Couple of months ago, i went to a new dentist &i feel as if the hygienist didnt properly placed the lead shield on me&it didnt have a collar. worried?

Understandable: As evidence changes practice changes. with newer technologies we are able to minimize exposure to potentially harmful xrays to almost neglible amounts. Lead aprons are now no longer neccessary with most modern xray systems however the collars are still in use as there is some evidence which suggest the thyroid and other structures are still susceptible.However adoption of this practice is minimal

Lead Apron: The beam which carries minimal radiation (unlike a nuclear power plant) is directed at your teeth and jaw. The lead apron and collar is meant to minimize scatter exposure. For this one instance you will be fine, but for future radiographs and for minimizing exposure make sure an apron with a collar is placed. Do not worry.