Hello . I understand your concern. The black mark is nothing but post pigmentation scar. Just like any scar in our body . Next mouth burning, you should go certain vitamin blood tests to detect the deficiency of vitamins if /any. After that you can go for supplements . Till than you can use Benziglo Mouthwash before food to give a soothing affect and prevent burning.

Based on your description, this does not sound immediately alarming, especially since the ulcer healed around 8 months ago and your dentist did not find any suspicious changes on examination. The dark pigmentation is likely post-inflammatory pigmentation, which can occur after a deep ulcer heals. The thin whitish area may simply represent healed scar tissue, which tends to be more sensitive. A burning sensation only while eating spicy, hot, or acidic foods can occur because the healed mucosa remains more sensitive than the surrounding tissue. However, since the symptoms have persisted for several months, it is worth ruling out contributing factors such as vitamin B12, iron or folate deficiency, oral candidiasis, allergies, dry mouth, or early burning mouth syndrome.

Hello Understand your concern, but burning sensation my be due to sensitive skin over healed ulce or nutritional deficiencies.

Hello Looking at the image no abnormalities detected Sometimes the skin is delicate in that area so can experience this observe for few days

Picture is not much clear, but burning sensation after eating spicy food items indicate OLP or lichenoid reation. Some whitish strie around the ulcer should be present. Its an autoimmune type rxn in body which can be supress with medication. Any history of frequent tooth paste change/ switching to ayurvedic tooth paste like dantkanti or other.