Contrary to what I often hear, do NOT bathe it in acid!
My thought on this is the wood is tightly driven into the pockets that were driven up to make the teeth. This might prevent any chemical from fully penetrating the wood. Another factor would be the wood itself. If it had any alkaline properties it would neutralize the acid.
A sharp pick and patience can dislodge compacted wood without even touching the tooth.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)