Dental products are specially fabricated materials, designed for use in dentistry. There are many different types of dental products, and their characteristics vary according to their intended purpose.

Temporary dressings

A temporary dressing is a dental filling which is not intended to last in the long term. They are interim materials which may have therapeutic properties. A common use of temporary dressing occurs if root canal therapy is carried out over more than one appointment. In between each visit, the pulp canal system must be protected from contamination from the oral cavity, and a temporary filling is placed in the access cavity. Examples include:

  • Zinc oxide eugenol—bactericidal, cheap and easy to remove. Eugenol is derived from oil of cloves, and has an obtundant effect on the tooth and decreases toothache. It is suitable temporary material providing there are no biting forces on it. It is also contraindicated if the final restorative material is composite because eugenol adversely effects the bond/polymerization process; also, when applied directly on the pulp tissue, it can produce chronic inflammation and result in pulp necrosis. Brands include Kalzinol and Sedanol.

Cements

Dental cements are used most often to bond indirect restorations such as crowns to the natural tooth surface. Examples include:

  • Zinc oxide cement—self setting and hardens when in contact with saliva. Example brands: Cavit, Coltosol.
  • Zinc phosphate cement
  • Zinc polycarboxylate cement—adheres to enamel and dentin. Example brand: PolyF.
  • Glass ionomer cement
  • Resin-based cement
  • Copper-based cement

Impression materials

Dental impressions are negative imprints of teeth and oral soft tissues from which a positive representation can be cast. They are used in prosthodontics (to make dentures), orthodontics, restorative dentistry, dental implantology and oral and maxillofacial surgery.

Because patients' soft-tissue undercuts may be shallow or deep, impression materials vary in their rigidity in order to obtain an accurate impression. Rigid materials are used with patients with shallow undercuts, while elastic materials are used with patients with deep undercuts, as the material must be flexible enough to reach the end-point of the undercut.

Impression materials are designed to be liquid or semi-solid when first mixed, then set hard in a few minutes, leaving imprints of oral structures.

Common dental impression materials include sodium alginate, polyether and silicones. Historically, plaster of Paris, zinc oxide eugenol and agar were used.

Lining materials

Dental lining materials are used during restorations of large cavities, and are placed between the remaining tooth structure and the restoration material. The purpose of this is to protect the dentinal tubules and the sensitive pulp, forming a barrier-like structure. After drilling the caries out of the tooth, the dentist applies a thin layer (approximately 1/2mm) to the base of the tooth, followed by light curing. Another layer might be applied if the cavity is very large and deep.

There are many functions to dental lining materials, some of which are listed below:

  • Lining materials protect the weak tooth from post-operative hypersensitivity, reducing patient discomfort and allowing the tooth to heal at a faster rate after the procedure.
  • Some dental restorative materials, such as acrylic monomers in resin-based materials and phosphoric acid in silicate materials, may pose toxic and irritable effects to the pulp. Lining materials protect the tooth from such irritants.

Calcium silicate-based liners have become alternatives to calcium hydroxide and are preferred by practitioners for their bioactive and sealing properties; the material triggers a biological response and results in formation of bonding with the tissue. They are commonly used as pulp capping agents and lining materials for silicate and resin-based filling materials.

  • Bactericidal due to zinc
  • Thermal and electrical insulator
  • Radiopaque due to zinc
  • Obtundant

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  • Lowest compressive and tensile strength of all linings; can only be used on areas with little or no stress Examples of these materials include zinc oxide, zirconium dioxide, titanium dioxide, barium sulfate, and ytterbium(III) fluoride.
  • Ideally, filling materials should match the surrounding tooth structure in shade, translucency, and texture.
  • Dental operators require materials that are easy to manipulate and shape, where the chemistry of any reactions that need to occur are predictable or controllable.

