Dear doctors, My wife has a bad odour mouth, constipation and dental cavities so we consulted dentist, but bad odour is still there, what to do?

Bad breath. Bad breath can be from gum disease ,cavities, diet high in sugary foods, dry mouth ,sinusitis, medications, reflux, cancer. To control bad breath consider mouth washes, brushing the tongue, flossing, treatment of peridontal disease, use of chlorhexadine digluconate mouth wash ,zinc rinses, hydrogen peroxide rinse,herbs like parsley, cardamom,sage and also probiotics like Strep salivarius.
Many reasons. There are many possibility of bad mouth odor, such as cavity, periodontal disease, food, medication, health condition, etc.... Taken care of cavity is just a first step. you can tell your dentist to run an mouth odor test with a test device. It should help you to rule out what cause it and properly treated.