Do you have to drill a tooth before bonding?

Hi Roseie2644,
Some teeth need to be roughened or beveled to increase the retention of the composite material.
In other cases where retention is not the issue and where there is adequate space for the placement of composite, the procedure can be done without drilling.
Drilling should be considered on a case by case basis.
All the best,
Amir H. Motamed, D.D.S.

It depends on the situation. If a tooth has recently chipped, and there are thin fragments of weak unsupported enamel that can eventually flake off, it doesn't make sense to bond to them as the foundation for your restoration will then be weak. In these cases I will use the drill slightly to bevel the enamel and ensure the tooth structure is sound before bonding to it. 
Likewise, If the area in need of bonding already has sound, supported enamel, then so long as the enamel surface is otherwise clean, drilling wouldn't be necessary. Hope this helps.

Not necessarily, it depends on a number of factors, but each situation is unique.  If the tooth will protrude by adding bonded composite, then I would slightly reduce the enamel.  Otherwise, I have bonded composite successfully without drilling at all, because the bond to etched enamel is very strong.  Lightly roughening the surface will make the bond even stronger, if the patient does not object to the slight amount of drilling and modification of the enamel of their teeth.