The acellular substance that protects the tooth against abrasion and acids produced by bacteria is .

The acellular substance that protects the tooth against abrasion and acids produced by bacteria is enamel.

Enamel is the hardest substance in the human body and it covers the crown which is the part of the tooth that's visible in the mouth. It is the first line of defense for your teeth against the variety of substances that pass through your mouth each day.

The enamel on your teeth is built to withstand a lot of use. However, it can be worn down by acids produced by bacteria, and it can also be damaged by abrasion from brushing too hard, using a hard-bristle toothbrush, or grinding your teeth.

Once the enamel is worn away, it does not regenerate, unlike other tissues in the body. Therefore, it's important to take steps to protect your enamel, such as using a soft-bristle toothbrush, avoiding acidic foods and drinks, and getting regular dental check-ups.