restoration prognosis.

SUMMARY

This study aimed to conduct a systematic review of the literature on laboratory studies assessing bonding performance to dentin of conventional and self-adhesive resin cements, in cementing indirect restorations. This review was reported according to the PRISMA Statement. Of a total of 518 studies, 36 were screened full text and reviewed according to exclusion criteria. Nineteen papers were included in the systematic review and meta-analyses, according to the following inclusion criteria: studies that evaluated the bond strength to dentin of indirect restorations cemented with dual conventional or self-adhesive resin cements and those that presented bond strength data in MPa as an outcome. Statistical analyses were conducted using Rev-Man 5.1. Comparisons were performed with random effects models at 5% significance level. A global analysis comparing conventional and self-adhesive cements and three subgroup analyses comparing immediate and long-term results were performed. Global analysis showed a difference between groups, with conventional resin cements presenting higher bond strength results than self-adhesive resin cements, in immediate and long-term time periods (both p=0.03). Immediate and longterm bond strength results were different for self-adhesive cements, favoring immediate bond strength (p=0.03), but immediate and long-term bond strength results for conventional resin cements were not different (p=0.06). Medium or high risk of bias was found in all studies. Conventional multistep resin cements showed superior overall adhesive performance compared with simplified self-adhesive resin cements when used to cement indirect restorations to dentin.

Effect of double-layer application on the early enamel bond strength of universal adhesives

OBJECTIVES

The present study aimed to investigate the changes in the enamel bond strengths of universal adhesives in the early phase of specimen creation and evaluate the effect of double-layer application on enamel bond effectiveness using different etching modes.

METHOD

Four universal adhesives, namely Clearfil Universal Bond Quick, G-Premio Bond, Scotchbond Universal, and Tokuyama Universal Bond, were used. Clearfil SE Bond two-step self-etch adhesive system was used as a comparison. Fifteen specimens per group were used for determining the shear bond strength (SBS) to bovine enamel in the etch-and-rinse or self-etch mode. The adhesive was applied to specimens in accordance with the manufacturers' instructions (single-layer application), or the adhesive was applied twice (double-layer application). The bonded specimens were stored in distilled water at 37 °C for 5 min or 1, 6, 12, or 24 h before SBS testing. The flexural properties of the resin composite Clearfil AP-X were measured for the same storage periods.

RESULTS

All universal adhesives exhibited increased SBS values with prolonged storage periods regardless of the application technique or etching mode used. Double-layer application was associated with higher SBS values than single-layer application for most universal adhesives over the same storage period.

CONCLUSION

Phosphoric acid pre-etching and double-layer application of universal adhesives resulted in increased enamel bond strength in the early phase of specimen bonding.

CLINICAL RELEVANCE

Care should be taken when using universal adhesives in the self-etch mode for enamel bonding because the enamel adhesion is sensitive to the duration after filling.

Effects of Polymerization Mode and Interaction with Hydroxyapatite on the Rate of pH Neutralization, Mechanical Properties, and Depth of Cure in Self-Adhesive Cements

Objective The aim of the study was to evaluate the physicochemical properties of self-adhesive resin cements associated with hydroxyapatite (HAp) according to the polymerization activation.

Materials and Methods Specimens of cements (PermaCem 2.0 [DMG]; MaxCem Elite [Kerr], and RelyX U200 [3M ESPE]) were distributed into three groups: activation mode; self-cured and dual-cured modes; and association or not with HAp powder mode. The pH neutralization was evaluated as a function of time. Flexural strength and elastic modulus were also tested (0.5 mm/min.). The depth of cure was also analyzed using the scraping test (ISO 4049). Infrared spectroscopy was also used to collect the spectra of specimens to evaluate the chemical bonds. Statistical comparisons were conducted at 5% of significance.

Results The aggressiveness of the self-adhesive resin cements evaluated varied among the materials with a tendency for neutralization. Self-cure groups exhibited lower pH throughout the entire evaluation when compared with that of the dual-cure ones, irrespective of the addition of HAp. MaxCem Elite when photoactivated was the only cement influenced by the addition of the HAp in terms of mechanical properties. The self-adhesive cements tested presented equivalent depth of cure based on the ISO 4049 requirements, regardless of the evaluated factors.

Conclusions Based on the parameters evaluated, the results demonstrated that most of the self-adhesive cements remained unaltered or improved when mixed with HAp, regardless of the activation mode.

Improved mechanical performance of self-adhesive resin cement filled with hybrid nanofibers-embedded with niobium pentoxide

OBJECTIVES

In this study hybrid nanofibers embedded with niobium pentoxide (Nb₂O₅) were synthesized, incorporated in self-adhesive resin cement, and their influence on physical-properties was evaluated.

METHODS

Poly(D,L-lactide), PDLLA cotton-wool-like nanofibers with and without silica-based sol-gel precursors were formulated and spun into submicron fibers via solution blow spinning, a rapid fiber forming technology. The morphology, chemical composition and thermal properties of the spun fibers were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC), respectively. Produced fibers were combined with a self-adhesive resin cement (RelyX U200, 3M ESPE) in four formulations: (1) U200 resin cement (control); (2) U200+1wt.% PDLLA fibers; (3) U200+1wt.% Nb₂O₅-filled PDLLA composite fibers and (4) U200+1wt.% Nb₂O₅/SiO₂-filled PDLLA inorganic-organic hybrid fibers. Physical properties were assessed in flexure by 3-point bending (n=10), Knoop microhardness (n=5) and degree of conversion (n=3). Data were analyzed with One-way ANOVA and Tukey's HSD (α=5%).

