Custody and Visitation Issues: What is the Criteria in Massachusetts to Determine an Unfit Parent

My question involves a child custody case from the State of: Massachusetts

What is the general criteria to determine if a parent is fit in the state of Mass? I understand this is a very complicated and next to impossible thing to do, however there is overwhelming evidence of past/current drug abuse, criminal convictions as well as basic child neglect (never brushing teeth, hair, routine, food, dentist etc...)

Also if a parent is unfit, what criteria is needed to terminate parental rights?

Custody and Visitation Issues: What is the Criteria in Massachusetts to Determine an Unfit Parent