1.Dental caries When the caries develops to a certain depth and reaches the pulp or close to the pulp, the bacteria in the cavity can enter the pulp cavity directly or through the dentin tubules and cause pulpitis. The tooth pain caused by pulpitis is extremely difficult to bear, and it can produce severe pain without external stimulation, and the pain is intermittent. Most patients have more pain during sleep at night because the head is in a lower position when lying down than when standing, which makes the pulp cavity more likely to be filled with blood, thus increasing the pressure in the pulp cavity and compressing the nerve, so the pain is worse. Hot and cold stimulation can make toothache worse. When suffering from pulpitis, pain often radiates along the trigeminal nerve distribution area to the ipsilateral upper and lower teeth and head and face, so patients often have hemilateral headache and temple pain. Because the nerve endings in the pulp only have nociceptive receptors but no localization receptors, so the patient often cannot distinguish which tooth is the diseased tooth, and sometimes the upper tooth pain feels like the lower tooth pain. If the caries develops into pulpitis, the pain will be more intense and jumping, and the heat stimulation can aggravate it, while the cold stimulation can relieve the pain, and such patients often like to take a mouthful of cold water. When it develops to apical inflammation, the patient feels that the tooth grows taller and dare not bite something with the diseased tooth. 2, periodontal disease Periodontal disease can cause two different nature of toothache. The most common one is chewing pain. Due to the inflammation of periodontal tissues, pus is formed in the periodontal pocket, and it is very painful when the patient bites something. The other type of pain is similar to pulpitis caused by dental caries. It is mainly because when the tooth is very loose, the bacteria reaches the root end hole at the end of the root from the periodontal pocket, and then enters the pulp cavity through the root end hole to cause pulpitis and pain. 3.Wedge-shaped defect and abrasion The elderly people have been using the teeth for decades, and the abrasion of the chewing surface and the defect of the cervical part of the teeth are quite serious. When the abrasion of the chewing and the defect of the cervical part are close to or reach the pulp, the bacteria in the mouth can enter the tooth tissue and cause pulpitis, apical inflammation, and even inflammation and swelling of the soft tissue of the jaw surface, thus causing pain. 4. Microcracks Sometimes there are extremely fine and undetectable cracks on the teeth, and when these cracks reach into the dentin near the pulp, they often cause pulpitis. Sometimes the microfracture extends along the root towards the tip of the tooth, and then periodontal tissue infection or periodontal pocket formation can occur, causing toothache. Periodontal disease periodontal disease can cause two different types of toothache. The most common one is chewing pain. Due to the inflammation of periodontal tissues, pus is formed in the periodontal pockets, and it makes it very painful for the patient to bite something. The other type of pain is similar to pulpitis caused by dental caries. It is mainly because when the tooth is very loose, the bacteria reaches the root end hole at the end of the root from the periodontal pocket and then enters the pulp cavity through the root end hole causing pulpitis and pain.