1. Why is a silane coupling agent used in composite resin?
The organic resin matrix is bonded to inorganic filler by means of a silane coupling agent. It increases the strength of the composite and reduces the solubility and water absorption.
2. Why resin-modified glass ionomer and polyacid-modified composites are not the same?
The primary intention of both these materials is to preserve and utilize the favourable properties of glass ionomer. Resin modified glass ionomer is primarly glass ionomer, which sets chemically by acid-base reaction. Resins are added to this for improving the physical and esthetic properties. Incorporation of resin component makes this cement to set fast by light curing. Polyacid-modified composites are primarly resin composites which sets only by light cure. Some of the glassionomer components are added to this cement to incorporate the favourable properties of glass ionomer. They are also termed as compomers.
3. How do chemically activated resins polymerize?
The chemically activated resins have a benzoyl peroxide initiator and a tertiary amine activator. When the two pastes are mixed, the amine reacts with the benzoyl peroxide and free radicals are formed to start the polymerization.
4. Why were Visible light activated systems developed?
Initially, ultra violet light was used to initiate free radicals. But the depth of penetration of UV light into the resin was limited and there was no penetration through the tooth structure. So visible light activated systems were developed which can polymerise thicker increments.
5. How does polymerization of light activated systems occur?
The amine activator and the photoinitiator are present in the same paste of the light cure system. When it is not exposed to light, no reaction takes place. When light of the correct wavelength is exposed on this material, the photo initiator gets excited and free radicals are produced by reacting with the amine.
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