Direct restorative materials

Direct restorations are ones which are placed directly into a cavity on a tooth, and shaped to fit. The chemistry of the setting reaction for direct restorative materials is designed to be more biologically compatible. Heat and byproducts generated cannot damage the tooth or patient, since the reaction needs to take place while in contact with the tooth during restoration. This ultimately limits the strength of the materials, since harder materials need more energy to manipulate. The type of filling material used has a minor effect on how long they last. The majority of clinical studies indicate the annual failure rates (AFRs) are between 1% and 3% with tooth colored fillings on back teeth. Root canaled (endodontically) treated teeth have AFRs between 2% and 12%. The main reasons for failure are cavities that occur around the filling and fracture of the real tooth. These are related to personal cavity risk and factors like grinding teeth (bruxism).

Amalgam

Amalgam is a metallic filling material composed from a mixture of mercury (from 43% to 54%) and a powdered alloy made mostly of silver, tin, zinc and copper, commonly called the amalgam alloy. Amalgam does not adhere to tooth structure without the aid of cements or use of techniques which lock in the filling, using the same principles as a dovetail joint.

Amalgam is still used extensively in many parts of the world because of its cost effectiveness, superior strength and longevity. However, the metallic colour is not aesthetically pleasing and tooth-coloured alternatives with increasingly comparable properties have been developed. Due to the known toxicity of mercury, there is some controversy about the use of amalgams. The Swedish government banned the use of mercury amalgam in June 2009. Research has shown that while amalgam may increase mercury levels in the human body, these levels are below safety threshold levels established by the World Health Organization and the U.S. Environmental Protection Agency. However, there exist subpopulations whose members, because of inherited genetic variabilities, are more sensitive to mercury than these threshold levels. They may experience adverse effects caused by amalgam restoration, including neural defects caused by impaired neurotransmitter processing.

Composite resin

thumb|Enamel and dentin shades of composite. Other A2 universal shade for direct and indirect restorations, and flowable composite.

Composite resin fillings (also called white fillings) are a mixture of nanoparticles or powdered glass and plastic resin, and can be made to resemble the appearance of the natural tooth. Although cosmetically superior to amalgam fillings, composite resin fillings are usually more expensive. Bis-GMA based resins contain Bisphenol A, a known endocrine disrupter chemical, and may contribute to the development of breast cancer. However, there is no added risk of kidney or endocrine injury in choosing composite restorations over amalgams. or when control of moisture cannot be achieved.

Generally, RMGICs can achieve a better aesthetic result than conventional GICs, but not as good as pure composites.

Compomers

Another combination of composite resin and GIC technology, compomers are essentially made up of filler, dimethacrylate monomer, difunctional resin, photo-activator and initiator, and hydrophilic monomers. The filler decreases the proportion of resin and increases the mechanical strength, as well as improving the material's appearance.

Although compomers have better mechanical and aesthetic properties than RMGIC, they have some disadvantages which limit their applications:

  • Compomers have weaker wear properties.
  • They cannot adhere to tooth tissue due to the presence of resin, which can make it shrink on polymerisation. They therefore require bonding materials.
  • They release low levels of fluoride, so cannot act as a fluoride reservoir.
  • They have high staining susceptibility; uptake of oral fluid causes them to show staining soon after placement.

Due to its relatively weaker mechanical properties, Compomers are unfit for stress-bearing restorations but can be used in the deciduous dentition where lower loads are anticipated.

Cermets

Dental cermets, also known as silver cermets, were created to improve the wear resistance and hardness of glass ionomer cements by adding silver. Their other advantages are that they adhere directly to tooth tissue, and are radio-opaque, which helps with identification of secondary caries when future radiographs are taken.

However, cermets have poorer aesthetics, appearing metallic rather than white. They also have a similar compressive strength, flexural strength, and solubility as GICs, some of the main limiting factors for both materials. In addition, their fluoride release is poorer than that of GICs. Clinical studies have shown cermets perform poorly. All these disadvantages led to the decline in the use of this restorative material.

Indirect restorative materials

thumb|A fabricated indirect restoration (inlay) made of porcelain

An indirect restoration is one where the teeth are first prepared, then an impression is taken and sent to a dental technician who fabricates the restoration according to the dentist's prescription.

