Fissure Sealants In Modern Dentistry

CHAPTER 2: FISSURE SEALANTS AND THEIR PROPERTIES

2.1 RESIN-BASED FISSURE SEALANTS

In modern dentistry the first one and most commonly used fissure sealants are the materials on the basis of BIS-GMA (Bisphenol A glycidyl methacrylate) [6, 28]. These have been used since the 1970s [4]. They have the same structure as composite materials which are used for restorations but contain less filler, in order to reduce their viscosity and at the same time to allow a better penetration into pits and fissures [28].

The chemical’s nature of resin sealants is a radical polymerizable monomer mixture. BIS-GMA and urethane dimethacrylate are very popular as they are the main monomers for resin sealants. Other monomers that are less viscous are added

4. Dimensional stability

- Volatility, polymerization shrinkage and thermal contraction affect the placement and stress developed which in turn influences the mechanical properties and the durability of the bonding.

- The extent of curing shrinkage is affected by the degree of conversion of monomer to polymer.

- The combination of thermal and polymerization shrinkage may produce high internal stresses. Cracks may develop in thin marginal layers of this kind of sealants on hardening.

- Inhibition of polymerization by atmospheric oxygen producing a non polymerized layer of monomer on the surface of a resin material and around the interior surface of air bubbles within the body of the material.

5. Physical and mechanical properties

- Thermal expansion and contraction as a result of hot and cold foods affect stresses generated at the interface with enamel.

- It is also affected by water absorption

- Coefficient of thermal expansion of sealants is 7-10 times more than tooth.

6. Micro-leakage and Bacterial

This treatment changes the enamel surface to a microrugged structure, which aids in penetration of the sealants into the fissures and results in strong micromechanical adhesion between the sealants and the tooth substance. (Figure 11) Pits and fissures are treated with phosphoric acid, citric acid or any other acidic agents [6]. The most commonly used acid is phosphoric acid in concentration usually between 35-50%. The time of acid application depends on manufacturers instructions. When the time is complete the tooth is thoroughly rinsed and completely dried. The tooth surface will have a frosted or chalky appearance [41]. If not, the procedure must be repeated. Moisture control is essential for the bonding of resin sealants. Salivary contamination of the tooth surface before the application of the sealant can result in failure of the resin sealant and procedure must be redone [10,