As someone who had very very bad glandular fever a few years ago, to the extent that opening my mouth caused excruciating pain - I found it really hard to brush my teeth for as long or as regularly as I had the rest of my life. I was pretty much on liquid foods for months too - like I said it was a really really bad case that escalated into other things. Now, I'm fine but the amount of plaque and gum damage I had done by not being as good with my dental hygiene then, is still something I'm repairing years later. My gums still bleed at times (but much much less than they used to) and I personally think there's more discolouration from my teeth beyond what was already there from growing up in a household with heavy smokers as parents until my teens.
So from first hand experience I know even lapsed dental hygiene or less dental hygiene is bad for your mouth. I've also known people who stopped brushing cold turkey because 'they can't be bothered' or 'there's no point' and their teeth are fine... for now. By the time they're older, I've seen what happens to people with that attitude. I would say, even if you think like these people, please try to brush at least once a day (which still isn't enough imo) to give your mouth a cleanse and freshen up that breath. It is important!
