Composite (dentistry)

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Composite
Composite

Composites ( Latin composĭtum 'the composite') are tooth-colored, plastic filling materials for dental treatment. In layman's terms, the materials used since the 1960s are often referred to as plastic fillings , sometimes mistakenly confused with ceramic fillings (synonym: ceramic inlay or ceramic inlay). Composites are used in dental medicine for fillings and the cementation of ceramic restorations, crowns and root posts.

They consist of an organic plastic matrix, which is mixed with inorganic fillers. Initially, the composites were used almost exclusively in the anterior region . In the meantime, composites with an increased filler content are also used in the posterior region. The further development of bonding agents and dentine adhesive technology made this use possible.

Modifications of the composites are compomers and ormocers . Glass ionomer cements belong to a different class of materials. They are also available with composite parts.

processing

The composites are considered to be relatively technology-sensitive. When processing composites, relative or absolute drainage is necessary, which can be achieved with cotton rolls or by putting on a rubber dam (a rubber cloth stretched over the teeth). Moisture reduces durability and adhesion to dentin and enamel.

Advantages over amalgam fillings

Composites are available in several colors, so that a color difference to the existing teeth is difficult to see if the color is chosen carefully.

Amalgam fillings are fixed in the tooth through small undercuts if the cavity is not designed from the outset in such a way that it tapers towards the outside as a so-called form fit . Amalgam is one of the few alloys that expand when it sets. In this way, the material ensures a tight seal. On the other hand, a tooth in which the hard tooth substance is already severely reduced can be “blown up”. In the case of composite fillings, the material actually sticks in the tooth, so that on the one hand only the carious tooth substance has to be removed and no retention form has to be ground. In some cases, the adhesive can be used to stabilize the tooth.

Advantages over ceramic fillings

Compared to inlays , composites can be used in less time and more cost-effectively. The completion usually takes place in one session. By fabricating the composite restoration directly in the tooth, the cavity can be prepared in a way that is gentle on the substance because, in contrast to the laboratory-made ceramic inlay, no insertion direction has to be taken into account. The direct method means that there is no need to take an impression .

disadvantage

The processing of the composite filling material is more complex and time-consuming compared to an amalgam filling, as it is applied in several layers and cured in layers with a polymerization lamp in order to reduce the polymerization shrinkage of the material. A prerequisite for a permanently leak-proof composite filling is adhesive attachment to the tooth by etching with phosphoric acid and then applying an adhesive. Correspondingly, the financial outlay is higher compared to amalgam fillings, albeit lower than with inlay fillings made of gold or ceramic. A better durability of inlays is being discussed, since a larger selection of materials is possible for inlays and there is no polymerization shrinkage and thus less material tension (see section Durability ). In the case of large cavities, the adhesive cementation can cause infractures (fine enamel cracks) on the enamel walls, which can lead to fracture of the cavity wall.

The more true-to-color the composite filling is, the more difficult it can be to remove it because the boundary between enamel and composite is barely noticeable when the composite is ground out.

Discoloration of the filling from tea, coffee, etc. is possible.

Effects discussed

With the increase in composite fillings, which gradually replace the amalgam fillings more and more, the criticism shifts from the amalgam fillings to the composite fillings. Possible harmful effects from:

through the composite fillings.

Toxicity, mutagenicity and estrogenicity could not be proven in studies and should be answered in the negative according to the current state of knowledge.

Allergy

The risk of allergy mainly affects the dentist who uses it, who comes into skin contact with the monomer of the composite and with the dentin adhesives. This can trigger allergic skin reactions up to severe allergic contact eczema up to occupational disability. A disposable glove does not prevent monomer penetration as the relatively small monomer molecules penetrate it within just three minutes. Therefore, if there is any contact, an immediate change of gloves is advisable. Monomers and dentin adhesives should therefore not be touched by the dentist or assistant. The allergy rate for the practitioner is 1 to 2 percent higher than with amalgam, but is still far below the allergy rate for strawberries. When weighing up the risks and benefits (preserving the tooth with a composite filling or caries, abscess and tooth loss), the risk of allergy for the patient is negligible.

toxicity

No cases of symptoms of poisoning caused by composites are documented in the medical literature. No clinical data are available to suggest that the composite fillings are harmful. However, the toxicity of composites has been shown in in vitro studies on cell cultures. However, the concentrations used were so high that clinical relevance appears questionable. The zinc oxide eugenol used in dentistry, for example, is much more toxic in vitro.

