6.Dental composites.pdf

Composite Resins Salma Abuelgasim Mohamed 2022 Contents Definition. Introduction Compounds Classification of Composites Properties Setting reaction. Advantage & Disadvantage Uses Manipulation Failure Definition A composite is a physical m...

Composite Resins Salma Abuelgasim Mohamed 2022 Contents Definition. Introduction Compounds Classification of Composites Properties Setting reaction. Advantage & Disadvantage Uses Manipulation Failure Definition A composite is a physical mixture of materials. A compound of two or more distinctly different materials with properties that are superior or intermediate to those of the individual constituents.  Composite is polymeric filling material reinforced with filler particles. It was developed in 1962s to overcome the disadvantages in physical and mechanical properties of acrylic filling and of silicate cement. It is most popular anterior filling material.  1962, Bowen synthesized an acrylate epoxy using glycidyl methacrylate and bisphenol A epoxy for use as a matrix for dental composites. 1950 composites had improved mechanical properties and good esthetics poor bond to the tooth structure and still exhibited significant polymerization shrinkage. 1930 polymethyl methacrylate: first polymeric tooth- colored restorative material initially esthetic with variety of problems poor color stability, high polymerization shrinkage, a 1870 lack of adhesion Silicate Cement: first tooth colored alumino-fluoro-silicate glasses and phosphoric acid brittle, soluble, required mechanical retention and had an average longevity Evolution of composite resins  Due to solubility problems the silicate cements were replaced by unfilled acrylic resins based on polymethylmethacrylate (PMMA). Components 1. Organic resin (matrix) 2. Inorganic filler particle 3. Coupling agent to unit the resin with the filler 4. Initiator system, to activate the setting mechanism. 5. Stabilizers (inhibitors) 6. Pigments Components 1. Organic resin Bis-GMA monomer is most commonly used. MMA-based matrices were replaced by BIS-GMA (alternatively Bis-GMA). Why? BIS-GMA is a difunctional monomer originally produced as the reaction product of bisphenol-A and glycidyl methacrylate so difunctional monomers either BIS-GMA or urethane dimethacrylate (UEDMA) can be used in composite. Components 2. Filler particle The filler particles used are either barium silicate glass, quartz or zirconium silicate. usually combined with 5-10% weight of very small-sized (0.04µm) particles of colloidal silica. Most composites are now produced using silicate glass. Barium, zinc, and yttrium- modified silicate glasses are currently the most popular fillers. These ions(Ba,Zn,Y)have been used to produce radiopacity in the filler particles. 2. Filler particle As the overall filler content increases, the physical, chemical, and mechanical properties improve. However there is a limit to the amount of filler that can be added to a resin because as the filler level is increased, the fluidity decreases. Which affect surface roughness finishing and polishing. 3. Coupling agent These molecules are difunctional. Coupling agents bond the filler particles to the resin matrix. This allows the more plastic resin matrix to transfer stress to stiffer filler particles. The most commonly used coupling agent is organosilane. Sialine Function of Coupling agent They improve the physical and mechanical properties of resin. Prevent the filler from being dislodged from the resin matrix. They prevent water from penetrating the filler- resin interface, microleakage of fluids into filler- resin interface led to surface staining. Filler Matrix Coupling agent  Classification of Composites Classifications according to: 1. Filler particle size. 2. Based on specific handling characteristics. 3. Based on polymerization reaction.  Classification of Composites Classifications according to: 1. Filler particle size Macrofill (traditional composites) ~ 10-100 µm Midifill (small particle composites) ~ 1-10 µm Minifill ~ 0.1-1 µm Microfill (fine particle composites) ~ 0.01-0.1 µm develop smoothest finish. Microfilled composites are recommended for low stress bearing class 3 and class 5 restorations. Hybrid ~ mixture of particles usually midifill or minifill with microfill Classification of composite resins based on filler particles size.  Nanofillers (new fillers) - Range in size from.005 to 0.01 micron have recently been developed. - These particles are so small that very high filler levels can be achieved while still maintaining workable consistencies  Hybrid and microfill resins utilize colloidal silica fillers which are useful for increasing the hardness and wear resistance of the base resin material while maintaining high polish ability and overall aesthetics qualities. 