Rebilda DC Research Articles

Effect of degree of conversion on the surface properties of polymerized resin cements used for luting glass fiber posts

Statement of problemLack of conversion of resin cements for luting glass fiber posts in deeper levels of the root canal may compromise clinical performance. PurposeThe purpose of this in vitro study was to evaluate the effect of the degree of conversion on the surface properties of dual-polymerized resin cements used for cemented glass fiber posts according to the root level. Material and methodsFifty maxillary central incisor teeth were endodontically treated, and glass fiber posts were cemented using the following systems: self-adhesive dual-polymerized resin luting cement (RelyX U200) and dual-polymerizing flowable core and a post luting system (Rebilda DC) with a self-etching adhesive (Futurabond DC). The degree of conversion was determined via attenuated total reflectance and Fourier transform infrared spectroscopy, and surface microhardness and cement film thickness were measured. The intraradicular fit was evaluated with microscopy. All tests were performed in the coronal, middle, and apical third of the root canal. Statistical analysis was done with ANOVA and the multiple comparison Tukey test (α=.05). ResultsThe degree of conversion was higher in the coronal third using Rebilda DC (65.3 ±4.8%) than RelyX U200 (38.7 ±5.3%) (P<.05); on both resin cements, these values decreased from the coronal to the apical third (30.9 ±3.7%, 61.9 ±8.7%, respectively). The cement film thickness was higher for RelyX U200 in the 3 thirds than for Rebilda DC; significant differences (P<.05) were recorded in both cementing systems in the coronal and apical thirds. In the middle third, no significant differences were observed (P>.05). The mean surface microhardness values increased in the coronal thirds and decreased with increasing root canal depth. The marginal seal in the coronal thirds and the intraradicular fit in the middle thirds showed closer adaptation; however, some tags were observed in the interface resin cement and radicular dentin. Gap and tag formations were observed in the apical third. ConclusionsDepending on the root canal third, the surface properties of dual-polymerized resin cements are influenced by the degree of conversion.

The Influence on Fracture Resistance of Different Composite Resins and Prefabricated Posts to Restore Endodontically Treated Teeth.

Recent formulations of resin-based composites have incorporated different combinations of materials. However, the mechanical and bonding behavior of these materials with intraradicular posts are unclear. This study aimed to evaluate the effect of light-cure and dual-cure resin composite posts on the fracture resistance of endodontically-treated teeth. Materials and Methods: Ninety extracted human upper canines were selected and randomly divided into nine groups (n=10): (G1) endodontically treated teeth without endodontic posts; (G2) glass-fiber post cemented with glass-ionomer cement; (G3) endodontic post by dual-cure composite resin (Rebilda DC); (G4) endodontic post by dual-cure composite resin (Cosmecore); (G5) endodontic post by dual-cure composite resin (Bis-Core); (G6) endodontic post by light-cure composite resin; (G7) glass-fiber post customized with flowable composite resin; (G8) glass-fiber post cemented with light-cure composite resin; (G9) glass-fiber post cemented with self-adhesive resin cement. After the post insertion, all specimens were subjected to mechanical (250,000 cycles) and thermocycling (6000 cycles, 5 °C/55 °C) and immediate loading at 45 degrees in a universal testing machine until fracture. The data were analyzed by one-way ANOVA and multiple comparisons using the Fisher LSD Method (p < 0 05). Results: The mean failure loads (±SD) for the groups ranged from 100.7 ± 22.6 N to 221.9 ± 48.9 N. The G1 group (without endodontic posts) had a higher fracture strength than all experimental groups (p < 0.001). Conclusions: Within the limitations, the light- and dual-cure post technique did not present lower fracture resistance values as compared to the conventional glass-fiber post.

