Synthetic Filling (Composite Filling)

Plastic fillings (composite fillings) are used for tooth-colored restoration of carious defects in both the anterior and posterior regions. They are placed in the cavity (hole) in a plastic state and harden there by polymerization (chemical setting). In the process, they form a micromechanical bond with the tooth substance when the dentine adhesive technique is used. The advantages of a resin filling compared to an amalgam filling are:

  • The possibility of tooth-colored restoration
  • The stabilization of the tooth structure by the dentin adhesive (adhering to the dentin) bond.
  • In contrast to amalgam mercury-free and
  • The abandonment of tooth substance demanding undercuts with which an amalgam filling must be wedged in the tooth against withdrawal forces.

Their disadvantages lie in the comparatively time-consuming multi-layer technique, which must be used to counteract the shrinkage of the composite material during polymerization (chemical setting). In addition, the material is under discussion with regard to its biocompatibility. Composites have been shown to be contact allergens, a problem that primarily concerns dental personnel, as the risk of allergy comes from the material that has not yet polymerized (chemically set).

Composite material

I. Components

Synthetic materials (composites) for restorative therapy are composed of the following components:

1. organic matrix, consisting of, among other things:

  • Various methacrylates (Bis-GMA, UDMA) as monomer molecules (basic plastic components),
  • Thinners for better processability (comonomers TEGDMA and EGDMA).
  • Initiators (e.g. benzoyl peroxide, camphorquinone), which initiate the chemical setting reaction by releasing free radicals.
  • Accelerators to accelerate the setting reaction.
  • Color and other stabilizers
  • Silica clusters that reduce the setting shrinkage of the matrix.
  • Nanoparticles, 2 to 3 nm in size, to improve flexural strength, translucency (partial light transmission) and biocompatibility.

2. inorganic fillers improve quite a few material properties, such as abrasion resistance (wear resistance), shrinkage, fracture resistance, and more:

  • Microfiller composites: contain splinter or spherical prepolymers of organic matrix or silica particles. One of their disadvantages is their lack of visibility on radiographs.
  • Hybrid composites: contain 0.5 to 10 µm glass particles and additives that make the material radiopaque. The filling particles take up about 85% of the volume.
  • Nano-hybrid composites: with filler particles in the nano range, partly with conventional fillers, partly with prepolymers.

3rd composite phase: it enables the chemical bonding of the organic matrix with the inorganic fillers and is formed by silanization (reaction with a silane). This primarily significantly improves the abrasion properties (abrasion properties) of plastics. II. Consistency

Plastics are processed in the following viscosities, depending on the indication:

  • Flowable composites (flowable) contain fewer fillers and thus have a higher polymerization shrinkage of approx. 3%. Their application is thus limited to cervical fillings and very small occlusal and proximal defects.
  • Universal composites: must withstand chewing pressure and therefore have high flexural strength, surface hardness, and a large volume fraction of fillers.
  • Packable composites (packable) are highly viscous and contain more highly dispersed silica, sometimes in combination with coarser fillers. They are not more abrasion resistant than universal hybrid composites.

III. color spectrum

In order to come as close as possible to the natural model, the composites are processed in a wide spectrum. This is nuanced with regard to:

  • The brightness
  • Of the hue
  • Of translucency (partial light transmission): the enamel mass is more permeable than the dentin mass, in addition, opaque colors (opaque colors) are offered to cover dark tooth substance.

IV. Chemical setting reaction

Resin fillings harden by the fact that the acrylate monomers (acrylate basic building blocks) are cross-linked by a chain reaction triggered by free radicals to form a polymer.The radicals, in turn, are released by a chemical startup reaction or via a photoinitiator that reacts to a light spectrum of 350 to 550 nm, to which the polymerization lamps are directed.

