Hello and thank you for contacting us. This is Dwayne B. and I’m an expert here and looking forward to assisting you today. If at any point any of my answers aren’t clear please don’t hesitate to ask for clarification. Also, I can only answer the questions you specifically ask and based on the facts that you give so please be sure that you ask the questions you want to ask and provide all necessary facts.
It depends on what you mean by "a case".
Do you have a cause of action? Absolutely. While there are some occasion when a foreign object in food isn't really a lawsuit (ex. you bite into a cherry pit in a cherry pie or a chicken bone in a chicken pot pie) when you have an object like a piece of plastic that obviously doesn't belong in the food then you have a cause of action, which just means the grounds to bring a lawsuit.
However, the hard part about a case like this is the second part which is "damages". For some reason people have gotten the impression that cases where they find something in their food that doesn't belong there then they automatically have a case worth a lot of money and that's not the case. If you had been seriously injured by the piece of plastic and had a lot of medical bills then you would have sufficient damages to pursue a lawsuit. However, since you don't mention that you had any medical bills, I am assuming any injury you received form biting into the plastic were minimal that didn't require any medical attention. That would mean that your case is likely worth, at most, a few hundred dollars and the cost of filing the case is close to that even if you don't use an attorney.
In Ohio the small claims court can hear matters up to $3000 so you could certainly represent yourself and sue and try to get the most the court would award. All you would really be risking is the cost of filing and service of process on the company.
There is a website for people representing themselves which has an article on a similar topic at http://www.lessonsinlaw.com/i-found-a-foreign-object-in-my-food-can-i-sue/
Feel free to ask any follow up questions in this thread.