PG entrance exams for dental students are tricky business. Mostly because there are so many of them and each one has a peculiar pattern. If you want to crack the all-India exam for MDS, you might need to come down to Delhi and specifically AIIMS campus in the month of November-December.
The xerox shops in the campus sell photocopies of question papers from the entrance exams for SR-ships from the same year. Those question papers along with the previous year question papers (Amit Ashish- Mudit Khanna) are crucial for your preparation.
A basic reading of the syllabus by any of the compendiums (eg Dental Pulse) is also a given. The competition is pretty tough and you need a dedicated preparation of 6 months for cracking the exams.
All the best.
Also, make sure that you want to do post-graduation in a particular field out of interest and not because of the rat-race. There is immense saturation in all the fields of dental sciences right now and only the most hardworking doctors are able to make their way across it.