Bit of a weird one and name changed in case it is judged, but will say the reason I didn't always brush my teeth regularly/twice a day was due to depression.
Throughout my life since my teen years (now early 30s) I've had periods of not brushing my teeth or going months and only brushing once.
Never in my life have I needed a filling and I've had check ups at the dentist recently.
I know people who have had many and have always consistently brushed twice a day? Is it surely just genetics?