RESULTS

Composite fibers formed of PDLLA-Nb₂O₅ exhibited an average diameter of ∼250nm, and hybrid PDLLA+Nb₂O₅/SiO₂ fibers were slightly larger, ∼300nm in diameter. There were significant differences among formulations for hardness and flexural strength (p<0.05). Degree of conversion of resin cement was not affected for all groups, except for Group 4 (p<0.05).

SIGNIFICANCE

Hybrid reinforcement nanofibers are promising as fillers for dental materials. The self-adhesive resin cement with PDLLA+Nb₂O₅ and PDLLA+Nb₂O₅/SiO₂ presented superior mechanical performance than the control group.

Adhesive Systems Used in Indirect Restorations Cementation: Review of the Literature

New technologies are changing the therapeutical options to do indirect restorations and new adhesive systems are continuously introduced to be used by clinicians. Different interactions between restorations, adhesive systems components, enamel and dentin require having criteria based on the selection of the adhesive system, ensuring the longevity of the restorations and the preservation of the biological remnant. The adhesion force to the dental tissue is one of the indicatives of the behavior of the adhesive systems and influences the behavior of the treatments with direct and indirect restorations. The objective of this search was to find the adhesive systems with the best results in terms of the adhesion strength of indirect restorations on the dental tissues. The search was conducted in two MEDLINE digital databases (PubMed), and the Cochrane Library with a search strategy based on the combination of MeSH (Medical Subject Headings) keywords. This systematic review used the PRISMA guide (Preferred Reporting Items for Systematic Reviews and Meta-Analysis). According to this review, the 3-step adhesive systems were the best performing and still are the gold standard for the cementing of indirect restorations. In addition, it can be concluded that self-etched adhesive systems reduce the time spent in clinical practice, however at the interface level they behave as permeable membranes more susceptible to degradation.

Bonding of different self-adhesive resins to high-strength composite resin block treated with surface conditioning

PURPOSE

This study aimed to evaluate the effects of chemical conditioning and self-adhesive resins (SARs) on the bonding of mechanically conditioned high-strength composite resin block (HSCRB).

METHODS

Eighteen sections of HSCRB (KZR-CAD HR 3 Gammatheta, Yamakin) were treated with alumina air abrasion and randomly divided into 3 groups according to the SARs for bonding: RelyX Unicem 2 (RXU), SA Luting Plus (SAL), and G-Cem ONE (GCO). The sections were further divided into 3 subgroups according to the chemical conditioning of the adherend surfaces: no conditioning (C), universal adhesive (UA), and a mixture of γ-MPTS and 10-MDP (MM). After the surface conditioning, the sections were cemented with the SARs. Each cemented section was cut into 40 beams. Half of the beams were thermocycled (4°C/60°C, 10,000 cycles). The micro-tensile bond strength (μTBS) values were measured using a universal testing machine. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), contact angles, and surface roughness measurements were performed on the adherend surfaces of each subgroup.

RESULTS

RXU showed the highest μTBS values among the 3 SARs tested, while MM application exhibited the highest μTBS values among the 3 chemical conditioning methods tested. After thermocycling, the samples in the RXU/MM, RXU/UA, and GCO/MM groups showed no significant changes in the μTBS values, whereas the others showed a significant reduction.

CONCLUSIONS

The bond strength of HSCRB was influenced by the chemical conditioning, SARs, and aging. γ-MPTS and 10-MDP application yielded higher μTBS values of mechanically treated HSCRB than the UA.

Evaluation of the Microshear Bond Strength of MDP-containing and Non-MDP-containing Self-adhesive Resin Cement on Zirconia Restoration

OBJECTIVES

The purpose of this study was to measure the microshear bond strength (μSBS) of four different self-adhesive resin cements with/without 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing primer to zirconium ceramics and to evaluate the effect of zirconia primers on these self-adhesive resin cements (SARCs).

METHODS AND MATERIALS

Zirconia blocks (20 × 20 × 8 mm³) were prepared and divided into eight groups (n=20). They were sandblasted (50 μm Al₂O₃) and treated as follows: no primer or primer (Z-Primer Plus). Four self-adhesive resin cements (MDP-containing: Permacem 2.0 [PC], Clearfil SA luting [CS]; non-MDP-containing: Rely-X U200 [RU], Maxcem Elite [ME]) were bonded to the zirconia surface. After thermocycling, a μSBS test was performed. The failure mode was analyzed using light microscopy. Statistical analysis of μSBS was performed using one-way analysis of variance and two-sample t-test with post hoc Tukey test. The loss rate was evaluated using the Fisher's exact test and χ² test with post hoc Tukey test (p<0.05).

RESULTS

Within the no primer groups, the PC and CS groups showed higher bond strength than the RU and ME groups. Comparing the μSBS of the no primer and primer groups in the same SARCs, the RU/P group was higher than the RU group, and the ME/P group was higher than the ME group. No significant difference was observed between the PC and PC/P groups and between the CS and CS/P groups.

CONCLUSIONS

Non-MDP-containing SARC showed the increased bonding value with MDP-containing primer to zirconia ceramics. The bond strength of MDP-containing SARCs was not affected significantly by the use of zirconia primer.

