Microtensile bond strength of dual-polymerizing cementing systems to dentin using different polymerizing modes

Effect of dentin surface conditions and curing mode of resin cement on the dentin bond strength

This study investigates the effects of dentin's drying time, roughness, and curing modes of resin cement on bond strength. Forty human teeth were divided into eight groups based on three experimental factors: dentin's roughness by 240-or 600-grit SiC paper (coarse or fine), dentin wetness with air-drying time (5-s or 10-s), and Single Bond Universal adhesive's curing mode by co-curing with RelyX Ultimate cement or light-curing separately (co-curing or light-curing). The micro-tensile bond strength of fifteen resin-dentin stikcs per groups was measured. Failure mode and adhesive layers were observed using stereoscopic and confocal laser scanning microscopy, respectively. The curing mode of the adhesive layer affected the bond strength of the dentin-resin cement (p<0.05). In particular, the light-curing mode exhibited a significantly higher bond strength than the co-curing one (p<0.05). The bond strength between the resin cement and dentin was improved in the 5-s drying groups than in the 10-s drying groups.

Simultaneous implant placement and restoration with guided bone regeneration in the mandibular anterior region

BACKGROUND

Restoring the mandibular anterior teeth by implants can be difficult due to potential complications arising from using prosthetic implant connections that are larger than the incisors at the cementoenamel junction level.

METHODS

This retrospective study is aimed at determining the survival and esthetic outcomes of anterior mandible implants immediately placed and restored in patients diagnosed with stages 3-4 periodontitis. The study included 75 implants that were inserted along with guided bone regeneration in 42 patients. Over a follow-up period of 3 to 8 years (mean of 6.95 ± 1.78 years), the study evaluated esthetic, marginal bone loss (MBL), and biological and prosthetic complications.

RESULTS

No failures were recorded during the follow-up period; after eight years, the survival rate was 100%. Patient's age and gender did not have a statistically significant impact on MBL, but smokers had a greater MBL than non-smokers at the 8-year (2.98 mm vs. 1.23 mm, respectively, p = 0.016) time-point. At 3 years, only 13.3% of the implants had mesial papillae, 36.0% had distal papillae, and 16.0% had the cervical metallic part of the abutment exposed. Peri-implantitis was diagnosed in 20.7% of the patients at the 8-year follow-up time.

CONCLUSIONS

Based on the limitations of this study, immediate placement and restoration of the mandibular incisors can be a feasible procedure, but only a few implants achieved the complete restoration of the papillae.

In vitro performance of an autocured universal adhesive system in bonding to dentin

BACKGROUND

The successful integration of resin-based dental adhesives significantly impacts restorative dentistry, providing efficient and aesthetically pleasing caries treatments. Among various adhesives, one-step self-etching adhesives (1-SEAs) have gained popularity due to their simplicity and short application time. However, concerns have been raised regarding their bonding performance and marginal adaptation characteristics, which differ from two-step self-etching adhesives (2-SEAs) and three-step etch-and-rinse adhesives. Additionally, light-cured bonding materials may encounter challenges in deep cavities and inaccessible areas, necessitating extended light irradiation time. Autocured bonding materials are a potential solution, but limited comparative studies have been conducted on their performance.

METHODS

In this in vitro study, we evaluated a new autocured universal bonding material (Bondmer Lightless 2) and compared the results with recent light-cured bonding materials. Microshear bond strength (μSBS) tests were performed on 25 human molars using five different combinations of adhesives and composite resins: Bondmer Lightless 2 with Estelite Bulk Fill Flow (BE group), Bondmer Lightless 2 with a prototype composite resin (BO group), Prime&Bond Universal with SDR flow + (PS group), Scotchbond Universal with Filtek Bulk Fill (SF group), and G-Premio Bond with Gracefil BulkFlo (GG group). The bond strengths and failure modes were assessed using a universal testing machine and scanning electron microscope (SEM), respectively. Marginal adaptation was evaluated using swept-source optical coherence tomography (SS-OCT) and confocal laser scanning microscopy (CLSM) on 40 sound bovine maxillary incisors.

RESULTS

The μSBS test showed no significant differences in bond strength among the tested groups. Most failure modes were observed at the bond interface between the adhesive and the dentin. The autocured bonding material demonstrated significantly higher marginal adaptation (SI%) than PS, SF, and GG. The CLSM images corresponded with gaps observed in the SS-OCT images, indicating improved marginal sealing in the autocured group.

CONCLUSIONS

The new autocured universal bonding material exhibited comparable bond strength to a conventional light-cured material while demonstrating a superior marginal adaptation level. This finding suggested that the autocured material could be a valuable alternative, especially when extended light irradiation would pose a challenge. Further clinical studies would be warranted to evaluate the performance of the autocured bonding material in actual restorative dental practice.

Fracture resistance of CAD/CAM blocks cemented on dentin using different cementation strategies

PURPOSE

To determine whether the fracture resistance of computer-aided design/computer-aided manufacturing (CAD/CAM) resin-based composites and polymer-infiltrated ceramic network materials cemented on dentin is influenced by the restoration thickness and composite cement application strategy.

