Root canal pre-treatment and adhesive system affect bond strength durability of fiber posts ex vivo.

OBJECTIVES: To investigate the effect of different pre-treatments on the long-term bond strength of fiberglass posts luted either with dual-curing self-etch adhesives and core build-up composites or with a self-adhesive resin (SAR) cement. MATERIALS AND METHODS: In total, 180 human root-filled teeth received post-space preparations and three different dentin pre-treatments (PTs): PT1, ethanol (99%); PT2, ethanol-tertiary-butanol-water-solution (AH Plus Cleaner, Dentsply Sirona; York, USA); and PT3, distilled water (control). Five luting systems were used: FU, Futurabond U (Voco; Cuxhaven, Germany); CL, Clearfil DC Bond (Kuraray Noritake; Okayama, Japan); GR, Gradia Core SE Bond (GC Europe NV; Leuven, Belgium); LU, LuxaBond Universal (DMG; Hamburg, Germany); and RX, RelyX Unicem 2 (3M; Minnesota, USA). Roots were cut into six slices (1 mm thick). From each root canal region, three slices were submitted to immediate and three to post-storage push-out testing. The latter were subjected to thermocycling (5-55°C, 6.000 cycles) and stored for six months in saline solution (0.9%, 37°C). Data were analysed using repeated measures ANOVA and chi-square tests (MV±SD). RESULTS: Bond strength was significantly affected by material (p<0.0005), pre-treatment (p=0.016), and storage (p<0.0005; repeated-measures ANOVA). LU (18.8±8.1MPa) revealed significantly higher bond strength than RX (16.08±6.4MPa), GR (15.1±4.6MPa), CL (13.95±5.2MPa), and FU (13.7±6.3MPa). PT1 (16.5±6.9MPa) revealed significantly higher bond strength than PT3 (14.5±5.7MPa). CONCLUSIONS: A universal adhesive in self-etch mode combined with a core build-up material revealed higher bond strength than a SAR cement, both interacted positively with Ethanol pre-treatment. CLINICAL RELEVANCE STATEMENT: Ethanol (99%) rinsing can be recommended as part of post and core pre-treatment for the investigated luting systems.

Interface analysis after fatigue loading of adhesively luted bundled fiber posts to human root canal dentin.

OBJECTIVES: The aim of this study was to assess the fatigue loading behavior and fracture resistance of endodontically treated teeth restored with adhesively luted bundled fiber posts in comparison to solid fiber posts. Image analysis (2D and 3D) was applied to evaluate modes of failure and to characterize susceptible parts of the post-and-core interface. METHOD: Crowns of 72 human similar-sized central upper incisors were removed and roots received a conventional root canal filling prior to establishing 4 groups of core build-up: No Post group (nP) received a 4 mm deep filling made of composite inside the canal with no dental post, fiber post group (FP) received a conventional solid post, and two experimental groups received bundles of 6 (FB6) or 12 (FB12) 0.3 mm thin fiber posts, respectively. Posts were placed adhesively inside the root canal using a dual-curing build-up composite in combination with a self-etch adhesive, the latter was also used for nP group. Upon completion of core build-ups, all teeth received full-ceramic crowns that recreated the original tooth form. Samples were subjected in a 135° angle to thermo-mechanical loading (TML) for 1.2 Mill. chewing cycles followed by static load tests (fracture resistance). Fracture modes as well as intracanal failure modes with respect to failed interfaces were analyzed using optical and electron microscopy (SEM). Microcomputer tomography (µCT) was used to exemplary compare pre and post TML geometries. RESULTS: Static load test was significantly different between groups (p < 0.0005; Kruskal-Wallistest). Pairwise comparison showed that the nP group (221 ± 103N) failed at significantly lower forces compared to the FP (454 ± 184N), FB6 (477 ± 250N) and FB12 (478 ± 260N) groups (p ≤ 0,001; Mann-Whitney-U-test). Fracture modes were significantly affected by the presence or absence of a post (p ≤ 0,016; Chi-square test) revealing increased incidence of restorable fractures at the cervical region for nP group. Microscopic analysis revealed more intracanal failures at interfaces between post surfaces and composite for solid posts, whereas fiber bundled posts mostly failed at the interfaces between composite and dentin. Micro-CT analysis showed no alterations of the root-post-and-core structure after TML except slight deformations of occasionally entrapped voids. CONCLUSION: Fracture resistance and fracture modes were significantly affected by the presence or absence of a post, whereas the investigated post groups did not differ from each other. However intracanal failure revealed differences in adhesive failures between solid fiber posts and bundled fiber posts. Deformations of entrapped voids, revealed by micro-Ct analyses after TML, lead to the assumption that applied forces result in alterations in the regions of voids.

Hard X-ray phase-contrast-enhanced micro-CT for quantifying interfaces within brittle dense root-filling-restored human teeth.

Bonding of resin composite fillings, for example following root-canal treatment, is a challenge because remaining gaps grow and lead to failure. Here, phase-contrast-enhanced micro-computed tomography (PCE-CT) is used to explore methods of non-destructive quantification of the problem, so that countermeasures can be devised. Five human central incisors with damaged crowns were root-filled followed by restoration with a dental post. Thereafter, the crowns were rebuilt with a resin composite that was bonded conventionally to the tooth with a dental adhesive system (Futurabond U). Each sample was imaged by PCE-CT in a synchrotron facility (ID19, European Synchrotron Radiation Facility) with a pixel size of 650 nm. The reconstructed datasets from each sample were segmented and analysed in a semi-automated manner using ImageJ. PCE-CT at sub-micrometre resolution provided images with an impressive increased contrast and detail when compared with laboratory micro-computed tomography. The interface between the dental adhesive and the tooth was often strongly disrupted by the presence of large debonded gaps (on average 34% ± 15% on all surfaces). The thickness of the gaps spanned 2 µm to 16 µm. There was a large variability in the distribution of gaps within the bonding area in each sample, with some regions around the canal exhibiting up to 100% discontinuity. Although only several micrometres thick, the extensive wide gaps may serve as gateways to biofilm leakage, leading to failure of the restorations. They can also act as stress-raising `cracks' that are likely to expand over time in response to cyclic mechanical loading as a consequence of mastication. The observations here show how PCE-CT can be used as a non-destructive quantitative tool for understanding and improving the performance of clinically used bonded dental restorations.

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

PURPOSE: 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. MATERIALS AND METHODS: 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). RESULTS: 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. CONCLUSION: 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.