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Introduction to composite Restorations (Sturdevant, ch. 11, pg. 497-516) (Sturdevant-Southasian Ed., ch.12, pg. 225-239) A composite is: • Bowen1962 • Physical mixture or blend of two or more chemically different materials having a dispersed (Filler) phase mixed into a continuous (Matrix) phase wi...
Introduction to composite Restorations (Sturdevant, ch. 11, pg. 497-516) (Sturdevant-Southasian Ed., ch.12, pg. 225-239) A composite is: • Bowen1962 • Physical mixture or blend of two or more chemically different materials having a dispersed (Filler) phase mixed into a continuous (Matrix) phase with a distinct interface between them. • In resin composites a resin is the matrix. 3 Composition I. Matrix phase (organic) II. Inorganic Filler III. Silane Coupling Agent IV. Photo-initiator 4 Composition • I. Matrix phase (organic) • Monomer, bisphenolA and glycidyl methacrylate (BisGMA) • Urethane dimethacrylate (UDMA) • TEGDMA as diluents • II. Inorganic Filler • Most composites filler are now produced using modified silicate glass. • Filler composition often are modified with other ions to produce desirable changes in properties. • E.g Lithium and aluminum ions make glass easier to crush • Barium, zinc, boron, zirconium: produce radiopacity 5 Fillers offers : 1. Polymerization shrinkage is reduced compared to unfilled resins. 2. Coefficient of thermal expansion is reduced 3. Fillers improve mechanical properties such as hardness and compressive strength 4. The use of heavy metals such as barium and strontium in the glass provide radiopacity 5. Fillers provide aesthetic properties such as color, translucency. III. Silane Coupling Agent • It is important to provide interfacial bonding between the organic matrix and the inorganic filler particles phases. • di-functional • Work best with silica particles C OH Bis2 CH3H -C-C-O-CH 2-CH2-CH2GMA Bonds with Bonds with IN Si-OHO OH ORGANIC filler ORGANIC Silane resin 7 IV. Photo-initiator • Most current composites are polymerized with the help of light. • Photo‐initiator: Camphorquinone CQ • It absorbs photons of light energy at about 470 nm (wavelength). 8 Classification of Composites 1. Based on filler particle types: I. Homogeneous :If the composite simply consists of filler particles and uncured matrix material, it is classified as homogeneous. II. Heterogeneous : If it includes precured composite or other unusual filler, it is called heterogeneous. III. Hybrid: with mixed ranges of particle sizes are called hybrids. 9 10 Classification of dental composites • Based on polymerization method i. Self (chemical) cured ii. Light cured iii. Dual cured • Based on viscosity i. Packable ii. flowable 11 I. Macrofill Composite • First type 1960 • Filler particles sizes averaged 10-20 µm in diameter, with many of the larger particles 50 µm • Rough surface texture. • No longer used 12 II. Midfill composite (conventional) • Approximately 8 µm • 75-80% inorganic filler by weight. • More susceptible to discoloration from extrinsic staining. 13 III. Microfill Composite • Diameter of filler particles is 0.01-0.04 µm • A smooth, polished surface, less receptive to plaque or extrinsic staining. • Material of choice in restoring low occlusal wear- high esthetic areas • Low modulus of elasticity may allow microfill composite restoratons to flex during tooth flexture, makes it appropriate for restoring class V cervical lesions. • An inorganic filler 35-60% by weight. • There are two types of microfilled composites –Heterogeneous microfill: blend of precured microfill composite with uncured material. –Homogeneous microfill: consists of filler particles and uncured matrix material 14 IV. Hybrid Composite Combined, macrofill composites. Inorganic filler, 75-85% by weight. Particle size (0.4-1µm) Superior to those of conventional composites. • Also called Mini-micro hybrid composites. • Newer called: nano hybrid composites • • • • 15 V. Nanofill Composite • Extremely small (0.005-0.01 µm) • Nano-particles also may be clustered or aggregated into large units • High filler levels can be generated which results in Good physical properties, improved esthetics. • The small primary particle size also makes naonofills highly polishable • Low wear rates 16 VI. Packable Composite • Developed to accomplish two goals: • 1. Easier restoration of a proximal contact. • 2. Improve the handling properties of the composite. • Less stickiness, higher viscosity (stiffness) • More difficult to attain optimal marginal adaptation. 