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

Influence of the hydroperoxide structure on the reactivity and mechanical properties of self-cure dental composites

OBJECTIVES

Hydroperoxides are key constituents of two-component dental materials. The objective of this study was to evaluate the influence of the hydroperoxide structure on the reactivity and on the mechanical properties of self-cure composites.

METHODS

Hydroperoxides HP1-3 were synthesized by selective catalytic oxidation of the corresponding para-substituted cumene precursors and isolated in high purity. They were characterized by 1H NMR and 13C NMR spectroscopy. 16 self-cure composites, based on the redox initiator system hydroperoxide (Cumene hydroperoxide (CHP), HP1-3 or tert.-Amyl hydroperoxide (TAH))/polymerizable thiourea ATU1/copper(II) acetylacetonate, were formulated in Sulzer Mixpac two-component syringes. An equimolar hydroperoxide/ATU1 ratio was selected for each self-cure composite. The reactivity and the final double-bond conversions obtained with these two-component materials was assessed using RT-FTIR spectroscopy. The flexural strength and modulus were measured using a three-point bending setup, after storage of the specimens for 45 min at 37 °C (dry) and for 24 h in water at 37 °C. The working time of each self-cure composite was measured using an oscillating rheometer.

RESULTS

CHP derivatives bearing an electron withdrawing group (HP2: ester or HP3: nitrile) in the para position were found to be more reactive than CHP, whereas the compound bearing an electron donating group (tert-butyl, HP1) was less reactive; molecular modelling data were reported for a better understanding of this structure/reactivity/efficiency relationship. All CHP derivatives were more reactive than the aliphatic hydroperoxide TAH. Excellent mechanical properties were obtained with self-cure composites containing either CHP or a para-functionalized CHP derivative. By carefully selecting the amounts of oxidizing/reducing agents and metal catalyst, suitable working times can be obtained with all evaluated hydroperoxides. HP3, thanks to its high reactivity, is nonetheless the most promising compound.

SIGNIFICANCE

The curing rate of self-cure composites can be adapted by modifying the structure of the hydroperoxide. In agreement with molecular modelling data, the incorporation of CHP derivatives bearing an electron withdrawing group in the para position is particularly attractive. Indeed, due to a significant reactivity enhancement, the desired properties (working time, flexural strength/modulus) can be obtained by incorporating moderate amounts of hydroperoxide/acylthiourea as well as particularly low contents of metal catalyst to the two-component dental materials.

Effect of post-curing conditions on surface characteristics, physico-mechanical properties, and cytotoxicity of a 3D-printed denture base polymer

OBJECTIVE

This study aims to investigate the influence of post-polymerization (post-curing) conditions on surface characteristics, flexural properties, water sorption and solubility, and cytotoxicity of additively manufactured denture base materials.

METHODS

The tested specimens were additively manufactured using digital light processing and classified into different post-curing condition groups: submerged in water (WAT), submerged in glycerin (GLY), and air exposure (AIR). An uncured specimen (UNC) was used as a control. The surface topography and roughness were observed. The flexural strength and modulus were determined via a three-point bending test. The water sorption and solubility were subsequently tested. Finally, an extract test was performed to assess cytotoxicity.

RESULTS

Different post-curing conditions had no significant effects on the surface topography and roughness (Sa value). Various post-curing conditions also had no significant effects on the flexural strength. Notably, the flexural modulus of the WAT group (2671.80 ± 139.42 MPa) was significantly higher than the AIR group (2197.47 ± 197.93 MPa, p = 0.0103). After different post-curing conditions, the water sorption and solubility of the specimens met the ISO standards. Finally, all post-curing conditions effectively reduced cytotoxic effects.

SIGNIFICANCES

Post-curing with different oxygen levels improved flexural properties, and flexural modulus significantly increased after the specimens were submerged in water. In addition, water sorption and solubility, and cytocompatibility were optimized by post-curing, irrespective of the post-curing conditions. Therefore, the water-submerged conditions optimized the flexural modulus of the 3D-printed denture base materials.

Resin cement selection for different types of fixed partial coverage restorations: A narrative systematic review

OBJECTIVE

The aim of this study was to review the selection criteria of resin cements for different types of partial coverage restorations (PCRs) and investigate if the type of restorations or restorative materials affect the type of selected resin cement.

MATERIALS AND METHODS

An electronic search (1991-2023) was performed in PubMed, Medline, Scopus, and Google Scholar databases by combinations of related keywords.

RESULTS

A total of 68 articles were included to review the selection criteria based on the advantages, disadvantages, indications, and performance of resin cements for different types of PCRs.

CONCLUSIONS

The survival and success of PCRs are largely affected by appropriate cement selection. Self-curing and dual-curing resin cements have been recommended for the cementation of metallic PCRs. The PCRs fabricated from thin, translucent, and low-strength ceramics could be adhesively bonded by light-cure conventional resin cements. Self-etching and self-adhesive cements, especially dual-cure types, are not generally indicated for laminate veneers.

Acylthiourea oligomers as promising reducing agents for dimethacrylate-based two-component dental materials

OBJECTIVES

Currently used thiourea-based two-component dental materials may release bitter compounds if they are not properly cured. To address this issue, the objective of this study was to evaluate the potential of acylthiourea oligomers as reducing agents for the development of self-cure composites.

METHODS

Acylthiourea oligomers ATUO1-3 were synthesized via cotelomerization of the acylthiourea methacrylate ATU1 with butyl methacrylate. They were characterized by 1H NMR spectroscopy and size exclusion chromatography. Self-cure composites based on the redox initiator system cumene hydroperoxide/acylthiourea oligomer/copper(II) acetylacetonate were formulated. The flexural strength and modulus were measured using a three-point bending setup. The double bond conversions were determined using NIR spectroscopy. The working time of each self-cure composite was measured using an oscillating rheometer. Leaching experiments using light-cure composites were performed in DMSO-d6.

