Treatment of tooth fracture and deformation during machining

While zirconia is highly durable, improper handling during dental restoration manufacturing can lead to issues like breakage or deformation. This article outlines common problems faced during zirconia processing and provides practical solutions for technicians to maintain high-quality results.

1. Zirconia Block Breaks During Clamping

• Cause: Uneven force applied to the zirconia block during clamping.
• Solution: Clear any debris under the block, use 3-4 screws to ensure even force, and tighten screws gradually.

2. Breakage During Processing

• Cause: Poor layout, excessive machine vibration, or tool-related issues.
• Solution: Refer to the CAD/CAM manual for proper layout; stabilize the machine to reduce vibrations; if the tool is worn, replace it.

3. Material Falls During Processing

• Cause: Machine tool parameters or poor layout.
• Solution: Ensure that the connecting rod is firmly balanced, and refer to the CAD/CAM manual for proper layout; check the machine’s parameters to correct errors.

4. Fracture During Sintering

• Cause: Rapid heating/cooling or high furnace temperature.
• Solution: Control the heating and cooling speed, following the specified sintering curve, and manage the furnace temperature to prevent fractures.

5. Hidden Cracks or Breakage During Post-Sintering Grinding

• Cause: Localized overheating or poor tool selection.
• Solution: Use water to cool the zirconia during grinding; select appropriate grinding heads to minimize heat buildup; adjust speed as needed.

6. Fracture After Exiting the Porcelain Furnace

• Cause: Excessively high porcelain furnace temperature.
• Solution: Lower the temperature to 600°C or 400°C to avoid overbaking the material.

Tooth Deformation Causes and Solutions

1. Loose or Tight Teeth

   • Cause: Issues with shrinkage ratio, machine parameters, or inaccurate milling.
   • Solution: Verify the shrinkage ratio, recalibrate the milling machine, and adjust parameters accordingly.

2. Long Bridge Deformation

   • Cause: Poor layout or improper sintering curve settings.
   • Solution: Adjust the layout according to CAD/CAM recommendations and use the correct sintering curve for long bridges.