Behavior is common. Many people with dementia are confused and have trouble understanding what people say to them so this can lead to agitation or aggression with personal cares. There are behavioral interventions that can often lesson this but if there is significant aggression, medications may be needed. A geriatric psychiatrist can help you, if one is available.
Try more potent drug. These problems are common and occur as the disease progresses. Namenda may help agitation, and Exelon (rivastigmine) has been shown to help aggression, but if the temper tantrums become violent, it is best to try major tranquilizers such as seroquel to prevent harm. (but these drugs do have risks and must be used with caution).