A dissertation will let you show how you can make a valuable contribution to the field with your theory, acquired knowledge, and practical skills in the course of your doctorate program. Your primary aim is to present a new concept for further development and defense. When writing dissertations one makes use of the research done by others to create your concepts, theories and hypotheses on the basis of the previous guidance.
When dealing with thesis, one makes a research compilation to show how much you know and how much you have learned during the period you were a graduate student. A thesis is supposed to demonstrate the level of your critical thinking abilities and your capacity of knowledgeable discussion of the collected information. What you do in your thesis is trying to broaden the subject in the framework of the pursued specialty.