Bond Strength Evaluation between Different Glass Fiber Post Systems to Restore Weakened Roots

A new bundled glass fiber-reinforced resin post was developed to be used in post-endodontic restoration. We evaluated the bond strength of a single prefabricated glass fiber post (GFP) and a bundled glass fiber-reinforced resin post (GT), used alone or combined, to restore weakened roots. Fifty bovine incisors roots were weakened with a diamond bur, except for those from the control group. The root canals were endodontically treated (Pro Taper Next system, gutta-percha, and endodontic cement), and the roots were divided into five groups (n = 10): Reb—single prefabricated GFP (Rebilda Post—Voco); GT—bundled glass fiber-reinforced resin post (Rebilda Post GT—Voco); RebGT—association between the prefabricated GFP (Reb) and the bundled one (GT); CP—prefabricated GFP customized with composite resin; and Cont—singular post in a non-weakened root (Control). All posts were cemented using a universal adhesive system (Futurabond U) and dual-cure resin cement (Rebilda DC—Voco). Afterwards, two slices were obtained from each root third (cervical, middle, and apical) and submitted to a push-out bond strength test. Data were analyzed regarding the post system used and the root thirds by two-way ANOVA, followed by Tukey’s test (p &lt; 0.05). There were higher bond strength means for the RebGT and CP groups, presenting values similar to the control. The Reb and GT groups showed lower values. The adhesion to deeper thirds of the root canal remains a challenge for adhesive dentistry and is not related to the design of the post. Additionally, the rehabilitation of teeth with weakened roots requires the customization of the glass fiber post with composite resin or the association between prefabricated options with multiple posts.

Influence of geometric dimensions on early failures of adhesively retained composite resin core build-ups.

To determine the influence of the geometric dimensions of core build-ups on early core build-up failure, that is, loss before definitive prosthesis cementation. Adhesive core build-ups of exclusively vital teeth in 114 participants were evaluated (n materials: 40 Rebilda DC, 38 Multicore Flow, 36 Clearfil DC Core; n teeth: 8 incisors, 54 premolars, 52 molars). Impressions of the abutment teeth were made (1) after removal of insufficient restorations/caries and (2) after core build-up and preparation for a fixed prosthesis. Digitized model surfaces of both situations were aligned (Geomagic Design X) and core build-up volume (VCBU ), remaining hard tissue volume (VAbut ), and size of the adhesive surface (Aadh ) were assessed. The derived measure dCBU =VCBU /Aadh can be interpreted as mean arithmetic core build-up thickness. Associations between participant or core build-up design characteristics and the occurrence of early failures were statistically evaluated (SPSS v27, α=0.05). A total of six (5.3%) core build-up failures were registered. Higher participant age, greater core build-up volume VCBU and greater arithmetic uniform thickness dCBU were associated with a greater incidence of failure in bivariate and univariate, however, not in multivariate statistics. Core build-up volume and thickness were associated with early success or failure. In the case of voluminous/thick core build-ups in relation to the adhesive surface, additional measures, such as the preparation of retentive elements to increase the bonding area, might be considered to reduce the risk of early core build-up failure.

A Comparative Study of the Mechanical Properties of Selected Dental Composites with a Dual-Curing System with Light-Curing Composites

Dual-curing composites have a wide spectrum of use in practice (rebuilding, reconstruction, and luting). The characterization of this type of material and comparative study of selected mechanical properties with light-cured materials were carried out for this paper. In this study, we used six materials with a dual-cure system—Bulk EZ, Fill-Up!, StarFill 2B, Rebilda DC, MultiCore Flow, Activa Bioactive-Restorative—and three light-cured materials—Filtek Bulk Fill Posterior, Charisma Classic, and G-aenial Universal Flo. The materials were conditioned for 24 h in water at 37 °C before testing. Selected material properties were determined: three-point bending flexural strength, diametral tensile strength, hardness, microhardness, and shrinkage stress. The highest three-point bending flexural strength (TPB) was 137.0 MPa (G-aenial Universal Flo), while the lowest amounted to 86.5 MPa (Activa Bioactive). The diametral tensile strength (DTS) values were in a range from 39.2 MPa (Rebilda DC) to 54.1 MPa (Charisma Classic). The lowest hardness (HV) value of 26 was obtained by the Activa Bioactive material, while the highest values were recorded for Filtek Bulk Fill Posterior and Charisma Classic-53. The shrinkage stress of the tested materials ranged from 6.3 MPa (Charisma Classic) to 13.2 MPa (G-aenial Universal Flo). Dual-curing composites were found to have similar properties to light-cured composites.