Dental Cements for Luting and Bonding Restorations: Self-Adhesive Resin Cements

Self-adhesive resin cements combine easy application of conventional luting materials with improved mechanical properties and bonding capability of resin cements. The presence of functional acidic monomers, dual cure setting mechanism, and fillers capable of neutralizing the initial low pH of the cement are essential elements of the material and should be understood when selecting the ideal luting material for each clinical situation. This article addresses the most relevant aspects of self-adhesive resin cements and their potential impact on clinical performance. Although few clinical studies are available to establish solid clinical evidence, the information presented provides clinical guidance in the dynamic environment of material development.

Phosphoric and carboxylic methacrylate esters as bonding agents in self-adhesive resin cements

The aim of the present study was to investigate the effect of pH and phosphoric ester structure (phosphonate or phosphate) on the bond strength of different dental restorative materials. The following three self-adhesive resin cements were used in the present study: RelyX^™ Unicem, Maxcem and Multilink Sprint The pH of each cement was measured using a pH meter. The cements were used to attach a variety of restorative materials to human dentin and the bond strength was measured by assessing shear strength using a universal testing machine. The pH values of RelyX Unicem, Maxcem and Multilink Sprint were 3.78, 1.78 and 3.42, respectively. Maxcem, a phosphate-based self-adhesive cement, was demonstrated to form the weakest bonds. No significant difference in bond strength was observed between RelyX Unicem and Multilink Sprint, which are phosphonate-based cements. The results of the present study suggest that the chemical structure of the functional monomer influences the performance of an adhesive material. Furthermore, the pH of acidic functional monomers containing phosphonate or phosphate groups has an effect on the strength of bonds formed between dentin and restorative materials.

Hygroscopic expansion of self-adhesive resin cements and the integrity of all-ceramic crowns

OBJECTIVE

Low pH neutralization and subsequent remnant hydrophilicity can lead to hygroscopic expansion of self-adhesive resin cements (SARCs) after water storage. The aim of this in vitro study was to investigate the effects of hygroscopic expansion of SARCs, used as luting and partial core build-up material, on integrity and cement gap thickness increase of all-ceramic CAD/CAM crowns.

METHODS

Human third molars (n=48) were prepared and anatomical all-ceramic CAD/CAM crowns were manufactured (VITABLOCS Mark II, VITA Zahnfabrik). Crowns internal surfaces were HF etched and silanized. The prepared teeth with their respective crowns were divided into 6 groups (n=8). In groups 1, 3 and 5 the coronal dentin was removed to simulate a partial core build-up. Groups 1 and 2 were luted with iCEM (Heraeus Kulzer), 3 and 4 with RelyX Unicem 2 Automix (3M), 5 and 6 with Variolink Esthetic DC (Ivoclar Vivadent). All specimens were dual cured and stored in distilled water at 37°C. Crown integrity was controlled at baseline and in regular intervals until 180 days. Cement gap thickness was measured using an optical 3D scanner (ATOS Triple scan, GOM) at baseline and after 180 days. Crown integrity was statistically analysed using Kaplan-Meier survival analysis and cement gap thickness increase using two-way ANOVA (α=0.05).

RESULTS

After 180 days storage, crack formation was observed in all specimens of group 1 (mean survival time of 85.5 days), in one specimen of group 2 and in two specimens of group 4. Two-way ANOVA analysis revealed a statistically significant interaction between material type and build-up on cement gap size increase for iCEM.

SIGNIFICANCE

Within the limits of this study, the application of SARCs with low pH neutralization as partial build-up material under CAD/CAM crowns is not recommended for clinical use.

Effect of two-step and one-step surface conditioning of glass ceramic on adhesion strength of orthodontic bracket and effect of thermo-cycling on adhesion strength

PURPOSE

The adhesion strength of orthodontic brackets bonded to dental glass ceramics was evaluated after ceramic surface was treated with two-step and one-step surface conditioning systems, and subjecting to thermo-cycling.

MATERIALS AND METHOD

A total of forty specimens were fabricated from silica based glass ceramic (lithium disilicate) by duplicating the buccal surface of maxillary first premolar. The specimens were randomly assigned to two experimental groups (n = 20), group one specimens were treated with two-step surface conditioning system (IPS ceramic etching gel™ and Monobond plus™) and group two specimens were treated with one-step surface conditioning system (Monobond etch and prime™). The surface roughness of the specimens after treatment with two-step and one-step surface conditioning system was measured using non-contact surface profilometer. Ten randomly selected specimens from each group were subjected to thermo-cycling and the remaining ten served as baseline. The shear bond strength of the specimens was measured using universal material testing machine. The adhesive remnant index score was calculated, and the results of surface roughness and bond strength were tabulated and subjected to analysis of variance and post hoc tukey's test at a significance level of p < 0.05.

RESULTS

The results of the study showed that the specimens treated with two-step conditioning system had higher surface roughness and bond strength than one-step conditioning system. The majority of the specimens treated with both two-step and one-step conditioned specimens showed adhesive failure after subjecting thermo-cycling.

CONCLUSIONS

Traditional two-step conditioning provides better bond strength. The clinical importance of the study is that, the silane promoted adhesion significantly reduces on exposure to thermo-cycling.