Mutagenicity

BisGMA and UDMA are not mutagenic in cell cultures. However, a mutagenic effect was demonstrated in cell cultures with TEGDMA, but a very high concentration was used here.

Durability and loss rate of composite fillings

Durability compared to inlays

Compared to composite fillings, the durability of the several times more expensive ceramic inlays was classified as similar in a meta study for a period of up to one year. The data of the available long-term clinical studies did not allow reliable statements to be made for longer periods of observation. In the long-term clinical studies themselves, it was found that there was no significantly lower failure rate of inlays.

For composite inlays, too, no significantly higher shelf life values ​​were found in long-term clinical studies, or shelf life benefits were found which, however, were rated as too low to justify the additional effort.

Durability compared to amalgam

The rate of loss of composite fillings in clinical studies over 7 years was 16% higher than that of amalgam fillings. Over the entire period, however, this value was below the significance threshold, since both amalgam and plastic fillings have an overall good shelf life. The "survival rate" ( english probability of survival ) of composite was 90% after 7 years.

In 2005 longitudinal studies over 15 years already showed the same lifespan for amalgam fillings and composite fillings, assuming correct indication and processing technique. Long-term studies of the last ten years with fine hybrid composites also show good results. For ormocers and packable composites only a few studies with an observation period of two years are available. Compomers and microhybrid composites are less suitable for restorations with chewing force and showed filling fractures.

Whether a composite filling should be placed under or without a rubber dam is controversial. It is crucial that no saliva can take place.

Critical appraisal

A literature study, which compared the durability of various restorations with inlays and fillings, identified a large number of influencing variables on the durability, for inlays a slightly longer durability with limited informative value could be determined. The lifespan of any form of dental restoration is influenced by a variety of factors that depend on the dentist, dental technician, patient and the materials used. The results of the studies depend on these factors. Studies are often carried out at universities, where the restorations are placed by students according to different specifications and then assessed by students according to different criteria. Numerous studies are financed by the material manufacturers and are therefore not independent. With what precision did the dentist and, if applicable, the dental technician work? What expansion and what degree of destruction of the tooth did the respective restoration have? Which materials - which are subject to constant change due to further developments - in which combination (etchant, primer, enamel and dentine adhesive, composite) were used? Which manufacturer do the ceramic blanks come from? Which gold alloy, which in turn is produced in different degrees of hardness, which manufacturer was used? How was the patient's oral hygiene? Did the patient regularly take advantage of dental screening examinations and professional tooth cleaning? How was the eating behavior and how high was the individual risk of caries of the patients examined? All of these factors have a decisive influence on the service life and thus the results of the studies.

materials

The matrix of composites mostly consists of methacrylate- based plastics . It can also contain traces of formaldehyde, glutaraldehyde and acids. Glass, ceramic and quartz particles (silicates, sands) are used as fillers, and their connection with the plastic is improved by a coating with silanes .

Inorganic phase

The fillers are called the inorganic phase of the composites.

Fillers can be:

  • Glasses or glass ceramics (e.g. barium aluminum glass)
  • Silicates
  • Silicon dioxide

According to the size of their fillers, composites are divided into:

  • Macro filler
  • Microfiller
    • homogeneous microfiller composites
    • inhomogeneous microfiller composites
  • Microfiller complexes
    • Hybrid composites
      • Coarse Particle Hybrid Composites
      • Fine particle hybrid composites
  • Nanoparticles (nano hybrid composites)

The fillers are the inorganic matrix of the composite. The surface of the fillers is silanized in order to enable a connection with the organic matrix (mostly methacrylate cement). The silanization serves as a bonding phase between the organic and the inorganic matrix.

Macro fillers have a size of more than 5 μm and approx. 75% by weight of the macro filler composite. The macro-fillers give this composite a high level of hardness , but only a very rough surface that has a strong tendency to discoloration and abrasion. These first-generation composites were later supplemented by micro-filler composites, in which the fillers have a grain size of less than 0.2 μm and, due to the resulting greater packing density, only make up approx. 50% of the weight of the micro-filler composite. The small grain size gives the material very good polishability . However, the material has poorer mechanical properties: it is not that hard, it has a high level of abrasion, and because of the higher monomer content, the polymerization shrinkage is greater.

