Tiêu đề chapter 3 - glass ionomer P1.pdf ✅

G.I pre-clinic op 2 2025 Kasr Dr_M.Bedawi - this results in increased wear as the poorly attached metal particles are plucked from the surface. 3- ceramic-metal G.I Or cermet - the silver metal can be sintered to the glass fillers. - a commercial example is Ketac-Silver (3M ESPE). - the resulting metal-fused-to-glass filler particles can react with polyacid copolymers to form a GIC with improved abrasion resistance. - however, silver discolors the surrounding tooth structure.  both metal-reinforced GICs are not used as esthetic restorations, but rather used as core buildup, base & for repair of crowns and amalgam restorations. 4- highly-filled, high-viscosity G.I - modifications in filler size & loading were also made to improve physical & mechanical prop. of G.I. - a commercial example is Fuji IX & Ketac-Molar. 5- resin-modified glass ionomer RMGI - incorporation of resin into the G.I. 6- nano-ionomer - type of resin-modified glass ionomer that have nano-sized fillers to improve the strength, optical properties. - a commercial example is Ketac-Nano. adv. of G.I 1- adhesion to tooth structure - GIC undergoes chemical adhesion to tooth structure. - adhesion is initiated by polyalkenoic acid when freshly mixed material contacts the tooth surface. - phosphate ions are displaced from apatite by carboxyl groups (COO-), each phosphate ion taking a calcium ion with it to maintain electrical neutrality. - these ions will combine with the surface layer of cement & develop an ion-enriched layer Or inter- diffusion zone adhered to tooth structure. - this ion-enriched layer is firmly attached to tooth structure, even if G.I is de-bonded, it remains sealing the dentinal tubules. 2- sealing potential - the proper sealing potential of GIC, owing to ion-exchange chemical adhesion, desensitizes dentin, sedates the pulp & eliminates microleakage at tooth/restoration interface.  combined with its fluoride release, this property aids in prevention of recurrent decay & allows for remineralization of any demineralized tooth tissues.
G.I pre-clinic op 3 2025 Kasr Dr_M.Bedawi 3- fluoride release & recharge - prolonged & substantial release of fluoride ion from all G.I materials is of major clinical significance. - the large release of fluoride ions (fluoride burst) during the first few days after placement, declines rapidly during the first week but stabilizes after 2-3 months. - fluoride release appears to be sufficient to ensure protection from caries for the surrounding tooth structure as well as adjacent teeth. - it is also of clinical significance in remineralization of affected demineralized tooth structure. - it has been shown that, a subsequent professional application of a topical fluoride will result in a further uptake of fluoride ions by restoration (recharging). - thus, a GIC can be regarded as a fluoride reservoir. ➢ the fluoride cycle : a) leaching phase → immediately following placement, the fluoride content in G.I is much higher than that of the tooth. - thus, fluoride ions diffuse from area of high concentration (G.I) to area of lower concentration (tooth), causing hydroxyapatite of the tooth to transform into fluoro-apatite ẁ is resistant to caries. b) equilibrium phase → by time, the fluoride content of tooth & GI reaches equilibrium. c) depleting → at the surface, G.I begins to release fluoride into the saliva. d) depleted → most of the fluoride from the G.I surface is lost to the oral fluids. e) recharging → topical application of fluorides through fluoride gel, rinse or toothpaste can recharge the GIC & the fluoride cycle is thus continued. 4- biocompatibility & soft tissue response - anti-cariogenic potential due to fluoride release. - fluoride decreases the surface energy of the tooth, thus decreasing plaque retention. - fluoride also has a bacteriostatic effect on Streptococcus mutans (major pathogen in dental plaque).  it has been shown that, bacterial plaque fails to survive on the surface of glass-ionomer. - it is biologically compatible to tooth & soft tissues because compositional polyacrylic acid is weak & has high molecular weight ẁ limits its diffusion through dentinal tubules to the pulp. - it also rapidly neutralizes under the buffering action of dentinal fluid. 5- dimensional stability - G.I has a low setting contraction of 3% by volume. - also, the coefficient of thermal expansion and contraction of GIC is close to that of tooth structure. 6- good thermal insulating capacity - its thermal insulating capacity is an important characteristic that allows its use as a liner & base.  this property increases with increase in powder/liquid ratio.