Effect of Resin Composite Filling Thickness in Zirconia Abutment Screw-Access on the Fatigue Behavior of a Cement-Retained Lithium Disilicate Material.

To investigate the influence of different resin composites used for sealing the screw-access hole of zirconia abutments on the fatigue behavior of lithium disilicate ceramic. Eighty 3YSZ abutment discs (IPS e.max ZirCAD MO, Ivoclar AG) (Ø = 10mm; 3mm thickness; Ø = 2.5mm access channel) and lithium disilicate restorative discs (IPS e.max CAD, Ivoclar AG) (Ø = 10mm; 1mm thickness) were obtained and randomly allocated into four groups based on the sealing protocol (2mm of thickness): Ctrl (PFTE Tape); PFTE tape + nanohybrid resin; PFTE tape + bulk-fill resin; and PFTE tape + Flow resin. After cementation procedures, monotonic (n = 5) and cyclic fatigue tests were conducted (n = 15; initial load of 100N for 5000cycles, increments of 100N every 10,000cycles at 20Hz, immersed in distilled water) until failure. Fractographic and finite element analysis were also performed. One-way ANOVA and Tukey post-hoc tests were carried out for the monotonic data, while Kaplan-Meier and Mantel-Cox tests were used for survival rates. No statistically significant effect of the presence neither the type of resin composite material was observer after the monotonic tests. For the fatigue test, the Bulk and Nano groups exhibited significantly better performance than the Ctrl and Flow (Ctrl: 1100N ≤ Flow: 1213N < Nano: 1340N ≤ Bulk: 1380N, p ≤ 0.05). Nanohybrid or bulk-fill resin composites are recommended for sealing the abutment screw-access hole and optimize the performance of lithium disilicate restorations.

The present study aimed to evaluate the impact of the existence of an abutment screw-access hole and the filling effects on the fatigue mechanical behavior of a luted lithium-disilicate glass-ceramic. Seventy-two discs (Ø = 10 mm, 1.0 mm in thickness) of lithium disilicate (IPS e.max CAD, Ivoclar AG) were obtained from prefabricated blocks. Thirty-six abutment specimens of an opaque zirconia (Yz - IPS e.max ZirCAD, Ivoclar AG) and titanium (Ti - Luminesse Ti-Cam discs, Talladium Inc.) were confectioned, and allocated according to 6 groups: Yz and Ti rigid (without screw access hole); Yz unfilled, Yz filled, Ti unfilled and Ti filled (with the screw access (Ø = 2.5 mm) in the center). For the unfilled groups, only a polytetrafluoroethylene tape was used. Resin composite (Tetric N-Ceram, Ivoclar AG) was applied to the screw access hole for the filled groups (Yz and Ti). A cyclic fatigue test was carried out (load of 200 N, 10,000 cycles each; 20 Hz of frequency, step size of 100 N until failure detection (radial/cone crack). The fatigue failure load (FFL) and number of cycles until failure (CFF) were recorded for statistical purposes. The stress distribution (MPa) was evaluated by finite element analysis. A statistically positive effect of the abutment material and the presence of the screw access hole was observed (p ≤ 0.05). The rigid groups (without screw access holes) depicted almost 100% of survival after the fatigue tests. Among the other groups, the Yz-filled group showed the best performance (p ≤ 0.05), followed by the Yz unfilled group. The Ti groups depicted lower values of FFL and CFF, with the Ti unfilled group showing the most unfavorable fatigue behavior (p ≤ 0.05). The lowest tensile stress concentration in the restorative material was observed with the use of rigid abutments, the filled groups depicted intermediate values, while unfilled groups showed the highest stress concentration (Yz rigid = 306.3 MPa; Ti rigid = 310.4 MPa < Yz filled = 490.7 MPa; Ti filled = 498.9 MPa < Yz unfilled = 707.6 MPa; Ti unfilled = 719.7 MPa). Therefore, the presence of a screw-access hole decreases the mechanical performance of a lithium disilicate ceramic regardless of the abutment material. In the presence of a screw-access hole, zirconia abutments depicted a higher fatigue failure load when compared with titanium. The filling of the abutment screw-access hole with resin composite increased the mechanical performance of the simulated restoration.