Evaluation of long-term bond strength and selected properties of self-adhesive resin cements

This study evaluated the shear bond strength (SBS) of self-adhesive resin cements (SARCs) to dentin and their physical-chemical properties. Five commercial SARCs were evaluated [SmartCem®2 - DENTSPLY (SC2); BisCem® - Bisco (BC); SeT PP® - SDI (SeT); Relyx U100® - 3M ESPE (U100) and YCEM® SA - Yller (YCEM)]. The SARCs were evaluated for SBS to dentin (n = 10) after 24 h, 6 months, and 12 months. The dentin demineralization caused by acidic monomers was observed by SEM, and pH-neutralization of eluate was observed for 24 h. Degree of conversion (DC), rate of polymerization (Rp), flexural strength (FS), and elastic modulus (E) were evaluated. Immediate SBS of SC2, SET, U100, and YCEM were statistically higher than that of BC (p < 0.001). After 12 months, all SARCs showed reduced SBS values and U100 showed values similar to those of SET and YCEM, and higher than those of BC and SC2 (p = 0.001). Demineralization pattern of SARCs was similar. At 24h, all SARCs showed no differences in the pH-value, except BC and U100 (p < 0.001). YCEM showed the highest Rp. U100, YCEM, and SC2 showed statistically higher FS (p<0.001) and E (p < 0.001) when compared with SET and BC. U100 and YCEM showed the best long-term bonding irrespective of the storage period. A significant reduction in SBS was found for all groups after 12 months. SBS was not shown to be correlated with physical-chemical properties, and appeared to be material-dependent. The polymerization profile suggested that an increased time of light activation, longer than that recommended by manufacturers, would be necessary to optimize DC of SARCs.

Comparison of the shear bond strength of self-adhesive resin cements to enamel and dentin with different protocol of application

AIM

The aim of the present study was to determine the shear bond strength of self-adhesive resin cements to enamel and dentin with and without surface treatments, and compare them with conventional resin cement as the control group.

METHODS

In this experimental study, buccal and lingual surface of the thirty sound human premolars were polished in order to obtain a flat surface of enamel (E) in buccal, and dentin (D) in lingual. Sixty feldspathic ceramic blocks (2×3×3 mm) were prepared and randomly divided into six groups (n=10). Each block was cemented to the prepared surface (30 enamel and 30 dentin surface) according to different protocol: E1 and D1; RelyX ARC as control group, E2, D2; RelyX Unicem, E3, D3; acid etching +RelyX Unicem. The specimens were termocycled and subjected to shear forces by a universal testing machine at a cross head speed of 0.5 mm/min. The mode of fracture were evaluated by stereomicroscope. Data were analyzed with descriptive statistical methods using SPSS version 15. One-way ANOVA, and post hoc Tukey tests were used to compare bond strengths between the groups with different adhesives at α=0.05.

RESULTS

Statistical analysis showed no significant differences within the enamel subgroups, but there were significant differences within the dentinal subgroups, and statistically significant differences were found between the groups D1and D3 (p=0.02). Comparison between similar enamel and dentinal subgroups showed that there was a significant difference just between the subgroups E3 and D3 (p=0.01).

CONCLUSION

Elective etching of enamel did not lead to significant increase in the shear bond strength of RelyX Unicem in comparison to RelyX ARC. On the other hand, elective etching of dentin reduces the bond strength of RelyX Unicem with the dentin.

Adhesive Durability Inside the Root Canal Using Self-adhesive Resin Cements for Luting Fiber Posts

OBJECTIVES

The aim of the study was to investigate the effects of various self-adhesive resin cements on the push-out bond strengths and nanoleakage expression at the luting interfaces of fiber posts immediately and after one year of aging.

METHODS AND MATERIALS

One hundred forty-four extracted human anterior teeth were endodontically treated. After post space preparation, fiber posts were luted using five commercially available self-adhesive resin (SAR) cements and a core build-up material applied with a self-etch adhesive (BF: Bifix SE/Rebilda Post, VOCO; CSA: Clearfil SA Cement/Rely X Fiber Post, 3M ESPE; RX: RelyX Unicem 2/Rely X Fiber Post, 3M ESPE; SPC: Speed Cem/FRC Postec, Ivoclar Vivadent; SMC: Smart Cem/X Post, Dentsply; RB: Rebilda DC-Futurabond/Rebilda Post; n=22). For each group, half of the specimens were subjected to thermocycling (TC) (5°C-55°C, 10,000 cycles) and stored humid for one year at 37°C. Push-out bond strength data of six slices (thickness 1 mm) per root and nanoleakage expression of representative specimens were evaluated after 24 hours (baseline) and after TC and storage for one year (aging), respectively.

RESULTS

Bond strength differed significantly among resin cements (p<0.0005) and the location inside the root canal (p<0.0005), but not by aging (p=0.390; repeated-measures analysis of variance). SMC (14.6±5.8 MPa) and RX (14.1±6.8 MPa) revealed significantly higher bond strength compared to BF (10.6±5.4 MPa) and RB (10.0±4.6 MPa) but differed not significantly from SPC (12.8±4.8) MPa; CSA (6.1±4.6 MPa) revealed significantly lower bond strength compared to all other investigated materials (p<0.05; Tukey Honestly Significantly Different). Qualitative nanoleakage analysis revealed more silver deposits at the interface in all groups after aging. For CSA, a large amount of silver deposits inside the cement was also observed at baseline and after aging.

CONCLUSIONS

Fiber post luting using SAR cements demonstrated reliable bond strengths. Product-specific differences and initial degradation effects could be demonstrated.

Effect of Storage Medium and Aging Duration on Mechanical Properties of Self-Adhesive Resin-Based Cements

Background

The aim of this study was to investigate the effects of storage medium and aging duration on Martens hardness (HM) and indentation modulus (EIT) of self-adhesive resin-based cements (SARCs).

