A patient with Type 2 diabetes mellitus (on metformin) and a removable partial denture (RPD) presents. All of the following can cause xerostomia EXCEPT:

Correct answer: B. Removable partial denture (RPD)

• A. INCORRECT (medication CAN cause xerostomia). Many medications cause xerostomia as a side effect, though metformin itself is not a major cause of xerostomia. However, the question refers generally to the patient's medication regimen — diabetic patients are often on multiple drugs, many of which can cause dry mouth.
• B. CORRECT — EXCEPTION. A removable partial denture (RPD) does NOT cause xerostomia. The RPD is a prosthetic appliance resting on oral mucosa; it has no pharmacological effect on salivary gland function. While an ill-fitting RPD can cause discomfort or mucosal irritation, it does not reduce salivary output.
• C. INCORRECT (diabetes CAN cause xerostomia). Type 2 diabetes mellitus is associated with reduced salivary flow (hyposalivation) and xerostomia, particularly in poorly controlled patients. Autonomic neuropathy and dehydration from glycosuria contribute to this effect.
• D. INCORRECT (dehydration CAN cause xerostomia). Dehydration reduces overall fluid volume in the body including salivary secretion, resulting in xerostomia and thick, viscous saliva.