RESULTS

Acylthiourea oligomers ATUO1-3 were successfully synthesized in good yields. Both the oligomer molecular weight and the amount of thiourea groups were varied. Self-cure composites containing ATUO1 or ATUO2 as reducing agents exhibited excellent mechanical properties and high double-bond conversions. The amounts of reducing agent, cumene hydroperoxide and copper(II) acetylacetonate were shown to have a significant impact on the working time. Moreover, a correlation between flexural modulus and the amount of metal salt was clearly established. Self-cure composites containing the oligomer ATUO1 exhibited a longer working time than materials containing ATU1 or acetylthiourea. Contrary to acetylthiourea, ATUO1 was not able to leach out of light-cured composites.

SIGNIFICANCE

Acylthiourea oligomers are promising reducing agents for the formulation of two-component dental materials that do not induce a bitter taste in mouth.

Degree of conversion of resin-cements (light-cured/dual-cured) under different thicknesses of vitreous ceramics: systematic review

PURPOSE

This systematic review synthesized and analyzed the scientific evidence on the degree of conversion (DC) obtained by Fourier-transform infrared spectroscopy (FTIR) of light-cured and dual-cured resinous cements, photopolymerized under different thicknesses of vitreous ceramics.

STUDY SELECTION

The study protocol of this systematic review was registered at the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42017069319). A comprehensive search (PubMed/MEDLINE, Scopus, EMBASE, and LILACS) was performed for papers including an in vitro design and indexed from January 2007 to December 2020 according to the study purposes. A quality appraisal (specific instrument) and descriptive analysis of the articles that met the inclusion criteria were conducted.

RESULTS

Nine included studies were analyzed. Two of them used feldspathic ceramics, six used lithium disilicate, and one used both (comparing different types and opacities of ceramics). Three studies found a higher DC in dual cements, while one did not find any significant differences, and five studies found a higher DC in light-cured resin cements. Light-cured cements showed a better DC in relation to dual-cured cements in vitreous ceramic restorations with thicknesses up to 2 mm.

CONCLUSION

According to the findings, the use of good photoactivation is the most relevant variable to achieve an adequate DC in light-cured and dual-cured resin cements. The use of vitreous ceramic restorations with a thickness of less than 2 mm (light-curing cements) shows a better DC. Standardized in vitro studies are required to generate accurate scientific evidence.

Polymerizable thioureas as innovative reducing agents for self-cured and dual-cured dental materials

OBJECTIVE

To evaluate polymerizable acylthioureas as reducing agents in two-component dental materials.

METHODS

Acylthioureas 1 and 2 were synthesized and characterized by ¹H and ¹³C NMR spectroscopy. Self-cured composites based on the redox initiator system cumene hydroperoxide/acylthiourea 1 or 2/copper(II) acetylacetonate were formulated. Various amounts of cumene hydroperoxide, acylthiourea and copper(II) acetylacetonate were used. An equimolar cumene hydroperoxide/acylthiourea ratio was selected for each self-cured composite. The reactivity and the final double-bond conversions obtained with these two-component materials was assessed using RT-FTIR spectroscopy. The flexural strength and modulus were measured using a three-point bending setup, after storage of the specimens for 45 min at 37 °C (dry) and for 24 h in water at 37 °C. The working time of each composite was determined using an oscillating rheometer.

RESULTS

Acylthioureas 1 and 2 were synthesized in three to four steps. In combination with cumene hydroperoxide and copper(II) acetylacetonate, both prepared compounds were found to be effective reducing agents. The higher the amount of cumene hydroperoxide and acylthiourea in the self-cured composite, the higher the flexural modulus and the faster the polymerization (lower working times). Similarly, it was shown that increased copper(II) acetylacetonate amounts result in an acceleration of the curing as well as in an improvement of the mechanical properties. The self-cured composite containing 1.25 wt% of cumene hydroperoxide in the monomer mixture of the first paste and 2.00 wt% of acylthiourea 1 in the monomer mixture of the second one provided excellent mechanical properties as well as an optimal working time.

SIGNIFICANCE

Polymerizable acylthioureas can be used as reducing agents in two-component dental materials. Due to the presence of the methacrylate group, such structures should be efficiently incorporated into the network during polymerization and should not leach out of the composite after curing. As a result, such dental materials are not expected to exhibit bitterness properties.

Revolution of Current Dental Zirconia: A Comprehensive Review

The aim of this article is to comprehensively review the revolution of dental zirconia (Zir), including its types, properties, applications, and cementation procedures. A comprehensive search of PubMed and Embase was conducted. The search was limited to manuscripts published in English. The final search was conducted in October 2021. Newly developed monolithic Zir ceramics have substantially enhanced esthetics and translucency. However, this material must be further studied in vitro and in vivo to determine its long-term ability to maintain its exceptional properties. According to the literature, monolithic translucent Zir has had promising results and a high survival rate. Thus, the utilization of this material is indicated when strength and esthetics are needed. Both the materials and methods used for cementation of monolithic Zir have significantly improved, encouraging dentists to use this material, especially when a conservative approach is required. Zir restorations showed promising outcomes, particularly for monolithic Zir crowns supported with implant and fixed dental prostheses.

Color stability of a resin nanoceramic after surface treatments, adhesive cementation, and thermal aging

STATEMENT OF PROBLEM

Whether color changes in resin nanoceramic (RNC) restorations can occur because of material and adhesive interface degradation is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the color of RNCs submitted to surface treatments, cementation, and aging.

MATERIAL AND METHODS

RNC specimens (N=120) were produced with a thickness of 0.5 mm. The No Treatment-High/Low Translucency (NT-HT/LT) groups did not receive treatments; the Airborne-particle Abrasion-High/Low Translucency (AA-HT/LT) groups were airborne-particle abraded, and the Airborne-particle Abrasion Silane-High/Low Translucency (AASIL-HT/LT) groups received airborne-particle abrasion and a silane agent. Single specimens (n=60) were measured on a spectrophotometer before and after aging (50 000 cycles). The other half was mounted on composite resin bases and measured. The cleaned specimens were cemented (C) on the bases and measured (T0 and T1). ΔE₀₀, ΔL', ΔC', and ΔH' were obtained by using the CIEDE2000 formula and analyzed by using ANOVA and repeated-measures ANOVA. Multiple comparisons were made by using the Tukey HSD test (α=.05).

