My first dog had the kind of breath that made my eyes water when she yawned near me.

Her teeth had yellow buildup near the gumline, and parts of her gums looked red. But she still ate normally, played normally, and followed me everywhere, so I assumed her mouth was simply showing her age.

Later, she unexpectedly developed kidney problems.

My next dog had the same sour breath and increasingly visible buildup. 

I gave him expensive dental sticks and told myself I was being responsible.

He eventually developed heart problems.

At the time, I treated everything as unrelated. Bad breath was bad breath. Internal illness was internal illness. 

Some dogs simply did not live as long as others.

Then I began paying attention to the older dogs around me – friends and family's dogs.

The dogs thriving well into their teens did not have perfectly white puppy teeth—but their gums looked calm, their mouths were well maintained, and they did not have the same rotten odor I had learned to accept in my own dogs.

I still could not prove a connection at that time.

But I could no longer ignore the pattern.