Thin and thick layers of resin‐based sealer cement bonded to root dentine compared: Adhesive behaviour

This study aims to evaluate tensile and shear bond strengths of one epoxy (AH) and two methacrylate resin‐based sealers (EZ and RS) in thin and thick layers bonded to root dentine. An alignment device was prepared for accurate positioning of 20 root dentine cylinders in a predefined gap of 0.1 or 1 mm. Sealer was placed in the interface. Bond strength tests were conducted. Mode of failures and representative surfaces were evaluated. Data were analysed using anova and post‐hoc tests, with P < 0.05. The thick layer of sealer produced higher bond strength, except for the shear bond strength of EZ. Significant differences between thin and thick layers were found only in tensile bond strengths of AH and RS. Mixed type of failure was constantly found with all sealers. Bond strengths of thick layers of resin‐based sealers to root dentine tended to be higher than with thin layers.     

Push‐out bond strength of an experimental self‐adhesive resin cement

The adhesion of fiber posts luted with simplified adhesive systems has been a matter of great interest over the past years. The aim of this study was to assess the post retentive potential of experimental self‐adhesive resin cement (EXP) when used alone and in combination with a self‐etch adhesive. Fiber posts were placed in endodontically treated teeth and divided into four groups (n = 6) according the luting material, as follows: group 1 (EXP alone); group 2 (EXP used with self‐etch adhesive); group 3 (marketed dual‐cured cement used with self‐etch adhesive); and group 4 (marketed self‐adhesive cement). The push‐out test was used to assess the retentive strength of fiber posts (expressed in MPa), and specimens were analyzed under a stereomicroscope to determine failure mode. The adhesive interface between the cement and root canal dentin for each group was evaluated using scanning electron microscopy. The post retentive potential of group 1 (EXP) (7.48 ± 4.35 MPa) was comparable with that of marketed cements from group 4 (6.79 ± 3.68 MPa) and group 3 (8.77 ± 4.58 MPa). When EXP was used in combination with self‐etch adhesive (group 2), significantly higher push‐out bond‐strength values were measured (15.87 ± 4.68 MPa) compared with the other groups.     

Influence of endodontic sealer cement on fibreglass post bond strength to root dentine

Aim To test the hypothesis that the composition of endodontic sealer cements and the time elapsed between root filling and fibreglass post fixation interferes with adhesion to root canal dentine. Methodology Sixty bovine incisor roots were divided into five groups (n = 12): CI, unfilled; SI, filled with a calcium hydroxide‐based cement‐Sealer 26, and immediate post fixation; S7, Sealer 26 and post fixation after 7 days; EI, filled with a zinc oxide and eugenol‐based cement‐Endofill and immediate fixation; and E7 Endofill and post fixation after 7 days. The posts were cemented with adhesive system and dual resin cement. Ten roots were cross‐sectioned to obtain two 1‐mm‐thick discs for each cervical (TC), middle (TM) and apical (TA) third of the prepared root portion. The posts were submitted to a micropush‐out test. The other two teeth were evaluated using scanning electron microscopy to analyse the bond interface. Data were analysed using anova , Tukey and Dunnett tests (P < 0.05). Results Group EI was associated with a significant reduction in bond strength values irrespective of the root region; TC = 3.50 MPa (P = 0.0001); TM = 2.22 MPa (P = 0.0043) and TA = 1.45 MPa (P = 0.003). Region of canal had an influence on the values for the cement used in group E7, in which only the TA presented differences from the CI. Conclusions Endofill interfered negatively with the bond to root dentine along its full length and in the TA when post fixation was delayed for 7 days. Bond strength decreased from crown to apex in all groups.     

The influence of methodological variables on the push‐out resistance to dislodgement of root filling materials: a meta‐regression analysis

The aim of this systematic review was to evaluate the influence of several methodological variables on the push‐out resistance to dislodgment of root filling materials by a meta‐regression analysis of the literature. A systematic review was performed by searching the PubMed database using the terms ‘push‐out’ and ‘pushout’. Laboratory studies published before March 2015 were included. Two reviewers extracted data regarding country of origin, year of publication, tooth type, smear layer removal, root canal sealer, core material, obturation technique, sample storage, tooth portion, test machine load velocity and slice thickness. Pooled mean resistance to dislodgement of all groups from the included studies was used in a linear meta‐regression of random effects (α = 0.05). Of the 850 identified studies, 53 met the inclusion criteria. A meta‐regression of the 341 groups extracted from these articles was performed to analyse the influence of each variable on resistance to dislodgement (in MPa). The sealer, core material, obturation technique, slice thickness, storage time, load velocity and tooth portion significantly influence the results (P < 0.05). Irrigant solution and smear layer removal did not influence the resistance to dislodgement of the root filling materials (P > 0.05). Methodological variables such as sealer, core material, root filling technique, tooth type, tooth portion, slice thickness, storage time and load velocity influenced the resistance to dislodgment. The inclusion and standardization of all related variables could lead to a more comparable and reproducible analysis of the resistance to dislodgment of the root canal sealers.     