RESULTS

For single specimens, the greatest ΔE₀₀ values were observed in the AA-T1-LT resin (5.87). For mounted and cemented conditions, the greatest ΔE₀₀ values were found in the AA-C-T1-LT resin (1.74), and the ΔE₀₀ ranged from 0.75 (NT-OL) to 1.44 (AASIL-C-T1) for the HT resin (P<.001). The mounted and cemented specimens tended toward red and yellow, whereas lighter specimens were observed after cementation.

CONCLUSIONS

Aging affected the color of the RNCs evaluated. The single specimens showed greater color differences than the cemented specimens, reinforcing the importance of the adhesive cement in the optical behavior of thin restorations.

A comparative evaluation of colour stability of different resin cements and its influence on the final shade of All-Ceramic Restorations: An in-vitro Study

Introduction

Colour changes of the luting material can become clinically visible affecting the aesthetic appearance of thin ceramic veneers. Therefore, unfortunately, the long-term success of veneers is tied to the colour stability of the luting agent used to cement them.

Aim

To compare the colour stability of different resin cements and its influence on the final shade of overlying ceramic using two different thicknesses of ceramic.

Material and Methodology

Sixty disc-shaped specimens of high translucency (HT) A2 shade of two thicknesses (0.5 mm & 1 mm) were prepared from lithium disilicate glass-ceramic. The discs of each thickness were further divided into three groups randomly depending upon the resin cements used. Group A - light cure resin cement - Variolink N LC by Ivoclar Vivadent in clear shade, Group B - base paste of dual-cure resin cement - Variolink N by Ivoclar Vivadent in transparent shade and Group C dual-cure resin cement - Clearfil esthetic cement EX by Kuraray in clear shade were used to compare their colour stability. A spectrophotometer was used for the colour measurements of the specimens before and after accelerated ageing. The colour stability was determined by colour differences (ΔE) using the coordinates L*, a* and b* in the pre and post accelerated ageing. Results: On comparing the three resin cements, Group A showed the lowest ΔE, whereas the highest ΔE was observed in Group B. This finding was constant for discs of both thicknesses.

Conclusion

Even though statistically significant results were observed between the groups, they were not visibly differentiable.

Design and Preparation Technology of Single/Dual-Cross-Linking Copolymers Based on Swida wilsoniana Oil

To fully utilize the forestry bioresources, a novel dual-cross-linkable resin monomer of MAHSWAGMA was prepared from Swida wilsoniana oil (SWO). FT-IR and ¹H-NMR analysis demonstrated the successful synthesis of the target product. Five different cross-linking copolymers, including a polymerized vinyl ester/single-cross-linking (PVESC) polymer, a polymerized epoxy/single-cross-linking (PESC) copolymer, a thermal-photo-initiated/dual-cross-linking (TPIDC) copolymer, a photo-thermal-initiated/dual-cross-linking copolymer (PTIDC), and a thermal-initiated/dual-cross-linking copolymer (TIDC), were obtained with different preparation technologies by different initiated cross-linking processes. Thermal and mechanical properties of the five copolymers were all tested, and the effects of different preparation technologies on the properties of prepared copolymers were investigated. The prepared three dual-cross-linking copolymers had higher hardness, relative cross-linking density, glass transition temperature, and more excellent mechanical property than the other two single-cross-linking copolymers. The PTIDC copolymerized system obtained with photo first and thermal latter initiated dual-cross-linking preparation technology had the most excellent comprehensive properties. This study can provide an ideal idea for the design and preparation of dual-cross-linking copolymers based on forestry vegetable oil.

Effect of aging on color stability and bond strength of dual-cured resin cement with amine or amine-free self-initiators

This study aimed to evaluate the effect of aging on the color stability and bond strengths of dual-cured resin cements containing amine or amine-free self-initiators. Three dual-cured and one light-cured resin cements were used. The covered (by lithium disilicate ceramic disks) and uncovered groups (n=10) were included. Color measurements were tested after 24 h, 10,000 and 20,000 thermal cycles (TCs). Micro-shear bond strengths (µSBS) were tested after 24 h, 10,000 and 20,000 TCs, and failure modes were analyzed (n=14). Two-way ANOVA and Tukey's test were implemented for color difference (ΔE*_ab) and µSBS (α=0.05). The mean ΔE*_ab difference was significant among groups (p<0.001). The lowest ΔE*_ab values were obtained for dual-cured resin cement with amine-free self-initiators dual-cured cement after aging in all dual-cured resin cements, and the µSBS of the dual-cured resin cements on ceramic was significantly higher than that of the light-cured ones after aging (p<0.001).

Adhesive strength of fiberglass posts treated with thio-urethane-based experimental silanes

Purpose:

The aim of this study was to evaluate the adhesive bond strength of fiberglass posts treated with experimental silanes based on thio-urethane and submitted to thermo and mechanical cycles.

Materials and methods:

Bovine roots were divided into six groups: RX-RU2 (RelyX CP + RelyX U200); PETMP-HDDI-RU2 (PETMP-HDDI + RelyX U200); PETMP-BDI-RU2 (PETMP-BDI + RelyX U200); RX-RU (RelyX CP + RelyX Ultimate); PETMP-HDDI-RU (PETMP-HDDI + RelyX Ultimate); PETMP-BDI-RU (PETMP-BDI + RelyX Ultimate). One slice from each root third (n=10) was submitted to the push-out test and the values evaluated with R Program statistical analysis, while the failure pattern assessed in percentage.

Results:

Among root thirds, RX-RU2 promoted greater strength at the cervical and apical thirds; PETMP-HDDI-RU2 showed highest values at the three thirds; and PETMP-BDI-RU2 was strongest at the apical third. RX-RU presented higher strength at the apical third, and PETMP-HDDI-RU and PETMP-BDI-RU had similar values at the three thirds. In each root third, PETMP-HDDI-RU2 showed similar strength at all thirds, and similar strength at the apical third was observed for other associations. Mixed and adhesive failures predominated.

Conclusion:

Experimental silanes promoted different bond strength values in the adhesion of fiberglass posts to the root thirds, with better results for PETMP-HDDI silane. The root region did not influence the failure pattern and most slices showed mixed (MCDP) or adhesive (ADP) failure.

Effect of Tack Cure on Polymerization Shrinkage of Resin-based Luting Cements

CLINICAL RELEVANCE

Self-cure after tack cure could result in a lower polymerization shrinkage in some resin-based luting cements, which is closely related to lower degree of cure.

