Differential diagnosis of aphthous ulcer are :
-squamous cell carcinoma
-herpes simplex
-drug reaction
-erythema multiforme
-SLE
-lichen planus
-bullous pemphigoid
-pemphigus
-coxsackie virus
-parvovirus
-necrotizing ulcerative gingivostomatitis
-inflammatory bowel disease
-reactive arthritis
-oral candidiasis
-syphilis
-varicella zoster
-acute HIV infection
-squamous cell carcinoma
-herpes simplex
-drug reaction
-erythema multiforme
-SLE
-lichen planus
-bullous pemphigoid
-pemphigus
-coxsackie virus
-parvovirus
-necrotizing ulcerative gingivostomatitis
-inflammatory bowel disease
-reactive arthritis
-oral candidiasis
-syphilis
-varicella zoster
-acute HIV infection