In hybrid composites, the fillers make up approx. 85% by weight, 85 to 90% of the fillers being made up of macro-fillers and 10 to 15% of micro-fillers. This combination of large and small filler particles further increases the packing density of the fillers in the composite.

Hybrid composites are further subdivided into:

  • Hybrid composites (average packing size up to 10 μm)
  • Fine particle hybrid composites (average packing size up to 5 μm)
  • Ultra-fine particle hybrid composites (average packing size up to 3 μm)
  • Submicrometer hybrid composites (mean packing size down to less than 1 μm).

In nano-hybrid composites, nanoparticles with particle sizes below 20 nm are used as fillers. The nanoparticles can make up to 40% by weight of the composite without changing the viscosity of the composite. This nano-gel, in which sol-gel processes take place, is filled with additional fillers (macro or micro filler) so that a hybrid composite is created.

Organic phase

The organic phase of the composite is usually a methacrylate ( acrylic ), which is radiation-hardened . There are hydroxyethyl methacrylate (HEMA), triethyleneglycol dimethacrylate (TEGDMA) or Bisphenolglycidylmethacrylat (BisGMA) was used.

In addition to the actual monomer as the main component of the organic phase, BisGMA composites, for example, contain many other components:

  • Mono-, di- and triacrylates (as comonomers) - see: Copolymer
  • Camphorquinone or phenylpropanediol (as initiator of photopolymerization after illumination with the blue light of the polymerization lamp)
  • Toluidine (as an accelerator of photopolymerization)
  • Hydroquinone (as an inhibitor of photopolymerization so that it does not start during the normal day)
  • Benzophenone (as a UV stabilizer so that the plastic filling remains color-stable in the patient's mouth over the years)
  • Colors and pigments (for coloring the plastic filling)

Composite phase

The silanization serves as a composite phase between the organic matrix (methacrylic) and the inorganic matrix (fillers). Silanes can chemically bind glass to an organic matrix. On the one hand, the silanol groups of the silane enter into a condensation reaction with the glass surface of the fillers. On the other hand, there is a covalent bond between the methacrylic acid group of the silane and the matrix plastic of the organic phase.

Polymerization shrinkage

The polymerization shrinkage of composites is in the order of 1 to 6 percent. The polymerization shrinkage leads to the formation of a marginal gap ( microleakage ) between the tooth and the filling material. During the polymerization of the monomers, the volume of all filling materials with added monomers is reduced. This is due to the fact that the distance between the monomer molecules is approx. 4 Å , while the distance between the carbon atoms after the polymerization is only about 1.9 Å.

In order to counteract and reduce polymerisation shrinkage, the various forms of fillers were developed.

The dentist can reduce the polymerization shrinkage by preparing the smallest possible cavities (volume reduction) and by specifically selecting composites with low polymerization shrinkage. The polymerisation shrinkage is partially compensated by multi-layer technology. The marginal gap enables bacteria, chemical substances and liquids to pass between the cavity wall and the composite filling. This marginal gap is usually not clinically detectable, but only verifiable in experimental in vitro studies. As a result of these marginal gaps, tooth fractures can occur on the edge of the filling, as well as hypersensitivity of the tooth (postoperative hypersensitivity). Secondary caries, which was previously feared, only rarely occurs due to the marginal gap.

Fluidity

According to their flowability , composites are divided into:

  • highly viscous, packable composites - high filler content
  • Low-viscosity, flowable composites - reduced filler content - as an intermediate layer under the packable composites

Polymerization

According to the type of polymerization mechanisms, composites are divided into:

  • chemically hardening composites (two-component system)
  • light-curing composites (one-component system)
  • dual-curing composites (light-curing and chemical-curing at the same time; two-component system)

Chemically curing composites

The first generation composites in the 1970s were chemically curing composites. These are two-paste systems or powder-liquid systems. The polymerization process began when the two components were mixed. These first composites had a very high pulp toxicity, so that a correctly placed underfill was necessary. Otherwise, inflammation and death of the pulp (chemotoxic pulpitis ) very often occurred . Because of the slow setting of the chemically hardening composites, there are only slight tensions in the material, as these can even out during hardening. In addition, even thick layers are certain to harden. The disadvantage of chemically curing composites has been shown to be that they cannot be used for layering, since the total curing time would be impractically long due to the low rate of polymerization. Unlike light-curing composites, their curing time cannot be controlled. They also have a relatively thick oxygen inhibition layer of around 300 μm and are not very color-stable.