SUMMARY

Effect of fiber post space irrigation with different peracetic acid formulations on the bond strength and penetration into the dentinal tubules of self-etching resin cement

STATEMENT OF PROBLEM

The post space must be irrigated with solutions that do not interfere with the bond strength and enhance penetration into the dentinal tubules of self-etching resin cement. Which solution is best is unclear. Peracetic acid with different formulations appears to be a good option.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of irrigating the fiber post space by using 1% peracetic acid (PA) at low (LH) or high (HH) hydrogen peroxide concentration on the bond strength and penetration into the dentinal tubules of RelyX U200 self-etching resin cement.

MATERIAL AND METHODS

After intraroot preparation for fiber posts in 60 endodontically treated teeth, the specimens were divided into 4 groups (n=15) according to the irrigation protocol: CG (control), distilled water; NA (NaOCl), 2.5% sodium hypochlorite; LHPA, PA with a low concentration of hydrogen peroxide; and HHPA, PA with a high concentration of hydrogen peroxide. The fiber posts were then cemented with self-etching resin cement labeled with rhodamine. Cross sections of the thirds were obtained by confocal scanning microscopy and submitted to the push-out and cement penetration tests. The data obtained in the push-out tests were evaluated by using ANOVA and the Tukey post hoc test, and those data obtained in the confocal screening were evaluated by using the Kruskal-Wallis and Dunn (Bonferroni correction) tests (α=.05).

RESULTS

Bond strength values in the cervical third of the CG were higher than those in NA (P=.035) but similar to those of the other groups (P=.05). In the other thirds, CG and LHPA values were similar to one another (P=.05) but higher than those of NA and HHPA (P<.001). The penetration rate assessed by confocal scanning microscopy revealed similar results in the cervical third for all groups (P=.075), except for NA which provided the lowest penetration. In the remaining thirds, CG and LHPA provided the highest penetration rate (P=.015).

CONCLUSIONS

The LHPA group had no negative effects on the bond strength and penetration into the dentinal tubules of the self-etching resin cement.

The effectiveness of glass ionomer cement as a fiber post cementation system in endodontically treated teeth

This study compared the performance of a glass ionomer (GC Gold Label 1, GIC) as a fiber post cementation system for glass fiber posts with a self-adhesive resin cement (Relyx U200, RUC) and a conventional resin cement system (Scotchbond Muli-Purpose and Relyx ARC, RAC). Thirty endodontically treated canines were randomly divided in three groups (n = 10), according to the fiber post cementation system: (RAC)-Scotchbond Multi-Purpose and Relyx X ARC; (RUC)-Relyx U200 and (GIC)-GC Gold Label 1 Luting & Lining. Rhodamine was incorporated into the cementation system prior to the fiber post cementation. After glass fiber post cementation, roots were incubated in artificial saliva for 6 months. After that, specimens from the cervical, middle, and apical thirds of the post space were prepared and analyzed using a push-out bond strength test and confocal laser microscopy. ANOVA one way and Tukey tests showed that GIC and RUC demonstrated similar push-out bond strength values, independently of the post space third (p > .05); however, values were greater than those shown by RAC (p < .05). For dentin penetrability, GIC and RUC also had similar results (p > 0.05) and lower than RAC (p < 0.05). Inside the root canal, the cementation system using glass ionomer cement (GC Gold Label 1 Luting & Lining) has similar push-out bond strength to the self-adhesive resin cement (Relyx U200) and these were higher than the conventional resin (Relyx ARC), despite its higher dentin penetrability.

The design, preparation, and properties of dual-crosslinking copolymerized systems based on hemp oil

Novel, dual-crosslinking, resin monomers of MAHHAGMA and HHAGE were synthesized using hemp oil.

Effect of Different Adhesive Strategies and Time on Microtensile Bond Strength of a CAD/CAM Composite to Dentin

PURPOSE

The aim of this study was to evaluate the effect of adhesive strategy and time on the microtensile bond strength of a computer-aided design/computer-aided manufacturing (CAD/CAM) composite to dentin.

METHODS AND MATERIALS

Sixty CAD/CAM composite blocks were bonded to human dentin with simplified bonding agents using etch-and-rinse and self-etching approaches and amine-based and amine-free resin cements, with and without the application of a dual-cure activator (DCA; n=10): SBP-ARC (Adper Single Bond Plus + RelyX ARC), SBP-RXU (Adper Single Bond Plus + RelyX Ultimate), SBP-DCA-RXU (Adper Single Bond Plus + DCA + RelyX Ultimate), SBU-ARC (Scotchbond Universal + RelyX ARC), SBU-RXU (Scotchbond Universal + RelyX Ultimate), and SBU-DCA-ARC (Scotchbond Universal + DCA + RelyX ARC). Each specimen was light cured for 40 seconds under load and stored in distilled water at 37°C for seven days. Stick-shaped specimens (1.0 mm²) were obtained. Half of the specimens underwent microtensile bond strength testing, and the other half were subjected to the same tests after six months of storage. Failure mode was determined using an optical microscope (40×). The data were analyzed by a two-way analysis of variance followed by the Games-Howell test and Student t-test (preset alpha of 0.05).

RESULTS

After seven days, SBU-RXU presented the highest mean bond strength, statistically different from only SBU-ARC (p<0.05). Most of the groups exhibited a statistically significant reduction in bond strength after 6 months (p<0.05), except SBP-RXU and SBU-ARC (p>0.05).

CONCLUSION

The adhesive strategy, with different associations between adhesive systems and resin cements, as well as the use of a DCA, affected the bond strength of both amine-free and amine-based resin cements to a CAD/CAM composite.

Influence of polymerization time on properties of dual-curing cements in combination with high translucency monolithic zirconia

PURPOSE

The aim of this in vitro study was to assess conversion degree (DC), micro-hardness (MH) and bond strength of two dual-curing resin cements employed under translucent monolithic zirconia irradiated with different time protocols.

