
There are a few reasons for this: if you eat 5 candy bars at one time, your mouth will salivate more than if you eat one each hour for 5 hours. All that saliva will neutralize the harmful acids that corrode teeth. If you eat one each hour, there is more acid than saliva, which harms them.
The other reason is that people who eat a lot of candy will most likely brush their teeth after eating, whereas just one candy bar might not tip the scales. How much candy did you eat this Halloween?