Early failures when using three different adhesively retained core build-up materials\u2014a randomized controlled trial

ObjectivesTo compare the failure rates for three different adhesively retained core build-up composites up to the incorporation of a permanent fixed dental prosthesis (FDP), and to identify potential failure risk factors.Material and methodsA randomized controlled trial of 300 participants in need of a core build-up to restore a vital abutment tooth before prosthetic treatment was conducted. Participants were assigned by stratified block randomization to one of three study groups: Rebilda DC (RDC), Clearfil DC Core (CDC), or Multicore Flow (MF). Test teeth were prepared by use of the respective manufacturer’s adhesive system. The total-etch technique was used for RDC and MF, and the self-etch technique for CDC. Participants were treated by dentists (n = 150) or dental students (n = 150). Failure rates of core build-ups before incorporation of FDPs were investigated using univariate and multiple logistic regression.ResultsThe overall failure rate was 8% (n = 23). Rate differences between the three investigated groups did not reach statistical significance (p > 0.05). The mean time between placement of core build-ups and placement of fixed dental prostheses was 12.2 (SD: 14.2) weeks. Conversely, larger cavities (> 3 surfaces) and treatment by dental students were independently associated with an increased failure risk (p < 0.05).ConclusionsThe main risk factors for early failure seem to be the size of the core build-up and clinical experience of the operator, whereas failure rates of core build-up materials combined with a self-etch approach seem to be similar to the rates of materials combined with the total-etch technique.Clinical significanceThis research article should give clinicians an impression of the short-term performance of different adhesively retained core build-ups using different adhesive techniques/materials. Moreover, predominant influencing factors for the success or failure should be pictured.

Push-Out Bond Strength of Composite Polymerization Methods with Universal Adhesive to Coronal Dentin

Abstract Objective This in vitro study was aimed to determine the effect of composite polymerization methods with universal adhesive on push-out bond strength in coronal dentin. Materials and Methods Using 48 healthy premolar teeth, the almost conical access cavities were excised to the canal entry. Cavity preparations were treated with a universal adhesive in the self-etch mode. Teeth were randomly divided into four groups (n = 12). It was used to restore the cavities with a bulk-fill composite; Tetric N-Ceram, a conventional composite; Filtek Z250, a dual-cure composite; Rebilda DC VOCO, and chemical cure composite; Master-Dent. After applying 10,000 thermal cycles, 1-mm incisions were made in coronal dentin, and slices were placed in a UTM machine in a special jig and tested for push-out bond strength at a crosshead speed of 0.5 mm/min. Data were analyzed using one-way analysis of variance and Games–Howell tests (p &lt; 0.05). Results The highest mean bond strength was of the conventional composite (18.36 ± 5.63) and the lowest mean of bond strength was for the dual-cure composite (5.10 ± 2.74). There was a significant difference among the means of bond strength for various composite resins curing (p &lt; 0.001). Conclusion The bulk-fill and conventional light-cured composites had higher bond strength than self- and dual-cured composite resins.

Microtomographic Analysis of Resin Composite Core Material Porosity.