METHODS

84 square shaped samples of 1mm thickness were prepared from high translucency zirconia blocks and divided into two groups (n=24) according to the cement employed: (1) Rely-X Ultimate; (2) Panavia SA. Each group was further divided into 3 subgroups (n=8) according to the irradiation time: (a) no light; (b) 20s; (c) 120s. Light curing was performed 60s after the sample was placed on the diamond support of a FT-IR spectrophotometer with a high power multiLED lamp. Final DC% were calculated after 10min. After 24h, Vickers Test on the cement layer was performed. The same protocol was used to lute composite cylinders in order to evaluate microshear bond-strength test. ANOVA and Bonferroni tests were performed to find differences between MH and bond-strength to zirconia, while for DC% the Scheirer-Ray-Hare two-way test was used.

RESULTS

The two cements reached higher DC% in subgroup (b) and (c). As concern MH, statistics showed an increase in curing time was able to improve MH significantly. Bond-strength was not affected by irradiation time only for Panavia SA.

CONCLUSIONS

The first null hypothesis has to be rejected since DC% and MH of the dual-cements tested were influenced by the curing time. The second null hypothesis is partially rejected since the bond strength was influenced by the curing time only for Rely-X Ultimate.

Light curing in dentistry and clinical implications: a literature review

Contemporary dentistry literally cannot be performed without use of resin-based restorative materials. With the success of bonding resin materials to tooth structures, an even wider scope of clinical applications has arisen for these lines of products. Understanding of the basic events occurring in any dental polymerization mechanism, regardless of the mode of activating the process, will allow clinicians to both better appreciate the tremendous improvements that have been made over the years, and will also provide valuable information on differences among strategies manufacturers use to optimize product performance, as well as factors under the control of the clinician, whereby they can influence the long-term outcome of their restorative procedures.

Color stability of ceramic laminate veneers cemented with light-polymerizing and dual-polymerizing luting agent: A split-mouth randomized clinical trial

STATEMENT OF PROBLEM

The color stability of luting agents influences the esthetics of ceramic laminate veneers. Clinical studies that have evaluated the color changes of veneers cemented to enamel with light- and dual-polymerizing resin cement are lacking.

PURPOSE

The purpose of this split-mouth randomized clinical trial was to evaluate the color change and marginal discoloration of dual- and light-polymerizing cement used for cementation of ceramic laminate veneers.

MATERIAL AND METHODS

In 10 participants, 0.3-mm-thick ceramic laminate veneers were cemented on the buccal surface of the second premolars without tooth preparation. A randomized application of light-polymerized cement was used on one side and a dual-polymerized cement on the contralateral side. The operator and participants were blinded to the activation mode. Color was evaluated by a blinded evaluator with a spectrophotometer at 24 hours and at 2, 6, 12, and 24 months after cementation. The CIELab (ΔE*_ab) and CIEDE2000 (ΔE*₀₀) formulas were used to quantify color alteration, and Δa*, Δb*, and ΔL* were calculated between the first and subsequent measurements. US Public Health Service guidelines were used to evaluate the marginal discoloration.

RESULTS

Wilcoxon tests did not show a statistical difference in ΔE*_ab and ΔE*₀₀ between the groups (P>.05). At 24 months, the median ΔE*_ab was 2.31 (interquartile ranges [IQR]: 3.34) for the light-polymerizing mode and 1.57 (IQR: 0.41) for the dual-polymerizing mode, while the median ΔE*₀₀ was 1.65 for the light-polymerizing mode (IQR: 2.34) and 1.18 for the dual-polymerizing mode (IQR: 0.25). The thresholds for clinically acceptable color changes ΔE*_ab>3.46 and ΔE*₀₀>2.25 were found for both curing modes. Marginal discoloration was observed from the 2-year assessment.

CONCLUSIONS

The color stability of ceramic laminate veneers was similar for both of the polymerizing modes for all evaluated periods. Marginal discoloration increased over a 2-year period for both the light- and the dual-polymerizing modes.

Degree of conversion and bond strength of resin-cements to feldspathic ceramic using different curing modes

Resin cements have led to great advances in dental ceramic restoration techniques because of their ability to bond to both dental structures and restorative materials.

Análise comparativa da resistência de união de um cimento convencional e um cimento autoadesivo após diferentes tratamentos na superfície de pinos de fibra de vidro

Resumo Introdução Os pinos de fibra de vidro são uma alternativa aos núcleos metálicos e apresentam vantagens, tais como: estética, módulo de elasticidade semelhante à dentina e cimentação imediata após o término do tratamento endodôntico. Ainda, apresentam a capacidade de aderir ao cimento resinoso e este, à dentina, por meio de técnicas adesivas. Objetivo Comparar a adesão de um cimento resinoso convencional e um autoadesivo a pinos de fibra de vidro, e os efeitos de diferentes tratamentos de superfície na resistência adesiva dos pinos. Material e método Trinta pinos foram divididos em três grupos: Controle: sem tratamento na superfície; Jateamento: jateamento com óxido de alumínio por 30 segundos, e Peróxido: imersão em peróxido de hidrogênio 24% por um minuto. Em seguida, corpos de prova foram obtidos a partir de cilindros de cimento resinoso contendo o pino de fibra posicionado no centro de seu longo eixo. Em cada grupo, cinco pinos foram associados ao adesivo Âmbar + cimento convencional AllCem Core e os outros cinco pinos, ao cimento autoadesivo RelyX U200. O conjunto pino/cimento foi segmentado e avaliado em relação à resistência de união (RU) por push-out. Os dados foram analisados estatisticamente pelos testes de ANOVA e Tukey (p<0,05). Resultado Os cimentos avaliados exibiram valores de RU semelhantes. Em relação aos tratamentos de superfície, os maiores valores de RU foram encontrados no grupo Jateamento. Conclusão O cimento convencional, AllCem Core, e o cimento autoadesivo, RelyX U200, mostraram valores de resistência de união semelhantes. Ainda, o jateamento com óxido de alumínio favoreceu a adesão dos pinos aos cimentos.