Polymerization lamp illuminating a composite filling

Light-curing composites

Light-curing composites are the most common. The polymerization process is started by illuminating with the blue light of a polymerization lamp . The light energy, with a certain wavelength in the range of blue visible light, activates a chemical initiator (photoinitiator, starter) in the composite, which, together with an accelerator (accelerator), sets the polymerization in motion so that the monomer enters the organic phase Polymer is transferred. The initiator forms radicals which lead to the polymerisation of the composite. Camphorquinone , which absorbs light with a wavelength of 440 to 480 nm and is activated as a result, or phenyl propanediol, which is activated by light with a wavelength of 300 to 450 nm, serves as initiator . The hardening of thick layers is not always guaranteed because of the reduced penetration of light into deeper layers.

The advantage of light-curing composites is the higher degree of polymerization. Less monomer remains in the polymerized filling, which is why it is more stable against abrasion or discoloration for years. Another advantage is the better color stability and the better overall aesthetic results. In addition, these materials can be processed and modeled for as long as required in each case, since curing is only started with the targeted use of light. This also enables a multilayer technique with which the polymerization shrinkage can be partially reduced. Because of the low depth of hardening, a multi-layer technique is often unavoidable.

The polymerization is hindered (inhibited; polymerization inhibitors) by oxygen or by eugenol . Eugenol is used in some root filling materials for root canal treatment , which is why composite fillings are only made a few days after such root fillings have hardened.

Oxygen inhibition layer

The oxygen enters the filling surface from the surrounding air. During the polymerization, this leads to the formation of a thin, superficial smear layer of unpolymerized or insufficiently polymerized composite. However, this oxygen inhibition layer is of no further importance for the quality of the composite filling, as it is very thin and is removed during polishing or functional use of the filling (chewing, brushing teeth). If the composite filling is made with a plastic band lying on the material as a matrix , then this leads to oxygen exclusion on the corresponding surfaces and an oxygen inhibition layer does not form here. With the multi-layer technique, the oxygen inhibition layer is even an advantage and wanted, as the next new composite layer applied chemically adheres particularly well to this layer.

The shrinkage of the composite filling to the light source, which has been propagated for years, has ultimately proven incorrect in studies. The direction of shrinkage is much more dependent on the cavity design and on the adhesion to the hard substance.

Dual-curing composites

Dual curing composites are used when the supply of light to the composite material is partially excluded. This is the case with mostly opaque ceramic inlays, partial or full crowns. The supply of light from the side through the hard tooth substance usually fails here, as this leads to a reduction in luminance of 90 to 99%. Light-curing dual cements are only cured with light at the edges that can be reached, while chemical polymerization takes place in the areas inaccessible to light. This is why these systems are mixed from two components shortly before use. Dual-curing composites still have a very high residual monomer content of up to 45% after curing.

application

  • 1. Tooth with filling in need of renewal

  • 2. Old filling removed

  • 3. Caries removed

  • 4. Areas close to the pulp are covered with drug containing Ca (OH) 2 , etching gel applied

  • 5. Etched, the milky zone of the enamel can be seen

  • 6. Bonding applied, die and light-conducting wedges attached

  • 7. Slight excess of composite applied

  • 8. Filling worked out and polished

First of all, as with any filling, any old filling (Fig. 1) and the caries (Fig. 2) are removed (Fig. 3). The cavity is prepared by etching the enamel edge with high percentage phosphoric acid (35–37%) (Fig. 4). By exposing the enamel prisms , the connection between tooth and filling material is improved, visible in the milky surface of the otherwise high-gloss enamel (Fig. 5). After the cavity has been rinsed and dried, the primer, hydroxyethyl methacrylate (HEMA), which is both hydrophilic and hydrophobic , is applied to the mesh of collagen fibers . Then a thin liquid monomer (bonding) (Fig. 6) is applied and polymerized with blue light. The composites are then introduced into the cavity in layers and cured with blue light (halogen or LED lamp ) (Fig. 7). The layer-by-layer procedure prevents the formation of marginal gaps as a result of the inevitable polymerisation shrinkage of the plastic. Finally, the shaping and removal of excess plastic with grinding tools, as well as the polishing (Fig. 8).