To nondestructively evaluate the porosity of ten contemporary resin composite core materials using microtomographic (microCT) analysis. Resin composite core material samples (n = 12) including dual-cure, visible light cure only, and a self-cure material were fabricated using a standardized mold following manufacturer's recommendations. After storage in phosphate buffered saline for one week, specimens were analyzed using a microCT unit at 5.3-µm resolution over a rotational range of 360°. Image 3D recombination and analysis was accomplished using microCT software. Evaluated parameters included material volume investigated, closed pore number and volume, as well as closed pore percentage. Parameter mean values were evaluated with Kruskal-Wallis/Dunn at a 95% confidence level (α = 0.05). Mean percent total porosity with standard deviation identified significant differences in decreasing order as Ti-Core: 2.2 (0.4) > Ti-Core Auto E: 1.3 (0.3) = Ti-Core Flow Plus: 1.1 (0.02) > Clearfil Photo Core: 0.94 (0.5) = Clearfil DC Core Plus: 0.6 (0.18) = MultiCore Flow: 0.58 (0.1) > Fluorocore 2+: 0.14 (0.2) = Build-It FR: 0.068 (0.02) = Gradia Core: 0.03 (0.02) = Rebilda DC: 0.02 (0.01). A pilot microCT evaluation evaluating a mixing tip revealed incomplete mixture between the two resins with porosity introduced from turbulence as the materials are forced through the tip during preparation. A wide range of porosity was identified between the ten materials evaluated. These preliminary results warrant more investigation evaluating additional resin composite core materials, the preparation capabilities of automix tips, and porosity presence in the unmixed materials.

Monobloco – cimentação de pino e preenchimento em único passo em dente tratado endodonticamente

The literature reports several materials for the restoration of endodontically treated teeth, with coronal destruction that requires an intra-root fiber post to stabilize the prosthetic part. The intra-radicular post of composite resin reinforced with fiberglass can be used as retainers in rehabilitating endodontically treated teeth due to their adhesiveness, pleasing aesthetics, and elasticity module close to the dentin less wear on the remaining structure. This clinical case reports the step-by-step application of dual resin cement (Rebilda DC Dentine - Voco) used as the cementation material of the post and material for the filling core in a single step, in an upper right lateral incisor. Moreover, it describes the advantages and indications of the post-and-core technique, also called “monobloc” which can be used in both anterior and posterior teeth. This protocol minimizes the adhesive interfaces, the chair time, and the steps of the clinical procedure.

Effect of Application Mode on Bond Strength of Adhesively Luted Glass-fiber Bundles Inside the Root Canal.

The aim of the present study was to measure the bond strength of adhesively luted glass-fiber bundles inside the root canal with respect to the application procedure in comparison to conventional solid glass-fiber posts. 104 human anterior teeth were endodontically treated, root filled and divided into 8 groups (n = 13). After post space preparation, fiber bundles consisting of 6 and 12 glass fibers, respectively, were luted adhesively with a multi-mode adhesive (Futurabond U; Voco, Cuxhaven, Germany) and a dual-curing composite (Rebilda DC, Voco) with the following application modes into the root canal: (1) direct application with tweezers, (2) distribution of the fibers using a spreader, (3) application of ultrasound after insertion of fibers. Two different solid posts (Rebilda DC, Voco; and DentinPost, Komet, Lemgo, Germany) were used as controls. Roots were sectioned into 6 slices per root (thickness 1 mm). Bond strengths were measured using thin-slice push-out tests for 3 slices 24 h after post insertion and for 3 slices per sample following thermocycling (TC) for 6000 cycles and storage in 0.9% NaCl for 6 months. Homogeneity of the slices was analyzed using a stereomicroscope and, for representative samples, micro-computed tomography (µCT). Mean push-out bond strengths (MPa) were significantly affected by post system (p < 0.0005) and location inside the root canal (p = 0.004) but not by application mode (p = 0.544) or TC (p = 0.098; repeated measurement ANOVA). Fiber bundles consisting of 6 (13.2 ± 4.7) and 12 fibers (14.5 ± 4.3) revealed bond strength comparable to that of Rebilda Post (13.67 ± 3.2) but significantly higher than that of Dentin Posts (8.7 ± 3.02). Inhomogeneities were detected among 35.5% to 43.1% of the fiber-bundle samples, irrespective of number of fibers and application mode, and among 24.4% to 27.3% of the solid posts (p = 0.010; chi-squared test). µCT revealed voids inside the composite bulk between the fibers as well as between composite and dentin of adhesively luted fiber bundles. Adhesively luted fiber bundles achieved bond strengths comparable to those of solid fiber posts for one investigated post type, and even higher values compared to another post type. Inhomogeneities were frequently detected irrespective of application mode.

