Complex sentence: Careful and frequent brushing with a toothbrush and flossing help to prevent build-up of plaque bacteria that change carbohydrate in our meals or snacks to acid which demineralises tooth eventually leading to tooth decay and toothache if acid episodes are frequent or are not prevented.
Split into simpler sentences: Careful and frequent brushing with a toothbrush and the use of flossing help to prevent build-up of plaque bacteria on the teeth. These bacteria metabolize carbohydrates in our meals or snacks and excrete acid which demineralizes tooth enamel, eventually leading to tooth decay and toothache if acid episodes are frequent or are not prevented.