Why is the metal partly left uncovered in white gold crowns?
I find it irritating at the backside of my upper front teeth.
It slightly reminds me of testing the voltage of batteries by
touching the electrodes with your tongue.

En finne igen.

     If you have an unlike metal (not gold) filling also, you may
actually have a de facto battery in your mouth, saliva acting
as electrolite.  This would explain the taste when you touch it.
If so, a sensitive ammeter or voltmeter touched to the two
different metals would give a reading.
                    earl

With any porcelain bonded to metal crowns the inside margin is left as metal.
This can be because there is not enough room for porcelain and metal, or a metal
margin is prefered as it is usually more accurate than a porcelain margin, and
aesthetic considerations are not so important for a margin that does not show.

White "gold" doesn't have a lot of gold in it so electrolytic activity is not
unusual.
--
Graham Lovis
Leeds England

Dental tech that made your crown wasn"t big on esthetics.