METHODS

Disc-shaped specimens (Ø = 7 mm) of 0.8 mm and 1.5 mm thicknesses were milled from two CAD/CAM materials: resin-based composite (RBC, Cerasmart 270) and polymer-infiltrated ceramic network (PICN, Vita Enamic). The discs (n = 8 per group) were cemented on flattened dentin using three different cementation strategies: 1) self-adhesive composite cement (RelyX U200) in light-curing mode (LC-SAC), 2) universal adhesive (Single Bond Universal) with composite cement (RelyX Ultimate) in auto-curing mode (AC cement), and 3) adhesive and composite cement as in 2) but in light-curing mode (LC cement). The restorative surface was indented perpendicularly with a compressive load using a universal testing machine until fracture. The fracture resistance (N) of RBC and PICN was separately analyzed using two-way ANOVA and Tukey's post-hoc test (α = 0.05).

RESULTS

The fracture resistance of each material was significantly influenced by the material thickness and cementation strategy (P < 0.05). Irrespective of the material type and cementation strategy, thicker materials exhibit higher fracture resistance. For RBC, the fracture resistance of the LC cement group was significantly higher than that of AC cement only at 0.8 mm thickness. For PICN, the LC-cement cementation strategy produced superior fracture resistance, regardless of the restoration thickness.

CONCLUSIONS

The fracture resistance of Cerasmart 270 was higher for the thicker material; the fracture resistance of LC cement was higher than that of AC cement at 0.8 mm thickness cemented to dentin. In comparison, LC cement showed the highest fracture resistance for Vita Enamic for both material thicknesses.

The effect of curing mode of dual-cure resin cements on bonding performance of universal adhesives to enamel, dentin and various restorative materials

The effect of curing mode of dual-cure resin cements on the tensile bond strength (TBS) of universal adhesives to enamel, dentin, zirconia, lithium disilicate ceramics (LDS), feldspathic porcelain (FP), and a Pd-Au alloy was evaluated. The substrates were bonded using Tokuyama Universal Bond (TUB) or Scotchbond Universal Adhesive (SBU), followed by luting with Estecem II (ECII) or Rely-X Ultimate (RXU), respectively, which were used either in light-curing or self-curing mode. The TBS test was performed after 24 h or 5,000 thermal cycles. Light-curing significantly improved the 24-h TBS of TUB/ECII to enamel, dentin and FP, as well as the TBS of SBU/RXU to all substrates except LDS. After thermal cycling, light-curing significantly increased the TBS of both adhesives/cements to dentin, but significant differences between curing modes were seldom observed for other substrates. This suggested that light-curing is essential for the hydrophilic dentin, but self-curing might be sufficient for other substrates.

Effect of elapsed time after air abrasion on bond strength of luting agent to CAD/CAM resin blocks

This experiment assessed the effect of elapsed time between air abrasion and bonding on tensile bond strength (TBS) between computer-aided design/computer-aided manufacturing (CAD/CAM) composite resin blocks and luting agents. Specimens were divided into eight groups classified by block type (Estelite Block or HC Block), elapsed time after air abrasion (none [D0] or 1 week [D7]), luting agent type (Estecem [ESC] or Rely X Ultimate [RLU]), and polymerization condition (chemical cured [CC] or light cured [LC]). In the CC+ESC group, TBS was significantly higher at D0 than at D7. There was also a significant difference between blocks in all groups except the LC+ESC group. Scanning electron microscopy and atomic force microscopy were used to observe the surfaces of blocks after air abrasion and indicated that blocks absorbed water in air with elapsed time, which affected TBS between CAD/CAM composite resin blocks and luting agents.

Effect of light absence or attenuation on biaxial flexural strength of dual-polymerized resin cements after short- and long-term storage

OBJECTIVE

To evaluate whether biaxial flexural strength (BFS) of dual resin cements is affected by light absence or attenuation, storage time, or cements' chemical nature.

MATERIALS AND METHODS

One hundred and twenty disk-shaped specimens were made from each cement (non-self-adhesive cement and self-adhesive cement) using Teflon molds on a controlled temperature surface (35°C). Specimens were polymerized as follows (N = 30): self-cured, directly light-cured, light-cured at a distance of 6 mm between the light tip and the specimen, and through a 6-mm thick composite resin barrier (indirectly light-cured). Each group was divided (N = 10) for storage purposes (15 minutes, 24 hours, and 6 months). Specimens were placed into a biaxial-flexure jig and a vertical load was applied until failure. The BFS values were subjected to generalized linear models statistical analysis and Weibull distributions (α = 0.05).

RESULTS

After 15 minutes aging, neither material achieved enough polymerization to perform the BFS test when polymerized using the self-curing mode. The self-adhesive product demonstrated much lower variation in strength with storage time than did the non-self-curing cement.

CONCLUSIONS

Attenuated/light-curing reduced BFS values only for 15-minutes storage period for both materials. Flexural strength of the self-adhesive cement was less affected by light absence/attenuation and storage time.

CLINICAL SIGNIFICANCE

Biaxial flexural strength of a self-adhesive resin cement is less sensitive to variation in light application and storage time than is a non-self-adhesive cement.

Influence of abutment height and convergence angle on the retrievability of cement-retained implant prostheses with a lingual slot

PURPOSE

Cement-retained implant prostheses can lack proper retrievability during repair, and residual cement can cause peri-implantitis. The purpose of this in vitro study was to evaluate the influence of abutment height and convergence angle on the retrievability of cement-retained implant prostheses with lingual slots, known as retrievable cement-type slots (RCS).

