*Why are temporary crowns usedin restorative dentistry? Give twoexamples of different types oftemporary crowns manufacturedwithin the laboratory.

*Why are temporary crowns usedin restorative dentistry? Give twoexamples of different types oftemporary crowns manufacturedwithin the laboratory.

1. Like other interim restorations, it serves until a final restoration can be inserted.

2. Where medium- to longer-term temporization is envisaged (some months or more), consideration should be given to an indirect temporary restoration, which is constructed in the dental laboratory.

3. Functions:

   • Protect the remaining tooth structure and prevent sensitivity
     • Some 30 000 to 70 000 dentinal tubules are opened per square millimetre during tooth preparation. The passage of oral bacteria into the freshly cut dentine must be minimized as this will cause pulpal inflammation, which manifests as sensitivity if the dentine is exposed to stimuli from the oral environment such as hot, cold and sweet.
   • Shape the gum tissue properly
   • Provisional restorations offer dental aesthetics purposes especially for anterior teeth.
   • Patient can evaluate the aesthetic of the temporary crown so that it can be changed in the definitive restoration.
   • Maintain the tooth’s function, masticatory function for posterior teeth can be restored as well.
   • Prevent teeth shifting, Overeruption of opposing teeth and drifting of adjacent teeth can be prevented by providing provisional restoration.
   • It also allows the area to be cleaned more effectively and thus maintains a state of gingival health. This decreases the incidence of gingival inflammation and bleeding at the time of fitting the definitive restoration, which is particularly important when the restoration is being bonded using a hydrophobic resin-based composite material.

4. Example 1-

   • An acrylic, such as heat- or self-cured polymethylmethacrylate
     • Advantages
       • • Strong • High wear resistance • Good aesthetics • Easy to modify
     • Disadvantages
       • • Polymerisation shrinkage - can affect fit • Setting reaction exothermic - can cause damage to dental pulp • Unreacted monomer can damage gingivae and pulp

5. Example 2-

   • ceramic bonded to metal – non-precious metal alloys are normally chosen on grounds of lower cost.-
     • Advantages
       • • Very strong and durable • Highly resistant to wear • Porcelain can mimic natural tooth appearance
     • Disadvantages
       • • Aggressive tooth reduction required • Porcelain can rapidly wear opposing teeth if its surface becomes rough • Porcelain prone to impact fracture