Compomers (polyacid Modified composite resin) Compomers are class of dental materials that provide combined advantages of composites

(term Comp in their name) and glass ionomer (Omers in their name). These materials consist of 2 components viz; dimethcrylate monomers with two carboxylic acid groups present. They are available in single paste, light enable material in syringe or composites. History The first compomer was introduced in 1993 under the name Dyract. Initially the compomers were introduced as a type of glass-ionomers which offered fluoride release along with improved physical properties. But in terms of clinical use and performance, it considered as a type of composite resin. Composition Resin matrix: Dimethacrylate monomers with two carboxylic group present in their structure Filler: Reactive silicate glass containing filler Photoinitiators and stabilizers There is no water in the composition and ion leachable glass is partially silanized to ensure bonding to matrix.

Setting Reaction These materials set by free radical polymerization reaction. These are two stages in the polymerization reaction. 1. Stage 1: Typical light activated composite resin polymerization reaction occurs which helps in forming resin networks enclosing the filler particles. This reaction causes hardening of products. 2. Stage 2: It occurs after the initial setting of material. The restoration absorbs water and carboxyl groups present in the polyacid and metal ions in the glass ionomers show slow acid-base reaction. This results in formation of hydrogel. It is like glass ionomer cement within the set resin structure. There occurs slow release of fluoride also. Properties There characteristics are very similar to composite resins. Adhesion: Adhesion to tooth structure is by micromechanical means and requires acid etching and use primer/ adhesive.

 Physical properties: Physical properties such as strength, fracture toughness are very much similar to composite. Bond strength: It is similar to composite. Adaptation at cervical margin is similar to composite resins. Fluoride release: It is greater than composite resins but less than glass ionomer systems. They initially release high levels of fluorides but after some time the level falls rapidly to low level. Color matching and optical properties are superior to glass ionomer cements. Advantage Optimal aesthetics Easy to handle Easy to polishing Easy to place Require no mixing Bond strength is higher than glass ionomers. Disadvantage

 Requires use of bonding agent Technique sensitive Limited fluoride release Microleakage more than resin modified glass ionomers Expantion of matrix due to water absorption Physical properties decreases with time Clinical Usages They are preferred in anterior proximal and cervical restorations as an alternative to composite and glass ionomer cements. Ormocer (Organically Modified Ceramic) Ormocer is an organically modified non metallic inorganic composite material. It is three dimentionlly cross-linked copolymer. First time, it was introduced as dental restorative material in 1998. Compositon Ormocers have both organic as well as inorganic networks. They are characterized by presence of three main units:

 Organic molecules segment having methacrylate groups which form a highly cross-linked matrix. Inorganic condensing molecules to make three dimensional network which is formed by inorganic polycodensation. This forms the backbone of ORMOCER molecules. Properties 1. More biocompitable than conventional composites. 2. Higher bond strength. 3. Polymerization shrinkage is least among resin based filling material. 4. Highly aesthetic, comparable to natural tooth. 5. High compressive(410 MPa) and transverse strength(143 MPa) Indication 1. Restoration for all type of preparations 2. For aesthetic veneers 3. As orthodontic bonding adhesives. Antibacterial Composites / Ion Releasing Composites

Since composites show more tendency for plaque and bacteria accumulation in comparison to enamel, attempts have been made to develop caries resistant antibacterial composites. For this, following have been tried to incorporate in the composites. Chlorhexidine Though chlorhexidine has shown antibacterial properties but is addition to composites has been unsuccessful because of the following reasons: Weakening of the physical properties of composites. Release chemicals which show toxic affects. Temporary antibacterial activity. Shift in microorganisms and plaque to adjacent areas of the tooth. Methacryloxydecyl Pyridinium Bromide (MDPB) Use of MDPB was recommended by Imazato in 1994. It has following features: Its antibacterial property remains constant and permanent. It has shown to be effective against streptococci.

