Apes yes, humans not so much. The slight gap is call the freeway space and it is conventional wisdom that it is not only normal, it is important. Personally I don't think it matter much as it changes all the time. read more
Not always.Sometimes teeth are together sometimes not..there is leeway space of 2–3mms between the teeth when mouth is closed but teeth are not together. read more
No mouth closed teeth together, teeth should touch. Sitting up, with just your lips closed, your teeth should be discluded about 2 mm. This is what is called the rest vertical dimension. edited to add: Lick your lips, close and swallow, then just relax with your lips closed. Your teeth should be apart just a little bit. read more
If you tilt your head forward, your teeth still should not normally touch. However, if you close to your normal bite with your head forward, you very slightly change the way your teeth contact together. read more