getting ghosted by dentist

hi all, i am currently in the process of finishing up my application to be submitted by the beginning of august, hopefully. i have four lor’s requested:

1. chair of the chem department (academic advisor)
2. orgo prof that taught me for a year
3. biomed engineering prof that i am also doing research with
4. dentist that i worked with for two years

the timeline for the letters to be submitted is end of july and august 1st. the first three have been very communicative and helpful with the process, however the doctor has stopped responding to my messages. i originally asked for the letter to be submitted by the beginning of july but i’ve since delayed it. it’s been around 15 days and no response. all i asked was for an email so i can submit the formal request through aadsas. i’m kind of scared that im getting ghosted and i really don’t know what to do with my application already not being submitted early. should i be looking for a different doc to write an lor? this is just so short notice with my timeline. should i delay my submission?