Most often, a fixed dental indirect restoration (crown or bridge) consists of 2 parts :

• a metal or zirconium frame that provides strength and support
• aesthetic materials (porcelain, composite etc.) that are fused on the metal (or zirconium) substructure and aim to restore physiognomy and aesthetics

There are some exceptions: all porcelain, full metal, full zirconia or full gold restorations.

The perfect fitting of the substructure on the abutment teeth is essential. The dentist has the means by which he can determine how well the metal frame fits on the prepared teeth and the changes that have to be taken if fitting is not perfect.

metal frame fitting for a dental bridge

If a small restoration is designed (dental crown, small dental bridge), this stage is optional but very useful. However, in case of a large restoration, it is not advisable to skip this step. The dental technician constructs the metal or zirconium core and sends it to the dental office for this intermediate appointment.

Procedure

The fitting of the metal structure is perfect when several conditions are met :

• The insertion of the metal frame on the abutment teeth should be smooth and without applying unnecessary pressures. The structure must be able to fit onto the abutment teeth simultaneously until reaching the final position.

  If certain obstacles prevent the perfect fitting, they must be removed. There are 2 way of doing this :

  • adjustments are made from the abutment teeth
  • adjustments are made from the inside of the metal frame

  Normally, such adjustments are minimal.

  
  

• The metal structure should not be "too loose" on the abutment teeth because this lowers the restoration stability and grip.

  
  

• The frame must slightly penetrate below the gumline of the prepared teeth. Most often, tooth preparation goes bellow the gumline to mask the line of tooth-to-restoration contact.

  
  

  

  extended porcelain dental bridge : metal frame perfectly fits

  
  

• After the metal frame is fully inserted, the dentist examines the existing space to the opposite teeth. This operation is performed when the jaws are fully closed.

  There should be enough space to properly build up all porcelain layers that will be fused on top of the metal frame. Normally, on the occlusal side of teeth, ceramics has a 1.5 to 2 mm thickness.

  

  metal frame fitting when
  the jaws are closed in static occlusion

  
  

• Enough space must remain between the metal frame and the adjacent teeth to properly buildup all ceramic layers. The metal frame should not be too thick (generally, it has a 0.3 to 0.5 mm thickness for porcelain restorations).

  
  

• When the occlusal side of the restoration will remain bare metal (in case of acrylic, full metal or some composite restorations), the bite can be adjusted in this stage. In this situation, it is very important not to leave the restoration too high or too low.

  
  

It is possible to make another bite registration after the framework was fully inserted onto the abutment teeth. This registration is made on top of the framework. The impression gives the technician extra details about the space between the frame and the opposing teeth.

The session ends with the re-fixing of the temporary crowns (if they were constructed). The metal or zirconium structure along with the impressions and other potential indications are sent back to the dental laboratory for the application of the aesthetic materials.