Dear Aditi, Yes both the fields are different but not entirely. It completely depends on the person’s knowledge and interest in the subject and the urge for knowing more and more.  I have seen many professors who have ample amount of knowledge not only confined to dentistry but about the entire human body.

One cannot compare between BDS and MBBS as we cannot compare between a civil engineer , a mechanical engineer ,electrical engineer ,etc. Still they all are categorised as engineers. Similary a BDS doctor and MBBS doctor both serve the function of treating patients no matter whether the patient complains of oral problem or problem related to any other part of the body. They are two different specializations.

Also the basic biology is same when one studies the human body. BDS students study oral pathology, oral medicine, oral radiology, oral surgery, forensic dentistry, dental anatomy and histology and many more along with general pathology, general medicine, general surgery etc. So the syllabus is huge. It's not like that only the mbbs people have to study hard.

Dentistry itself is a huge field that's why it was not included with the mbbs course. Thanks to those great men who realised this soon and made it a separate field in medical science :-D

Afterall mbbs people also undergo MD/MS to gain specialisation so as to gain license to practice in the field of their interest. Similarly  bds people too undergo MDS to gain specialisation so that they can chose their subject of interest and practice further.

B.D.S in Oral medicine and Radiology deals with the study, diagnosis and non-surgical treatment of oral and orofacial diseases with the help of radiant energy.

A radiologist doctor does post graduation after MBBS for 2 or 3 years and then can call themselves a specialist in radiology. The can give reports and take medical decisions for and recommend further clinical treatment. Sometimes the radiologist is required to discuss particular imaging protocols with the radiographer or technologist to get best results during an imaging study.

I think, I have cleared your doubt. 

All the best 

Feel free to ask for any query