Why tooth preparation design is important
· Smooth edges result in lower stress on the crown. This lower stress decreases the percentage of fractures occurring.
· Ceramic restorations require a passive fit.
· Uniform reduction results in excellent ceramic strength.
· Sufficient reduction leads to the best aesthetic results.
· Digital scanners read smoother preparations with more accuracy.
Preparation guidelines for an anterior zirconia crown
· When prepping a tooth for an anterior Zirconia crown, you will need to ensure sufficient room for the wall thickness to have a minimum of 0.3 mm and ideally between 1.0 mm and 1.5 mm, or 1.8 to 2.0 mm incisal reduction.
· There should be a visible and continuous circumferential chamfer with at least a 0.5 mm reduction at the gingival margin.
· The horizontal and vertical preparation of the tooth should have an angle of approximately 5°, and a bevel is not advisable.
· All the incisal edges should be rounded, and the lingual aspect of the anterior should be reduced with a football diamond to create a concave lingual.
Preparation guidelines for a posterior zirconia crown
· When prepping a tooth for a posterior Zirconia crown, you will need to ensure sufficient room for the wall thickness to have a minimum of 0.5 mm and ideally between 1 mm and 1.5 mm or 1.5 to 2 mm occlusal reduction.
· The prep should be tapered between 4°and 8°. It will also need to have a visible and continuous circumferential chamfer, and a reduction of at least 0.5 mm is required at the gingival margin.
· Just as with the preparation for an anterior crown, a bevel is not recommended. Ensure that all occlusal edges should be rounded.
· Shoulder and Chamfer preparations are ideal for zirconia. Feather Edge preparations are not recommended but can be acceptable for full-Zirconia crowns. Check with your dental laboratory to see if their fabrication process will allow for this prep form.