Background: The retention of cement retained implant-supported restorations can be affected different luting agents and abutment types. This is significant because success of cement-retained implant-supported restorations depends on adequate retention. Objectives: The aim of this study was to evaluate the retentive strength of different luting cements of zirconia restorations, performed on short titanium and zirconia abutments. Materials and Methods: Totally, 32 titanium abutments were shortened from 8 to 3 mm in height. Zirconia abutments were produced from this assembly, using a computer-aided design/computer-aided manufacturing (CAD/CAM) system. Zirconia copings were produced using a CAD/CAM system individually for titanium abutments and zirconia abutments. Four different cements were used in the study: polycarboxylate cement, dual composite resin cement, self-adhesive composite resin cement, and implant cement. A universal testing machine was used to test the cement failure load values for each specimen. Results: In zirconia abutments, the highest tensile strength mean value found was for self-adhesive resin cement (367,89 N), followed by the dual-cured resin cement (111,69 N), polycarboxylate (67,17 N) and the implant cement (60,42 N). In titanium abutments, the highest tensile strength mean value found was for self-adhesive resin cement (227,22 N), followed by the polycarboxylate (57,87 N), implant cement (54,39 N), and dual-cured resin cement (53,01 N). Conclusion: In light of the results obtained in this study, the self-adhesive resin cement presented higher tensile strength. Retentive strengths of the same size zirconia abutments are greater than those of titanium abutments.

Characteristic fatigue strength and reliability of dental glass-ceramics: Effect of distinct surface treatments – Hydrofluoric acid etching and silane treatment vs one-step self-etching ceramic primer

Fracture resistance of cement-retained and screw-cement–retained milled posterior crowns with screw-access hole preparations before and after firing: An in vitro study

Background This study investigated the impact of luting procedure and restoration thicknesses on the flexural strength of CAD/CAM restorations. Traditional luting agents have been questioned in favor of pre-heated resin composites or flowable composites. Materials and Methods 400 disc-shaped restorations (lithium disilicate [IPS e.max CAD] or resin composite [Tetric CAD, Ivoclar]) were cemented onto dentin analog discs using different procedures (n = 20): dual-curing resin cement (Panavia V5), light-curing resin cement (Panavia Veneer LC), pre-heated resin composite (Clearfil™ AP-X) with or without pre-heated restoration, and high-filled flowable composite (Clearfil Majesty™ Flow). The biaxial flexural strength was calculated. Results There were significant effects of material, thickness, and luting procedure on flexural strength (p < 0.001). Resin composite specimens exhibited lower flexural strength (90 MPa) compared to lithium disilicate specimens (571 MPa), with thicker restorations (338 MPa) being stronger than thinner ones (323 MPa). Light-curing cement showed the highest strength (408.8 MPa)A, followed by dual-curing cement (362 MPa)B, pre-heated cement with pre-heated composite (318 MPa)C, pre-heated composite (304 MPa)C, and flowable resin composite (259 MPa)D. The light-curing cement yielded similar results to the pre-heated resin composite associated or not with the pre-heated crown for the thicker lithium disilicate specimens, whereas for the thinner lithium disilicate specimens all luting procedures performed similarly. Thin resin composite discs showed higher flexural strength when luted with light-curing cement, whereas the luting procedure had less influence for the thicker restorations. Conclusion Luting procedures impact the flexural strength of CAD/CAM lithium disilicate and resin composite restorations. Pre-heated resin composite, with or without pre-heated restoration, can replace dual-curing cement. Nevertheless, light-curing cement is superior for resin composite and 1.5 mm lithium disilicate restorations.

Aim: This study aimed to evaluate the effect of polymerization with either a monowave (MW) or a polywave (PW) light-curing unit (LCU) on the degree of conversion (DC) and marginal adaptation following thermomechanical aging of an ormocer bulk-fill resin composite (RC) (Admira fusion X-tra Bulk Fill – AB), a methacrylate-based bulk-fill RC (Tetric N-Ceram Bulk Fill – TB) and a conventional RC (Tetric N-Ceram – TC). Methods: DC was assessed in five samples of each RC using Fourier transform infrared spectroscopy. For determination of marginal adaptation, standard preparations were made in 60 bovine incisors, divided into three groups, according to the RC. The bulk-fill RC was inserted in a single increment of 4 mm. In contrast, the conventional RC was inserted in three increments. Marginal gap was evaluated after thermomechanical aging. Data were analyzed using a two-way analysis of variance (ANOVA) and Tukey’s tests for multiple comparisons (α = 0.05). Results: The two-way ANOVA showed a significant effect (p<.05) of the RC factor but not of the LCU factor. The Tukey test showed that TB had the significantly lowest DC followed by TC, and with AB having the significantly highest DC. For the marginal adaptation, a significant effect was found for the LCU factor and the for the interaction RC × LCU (p<.05). Groups light-cured with PW showed significantly wider marginal gaps than MW. TC presented wider marginal gaps (17.36 µm) when cured with PW than when cured with MW (13.05 µm). The two bulk-fill RC resulted in similar marginal gap formation to each other. Conclusion: The ormocer-based bulk-fill RC showed a higher DC than the methacrylate-based bulk-fill RC but similar marginal adaptation. The LCU, MW or PW, had no significant influence on the DC, and no relevance on the marginal adaptation.

