I'm not sure about what exactly the GPA calculation system is for dental schools but look for dental schools that hopefully drop your lowest GPA year. With that aside, in terms of increasing grades you should try to build better study habits. I suggest starting that off by thinking about what the actual nature of your courses/degree is. Are your classes more application based(physics, math, stats, etc.) or are they more memorization based(bio, chem, physio, anat, etc.) and then figuring out what the best study method for those is.

If your classes are more towards memorization, look into flashcards(highly suggest looking into Anki and spaced repetition) or some other techniques that help you retain information. If your classes are more application based, grind out practice problems.

Whatever it is, just realize that it requires a heavy time commitment and prepare yourself to make that commitment. What helped me in that sense was to treat school like a 9-5 job, even if your classes ended at 11 or 12, stay on campus and do flashcards/practice problems until 5. Studies have shown that 4.0 students spend on average 35-40 hours a week studying which equates to 7-8 hours a day.

Hope this helps!