The part of yellow deposition on teeth.

That yellow part that came out was a portion of the hard deposits On The Teeth called as calculus. These deposits are formed from the plaque which is deposited daily on the teeth and needs to be removed meticulously while tooth brushing, but when it is not removed properly it calcifies with time and turns into a hard deposit which cannot be removed by tooth brushing. This chunk of Calculus can sometimes fracture under its own weight or an oblique force just like it happened in your case. You should get a session of teeth cleaning by a process called as scaling done as soon as possible to remove all such deposits On The Teeth for better gum health. Although smoking does not lead to the formation of Calculus, it is dangerous in its own ways and I hope you understand that very well. So as an ethical responsibility I will suggest you to quit that habit also as soon as possible. Regards.