MATERIALS AND METHODS

We fabricated six types of titanium abutments (10 of each type) with two different heights (4 mm and 6 mm), three different convergence angles (8°, 10°, and 12°), a sloped shoulder margin (0.6 mm depth), a rectangular shape (6 mm × 6.5 mm) with rounded edges, and a rectangular ledge (2 mm × 1 mm) for the RCS. One monolithic zirconia crown was fabricated for each abutment using a dental computer-aided design/computer-aided manufacturing system. The abutments and crowns were permanently cemented together with dual-curing resin cement, followed by 24 hours in demineralized water at room temperature. Using a custom-made device with a slot driver and torque gauge, we recorded the torque (N·cm) required to remove the crowns. Statistical analysis was conducted using multiple regression analysis and Mann-Whitney U tests (α=.05).

RESULTS

Removal torques significantly decreased as convergence angles increased. Multiple regression analysis showed no significant interaction between the abutment height and the convergence angle (Durbin-Watson ratio: 2.186).

CONCLUSION

Within the limitations of this in vitro study, we suggest that the retrievability of cement-retained implant prostheses with RCS can be maintained by adjusting the abutment height and convergence angle, even when they are permanently cemented together.

The effect of light sources and CAD/CAM monolithic blocks on degree of conversion of cement

PURPOSE

To assess the degree of conversion (DC) and light irradiance delivered to light-cured and dual-cured cements by application of different light sources through various types of monolithic computer-aided design and computer-aided manufacturing (CAD/CAM) materials.

MATERIALS AND METHODS

RelyX Ultimate Clicker light-cured and dual-cured resin cement specimens with 1.5-mm thicknesses (n=300, 10/group), were placed under four types of crystalline core structure (Vita Enamic, Vita Suprinity, GC Ceresmart, Degudent Prettau Anterior). The specimens were irradiated for 40 seconds with an LED Soft-Start or pulse-delay unit or 20 seconds with a QTH unit. DC ratios were determined by using Fourier transform infrared spectroscopy (FTIR) after curing the specimen at 1 day and 1 month. The data were analyzed using the Mann-Whitney U test (for paired comparison) and the Kruskal-Wallis H test (for multiple comparison), with a significance level of P<.05.

RESULTS

DC values were the highest for RelyX Ultimate Clicker light-cure specimens polymerized with the LED Soft-Start unit. The combination of the Vita Suprinity disc and RelyX Ultimate Clicker dual-cure resin cement yielded significantly higher values at both timepoints with all light units (all, P<.05).

CONCLUSION

Within the limitations of this study, we conclude that the DC of RelyX Ultimate Clicker dual-cure resin cement was improved significantly by the use of Vita Suprinity and the LED Soft-Start light unit. We strongly recommend the combined use of an LED light unit and dual-cure luting cement for monolithic ceramic restorations.

The strategies used for curing universal adhesives affect the micro-bond strength of resin cement used to lute indirect resin composites to human dentin

We evaluated the effect of different curing strategies for universal adhesives on micro-tensile bond strength (μTBS) between resin cement and dentin and/or between resin cement and indirect resin composite. Flat coronal dentin surfaces and composite resin disks were pretreated with silane-containing universal adhesives, with or without light-curing on the dentin-side and/or composite resin disk-side. Resin disks were luted onto the pretreated dentin surfaces with the corresponding dual-cure adhesive resin cements and light-cured, and cut into beams after 24-h water storage. After 0 or 10,000 thermocycles (5ºC/55ºC) in a water bath, the μTBS of the composite resin disk-dentin beam was tested. The μTBS was highest when universal adhesives were applied to both the dentin- and the indirect composite resin disk-side, followed by light-curing. Thermocycling decreased μTBS in all but the Scotchbond Universaltreated group, with light-curing on both sides. The effect of curing strategies is dependent upon the materials.

Effect of priming agents on shear bond strengths of resin-based luting agents to a translucent zirconia material

PURPOSE

The purpose of the present study was to evaluate the effect of priming agents and artificial aging with thermocycling on shear bond strengths of two resin-based luting agents to a translucent zirconia material.

METHODS

A total of 308 pairs of translucent zirconia disk specimens were divided into seven treatment groups: Alloy Primer (ALP), Clearfil Ceramic Primer Plus (CCP), Meta Fast Bonding Liner (MFB), MR. bond (MRB), Super-Bond PZ Primer Liquid B (PZB), V-Primer (VPR), and an unprimed group (UP). The specimens in each group were bonded with Panavia V5 Universal (UNI) and Opaque shade (OPA). Shear bond strengths (n=11 each) were tested before and after 5000 thermocycles. The data were analyzed with the Kruskal-Wallis test and the Steel-Dwass test.

RESULTS

For both 0 and 5000 thermocycles, the ALP (47.8 and 41.5MPa, respectively) and CCP (45.8 and 42.3MPa, respectively) groups showed significantly higher bond strengths than other groups in the UNI luting agent. For the OPA luting agent, CCP group (45.8MPa) exhibited the highest pre-thermocycling bond strength in all groups. The ALP (32.4MPa) and CCP (36.5MPa) groups had significantly higher post-thermocycling shear bond strengths than other groups. In several groups, the shear bond strengths of the UNI luting agent were significantly higher than those of the OPA luting agent before and after thermocycling.

CONCLUSIONS

Application of priming agents containing hydrophobic phosphate monomer (MDP) yielded the durable bond strengths of resin-based luting agents to a translucent zirconia material.