Root canal adaptation and intra-tubular penetration of three fiber-post cementation systems

BackgroundTo measure the penetration of three bonding systems for the luting of fiber glass posts in endodontically treated teeth, using confocal laser scanning microscopy (CLSM).Material and MethodsA total of 30 maxillary incisors were shaped with the Mtwo system and filled with gutta-percha and Top Seal cement. The sample was divided into three groups (ni=10) according to the bonding system used to cement the posts: Group 1 (Prime&Bond NT and Rebilda DC with a total-etch technique); Group 2 (Futurabond DC and Rebilda DC with a dentin self-etch technique); and Group 3 (BisCem self-adhesive cement). Rhodamine B was added to the bonding systems to allow visualization by CLSM. Three 1-mm thick cross-sections were obtained of each root at a distance of 2, 5 and 8 mm from the coronal limit of the root. The specific software of the CLSM system was used to measure the percentage of the root canal perimeter showing penetration of the bonding system in the dentinal tubules, together with the maximum depth of penetration. Comparison between groups were made by Kruskal Wallis test, and comparison two by two groups with Mann-Whitney U-test.ResultsDepth of penetration of the resin tags, were distributed from greater to lesser depth as follows: BisCem > Prime&Bond NT > Futurabond DC. BisCem showed significantly greater penetration in the middle and apical thirds than the rest of the systems (906.14±67.42 and 699.27±76.26 µm, respectively). The percentage perimeter exhibiting penetration in the coronal third was significantly greater with BisCem versus Futurabond DC (56.08±7.24 and 44.38±5.23%, respectively). No significant differences were recorded in the middle and apical thirds among the three systems.ConclusionsBisCem resulted in greater depth of intratubular penetration at all studied levels. The percentage perimeter of the canal showing penetration was similar for all the bonding systems. Key words:Fiber post luting, sealer adaptation, confocal laser scanning microscope.

Bond Strength of Zirconia to Different Core Materials

ABSTRACT Background Since bonding to zirconia is still questionable, the aim of this study was to evaluate the bond strength of yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) to different materials used to manufacture dental cores, employing a universal self-etching adhesive system. Materials and methods Cylinders obtained from blocks of Y-TZP Zirconia were sintered in a high-temperature oven. The surfaces to be bonded were blasted with aluminum oxide, then silica-coated aluminum oxide, and finally cleaned in ultrasonic bath. The specimens were divided into six groups according to the core material tested: Silver alloy (Ag/Sn/Cu, Tecnofix), copper alloy (Cu/Ni/Zn, Goldent LA), core buildup resin (Rebilda DC — VOCO), Y-TZP zirconia (IPS e.max ZirCAD, Ivoclar Vivandent), enamel, and dentin. The zirconia cylinders were bonded to the core substrates using the Futurabond U adhesive system (VOCO) and resinous cement (Bifix QM — VOCO). The specimens were shear tested in a universal testing machine at 1 mm/ min. Data was analyzed using ANOVA and Tukey's test. Results Bond strength in MPa (±SD) for the different materials tested were dentin: (12.80 ± 3.18)a; enamel: (15.13 ± 3.09) ab; resin: (17.20 ± 4.67)ab; copper alloy: (18.93 ± 4.66)bc; silver alloy: (22.86 ± 5.47)c; and zirconia: (23.65 ± 3.64)c. Groups followed by the same letters are not significantly different at p &lt; 0.05. Conclusion The metallic alloys and zirconia core materials showed significantly higher bond strength than those obtained directly on dentin. The core buildup resin bond strength to zirconia is similar to that obtained with enamel and dentin. How to cite this article Frattes FC, de Oliveira JBS, Pucci CR, Borges AB, Torres CRG. Bond Strength of Zirconia to Different Core Materials. World J Dent 2016;7(4):169-174.

