These are not done quite the same way they used to be.

Before current times, a dentist would paint a sealer over the grooves of the tooth to hopefully seal the decay germs OUT and not seal them IN.  So, we tried to catch the teeth as soon as they erupted for this reason.   

But now, with the aid of my DIAGNODENT laser, I first determine whether there is early decay in the grooves, and then, if there is, I remove only the decay with either the waterlase, or air abrasion.  No shot here!  And no large hole to fill.  This way I am certain not to seal decay under the sealant.   Before I had the DIAGNODENT I would “watch” an area to see if it got bigger, or developed a hole.  Now I can confirm decay, or no decay, and act accordingly before more of your tooth structure is destroyed.