A metaphor is a figure of speech which makes a comparison between two things or situations which would not usually be associated with each other. It adds interest to a situation, or in this case, a sensation- pain. When using metaphor, you want to create a visual picture so that others can experience the same thing that you have. You want them to understand and to empathize with your situation. When discussing pain regarding teeth, people often cringe because they can imagine what you are going through and this makes you all the more credible. Simile does a similar thing by making an unlikely comparison but the word like or as appears in the description. Similes are not as strong as metaphors because they sometimes like originality. Always try to create your own so that they have are more effective.
First, think of the words which are associated with your pain by asking yourself some questions. Did you fall? When was the first sign of a problem? Did the chipped tooth cut your lip, perhaps? Was the pain of visiting the dentist worse than the actual chipped tooth? Did the dentist remove the tooth or fill the tooth? How long was it before you could eat comfortably? Did others make fun of you which would also perhaps have caused embarrassment?
Once you have thought of answers to these questions, note down the key words such as sore, shock, fear, spoiled, discomfort, headache, mouth, tooth, pain, embarrassment, dentist, dentist's chair, time. Not knowing the circumstances of chipping your tooth means i have chosen random examples but hopefully they will help.
It happened as fast as Justin Bieber / One Direction made the Number 1 spot but not nearly so glamorous.
My legs were like skittles as I fell to the ground.
It was like a bad school report; to be expected (as I was riding / running too fast or fighting too hard) but still such a shock that the engine of my brain took the knocks hard.
It (whatever hit you) was a runaway train and I was the stop sign.
I waited in the dentist's chair and time passed as slowly as a clock that's already stopped!
My headache was a freight train which had no station to stop at as it thundered through my brain.
My mouth was an Emergency Room with blood everywhere and cries of pain from all sides.