2. Handling characteristics Flowable composites Are low viscosity materials that have particle sizes and distributions similar to those of hybrid composites, but with reduced filler content, which allows the increased amount of resin to decrease the viscosity of the mixture. Are recommended for cervical lesions, restorations in deciduous teeth, and other small, low or non-stress-bearing restorations. Packable composites (condensable composites) Were developed to produce a composite with handling characteristics similar to amalgam. Packable composites are less sticky and higher in viscosity (stiffness) than traditional hybrid composites, which allows them to be placed in a manner that resembles amalgam placement. Recommended for use in classes 1 and 2 cavity preparations. 3.Polymerization reaction Composite resins are dimethacrylate monomers and polymerize by the addition mechanism that is initiated by free radicals. These free radicals can be generated by chemical activation or external energy (heat, light).  Polymerization reaction Chemically activated (self-cured) Two paste system, one contains the benzoyl peroxide initiator, the other a tertiary amine activator. Light-activated Visible light has replaced UV light. One paste system which contains a diketone photo initiator molecule (generally camphoroquinone) and an a mine activator. Dual-cure Curing is initiated by a conventional light source, but continues chemically to help ensure polymerization throughout the restoration. Polymerization Reaction Polymerization reaction The conversion of monomer molecules into polymers. Addition polymerizations involve the addition of a reactive species with a monomer to form a larger reactive species which is capable of further addition with monomer. Chemically cured composite Polymerization reaction R* + M → R − M* R − M* + M → R − M − M* R − M − M* + M → R − M − M − M* etc. The initial reactive species is represented by R* and the monomer molecules by M. It can be seen how monomer molecules are added during each stage of the polymerization reaction and eventually a long-chain molecule is produced. Formation of free radicals The reactive species which is involved in the addition reaction may be ionic in nature or it may be a free radical. The free radicals are produced by reactive agents called initiators. These are, generally, molecules which contain one relatively weak bond which is able to undergo decomposition to form two reactive species each carrying an unpaired electron Polymerization reaction One very popular initiator, which is used extensively in dental polymers, is benzoylperoxide. Under certain conditions the peroxide linkage is able to split to form two identical radicals as shown Polymerization reaction The decomposition of benzoyl peroxide may be accomplished either by heating or by reaction with a chemical activator. The use of a chemical activator allows polymerization to occur at low temperatures. Polymerization reaction Activators commonly used with peroxide initiators are aromatic tertiary amines such as N, N′ dimethyl-p-toluidine. Polymerization reaction The reaction of a benzoyl peroxide radical with methylmethacrylate to form a new radical species. This is the initiation reaction in free radical polymerisation of methyl methacrylate.  Polymerization reaction The polymerization processes follow a well documented pattern which consists of four main stages:- Activation Initiation Propagation and Termination Polymerization reaction Formation of free radical Activation This involves decomposition of the peroxide initiator using either thermal activation (heat), chemical activators or radiation of a suitable wavelength if a radiation-activated initiator is present. For benzoyl peroxide the activation reaction is represented by its decomposition to form the free radicals. Polymerization reaction initiation Radicals ,reacts The polymerisation reaction with monomer molecule is initiated when the radical, formed on activation, reacts with a monomer molecule. Propagation Following initiation, New free radicals , reacts with further the new free monomer molecule radical is capable of reacting with further monomer molecules Polymerization reaction Termination: It is possible for the propagation reaction to continue until the supply of monomer molecules is exhausted.  Forms of chemically cured composite 1) Powder/liquid systems, in which the powder contains filler particles and peroxide initiator whilst the liquid contains monomer, comonomer and chemical activator. 