Full Gold Crowns - Posting #5

Full gold crown preparations are done to conserve as much tooth structure as possible, provide the best adaptation at the margins (second only to what is possible with exposed margins on inlays, onlays, etc), antagonize the pulp chamber to the minimal extent, and be the most kind to the opposing teeth, particularly when there is a loss of anterior guidance and parafunctional habits create posterior attrition in group function.

While many dentists are quite aggressive about occlusal reduction, for younger patients this can be a really bad idea with the proximity of the pulp and the gingival limitations on crown height and thus retention and resistance form. So the circumstances need to be studied with some care to see how conservative you really need to be, but, in general, a more strategic approach to the crown preparation will require little if any additional time, and yet allow total control of the reduction and/or clearance of the occlusal reduction.

What is the difference between occlusal reduction and clearance? Most of the time there is no difference. If the particular part of the occlusal surface is originally in occlusion, probably it will be waxed into occlusion, and therefore the amount of reduction is geometrically identical to the amount of clearance between the preparation and the opposing surface. When the original tooth is NOT in occlusion and we want it to be, then we will reduce only to the extent that the clearance is adequate to build the occlusal surface of the gold crown in that area - this may be 1.0 mm or 1.5 mm. On the other hand, if the original tooth surface at some point is not in occlusion and we don't want it to be, we simply reduce it the 1.0 or 1.5 mm to get the thickness of the gold right, and we don't care how much clearance there is at the end. If we stop reducing, say, the ML cusp on a mandibular first molar when there is only 1 mm clearance, it will have little reduction and the cusp will be much higher than original and the patient will feel that it is a very sharp area on the crown.

As far as axial reduction is concerned - the major issues involve appropriate wall form, generally flat until sloping gingivally at the gingival .5 mm or so, axial reduction at the gingival margin approximating .5 mm and appropriate taper and reduction to construct the proximal contacts and F/L surfaces with natural contours. Generally, we can select a particular diamond bur that will accomplish the axial reduction with minimal problems if the tip of the bur is kept at the margin, if the gingival position of the margin is appropriate, and the taper is 10-12 degrees. All three of these criteria can be controlled as long as the operator is looking in the correct direction relative to the surface being prepared.

If you would like to ask some questions about the issues mentioned here, or would like to contribute, or are uncertain about anything, feel free to answer this post - we can get a lively discussion going.