Old Bonding Has Discolored. Can This Be Retouched Up Without Drilling?

Hi there,
there is unfortunately no way to effectively whiten composite, as it is not made of the same material as tooth.  If it is in thin layers, then the underlying tooth may whiten slightly, causing the composite to camouflage and blend in, thus appearing whiter, but other than that the colour of composite is what it is.  Staining can be addressed by your dental hygienist with a thorough prophylaxis appointment.  My patients attend regularly to have their composite bonding repolished, to keep them looking nice and shiny and to check that the composite is still performing to the best possible standard.  One option may be to add a further layer of composite over the top if you needed to change the colour.  This could be achieved by preparing the surface layer slightly, either with a drill or with a sandblaster.  After this a special type of resin prepared the old composite, on which a new layer can be added.  This is easier with composite types which have been designed for high aesthetics such as Renamel (Cosmedent) and HFO (Mycerium).  You should most likely seek advice of your dentist who I am sure would be super happy to help you.  There are things that can often be done conservatively and I am sure they will look after you very well.
Hope this helps!
Best,
MJ x

Bonding material will absorb color and stain or darken over the years. If the color is still pleasing to you, then bonding can be touched up to repair areas of wear. However, bonding cannot be bleached out or whitened with toothpastes or even professional whitening systems. 
If they had to numb you the first time to do your bonding, then I am assuming the dentist removed some enamel off the front of your teeth. This is sometimes needed in a small percentage of situations. More commonly, bonding is done without numbing.