When a tooth has very
little left to rebuild upon, pins can be used to help hold the filling
on. Pins do have a certain level of risk attached to them. There could
be a chance that the pin will drill too close to the nerve of the tooth,
causing pain (and leading towards root canal treatment). Also pins can
weaken the remaining tooth structure causing microfractures in the tooth.
Some dentists refrain from using pins for these reasons. However, without
pins, the biting forces on a tooth like this would most probably knock
the filling off.