Do i have a good case againt a restaurant if i found and have video of a melted piece of plastic on my sandwhich which you can tell its not cheese..

As a rule (with a few exceptions which don't seem present here), any type of civil claim requires not only a wrong (here negligence) but damage caused by that wrong.  Thus, for example, if a driver runs a red light and hits your car, you could sue for the damage done to your vehicle, medical bills arising from the accident, lost wages if you had to miss work due to the accident, etc.  If, however, you swerve and miss the guy who ran the light, you have no claim.  The other driver has committed the same wrong in both cases, and could conceivably face reckless driving criminal charges, but you have no civil claim because you suffered no damages.  The same is true here.  Did you eat the plastic?  Did it cause you any harm?  Did it cost you any money?  I assume that if the answer to any of the foregoing questions was yes, you would have mentioned it.  You may have a claim for the price of the sandwich, but you have no other damages.  That being said, it is possible that the restaurant will be willing to compensate you in some way to avoid bad publicity.  But I wouldn't expect much.