Degree of Conversion and Mechanical Properties of Resin Cements Cured Through Different All-Ceramic Systems

Abstract: The aim of this study was to verify the degree of conversion (DC), Vickers microhardness (VH) and elastic modulus (E) of resin cements cured through different ceramic systems. One 1.5-mm-thick disc of each ceramic system (feldspathic, lithium dissilicate and zircônia veneered with feldspathic) was used. Three dual-cured (Allcem, Variolink II and RelyX U200) and one chemically-cured (Multilink) resin cements were activated through ceramic discs. For dual-cured resin cements was used a conventional halogen light-curing unit (Optilux 501 at 650 mW/cm2 for 120 s). Samples cured without the ceramic disc were used as control. The samples were stored at 37 °C for 24 h. ATR/FTIR spectrometry was used to evaluate the extent of polymerization in the samples (n=5). Micromechanical properties - VH and E - of the resin cements (n=5) were measured with a dynamic indentation test. Data were statistically analyzed with two-way ANOVA, Tukey's test and Pearson's correlation (α=0.05). DC was affected only by the type of resin cement (p=0.001). For VH, significant interaction was detected between resin cement and ceramic (p=0.045). The dual-cured resin cements showed no significant differences in mean values for E and significantly higher values than the chemically-cured resin cement. The degree of conversion and the mechanical properties of the evaluated resin cements depend on their activation mode and the type of ceramics used in 1.5 mm thickness. The dual-cured resin cements performed better than the chemically-cured resin cement in all studied properties.

Effect of Different Thicknesses of Pressable Ceramic Veneers on Polymerization of Light-cured and Dual-cured Resin Cements

AIM

This study evaluated the effects of ceramic veneer thicknesses on the polymerization of two different resin cements.

MATERIALS AND METHODS

A total of 80 ceramic veneer disks were fabricated by using a pressable ceramic material (e.max Press; Ivoclar Vivadent) from a Low Translucency (LT) ingot (A1 shade). These disks were divided into light-cured (LC; NX3 Nexus LC; Kerr) and dual-cured (DC; NX3 Nexus DC; Kerr) and each group was further divided into four subgroups, based on ceramic disk thickness (0.3, 0.6, 0.9, and 1.2 mm). The values of Vickers microhardness (MH) and degree of conversion (DOC) were obtained for each specimen after a 24-hour storage period. Association between ceramic thickness, resin cement type, and light intensity readings (mW/cm(2)) with respect to microhardness and degree of conversion was statistically evaluated by using analysis of variance (ANOVA).

RESULTS

For the DOC values, there was no significant difference observed among the LC resin cement subgroups, except in the 1.2 mm subgroup; only the DOC value (14.0 ± 7.4%) of 1.2 mm DC resin cement had significantly difference from that value (28.9 ± 7.5%) of 1.2 mm LC resin cement (p < 0.05). For the MH values between LC and DC resin cement groups, there was statistically significant difference (p < 0.05); overall, the MH values of LC resin cement groups demonstrated higher values than DC resin cement groups. On the other hands, among the DC resin cement subgroups, the MH values of 1.2 mm DC subgroup was significantly lower than the 0.3 mm and 0.6 mm subgroups (p < 0.05). However, among the LC subgroups, there was no statistically significant difference among them (p > 0.05).

CONCLUSION

The degree of conversion and hardness of the resin cement was unaffected with veneering thicknesses between 0.3 and 0.9 mm. However, the DC resin cement group resulted in a significantly lower DOC and MH values for the 1.2 mm subgroup.

CLINICAL SIGNIFICANCE

While clinically adequate polymerization of LC resin cement can be achieved with a maximum 1.2 mm of porcelain veneer restoration, the increase of curing time or light intensity is clinically needed for DC resin cements at the thickness of more than 0.9 mm.

Effect of ultraviolet aging on translucency of resin-cemented ceramic veneers: an in vitro study

PURPOSE

The aim of this in vitro study was to evaluate the translucency of ceramic veneers cemented with light- or dual-cured resin cements after accelerated aging.

MATERIALS AND METHODS

A total of 392 specimens were made of shade A1 with 0.5- and 1.0-mm thickness. Light-cured RelyX Veneer and dual-cured Maxcem Elite and Variolink II resin cements were applied on the porcelain discs with a thickness of 0.1 mm. Translucency parameter (TP) values of the ceramic veneers after cementation and UV aging test were evaluated. Statistical analyses were done with ANOVA and Tukey's tests and paired sample t-test (p < 0.05).

RESULTS

All the resin cements affected the TP values of 0.5-mm-thick ceramic, while RelyX Veneer Tr (TP = 11.15; p = 0.608), Variolink II Tr (TP = 10.98; p = 0.55), and Maxcem Clear (TP = 11.81; p = 0.702) did not affect the translucency of 1-mm-thick ceramics (TP = 11.38). The aging process affected TP values of both ceramics and cemented ceramics, as the TP values decreased after aging. Among the TP values of opaque shade resin cements, there were significant differences between the "ceramic," "ceramic + RelyX Veneer WO," "ceramic + Variolink II WO," and "ceramic + Maxcem WO" variables for both 0.5 and 1 mm thicknesses (p < 0.05). There were no significant differences between "ceramic," "ceramic + RelyX Veneer Tr," "ceramic + Variolink II Tr," and "ceramic + Maxcem Clear" variables at 0.5 mm thickness, and there were no significant differences between "ceramic," "ceramic + RelyX Veneer Tr," and "ceramic + Variolink II Tr" variables after aging (p > 0.05).

CONCLUSIONS

The TP of the same color of resin cements varied related to the type or brand. Aging caused both the ceramics and cemented ceramics to become more opaque.

Effects of refractive index solutions on the color of different luting cements

PURPOSE

The purpose of this study is to determine the effects of refractive index solutions on the color of different luting cements at different periods.

MATERIALS AND METHODS

Fourteen disc-shaped specimens were prepared for three different universal shade luting cements. All specimens were divided into two groups and a phthalate ester and glycerol refractive index solution was applied to the specimens at different periods. Color differences (ΔE*) were calculated for before and after 5, 15, 60 min and 24 h periods of applying refractive index solutions. Data were analyzed with multiple analysis of variance (ANOVA) and mean values were compared by the Tukey HSD test (α = 0.05).

RESULTS

Periods and periods-cement interaction were statistically significant (p ≤ 0.05). There was no statistically significant difference between the mean ΔE values of refractive index solutions and cement groups (p > 0.05).

CONCLUSION

Refractive index solutions affected the color of luting cements.

