Medicine and dentistry PS need to concentrate on work shadowing, what the applicant leaned about the job and why they would be good at it .
The only point of mentioning the community volunteering is to demonstrate how he can meet the person spec of a doctor / dentist.
I know this sounds harsh, but every single applicant wil have a list of interesting EC activities, be a school prefect, will have done community work . There's no point in listing it, it's not a CV.
Doing lots of worthwhile things in the community shows that he's a great kid who cares about his community. It doesn't , on its own, show why he would make a great Dental student . It could even be argued that he shoudl study politics or social work or community education .
He needs to make the link, not the admissions officer.
I know it's hard , because you are clearly very fond of him and feel he's done well considering his background. But he doesn't know what he wants and it's getting too late .
I agree with those who said he might be better to apply next year. He might feel he has nothing to lose by applying this year , but He needs to check if any of his chosen universities won't accept reapplicants .