PubMed · 12666744
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Michel Degrange. 2002. Back to the future.. https://pubmed.ncbi.nlm.nih.gov/12666744/
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The interfacial microstructure and spatial distribution of the modulus of elasticity have a profound effect on load transfer at the dentin/adhesive (d/a) interface. The microstructure is influenced by the varying degree of demineralization of intertubular and peritubular dentin during etching as well as the depth of adhesive penetration into the hybrid layer. These factors lead not only to a unique microstructure in the vicinity of the dentinal tubules, but also to a mechanically graded hybrid layer. This article investigates the micromechanical stress distribution at a d/a interface with the use of finite element analysis (FEA). Such analysis is now feasible given the newly measured moduli of elasticity at micro- and nanoscales. The results indicate that the morphological and micromechanical properties of the d/a interface affects the stress field such that the fracture/failure is likely to initiate in the stress-concentration zone of peritubular dentin next to the hybrid/exposed-collagen layer. The results suggest that devising a full-depth high modulus hybrid layer may considerably reduce the stress concentration zone and the magnitude of stress concentration in the peritubular dentin next to the hybrid/exposed-collagen layer.
Bioadhesive buccal tablet formulations for delivery of nicotine into the oral cavity were developed. Carbomer (Carbopol)974P NF) (CP) and alginic acid sodium salt (NaAlg) were used as bioadhesive polymers in combination with hydroxypropyl methylcellulose (HPMC) at different ratios. Magnesium carbonate was incorporated into the formulations as a pH increasing agent. In vitro release and bioadhesion studies were performed on the developed tablets. In the formulations containing CP:HPMC, the NHT released increased with the increasing HPMC concentration whereas a decrease was observed with increasing HPMC concentration in formulations containing NaAlg:HPMC. The bioadhesive properties of the tablets containing NaAlg:HPMC was not affected by the concentration of the NaAlg (P>0.05) but increased significantly with the increasing CP concentration (P>0.05). A decrease in pH of the dissolution medium to acidic values was avoided by incorporation of magnesium hydroxide into the formulations. The developed formulations released NHT for 8h period, and remained intact except for the formulation containing CP:HPMC at 20:80 ratio.