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| Features of a PFM crown preparation |
For posterior tooth preparation, one should start from occlusal surface, then buccal surface from mesial to distal direction and then move to break the contact areas. After breaking contact points, start doing reduction of lingual surface from mesial towards distal direction.
The above view of the sequence of tooth reduction is of the Author, though, in the book "Fundamentals of Fixed Prosthodontics" by Herbert T. Shillingburg jr., it is given differently. The author found it better suited for himself after modifying the Shillingburg's recommended sequence to get better access.
Always remember the type and final dimensions of your preparations. The recommended dimensions are given in the following tables. Always aim to reduce the tooth surface 0.1-0.2 mm less than the dimension given below so that you can do final finishing and not doing over reduction.
Before making final impression, always check for any irregularity, sharpness, undulations on prepared surfaces and finish lines or any lacunae in your tooth preparation.
As per Shillingberg, the following features should be incorporated in a crown preparation.
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Recommended preparation features of posterior crowns |
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Crown type |
Posterior crown preparation features |
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Occlusal reduction |
Finish line depth and configuration |
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VMC |
1 mm. non-functional cusp 1.5 mm. functional cusp |
0-1.0 mm Chamfer, knife-edge, shoulder or shoulder with bevel |
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HSPC |
2 mm non-functional cusp 2.5 mm functional cusp |
0.8-1.0 mm Shoulder or heavy chamfer |
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PFM |
Same as VMC if metal surface 2 mm for non-functional cusp 2.5 mm functional cusp |
1.2 mm labial shoulder 0.5 mm lingual chamfer |
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Recommended preparation features of anterior crowns |
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Crown type |
Anterior crown preparation features |
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Occlusal reduction |
Finish line depth and configuration |
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PJC |
2 mm. incisally 1 mm- labial & lingual aspect |
0.8-1.0 mm Shoulder |
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RBPC |
2 mm incisally 0.5-1.0 mm-lingual aspect |
>0.4 mm chamfer |
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PFM |
2 mm incisally 0.5-1.0 mm lingual aspect (porcelain guidance requires greater clearance) |
1.2 mm labial shoulder or heavy chamfer 0.5 mm lingual chamfer |
# PJC - Porcelain Jacket Crown
# Where the tooth is tilted or vertical dimension is to be increased, the amount of reduction required will vary.
# Too deep a reduction for diminutive teeth or for long clinical crowns where a metal collar is preferable
