The short answer – NO - it is not the size or type of the biscuit that matters, it's the quality of food.
The long answer is:
It’s a bit of a myth that biscuits will help ‘brush’ their teeth or remove plaque- there is actually no science to suggest this is the case. I liken it to us eating gingernuts to clean our teeth… it just doesn’t really stack up; so if the effects are negligible, then the difference between one kibble and another is pretty much immaterial.
Practically speaking, the best way to manage dental health is either through regular gentle brushing or dedicated dental chews.
Diet can still help a little, but what is much more important than the size of biscuit is the quality of food they are eating and how that affects plaque build up.
In terms of one kibble vs another, what you want to look for is good quality ingredients that don’t sugar easily. Ingredients like rice, corn, soy and wheat all have very high GL (glycaemic load) and are best avoided if you can, so grain free is a good way to go. Food like Feed My Furbaby Chicken Dog Box use peas, potatoes and tapioca instead of high GL ingredients and has high animal meat content, which also helps reduce the effect of those cheaper fillers. Peas have the lowest GL of any of the starchy ingredients required to make dry pet food.
Generally speaking raw meat/ wet food will accelerate dental problems vs kibble. This is because wet/raw food typically has more acid in it.
So to sum it up, a good quality food can help dental health because it’s all natural and made from good quality ingredients. The quality of food is far more important than the size of any biscuit and specific dental health products are the best way to keep your dogs teeth in great condition.