Tooth Preparation Guidelines

For many years tooth preparation for metal supported ceramics was as varied as the clinician who performed them. Metal can be cast into any configuration imaginable including sharp angles and tips. It is also strong enough to be polished to a thin edge to accommodate a knife edge margin preparation.

All-ceramic restorations require a totally different mindset when preparing a tooth. Whether the crown is made by press technology or by CAD/CAM technology the guidelines are still the same.

1. First and foremost requirement is a smooth preparation.
Remember, ceramic crowns are a type of glass and any sharp angles or corners create stress points that can lead to fractures.

2. Uniform reduction is necessary for optimal strength and esthetics.
Once again, thin areas compromise strength and esthetics.

Remember
Uniform reduction results in optimum ceramic strength
Adequate reduction leads to better esthetics
Smooth edges result in lower stress
Lower stress decreases potential for fracture
Ceramic restorations require a passive fit
Scanners read smooth preparations more accurately

Guidelines
Uniform, circumferential, tooth reduction of 1.0-1.5 mm
Circumferential chamfer margin
Occlusal reduction of 1.5-2.0 mm
Rounded line angles
Reduce linguals of anteriors with football diamond to create concave lingual

Another very important point to understand is how crowns are milled with CAD/CAM. The preparation needs to be smooth for an accurate scan, but also so the milling burs can reach every area. The burs used are 1mm in diameter at the tip. If the preparation is left with a sharp incisal edge or sharp line angles on the axial wall, or even sharp irregularities on the margin the burr will not be able to reach into those areas leaving a crown that will not seat completely.

We hope these guidelines will help you.

At Oral Design Dental Laboratories Inc. we have been working with all-ceramic restorations for over 25 years.

Feel free to contact us with any questions.

info@oraldesign.ca