Репозиторий Университета

© 2018 by the authors. Objectives: Resin-modified glass ionomer cements (RMGIC) are considered excellent restorative materials with unique therapeutic and anti-cariogenic activity. However, concerns exist regarding the use of polyacrylic acid as a dentine conditioner as it may influence the bonding performance of RMGIC. The aim of this study was to evaluate the effect of different protocols for cycling mechanical stress on the bond durability and interfacial ultramorphology of a modern RMGIC applied to dentine pre-treated with/without polyacrylic acid conditioner (PAA). Methods: The RMGIC was applied onto human dentine specimens prepared with silicon-carbide (SiC) abrasive paper with or without the use of a PAA conditioner. The specimens were immersed in deionised water for 24 h then divided in 3 groups. The first group was cut into matchsticks (crosssectional area of 0.9 mm2) and tested immediately for microtensile bond strength (MTBS). The second was first subjected to load cycling (250,000 cycles; 3 Hz; 70 N) and then cut into matchsticks and tested for MTBS. The third group was subjected to load cycling (250,000 cycles; 3 Hz; 70 N), cut into matchsticks, and then immersed for 8 months storage in artificial saliva (AS); these were finally tested for MTBS. The results were analysed statistically using two-way ANOVA and the Student- Newman-Keuls test (α = 0.05). Fractographic analysis was performed using FE-SEM, while further RMCGIC-bonded dentine specimens were aged as previously described and used for interfacial ultramorphology characterisation (dye nanoleakage) using confocal microscopy. Results: The RMGIC applied onto dentine that received no pre-treatment (10% PAA gel) showed no significant reduction in MTBS after load cycling followed by 8 months of storage in AS (p > 0.05). The RMGIC- dentine interface created in PAA-conditioned SiC-abraded dentine specimens showed no sign of degradation, but with porosities within the bonding interface both after load cycling and after 8 months of storage in AS. Conversely, the RMGIC-dentine interface of the specimens with no PAA pre-treatment showed no sign of porosity within the interface after any of the aging protocols, although some bonded-dentine interfaces presented cohesive cracks within the cement after prolonged AS storage. However, the specimens of this group showed no significant reduction in bond strength (p < 0.05) after 8 months of storage in AS or load cycling (p > 0.05). After prolonged AS storage, the bond strength value attained in RMGIC-dentine specimens created in PAA pretreated dentine were significantly higher than those observed in the specimens created with no PAA pre-treatment in dentine. Conclusions: PAA conditioning of dentine prior to application of RMGIC induces no substantial effect on the bond strength after short-term storage, but its use may increase the risk of collagen degradation at the bonding interface after prolonged aging. Modern RMGIC applied without PAA dentine pre-treatment may have greater therapeutic synergy with saliva during cycle occlusal load, thereby enhancing the remineralisation and protection of the bonding interface.

© 2017 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM) The Nicotiana tabacum 4/1 protein (Nt-4/1) of unknown function expressed in plant vasculature has been shown to localize to cytoplasmic bodies associated with endoplasmic reticulum. Here, we analyzed molecular interactions of an Nt-4/1 mutant with a deletion of 90 N-terminal amino acid residues (Nt-4/1d90) having a diffuse GFP-like localization. Upon transient co-expression with VAP27, a membrane protein known to localize to the ER, ER-plasma membrane contact sites and plasmodesmata, Nt-4/1d90 was concentrated around the cortical ER tubules, forming a network matching the shape of the cortical ER. Additionally, in response to mechanical stress, Nt-4/1d90 was re-localized to small spherical bodies, whereas the subcellular localization of VAP27 remained essentially unaffected. The Nt-4/1d90-containing bodies associated with microtubules, which underwent noticeable bundling under the conditions of mechanical stress. The Nt-4/1d90 re-localization to spherical bodies could also be induced by incubation at an elevated temperature, although under heat shock conditions the re-localization was less efficient and incomplete. An Nt-4/1d90 mutant, which had phosphorylation-mimicking mutations in a predicted cluster of four potentially phosphorylated residues, was found to both inefficiently re-localize to spherical bodies and tend to revert back to the initial diffuse localization. The presented data show that Nt-4/1 has a potential for response to stresses that is manifested by its deletion mutant Nt-4/1d90, and this response can be mediated by protein dephosphorylation.