## 3 Discussion
Only one report described an association between OHL and oral lichen plants; however, it is probable that the local corticosteroid therapy used to treat OLP has favoured the action of EBV in the determinism of OHL. OHL diagnosis can be clinically made and does not require a confirmatory biopsy if retrieved from the putative causes [23]. On the other hand, the clinical manifestations of a contact allergy to dental materials are not uniform: lichenoid reactions, chemitis, and oral aphthous stomatitis are the most reported, but, to the best of our knowledge, this is the first report describing an OLL due to amalgam fillings mimicking OHL [24]. Although this is only a single report, the rapid and complete healing observed and the lack of recurrence during follow-up suggests that amalgam restorations, especially those which are outdated, may cause mucosal lesions to be diagnosable as OHL. The diagnosis of OHL induced by an amalgam is performed \"a posteriori\" since only the removal of the filling and the disappearance of the lichenoid signs can confirm the initial diagnostic hypothesis. The main guidelines suggest that a biopsy should be performed if lesions persist 14 days after removing potential causes and/or treatment [25]. Removal of amalgam fillings must be followed by a close 2-week follow-up, after which OLLs must be surgically removed (with a histopathological evaluation) if they do not heal or improve significantly. However, histopathological examination does not allow for distinguishing between oral lichen plants and OLLs as the two entities share the same pathological aspects [26]. The patch test for the dental metal series is not always of diagnostic support. Topographical congruence between lesions and fillings should guide clinicians in placing the diagnostic suspicion on OLLs [16]. Debate exists about the malignant transformation of OLLs, but more data are needed about the malignant transformation of OLLs explicitly caused by amalgam fillings [27]. To date, only five cases of malignant transformation of OLLs related to amalgams are reported. The first four cases were described by [PERSON] et al. [28], who histopathologically documented the neoplastic changes that occurred in a mean time of 8.5 years. All the reported cases arose on the tongue margins. More recently, [PERSON] et al. reported a case of OLLs due to an amalgam, which transformed into oral squamous cell carcinoma 10 years after the initial diagnosis and the amalgam substitution [29]. OLLs and OHL may share clinical aspects but are two different nosological entities. During the diagnostic process, before histopathological sampling, any systemic and local irritative causes must be excluded. Patients should follow up in the following 12 months to evaluate the complete remission of the lesions and monitor any eventual neoplastic derailment. Conceptualization, M.P. ; methodology, F.d.V. ; data curation, D.D.S. and D.L. ; writing--original draft preparation, M.P. ; writing--review and editing, G.C. and D.L. ; supervision, M.P. and G.C. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The study was conducted in accordance with the Declaration of Helsinki, and the local independent ethical committee of \"Azienda Ospedaliero-Universitaria Policlinico Consorziale\" of Bari approved our studies on oral mucosal diseases (protocol number is 46815/C.E.). Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. The authors declare no conflict of interest.