2) Paste/liquid materials in which the paste contains monomers, comonomers, filler and peroxide whilst the liquid contains monomers and chemical activator. 3) Encapsulated materials in which the filler, mixed with peroxide, is initially separated within a capsule from the monomers and comonomers containing the chemical activator.  Light-activated materials are generally supplied as a single paste which contains monomers, comonomers, filler and an initiator which is unstable in the presence of either ultraviolet (uv) or high intensity visible light. For uv activated materials, the most commonly used initiator is benzoinmethyl ether.  At certain selected wavelengths within the uv range, this molecule is able to absorb radiation and undergo heterolytic decomposition to form free radicals. The radicals initiate polymerisation. The use of uv-activated materials has diminished greatly since the possible dangers of longterm exposure to ultraviolet radiation were highlighted.  For visible light activated materials the initiator system comprises a mixture of a diketone and an amine. Camphorquinone is a commonly used diketone which rapidly forms free radicals in the presence of an amine and radiation of the correct wavelength and intensity. Light-activated materials require the use of a specialist light source, capable of delivering radiation with the appropriate characteristics to the surface of the freshly placed material in situ. Light units Light-curing can be accomplished I. with quartz-tungsten-halogen (QTH)curing units. II. plasma arc curing (PAC) units. III. laser curing units. IV. light-emitting diode (LED) curing units. Light units The curing units shown here are a QTH unit (on the right) and an LED unit (on the left).  LED units do not require a filter, have a long life span, and do not produce as much heat as QTH devices. Composites cured with LED units have flexural properties similar to those cured with QTH units. Depth of cure with LED units appears to be higher. Indications 1.Classes 1, 11, III, IV, V and VI restorations 2. Foundations or core build ups. 3. Sealants and conservative composite restorations (preventive resin restorations). Dual-curing composite for core build-ups.. 4. Esthetic enhancement procedures Partial veneers Full veneers Tooth contour modifications Diastema closures 5. Cements (for indirect restorations). 6. Periodontal splinting. Contraindications 1. When the operating site cannot be appropriately isolated 2. With heavy occlusal stresses 3. With all the occlusal contacts only on composite Advantages 1. Esthetic. 2. Conservative of tooth structure removal (less extension; uniform depth not necessary; mechanical retention usually not necessary). 3. Less complex when preparing the tooth. Advantages 4.Used almost universally. 5. Bonded to tooth structure, resulting in good retention, low micro leakage, minimal interfacial staining, and increased strength of remaining tooth structure. 6.Repairable Disadvantages 1. May have a gap formation, usually occurring on root surfaces as a result of the forces of polymerization shrinkage of the composite material being greater than the initial early bond strength of the material to dentin. 2. Are more difficult, time-consuming, and costly (com- pared to amalgam restorations) because: Tooth treatment usually requires multiple steps. Insertion is more difficult. Establishing proximal contacts, axial contours , embrasures, and occlusal contacts may be more difficult. Finishing and polishing procedures are more difficult. 3. Are more technique sensitive because the operating site must be appropriately isolated and the placement of etchant, primer, and adhesive on the tooth structure (enamel and dentin) is very demanding of proper technique. 4. May exhibit greater occlusal wear in areas of high occlusal_ stress or when all of the tooth's occlusal contacts are on the composite material. 5. Have a higher linear coefficient of thermal expan- sion, resulting in potential marginal percolation if an inadequate bonding technique is utilized.  Properties 1. Biocompatibility Fully polymerized polymers cause no pulpal response. Unpolymerized polymers are a potential hazard. This is evident if: 1. Composite is placed in large increments 2. Polymerization has been inhibited by air or moisture. HEMA is a recognized allergen  Prolonged exposure of the 470 nm wave length visible light can cause: 1. Damage to the retina. A process shield should be used at all times 2. Pulpal injury 1. Biocompatibility Gingival irritation may result from:- 1. Incomplete cured resin 2. Any surface roughness will tend to accumulate plaque. 