lec: Dental material dr. Aseel Mohammed

Filling material

Classification of composite based on size of filler particles

1.Conventional composite (Traditional or macrofilled composite): The early composites were macrofills, These composites contained large spherical or irregular shaped filler particles, There is a wide distribution of particle size of average filler diameter of 10 to 100 μm, Filler loading is 70-80 wt % or 50-60 vol %. Ground quarts are most commonly used as filler.

The conventional composite have improved properties compared to unfilled restorative resin (acrylic) it has more compressive strength, tensile strength, elastic modulus and hardness, and it has less water sorption and low coefficient of thermal expansion. Although the conventional composite were superior to unfilled resin, they had certain disadvantages:

1. Surface finish was very poor and dull appearance (Polishing was difficult and results in a rough surface) this is due to selective wear of the softer resin matrix leaving the hard filler particles elevated.

2. Poor resistance to occlusal wear.3. Tendency to discolor, the rough surface tends to stain.

The conventional composite after polishing

2.Micro filled composite: They were developed to overcome the problems of surface roughness of conventional composite. The microfilled composite achieved the smoothness of unfilled acrylic direct filling resins and the advantages of having filler. The smoother surface is due to the incorporation of micro fillers, Colloidal silica is used as micro filler with size 0.01 to 0.1 μm, Filler loading is 50 vol. wt %. The problem with colloidal silica was that it had a larger surface area that could not be adequately wetted by matrix resin. Thus addition even small amounts of micro filler result in thickening of the resin matrix. Thus it was not possible to achieve the same filler loading as conventional composite. With exception of compress strength their mechanical properties are inferior to other

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lec: Dental material dr. Aseel Mohammedcomposite type (This is because of their higher resin content (50 vol. %)). Their biggest advantage is their esthetics (the small size of the filler particles means that the composite can be polished to a very smooth surface). The microfilled composite is the resin of choice for esthetics restoration of anterior teeth, especially in non-stress bearing Area. While in stress bearing situations like CI IV and CI II restoration, they have a greater potential for fracture (bond between the composite microfilled particles and the cured matrix is relatively weak which facilitating wear by a chipping mechanism, because of this micofilled composites are not suitable for use as stress-bearing surfaces).

3.Small particles composite: Small particles composite were introduced in an attempt to have good surface smoothness (like microfilled composite) and yet retain or improve the physical and mechanical properties of conventional composite. The small particles composite use fillers that have been ground to smaller filler size about 0.1 – 10 μm. The smaller size filler particles allow these composite to be polished to a smoother surface finish (can be used in anterior restoration , have reasonably smooth surface for anterior are but still not as good as the microfilled and hybrid composite in this regard).

Due to the higher filler content ( 65 to 77 vol. % or 80 to 90 wt. %) the beast physical and mechanical properties are observed with this type. they can be used in areas of stress such as CI II and CI III restorations (Due to the improved strength and abrasion resistance). The filler employed are:

1. Glass containing heavy metals, Ground quartz is also used 2. Colloidal silica is also added in small amount. 5 wt % to adjust the paste viscosity.

4. Hybrid composite: - These were developed so as to obtain better surface smoothness than that of small particle, but yet maintain the properties of latter. The hybrid composites have a surface smoothness and esthetics competitive with microfilled composite for anterior restoration.

Hybrid composites are formulated with mixed filler systems containing both microfine (0.01 to 0.1 μm) and fine (0.1 to 10 μm) particle fillers. Most modern hybrid fillers consist of colloidal silica and ground particles of glasses containing heavy metals, the filler loading is 60-50 vol % or 75- 80% by weight, the overall filler loading is not as high as small particle composition.

Their properties range between conventional and small particle they are generally superior to microfilled composite. The hybrid composites are widely used for anterior restorations because of its smooth surface and good strength. The hybrid are also being widely employed for stress bearing restoration ,even though its mechanical properties are somewhat inferior to small particle composites .

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5.Nanocomposite/ Nanofillers :Nanofillers and Nanocomposites the latest advancement in composite technology has been the use of nanotechnology in development of fillers. Nanotechnology is the production of functional materials and structures in the range of 1 -100 nanometers (nm) by various physical and chemical methods. It has novel properties and functions because of their small sizes. it has superior gloss retention, optical properties and superior polishability (used in anterior restoration) without seriously decreasing in the mechanical properties (used in posterior stress bearing restoration).

Manipulation of the composite: Composites used for restoring teeth are usually supplied in a kit containing the following: Syringes of composite resin paste in various shades. Etching liquid (37% phosphoric acid). Enamel dentin bonding agent. Shade guide.

The manipulation is1. pulpal protection: with cavity liner 2. Etching: the enamel at the cavity margins is acid etched with 37% phosphoric acid

solution or gel for 30 seconds. Flush the acid away with water, and gently dry the surface with a stream of air.

3. Bonding agent an enamel and dentin bond agent is applied and polymerized that provides micromechanical retention of the restoration. The cavity is now ready for the composite.

4. dispensing: For light-Cured Composites, dispense small increments and pack into the cavity preparation, while controlled setting time allows for the individual polymerization of small increments of composite which help in:

A- Use of multiple shades of composite within a single restoration.B- Accommodating polymerization shrinkage within each increment.

For Self- and Dual-Cured Composites, Mix equal amount of base and catalyst pastes thoroughly for 20 to 30 seconds use plastic or wooden spatulas (avoid metal spatulas because the inorganic filler particles are abrasive and small amounts of the metal can abraded and discolor the composite.

