The reasons why the freshly filled tooth is still sour include:1. In the process of removing decay and preparing cavities, sharp turning needles will cut the tooth tissue, causing the end of the dentin tubules to open up, making it easy to feel the stimulation of cold, hot, sour and sweet, and producing soreness.2. When there is occlusal interference on the surface of the filling, the upper and lower jaws of the upper and lower teeth will cause periodontal trauma, and there is a feeling of soreness.3. Composite resins and glass ionized water cementums in the filling materials constantly release chemicals, stimulating the pulp to produce soreness.4. The bottom of the cavity is close to the pulpal cavity, and when there is no cushioning, the pulp is in a sensitive state, and it takes some time to produce restorative dentin before the symptoms can be relieved.