2. Water sorption & solubility Water sorption & solubility of different composite resins depend on: 1. The type & amount of monomer i.e UDEMA composites show less sorption & solubility. eg:water sorption for microfilled resin is greater than for hybrid or macrofilled resins. 2. Water sorption & solubility 3. The degree of polymerization. Polymerization time Solubility NB! Both long term durability of the composite & color stability will be affected by inadequate polymerization 3. Degradation in the oral invoronment Can be caused by: 1. Rapid thermal changes 2. Water or chemical attack causes breakdown the saline coupling agent which leads to failure between the filler & matrix. 3. Un reacted methacrylate groups degrade rapidly 4. Color stability Composite may udergo extensive surface staining, intrinsic color change or both. Surface staining maybe caused due to: 1. Incorporation of staining beverages (i.e. tea, coffee & cola drinks) during the first 7- 10 days after placement when water sorption by composite is the highest. 3. Color stability Intrinsic color change maybe caused due to: 1. In chemical activated composite: Yellowish discoloration within 1-3 yrs Due to oxidation of excess amine from the initiator system. 4. Polymerization Contraction Composite undergoes substantial polymerization contraction during setting. In light activated composites: 60% of the contraction occurs in the first minute after photo-initiation. The contraction occurs towards the light placing stress on the weaker bond on the pulpal & axial walls.  Composite undergoes substantial polymerization contraction during setting. In chemically activated composites: The contraction develops more slowly & evenly & is directed towards the centre. This results in less stress at the restoration tooth interface with a concavity developing on the free surface.  Properties chemically activated light activated composites composites The effect of polymerization shrinkage could be decreased by : 1. The incremental build up of composite in layers. 2. The use of a Glass- ionmer base material beneath composite to decrease the total amount of composite required to fill the cavity. 4. Mechanical properties Hardness Microfilled composites have higher surface hardness (than hybrid & macrofilled composite 4. Mechanical properties Wear Wear resistance of composite materials is generally good. While not yet as resistant as amalgam, the difference is becoming smaller The normal wear mechanism of the composite resins is best explained by the following events: 4. Mechanical properties Rigidity The modulus of elasticity indicates the stiffness of the material. The more filler particle of the composite the higher the stiffness. 4. Mechanical properties Fracture toughness It indicates the resistance to crack growth. More heavily filled composites and those with coarser particles have greater fracture toughness  Properties 4. Mechanical properties Creep Microfilled composites have greater creep values because they have a high proportion of resin matrix than other types. Absorption of water increases creep 4. Mechanical properties Strength Microfilled composites have the lowest values of strength among all types. 5. Thermal properties Ideal dental restorative materials should have a coefficient of thermal expansion similar to tooth (very low) The thermal coefficient of expansion for composite resins is substantially greater than the tooth. 5. Thermal properties Thermal diffusivity of composites that contain either glass or ceramic fillers have values similar to dentine. 6. Radioapcity Radioapcity of composite resins is not far to that of enamel. This enables detection of secondary caries and marginal defects. This is why caries diagnosis maybe higher for composite than with amalgam  Clinical handling notes for composite Cavities designed for tooth-coloured restorations rely heavily on their bonding to enamel and/or dentine to achieve retention and resistance to displacement. Attachment of composites to enamel is achieved primarily by etching the enamel surface with acid.  ACID-ETCH TECHNIQUE 30-50% buffered phosphoric acid provides the best etch pattern. An etching time of 15-20 sec is adequate. Rinse for at least 15 sec. Application of dentine bonding agent for15 sec. Light curing of dentin bonding agent. Pre-curing the adhesive bonding agent before placing the composite ⇑ bond strength.  Application of composite incrementally. Light cure of each increment.  Instruments and devices used for shaping, contouring and polishing composite filling materials. Conventional vs bulk-fill composite resin placement techniques Thank You