Mechanical and morphological evaluation of the bond-dentin interface in direct resin core build-up method

OBJECTIVES

The purpose of this study was to evaluate the interfacial adhesion between resin and root canal dentin in the direct resin core build-up method in terms of microtensile bond strength (μTBS) and dentin micro morphology.

METHODS

Single-rooted human teeth were decoronated at the cementoenamel junction and endodontically treated. Post spaces were prepared in the roots to a depth of 10mm. The spaces were then treated with a dual-cure bonding system, and filled with dual-cure resin composite. After 24-h storage in water at 37 °C, they were trimmed into approximately 1.0-mm(2) beams for μTBS. Bond strength was analyzed with one-way ANOVA and Tukey's test. The fractured surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). Sectioned specimens were observed by ultra-high-voltage transmission electron microscopy.

RESULTS

The bond strength of root dentin decreased gradually from the coronal to apical side, and the bond strength of the coronal section was significantly higher than that of the radicular section. Moreover, the failure modes in the coronal and apical sides of the specimens differed. The apical specimens fractured within the core material, while the coronal specimens fractured at the bonding layer. SEM and EDX analyses revealed that the core material penetrated into dentinal tubules in the apical region.

SIGNIFICANCE

In the direct resin core build-up method, the interfacial adhesion of resin to root canal dentin may be insufficient in the apical region of the root canal due to poor polymerization.

Effect of Ceramic Veneer Opacity and Exposure Time on the Polymerization Efficiency of Resin Cements

The objective of this study was to determine the degree of conversion (DC), hardness (H), and modulus of elasticity (E) of a dual-cured resin cement, a light-cured resin cement, and a flowable resin cured through opaque or translucent ceramic with different exposure times. RelyX ARC (dual), RelyX Veneer (light-cured), and Filtek Z350 Flow resin specimens 0.5 mm thick were cured for 40, 80, and 120 seconds through 1-mm thick translucent or opaque feldspathic ceramic disks (n=10). The specimens were stored at 37°C for 24 hours. Half of each specimen was used to test the DC and the other half to test H and E. The DC was determined in a Fourier transform infrared spectrometer in absorbance mode at peaks of 1638 cm−1 and 1610 cm−1. H and E were determined using nanoindentation with one loading cycle and a maximum load of 400 mN. The data were analyzed with three-way analysis of variance (ANOVA), the Games-Howell test, and the Pearson correlation test (α=0.05). Statistically significant differences were found for all three factors (material, opacity, and exposure time), as well as interaction between them. The opaque ceramic resulted in lower DC, H, and E than the translucent ceramic for an exposure time of 40 seconds. An exposure time of 120 seconds resulted in a similar DC for all materials, irrespective of the opacity of the ceramic. Materials cured for 120 seconds had higher H and E than those cured for 40 seconds. The exposure time and opacity of the ceramic exerted an influence on the DC, H, and E of the materials evaluated.

The effect of ceramic restoration shade and thickness on the polymerization of light- and dual-cure resin cements

OBJECTIVES

Inadequately polymerized resin cements may negatively affect the clinical performance of cemented all-ceramic restorations. The purpose of this in vitro study was to evaluate the effect of ceramic thickness and shade on the microhardness of various light-cured (LC) and dual-cured (DC) resin cements. The amount of light transmission through the restoration was also evaluated to correlate the results.

METHODS

Three different brands of resin cements (Appeal/Ivoclar; Calibra/Dentsply; Nexus 2/Kerr) were used in LC and DC forms to prepare disk-shaped samples (0.5-mm thickness × 5-mm diameter) (n=15). Study group samples were light-cured for 40 seconds (Flashlite 1401/Discus Dental) through four shades (ETC1, ETC2, ETC3, ETC4) and four thicknesses (1 mm, 2 mm, 3 mm, 4 mm) of all-ceramic ingot discs (IPS Empress Esthetic/Ivoclar). Control samples were directly cured without the presence of ceramic. The light transmission through various shades and thicknesses of ceramics was measured using a hand-held radiometer (Demetron, Kerr). Vickers microhardness measurements were performed (Micromet/Buehler) at 24 hours following dark storage in 37°C water. Correlation between ceramic shade, thickness, and light intensity readings (mW/cm2) with respect to microhardness was statistically evaluated using analysis of variance (p=0.05).

RESULTS

Ceramic thickness of 3 mm and/or above significantly decreased the microhardness values in all LC and DC groups (p<0.0001). Ceramic shade had a significant effect only on Calibra in both LC and DC groups (p<0.0001). Microhardness values of LC groups were significantly lower than DC groups (p<0.0001). Control groups had significantly higher hardness values in all cement groups (p<0.0001). There was a significant correlation between the amount of light transmitted and hardness (p=0.000).

CONCLUSION

The ceramic thickness has a more intense effect on polymerization compared to the ceramic shade. Overlying ceramic thickness of 3 mm and above was found to adversely affect the polymerization of LC and DC resin cements and therefore a 3-mm thickness was considered the critical threshold.

In vitro evaluation of color replication of metal ceramic specimens using visual and instrumental color determinations

STATEMENT OF PROBLEM

It remains unclear whether or not the performance of intraoral colorimetric devices is accurate.

PURPOSE

The purpose of this study was to evaluate the color replication of metal ceramics using an intraoral colorimeter and visual shade determination.

MATERIAL AND METHODS

Twenty-five metal ceramic specimens were prepared to match 5 different shades (A1, B1, C3, D3, A3.5) of the Vitapan Classical shade guide. Five clinicians determined the shades of the specimens using the same shade guide. The shade determination was based on the agreement of at least 3 of the 5 observers. Instrumental shade determinations were made with an intraoral colorimeter (ShadeEye NCC) to obtain results in terms of the Vitapan Classical shade guide. Based on these shade determinations, 50 additional metal ceramic specimens (25 visually determined and 25 instrumentally determined) were prepared. The master (initial) and definitive (additional) specimens were analyzed with a spectrophotometer. L*, a*, b* values of each specimen were measured, and the color difference between the master and definitive specimens was calculated. The Wilcoxon signed rank test was used to analyze the color difference (ΔE) values (α=.05).