Adhesive Bonding to Computer-aided Design/ Computer-aided Manufacturing Esthetic Dental Materials: An Overview

AIM

To review the adhesive bonding to different computer-aided design/computer-aided manufacturing (CAD/CAM) esthetic restorative materials.

BACKGROUND

The use of CAD/CAM esthetic restorative materials has gained popularity in recent years. Several CAD/ CAM esthetic restorative materials are commercially available. Adhesive bonding is a major determinant of success of CAD/ CAM restorations. Review result: An account of the currently available bonding strategies are discussed with their rationale in various CAD/ CAM materials.

CONCLUSION

Different surface treatment methods as well as adhesion promoters can be used to achieve reliable bonding of CAD/CAM restorative materials. Selection of bonding strategy to such material is determined based on its composition. Further evidence is required to evaluate the effect of new surface treatment methods, such as nonthermal atmospheric plasma and self-etching ceramic primer on bonding to different dental ceramics.

CLINICAL SIGNIFICANCE

An understanding of the currently available bonding strategies to CA/CAM materials can help the clinician to select the most indicated system for each category of materials.

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.

Blue-Light Transmittance of Esthetic Monolithic CAD/CAM Materials With Respect to Their Composition, Thickness, and Curing Conditions

Determining the amount of blue light (360-540nm) passing through nine monolithic computer-aided design/computer-aided manufacturing (CAD/CAM) materials depends on material thickness, initial irradiance, and the distance between the curing unit and the specimen's surface. A total of 180 specimens of two thicknesses (1 mm and 2 mm, n=10/subgroup) were fabricated from TelioCAD, VITA CAD-Temp (VCT), experimental nanocomposite, LAVA Ultimate (LU), VITA ENAMIC (VE), VITA MarkII (VM), IPS EmpressCAD (IEC), IPS e.maxCAD (IEM), and CELTRA DUO (CD). The irradiance passing through the CAD/CAM materials and thicknesses was measured using a light-emitting-diode curing unit with standard-power, high-power, and plasma modes by means of a USB4000 spectrometer. The curing unit was placed directly on the specimen's surface at 2- and 4-mm distances from the specimen's surface. Data were analyzed using a multivariate analysis and one-way analysis of variance with the post hoc Scheffé test (p&lt;0.05). The highest transmitted irradiance was measured for VM and LU, followed by VCT and IEC, while the lowest values showed VE, followed by IEM and CD. The highest transmitted irradiance was recorded by exposing the material to the plasma mode, followed by the high- and standard-power modes. The measured irradiance was decreased by increasing the specimen's thickness from 1 to 2 mm. Fewer differences were measured when the curing unit was placed at 0 or 2 mm from the specimen's surface, and the irradiance passing through the specimens was lower at a distance of 4 mm.

Effect of Curing Mode on Shear Bond Strength of Self-Adhesive Cement to Composite Blocks

To overcome the disadvantages of computer-aided design/computer-aided manufacturing (CAD/CAM) processed indirect restorations using glass-ceramics and other ceramics, resin nano ceramic, which has high strength and wear resistance with improved polish retention and optical properties, was introduced. The purpose of this study was to evaluate the shear bond strength and fracture pattern of indirect CAD/CAM composite blocks cemented with two self-etch adhesive cements with different curing modes. Sand-blasted CAD/CAM composite blocks were cemented using conventional resin cement, Rely X Ultimate Clicker (RXC, 3M ESPE, St. Paul, MN, USA) with Single Bond Universal (SB, 3M ESPE, St. Paul, MN, USA) for the control group or two self-adhesive resin cements: Rely X U200 (RXU, 3M ESPE, St. Paul, MN, USA) and G-CEM Cerasmart (GC, GC corporation, Tokyo, Japan). RXU and GC groups included different curing modes (light-curing (L) and auto-curing (A)). Shear bond strength (SBS) analyses were performed on all the specimens. The RXC group revealed the highest SBS and the GC A group revealed the lowest SBS. According to Tukey's post hoc test, the RXC group showed a significant difference compared to the GC A group (p < 0.05). For the curing mode, RXU A and RXU L did not show any significant difference between groups and GC A and GC L did not show any significant difference either. Most of the groups except RXC and RXU L revealed adhesive failure patterns predominantly. The RXC group showed a predominant cohesive failure pattern in their CAD/CAM composite, Lava^TM Ultimate (LU, 3M ESPE, St. Paul, MN, USA). Within the limitations of this study, no significant difference was found regarding curing modes but more mixed fracture patterns were showed when using the light-curing mode than when using the self-curing mode.

Influence of proximal box elevation on bond strength of composite inlays

OBJECTIVES

The objective of the present study was to evaluate the influence of proximal box elevation on microtensile bond strength (mTBS) of composite inlays to the proximal box floor, using either a total-etch or a self-adhesive resin cement.

MATERIALS AND METHODS

Twenty-five human molars were selected, and a class II OM (inlay) cavity preparation was performed in each tooth. Cavities were randomly assigned into four experimental groups, according to the location of the proximal cervical margin (located 1 mm below cementoenamel junction (CEJ), or with proximal box elevation with composite resin) and the resin cement used for luting (a total-etch resin cement RelyX ARC or a self-adhesive resin cement G-Cem). After 1-week water storage, samples were subjected to mTBS test. Results were analyzed by Kruskal-Wallis and Mann-Whitney U tests (p < 0.05).

