After signing the informed consent, the participant will be allocated to either intervention or control group, then each participant in the intervention group will receive intralesional injections of platelet rich plasma extracted from their own blood in each visit as following:

1. 12 ml of blood will be assembled from the veins of antecubital fossa
2. PRP preparation will be done according to Mostafa et al., 2013
3. 0.5 ml of PRP will be injected per 1 cm2 of ulcerated mucosa

The second group will receive triamcinolone acetonide 40 mg injected 1 ml per 1 cm2 of ulcerated mucosa

Both groups will receive a total of 4 injection, the injections will be carried out once a week.

Pain, lesions size and remission time are the outcomes will be assessed using a numerical rating scale (Seymour, 1982), clinical score according to Thongprasom et al., 1992 and binary scale for remission time according to Conrotto et al., 2006, respectively.

Assessment of the outcomes will be carried before the trial (baseline records) and before receiving the treatment in each visit by the primary investigator (H.A.) and the blinded assessor (Dr. A.W.) separately.

Each participant will have a total of 11 visits during the trial, 5 visits will be once every week during the trial and every 2 weeks for 3 months treatment free.

Inclusion Criteria:

• Patients presenting with a clinical picture that assumes the diagnosis of erosive oral lichen planus (bilateral, more or less symmetrical erosive lesions with lacelike network of slightly raised gray white lesions (reticular pattern), and a histological findings that confirms the diagnosis (liquefaction degeneration of the basal cell layer with irregular-saw teeth like rete pegs.

Exclusion Criteria:

• Systemic disorders such as hematological diseases, severe cardiovascular diseases, treatment with any drugs that could cause Lichenoid reaction.
• Pregnancy or active breastfeeding
• Patients who had lesion/lesions with dysplasia
• Patients who received topical treatment for Oral Lichen planus in the last 2 weeks (Lee et al., 2013) or systemic treatment for OLP in the past 3 months.
• Platelet count < 150,000/mm3; Hgb < 11 g/dl.
• Immunosuppressed patients
• Patients receiving therapy with anticoagulants and use of non-steroidal anti-inflammatory drugs in the 5 days before taking the blood sample.