Isolation and characterization of cellulose nanofibrils from Colombian Fique decortication by-products.

Fique fibers are extracted from Furcraea spp. leaves, with 5% average mass yield, using mechanical decortication. Juice, pulp and tow, the by-products of this process, amount 95% of the leaf weight and are considered waste. We extracted cellulose nanofibrils (CNF) from Fique tow, via ultrasound-assisted TEMPO followed by mechanical disintegration with sonication. Fique CNF exhibit diameters around 100 nm, degree of oxidation (DO) of 0.27 and surface charge density (σ) of 1.6 mmol/g. Fique CNF aqueous suspensions show optical birefringence and high colloidal stability due to a high ζ potential (-53 mV). The morphology, chemical structure, crystallinity and phase transitions of Fique CNF were studied using FESEM, IR-ATR, XRD and TGA. We observed that the delignification pretreatment and the TEMPO reaction assisted by ultrasound significantly increase Fique CNF σ and ζ potential, in contrast with the oxidation carried out without ultrasound or with raw (lignified) tow.

Sealing properties of three luting agents used for complete cast crowns: a bacterial leakage study.

OBJECTIVE: To assess the sealing properties of three different luting materials used for cementation of full cast crowns on extracted human premolars. METHODS: Thirty noncarious human premolars were prepared in a standardized fashion for full cast crown restorations. All margins were placed in dentin. After impressions of the preparations, stone dies were fabricated on which copings were waxed, which were cast in type III alloy using standardized laboratory methods. Teeth were randomly assigned to three groups of 10 samples each (n=10), for which the following cements were used: 1) a resin-modified glass ionomer cement, Rely X Luting Plus (3M ESPE, St Paul, MN, USA); 2) a self-adhesive resin cement, Maxcem Elite (Kerr Corporation, Orange, CA, USA); and 3) a glass ionomer cement, Ketac Cem (3M ESPE), the latter used as control. After cementation the samples were allowed to bench-set for 10 minutes, stored in water at 37°C, subjected to thermal cycling (2000×, between 5°C and 55°C, dwell time 35 seconds), and then stored in sterile phosphate buffer for seven days at 37°C. Subsequently, the occlusal surface was carefully reduced until the dentin was exposed. Finishing on wet sand paper removed the gold flash caused by grinding. After sterilization, the specimens were subjected to bacterial microleakage in a dual chamber apparatus for 60 days. Bacterial leakage was checked daily. Data were analyzed using the Kaplan-Meier survival test. Significant pairwise differences were analyzed using the log-rank test followed by Fisher exact test at a p<0.05 level of significance. RESULTS: Rely X Luting Plus showed the lowest microleakage scores, which statistically differed significantly from Maxcem Elite and Ketac Cem (p<0.05). CONCLUSIONS: Rely X Luting Plus cement displayed significantly lower microleakage scores than a self-adhesive resin-based and conventional glass ionomer cement.