RESULTS

Kruskal-Wallis revealed statistically significant differences among experimental groups (p = 0.007). Both resin cements showed similar bond strength values when cervical margin was located below CEJ. The proximal box elevation improved the bond strength of composite inlays for both resin cements. However, only for G-Cem was this improvement statistically significant.

CONCLUSIONS

The proximal box elevation improved the bond strength attained by G-Cem resin cement. For RelyX ARC, the position of the cervical margin did not affect composite inlays bond strength.

CLINICAL RELEVANCE

Proximal box elevation does not decline bond strength of composite inlays to the proximal floor when a total-etch or a self-adhesive resin cement is used.

Correlation between clinical performance and degree of conversion of resin cements: a literature review

Resin-based cements have been frequently employed in clinical practice to lute indirect restorations. However, there are numerous factors that may compromise the clinical performance of those cements. The aim of this literature review is to present and discuss some of the clinical factors that may affect the performance of current resin-based luting systems. Resin cements may have three different curing mechanisms: chemical curing, photo curing or a combination of both. Chemically cured systems are recommended to be used under opaque or thick restorations, due to the reduced access of the light. Photo-cured cements are mainly indicated for translucent veneers, due to the possibility of light transmission through the restoration. Dual-cured are more versatile systems and, theoretically, can be used in either situation, since the presence of both curing mechanisms might guarantee a high degree of conversion (DC) under every condition. However, it has been demonstrated that clinical procedures and characteristics of the materials may have many different implications in the DC of currently available resin cements, affecting their mechanical properties, bond strength to the substrate and the esthetic results of the restoration. Factors such as curing mechanism, choice of adhesive system, indirect restorative material and light-curing device may affect the degree of conversion of the cement and, therefore, have an effect on the clinical performance of resin-based cements. Specific measures are to be taken to ensure a higher DC of the luting system to be used.

Effect of dentin pretreatment and curing mode on the microtensile bond strength of self-adhesive resin cements

PURPOSE

The aim was to evaluate the effect of curing mode and different dentin surface pretreatment on microtensile bond strength (µTBS) of self-adhesive resin cements.

MATERIALS AND METHODS

Thirty-six extracted human permanent molars were sectioned horizontally exposing flat dentin surface. The teeth were divided into 12 groups (3 teeth/group) according to the dentin surface pretreatment methods (control, 18% EDTA, 10% Polyacrylic acid) and curing mode (self-curing vs. light-curing) of cement. After pretreatment, composite resin blocks were cemented with the following: (a) G-CEM LinkAce; (b) RelyX U200, followed by either self-curing or light-curing. After storage, the teeth were sectioned and µTBS test was performed using a microtensile testing machine. The data was statistically analyzed using one-way ANOVA, Student T-test and Scheffe's post-hoc test at P<.05 level.

RESULTS

For G-CEM LinkAce cement groups, polyacrylic acid pretreatment showed the highest µTBS in the self-cured group. In the light-cured group, no significant improvements were observed according to the dentin surface pretreatment. There were no significant differences between curing modes. Both dentin surface pretreatment methods helped to increase the µTBS of RelyX U200 resin cement significantly and degree of pretreatment effect was similar. No significant differences were found regarding curing modes except control groups. In the comparisons of two self-adhesive resin cements, all groups within the same pretreatment and curing mode were significantly different excluding self-cured control groups.

CONCLUSION

Selecting RelyX U200 used in this study and application of dentin surface pretreatment with EDTA and polyacrylic acid might be recommended to enhance the bond strength of cement to dentin.

Indirect Restoration Thickness and Time after Light-Activation Effects on Degree of Conversion of Resin Cement

<p>This study evaluated the effects of indirect restorative materials, curing conditions and time on the degree of conversion (DC) of a dual-cured resin cement using infrared spectroscopy. The resin cement (RelyX Unicem 2, 3M ESPE) was applied to the diamond surface of a horizontal attenuated-total-reflectance unit and activated using one of following conditions: self-cure, direct light exposure, light exposure through indirect restorative materials (resin nano-ceramic: Lava Ultimate, 3M ESPE or feldspathic ceramic: Vita Blocks Mark II, Vita Zahnfabrik). Four thicknesses (0.5, 1.0, 1.5 or 2.0 mm) of each indirect material were analyzed, and the light-activation was performed using a blue LED light. Data (n=5) were analyzed by three-way ANOVA, Tukey's post hoc and Dunnett's tests (α=5%). No significant differences in DC were observed between indirect materials of similar thickness. All groups exhibited higher DC after 10 min than after 5 min. At both times points, the self-cure group exhibited significantly lower DC than all the light exposure groups. Only when the overlying indirect restoration had a thickness of 2 mm did DC decrease significantly. The presence of a thick, indirect restoration can decrease the DC of resin cement. DC after 10 min was higher than after 5 min. The self-cure mode yielded lower DC than the light-activating one.</p>

Analysis of resin-dentin interface morphology and bond strength evaluation of core materials for one stage post-endodontic restorations

Purpose

Restoration of endodontically treated teeth using fiber posts in a one-stage procedure gains more popularity and aims to create a secondary monoblock. Data of detailed analyses of so called “post-and-core-systems” with respect to morphological characteristics of the resin-dentin interface in combination with bond strength measurements of fiber posts luted with these materials are scarce. The present study aimed to analyze four different post-and-core-systems with two different adhesive approaches (self-etch and etch-and-rinse).

