When I was a lad, I was told to clean my teeth, but no-one explained why. Maybe dentists think that it's sufficient to tell me what to do, but if I'd known why, it would have made a big difference. When you know why you're doing soemthing, you do it more assiduously than if it's just one of the 613 commandments.
When I was a lad, if you had a cavity, the dentist would drill it out very throughly, removing quite a lot of tooth, then fill it up with a mercury amalgam filling. It turns out that this isn't the best approach; it meant that I had a number of almost hollow teeth, and in later life sometimes bits broke off. But that's the hand I was dealt. All in all, I'm OK with my teeth, but that's partly because I've been lucky to get a really good dentist.
Here's why you should claen your teeth. And how.
There's two reasons. One is acid. You get acid in your mouth from fruit. Eating fruit is a good idea, in moderation, but you don't want to leave the acid in your mouth to dissolve the teeth. Brushing helps with that.
The other reason is plaque. That's bacteria that grows on your teeth, which hardens into tartar. And plaque harms your teeth in three ways. A) it helps your teeth to get caries, B) you can get Gingivitis (inflammation of the gums) and C) your gums don't like it, so they shrink away. This means that your teeth get longer (hence the expression "long in the tooth") but it means there's less holding them in place, which is obviously bad.
You need to brush your teeth each day, because when the plaque first gets into place, it's soft and easy to remove. If it's allowed to harden, then it can only be removed by a professional dentist (or dental hygenist). Your dentist will be able to recommend one.
I use an electric toothbrush. A manual is probably just as good if you use it right, but an electric is quicker. I use a Braun Oral-B, with AA batteries. I use AAs because if you buy the kind of toothbrust that is rechargable, you'll find that after a couple of years, the battery inside won't take a charge; if you use rechargable AAs then if the batteries won't take charge, you replace them.
I use two brushes (and because I'm lazy, I have two toothbrushes so I don't have to swap the brush heads). The first is the ordinary kind. The other is called "interspace". Instead of having a head that's half an inch across, the brushes converge to a point. This gets down to the gum, and to some extent between the teeth. The Oral-B part number is IP17. I usually buy these on Ebay; you can also get them from Amazon, Boots and probably lots of other places.
Brushes don't clean between your teeth, the "interdental" spaces. Some people use dental floss for this; my dentist told me that interdental brushes are just as good, and I find them a lot easier to use. I use the Tepe brand of brush; they come in a good range of sizes. In practice, I find that just two sizes will give me the range I need. Again, Ebay.
Listen to Pam Ayres.