Removing Fractured Endodontic Instruments with a Modified Tube Technique Using a Light-curing Composite

IntroductionThe aim of this in vitro study was to assess an alternative method using light-curing composite for removing fractured endodontic instruments with a tube technique. MethodsTwo different stainless steel endodontic instruments (ISO 20: Hedstrom files, K-files; VDW, Munich, Germany) were cut at the diameter of 0.4 mm. These fragments were fixed in a vise leaving a free end of 1 or 2 mm. Cyanoacrylate (Instant Fix; Henry Schein Dental, Melville, NY), dual-curing Rebilda DC (VOCO, Cuxhaven, Germany), and light-curing SureFil SDR (Dentsply, York, PA) were placed into microtubes (N'Durance Syringe Tips; Septodont, Saint-Maur, France) and shifted over the instruments (n = 20 in each group). After polymerization, pull-out tests were performed with a constant speed of 2 mm/min; failure load was measured digitally. Data were analyzed using the Kruskal-Wallis test followed by the Dunn test for pairwise comparison. ResultsThe median failure load was up to 62.5 N for SDR, 35.8 N for Rebilda, and 14.7 N for cyanoacrylate, respectively. Both tested composites yielded significantly higher values in pull-out tests than cyanoacrylate. The disconnecting force was highest when light-cured composite SDR was used for fixation. Removing Hedstrom files resulted in higher values than removing K-files. The median force when using SDR was 79.7 N (interquartile range, 66.0–86.8 N) in Hedstrom files and 53.3 N (interquartile range, 47.1–58.5 N) in K-files. ConclusionsWithin the limitations of this study, the use of light-curing composite inside of the microtube was superior compared with the use of cyanoacrylate or chemically cured composite, which are being used presently.

Effect of different bonding techniques on the bond strength of two different fiber posts

Aim: The aim of this study was to investigate the effect of three different bonding techniques on the bond strength of two different fiber posts to root dentin with push out test. Materials and Methods: A total of 30 extracted teeth were sectioned at the cement-enamel junction using a diamond disc under water-coolant to obtain 18 mm root length. All roots were treated endodontically and filled with sealer and Gutta-percha points. The roots were randomly divided into two groups according to chosen post systems (Rebilda DC [VOCO, Cuxhaven, Germany] or UniCore [Ultradent, South Jordan, UT]). Following preparation specimens were randomly divided into three subgroups of 3 teeth each. Luting of the posts were completed with Rebilda DC (self-etch); BisCem (self-adhesive, Bisco, Schaumburg, IL) Duo-Link (etch and rinse Bisco). Specimens were transversally sectioned into 2 ± 0.05 mm thick discs and push-out test was performed. The data was analyzed statistically by using three-way ANOVA and Tukey tests. Results: The bond strengths between fiber posts and root dentin were affected by type of resin cement and post ( P P Conclusion: It can be concluded that, bond strength between fiber post and root dentin affected by the using of different post and cement types. Self-adhesion techniques were showed lower bond strength than both self-etch and etch and rinse techniques

Effect of different core build‐up materials on strength of post restored teeth

The aim of the present paper is to determine shear bond strengths (SBSs) of core build‐up materials placed on post retained endodontically treated teeth. Following endodontic treatment, prefabricated posts were placed on 84 extracted maxillary first molar teeth. Core materials including high copper admixed silver amalgam (Duralloy; control group), dual cured adhesive core materials (Bis‐Core, LuxaCore Dual and Rebilda DC), organically modified ceramic (Admira), light cured resin composite (Filtek Z250) and silver reinforced glass ionomer cement (Argion Molar) were placed. Shear bond strength was tested in a universal testing machine (crosshead speed = 1 mm min−1). The Mann–Whitney U test followed by Bonferroni post hoc correction was used for statistical analysis (significance level = 0·05). While Filtek Z250 exhibited the highest SBS values (p<0·05), Argion Molar showed the lowest values (p<0·05). Bis‐Core, LuxaCore Dual, Rebilda DC and Admira groups had similar bond strengths (p>0·05). Duralloy revealed higher SBS values in comparison to Rebilda DC group (p<0·05). According to SBS values, dual or light cured resin composites may be used as alternatives to amalgam.