Materials and Methods

Human anterior teeth (n = 80) were endodontically treated and post space preparations and post placement were performed using the following systems: Rebilda Post/Rebilda DC/Futurabond DC (Voco) (RB), Luxapost/Luxacore Z/Luxabond Prebond and Luxabond A+B (DMG) (LC), X Post/Core X Flow/XP Bond and Self Cure Activator (Dentsply DeTrey) (CX), FRC Postec/MultiCore Flow/AdheSE DC (Ivoclar Vivadent) (MC). Adhesive systems and core materials of 10 specimens per group were labeled using fluorescent dyes and resin-dentin interfaces were analyzed using Confocal Laser Scanning Microscopy (CLSM). Bond strengths were evaluated using a push-out test. Data were analyzed using repeated measurement ANOVA and following post-hoc test.

Results

CLSM analyses revealed significant differences between groups with respect to the factors hybrid layer thickness (p<0.0005) and number of resin tags (p = 0.02; ANOVA). Bond strength was significantly affected by core material (p = 0.001), location inside the root canal (p<0.0005) and incorporation of fluorescent dyes (p = 0.036; ANOVA). CX [7.7 (4.4) MPa] demonstrated significantly lower bond strength compared to LC [14.2 (8.7) MPa] and RB [13.3 (3.7) MPa] (p<0.05; Tukey HSD) but did not differ significantly from MC [11.5 (3.5) MPa].

Conclusion

It can be concluded that bond strengths inside the root canal were not affected by the adhesive approach of the post-and-core-system. All systems demonstrated homogenous hybrid layer formation and penetration into the dentinal tubules in spite of the complicating conditions for adhesion inside the root canal.

The Effect of Light Exposure on Water Sorption and Solubility of Self-Adhesive Resin Cements

Purpose. To investigate the effect of light activation on the water sorption (WS) and solubility (SL) of resin cements after 24 h and 7 days. Methods. Disk-shaped specimens were prepared using five dual-polymerized cements (four self-adhesive [RelyX Unicem, MaxCem, SeT and G-Cem] and one conventional [Panavia F 2.0]) and divided according to the curing mode (direct light exposure or self-cure) and water immersion period (24 h or 7 days). Specimens were dry-stored and weighed daily until a constant mass was recorded (M1). Then, specimens were stored in water for either 24 h or 7 days and immediately weighed (M2). After desiccation, specimens were weighed again until a constant mass was achieved (M3). WS and SL were calculated and statistically analyzed by Kruskal-Wallis, Dunn and Mann-Whitney U tests (α = 0.05%). Results. There was a significant increase in WS for all products after one-week immersion in water. The highest water uptake was observed for autopolymerized groups. Extended water immersion significantly affected the SL for most of autopolymerized cements. Significant differences between products were observed in both tests. Conclusions. The curing mode and the water immersion period may affect the mechanical stability of the resin cements, and these differences appear to be product-dependent.

Effect of temperature on the degree of conversion and working time of dual-cured resin cements exposed to different curing conditions

OBJECTIVES

This study evaluated the degree of conversion (DC) and working time (WT) of two commercial, dual-cured resin cements polymerized at varying temperatures and under different curing-light accessible conditions, using Fourier transformed infrared analysis (FTIR).

MATERIALS AND METHODS

Calibra (Cal; Dentsply Caulk) and Variolink II (Ivoclar Vivadent) were tested at 25°C or preheated to 37°C or 50°C and applied to a similar-temperature surface of a horizontal attenuated-total-reflectance unit (ATR) attached to an infrared spectrometer. The products were polymerized using one of four conditions: direct light exposure only (600 mW/cm(2)) through a glass slide or through a 1.5- or 3.0-mm-thick ceramic disc (A2 shade, IPS e.max, Ivoclar Vivadent) or allowed to self-cure in the absence of light curing. FTIR spectra were recorded for 20 min (1 spectrum/s, 16 scans/spectrum, resolution 4 cm(-1)) immediately after application to the ATR. DC was calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios precuring and 20-min postcuring as well as during each 1-second interval. Time-based monomer conversion analysis was used to determine WT at each temperature. DC and WT data (n=6) were analyzed by two-way analysis of variance and Tukey post hoc test (p=0.05).

RESULTS

Higher temperatures increased DC regardless of curing mode and product. For Calibra, only the 3-mm-thick ceramic group showed lower DC than the other groups at 25°C (p=0.01830), while no significant difference was observed among groups at 37°C and 50°C. For Variolink, the 3-mm-thick ceramic group showed lower DC than the 1-mm-thick group only at 25°C, while the self-cure group showed lower DC than the others at all temperatures (p=0.00001). WT decreased with increasing temperature: at 37°C near 70% reduction and at 50°C near 90% for both products, with WT reduction reaching clinically inappropriate times in some cases (p=0.00001).

CONCLUSION

Elevated temperature during polymerization of dual-cured cements increased DC. WT was reduced with elevated temperature, but the extent of reduction might not be clinically acceptable.

Effects of curing protocol and storage time on the micro-hardness of resin cements used to lute fiber-reinforced resin posts

OBJECTIVES

To determine the micro-hardness profile of two dual cure resin cements (RelyX-U100, 3M-eSPe and Panavia F 2.0, Kuraray) used for cementing fiberre inforced resin posts (Fibrekor-Jeneric Pentron) under three different curing protocols and two water storage times.