Methods

A total of 416 discs were fabricated from 8 SARCs (n = 52 per SARC): (i) BeautyCem (BEA), (ii) Bifix SE (BIF), (iii) Clearfil SA Cement Automix (CLE), (iv) RelyX Unicem2 Automix (RXU), (v) SeT (SET), (vi) SmartCem 2 (SMC), (vii) SoloCem (SOC) and (viii) SpeedCEM (SPC). The specimens were ground and stored in (a) physiological saliva, (b) artificial saliva, (c) sodium chloride and (d) distilled water, at 37°C for 1, 7, 14, 28, 90 and 180 days. Non-aged specimens (3 hours after photo-initiation) of each SARC acted as control groups. HM and EIT were assessed using a universal hardness testing machine. Data were analyzed using Kolmogorov-Smirnov and Kruskal-Wallis tests and paired t-test, and 3-, 2- and 1-way ANOVA with post hoc Scheffé test (p<0.05).

Results

SARC materials exerted the highest influence on HM and EIT values (p<0.001, partial eta squared [ηP²] = 0.753 and 0.433, respectively), closely followed by aging duration (p<0.001, ηP² = 0.516 and 0.255) and storage medium (p<0.001, ηP² = 0.043 and 0.033). The interaction effect of the combinations of the 3 independent parameters was also significant (p<0.001, ηP² = 0.163 and 0.133). The lowest initial HM and EIT was presented by CLE, followed by SET and SPC; highest HM was for BIF, followed by RXU and SMC. SET gave a greater HM and EIT percentage decrease than SOC, SPC, BEA, SMC, RXU or CLE.

Conclusions

Aging duration is a major factor affecting the micromechanical properties of SARCs, while storage medium was shown to have a significant but minor role.

The Effect of Different Storage Media on Color Stability of Self-Adhesive Composite Resin Cements for up to One Year

The aim of this study was to analyze the long-term color stability of eight self-adhesive composite resin cements (SACRCs) after storage in diverse media for up to one year. 480 discs (diameter: 12 mm/thickness: 1.0 ± 0.05 mm) were fabricated (n = 60/SACRC): (1) BeautyCem (BEA); (2) Bifix SE (BIF); (3) Clearfil SA Cement Automix (CLE); (4) RelyX Unicem 2 Automix (RXU); (5) SeT (SET); (6) SmartCem 2 (SMC); (7) SoloCem (SOC); and (8) SpeedCEM (SPC). After polishing, specimens were immersed in (a) red wine (RW); (b) curry-solution (CU); (c) cress-solution (CR); and (d) distilled water (DW) at 37 °C and measured after 7, 28, 90, 180, and 365 days for color differences (ΔE) and water absorption (WA). Non-aged specimens were used as baselines. After 365 days, all of the discs were polished and their ΔE was measured. Data were analyzed using Kolmogorov-Smirnov, partial-eta-squared/η_P², 3-/1-way ANOVA with Tukey-HSD post-hoc test (α = 0.05). Significant differences occurred between all SACRCs for WA (p ≤ 0.003), except in RXU and in SET and in ΔE (p ≤ 0.002), except in SET and SPC. The significantly highest WA presented in SOC; the lowest showed in BEA. Significant ΔE differences and a decrease after polishing between all storage media were found (p < 0.001) with highest values for RW, followed by CU, CR, and DW. The lowest ΔE was measured for CLE, followed by SOC, BIF, RXU, BEA, SPC, SET, and SMC (p < 0.001) and increased significantly during aging. The highest ΔE decrease presented in BEA. SACRCs showed an increase in WA/ΔE within total aging time. Discoloration could not be removed completely by polishing. SACRCs need to be carefully selected for restorations in the esthetical zone with visible restoration margins. Polishing can significantly reduce the marginal discoloration.

Does hybridized dentin affect bond strength of self-adhesive resin cement?

Background

Evaluate the influence of different hybridization bonding techniques of a self-adhesive resin cement.

Material and Methods

30 human health molars were divided into six groups (n=10). The specimens received three longitudinal sections, allowing insertion of central cuts in PVC matrices. Each group received a different dentin pretreatment according to the manufacturer’s recommendations, except the control group (G1), as follows. G2 - a 3-step total-etch adhesive system (Optibond™ FL, Kerr); G3 - a 3-step total-etch adhesive system (Adper™ Scotchbond™ Multi-Purpose, 3M ESPE); G4 - a 2-step total-etch adhesive system (Adper™ Single Bond 2, 3M ESPE); G5 - a single-step self-etching system (Bond Force, Tokuyama); and G6 - universal bonding system (Single Bond Universal, 3M ESPE). Then, cylinders made of self-adhesive resin cement with polypropylene matrix was cemented in all groups (RelyX U200, 3M ESPE). Bond strength was assessed by submitting the specimens to micro-shear test and was characterized according to the fracture pattern observed through optical microscopy.

Results

The results were submitted to the Kruskal-Wallis test, which indicated a statistically significant difference between the groups (p=0.04), and Tukey’s multiple comparisons, which indicated a statistically significant difference between G1 and G3 (p<0.05). The microscopic analysis revealed a high prevalence of adhesive failures, followed by mixed fractures, and cohesive failures in the dentin.

Conclusions

The use of a previous dentin hybridization protocol is able to increase adhesive bonding resistance of self-adhesive resin cement, especially when used Adper™ Scotchbond™ Multi-Purpose system.