The aim of this study was to compare the effect of different surface treatments applied to short titanium and zirconia abutments on the bond strength of single-unit zirconia crowns. Sixty titanium abutments were shortened to 3 mm in length, fixed to analogs, and embedded in acrylic blocks. Three-dimensional views of abutments were obtained by scanning; then, zirconia abutments and copings were produced. The samples, which included titanium (n = 60) and zirconia (n = 60) abutments, were divided into five different groups (n = 12), and surface treatments were carried out; 1.5-W and 3-W Er,Cr:YSGG laser treatment, AL2O3 sandblasting, and tribochemical silica coating were applied to the groups, and the control group had no surface treatment. Copings were cemented to the samples with self-adhesive resin cement. The samples were then subjected to the pull-out test, and the results were processed via statistical analysis. There was a significant difference between the titanium and zirconia groups (P < .001). The mean bond strength values of the titanium samples were higher than those of the zirconia samples. The tribochemical silica coating gave a higher bond strength than the other treatments when applied to titanium abutments. For the zirconia abutments, the 1.5-W laser treatment, 3-W laser treatment, tribochemical silica coating, and Al2O3 sandblasting groups differed significantly from the control group; however, they were not significantly different from each other. The bond strength of zirconia crowns to short titanium and zirconia abutments increases with surface treatments. Furthermore, the surface treatments were more effective in increasing the bond strength for the titanium abutments than for the zirconia abutments.

Objectives This study aimed to compare the shear bond strength of three resin cements (light-cured resin cement, pre-heated composite resin, and dual-cured self-adhesive resin cement) when bonding to lithium disilicate discs. Materials and methods Thirty-six discs made of lithium disilicate were fabricated and etched with 9.5% (HF), and 36 human premolars were collected and immersed in the acrylic molds, then randomly divided into three equal groups (n = 12): Group 1: light-cured resin cement, Group 2: pre-heated resin composite, and Group 3: dual-cured resin cement. The resin composite was heated between 55°C and 65°C by a heater device. The shear bond strength test was performed using the general mechanical testing device. The data were analyzed using two-way ANOVA and Bonferroni tests (p < 0.05). Results The highest shear bond strength was demonstrated by the light-cured resin cement group (26.61 ± 5.16 Mpa), followed by the dual-cured resin cement group (17.76 ± 4.67 Mpa), and the least by the pre-heated composite resin group (15.58 ± 3.36 MPa). The shear bond strength in the light-cured resin cement group was significantly higher than the dual-cured resin cement and pre-heated composite resin groups. Conclusion The light-cured resin cement has higher shear bond strength when compared to pre-heated resin composite and dual-cured resin cement with a self-etch system. Although pre-heating composite resins may increase its mechanical proprieties and make it suitable for luting ceramics it may not increase bond strength.

Influence of surface treatment of resin composite substrate on the load-bearing capacity under fatigue of lithium disilicate monolithic simplified restorations