Retentive Force of FRC Posts Inserted with Core Build-up Composites and Resin Cements

The aim of this study was to determine the retentive forces of fiber-reinforced composite (FRC) posts luted with different core build-up composite resins, and resin cements. Extracted single-rooted teeth were restored using FRC posts luted with the core build-up composites Build-It, Culmat, Flow White, Luxacore, Multi-Core Flow, Rebilda DC and luted with the resin cements Calibra, Cement-It, Multilink, and RelyX Unicem (control group, no separate etching, priming or bonding steps). The Rebilda DC was used with both the light-polymerizing Solobond and the dual-polymerizing AdheSE. Following water storage (37°C, 24 h) and thermal cycling (5000 cycles, 5–55°C, 30 s) tensile strength testing was performed and fracture modes were assessed. Statistical analysis of the data was done by one-way ANOVA, Bonferroni/Dunn correction, and unpaired t-test with α = 0.05. Except for Multilink (319 N, SD 50 N) and Cement-It (331 N, SD 85 N) significantly higher retentive forces were obtained for the core build-up composite Build-It (422 N, SD 43 N) and for the resin cements Calibra (408 N, SD 50 N) and RelyX Unicem (405 N, SD 64 N) compared to the other materials (p < 0.001). The lowest retentive forces were found for the core build-up composites Luxacore (145 N, SD 36 N) and Rebilda DC/Solobond (148 N, SD 39 N) (p < 0.001). Fracture modes were mainly interfacial. The use of core build-up composites did not improve the retentive forces of FRC posts compared to resin cements. Except for Culmat, core build-up composites as well as resin cements in combination with dual-polymerizing bonding materials were superior to composites with light-polymerizing bonding materials.

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

Objective. To investigate the influence of time delay and duration of photo-activation on subsurface microhardness of a dual-cured resin composite. Material and methods. A commercially available dual-cured core build-up resin composite (Rebilda DC) was filled in cavities (diameter: 4.0 mm; height: 6.0 mm) of polystyrene molds and light-cured for 20 or 60 s either immediately after the filling procedure (time delay 0 s) or after a time delay of 30, 90, 180 or 300 s. Non-irradiated self-cured specimens served as a control group (n = 15). Specimens were stored in complete darkness and at 100% relative humidity at 37°C for 2 weeks and cross-sectioned. Knoop Hardness Numbers (KHNs) were measured six times per depth and averaged at distances of 0.25, 0.50, 1.00, 2.00, 3.50 and 5.50 mm from the light-exposed surface. Data were statistically analyzed using one- and two-way ANOVA followed by Scheffé's post-hoc test at a level of significance of 0.05. Results. Mean hardness values in all experimental groups ranged between 54.3 ± 2.1 and 58.1 ± 2.3 KHN. Light-curing did not significantly increase composite KHN at any depth measured. Delaying light exposure had no influence on KHN, irrespective of depth. A longer light-exposure time (60 versus 20 s) resulted in significantly higher KHN only at depths of 3.50 and 5.50 mm. Conclusion. Photo-activation of the tested dual-cured resin composite provided no clinically relevant benefit compared to self-curing regarding the degree of hardening.