Key words:Bonding, self-adhesive resin cement, adhesive systems, microshear.

Self-adhesive resin cements: pH-neutralization, hydrophilicity, and hygroscopic expansion stress

OBJECTIVES

The objective of the study was to investigate the relationship between pH-neutralization, hydrophilicity, and free hygroscopic expansion stress of self-adhesive resin cements (SARCs) after storage in artificial saliva.

MATERIALS AND METHODS

The SARCs RelyX Unicem Automix 2 (RX2, 3 M ESPE), iCEM (iCEM, Heraeus) and Maxcem Elite (MCE, Kerr) were under investigation in this study. Cylinders (height × diameter, 6 × 4mm) were prepared from each material and stored in artificial saliva (7d at 37 °C). Cylinder height was measured at baseline and after 7 days. After storage, the compression modulus was measured to calculate the free hygroscopic expansion stress. For pH-neutralization and hydrophilicity assessment, disks (height × diameter, 1 × 1.5 mm) were prepared, covered with electrolyte, and monitored over 24 h at 37 °C. Hydrophilicity was assessed using the static sessile drop technique at baseline and at different time intervals up to 24 h. Data were analyzed using one-way ANOVA and post hoc Student-Newman-Keuls test (S-N-K, α = 0.05).

RESULTS

After 24 h, RX2 (pH_24h 4.68) had a significantly higher (p < 0.05) pH-value than MCE (pH_24h 4.2) and iCEM (pH_24h 3.23). iCEM showed the significantly highest hydrophilicity (p < 0.05) after 24 h (θ_24h 85.02°), while MCE resulted lower (θ_24h 113.01°) in comparison with RX2 (θ_24h 108.11°). The resulting hygroscopic expansion stress of iCEM (29.15 MPa) was significantly higher (p < 0.05) compared to RX2 (14.5 MPa) and MCE (21.02 MPa).

CONCLUSIONS

The material with lowest pH-neutralization capacity displayed higher hydrophilicity after 24 h and higher hygroscopic expansion stress after 7 days compared to those with high pH-neutralization.

CLINICAL SIGNIFICANCE

Remnant hydrophilicity due to low pH-neutralization of SARCs could lead to cement interface stress build-up and long-term failure of silicate ceramic restorations.

Influence of root dentin treatment on the push-out bond strength of fiber posts

The aim of the present study was to assess whether different dentin conditioning protocols with different acids [phosphoric acid, ethylene diamine tetra acetic acid (EDTA), and polyacrylic acid (PAA)] influence the bond strength of fiber posts along the radicular depth when luted with self-adhesive resin cement. Twenty single-rooted teeth were randomly divided into four experimental groups (n = 5) according to dentin treatment: Group 1: no treatment; Group 2: etching with 35 % phosphoric acid for 10 s; Group 3: 17 % EDTA application for 60 s; and Group 4: conditioning with 25 % PAA for 30 s. RelyX Fiber Posts were luted with the self-adhesive resin cement RelyX Unicem 2 Automix (3M ESPE). Roots were transversally sectioned into nine 1-mm thick specimens, three corresponding to each root third and a push-out test was performed. Data were analyzed by two-way ANOVA and Tukey test (p < 0.05). Failure mode was determined and specimens with representative failures for each group were observed under scanning electron microscopy. According to the results, dentin treatment influenced the bond strength (p < 0.001), whereas the root third did not (p > 0.05). Fiber posts luted after treating dentin with phosphoric acid, and PAA exhibited the highest push-out bond strength values, while the lowest were obtained after EDTA application. Intermediate results were obtained when dentin was not conditioned. In conclusion, the bond strength of the self-adhesive resin cement RelyX Unicem 2 improves when root dentin is treated with 35 % phosphoric acid or 25 % PAA, before fiber posts luting irrespective of the root depth.

Mechanical Properties and Sliding-impact Wear Resistance of Self-adhesive Resin Cements

The present study determined the mechanical properties and impact-sliding wear characteristics of self-adhesive resin cements. Five self-adhesive resin cements were used: G-CEM LinkAce, BeautiCem SA, Maxcem Elite, Clearfil SA Automix, and RelyX Unicem 2. Clearfil Esthetic Cement was employed as a control material. Six specimens for each resin cement were used to determine flexural strength, elastic modulus, and resilience according to ISO specification #4049. Ten specimens for each resin cement were used to determine the wear characteristics using an impact-sliding wear testing apparatus. Wear was generated using a stainless-steel ball bearing mounted inside a collet assembly. The maximum facet depth and volume loss were determined using a noncontact profilometer in combination with confocal laser scanning microscopy. Data were evaluated using analysis of variance followed by the Tukey honestly significantly different test (α=0.05). The flexural strength of the resin cements ranged from 68.4 to 144.2 MPa; the elastic modulus ranged from 4.4 to 10.6 GPa; and the resilience ranged from 4.5 to 12.0 MJ/m3. The results for the maximum facet depth ranged from 25.2 to 235.9 μm, and volume loss ranged from 0.0107 to 0.5258 mm3. The flexural properties and wear resistance were found to vary depending upon the self-adhesive resin cement tested. The self-adhesive cements tended to have lower mechanical properties than the conventional resin cement. All self-adhesive resin cements, apart from G-CEM LinkAce, demonstrated significantly poorer wear resistance than did the conventional resin cement.

