I sort of let myself get misguided along the tracks to address long term dental issues.

One primary cause, one side effect, and two primary effects.

Direct radiation hitting teeth and bone structure. Main effect is to the jawbone and you can lead to ORN, a bone disease.

Direct radiation also damages salivary glands that reduce saliva output and causes dry mouth. Tooth decay advances quicker due to the lack of saliva that helps kill bacteria that promote formation of carries and cavities.