Assistant duties?

What are usually dental assistant duties? I'm currently a dental assistant and I provide chair assistance, sterilize, keep the office clean, take impressions and many other things. Yesterday, the office was close but they asked me to come over to do some general cleaning which I did and then they called and were very mad that we didn't shovel the snow. Is this the assistant job? I' just want to know. i work there for 2 years, have $9 an hour and always do what they ask. is this fair?
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I think it depends on your situation. I am very close to my boss so if he ever asked me to shovel snow then I would not mind.I have to say though you are majorly underpaid. I make almost 20 dollars an hour as an assistant in New York. I have never heard of an assistant getting paid that low. Ask for a raise or go else where. Nine dollars an hour is a job at McDonalds not as an assistant.