Influence of oxygen‐inhibited layer on dentin bond strength of chemical‐cured resin composite

This study evaluated the influence of an oxygen‐inhibited layer on the surface free energies of three single‐step self‐etch adhesives and on the bond strength of chemical‐cured resin. Adhesives were applied to bovine dentin and light irradiated, and the oxygen‐inhibited layer was either retained or removed. Surface free energies were determined by measuring the contact angles of test liquids placed on the cured adhesives. Dentin bond strengths of chemical‐cured resin with and without the oxygen‐inhibited layer were measured. Ultrastructural observation of the restorative–dentin interface was made by scanning electron microscopy. For all surfaces, values of the estimated surface tension component, Lifshitz‐Van der Waals force (γ_S^LW), were relatively constant. Values for the Lewis acid (γ_S⁺) component increased slightly when the oxygen‐inhibited layer was removed, whereas those of the Lewis base (γ_S^?) component decreased significantly. The bond strength of the chemical‐cured resin composite was significantly higher in specimens without an oxygen‐inhibited layer (7.6–8.0 MPa) than in those with an oxygen‐inhibited layer (4.8–5.2 MPa). Small gaps between adhesive and resin composite were found for the group with an oxygen‐inhibited layer. These results indicate that the absence of an oxygen‐inhibited layer in single‐step self‐etch adhesives promotes higher dentin bond strength of the chemical‐cured resin.     

Adhesion to Er:YAG laser and bur prepared root and crown dentine

Background: The purpose of this study was to evaluate the bond strengths between dentine and resin composite obtained after Er:YAG laser treatment of crown or root dentine used together with self‐etch and total‐etch adhesive systems. Methods: One etch‐and‐rinse adhesive (Single Bond, 3M, USA) and one self‐etch system (Clearfil SE Bond, Kuraray, Japan) were applied to root and crown dentine prepared with a regular bur in a turbine or with an Er:YAG laser. The shear bond strength was determined after thermocycling and statistically analysed using independent t‐tests. Results: Crown sites bonded using Clearfil SE Bond and Single Bond adhesives yielded bond strengths similar to that of root dentine sites (p > 0.05). Clearfil SE Bond was stronger in both the lased and non‐lased groups (p < 0.05). The lowest bond strength was obtained when Single Bond without acid etching was used on Er:YAG ablated dentine. When total‐etch adhesive was used, there were significant differences (p < 0.05) between the laser‐ablated and laser‐ablated/acid‐etched and bur‐cut/acid‐etched groups. Conclusions: Er:YAG laser irradiation of root and crown dentine conducted prior to the adhesive protocol adversely affected adhesion and decreased bond strength compared with traditional preparation.     

Micro-mechanical bond strength tests for the assessment of the adhesion of GIC to dentine

Abstract

Background. The aim of this study is to critically evaluate the bond strength (BS) of Glass-Ionomer Cements (GIC) to dentine with microtensile (μTBS) and microshear (μSBS) BS tests by assessing their rankings and failure patterns. Methods. Samples were made on flat dentine surfaces and submitted to μTBS and μSBS. The materials used were: high viscosity GIC (Ketac^? Molar Aplicap-KM), resin-modified GIC (Fuji II-FII), nano-filled resin-modified GIC (Ketac^? N100-N100) and an etch-and-rinse adhesive system with a composite resin (Adper^? Single Bond 2 and Z100^?-Z100). All tests were performed with a Universal Testing Machine (24 h water storage, crosshead speed of 1 mm/min). Debonded surfaces were examined with a stereomicroscope (×40) to identify the failure mode. The data was analyzed with two-way ANOVA (p < 0.05) and LSD test. Results. Means were statistically different regarding the tests and materials, indicating that values for BS obtained for each material depend on the test performed. Failure analysis revealed that failures produced by μTBS were mainly cohesive for KM and FII. μSBS failures were mainly adhesive or mixed for all materials. For the μTBS, the rank was Z100 > FII > KM = N100, whereas for the μSBS it was Z100 = FII = KM > N100. Conclusion: It may be concluded that distinct micro-mechanical tests present different failure patterns and rankings depending on the material to be considered.     

Effect of different root canal obturating materials on push-out bond strength of a fiber dowel

Purpose: During dowel space preparation, the instrumentation forms a thick smear layer along with sealer‐occluded dentinal tubules. The purpose of this study was to evaluate the effect of different obturating materials on push‐out bond strength of a fiber dowel. Materials and Methods: Fifty human uniradicular teeth were decoronated and prepared using the step‐back technique. The specimens were divided into five groups on the basis of obturating materials: group I received no obturation; group II (ZOE) gutta‐percha and zinc oxide eugenol sealer; group III (ZOAH) gutta‐percha and AH plus sealer; group IV (GF) GuttaFlow; and group V (RE) with Resilon Epiphany system. Dowel spaces were made with manufacturer's provided drills, and a fiber dowel was luted. Horizontal slices were obtained from the middle third, and push‐out bond strength (S) was evaluated. Statistical analysis was carried out using one‐way ANOVA and post hoc Tukey's test. Results: The push‐out bond strength values in the control group, ZOE, ZOAH, GF, and RE were 9.303 ± 0.565 MPa, 8.859 ± 0.539 MPa, 8.356 ± 0.618 MPa, 9.635 ± 0.435 MPa, and 8.572 ± 0.256 MPa, respectively. There was no statistically significant difference between the S values of all the groups (p > 0.05). Conclusion: There was no effect of different tested obturating materials on the push‐out bond strength of fiber dowels; however, further studies should be conducted.