defamation case

I am a practicing dentist and very near to my clinic is a diagnostic center which happens to have a facility of specialized dental x-rays. Recently I happen to be visiting that facility checking one of my patients previous x rays on the computer of that diagnostic center. Same time a patient referred by some other dentist came their and thought i am a radiologist there, to which i told her that i am not rather i am a dentist of the nearby clinic. After some time she came to my clinic and started talking to me and to which I gave honest opinions and listening to this she got angry at her dentist as according to her she had gone to that dentist just for getting her teeth cleaned and their was no need for the said x-ray. After some time the said dentist called up the owner of the diagnostic center abusing him and me and also stating that we are in compliance and poaching on his patients. Their is also a group on Whatsapp of all the local dentists having around 100 people which i am not a member of and he also posted these false allegations in that group. I am an specialist post graduate dentist and many of the members in the group used to call me in their clinic for surgeries. His deeds have questioned my integrity and also spoiled my name in our community. My questions are 1) In this scenario can I file a defamation case.? 2) If yes ... how do I proceed..??