How do you tell the pain in the bottom father my mother of 87 years old with Dementia is in PAIN. I am a mother and mother's know this without any words. He says no she isn't she is fine, then asks her of course she says no. That's the only word she says besides milk or pee.
How about her facial expression? If in pain, she may frown or scrunch up her face.
Also, if it's acute pain, it most likely will raise her blood pressure. So, you may want to take her blood pressure often and regularly to see if/when it spikes and observe her over all demeanor to see if you can determine if she's at ease or uncomfortable or maybe in pain.
something more specific - like asking if her head ached, or about her back, knees etc - she was more likely to say yes. I knew my mother had multiple deteriorated discs, that her knees were bad enough that they likely would have required surgery if she had been younger and mobile, and that she had suffered from headaches all her life, so I assumed that some level of pain was always with her. She was prescribed tylenol with regularity daily with ibuprofen available when she was agitated and it appeared that she needed something more.
Furrowed brow
Grimace
groaning
pulling back or guarding an area of the body
crying, moaning
If you "Google" Non Verbal Signs of Pain in Dementia there is a whole list of different cues.