If your theory has a weakness, it's probably this. I would guess that people who have spirochetes living happily in their mouths also have spirochetes living happily in their bodies. In other words it's a general, body-wide susceptibility to spirochetes that's the cause, with spirochetes in the mouth as one of the symptoms. By treating the mouth you're only treating a symptom. What's required is a systemic treatment, something like the antibiotic used for lyme disease. At least that is what seems likely to me.
I don't doubt that your recommendation of using baking soda to brush with is a good one, and probably will kill the spirochetes in the mouth, but I'll bet the ones in the body will continue to live there happily.
Also, why is it that the composition of the plaques is unknown? You mentioned that someone had speculated that they were accumulations of dead spirochete bodies, but hasn't this been proven or disproven already? It seems like the plaques' composition would have been thoroughly researched at this point.
The problem with your thinking on this, yardstick, is that the inside of your mouth is EXTERNAL to your body. It's OUTSIDE your skin! There are millions of bacteria inside your mouth you would NOT want living inside your body! We put many things in our mouths we would not want under our skin. Think of what a baby puts in it's mouth. The mouth is a very dirty place! The mouth is also the only place where the skeleton sticks THROUGH the skin.
There is a seal at the gums with a natural flow of fluid from your body out to prevent the movement of bacteria inward... But if that seal is broken, or the gums bleed, you open a superhighway into your body that the bacteria can enter. The surface area of that seal is about the size of the palm of your hand! If it gets compromised, it's a major problem!
The plaques are not unknown, but what starts them and what forms their core is. The "framework" cage that holds the cholesterol and fatty acids could be made up of the dead wirery, entangled bodies of millions of spirochetes that are very tough, attached to the artery and cell walls. These are transparent.