I disagree. In my experience, engineering was significantly more challenging and demanding than pre-dental. And I speak from experience when I say this. I have completed the degree requirements for a degree in Computer Engineering AND have taken a suite of pre-dental classes(and have gotten straight A's in all of them).
I do agree, however, that it is hard to convince people that engineering is more challenging than pre-dental courses. If you haven't been through the engineering experience, you simply do not have an appreciation for the amount of work that is required to succeed and graduate with a high GPA.
That being said, I think the biggest thing someone from an engineering background can do is take a lot of dental-related science classes, such as biochemistry, physiology, histology, microbiology, and gross anatomy, and do
really well in them(I'm talking straight A's here). This shows the admissions committee that your low engineering GPA was due to the fact that your engineering classes were more difficult. It also shows that you can succeed in the dental-related science classes. And again, I base this statement on personal experience with people on admissions committees, and having gone through the interview process myself.
Good luck.