Mechanically, gold would usually be the superior choice of any dental material. Lasts a lifetime. However, how pure is it? Plus, the potential of reactions with existing metals already in the mouth is an unfortunate risk/reality and maybe a very bad choice. See below:

http://www.yourhealthbase.com/amalgams.html

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Trigeminal neuralgia linked to amalgam fillings
JACKSONVILLE, FLORIDA. Dr. William Cheshire, a physician at the Mayo Clinic, reports on a case where a woman's trigeminal neuralgia (tic douloureux) was traced to a galvanic reaction between an amalgam filling and an adjacent gold-alloy crown. Consumption of tomatoes and other acidic foods produced intense jolts described as being like those of an "electrical battery". The jolts in turn resulted in excruciating pain in the trigeminal nerve. Replacing the amalgam filling with a composite resolved the problem. Dr. Cheshire points out that dissimilar metals in contact with saliva can form a galvanic cell which can generate electrical currents with several hundred millivolts of potential. He points out that many patients with trigeminal neuralgia describe their pain in terms of "electrical" jolts and concludes that his patient's neuralgia may well have been triggered by the galvanic reaction between the amalgam filling and the gold crown.
Cheshire, William P., Jr. The shocking tooth about trigeminal neuralgia. New England Journal of Medicine, Vol. 342, June 29, 2000, p. 2003 (correspondence)


The cerec porcelain is an improvement from the old style porcelain crowns. It expands and contracts with heat. It does not require a metal base, plus alot more tooth structure is conserved. It is unlikely to create any reaction with existing metals already in the mouth and seems to be one of the more biocompatible materials around.

I have spoken with a few biologic dentist over emails over the years, and cerec porcelain was one of the materials quite a few of them were using. More seem to be coming onboard. Not only biologic, but mainstream also. One of these dentists I spoke to was trained not only in the mechanics of dentistry, but also oral toxicology. He uses only the dental materials that both perform well physically, but are also alot more biocompatible. His main one is cerec porcelain. He also uses some strong composite material too that he favours over others.

The toxicity potential is as important (if not more perhaps) than the mechanics. My mix metal mouth at age 15 was disastrous for my health on all levels. I developed blurred vision, severe depression, OCD, pallor, muscle tics, burning sensations in the mouth and throat, fatigue, etc etc. The list goes on.

Some people may do get away with it, but I personally wouldn't take the risk. I thought I was quite a healthy person before that. Evidentally I wasn't, or I doubt I'd have been so suseptible.

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Dental alloys affect cellular energy production
NOTE: We usually do not report test tube or animal experiments, but thought we would make an exception in this case. The findings that commonly used dental alloys may interrupt the normal function of human cells is a first and could have wide-ranging effects.

BIRMINGHAM, ALABAMA. Although nickel is known to be carcinogenic in humans it is still widely used in certain dental alloys. Researchers at the University of Alabama now report that other components of dental alloys (beryllium, chromium, and molybdenum) as well as nickel affect the very basic function of human cells - the production of energy (ATP). ATP is produced in the mitochondria of cells and involves highly oxidative processes. It is becoming increasingly clear that abnormalities in the mitochondrial processes are important causes of human disease. Some researchers believe that a slowing down of these processes actually heralds the very first stage in the proliferation of abnormal cells and cancer.
The Alabama researchers exposed cultures of human gingival (gum) cells to solutions of nickel, beryllium, chromium (tri- and hexavalent) and molybdenum (hexavalent) for periods of 24 and 72 hours. They then measured the energy production and oxygen consumption of the cells' mitochondria in the various solutions. Cells in contact with nickel or hexavalent chromium were most affected and showed decreased ATP (energy) production as well as a decrease in oxygen consumption. The effects of beryllium, molybdenum, and trivalent chromium were similar, but less pronounced. The researchers conclude that their findings may be the first indication that some components of common dental alloys may be detrimental to human health. They urge further research to establish possible synergisms between mixtures of these different metals on mitochondrial energy production. [54 references]
Messer, R.L.W., et al. An investigation of fibroblast mitochondria enzyme activity and respiration in response to metallic ions released from dental alloys. J Biomed Mater Res, Vol. 50, 2000, pp. 598- 604