I would advise against including this in your personal statement, or make it minimal as CleverThought said. I don't mean to sound insensitive, but we've all lost people close to us that we love, and admissions committees have seen that sort of thing in personal statements a million and a half times before. You want to tell a story about yourself that shows your passion for dentistry while illustrating that you're going to be successful in dental school and as a professional. You want to use your extracurriculars to show what you've learned, how you've grown, etc. (not just,"I did ____ activity that helps my qualifications.").
You want to inspire them and make them want you in their school, not make them feel sad and sympathetic.