Classification of filling materials

There are several classification of filling materials.

Depending to which group the tooth belongs, filling materials are distinguished:

For front group of teeth( filling materials should correspond to high esthetic requirements);

For molars and premolars (filling materials should stand high occlusion press)

1. Metals : amalgam, alloys, pure metals (gold);

2. Non metals: cements, plastic, composite materials.

1 2

According to the material from what restorative materials are produced, they

are divided into:

Filling materials are divided for:

Temporary fillings;Permanent fillings;Curative linings;Isolative linings;Sealing for the root canal.

According to the purpose

Separate group of filling materials consist from adhesives, sealants, varnishes. It’s not filling materials, but dentist can’t work without them. From the point of view of functionality and peculiarities of their usage in the clinic, all filling materials are divided into 2 groups:1. Restorative (should provide complete restoration of the shape of the tooth, and also renew the function of the tooth for long time);2. Curative-prophylaxis (should have good curative-prophylaxis qualities).

Several factors have to be taken into account when choosing the most appropriate restorative method and material for a clinical situation. The limiting factors include:

■ Patient motivation and suitability.■ The number of remaining teeth and their relative positions.■ The condition of their supporting tissues.■ The amount of remaining tooth structure.■ The restorative materials available, and their longevity as restoratives.■ The occlusion and opposing teeth and restorations.■ Aesthetic and other wishes of the patient, including cost factors.

Direct restoratives: clinical properties, handling and placement

The direct restoratives in current, general use are amalgam, composite, glass - ionomer cements and combinations of the last two groups

Available materials

Dental amalgam is a mixture of mercury and an alloy containing silver and tin with added copper and zinc. The alloy and mercury are held together in a capsule, with the two components separated by a plastic diaphragm. When the diaphragm is broken and the capsule is placed in the mixing machine (amalgamator), the two components are mixed together (triturated) to form a silver-coloured paste. This paste is then condensed into the cavity. This is a very important stage: well-condensed amalgams are stronger than poorly condensed ones, as more of the weaker, mercury-rich γ2-phase is removed during carving. Amalgam is weak in thin section so cavities have to be cut suitably deep (2 mm) and because amalgam does not adhere to tooth tissue, the cavity must be undercut.

Dental amalgam

Resin composites used in dentistry have several components:

■ Resin matrix: commonly a fluid monomer, Bis-GMA.

■ Filler particles of silica-based glass. ■ Silane: an agent that allows the resin

and filler particles to bond together. ■ Activator for the setting reaction:

normally camphorquinone. ■ Pigments.

Resin composites

Direct resin composites are the material of choice for anterior restorations and they are increasing in use and popularity for posterior restorations, mainly because of their appearance. Composites do not adhere directly to tooth tissue and rely on the acid-etch technique and the use of dental adhesives for adhesion to enamel and dentine.

Light curing of resin composites is initiated by light in the wavelength range 450–500 nm. This blue light can damage the eyes so an orange filter should be used when the light is in use. The tip of the light source should be placed as close as possible to the surface of the restoration and each increment of composite should be cured for 40–60 seconds. Under-cured composites will readily absorb stain and will rapidly degenerate.

Light curing

Polymerisation shrinkage of the resin during curing (in the order of 2–3%) still occurs and may contribute to marginal defects, cuspal distortion and crack formation in the enamel or dentine, and may therefore contribute to postoperative pain or sensitivity for the patient. There are, however, a number of clinical techniques available to overcome these problems and the longevity of restorations using the newer resin composites is much improved over that of the original materials.

Diagram showing incremental placement of resin composite

Reducing the effect of polymerisation shrinkage may be achieved by incremental packing of the composite. Each increment should touch as few walls of the cavity as possible . The stress induced by polymerization shrinkage is highest in cavities with more bonded than unbonded surfaces: the occlusal cavity has the potential for the most stress.

■ Deep subgingival preparations. ■ Lack of peripheral enamel. ■ Poor moisture control. ■ Load-bearing cusps.

Resin composites are not suitable in the following clinical situations:

Glass ionomers contain poly(alkenoic) acid and fluoro-aluminosilicate glass which set by an acid–base reaction to give a cement.

They adhere directly to tooth substance and to base metal casting alloys.

They release fluoride after placement, giving the materials cariostatic properties, although this may only be short term.

Glass ionomers

They also have a low tensile strength which makes them brittle and unsuitable for use in load-bearing areas in permanent teeth.

They are used as lining and luting materials and to restore abrasion and erosion lesions, cervical lesions and deciduous (primary) teeth and as interim restorations.

It must be appreciated, however, that they are less translucent than resin composite restoratives and therefore their appearance is less acceptable.

