For those unable to afford dental work, I would recommend beginning Dr. Ellie's tooth maintainence protocol, which after reading multiple pubmed studies, I was able to confirm the legitimacy of.

Her protocol consists of:

1. starting with a Closys sensitive mouth rinse, which in studies is as effective as Chlorhexidine, a potent prescription only mouth rinse, but without the negative side effects from long-term use. This step ensures the mouth is at the correct pH before brushing, and effectively penetrates the biofilm of caries causing bacteria between the teeth, where the brush can't reach.
2. Brush with a low abrasive toothbrush (soft bristle) and low abrasive, non-whitening toothpaste. I personally recommend standard Colgate Total, since it uses the more advanced Stannus Flouride, which is more resistant to acids compared to standard sodium flouride, but if on a tight budget, standard crest works too.
3. Rinse with a standard antiseptic rinse (Listerine original or equivalent off-brand). This step must be done after brushing, as Listerine is mildly acidic (which would make your enamel soft enough for your brush to wear it away), and Listerine is much more effective after the bacteria colonies have been broken up by physical agitation first.
4. Finish with a standard ACT flouride rinse or off-brand (tge smaller bottles usually gave a higher concentration of flouride). Flouride is actually most effective at binding to the teeth in an acidic environment, so doing it after Listerine is synergistic. It also is alkaline, countering the low pH of the Listerine. Lastly, it has its own unique antibacterial, cetylpyridinium chloride, that further kills caries causing bacteria.

The end result of that protocol is an insane reduction in caries causing bacteria that completely eliminates the ability for plaque to form for around 8 to 12 hours. If you do the protocol twice a day, you will likely never have another cavity for the rest of your life, unless an existing filling fails.

Taking a pinch of xylitol sugar between brushings, like after meals, can further deprive caries causing bacteria from growing, as it will ingest xylitol, but ultimately cannot use it for fuel, causing it to die.

I've been using this protocol personally for 2 years, and can confirm that I no longer have plaque buildup on my teeth, and as a side-effect of the closys and Listerine, no longer have bad-breath, even in the morning.

It also can potentially stop existing cavities from progressing, but only if they haven't breached the enamel yet.

If a cavity is already in the soft dentin, this protocol may slow it or mildly ease the pain, but it won't resolve the cavity.