When partial and/or non-retentive preparation, such as those for occlusal veneers, is indicated, a proper and stable adhesion is essential. Therefore, the aim of this in vitro study was to evaluate the effect of loss of adhesion in different regions of the bonding interface on the fatigue behavior of simplified lithium disilicate restorations. For this, lithium disilicate (IPS e.max CAD) discs (1 mm thick and Ø = 10 mm) were fabricated, polished with #400-, #600-, #1200-grit silicon carbide (SiC) papers, and crystallized. As substrate, fiber-reinforced resin epoxy discs (2.5 mm thick and Ø = 10 mm) were fabricated and polished with #600-grit SiC paper. The ceramic bonding surface was treated with 5% hydrofluoric acid and a silane-containing primer (Monobond N), while the substrate was etched with 10% hydrofluoric acid followed by the application of the bonding system primers (Primer A + B). A lacquer (nail polish) was used to simulate the loss of adhesion in specific areas according to the study design to compose the testing groups: bonded (control; did not received nail polish application); – non-bonded (loss of adhesion in the whole specimen area); – margin (loss of adhesion in the ceramic margin); – center (loss of adhesion in the ceramic central area). The adhesive area of partially bonded groups was 50% of the adhesive surface. Then, the discs (n = 12) were bonded to the respective substrate using a resin cement (Multilink N), light-cured, water-stored for 90 days, and subjected to thermocycling (25,000 cycles, 5° to 55 °C) before testing. A cyclic fatigue test was run (20 Hz, initial load of 200 N for 5000 cycles, 50 N step size for 10,000 cycles each until specimen failure), and the fatigue failure load and number of cycles for failure were recorded. As complementary analysis, finite element analysis (FEA) and scanning electron microscopy analysis were performed. Kaplan-Meier log-rank (Mantel-Cox) was conducted for survival analysis. The results showed that as the loss of adhesion reaches the central area, the worse is the fatigue behavior and the higher is the stress peak concentration in the ceramic bonding surface. The bonded specimens presented better fatigue behavior and stress distribution compared to the others. In conclusion in a non-retentive preparation situation, proper adhesion is a must for the restoration fatigue behavior even after aging; while the loss of adhesion reaches central areas the mechanical functioning is compromised.

To evaluate the influence of anterior monolithic zirconia and lithium disilicate thickness on polymerization efficiency of dual-cure resin cements. Twelve ceramic disks (4.0-mm diameter) with thicknesses of 0.5, 1, 1.5, 2, 2.5, and 3 mm were prepared from monolithic zirconia (Prettau® Anterior; n = 6) and lithium disilicate (IPS e.max® CAD HT; n = 6). Three dual-cure resin cements (Panavia F 2.0, DuoLink Universal™, and RelyX™ U200) were used for polymerization beneath ceramic disks. For each resin cement, 10 specimens were prepared by light curing under monolithic zirconia and lithium disilicate disks of each thickness. Vickers hardness measurements were conducted at four different measurement depths. Data were statistically analyzed using univariate four-, three-, two-, and one-way analysis of variance and independent samples t-tests. Microhardness of resin cements decreased significantly with increasing measurement depth and thickness of monolithic zirconia or lithium disilicate (P < .001). Cements polymerized under lithium disilicate showed higher microhardness values than did those polymerized under zirconia (P < .001). For both ceramics, Panavia F 2.0 exhibited the greatest microhardness, followed by DouLink Universal and RelyX™ U200 (P < .001). Different dual-cure resin cements may have different polymerization efficiencies, and the type and thickness of the overlying ceramic can influence polymerization. The findings of this study suggest that an increase in the thickness of monolithic lithium disilicate or anterior monolithic zirconia restorations can significantly decrease the microhardness of the dual-cure resin cement polymerized beneath the restoration. Dual-cure resin cements can be used for the cementation of anterior monolithic zirconia restorations up to 2 mm thickness and for monolithic lithium disilicate restorations up to 2.5 mm thickness. However, for lithium disilicate restorations with a ≥2.5 mm thickness and zirconia restorations with a ≥2-mm thickness, different cementation approaches must be further studied, such as: extended light curing; the use of dual-cure resin cement with a higher self-curing component than the ones used in this study; or a self-cure resin cement.

The influence of milling protocols on the fatigue behavior of different CAD-CAM materials.

Objective: To evaluate the effect of two types of light-curing units (second and third generations) and two types of bulk-fill composite resins with different photoinitiators - Tetric N-Ceram Bulk Fill (TNCB) and Xtra Fil (XTF) on gap formation at the gingival margins of Cl II restorations. Material and Methods: Fifty-six standard Cl II cavities were prepared on the mesial and distal surfaces of premolar teeth, with the gingival margin of the cavities 1 mm apical to the CEJ. The samples were randomly assigned to two groups based on the composite resin type and two subgroups based on the light-curing unit type and restored. After 5000 rounds of thermocycling, gingival margin gap in each sample was measured in µm under an electron microscope at ×2000 magnification. Data were analyzed by two-way ANOVA and Tukey tests (α=0.05). Results: Marginal gaps of TNCB composite resin were significantly smaller than those of XTF composite resin (p<0.001). There were no significant differences between the two light-curing units in each group (p=0.887 with XTF and p=0.999 with TNCB). Conclusion: The gaps at gingival margins of Cl II cavities with TNCB bulk-fill composite were smaller than XTF composite resin. Both composite resins can be cured with both the second- and third-generation LEDs.

Influence of the ceramic translucency on the relative degree of conversion of a direct composite and dual-curing resin cement through lithium disilicate onlays and endocrowns