A: You will need to review the Equipment Purchase Agreement for the cancellation clause regarding the terms and conditions specifically for the unforeseen circumstances/Acts of God. Is there a probationary period? I cannot answer this question without reviewing the aforementioned agreement.
A: Depending on your State's employment laws, usually an employee is hired as an employee at will meaning that employee can be fired or terminated at any time for no reason as long the reason is not illegal/discrinatory. If you do not have a written employment contract, the default is usually employee at will. Sorry to hear about your loss of job.
A: The first question is do you have a fully executed written contract? This is the first step to determine the terms and conditions such as your wages if there is a breach of contract, the dentist being able to assign the contract and if it can be modified.