MATERIAL AND METHODS

Sixty 16 mm long bovine incisor roots were endodontically treated and prepared for cementation of the Fibrekor posts. The cements were mixed as instructed, dispensed in the canal, the posts were seated and the curing performed as follows: (a) no light activation; (b) light-activation immediately after seating the post, and; (c) light-activation delayed 5 minutes after seating the post. The teeth were stored in water and retrieved for analysis after 7 days and 3 months. The roots were longitudinally sectioned and the microhardness was determined at the cervical, middle and apical regions along the cement line. The data was analyzed by the three-way ANOVA test (curing mode, storage time and thirds) for each cement. The Tukey test was used for the post-hoc analysis.

RESULTS

Light-activation resulted in a significant increase in the microhardness. This was more evident for the cervical region and for the Panavia cement. Storage in water for 3 months caused a reduction of the micro-hardness for both cements. The U100 cement showed less variation in the micro-hardness regardless of the curing protocol and storage time.

CONCLUSIONS

The micro-hardness of the cements was affected by the curing and storage variables and were material-dependent.

An ex vivo comparative study on the retention of custom and prefabricated posts

Aim:

This study was designed to comparatively evaluate the effect of cyclic loading on the retention of custom-fabricated fiber-reinforced composite (CF-FRC), prefabricated metal, and glass fiber posts.

Materials and Methods:

Thirty mandibular first premolars decoronated at the CE junction were divided into three groups (n=10). Groups A, B, and C were restored using Para Post (Whale dent), Reforpost (Angelus), and CF-FRC post (Ribbond-THM), respectively. Five specimens from each group were subjected to cyclic loading. Tensile bond strength (TBS) was evaluated.

Results:

Pre-loading TBS values were statistically, significantly higher for all posts (P<0.05). Before and after loading, there was a significant difference between group C as compared to groups A and B.

Conclusions:

Cyclic loading reduced the retention of all posts but was comparatively lesser for the CF-FRC post. This system provides sufficient retention required for clinical success.

Pre-heated dual-cured resin cements: analysis of the degree of conversion and ultimate tensile strength

This study evaluated the degree of conversion (DC) and ultimate tensile strength (UTS) of dual-cured resin cements heated to 50º C prior to and during polymerization. Disc- and hourglass-shaped specimens of Rely X ARC (RX) and Variolink II (VII) were obtained using addition silicon molds. The products were manipulated at 25º C or 50º C and were subjected to 3 curing conditions: light-activation through a glass slide or through a pre-cured 2-mm thick resin composite disc, or they were allowed to self-cure (SC). All specimens were dark-stored dry for 15 days. For DC analysis, the resin cements were placed into the mold located on the center of a horizontal diamond on the attenuated total reflectance element in the optical bench of a Fourier Transformed Infrared spectrometer. Infrared spectra (n = 6) were collected between 1680 and 1500 cm-1, and DC was calculated by standard methods using changes in ratios of aliphatic-to-aromatic C=C absorption peaks from uncured and cured states. For UTS test, specimens (n = 10) were tested in tension in a universal testing machine (crosshead speed of 1 mm/min) until failure. DC and UTS data were submitted to 2-way ANOVA, followed by Tukey's test (α= 5%). Both products showed higher DC at 50º C than at 25º C in all curing conditions. No significant difference in UTS was noted between most light-activated groups at 25º C and those at 50º C. VII SC groups showed higher UTS at 50º C than at 25º C (p < 0.05). Increased temperature led to higher DC, but its effects on resin cement UTS depended on the curing condition.

Influence of curing mode and time on degree of conversion of one conventional and two self-adhesive resin cements

This study evaluated the effect of curing mode (auto- and dual-polymerizing mode) and time interval (5, 10 and 15 minutes) on the degree of conversion of resin cements. One conventional dual-cured resin cement (Panavia F 2.0 [Kuraray Medical Inc]) and two self-adhesive cements (RelyX Unicem [3M ESPE] and BisCem [BISCO, Inc]) were evaluated. The products (n = 5) were manipulated according to the manufacturer's instructions and applied to the surface of a horizontal attenuated reflectance unit attached to an infrared spectrometer. The materials were either light-cured for 40 seconds (dual-polymerizing mode) or allowed to auto-polymerize. The degree of conversion was calculated according to changes in the aliphatic-to-aromatic peak ratios prior to and 5, 10 and 15 minutes after light-activation or after mixing when the specimens were allowed to auto-polymerize. Data (%) were analyzed by two-way repeated measure ANOVA (curing mode and time interval) and Tukey's post-hoc test (alpha = 0.05%). The light-activating mode led to a higher degree of conversion values than the self-curing mode in self-adhesive cements (RelyX Unicem and BisCem), while there was no difference in the degree of conversion between the self- and light-cured groups of Panavia F 2.0 resin cement. All products showed a higher degree of conversion at 15 minutes postcuring than any other evaluation interval. The self-adhesive cements provide a higher degree of conversion values when light-activated. After 15 minutes of polymerization initiation, the degree of conversion was higher in all resin cements, regardless of the curing mode.

Bi-axial flexural strength of dual-polymerizing agents cemented to human dentin after photo-activation with different light-curing systems

OBJECTIVES

This study aimed to assess the bi-axial flexural strength of two dual-polymerizing resin luting agents cemented to human dentin when photo-activated with different light-curing units.

