One of the most common questions I’m asked as a dental technician is “What is the perfect prep?”. The answer for a posterior is relatively the same for me, regardless of material, other than a full gold crown which will allow for less reduction. For the best result I recommend the following parameters for reduction:
Buccal and Lingual 1.5mm.
Axial walls 1.5mm
Chamfer or Shoulder margin .5-1.0 mm.
TIP: Make sure there is roughly a six degree taper from the margin to the occlusal aspect on all four walls. It is also very important to remember the morphology of the tooth being prepped. The last thing anyone wants is a tooth reduced 2mm. at the cusp tips and only .5 at the central facet.