Why did the doctor give me resin as the post and core of the metal casting crown?

The crack in your tooth should crack. If amalgam is used, it is brittle and hard, but it is not willful enough, which is easy to cause secondary cracking. Using resin instead of amalgam as post and core can effectively prevent the aggravation of cracked teeth.

Porcelain fused to metal teeth can effectively protect fragile teeth after root canal treatment. After restoration, they can bear a certain chewing force and completely wrap the teeth, so the post and core you said yourself will not break easily. It is correct to choose precious metal porcelain for porcelain teeth, and many advantages are not listed one by one. Under normal circumstances, it will not break, and porcelain restoration can be called permanent restoration. Value for money, this is always the truth. Money is not wasted. But you can't waste money.

After porcelain restoration, periodontal subgingival scaling can be performed. I hope it helps you!