INDIRECT POSTERIOR 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.  Orthodontic low angle cases and large masseter muscles generate high force.  Sharp point contacts from opposing teeth create immense force and are often altered with enamelplasty.  

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.  Tooth preparation requires adequate wall divergence to bond and cement the restoration and ideally, margins should finish in enamel.  The restoration floor is bonded and light cured.  Bonding agent is light cured to stabilize collagen fibers and avoid collapse during restoration placement.  A base of glass ionomer or composite is used if thermal sensitivity is anticipated.   

Restoration retention is judged by bonded surface area, number and location of retentive walls, divergence of retentive walls, height to width ratio and restoration internal and external shape.  Resistance form, reduction of internal stress and conversion of potential shear and tensile forces is accomplished by smoothing sharp areas and creating flat floors as opposed to external angular walls.

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.  Matrix bands are placed prior to etching to contain etch within prepared areas.  Trimming of excess cement where no etching has occurred is easier.  Composite surfaces are silinated and dual cure resin cement applied.  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.

Above defective amalgams are broken and have recurrent decay.  Excavation results in large buccal lingual width and cusp loss from undermining decay.  Extensive tooth loss on the second molar requires a porcelain fused to metal crown following a composite buildup.  The first and second bicuspid are restored with heat processed composite onlays.

Below a very large amalgam restoration is restored with a heat processed composite onlay.  The onlay is used because there is no opposing tooth and therefore, no force onto the restoration.  Normally, a restoration of this size with normal occlusion would require a stronger restoration such as a porcelain fused to metal crown.