Hello. I need

Hello. I need a crown as I’ve had 2 lots of root canal treatment & now have a temporary filling. I am allergic to nickel & possibly other metals – I don’t know which, as one can only get tested for common allergens. I don’t appear to be allergic to gold, most silver, or brass. My dentist says all crowns are as strong as each other, but I have found information suggesting that gold ones are better as they last longer & don’t risk wearing away neighbouring teeth. The laboratory won’t disclose which other metals mix with the gold as they suspect industry spies want the information. My dentist hasn’t replied to my question as to whether the same lab makes the all porcelain crowns as well as the gold. I suspect they all just want to force me, from fear of allergic reaction, to pay double the cost of a gold crown for an all porcelain one. Have I the right to know the metal content used? If so how can I find out? Should I accept perhaps not the best crown for me & double the cost simply because there is a risk of the metals causing me future problems. Should I go elsewhere for treatment – potentially difficult in that my dentist & the treatment quoted is partially funded by the NHS.
Many thanks.