 It does not have adverse effect on the physical properties of BIS-GMA based composites. On polymerization, it forms chemical bond to the resin matrix, therefore no release of any antibacterial component takes place. Silver Addition of silver in the composites has also been suggested so as to make antibacterial composites. Silver ions cause structural damage to the bacteria. In these composites, the antibacterial property is due to direct contact with bacteria and not because of release of silver ions. Addition of silver into composite without silica gel does not affect its physical properties like depth of cure, compressive strength, tensile strength, color stability and polymerization. Silver ions can be added in any of the following method: a. Incorporated into inorganic oxide like silicone dioxides. b. Incorporated into silica gel and the thin films are coated over the surface of composites. c. Hydrothermally supported into the apace between the crystal lattice network of filler particles.

Smart Composites In smart composites the micron size sensor particles are embedded during manufacturing process into composite. These sensors interact with resin matrix and generate quantifiable anions. This type if composites was introduced in 1998 under the name Ariston pHc(Vivadent). It release fluoride, hydroxyl and calcium ions if the pH falls in the vicinity of restoration. The fall in pH value is attributed to the deposition of plaque in that area. Smart composites work based on the recently introduced alkaline glass fillers which inhibit the bacterial growth and thereby reduce formation of secondary caries. The paste of smart composites contain Barium, Aluminium, Fluoride and Silica glass fillers with Silicon dioxide, Ytterbium trifluoride and Calcium silicate glass in dimethacrylate monomers. Filler content in these composites is 80% by weight. The fluoride release from smart composites is higher than that of composites but less than conventional glass ionomers. Expanding Matrix Resins for Composites As we know, composites show polymerization shrinkage on curing which can result in material leakage, postoperative sensitivity and secondary caries. Therefore, slight expansion of the composite

during polymerization is desired to reduce these effects. It has been tried to add Spiro-orthocarbonates (SOCS) in composites as these show expansion on polymerization. PROPERTIES OF COMPOSITE RESTORATIVE MATETIAL Coefficient of thermal expansion of composites is approximately three times higher then normal tooth structure. This results in more contraction and expansion than enamel and dentin when there are temperature changes, it can result in loosening of the restoration. This can be reduced by adding more filler content. Microfill composites show more coefficient of thermal expansion because of presence of more polymer content. Water Absorption Composites have tendency to absorb water can lead to the swelling of resin matrix, filler debonding and thus restoration failure. Composites with higher filler content exhibit lower water absorption and therefore better properties, than composites with lower filler content. Factor Affecting Water Absorption of Composites More is the filler content less is the water sorption

 Lesser degree of polymerization causes more sorption Type and amount of monomer and dilutent also affect water sorption. For example, UDMA based composites show less sorption and solubility. Water Resistance Composites are prone to wear under masticatory forces or use of tooth brushing and abrasive food. Wear resistance is a property of filler particles depending on their size and quantity. The site of restorations in dental arch and occlusal contact relationship, size, shape and content of filler particles affect the wear resistance of the composites. Factors Affecting Degradation/ Wear of Composites Lesser is the polymerization, more is the degradation Microfilled composites show less of degradation Hydrolytic degradation of strontium or barium glass fillers can result in pressure built up at resin filler junction. This may cause cracks and fracture of composite restoration

 Sudden temperature changes can result in disruption is silane coating and thus bond failure between matrix and filler Surface Texture The size and composition of filler particles determine the smoothness of the surface of a restoration. Microfill composites offer the smoothest restorative surface. This property is more significant if the restoration is in close approximation to gingival tissues. Radiopacity Resin are inherently radiolucent. Presence of radiopaque fillers like barium glass, strontium and zirconium makes the composite restoration radiopaque. Modulus of Elasticity Modulus of elasticity of a material determines its rigidity or stiffness. Microfill composites have greater flexibility than hybrid composite since they have lower modulus of elasticity. Creep Creep is progressive permanent deformation of material under occlusal loading. More is the content of resin matrix, more is the creep. For example,

microfilled composites show more creep since they contain more of resin matrix. Polymerization Shrinkage Composite materials shrink while curing which can result in formation of a gap between resin based composite and the preparation wall. It accounts for 1.67-5.68 percent of the total volume. Polymerization shrinkage can result in: Postoperative sensitivity Recurrent caries Failure of interfacial bonding Fracture of restoration and tooth Polymerization shrinkage can be reduced by: Decreasing monomer level Increasing monomer molecular weight Improving composite placement technique: placing successive layers of wedge-shaped composite(1-1.5 mm) decreases polymerization shrinkage Polymerization rate: soft-start polymerization reduces polymerization shrinkage.