Bonding measurement -Strength and fracture mechanics approaches

Full mapping tensile bond strength of luting in search for differences due to centripetal curing shrinkage

OBJECTIVES

testing if hypothetical transverse centripetal strains due to polymerization contraction of luting materials produce differential alterations in its bonding to luted structures, depending on distances to the center of the luting mass, and if this effect is C-factor related. Two hypotheses were tested: (1) there is a statistically significant decreasing relationship between the bonding strength and the transverse distances to the center of the luting material, and (2) there is a statistically significant difference between bonding strengths among luting spaces with different configuration factors.

METHODS

10 PMMA (15 mm Ø) pairs of cylinders were cemented (Scotchbond Universal adhesive & Relyx Universal, both chemically cured) in a compliant setup under two (20 and 70 N) luting forces forming 2 groups (5 samples each), resulting in different C-factors. Whole samples were sectioned in x and y directions obtaining non-trimmed beams from all along the luting surfaces. Their relative positions in each sample were assessed before separating and categorized (10 categories) according to their distances to the center of the sample. All beams were tested in tension and, because of their uneven bonding areas and to balance its influence, UTS results were transformed into UTS_res. First hypothesis was tested trough a linear relationship between UTS_res and distances to vertical centers per samples. Second hypothesis was tested using Mann-Whitney U tests to compare UTS_res between groups, along all categories. Further Weibull analysis was applied.

RESULTS

ANOVA's p of the regression UTS_res - categories were statistically significant for all samples in group 70 N and for all except one in group 20 N: first hypothesis is partially maintained. Although Mann-Whitney tests p comparing UTS_res of both groups for all categories but the first were statistically significant this hypothesis was maintained relying in Weibull analysis.

SIGNIFICANCE

bonded attachment of cemented materials decreases from centers to outbounds in plane, extensive surfaces, and this decrease is C-factor related.

On the behaviour of zirconia-based dental materials: A review

Zirconia-based dental materials are extensively used in clinical practice due to their tooth-like appearance, biofunctionality, biocompatibility, and affordability. However, premature clinical failures of veneering porcelains raise a concern about their integrity. Extensive studies have been performed over a decade to resolve this issue, but it is challenging to reference all information effectively. A single source identifying the significance of potential parameters on material performance has not previously been available. An evidence-based meta-narrative review technique was used to review the characteristic parameters that can affect the overall behaviour of zirconia-based materials. Keywords were chosen to assess manuscripts based on scientific coherence with this paper's research objective. Online keyword searches were carried out on ScienceDirect, PubMed, and SAGE databases for relevant published manuscripts from year 1985-2020.261 out of 3170 identified manuscripts were included. A total of 10 parameters were identified and classified into the material, manufacturing, and geometric aspects. The effect of every parameter was reviewed on the performance of the material. A discrepancy in findings was observed and is attributed to the fact that there is no standard methodology. This review acts as a single source that summarizes various parameters' contribution to zirconia-based dental materials' performance. This review facilitates manufacturing improvements by accounting for every parameter's effect on overall performance.

The Effect of Biodentine Maturation Time on Resin Bond Strength When Aged in Artificial Saliva

Biodentine is a calcium silicate cement (CSC) that has been broadly applied in vital pulp therapy. The quality of the Biodentine-composite bond has a significant effect on the longevity of the definitive restoration. The aim of this study is to investigate the shear bond strength (SBS) between Biodentine and composite restoration at different maturation times of Biodentine aged in artificial saliva. Fifteen Biodentine discs were allocated into three groups (n = 5) based on the timeframe of performance of composite restoration: immediate (after 12  min), after 14 days, and after 28 days of Biodentine maturation. Total etch and rinse adhesive system and bulk-fill regular resin composite were used. The shear bond strength and the failure pattern were assessed. One-way ANOVA with the Bonferroni post hoc test was applied for statistical analysis at p < 0.05. The highest (32.47 ± 8.18 MPa) and the lowest (4.08 ± 0.81 MPa) SBS values were recorded for 14 days and 12 min groups, respectively. Significant statistical differences were reported among the groups, and a high statistically significant difference was found between the immediate group and the other groups. Adhesive failure patterns were evident in all groups. More clinically acceptable bond strength between the Biodentine and overlaid composite restoration is at 14 days after Biodentine maturation. Delaying the coverage of Biodentine later than 14 days may significantly reduce the SBS. Using the artificial saliva as an aging medium may affect the SBS between Biodentine and composite material.

Glass coatings to enhance the interfacial bond strength between veneering ceramic and zirconia

The purpose of this study was to investigate the tensile bond strength (TBS) and shear bond strength (SBS) between a zirconia core and fluoroapatite-pressed ceramic after the application of glass 46SP6 and AP40 via the ISO-17095:2013 methodology. Sintered zirconia beams (n = 120) were divided into four groups: (a) control: no treatment; (b) ZirL: IPS-E max ceram ZirLiner coating; (c) glass AP40 coating; and (d) glass 46SP6 coating. A fluoroapatite ceramic (IPS e.max Zir Press, Ivoclar Vivadent) beam was injected perpendicularly on top of each zirconia (Zenostar, Wieland Dental) beam forming a cross-bonded specimen. All groups were sub-divided into two for tensile and shear bond strength tests using a universal testing machine. Data were analyzed using the Kruskal-Wallis, Pearson Chi²_, and Mann-Whitney U test (α = 0.05). The failure modes were measured using a stereomicroscope for each group. Scanning electron and atomic force microscopy were also employed. Zirconia surface modification with glass AP40 showed higher TBS values followed by the ZirL group with statistical differences (p < 0.05). SBS values showed no statistical differences between the groups. AFM analysis showed higher roughness values (Ra) in the 46SP6 and AP40 groups (p < 0.05). Glass coating AP40 exhibited promising bond strength results between zirconia and fluorapatite veneering ceramic, making it better for chemical and mechanical interlocking which may improve bilayered restorations longevity.