How Many Mm Longer Than the Real Teeth Veneer Can Be Used to Lengthen Teeth Without Easily Crack?

My recommendation would be to go to a dentist who is capable of mounting models of your teeth and doing a waxup to see how much length is possible without interfering with the contact of the back teeth in an ideal bite. Doing this procedure on a tool called an articulator will enable the design of a prototype which can then be transferred to your mouth. This gives you the ability to have a "trial run", if the plastic protoype chipss you will know that that length is not right. I have done this successfully many times. Really saves in the long run. Hope this helps! Good luck! Bernice Szafarek DMD

In general, It really depends on patient's bite. If the patient is deep bite or not. In your case as you described which there is minor gap between your teeth, you can close gaps by placing porcelaon veneers, not more than 2mm.

This all depends on your occlusion but making long teeth to close an open bite will result in seriously long teeth and will not look good or natural. I know you already had orthodontics but you may need to give it another chance or look into getting Invisalign because although you can fix many esthetic issues with veneers, it sounds like you are not a good candidate until you can result your orthodontic issues.

I would first try to get the orthodontist to fix the open bite problem you are having.  If that is not an option, you can lengthen up to 2mm.