Personally I do not think kibble makes a whole heck of a lot of difference as to whether a dog gets tooth decay. Regardless of (healthy) diet, I have some cavaliers (ONE!) with really good teeth, one with moderately OK teeth, and three that get gum and tooth problems, regardless of being given at times, kibble, raw bones, good chews, commercial wet, or raw diets.
Nothing but wet food without any chews, raw bones and/or regular home dental care is going to be a poor choice for teeth, however. But kibble as an effective teeth cleaner? Many dogs barely chew it or not at all -- most don't spend much time chewing it so most of the time, it isn't doing a whole lot of scraping that I can see.
Any kibble is going to a be a poorer choice than fresh or quality prepared (tinned or raw) food. Kibble is a processed food, no matter how many nice ingredients, how expensive, how well marketed, how 'holistic'. Most of the vitamins and minerals have to be added back in as supplements as they are processed out (exactly like every processed food we buy -- breakfast cereal being a very similar example).
Not one doctor or nutritionist will tell you to go buy processed foods for your home dinner table. But they will tell you quality tinned and frozen foods are the equal of fresh and sometimes better if the 'fresh' food has actually been on the shelf for a while and is days from when it was harvested (tinned and frozen are packaged very soon after picking). There's also now outstanding evidence that gut flora are critical to our health and a limited diet (ie processed food; a narrow range of fresh) means a far narrower range of gut flora, eliminating some that are very likely key to good health (we now know gut flora may actually activate genes, offer protection against or contribute to disease, all depending on the person, genes and gut environment AND, critically, whether a human, dog, cat or whatever is overweight -- which changes the gut environment and seems to trigger many unwanted conditions and diseases.
Vegetables & fruit are the least critical part of a dog's diet -- they only need a modest amount of these and get little direct nutrition from them. Definitely give them moderate amounts of fresh fruit and veg -- but I think it is a lot more important for dogs and cats to get good quality fresh/homecooked/prepared raw MEAT or a quality tinned meat diet. Supplement with kibble if wanted (I use kibble for travelling or to add to the occasional meal but I hardly buy any kibble any more.
My real turning point on this issue was a sick elderly cat -- she had had diarrhea or very soft, very smelly stools for years. Then she started to lose weight and became very listless -- she had the whole panel of tests, nothing definite found, tried this and that; vet felt she had very bad IBD or maybe a tumour and last ditch option was we'd put her on low dose daily prednisone to see if that gave her back some quality of life.
I decided to try one last thing -- switch Jessie (and therefore all the four cats) from kibble and a daily bit of commercial supermarket tinned food, to a raw diet, including her sister who had begun to go into early stage thyroid disease (a common condition in older cats but only since around the 70s -- the advent of a huge commercial pet food market). Putting Jessie on raw was literally an overnight miracle. The next day she had the first normal stool in years. No horrible stink. She started putting on weight. The vomity-rpone thyroid cat stopped vomiting almost entirely. Jessie started gaining weight again. I brought her into the vet after a month on raw and she'd put on 25% more weight and was nearly back to her normal weight a few years ago. She went from listless to mischievous, playing with toys again instead of sitting facing the wall. My vet was astonished -- and asked for the name of the frozen raw diet she was on (along with a commercial high quality wet food made for dogs -- comes in plastic trays, not tins, has normal meat and veg, not all that weird smelly stuff in much tinned food).
That and attending a European science forum in Dublin in the summer and hearing research on gut flora just totally changed my view on what to feed animals. Gut health is linked to an extraordinary range of illnesses, researchers are finding -- not just those involving the gut itself. Feeding the equivalent of Wheaties to a dog all its life (which is really what any kibble is --a fortified dried processed food) just cannot be very healthy, and I do think dietary choices we make, and overfeeding them so they are overweight or even worse, obese, can predispose them to a vast range of diseases (turns the genetic or environmental switch on, or eliminates the healthful environment for the good gut flora that is protective).
Even feeding, say, a prepared frozen raw diet a couple of times a week instead of kibble has got to be a massive improvement in healthful eating. Feeding raw is hardly more difficult than opening a tin or giving kibble, because it is easy to get prepared raw at pet shops or even mail order. Quality prepared frozen raw foods are balanced; most have raw bone ground in giving natural calcium; it's easy to add desired supplements (eg omega 3 or CoQ12). But opt for a quality tinned food if preferred. Or add fresh meats to a meal -- that's more valuable to diet than fruit/veg.
I do think there are risk elements in feeding fresh raw bones that every person needs to weigh up -- I find the dogs still can eat these in ways that produce bone fragments that could cause risks, while the cats seem to gnaw bones (say, in raw chicken wings) slowly down in a far safer way.