Dental composite

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Dental composites are a group of restorative materials used in dentistry. As with other composite materials, a dental composite typically consists of a resin-based matrix, such as a methacrylate resin like urethane dimethacrylate (UDMA), and an inorganic filler such as silicon dioxide silica. Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass-ceramics. The filler gives the composite wear resistance and translucency. A coupling agent such as silane is used to enhance the bond between these two components. An initiator package begins the polymerization reaction of the resins when external energy (light/heat etc.) is applied. A catalyst package can control its speed.

[edit] Direct Dental Composites

Direct dental composites can be used for:

Filling cavities in teeth, as fillings, inlays and/or onlays
Filling gaps (diastemas) between teeth using a shell-like veneer or
Minor reshaping of teeth
Partial crowns on single teeth

Direct dental composites are placed by the dentist in a clinic setting. Polymerization is accomplished typically with a handheld curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved.

The main advantage of a direct dental composite over traditional materials such as amalgam is improved aesthetics. Composites can be made in a wide range of tooth colours allowing near invisible restoration of teeth. Composites are glued into teeth and this strengthens the tooth's structure. The discovery of acid etching of teeth to allow a micromechanical bond to the tooth allows good adhesion of the restoration to the tooth. This means that unlike silver filling there is no need for the dentist to create retentive features destroying healthy tooth. The acid-etch adhesion prevents microleakage, however, all white fillings will eventually leak slightly. Very high bond-strengths to tooth structure, both enamel and dentine can be achieved with the current generation of dentine bonding agents. The downside to composite when compared to amalgam are a shorter lifespan of the filling, and the high likelyhood of requiring root canal therapy if the failure of the filling is not caught quickly. Amalgam fillings may crack a portion of the tooth off, but otherwise tend to fail at a much slower rate.

Initially, composite restorations in dentistry were very prone to leakage and breakage due to weak compressive strength. In the 1990s and 2000s composites were greatly improved and are said to have a compression strength adequate enough for them to be placed in back teeth. The placement of composite requires meticulous attention to procedure or it may fail prematurely. The tooth must be kept perfectly dry during placement or it will likely fail to adhere to the tooth. Composites are placed while still in a soft, dough-like state, but when exposed to light of a certain blue wavelength, they polymerize and harden into the solid filling. It is challenging to harden all of the composite, since the light often does not penetrate more than 2-3 mm into the composite. If too thick an amount of composite is placed in the tooth, the composite will remain partially soft, and this soft unpolymerized composite could ultimately irritate or kill the tooth's nerve. A good dentist will place a deep filling in numerous increments, curing each 2-3mm section fully before adding the next. In addition, the clinician must be careful to adjust the bite of the composite filling, which can be tricky to do. If the filling is too high, even by a subtle amount, that could lead to chewing sensitivity on the tooth. A properly placed composite is comfortable, aesthetically pleasing, strong and durable, and could last 10 years or more. (By most North American insurance companies 2 years minimum)

[edit] Indirect Dental Composites

Indirect dental composites can be used for:

Filling cavities in teeth, as fillings, inlays and/or onlays
Filling gaps (diastemas) between teeth using a shell-like veneer or
Reshaping of teeth
Full or Partial crowns on single teeth
And even bridges spanning 2-3 teeth

This type of composite is cured outside the mouth, in a processing unit that is capable of delivering higher intensities and levels of energy than handheld lights can. Indirect composites can have higher filler levels, and are cured for longer times. As a result, they have higher levels and depths of cure than direct composites. For example, an entire crown can be cured in a single process cycle in an extra-oral curing unit, compared to a millimeter layer of a filling.

As a result, full crowns and even bridges (replacing multiple teeth) can be fabricated with these systems. A stronger, tougher and more durable product is likely.