OP, you have a lot there:
1) Pursuit of higher education (noble, in and of itself)
2) Transformation of your clinical attitude (span of dentistry patients to the actual service delivery of our profession, i.e., perhaps your own supportive psychotherapy?, introspection?, whatever your thought-process that made you arrive at your present decision)
3) Intrinsic motivation of your desired profession after the loss of your Mom (Sorry for your loss). I personally also went through an emotional transformation when my Dad passed away (just before I graduated from undergrad). He was a highly-accomplished, internationally-trained physician, so I felt like I lost my biggest and best advisor (I love my older brothers for their collective memory of him, keeping me strong & grounded). I also wanted to write about him, but I didn't. I wrote about myself, much in the same way MCParent suggested because no one truly cared about his accomplishments or who he was to me...but, who he helped raise and produce was on the 'market,' as their best, most authentic, highly-motivated, empathic, empirically-driven doctoral candidate.
So agreed. Keep the focus on you. And who knows, maybe you'll be able to convey that deep, intrinsic motivation (your loved one instilled in you) with during your interview (I did get to briefly speak of his influences on me, in my interview - so I paid homage in my own way). It will be more relevant when pointedly asked, and much more apropos then.
(Also, some interviewers may still be blessed to have both parents alive, so may completely miss that mark that you're trying to hit. We all certainly don't need to lose someone close to understand loss, but you do open a chapter that others may not have, yet).
Good luck!