Effect of dentin dehydration and composite resin polymerization mode on bond strength of two self-etch adhesives

Background:

Dual-cured composite resins are similar to self-cured composite resins in some of their clinical applications due to inadequate irradiation, lack of irradiation, or delayed irradiation. Therefore, incompatibility with self-etch adhesives (SEAs) should be taken into account with their use. On the other, the extent of dentin dehydration has a great role in the quality of adhesion of these resin materials to dentin. The aim of this study was to investigate the effect of dentin dehydration and composite resin polymerization mode on bond strength of two SEAs.

Materials and Methods:

A total of 120 dentinal specimens were prepared from extracted intact third molars. Half of the samples were dehydrated in ethanol with increasing concentrations. Then Clearfil SE Bond (CSEB) and Prompt L-Pop (PLP) adhesives were applied in the two groups. Cylindrical composite resin specimens were cured using three polymerization modes: (1) Immediate light-curing, (2) delayed light-curing after 20 min, and (3) self-curing. Bond strength was measured using universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed with two-way ANOVA and Duncan post hoc tests. Statistical significance was defined at P < 0.05.

Results:

There were no significant differences for CSEB subgroups with hydrated and dehydrated dentin samples between the three different curing modes (P > 0.05). PLP showed significant differences between subgroups with the lowest bond strength in hydrated dentin with delayed light-curing and self-cured mode of polymerization.

Conclusion:

Within the limitations of this study, a delay in composite resin light-curing or using chemically cured composite resin had a deleterious effect on dentin bond strength of single-step SEAs used in the study.

Tensile Bond Strength of Self Adhesive Resin Cement After Various Surface Treatment of Enamel

INTRODUCTION

In self adhesive resin cements adhesion is achieved to dental surface without surface pre-treatment, and requires only single step application. This makes the luting procedure less technique-sensitive and decreases postoperative sensitivity.

AIM

The purpose of this study was to evaluate bond strength of self adhesive resin after surface treatment of enamel for bonding base metal alloy.

MATERIALS AND METHODS

On the labial surface of 64 central incisor rectangular base metal block of dimension 6 mm length, 5mm width and 1 mm height was cemented with RelyX U200 and Maxcem Elite self adhesive cements with and without surface treatment of enamel. Surface treatment of enamel was application of etchant, one step bonding agent and both. Tensile bond strength of specimen was measured with universal testing machine at a cross head speed of 1mm/min.

RESULTS

Least tensile bond strength (MPa) was in control group i.e. 1.33 (0.32) & 1.59 (0.299), Highest bond strength observed when enamel treated with both etchant and bonding agent i.e. 2.72 (0.43) & 2.97 (0.19) for Relyx U200 and Elite cement. When alone etchant and bonding agent were applied alone bond strength is 2.19 (0.18) & 2.24 (0.47) for Relyx U200, and 2.38 (0.27) 2.49 (0.16) for Max-cem elite. Mean bond strength was higher in case of Max-cem Elite as compared to RelyX U200 resin cement, although differences were non-significant (p > 0.05).

CONCLUSION

Surface treatment of enamel increases the bond strength of self adhesive resin cement.

Simulated Wear of Self-Adhesive Resin Cements

One of the primary areas of concern with luting agents is marginal gap erosion and attrition. The purpose of this laboratory study was to evaluate bulk and marginal slit (gap) generalized wear of self-adhesive resin cements. Three self-adhesive resin cements were used in this study: G-CEM LinkAce (LA), Maxcem Elite (ME), and RelyX Unicem2 Automix (RU). A custom stainless-steel fixture with a cavity 4.5 mm in diameter and 4 mm deep was used for simulated generalized (bulk) wear. For simulated marginal gap wear, a two-piece stainless-steel custom fixture was designed with a slit (gap) 300 μm wide and 3 mm in length. For both wear models, 20 specimens each for each of the three adhesive cements were made for both light-cure and chemical-cure techniques. The cured cements were polished with a series of carbide papers to a 4000-grit surface and subjected to 100,000 cycles using the slit (gap) wear model and 400,000 cycles for generalized (bulk) wear in a Leinfelder-Suzuki (Alabama machine) wear simulator (maximum load of 78.5 N). Flat-ended stainless-steel antagonists were used in a water slurry of poly(methylmethacrylate) beads for simulation of generalized contact-free area wear with both wear models. Before and after the wear challenges, the specimens were profiled with a Proscan 2100 noncontact profilometer, and wear (volume loss [VL] and mean facet depth [FD]) was determined using AnSur 3D software. Two-way analysis of variance (ANOVA) and Tukey post hoc tests were used for data analysis for the two wear models. Scanning electron microscopy (SEM) was used to examine polished surfaces of the resin cements and the worn surfaces after the wear challenges. The two-way ANOVA of VL using the generalized (bulk) wear model showed a significant effect among the three resin cement materials for the factor of resin cement (p<0.001) and the interaction of the cement and cure method (p<0.001), but not for the cure method (p=0.465). The two-way ANOVA for FD also found a significant difference for the factor of resin cement (p<0.001) and the interaction of the resin cement and cure method (p<0.001), but not for the cure method (p=0.277). The simulated generalized (bulk) wear for the light-cure groups was as follows: VL (mm(3)): RU 0.631 (0.094), LA 0.692 (0.112), and ME 1.046 (0.141) and FD (μm): RU 43.6 (6.5), LA 47.0 (7.7), and ME 72.5 (9.9). The simulated generalized (bulk) wear for the chemical-cure groups was as follows: VL (mm(3)): LA 0.741 (0.105), RU 1.231 (0.234), and ME 1.305 (0.143) and FD (μm): LA 50.7 (7.2), RU 84.5 (16.1), and ME 91.7 (10.2). Simulated wear using the slit (gap) model for the light-cure groups was as follows: VL (mm(3)): RU 0.030 (0.006), LA 0.031 (0.006), and ME 0.041 (0.009) and FD (μm): RU 49.6 (5.7), LA 57.2 (8.4), and ME 70.9 (10.7). The wear values for the chemical-cure slit (gap) groups were as follows: VL (mm(3)): LA 0.031 (0.004), ME 0.038 (0.007), and RU 0.045 (0.009) and FD (μm): LA 53.9 (6.7), ME 63.5 (9.1), and RU 74.2 (12.9). Pearson correlation tests revealed a strong relationship between the two wear models for the light-cure groups and a good relationship for the chemical-cure groups. The observations using SEM showed differences in filler particle shape and size among the cements and the resultant effect of the wear challenges. The worn surfaces of each cement were essentially the same for both light-cure and chemical-cure methods. The bulk wear model and new slit (gap) model for evaluation of simulated generalized wear of luting agents demonstrated significant differences (p<0.05) in relative wear among three self-adhesive resin cements and between visible light- and chemical-cure techniques.

