Hi With regard to your query, extraction of wisdom tooth will be considered under certain conditions like when the tooth is impacted, unrestorable, causing pressure on the adjacent tooth, causing malalignment of teeth in the arch are the common reasons so in your case may be your cavity is unrestorable so only advised extraction. Not only sugar will cause cavities there are many other reasons like decreased secretion of saliva, food impaction provided with spaces between the teeth,eating lot of sticky foods like choclates etc.. i would suggest you to gargle your mouth after every meal infact what ever you eat and check it out. i think in your case it is unrestorable with irreversible pulpitis so only considered for extraction. For further treatment you an visit your dentist.