The term 'composite' used for synthetic fillings originates from the verb 'to be composed of'.
Composites consist of synthetic materials used for fillings and containing a minimum of 50/50 weight/mass of an inorganic filling substance once they are hardened. Technically speaking, a composite is a combination of at least two chemically different materials (e.g. monomer and filler). This combination has physical and chemical properties which none of the individual components have alone.
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Hence, composites consist of an organic matrix (= synthetic substance) and inorganic fillers. A bonding phase consisting of silane bonding agents achieves close bonding of synthetic matrix (resin) and fillers (quartz and glasses). Depending on the brand, the filler content nowadays lies between 65 - 85 % weight or 55 - 75 % volume.
The synthetic material (organic matrix) that is used is almost always Bowen's resin (bisphenole A glycidyl methacrylate (Bis-GMA).
The composites are categorised by the size of the fillers used.
An advantage of composites is their aesthetic characteristics (they can match the colour of teeth) while disadvantages include their shrinkage during polymerisation (producing gaps around the margins) and their processing which requires a relatively high amount of work.
Categorisation of composites
Composites can be categorised according to the size of fillers used as follows:
- conventional composites (antiquated)
- hybrid composites
- homogeneous micro-filler composites
- unhomogeneous micro-filler composites
Nowadays, however, this categorisation is obsolete as most modern composites for use in anterior or lateral teeth are almost exclusively fine-particle hybrid composites due to their excellent properties
, with an average filler size of less than 1 µm. They are available in a liquid flowable form or with normal hardness, ie that can be condensed.
Most recent developments have started to use nanoparticles composed of silicon dioxide sized 20 to 60 nm as fillers (e.g. Grandio), making a filler content of up to 87 % weight possible. Only 13 % weight are dimethacrylates in order to reduce shrinkage during polymerisation.
Composites are marketed in rotary syringes or Unidose syringes. The latter require special pistol-like applicators.
The individual manufacturers' synthetic systems include phosphoric acid in a concentration of up to 35% and an enamel bonding agent or dentine adhesive.
Enamel bonding agents consist of highly fluid, unfilled synthetic material (Bis-GMA).
The bonding, or adhesion, of the composite to the tooth is only possible through initial etching of the enamel (or enamel and dentine if a dentine adhesive is used).
Application of a phosphoric acid gel roughens the enamel microscopically. Hardening of the enamel bonding agent causes the synthetic to 'shrink' to the roughened surface and thus 'cling' to it.
Hardening of the synthetic materials is achieved by exposure to a special blue light from the polymerisation lamp consisting of a halogen lamp with a blue filter. Blue LED lamps have recently been introduced to the market.
The blue light required for polymerisation can damage eyesight. Never look directly into the light of the polymerisation lamp; always close your eyes or turn your head away and make sure the patient's eyes are protected. The area that is polymerised can additionally be covered with a dental mirror (turn the mirror side towards the tooth) in order to cover scattered light from the polymerisation lamp and reflect it back to the tooth. Light from the treatment lamp (but also daylight or ceiling light) results in polymerisation of the composite. Therefore, the treatment lamp must always be turned away or an orange filter (e.g. TrollShade) is inserted when a composite filling is placed.
The etched enamel and/or dentine surface(s) is/are sensitive to contamination with blood, saliva and sulcus fluid. Even the air from the patient's respiration can negatively affect the etched surface of the tooth so that the bonding between tooth and synthetic will be insufficient. Furthermore, synthetics are 'hydrophobic' (Greek: hydros - 'water', phobos - 'fear') while the dental hard substance is 'hydrophilic' (Greek: hydros - 'water', philia - 'friendship').
Therefore, absolute, or controlled, drying using rubber dam is essential.
Insertion of a composite filling
Instruments and materials required
- 2 ml syringe with local anaesthetic, long injection cannula for regional block anaesthesia, short injection cannula for infiltration anaesthesia
- colour-coded ring fitting with the composite material used
- hand mirror
- rubber dam
- hole template
- rubber dam punch
- rubber dam clamp
- clamp collar
- rubber dam tenting frame
- dental floss
- red high-speed angle handpiece
- green right angle
- rotary instruments:
- pear-shaped diamond polishers,
normal grain (without colour mark),
fine / finest grain (with red or yellow colour mark),
- shaped like a flame, bud, or ball
- hard metal instrument interlocking crosswise, if required (to remove old amalgam fillings)
- rose-head burs in different sizes (e.g. ISO 010-018)
- large and small saliva ejector
- multi-functional syringe (air/water)
- Dappen glass with e.g. H2O2 (3 %) or CHX (2%) or NaOCl (5%)
- cotton wool pellets (ca. 5 pieces)
- glass ionomer or phosphate cement (powder and liquid)
- glass plate
- cement spatula
- cement condenser
- calcium hydroxide preparation for treatment of deep caries, indirect or direct pulp capping
- in the anterior tooth area:
cellophane or plastic strips used as matrix
- In the cheek tooth area, traditional matrixes with metal bands, such as Tofflemire's or Automatrix can also be used.
Furthermore, special metal matrixes (partial matrix systems) are available for composites. E.g.: Adapt Sectional Matrix system, Palodent
- suitable inter-dental wedge made of maple wood, colour-coded according to size,
(one inter-dental wedge is required for each proximal space to be filled)
- phosphoric acid for etching of the dental hard substance (ca. 30-35 %; the gel is usually blue or green)
- enamel bonding agent or dentine adhesive
- light-tight container (e.g. Vivapad)
- polymerisation lamp
- synthetic composite material (in cartridge or syringe systems)
- special instruments for condensing and final shaping of the composite made of synthetics or metal alloys preventing discolouration of the composite material
- bent, sickle-shaped scalpel (fig. 12)
- 2 flag holders with occlusal foil in different colours, e.g. black and red
- dental floss
- suitable polishers: e.g. with small sandpaper discs
(e.g.: Soflex; Soflex discs are available with the following colour marks: black = very coarse, dark blue = coarse, medium blue = normal, light blue = fine)
- polishing brushes
- sandpaper strips for approximate preparation
- fluoride (e.g. Duraphat toothpaste)
- colour selection
- rubber dam placement
- primary preparation and/or removal of old fillings
- cavity disinfection
- base lining
(not always required if dentine bonding agents are used)
- finishing of the edges of the cavity and base
- beveling of the edges of the cavity
- placement of matrix and inter-dental wedges
- enamel, or enamel and dentine, conditioning using etching gel (= phosphoric acid)
- application and polymerisation of enamel bonding agent or dentine adhesive
- application of the synthetic in layers (approx. 2 mm thick) (laminating technique)
- hardening of each synthetic layer for 40 seconds
- removal of inter-dental wedge and matrix
- directing the polymerisation lamp to the areas that were covered by the matrix (above all approximate)
- removal of the rubber dam
- finishing of the filling through preparation with rotary instruments
- occlusal control
- final preparation and polishing
- fluoridation of the tooth
The colour should be selected prior to placement of the rubber dam as the teeth will dry afterwards and seem lighter in colour. The patient should be made to look in a hand mirror and included in the selection of the right colour.
Caution is advised to avoid eye contact with the acid used: The patient should close their eyes and the dentist should eject the phosphoric acid etching gel before irrigation in order to avoid spraying acid as much as possible.
As composite fillings directly achieve their final hardness by light polymerisation, polishing of the filling is required in the same session as its placement. Therefore, the patient will be able to eat as soon as the anaesthesia wears off.
Fluoridation following the acid etching is essential in order to remineralise enamel that has received some initial etching but has not been covered by the filling.
Exchange of an amalgam filling through a composite filling
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