large molecule with high viscosity, for easier clinical handling. Inorganic filler such as silica, quartz or various glasses, are added to reduce polymerization shrinkage by occupying volume and to confirm radio-opacity of products due to translucency in property, which can be helpful in diagnosis of dental caries around dental restorations. The filler particles give the composites wear resistance as well. Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics. A coupling agent such as silane is used to enhance the bond between resin matrix and filler particles. An initiator package begins the polymerization reaction of the resins when external energy (light/heat, etc.) is applied. For example, camphorquinone can be excited by visible blue light with critical wavelength of 460-480 nm to yield necessary free radicals to start the process. After tooth preparation, a thin primer or bonding agent is used. Modern photo-polymerised composites are applied and cured in relatively thin layers as determined by their opacity. After some curing, the final surface will be shaped and polished. Glass ionomer cement A glass ionomer cement (GIC) is a class of materials commonly used in dentistry as direct filling materials and/or for luting indirect restorations. GIC can also be placed as a lining material in some restorations for extra protection. These tooth-coloured materials were introduced in 1972 for use as restorative materials for anterior teeth (particularly for eroded areas). The material consists of two main components: Liquid and powder. The liquid is the acidic component containing of polyacrylic acid and tartaric acid (added to control the setting characteristics). The powder is the basic component consisting of sodium alumino-silicate glass. The desirable properties of glass ionomer cements make them useful materials in the restoration of carious lesions in low-stress areas such as smooth-surface and small anterior proximal cavities in primary teeth. Advantages of using glass ionomer cement: The addition of tartaric acid to GIC leads to a shortened setting time, hence providing better handling properties. This makes it easier for the operator to use the material in clinic. GIC does not require bond, it can bond to enamel and dentine without the need for use of an intermediate material. Conventional GIC also has a good sealing ability providing little leakage around restoration margins and reducing the risk of secondary caries. GIC contains and releases fluoride after being placed therefore it helps in