Evaluation of pH, ultimate tensile strength, and micro-shear bond strength of two self-adhesive resin cements

The aim of this study was to evaluate the pH, ultimate tensile strength (UTS), and micro-shear bond strength (µSBS) of two self-adhesive resin cements to enamel and dentin. Sound bovine incisors (n = 10) and two self-adhesive resin cements (i.e., RelyX U-100 and seT PP) were used. The pH of the resin cements was measured using a pH-indicator paper (n = 3). Specimens for UTS were obtained from an hourglass-shaped mold. For µSBS, cylinders with internal diameter of 0.75 mm and height of 0.5 mm were bonded to the flat enamel and dentin surfaces. Bonded cylinders were tested in the shear mode using a loop wire. The fracture mode was also evaluated. The cement seT PP showed a low pH; U-100 showed significantly higher UTS (49.9 ± 2.0) than seT PP (40.0 ± 2.1) (p < 0.05) and high µSBS to enamel (10.7 ± 3.7). The lowest µSBS was found for seT PP to dentin (0.7 ± 0.6); seT PP to enamel (4.8 ± 1.7), and for U-100 to dentin (7.2 ± 1.9), showing an intermediate µSBS value (p < 0.05). Adhesive failure was the most frequently observed failure mode. The resin cement that presented the lowest pH and UTS also presented the lowest micro-shear bond strength to enamel and dentin.

Immediate and delayed photoactivation of self-adhesive resin cements and retention of glass-fiber posts

The aim of this study was to evaluate the effect of immediate and delayed photoactivation of self-adhesive resin cements (SARCs) on the retention of glass-fiber posts luted into root canals. Bovine incisors were endodontically treated, and post holes of 9 mm in depth were prepared. Fiber posts were luted using one of two SARCs, BisCem (Bisco Inc., Schaumburg, USA) or RelyX Unicem clicker (3M ESPE, Saint Paul, USA), or a regular (etch-and-rinse) resin cement (AllCem; FGM, Joinvile, Brazil). Photoactivation was performed immediately, or at 5 or 10 min after cementation. Root/post specimens were transversely sectioned 7 days after luting into 1-mm-thick slices, which were submitted to push-out testing in a mechanical testing machine. Bond strength data were analyzed by two-way ANOVA and Student-Newman-Keuls' method (α = 0.05). Immediate photoactivation resulted in the highest bond strength for Unicem. BisCem demonstrated higher bond strength values when photoactivated after a 10-min delay. Immediate photoactivation yielded the lowest bond strengths for AllCem, although no differences in bond strength were observed between photoactivation delayed by 5 and 10 min. In conclusion, the moment of resin cement photoactivation may affect the intraradicular retention of fiber posts, depending upon the resin cement used for luting.

Bond strength of self-adhesive resin cements to composite submitted to different surface pretreatments

Objectives

Extensively destroyed teeth are commonly restored with composite resin before cavity preparation for indirect restorations. The longevity of the restoration can be related to the proper bonding of the resin cement to the composite. This study aimed to evaluate the microshear bond strength of two self-adhesive resin cements to composite resin.

Materials and Methods

Composite discs were subject to one of six different surface pretreatments: none (control), 35% phosphoric acid etching for 30 seconds (PA), application of silane (silane), PA + silane, PA + adhesive, or PA + silane + adhesive (n = 6). A silicone mold containing a cylindrical orifice (1 mm² diameter) was placed over the composite resin. RelyX Unicem (3M ESPE) or BisCem (Bisco Inc.) self-adhesive resin cement was inserted into the orifices and light-cured. Self-adhesive cement cylinders were submitted to shear loading. Data were analyzed by two-way ANOVA and Tukey's test (p < 0.05).

Results

Independent of the cement used, the PA + Silane + Adhesive group showed higher microshear bond strength than those of the PA and PA + Silane groups. There was no difference among the other treatments. Unicem presented higher bond strength than BisCem for all experimental conditions.

Conclusions

Pretreatments of the composite resin surface might have an effect on the bond strength of self-adhesive resin cements to this substrate.