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Dental fillings are inserted as restorations in the treatment of dental cavities, after drilling out the cavities. The purpose of drilling is to remove the enamel and dentin that has had its structural integrity compromised by the invasion of acid-producing bacteria. However, once the infected hard tissues have been removed, the resulting cavity preparation must be filled in order to restore structural integrity to the tooth. This will prevent further damage to the tooth and hopefully avoid the eventual need for the tooth to be extracted.
Types
Amalgam (also called silver filling)
- See also: Dental amalgam controversy
After widespread adoption and wildly varying standards, the multitude of formulas for making amalgams were standardised into the gamma-2-phase amalgam formula in 1895.
The gamma-2-phase amalgams contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:
Around 1970, the ingredients changed for manufacturing cost reasons to the new non-gamma-2 form. The gamma-2-free amalgams (sometimes referred to as "high-copper" amalgams) contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:
- > 40% silver (Ag)
- < 32% tin (Sn)
- < 30% copper (Cu)
- < 2% zinc (Zn)
- < 3% mercury (Hg)
The possible difference in toxicology between the two has not been studied conclusively. Amalgams continue to be used today because they are hard, durable and inexpensive.
Composite resin (also called white or plastic filling )
Composite resin fillings are a mixture of powdered glass and plastic resin, and can be made to resemble the appearance of the natural tooth. They are strong and durable and cosmetically superior to silver or dark grey colored amalgam fillings. Composite resin fillings are usually more expensive than silver amalgam fillings. Bis-GMA based materials contain Bisphenol A a known endocrine disrupter chemical. PEX based materials do not.Most modern composite resins are light-cured photopolymers. Once the composite hardens completely, the filling can then be polished to achieve maximum aesthetic results. Composite resins experience a very small amount of shrinkage upon curing, causing the material to pull away from the walls of the cavity preparation. This makes the tooth slightly more vulnerable to microleakage and recurrent decay. With proper technique and material selection, microleakage can be minimized or eliminated altogether.
Besides the aesthetic advantage of composite fillings over amalgam fillings, the preparation of composite fillings requires less removal of tooth structure to achieve adequate strength. This is because composite resins bind to enamel (and dentin too, although not as well) via a micromechanical bond. As conservation of tooth structure is a key ingredient in tooth preservation, many dentists prefer placing composite over amalgam fillings when possible.
Generally, composite fillings are used to fill a carious lesion involving highly visible areas (such as the central incisors or any other teeth that can be seen when smiling) or when conservation of tooth structure is a top priority.
Composite resin fillings require a clean and dry surface to bond correctly with the tooth, so cavities in areas that are harder to keep totally dry during the filling procedure may require a less moisture-sensitive filling. The use of a rubber dam is highly recommend.
Glass Ionomer Cement
These fillings are a mixture of glass and an organic acid. Although they are tooth-colored, glass ionomers vary in translucency. Although glass ionomers can be used to achieve an aesthetic result, their aesthetic potential does not measure up to that provided by composite resins.The cavity preparation of a glass ionomer filling is the same as a composite resin; it is considered a fairly conservative procedure as the bare minimum of tooth structure should be removed.
Conventional glass ionomers are chemically set via an acid-base reaction. Upon mixing of the material components, there is no light cure needed to harden the material once placed in the cavity preparation. After the initial set, glass ionomers still need time to fully set and harden.
Glass ionomers do have their advantages over composite resins:
1. They are not subject to shrinkage and microleakage, as the bonding mechanism is an acid-base reaction and not a polymerization reaction.
2. Glass ionomers contain and release fluoride, which is important to preventing carious lesions. Furthermore, as glass ionomers release their fluoride, they can be "recharged" by the use of fluoride-containing toothpaste. Hence, they can be used as a treatment modality for patients who are at high risk for caries. Newer formulations of glass ionomers that contain light-cured resins can achieve a greater aesthetic result, but do not release fluoride as well as conventional glass ionomers.
Glass ionomers are about as expensive as composite resin. The fillings do not wear as well as composite resin fillings. Still, they are generally considered good materials to use for root caries and for sealants.
Resin-Ionomer Cement
A combination of glass-ionomer and composite resin, these fillings are a mixture of glass, an organic acid, and resin polymer that harden when light cured. (The light activates a catalyst in the cement that causes it to cure in seconds.) The cost is similar to composite resin. It holds up better than glass ionomer, but not as well as composite resin, and is not recommended for biting surfaces of adult teeth.In general, resin-ionomer cements can achieve a better aesthetic result than conventional glass ionomers, but not as good as pure composites.
Porcelain (ceramic)
Porcelain fillings are hard, but can cause wear on opposing teeth. They are brittle and are not always recommended for molar fillings.Gold
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 of gold fillings, 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. Recent advances in dental porcelains and consumer focus on aesthetic results have caused demand for gold fillings to drop in favor of advanced composites and porcelain veneers and crowns. Gold fillings are usually quite expensive, although they do last a very long time. It is not uncommon for a gold crown to last 30 years in a patient's mouth.Other historical fillings
Lead fillings were used in the 1700s, but became unpopular in the 1800s because of their softness and before lead poisoning was understood.According to U.S. Civil War-era dental handbooks from the mid-1800s, since the early 1800s metallic fillings had been used, made of lead, gold, tin, platinum, silver, aluminum, or amalgam. A pellet was rolled slightly larger than the cavity, condensed into place with instruments, and then shaped and polished in the patient's mouth. The filling was usually left "high", with final condensation — "tamping down" — occurring through the patient's chewing of food. Gold was the preferred filling material during the Civil War, with amalgam being the most common due to cost. Tin was also popular due to cost, but was held in lower regard.
One survey * of dental practices in the mid-1800s catalogued dental fillings found in the remains of seven Confederate soldiers from the U.S. Civil War; they were made of:
- Thorium — radioactivity was unknown at that time, and the dentist probably thought he was working with tin
- Lead and tungsten mixture, probably coming from shotgun pellets
- Tin and iron
- Amalgam
- Three soldiers had gold fillings
Replacement fillings
Fillings have a finite lifespan: an average of 12.8 years for amalgam and 7.8 years for composite resins*. Fillings fail because of changes in the filling, tooth or the bond between them.
Amalgam fillings expand with age, possibly cracking the tooth and requiring repair and filling replacement. Composite fillings shrink with age and may pull away from the tooth allowing leakage. As chewing applies considerable pressure on the tooth, the filling may crack, allowing seepage and eventual decay in the tooth underneath.
The tooth itself may be weakened by the filling and crack under the pressure of chewing. That will require further repairs to the tooth and replacement of the filling.
If fillings leak or the original bond inadequate, the bond may fail even if the filling and tooth are otherwise unchanged.
See also
References
- Dental Materials Fact Sheet, Dental Board of California, May 2004
"Dental fillings"