MATERIALS AND METHODS

Two dual-cured resin cements: choice (CH) and Variolink II (VL) were tested. Hybrid composite resin (Z-250) discs (12 × 1.5 mm) were fabricated. Three types of light-curing units were used halogen-curing unit (QTH), light-emitting diode (LED) and plasma arc (PAC). Sixty dentin discs of 0.5 mm thickness were prepared from extracted human teeth. A circular mold (2.5 mm in height and 12 mm diameter) was utilized to create supporting structure for dentin, resin cement complex. The resin luting cement (0.5 mm) was placed on the previously prepared dentin discs and covered with the prefabricated composite discs. Photo-activation of cements was performed for 40 s with QTH and LED units and for 3 s with PAC. The specimens were divided into 12 groups (20 specimens for each light source). Six groups were kept in distilled water for 24 h and the rest were stored for 6 weeks. Bi-axial flexural strength was determined using Instron machine. The data was analyzed using two-way ANOVA and Tukey test for comparison.

RESULTS

The findings indicated that the bi-axial flexural strength values for both cements CH and VL were higher for 24 h over 6 weeks but not statistically significant when cured with QTH. Meanwhile, when LED light was used for photo-activation the cements, the flexural strength values reported were statistically higher of 24 h over 6 weeks storage at P = 0.4(E-6) However, PAC light did not record any statistically significant difference between two duration for the CH cement although when used for polymerization of VL the reported value for 6 weeks were statistically significantly higher value than 24 h duration at P = 0.002.

CONCLUSION

When high immediate flexural strength is preferred in clinical situation photo-activation the cements with LED reported the greatest value.

Effect of curing mode on bond strength of self-adhesive resin luting cements to dentin

In this study, the in vitro bond strength of dual-curing resin cements to indirect composite restorations when the cement was either light polymerized or allowed to only autopolymerize was evaluated. Occlusal dentin surfaces of 56 extracted human third molars were flattened to expose coronal dentin. Teeth were assigned to eight groups (n = 7) according to resin cement products and polymerization modes: conventional cement (Panavia F 2.0; Kuraray Medical) and self-adhesive cements [RelyX Unicem (3M ESPE), BisCem (Bisco), and G-Cem (GC Corp.)]. Cements were applied to prepolymerized resin discs (2-mm-thick Sinfony; 3M ESPE), which were subsequently bonded to the prepared dentin surfaces. The restored teeth were either light-polymerized through the overlying composite according to manufacturers' instructions or were allowed to only self-cure. After 24 h, the teeth and restorations were sectioned to obtain multiple bonded beams (1.0 mm(2)) and tested in tension at a crosshead speed of 0.5 mm/min until failure. Data (MPa) were analyzed by two-way ANOVA and Tukey test (alpha = 0.05). Light activation of some cement systems (G-Cem and Panavia F 2.0) increased the bond strength, while the curing mode did not affect the bond strength for some (RelyX Unicem and BisCem). The bond strength in the autopolymerized mode varied among products. In general, the use of self-adhesive resin cements did not provide significantly higher bond strengths than that of a conventional material, and two self-adhesive cements yielded significantly lower bond values (regardless of cure mode) than the other products.

Effect of veneering materials and curing methods on resin cement knoop hardness

This study evaluated the Knoop hardness of Enforce resin cement activated by the either chemical/physical or physical mode, and light cured directly and through ceramic (HeraCeram) or composite resin (Artglass). Light curing were performed with either conventional halogen light (QTH; XL2500) for 40 s or xenon plasma arc (PAC; Apollo 95E) for 3 s. Bovine incisors had their buccal surfaces flattened and hybridized. On these surfaces a mold was seated and filled with cement. A 1.5-mm-thick disc of the veneering material was seated over this set for light curing. After storage (24 h/37 masculineC), specimens (n=10) were sectioned for hardness (KHN) measurements in a micro-hardness tester (50 gf load/ 15 s). Data were submitted to ANOVA and Tukey's test (alpha=0.05). It was observed that the dual cure mode yielded higher hardness compared to the physical mode alone, except for direct light curing with the QTH unit and through Artglass. Higher hardness was observed with QTH compared to PAC, except for Artglass/dual groups, in which similar hardness means were obtained. Low KHN means were obtained with PAC for both Artglass and HeraCeram. It may be concluded that the hardness of resin cements may be influenced by the presence of an indirect restorative material and the type of light-curing unit.

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.

Effect of light-curing methods on resin cement knoop hardness at different depths

This study evaluated, using Knoop hardness test, the polymerization depth of Rely-X dual-cured resin cement activated by chemical reaction alone (control group) or by chemical/physical mode with light curing through a 1.5-mm-thick ceramic layer (HeraCeram). Bovine incisors had their buccal surface flattened and hybridized. On this surface, a rubber mould (5 mm diameter; 1 mm high) was bulk filled with cement. Either a polyester strip or a 1.5-mm-thick disc of the veneering material was seated over this set. Light curing was performed with either conventional halogen light (QTH; XL2500) for 40 s, light-emitting diode (LED; Ultrablue Is) for 40 s or xenon plasma arc (PAC; Apollo 95E) for 3 s. In a control group, cement setting occurred by chemical reaction alone. After storage dry in dark (24 h/37ºC), the specimens (n=5) were sectioned for hardness (KHN) measurements at three depths in a microhardness tester (50 gf load/15 s). Data were submitted to ANOVA and Tukey's test (a = 0.05). Rely-X cement presented higher Knoop hardness values when the QTH and LED LCUs were used, compared to the control group and PAC. Light curing with PAC resulted in lower hardness compared to the control group. Cement hardness was significantly lower in deeper regions.