Explains how to prepare a tooth for a complete crown, starting with the aims of the preparation such as conserving structure, retention, resistance and margin health. It gives occlusal reduction depths, axial taper and extra reduction needed for metal-ceramic versus all-metal crowns. A table compares knife-edge, chamfer, shoulder and combined finish lines, with notes on the burs used for shoulders. The step-by-step cutting sequence is followed by a table running from preparation through impression, temporisation and casting to cementation.
Topic 39 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 6 sections, about 190 words (3 min of reading), with 13 flashcards.
In this note
Introduction
Principles
The numbers
Finish lines
Sequence
From preparation to cemented crown
Introduction
Tooth preparation is the removal of tooth substance all around the crown to make room for a complete veneer crown. Done well, the occlusal surface keeps its original relief, only smaller, and the widest point of the prepared tooth becomes its finish line.
The numbers
Occlusal reduction about 1.5 mm for metal and about 2.0 mm for metal-ceramic, following the cusp pattern; 1.5 mm on functional cusps at least.
Axial taper about 6° on each wall.
Reduction for material: all-metal crowns need the least; adding porcelain to metal needs at least 1 mm more on the veneered side.
The margin goes no more than 0.5 mm into the gingival sulcus.
Finish lines
Shoulders are cut with a torpedo diamond (Lustig) or a cylinder with a 33° or 45° tapered end (Marxkors).
Sequence
Separate the tooth from its neighbours with a thin diamond, without touching them.
Reduce the occlusal surface with depth grooves.
Reduce the axial walls (facial, lingual, proximal) and form the finish line.
Finish: round all sharp angles and smooth the walls.
Shillingburg's method starts with occlusal reduction, then proximal separation; many clinicians separate proximally first. High-speed diamonds with water cooling are used throughout.
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