RESULTS

Visual shade determination produced lower ΔE values than instrumental shade determination. The differences between ΔE values of different shade determination methods were significant for master specimens of the shades B1 and A3.5 (P=.02). The ΔE value calculated from the result of instrumental determination of shade B1 (ΔE=2.97) was within the clinically acceptable limit (ΔE=3.5), whereas the ΔE value for A3.5 (4.03) exceeded the limit for clinical acceptability. The ΔE values for C3 exceeded the acceptable limit for both shade determination methods (ΔE>3.5).

CONCLUSIONS

Color replication of metal ceramic specimens using visual shade determination was more accurate compared to instrumental shade determination. The replication of the high-value shades (A₁-B₁) was observed to be reliable with both shade determination methods.

Cements and adhesives for all-ceramic restorations

Dental cements are designed to retain restorations, prefabricated or cast posts and cores, and appliances in a stable, and long-lasting position in the oral environment. Resin-based cements were developed to overcome drawbacks of nonresinous materials, including low strength, high solubility, and opacity. Successful cementation of esthetic restorations depends on appropriate treatment to the tooth substrate and intaglio surface of the restoration, which in turn, depends on the ceramic characteristics. A reliable resin cementation procedure can only be achieved if the operator is aware of the mechanisms involved to perform the cementation and material properties. This article addresses current knowledge of resin cementation concepts, exploring the bonding mechanisms that influence long-term clinical success of all-ceramic systems.

Esthetic and functional consideration in restoring endodontically treated teeth

The selection of the best restoration for an endodontically treated tooth in the aesthetic zone depends on strength and the ability to recreate the form, function, and aesthetics of the natural tooth. The increased use of all-ceramic materials is a result of improved ceramic materials and adhesive systems. However, the advent of the current variety of translucent ceramic systems makes the shade of the abutment important in achieving the desired aesthetic outcome. This article discusses the different types of posts used in the restoration.

Effect of Dual Cure Composite as Dentin Substitute on the Marginal Integrity of Class II Open-Sandwich Restorations

Dual-curing composites may present a good alternative to RMGIC in open-sandwich restorations and act as a dentin substitute. However, this study showed that RMGIC remains the best intermediate material when open-sandwich restorations are indicated.

Color stability of indirect composite materials polymerized with different polymerization systems

The purpose of the current study was to evaluate the color stability of two indirect composite materials (Sinfony and Pearleste) polymerized with different laboratory polymerization systems. Disk specimens were prepared with their proprietary polymerization systems (Visio and Pearlcure systems) or with a metal halide light polymerization unit (Hyper LII) for 60, 120, and 180 s. After storage at 37 degrees C for 24 h, the specimens were immersed in either purified water or tea. Color change between baseline evaluation and after 4 weeks was determined with a dental chroma meter (ShadeEye NCC) using black and white backgrounds. CIE 1976 L(*)a(*)b(*) values were determined, and they were converted into DeltaE(*)(ab) values. The DeltaE(*)(ab) value of the Sinfony material immersed in tea was the highest when the material was polymerized with the proprietary Visio system. The Pearleste material immersed in purified water and tea was not affected substantially by the polymerization systems. Among the 12 groups polymerized with the Hyper LII units, DeltaE(*)(ab) values of 11 groups were significantly lower for the Pearleste material than for the Sinfony material. It can be concluded that the Pearleste material was stable against color change when the material was polymerized with either the Pearlcure system or with the Hyper LII unit.

Effects of photocuring strategy on bonding of dual-cure one-step self-etch adhesive to root canal dentin

This study evaluated the effects of light power density and light exposure time on regional bond strength of Clearfil DC Bond to root canal dentin. Post spaces were prepared in extracted premolars. Root canal dentin was treated with a dual-cure bonding system, Clearfil DC Bond, and light-cured for 10, 20, or 30 seconds using two halogen light curing units: Optilux 501 (830 mW/cm2) and Hyperlightel (1350 mW/cm2). Following which, all post spaces were filled with a dual-cure resin composite. After 24-hour storage, microtensile bond strengths (microTBS) at the coronal and apical regions were measured. At the coronal region, microTBS values were similar among all the experimental groups. At the apical region, bond strength improved when the curing time was extended to 30 seconds with Optilux 501, and likewise with Hyperlightel when curing time was extended to 20 or 30 seconds. In addition, significant differences in microTBS between the coronal and apical regions disappeared with prolonged curing times.

Effect of dual cure composite as dentin substitute on marginal integrity of class II open-sandwich restorations

The current study compared the marginal adaptation of Class II open-sandwich restorations with a RMGIC versus a dual-cure composite as dentin substitute. Class II cavities were prepared on 50 extracted human third molars. The teeth were randomly assigned to two groups of 25 teeth to compare one dual cure composite (MultiCore Flow) with one resin-modified glass-ionomer cement (Fuji II LC) in open-sandwich restorations recovered with a light cure composite. The teeth were thermomechanocycled (2000 cycles, 5 degrees C to 55 degrees C; 100,000 cycles, 50 N/cm2). The specimens were then sealed with a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for two hours and exposed to a photo-developing solution for six hours. The specimens were sectioned longitudinally and silver penetration was directly measured using a light microscope. The results were expressed as a score from 0 to 3. The data were analyzed with a non-parametric Kruskal and Wallis test. The degree of leakage significantly increased with MultiCore Flow (median 2) compared to Fuji II LC (median 1). Resin-modified glassionomer cements remain the best intermediate material when open-sandwich restorations are indicated. A comparison of the degradation of these materials over time remains a topic to be investigated by future studies.

The Effect of the Presence and Presentation Mode of Co-Initiators on the Microtensile Bond Strength of Dual-Cured Adhesive Systems Used in Indirect Restorations

The presentation mode of co-initiators added to bonding agents may affect the bond strength of indirect composite restorations to dentin.

Influence of Cement Shade and Water Storage on the Final Color of Leucite-reinforced Ceramics

Luting cement under 0.8 mm thick leucite-reinforced ceramic changed the final color of the ceramic and could be seen by the human eye. Therefore, clinicians may prefer to use try-in pastes or polymerized luting composite shade guides to compensate for the change in color of definitive restorations, such as laminate veneers. The final color differences between ceramics luted with cements in A1 and A3 shades were not clinically perceivable at each measurement. Within the limitations of this study, changing the color of an IPS Empress laminate veneer restoration via the shade of the cement seems not to be a preferred method.