Long-term evaluation of the stability of dentin matrix following treatments with aqueous solutions of titanium tetrafluoride at different concentrations

Enamel and Dentin Etching with Glycolic, Ferulic, and Phosphoric Acids: Demineralization Pattern, Surface Microhardness, and Bond Strength Stability

This study evaluated the etching pattern, surface microhardness, and bond strength for enamel and dentin submitted to treatment with phosphoric, glycolic, and ferulic acids. Enamel and dentin blocks were treated with phosphoric, glycolic, and ferulic acid to evaluate the surface and adhesive interface by scanning electron microscopy (2000×). Surface microhardness (Knoop) was evaluated before and after etching, and microtensile bond strength was evaluated after application of a two-step adhesive system (Adper Single Bond 2, 3M ESPE) at 24 hours and 12 months storage time points. Analysis of variance (ANOVA) and Tukey's test showed a decrease in the microhardness values for both substrates after application of each acid (p<0.0001). The reduction percentage was significantly higher for enamel treated with phosphoric acid (59.9%) and glycolic acid (65.1%) than for ferulic acid (16.5%) (p<0.0001), and higher for dentin that received phosphoric acid (38.3%) versus glycolic acid (27.8%) and ferulic acid (21.9%) (p<0.0001). Phosphoric and glycolic acids led to homogeneous enamel demineralization, and promoted the opening of dentinal tubules, whereas ferulic acid led to enamel surface demineralization and partially removed the smear layer. The adhesive-enamel interface showed micromechanical embedding of the adhesive in the interprismatic spaces when phosphoric and glycolic acids were applied. Ferulic acid showed no tag formation. Microtensile bond strength at both time points, and for both substrates, was lower with ferulic acid (p=0.0003/E; p=0.0011/D; Kruskal Wallis and Dunn). The bond strength for enamel and dentin decreased when using phosphoric and glycolic acids at the 12-month time evaluation (p<0.05). Glycolic acid showed an etching pattern and microhardness similar to that of phosphoric acid. Ferulic acid was not effective in etching the enamel or dentin, and it did not provide satisfactory bond strength to dental substrates.

Polyphenol-Enriched Extract of Lacquer Sap Used as a Dentine Primer with Benefits of Improving Collagen Cross-Linking and Antibacterial Functions

Commercial dentin adhesive systems are applied to restorations due to their resistant bonding properties, but they suffer from the lack of bioactivity and are prone to hydrolysis. Therefore, to overcome these limitations, an eco-friendly natural monomer, urushiol, was adopted to be a primer in dentin bonding due to its interaction with collagen and antibacterial activity, preventing further hydrolysis development. First, urushiol was determined to be capable of improving the biological stability of dentin collagen through cross-linking. Using high-fidelity analytical chemistry techniques, such as Fourier transform infrared spectroscopy, we quantified the effects of urushiol on collagen molecules. It could also effectively decrease weight loss after collagenase ingestion by improving the stability of dentin. Moreover, urushiol inhibited Streptococcus mutans growth as well as its biofilm formation. Finally, we demonstrated that the urushiol primer could improve the bonding strength, particularly after aging. The cross-linking and antibacterial functions of urushiol have provided promising developmental prospects for biomaterials in dentin adhesion.

Biomimetic Growth of Metal-Organic Frameworks for the Stabilization of the Dentin Matrix and Control of Collagenolysis

The dentin matrix is a collagenous scaffold structurally involved in anchoring resin-based materials to the tooth. Time-dependent degradation of this scaffold at the resin-dentin interface remains a core problem in adhesive dentistry, limiting the service life of dental fillings. This study explored the use of emergent materials termed metal-organic frameworks (MOFs)─formed by the self-assembly of metal ions and organic building blocks─to safeguard the collagen integrity in the functional dentin matrix. We demonstrate that collagen fibrils (from demineralized human dentin) can induce the biomimetic growth of MOF crystals as protective coatings to strengthen and stabilize the fibrils. Zeolitic imidazolate framework-8 (ZIF-8), a zinc-based microporous MOF, was used to fabricate the MOF composites via a "one-pot" reaction in water. The ZIF-modified dentin matrix presented superior mechanical strength and resistance to proteolysis, which can positively affect the longevity of collagen as an anchoring substrate. This work identifies a potential biomedical application of biomimetically synthesized MOFs in repairing dental tissues critical to restorative therapies.

Physicochemical characterization, water sorption and solubility of adhesive systems incorporated with titanium tetrafluoride, and its influence on dentin permeability

Titanium tetrafluoride (TiF₄) in an aqueous solution can decrease dentin permeability, but some effects of its incorporation into adhesive systems are not yet known. Therefore, the aim of this study was to characterize the physicochemical, water sorption (WS) and solubility (SL) properties of two adhesive systems (Clearfil SE Bond/C and Scotchbond Universal/S) incorporated with 0.0% (T0), 2.5% (T2) and 4.0% (T4) titanium tetrafluoride (TiF₄), and determine dentin permeability (L) after application of these adhesive systems both immediately afterwards (baseline) and after 6 months of storage. The physicochemical analyses of the incorporated solutions were performed based on evaluating particle size (PS), polydispersity index (PDI) by dynamic light scattering, and zeta potential (ZP) by electrophoresis. WS and SL tests followed ISO 4049 standards, and used a 7-day water storage period. The L test was performed by analyzing human dentin discs before and after adhesive system application, and after storage. PS and PDI were higher for CT0 and ST4 (p < 0.0001; ANOVA, Tukey). ZP was lower for CT4, ST2 and ST4 (p < 0.0001; ANOVA, Tukey). A 4.0% TiF₄ incorporation showed higher WS (p < 0.05; Mann Whitney, Kruskal Wallis, Dunn). Higher SL was observed for CT0 and ST4 (p < 0.05; Mann Whitney, Kruskal Wallis, Dunn). The L value at baseline was lower for ST4, but was not different from the CT4 groups after storage (p < 0.05; Mann Whitney, Kruskal Wallis, Dunn). It can be concluded that TiF₄ affected the colloidal stability of Scotchbond, but did not alter the other properties. The 2.5% TiF₄ did not affect the PDI, WS or L of the Clearfil, and can be considered an alternative for reducing hybrid layer degradation.