Dental composite build up

Dental composite resins are types of synthetic resins, which are used in dentistry as restorative materials. Dental composite can be used in 2 different ways :

• Direct dental composites are placed by the dentist in a clinical setting. Polymerization is accomplished typically with a hand held curing light. Direct dental composites can be used for filling cavities or small gaps between teeth, minor reshaping of teeth etc.

• Indirect composites are cured outside the mouth, in processing units normally at the dental lab. These composites are used for various types of prostheses : crowns, bridges, inlays, veneers etc.

Indirect composites can be traditionally processed or with the help of computerized systems (CAD/CAM dentistry). The CAD/CAM technique is used especially when inlays or veneers are manufactured.

Adhesive composite bridges are made by attaching a false composite tooth, that is modelled either by the dentist at the office or by the dental technician, to neighbouring teeth with the bonding technique.

Build up technique

When crowns or bridges are manufactured, indirect dental composites are generally applied in multiple layers and positioned only in specially prepared areas on the metal frame. These areas can have small retention beads that will hold the aesthetic material in place.

Most of the times, composite crowns (or bridges) have a metal shell but there are limited situations when it is possible to manufacture full composite crowns.

Metal-composite crowns are often made with a partial veneer that covers only the aspects of the crown that are visible. When aesthetic demands are high, it is possible to cover all sides of the crown with the aesthetic material.

metal composite crowns
with partial veneer and fully covered

Dental composite is applied in several layers (from 2 to 4). After each layer, the restoration is placed in specific processing units where polymerization takes place.

• The first layer is an opaque layer that prevents the metal framework visibility. It has a reduced thickness and its main goal is to block the passage of light.

• More layers may be added, some shade effects are possible, but the aesthetic results are not as good as in the case of porcelain.

• The final gloss is obtained by polishing with specific burs.

Dental acrylic build up

Acrylic resins restorations are still used in certain parts of the world as permanent restorations but their main indication is for temporary crowns or other temporary reconstructions.

The main advantage is their low cost and easy manufacturing but they are significantly inferior to both porcelain and dental composite.

When permanent restorations are design, they will always have a metal shell on which acrylic is placed in specially prepared areas. Most of the times, acrylic will cover only visible areas of the crowns in the form of partial veneers.

metal acrylic dental crown with a partial veneer

Build up technique

Acrylic resins are processed (true polymerization) in specific devices at lower temperatures than ceramic. The build up is made with specific brushes ; the number of layers is lower than in the case of ceramics or dental composite (2, maximum 3 layers).

• The opaque layer is placed just above the metal frame. It masks the metal visibility.

• The next layer (base layer) is usually the last. It is possible to apply different shades to different areas of the tooth but aesthetic results are limited.

• Final gloss is achieved by polishing with special burs.

metal acrylic dental bridge

Temporary crowns are usually manufactured without a metal frame since their main function is to protect the prepared teeth just until the definitive restoration is completed.