I"m going to guess my days in orthodontics and dentistry that they are talking about a prosthesis including teeth? Any kind of mouth piece that one would use 24/7 requires precision to construct. I would guess they want to do an impression of his mouth to do that. Not sure, I never made one for an adult/cancer survivor but for teens/adults and newborn babies with clefts

Spouse of 58 yr old with BOT cancer
Stage 4a HPV16 positive
3 chemo treatments cisplantin
35 radiation treatments 7000 cGy
former smoker/chewed tobacco for 38 yrs.
1/2020 diagnosed with cancer near TMJ
4/2020 chemo 5 days every 2 weeks
6/2020 proton therapy
9/21/2020 cancer free