Monolithic Zirconia Restorations Can Fracture!

Even though monolithic zirconia restorations are very hard with a flexural strength ranging from 900 to 1200 mpa, that doesn't mean that monolithic zirconia can't fracture! Microcracks can be introduced into the monolithic zirconia at the time of occlusal adjustment and during polishing. Excessive trauma, vibration or heat may be the underlying causes of these cracks in monolithic zirconia. Follow these steps when adjusting or polishing monolithic zirconia and exposed zirconia frameworks. An electric handpiece will be more efficient than an air turbine because it maintains its torque at slow speeds.

Steps for adjusting monolithic zirconia:

• Use a slow speed friction grip handpiece operated at a maximum speed of 20,000 rpm.  Example: Brasseler TiMax X20L, which has a 1:1 ratio slow speed electric handpiece attachment.
• Use a fine or extra fine diamond bur only!  Example: Brasseler Dialite Diamond 8369DF 025 or 8369DEF 025.
• Use air and water spray to keep the diamond and ceramic cool.
• Use a light touch.  Let the torque of the handpiece and bur do the cutting.

Steps for polishing monolithic zirconia:

• Use a slow speed latch handpiece attachment run at a maximum speed of 10,000 rpm.  Example: Brasseler TiMax X25L.
• Use a light touch to avoid generating heat.
• A medium grit rubber polisher should be used for initial polishing.  Example: Brasseler Dialite ZR (W18 MZR Knife, W17 MZR Cup, W16 MZR Point).

• A fine grit rubber polisher should then be used for high shine.  Example: Brasseler Dialite ZR (W18 FZR Knife, W17 FZR Cup, W16 FZR Point).

Following these steps induces minimal trauma to the ceramic, and provides a very efficient process for adjusting and polishing zirconia restorations.

Dr. Bob Winter, D.D.S., Spear Faculty and Contributing Author