This is Going to Hurt Just a Little Bit is a humorous poem by Ogden Nash.  It presents the experience of visiting a dentist in an exaggerated and hilarious manner.

The poet begins by saying that sitting in a dentist's chair with mouth wide open is one of the most undignified situations in life.  But our only hope then is that we won't have to do it again.  Dental torture is both mental and physical.  One is so tense that the clenched fist can even change the fortune lines on our palms.

The poet compares the mouth to a road that is being repaired.  The fearsome equipment used by dentists is compared to concrete mixers, drills and steam rollers.  They are enough to irk every nerve.  Even though your teeth are being polished it feels like they are being demolished. The most fearful fact is that the dentist is doing all these with the help of a mirror.  There is every  chance for him to mix up his left and right.

He then compares the dentist to a bear who mauls and suffocates its prey.  When you think that everything is over he coats your mouth with something awful.  Again you comfort yourself with the thought that it is only this once.  But just then he tells you to visit again after one month.

The poem ends with the thought that visiting the dentist is a vicious circle.  You go to a dentist to keep your teeth in good condition.  The reason why you want to keep your teeth in good condition is to avoid visiting a dentist.  But for that you have to visit him. You go to a dentist so that you don't have to visit him again.