Got my reply back from Walter Clifford today. Below is what he had to say about CERAC crowns, as well as some of the other restorative alternatives available:

"There is no such entity in nature as a non-metallic restorative material. NONE WHATSOEVER! (in spite of all of the ads for 'metal-free' restorations). Freshman chemistry courses teach the nature of anions and cations, and anywhere there is an anion, there needs to be a balancing cation. Cations are nearly always metals. There is a substantial difference between frankly reduced (shiny) metal and fully oxidized metal (think sodium in table salt). All restorative products, including ceramics, porcelains, acrylic materials, glass iomomers, etc., will contain metals, albeit they are usually in an oxidized state. CEREC crowns ALL contain oxidized metals. Nearly all CEREC crown materials (we are aware of about 30 different ones) are simply lab-cured and fabricated blanks which are prepared for carving rather than being cast into an impression piece taken from the mouth. In all cases, the resulting crowns will be cemented or bonded into place with similar agents. The CEREC materials are also available in conventional forms for the lab fabricating process using a mouth impression. CEREC crowns are milled at chair-side and can be placed all in one visit. This saves time and is convenient. Otherwise, they are made from the same ingredients as traditional ceramic and porcelain crowns. As to posts, I do not have any extensive list of posts which have been used with crowns. Today, various precious and non-precious alloys can be used to fabricate posts, if needed, and some will be formed from carbon (think aramide) and fiberglass. I suppose stainless steel and aluminum rod stock could be used.

Common metals used in CEREC crowns are the same as used in traditional ceramic and porcelain crowns. The basic lattice structures will either be aluminosilicate (aluminum, silicon and oxygen) or zirconia (zirconium, silicon and oxygen). Used with these basic lattice materials will be one or more other metals such as antimony, barium, boron (metalloid), cerium, cobalt, cadmium, europium, gallium, hafnium, indium, iron, lanthanum, lithium, manganese, molybdenum, neodymium, nickel, niobium, osmium, rhenium, rhodium, rubidium, ruthenium, samarium, strontium, tantalum, titanium, tungsten, vanadium, ytterbium, yttrium and zinc. I'm certain that I have forgotten a few, not to mention the classical presence of copper, gold, palladium, platinum and silver for framework compatibility. Exact composition is determined by manufacturer and brand or trade name."

I think at this point, my decision for replacement crowns would have to be between a zirconium-based CERAC crown, or a Diamondlite crown. I wish that I knew exactly what kinds of metals were contained in the Diamondlite crowns, as it seems that many on this board have used these with success. Would anyone on the forum have any links to any information about the Diamondlite crown composition?

Thanks,
Jason