Who's responsible for replacing my father's dentures when staff lost them?

Check the paperwork you signed when he was admitted. Many facilities limit the items they are responsible for.

My mother was constantly hiding her "valuables" then claiming they had been stolen when she couldn’t remember where she had hidden them. I would get calls from her asking if I knew where an item was, would go to her AL and toss her room only to find the stolen item tucked in a drawer shoe, even the fridge. She was obsessed with the thought that someone was coming into her room and stealing things.

I had no reason to believe the staff or other residents were taking things and we always found the item eventually.

A few people seem not to realise that old people can be very apt to misplace things especially those with dementia. So how can it be their responsibility to look after their own things when they don't know what the day of the week it is. My partner who has alzheimers was admitted to a psychiatric ward for the elderly. I informed the staff that of late she was apt to removing her top plate and was reassured when they told me they were used to events like this and her denture wouldn't get lost. Well they were lost within a week and when i raised it with the nurses I was told it was the nature of the ward. These patients are unable to think for themselves and so require staff to keep a close eye on them. Thank God my partner is back home with me and i can look after her properly.