Apicoectomy after root canal?

I have a problematic molar where I first did root canal about 15 years ago. Despite this, it always stayed painful to some degree. Last year I did a retreatment and another root was found. Despite this it still annoys me.
Now I'm thinking to remove it, since I have general health problems, treated so far with slow but good results as a mercury intoxication, but in which the tooth might have an influence. From the radiography it's not visible any cist or similar.
Would it make sense to still try to save the tooth with an apicoectomy?
I've read the " root canal cover up" of Dr. Meining, and he is writing a whole chapter about apicoectomy, but it's a little bit confusing.It looks like he is favorable to the technique.
In case I'll remove the tooth, I'm plannning to leave the space empty, since I don't want a bridge-crown, and not enough money for an implant, that maybe I still don't want anyway.
Are there any retainers available to be put just for the other teeths not to move and create other problems?
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