By seeing it seems starting of tooth decay. Sometimes it is in reversible stage. It is confirmed by probe and some other examination. For further query feel free to visit drsawhney's dental centre, delhi gate Agra
See..... best is to check the tooth clinically as well as radiographically (X-ray) and then a decision should be given. Still, as per pic I feel that u require a treatment even if there is no cavity. This yellow part is showing that ur tooth is hypocalcified (weak) so it shd be treated.
All d best, god bless u.
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