17 VII. Flowable Composites • Low viscosity material • Low filler content • Increased amount of resin to decrease the viscosity of the mixture. • Low modulus of elasticity (resist tooth flexure at the cervical areas e.g. used for restoring class V or abrasion cavities) • Generations – First generation • Uses such as pit and fissure sealants, small anterior restorations marginal repair materials. – Second generation • Materials with higher filler content have been suggested for use in class I, II, III, IV, and V restorations. • First small increments in the proximal box of a class II restoration in an effort to improve marginal adaptation. 18 Polymerization of Composite POLYMERIZATION SHRINKAGE: Can not be avoided It pulls the material from cavity walls during polymerization Usually does not cause a problem if all cavity margins in enamel When a tooth preparation has extended onto the root surface, polymerization shrinkage can cause a V-shape gap at the junction of the composite and root surface. • Compensation of polymerization shrinkage by: Incremental insertion and curing technique Soft-start polymerization instead of high intensity light-curing Stress-breaking liner, such as a filled dentinal adhesive or RMGI (resin modified glass ionomer) • Incremental insertion (1 t 2 mm increment): 1. reduce polymerization shrinkage 2. Ensure complete light curing and polymerization • Typical hybrid composites using BIS-GMA or UDMA as the matrix shrink approximately 2.4-2.8% • Silorane Polymer matrix: low shrinkage composite (0.7%) • Higher filler : less shrinkage (flowable?) 26 Light curing Variables (equipment; manipulation; restoration) I. Curing equipment • Light emitting diode (LED) • Quartz tungsten halogen (QTH) • Plasma are curing (PAC) • Lasers QTH PAC Laser LED 27 • Intensity of the light: • The minimum output should never be less than 300 mw/cm2 • • Radiometer: Device used to measure the output High-intensity plasma arc or laser lights can reduce curing times to 310 sec., • but generate much more unwanted heat Staged curing: low intensity for about 3 sec. followed by gradual increase in the intensity. The goal is to minimize shrinkage stress Curing Depth and Degree of Conversion Curing Light 3. DEPTH-OF-CURE 0 mm 1 2 65% 45% 25% DEGREE-OFCONVERSION 3 4 Z100 31 Method of Polymerization: Self-curing UV-light-curing Visible light-curing Dual-curing Staged curing • The use of light sources may cause retinal damage unless appropriate precautions are taken to avoid direct, prolonged exposure to the light source Important Properties of composites • Linear coefficient of thermal Expansion 3 times of that of tooth structure Amalgam: 2.5 times of that of tooth structure Conventional GIC: same as tooth structure Hybrid GIC: 1.5 to 2 times of that of tooth structure • Indications: • Isolation Factors • Occlusa Factors 1. Class I, II, III, IV, V, and VI restorations 2. Foundations or core build ups 3. Sealants and conservative composite restorations 4. Esthetic enhancement procedures: - direct veneers - tooth contour modifications - Diastema closure 5. Cements 6. Periodontal splinting • Contraindications Isolation factors Occlusal factors • Advantages 1. 2. 3. 4. 5. Esthetic Conservative less complex cavity prep. low thermal conductivity bonded to tooth structure results in improved retention, low micro-leakage, minimal interfacial staining, and increased strength of remaining tooth structure 6. Repairable • Disadvantages 1. gap formation when the cavity margins extends to root surface 2. technique sensitive because it requires complete dryness 3. greater occlusal wear in areas of high occlusal stress 4. Have a higher linear coefficient of thermal expansion 5. difficult to establish proximal contour and contact Cavity Prep. For Composite • Outline form: Outline should extends to sound tooth structue • Retention From: Primary retentions comes from micromechanical retention • Resistance Form: Depends on the bond strength between the composite and tooth structure Removal of carious lesion Pulp Protection Composite is thermal and electrical isolator, bonding agent act as a sealer to prevent microleakage Ca(OH)2 for the v. Deep prep. Differnces form Amalgam tooth Prep. • • • • Less outline extension No uniform depth Incorporation of an enamel bevel Rough cavity walls is recommended (Best prepared using diamond instruments) • Beveling of the cavo-surface The bevel is best prepared with either: a flame shaped or; round diamond instrument resulting in an angle approximately 45 degrees to the external tooth surface Beveling of enamel margins will: 1. Expose enamel rods ends for better etching pattern that etching the sides of enamel rods 2. Incrase surface area available for etching. This will increase the bond strength and improve the retention 3. improves aesthetics