What are Indirect Composites?

Sometimes the best dental treatment for a tooth is to use a restoration that is made in a laboratory from a mold. These custom-made restorations, which require two or more visits, can be a crown, an inlay or an onlay. A crown covers the entire chewing surface and sides of the tooth. An inlay is smaller and fits within the contours of the tooth.

An onlay is similar to an inlay, but it is larger and covers some or all chewing surfaces of the tooth. The cost of indirect restorations is generally higher due to the number and length of visits required, and the additional cost of having the restoration made in a dental laboratory. Materials used to fabricate these restorations are porcelain (ceramic), porcelain fused to a metal-supporting structure, gold alloys and base metal alloys and composites.

Indirect laboratory composite is indicated on teeth that required large restorations but have a significant amount of tooth remaining. It is used when a tooth defect is larger than indicated for direct composite and smaller than indicated for a crown. A common situation is fracture of a single cusp on a molar or a thin cusp on a bicuspid. Force analysis is critical to success as high force will fracture composite, tooth structure or separate bonded interfaces. High force is indicated on teeth furthest back in the mouth for example, a second molar receives five times more force than a bicuspid. teeth create immense force and are often altered with recountouring the enamel.

Indirect composite restorations are processed in a laboratory under heat, pressure and nitrogen to produce a more thorough composite cure. Pressure and heat increase cure while nitrogen eliminates oxygen that inhibits cure. Increased cure results in stronger restorations. Strength of laboratory processed composite is between composite and crown strength and requires adequate tooth support.

Tooth preparation requires removal of existing restorations and caries. Thin cusps and enamel are removed in combination of blocking out undercuts with composite, glass ionomer, flowable composite or the like.

Impressions are taken of prepared teeth, models poured and composite restorations constructed at a laboratory. Temporaries are placed and a second appointment made.

At a second appointment, temporaries are removed and a rubber dam placed. Restorations are tried on the teeth and adjusted. Manufacturers directions are followed. In general, bonding is completed on the tooth surfaces and bonding resin precured.

Restorations are seated, excess resin cement is wiped away with a brush and then facial and lingual surfaces are light cured. Interproximal areas are flossed and then light cured. Excess is trimmed with hand instruments and finishing flame shaped burs.

The rubber dam is removed and occlusion adjusted. Surfaces are finished and polished.

One advantage to indirect composites is that they do not excessively wear opposing teeth.However, their strength and durability is not as high as porcelain or metal restorations and they are more prone to wear and discoloration.