Re: trauma or filling?
The best way to determine if the nerve of a tooth is dying is to have an xray done - although most dentists should be able to determine if a tooth needs a rc or not I prefer endodontists in terms of actually having the procedure done since that is primarily what they are trained in. Most teeth however don't turn yellow when the nerve dies but more of a greyish or blackened color. It could be the composite itself can not be bleached - you may however be able to have it removed and redone in a more whiter color or tint. If the tooth is severely yellowed though you may want to see a specialist such as an OS, endodontist or periodontist and have it evaluated since that may indicate calcification of the tooth that can result in it possibly needing to be removed at some point in the future. Since its not hurting in anyway and does not overly respond to hot or cold or the pressure of chewing food, chances are it is fine.