Lupus can cause dry mouth leading to tooth issues. And often Lupus is accompanied by a secondary disorder, Sjogren's Syndrome, which also causes dry mouth leading to tooth decay.
I don't think the Plaquenil or the Prednisone are causing the issue -- you should check in with your rheumatologist.
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2002DIAGNOSING LUPUS & HW's LUPUS 101
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