Indications (areas of application)

Plastic fillings are used in both first and second dentition (in deciduous and permanent teeth) and on all tooth surfaces:

  • Anterior tooth fillings including corner abutments.
  • Tooth neck fillings e.g. for the supply of wedge-shaped plaster defects.
  • Occlusal fillings for the restoration of the occlusal surfaces with a filling width of max. 50% of the cusp distance.
  • Approximal fillings for the restoration of interdental defects, with occlusal portion corresponding maximum width of 50% of the cusp distance.
  • Aesthetic tooth reshaping e.g. for tooth substance sparing correction of shape anomalies (cone tooth).
  • Fillings in the 1st dentition (milk tooth fillings).
  • Build-up fillings before crown restoration

Contraindications

  • Allergy to any of the ingredients, especially methacrylate.
  • Too large tooth defect; in this case, switching to an inlay-onlay partial crown or crown restoration makes sense

Before the filling

Before the composite filling, the patient must be informed about alternative filling methods, possible contraindications and the cost factor due to the time involved.

The procedure

The application of resin fillings is indispensably linked to the careful use of the dentin adhesive technique. This is the only way to ensure that the filling adheres to the tooth in a way that is bacteria-proof and non-irritating to the pulp (the tooth’s pulp). The procedure is characterized by many partial steps.

  • Excavation (caries removal).
  • Shade selection: useful before preparation, when as much tooth substance as possible is still available. In addition, the tooth substance dries out somewhat during treatment and thus becomes brighter. The tooth must not only be free of caries, but also thoroughly cleaned (eg from nicotine or coffee discoloration).
  • Minimally invasive preparation (sparing tooth structure), as no mechanical undercuts against extraction forces must be placed. In anterior teeth, an enamel bevel of 0.5 to 1 mm is made to increase the adhesion surface and for esthetic reasons, as the preparation margin becomes visually more inconspicuous due to the beveling
  • Ideally, absolute draining with rubber dam (tension rubber, which prevents access of liquids).
  • If necessary, indirect or direct capping: in extreme pulp proximity or pulp opening application of a calcium hydroxide underfill, which withstands the further procedural steps.
  • Filling adhesion to the tooth: is achieved by the dentin adhesive technique procedure, which is composed of:
  • Conditioning of enamel and dentin with phosphoric acid (H3PO4): in the resulting enamel etching pattern, the monomers of the resin anchor themselves micromechanically in the following. In the dentin, the collagen framework is freed from the hard substance and prepared for the absorption of monomer by the following steps.
  • Priming of the conditioned dentin surface.
  • Application of the dentin adhesive to the prepared dentin and enamel (bonding): the dentin is impregnated with monomers, the enamel etching pattern is also penetrated. The so-called hybrid layer is formed as a connecting element between the tooth and the resin material.
  • Application of a flowable composite in the entire cavity with a thickness of max.1 mm to strengthen the hybrid layer and to avoid porosity in the marginal area.
  • Layering technique: introduction of the universal or tampable composite in several partial layers, which must be light-polymerized individually and for a sufficiently long time (usually 20 sec each) in order to keep the shrinkage stress of the material and the resulting stresses in the tooth as low as possible and to avoid pulp irritation, etc., by a high degree of polymerization. Here, the layers must not be placed horizontally from one side of the cavity to the other, but must run diagonally to be connected to only one cavity wall at a time during polymerization.
  • Removal of the oxygen inhibition layer on the filling surface, which is not polymerized due to the oxygen contact, e.g. with an Occlubrush.
  • Removal of the cofferdam
  • Contouring (finishing) the filling z.B. with fine-grained diamond grinders.
  • Occlusion control (checking and grinding in the final bite contacts).
  • Articulation control (correction of the filling surface in adaptation to the chewing movements).
  • Polishing e.g. with polishing pastes

After filling

The filling is immediately loadable by chewing pressure. However, it reaches its final hardness only in the course of the next 24 hours. Since it can be assumed that the acrylic material absorbs a small amount of water, it is advisable to check the filling margins for any protrusions at a later check-up appointment.

Possible complications

are mainly due to the complexity of the very technique-sensitive procedure. Errors in material selection, but especially in the procedure (overetching of the dentin, drying out of the dentin, errors in the application of primer and/ or bond, insufficiently long polymerization, incorrect layering, saliva ingress, etc.) will almost inevitably manifest in

  • Postoperative sensitivities (pulp irritation via the dentinal tubules).
  • Bite sensitivity
  • Loss of filling
  • Filling fracture when the filling is too large
  • Marginal fractures or marginal gap formation, subsequently secondary caries (marginal caries).
  • Too strong abrasion (abrasion).