system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If cat saliva is antibacterial, why do they suffer from tooth decay and gum disease?

Is their saliva only antibacterial to certain strains of bacteria?
gpt
Bacteria have adapted to live off sulfur in boiling water, a cat's mouth is easy to adapt to by comparison.  It's warm, wet, and frequently contains food - so yeah, something definitely lives there.  That said, there's not a lot of funding for feline dentistry research so it's not very well understood.

Cats don't have the same kind of tooth decay that humans get.  They don't get cavities.  Instead, they have

1) Gum disease.  Pretty much the same as human gum disease.  Tartar builds up on the tooth and creates a pathway for bacteria to get into the gums and eventually to the root of the tooth.

2) Tooth resorbtion.  Cats apparently re-absorb some of their juvenile teeth.  The cells responsible for this hang around, and later in life may attempt to re-absorb an adult tooth; causing loss of the tooth and a painful knob of exposed bone.  Generally this is resolved on its own as the gum grows to fill in the gap.