When there is a gap the teeth will tend to occupy the empty space. They would either move sideways leaving bigger gaps between the remaining teeth or lean in and therefore they would not provide optimal chewing surface.
The opposing teeth (in case of a lower tooth they are the upper ones on the same side) will not get any counterforce, therefore they would slowly start to move downwards. Any missing tooth in the long term will weaken the opposing one as well and eventually these will also erode.
Should you lose one or more teeth we recommend to get them replaced with implant-based crown or bridges. We provide free consultations and give free treatment plans to make the process easier and help you to find the optimal solution.