@jfannarbor i was an internist for many years. Xerostomia from prednisone was not taught at my medical school. After practicing for some while I noticed a percentage of my patients on long term prednisone did complain of it. I usually tied it to another medication they were taking. I did, one day look it up in goodman and gillman ( did u relay on this book in dental school, just curious) and found it was a side effect, listed as less common. The following is from AI:

Prednisone, a synthetic glucocorticoid, impairs salivary gland function primarily through long-term use, leading to reduced saliva production. It diminishes store-operated calcium entry (SOCE) in salivary acinar cells, which is essential for fluid secretion triggered by intracellular calcium signaling.

From a different AI source:

Long-term use inhibits store-operated calcium entry (SOCE) in salivary acinar cells, reducing intracellular calcium levels essential for saliva secretion. This occurs when prolonged corticosteroid exposure diminishes calcium influx after endoplasmic reticulum depletion, without altering key membrane proteins like TMEM16A, AQP5, or NKCC1.[pharmacytimes +1]
Supporting Factors
Corticosteroids may thicken saliva or affect the sympathetic nervous system, limiting flow, though this is less specific to prednisone. Short-term use typically spares salivary function, with effects prominent after weeks.

Sorry I didn’t look up specific studies.