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5. Insertion: The composite can be inserted with a plastic instrument, which does not stick to the composite during insertion or It can be injected into the cavity preparation by a syringe

6. Polymerization: for light cure composite the exposure times vary from 20 to 60 seconds for a restoration 2 mm thick depending on the type of light-curing unit and the (type, depth, and shade) of the composite. for Self-Cured Composites: After mixing, a working (or insertion) time is 1 to 1.5 minutes then the mix will begin to harden, the setting time is about 4 to 5 minutes from the start of the mix.For Dual-Cured Composites: They contain chemical accelerators and light activators, so polymerization can be initiated by light and then continued by the self-cured mechanism.

7. Finishing and polishing.

Glass ionomer cements: Glass ionomers are water-based self-adhesive restorative materials in which the filler is a reactive glass called fluoroaluminosilicate glass and the matrix is polymer or copolymer of carboxylic acids. The setting reaction of these materials involves an acid-base reaction and release fluoride ions. They are used as filling materials which release fluoride. There are two main types of glass ionomers:

1. Conventional glass ionomer2. Resin-modified glass ionomer which is subdivided into:

True light cure Glass Ionomer System Tri-Cure Glass Ionomer System Nanoionomer

1.Conventional glass ionomers have the following essential components:

• Polycarboxylic acid• Fluoroaluminosilicate (FAS) glass• Water• Tartaric acid: control the working and setting of the material

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2. Resin-Modified Glass Ionomers (RMGI) :

True RMGIs the essential components of are as follows:

• Polycarboxylic acid polymer• Fluoroaluminosilicate glass• Water• Hydrophilic methacrylate monomer• Free radical initiators

Two types of curing reactions take place in true light-cure glass ionomer

Acid-base glass ionomer reaction. Light-activated polymerization

It has to be cured in layers because penetration of visible light can occur only to a limited depth. This is not a disadvantage in applications where thin layers of materials are to be placed.

Tri-Cure Glass Ionomer System : These are resin-modified glass ionomers with an additional curing mode. Here, in addition to the photoinitiators, self-cure imitators are added so that the methacrylate polymerization can proceed in the absence of light. The three curing reactions are as follows:

Acid-base glass ionomer reaction. Light-activated polymerization Chemically activated polymerization

The introduction of tri-cure technology has allowed resin-modified glass ionomers to be used as bulk-cured materials, thus saving time for the practitioner.

Nanoionomer: The latest advancement in resin-modified glass ionomers is the nanoionomer, in which some nanoparticles such as nanomers and nanoclusters are added to the FAS glass. The addition of nanoparticles improves the polishability and the optical characteristics of the cured ionomer.

Uses of Glass Ionomers: both conventional and resin-modified glass ionomers are used for a variety of restorative applications, specially in:

1. High caries activity or where caries are likely to recur. 2. small caries lesions in non-stress-bearing restorations in permanent teeth

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lec: Dental material dr. Aseel Mohammed3. interim restoration in permanent teeth, 4. They make an excellent liner or base in all deep lesions 5. Resin-modified glass ionomers are often the material of choice for pediatric

restorations and preventive applications

Properties of Glass Ionomers:

1. The physical and mechanical properties of GIs are lower than that of composite resins and hence these materials are indicated for conservative restorations.

2. The coefficient of thermal expansion has been shown to be closer to tooth structure (dentin) than are resin composites. (Serve as good insulation against thermal shock, particularly when used as liners and bases).

3. Fluoride ion release and uptake these materials act as a reservoir of fluoride ions. The fluoride is released by an ion-exchange mechanism from these materials. The release of fluoride ion is sustained over prolonged periods.

4. Good adhesion to tooth structure Unlike composite materials (etching of the enamel or dentin surface is not needed). Hence these materials are sometimes referred to as being self-adhesive. (The mechanism of adhesion to the tooth structure is mostly chemical in nature and proceeds through an exchange of ions arising from both the tooth and restoration).

5. is radiopaque

Manipulation: Glass ionomers are supplied as powder and liquid either as two-part systems (powder component and a liquid component). The powder is commonly provided in a jar and is dispensed with a measuring spoon and the liquid is provided in a vial with a dropper tip for use of dispensing. After dispensing the recommended ratio of powder and liquid according to the manufacturers’ directions, the components are hand spatulated on to a paper or glass slab. The mixing time is (30 to 60 seconds). The cement must be inserted in the cavity immediately because the working time after mixing is about 2 minutes. In some cases, it is recommended that the mixed material be transferred to a syringe and injected into the tooth preparation (To aid in the dispensing and mixing)

The glass ionomers are also supplied in single-unit encapsulated version. The powder and liquid are kept separated in the capsule for shelf-stability. Prior to clinical use the capsule is activated and then triturated in an amalgamator to mix the two components. An applicator is provided that pushes the mixed material through a narrow tip so that it can be directly placed in the oral preparation.

Once the cement has achieved its initial set (about 7 minutes), coat the cement margins with the coating agent supplied with the cement.

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Compomers: Compomers or poly acid–modified composites have fluoride-releasing silicate glasses. They are used for restorations in low stress–bearing areas, Compomers are recommended for patients at medium risk of developing caries.

Compomers are packaged as single-paste formulations in compules and syringes. They require a bonding agent to bond to tooth structure. The material is to be cured by light in increments of 2 to 2.5 mm. setting occurs primarily by light-cured polymerization, but an acid-base reaction also occurs as the compomer absorbs water after placement and upon contact with saliva. Water uptake is also important for fluoride transfer. Compomers release fluoride by a mechanism similar to that of GIs and RMGI. Because of the lower amount of glass ionomer present in compomers, the amount of fluoride release and its duration are lower than those of GIs and RMGI. Also, compomers do not recharge from fluoride treatment or brushing with fluoride dentifrices as much as GIs and RMGI.

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