To understand why drilling is necessary, it is essential to know how caries can be done first. Bad teeth are the result of tooth decayed. High-sugar foods accumulate in the teeth over time. When these substances bind with saliva and bacteria, they release acid. These acids gradually dissolve the enamel. The enamel will decay if eroded more quickly than it can be replaced. Cavities may also develop in the teeth. It is caused by a buildup of food at the base of the tooth. Periodontal disease can also cause tooth decay.