Congenital lack of lower R M2; over-eruption of corresponding upper M2. Can small flat implant be used?

Congenital lack of lower R caudal molar (M2); no wisdom teeth bilaterally. Upper R M2 over-erupting--> painful ulcers gum. The only offered treatment in past was to wait until pain then upper molar extraction. Got 2nd opinion: told implant not option due to over-eruption upper molar. 29 with great dental health & $ is not (never has been) concern. Q: Can I have the upper molar shortened (root canal) &FLAT dental implant to protect gum & provides resistance to the bite?

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