Resin-modified glass ionomers have a resin (monomer) component as well as the poly(alkenoic) acid and fluoro-aluminosilicate glass of conventional glass ionomers.

They set by two mechanisms: acid–base reaction and curing of the monomer (chemically, by light or both).

They have improved appearance and physical properties compared with conventional glass ionomers.

They are used in similar situations to glass ionomers and may also be used for small core build-ups.

Resin-modified glass ionomers

Polyacid modified resin composites are also known as compomers.

Their properties are more like those of composites than glass ionomers.

They have limited fluoride release but are stronger and have a better appearance than glass ionomers.

Their wear resistance is less than that of composite restoratives.

They do not adhere directly to tooth substance without the use of a bonding system.

They may be utillised to restore cervical and anterior proximal cavities and for primary teeth.

Polyacid modified resin composites

Acid etching with phosphoric acid creates pores within the enamel into which resin flows to create tags.

This micromechanical retention is very reliable unless there has been contamination of the etched surface by saliva or blood.

This technique is used to retain fissure sealants, composite restorations, orthodontic brackets, resin-retained bridges, veneers and other tooth-coloured restorations.

Acid etching

There is some merit in etching preparations prior to placing a sealer, liner or base, as etching will remove the smear layer which is contaminated with bacteria. Removal of the smear layer in this way affords gross debridement of the preparation and will also improve the quality of the interface between the sealer/liner and the dentine substrate.

Bonding to dentine is more difficult than bonding to enamel as, unlike enamel, dentine contains water and has a greater proportion of organic material.

Bonding to dentine may be achieved reliably with current systems which involve between one and three steps and which either remove or modify the smear layer (this is a layer of debris created by cutting through dentine).

The bond to dentine is a combination of chemical and micromechanical bonding.

Dental adhesives

Current systems are classified as follows:

■ Total etch (or etch and rinse):3 step – comprising etch, prime and bond.2 step – etch followed by a single application of primer mixed with bond.■ Self etch:2 step – etch and prime step, followed by bond.1 step – etch, prime and bond in a single application.

To prevent noxious stimuli reaching the pulp it has been custom and practice to apply protective materials to the floor and/or the pulpo-axial wall of preparations. These materials were commonly placed under amalgams and resin composites to prevent thermal stimulation of the pulp and acid contamination of dentine.

Linings for pulp protection

Preparation liners also seal freshly cut dentine but have additional functions, such as adhesion to tooth structure, fluoride release and/or antibacterial action.

Preparation liners are applied in thin section (<0.5 mm) and materials currently used include RMGICs, dentine adhesive systems, flowable resin composites and hard-setting calcium hydroxide cements.

Liners

Temporary restorative materials and their placement

Temporary restorations are placed for the following reasons:

■ To improve patient comfort by:

Preventing sensitivity.Preventing food packing.Restoring appearance.Covering sharp margins of a cavity.

■ To provide a sedative effect on an infllamed pulp.

■ As an interim restoration before placing the final restoration; perhaps to allow improvement in gingival condition or to assess the patient’s response to diet and oral health advice.

■ As a planned procedure prior to placing a laboratory-made restoration.

■ To assess the prognosis of the tooth and/or pulp.

■ To prevent drifting, over-eruption, tilting or gingival overgrowth.

■ For caries prevention: by using a fluoride leaching material, such as glass ionomer.

■ How long the temporary restoration is to be in place: this depends on the wear characteristics of the material used.

■ The choice of eventual restoration: eugenol plasticizes composite resin restoratives so there is a risk that any eugenol remaining from the temporary restoration could adversely affect a subsequent composite resin restoration, although recent research suggests this is not a problem.

The ideal temporary material should be easy and quick to mix, place and shape. It should set quickly and have appropriate strength and wear characteristics.

The material used should be non-toxic and be non-irritant to the pulp, preferably with a sedative effect on the pulp.

Ideal temporary material

It should also have an acceptable colour, taste and smell and be cheap and readily available.

It is essential that it is easy to remove and is compatible with other materials.

This depends on:■ The size and shape of the cavity: a self-adhesive material such as a glass ionomer may be required if the cavity has no inherent retentive form.

■ The position in the mouth: tooth-coloured material should be used for anterior teeth. Stronger materials should be used for the occlusal surfaces of posterior teeth.

Choice of material

■ Zinc oxide eugenol based materials: these are quick and easy to insert and remove, but are unaesthetic, lack compressive strength and the taste is sometimes considered unpleasant.■ Polycarboxylates.■ Glass ionomers.■ Light-cured polymers.

Available materials