Influence of light‐curing protocols on polymerization shrinkage and shrinkage force of a dual‐cured core build‐up resin composite

This study investigated the influence of time delay and duration of photo-activation on linear polymerization shrinkage, shrinkage force, and hardening of a dual-cured core build-up resin composite. The test material (Rebilda DC) was light-cured for 20 or 60 s either early (2 min) or late (7 min) after the start of mixing. Non-irradiated self-cured specimens served as controls. Linear shrinkage and shrinkage force were measured for 60 min using custom-made devices. Knoop hardness was determined at the end of the observation period. Self-cured controls, showing a linear shrinkage similar to that of specimens early light-cured for 20 s generated the lowest shrinkage force and hardness. A shorter light exposure time (20 s vs. 60 s) reduced linear shrinkage, shrinkage force, and hardness when early light-curing was performed, but did not affect the three properties in specimens light-cured late after the start of mixing. Late photo-activation increased linear shrinkage, irrespective of irradiation time, and resulted in a higher shrinkage force and hardness for short light exposure time. A moderate correlation was found between the two shrinkage properties studied (r(2) = 0.65). In conclusion, improvements in shrinkage behavior of the tested core build-up material were associated with inferior hardening, making it important to adapt curing protocols to the clinical situation.

Effect of sodium hypochlorite contamination on microhardness of dental core build-up materials

This study aimed to determine the influence of sodium hypochlorite (NaOCl) contamination on the microhardness of build-up composites. Fifty-two samples, from each of three build-up materials (LuxaCore Dual, MultiCore flow and Rebilda DC) were prepared. Half of the samples from each material were stored in physiologic saline (baseline control) while the other halves were stored in NaOCl. After 1 h, the samples were rinsed with tap water, cut axially and measured for Knoop hardness at different depth levels. The results were analysed by ANOVA and unpaired t-tests (p<0.05). Significant differences in microhardness were observed for LuxaCore Dual up to 0.2 mm, Rebilda DC up to 0.3 mm, and for MultiCore flow up to 0.4 mm under the surface level. Contact with sodium hypochlorite on build-up materials causes reduction of the microhardness. The softening is not only limited on the surface, but can also be found in deeper layers of build-up materials.

Effect of surface conditioning on the retentive bond strengths of fiberreinforced composite posts

Debonding is a common cause of failure encountered with fiber-reinforced composite (FRC) posts, and usually occurs along the post space-dentin adhesive interface. Surface conditioning of posts is expected to increase the chemical and mechanical bond between the luting composite resin and the post, but the best method has not been definitively determined. The purpose of this in vitro study was to compare the effects of 3 surface-conditioning methods on the retentive bond strengths of FRC posts using 5 composite resin materials, and compare results to those of unconditioned FRC posts as well. Post space preparations (DentinPost ER root post system, length of 12 mm) were performed on 200 human anterior teeth. Groups of 50 FRC posts (ISO size 90) each were treated using 1 of the following conditioning methods: silanization, etching with 5% hydrofluoric acid, tribochemical coating (CoJet system), or were left untreated (control group). FRC posts (n=10) in each group were placed using 1 of 5 composite resin materials (Calibra or RelyX Unicem resin cements or Build-It, MultiCore Flow, or Rebilda DC foundation composite resins). Following water storage (37 degrees C, 24 hours) and thermal cycling (5000 cycles, 5 degrees -55 degrees C, 30-second dwell time), tensile strength testing was performed. Fracture modes were assessed using a light microscope. Data were analyzed statistically (1-way and 2-way ANOVA, Bonferroni-Dunn correction, alpha=.05). Retentive bond strengths of FRC posts luted with MultiCore Flow in combination with the CoJet system, and of posts inserted with Rebilda DC in combination with hydrofluoric acid (HF) etching as well as with the CoJet system, were significantly higher than those of the corresponding unconditioned FRC posts (P<.001). No significant differences were noted between the bond strength values of RelyX Unicem with CoJet, MultiCore Flow with CoJet, and Rebilda DC with either CoJet or HF etching (P>.05). Retentive bond strengths were significantly lower for HF etching (Calibra, RelyX Unicem, Build-It), and for the treatment with the CoJet system in combination with Build-It compared to the corresponding control groups (P<.001). Fracture modes were primarily adhesive at the post surface or cohesive within the composite resin layer or within the FRC post. The retentive bond strengths differed significantly with respect to the tested combinations of conditioning method and luting composite resin.