Porcelain

Porcelain fillings are hard, but can cause wear on opposing teeth. Their hardness and rigidity enables them to resist abrasion forces, and are good aesthetically as they mimic the appearance of natural teeth.

Nano-ceramic particles

Nano-ceramic particles embedded in a resin matrix are less brittle and therefore less likely to crack, or chip, than all-ceramic indirect fillings. They absorb the shock of chewing more like natural teeth, and more like resin or gold fillings, than do ceramic fillings; at the same time they are more resistant to wear than all-resin indirect fillings. They are available in blocks for use with CAD/CAM systems.

Gold fillings

Gold fillings have excellent durability, wear well, and do not cause excessive wear to the opposing teeth, but they do conduct heat and cold, which can be irritating. There are two categories: cast gold fillings (gold inlays and onlays) made with 14 or 18 kt gold, and gold foil made with pure 24 kt gold that is burnished layer by layer. For years, they have been considered the benchmark of restorative dental materials. However, recent advances in dental porcelains and a consumer focus on aesthetic results have caused the demand for gold fillings to drop. Gold fillings are sometimes quite expensive, but they last a very long time, meaning that gold restorations are less costly and painful in the long run. It is not uncommon for a gold crown to last 30 years.

Other historical fillings

Lead fillings were used in the 18th century, but became unpopular in the 19th century because of their softness. This was before lead poisoning was understood.

According to American Civil War-era dental handbooks, since the early 19th century metallic fillings had been made of lead, gold, tin, platinum, silver, aluminum, or amalgam. A pellet was rolled slightly larger than the cavity, condensed into place with instruments, then shaped and polished in the patient's mouth. The filling was usually left "high", with final condensation—"tamping down"—occurring while the patient chewed food. Gold foil was the most popular filling material during the Civil War. Tin and amalgam were also popular due to lower cost, but were held in lower regard.

One survey of dental practices in the mid-19th century catalogued dental fillings found in the remains of seven Confederate soldiers from the Civil War. They were made of:

  • Gold foil: preferred because of its durability and safety.
  • Platinum: rarely used because it was too hard, inflexible and difficult to form into foil.
  • Aluminum: failed because of its lack of malleability but has been added to some amalgams.
  • Tin and iron: believed to have been a very popular filling material during the Civil War. Tin foil was recommended when a cheaper material than gold was requested by the patient, but it wore down rapidly; even if it could be replaced cheaply and quickly, there was a concern, specifically from Chapin A. Harris, that it would oxidise in the mouth and cause a recurrence of caries. Due to blackening, tin was only recommended for posterior teeth.
  • Thorium: the element's radioactivity was unknown at that time, and the dentist probably thought he was working with tin.
  • Lead and tungsten mixture: probably from shotgun pellets. Lead was rarely used in the 19th century, as it is soft and quickly worn down by mastication, and had known harmful health effects.

Acrylic polymers

Acrylics are used in the fabrication of dentures, artificial teeth, impression trays, maxillofacial / orthodontic appliances and temporary (provisional) restorations. They cannot be used as tooth filling materials because they can lead to pulpitis and periodontitis, as they may generate heat and acids during setting, and in addition they shrink.

Failure of dental restorations

Fillings have a finite lifespan; composites appear to have a higher failure rate than amalgam over five to seven years. How well people keep their teeth clean and avoid cavities is probably a more important factor than the material chosen for the restoration.

Evaluation and regulation of dental materials

The Nordic Institute of Dental Materials (NIOM) performs several tests to evaluate dental products in the Nordic countries. In the European Union, dental materials are classified as medical devices according to the Medical Devices Directive. In USA, the Food and Drug Administration is the regulatory body for dental products.

References

  • User Guide of Dental Impression Material: https://www.youtube.com/watch?v=-keGMbCHC2A
  • Dental Materials Fact Sheet, Dental Board of California, May 2004