My New 2 Front Dental Fused to Metal Porcelain Crown Looks So Bright Compare to my Other Teeth Does It Lose Brightness in Time?

The short answer is "no".  My guess is that the crown was a porcelain-fused-to-metal crown, which oftentimes looks considerably brighter than other teeth if the porcelain is the wrong color or the porcelain is too thin over the underlying metal.  Shade A3 is only slightly lighter (i.e. higher in color "value") than shade A3.5.

We can expect natural teeth to get darker over time, not lighter.  Thus the thinking of most cosmetic dentists is to match the shade perfectly (if possible) for when it is placed to match the adjacent teeth.  Or, if you wanted to take into consideration that your adjacent teeth will darken, then make the crown slightly darker. 

You do have two options.  First, bleach your teeth (which won't change the color of your crown), and that may make the shade of the crown closer to your other teeth.  Second, to just have the crown redone.  Oftentimes with shades that are difficult to match we will have our patient go directly to the dental lab and the dental ceramist (who makes the crowns) can custom mix the porcelain color to best match the adjacent teeth.

BTW, shades A3 and A3.5 are very common tooth shade colors.

Unforfunately when porcelain is fused to metal a opaque material is used to block the metal from showing through the porcelain.  If this opaque is too close to the surface it can show through and make the tooth look bright.  There may have been a reason metal was used under the porcelain but most anterior cosmetic crowns are all porcelain which allows the light to transfer through them in a much more natural way to eliminate this problem from occuring.  This is a simple explanation.  I would talk to your dentist about your concerns and there may be ways to improve what you have.

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