There are many factors that might predispose a dog to periodontal disease and dental crowding is a really important one. Too many teeth or teeth that are too big for the available space means that there is less room for the supporting tissues (gingiva, alveolar bone). This is going to be the case in micro-dogs as well as in brachycephalic dogs.
It has been well established that the smaller the dog is, the larger the teeth are (in proportion to the mouth), so the smaller the dog, the worse the dental crowding. And in brachycephalic dogs, with their serious craniofacial deformity, the teeth really are jammed in tight. You can see more about the plight of brachycephalic animals on this page.
But back to dental crowding in particular. This is one risk factor for periodontal disease that can and should be eliminated at a very early age before it has time to cause trouble. By that I mean, at about 6-7 months of age, every micro-dog should have a detailed dental assessment under anesthetic to look for any/all possible developmental/anatomic oral liabilities and them at least, “weed the garden”. That is to say, selectively extract less-important teeth to improve the periodontal prospects for the more -teeth left in place.
For more details on this, please read this pdf document – Dental Crowding