Can my two front teeth made bigger with bonding or do I have to get veneers to lengthen them?

Certainly bounding is a good alternative to veneers and can be lengthened quite conservatively without any preparation to the underlying tooth. The only disadvantage to bonding is lifespan and often, after a few years, does stain. The newer bonding materials are quite aesthetic and highly polishable, the result, with skilful colour matching can be quite aesthetic. It does not have the lustre of porcelain veneers but in some cases can be equally as aesthetic. Particularly in lengthening, if a layering technique is used, with a skilful approach the aesthetic befits are almost comparable to veneers.

You mention that your teeth have gotten shorter from clenching.  In general, teeth don't get shorter from clenching, but rather from grinding, which mostly occurs at night.Your teeth can be made longer with either approach, however porcelain veneers are much stronger when it comes to lengthening teeth, and as such, should last you many times over what direct composite bonding will do, especially if you are "grinder."Also, the shape of the teeth tend to be much better with veneers than bonding, and likewise the color of the teeth is much better and more stable over time.Thus, I would advise porcelain veneers over direct composite bonding.You might be interested in seeing some examples of patients who have had their teeth lengthened with porcelain veneers.  See the web reference below.