Composite fillings as a cash benefit

Composite fillings on incisors and canines are a statutory health insurance benefit . However, this is only possible as long as this is carried out using the single-layer technique. If insured persons choose additional care for dental fillings, they have to bear the additional costs themselves. In this case, the health insurers must invoice the comparable, cheapest plastic filling as a benefit in kind and a written agreement must be made between the dentist and the insured person before the start of treatment ( Section 28 SGB ​​IV).

literature

  • Paul Weikart: Materials science for dentists. 4th edition. Carl Hanser Verlag, Munich 1966.
  • Gottfried Schmalz, Dorthe Arenholt-Bindslev: Biocompatibility of Dental Materials . Springer, Berlin a. a. 2009, ISBN 978-3-540-77781-6 .

Web links

Commons : composite fills  - collection of images, videos and audio files

Individual evidence

  1. ^ Shenoy, A. (2008). "Is it the end of the road for dental amalgam? A critical review ". Journal of Conservative Dentistry 11 (3): 99-107. doi: 10.4103 / 0972-0707.45247 PMC 2813106 (free full text). PMID 20142895 .
  2. ↑ a b Heintze, SD; Rousson, V. (2012). "Clinical effectiveness of direct class II restorations - a meta-analysis". The journal of adhesive dentistry 14 (5): 407-431. doi: 10.3290 / j.jad.a28390 PMID 23082310 .
  3. ^ Paul Weikart: Material science for dentists , 4th edition, Carl Hanser Verlag, Munich.
  4. ↑ Pulp protection under composite restorations Statement by DGZMK and DGZ (PDF; 37 kB) DZZ 54 99 1998.
  5. ^ Critchlow, S. (2012). "Ceramic materials have similar short term survival rates to other materials on posterior teeth". Evidence-Based Dentistry 13 (2): 49. (Review) doi: 10.1038 / sj.ebd.6400860 PMID 22722415 . Conclusions: “Ceramic materials perform as well as alternative restorative materials for use as inlay restorations. However, a lack of long-term data means that this conclusion can only be supported for periods up to one year for longevity. "
  6. ↑ RT Lange, P Pfeiffer; Clinical evaluation of ceramic inlays compared to composite restorations (2009) Oper Dent. ; 34 (3): 263-72 doi: 10.2341 / 08-95
  7. ↑ Thordrup, M .; Isidore, F .; Hörsted-Bindslev, P. (2006). "A prospective clinical study of indirect and direct composite and ceramic inlays: Ten-year results". Quintessence international (Berlin, Germany: 1985) 37 (2): 139-144. PMID 16475376 .
  8. ↑ Composite resin fillings and inlays. An 11-year evaluation .; U Pallesen, V Qvist; (2003) Clin Oral Invest 7: 71-79 doi: 10.1007 / s00784-003-0201-z
  9. ↑ Direct resin composite inlays / onlays: an 11 year follow-up. JWV Van Dijken; (2000) J Dent 28: 299-306; PMID 10785294 .
  10. ^ J. Manhart, H. Chen, G. Hamm, R. Hickel: Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. In: Operative dentistry. Volume 29, Number 5, 2004 Sep-Oct, pp. 481-508, ISSN  0361-7734 . PMID 15470871 . (Review).
  11. ↑ Direct restorations in the posterior region, statement of the DGZMK and DGZ (PDF; 236 kB), DZZ 60 (10) 2005.
  12. ↑ Goldstein, GR (2010). "The Longevity of Direct and Indirect Posterior Restorations is Uncertain and may be Affected by a Number of Dentist, Patient, and Material-Related Factors". Journal of Evidence Based Dental Practice (Review Article) 10 (1): 30–31. doi: 10.1016 / j.jebdp.2009.11.015 PMID 20230962 . Mean (SD) annual failure rate: amalgam: 3.0% (1.9%), composite fillings: 2.2% (2.0%); Ceramic inlays: 1.9% (1.8%), CAD / CAM ceramic inlays: 1.7% (1.6%); Gold: 1.4% (1.4%); Composite inlays: 2.9% (2.6%).
  13. ↑ Roulet, J.-F .: Degradation of dental polymers. Karger, Munich (1987).
  14. ↑ Kunzelmann, Material Science Komposite ( Memento of the original from June 16, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , University of Munich. @1@ 2Template: Webachiv / IABot / www.dent.med.uni-muenchen.de
  15. ↑ Plastic fillings as a health insurance service , www.medikompass.de, accessed on January 13, 2019.
This text is based in whole or in part on the entry composite in Flexikon , a wiki from DocCheck . The takeover took place on December 10, 2003 under the then valid GNU license for free documentation .