Case report: A 58-year-old and 56-year-old female patient with unremarkable medical history presented to Münster University Hospital with a painful ulcer on the hard palate. One patient described complaints that had been present for about 2 weeks after a root canal treatment under local anaesthesia by her dentist. Clinically, the ulcer was about 2 cm in size. A CT scan was performed and a biopsy taken. Histology revealed sialometaplasia and chronic granulating and fibrosing inflammation. There were no signs of malignancy. Close follow-up showed complete healing of the oral mucosa under local therapy in both cases.  
Discussion: The most common location of necrotising sialometaplasia is the lateral posterior hard palate in projection to the foramen palatinus majus, rarely the parotid gland, lips, or tongue are affected. Bone destruction has also been described in isolated cases. According to the literature, it mainly affects men between 40 and 50 years of age.
In the early stages, a pressure-suppressed swelling develops, which leads to an ulcer within a few days. In contrast to malignant neoplasms, there is no crossing of the midline. The ulcer heals spontaneously, but a superinfection may occur.
The pathogenesis of sialometaplasia is unclear. It leads to a so-called "salivary gland infarction" of the minor salivary glands, which results in the destruction of the salivary gland parenchyma. Histologically, squamous metaplasia of the acini of the local minor salivary glands is seen. The differential diagnosis must exclude malignant neoplasms such as squamous cell carcinoma or mucoepidermoid carcinoma.
Treatment is purely symptomatic to avoid superinfection and pain. Antibiotic therapy may be applied. The lesions heal completely within 6-12 weeks.
Summary: Necrotising sialometaplasia is a rare differential diagnosis of mucosal ulcer. It is a benign, self-limiting oral mucosal disease. The aetiology has not yet been conclusively clarified, but the ulcer appears to be caused by a local circulatory disorder. Early confirmation of the diagnosis with a biopsy can exclude a malignant tumour. Due to the good spontaneous healing rate, no specific therapy is required.