The 70-year-old went to hospital thinking his pain was related to his tooth.
Upon examination doctors noticed he had puffy skin on the left side of his face, but no rash or facial paralysis.
Medics at Osaka University Hospital in Japan initially suspected a bacterial infection caught during treatment at the dentist.
But further examination of the inside of his mouth found "white erosion" on the left side of his palate.
The man was tested for herpes but the results were negative, so doctors sent samples of the rash away for further testing.
He was eventually diagnosed with oral shingles and put on a course of antibiotics.
The symptoms went away within a week but the man was left with a burning sensation on the left side of his face and mouth.
Oral shingles can be difficult for doctors to diagnosed because the beginning stage of the illness can occur days before a rash appears in the mouth.
"Toothache, which the patient experienced at the beginning, could be an initial presentation of oral shingles in this case," Dr Hideharu Hagiya wrote in the BMJ case report.
The illness can also mimic herpes, making it harder to diagnose.
Shingles is an infection of the nerve and skin around it.
It's caused by the same virus that causes chickenpox.
The main symptoms are pain, followed by a rash that develops into itchy blisters.
The pain may cause a constant, dull or burning sensation and how painful it is varies from person to person.
It typically lasts around two to four weeks and requires treatment from a GP.
Any part of your body can be affected, including your face and eyes, but the chest and abdomen are the most common areas.
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