Buccal surface: trapezoidal, the occlusal margin is longer than the neck margin, the near middle margin is straight, and the far middle margin is protruding. There are two buccal tips and some distal tips on the buccal surface, and there is a point depression between the buccal sulcus and the distal buccal sulcus through the cusp.

Lingual surface: trapezoidal, smaller than buccal surface, slightly round. Two tips of the tongue can be seen at the occlusal edge, and the tongue groove passes between the two tips. Parallel to the long axis of the tooth, without obvious shaft ridge.

Proximal surface: quadrilateral, with sharp mesiobuccal ridge angle and lingual occlusal angle, protruding at 1/3 occlusion, and the mesiodistal contact area is mostly on the buccal side of 1/3 occlusion. The distal middle surface is smaller and more prominent than the proximal middle surface, and the crown is biased to the lingual side.

Occlusal surface: rectangular, with the proximal-distal median diameter larger than the buccal-lingual diameter, the buccal side longer than the lingual side, the proximal side straight, and the distal side short and protruding. You can see that there are five sharp points.

The buccal tip is short and round, the tip of the tongue is long and sharp, and the distal tip is the smallest, which is located at the junction of buccal surface and distal tip. The triangular ridge of the distal buccal tip is the longest and the triangular ridge of the distal buccal tip is the shortest.

Root: flat and thick double roots. The proximal and distal middle root is slightly larger than the proximal and distal middle root, and the root tip bends towards the proximal and distal middle root. The proximal and distal middle roots are similar to the proximal and distal middle roots, sometimes divided into buccal and lingual roots, and the distal middle tongue roots are short and curved, with great variation.

In the dental clinic, many patients go to see a doctor because of bruxism. Nocturnal molars are abnormal excitement of some brain cells in the cortical mandibular movement area of the central nervous system, which leads to trigeminal dysfunction.

The trigeminal nerve innervates the masticatory muscles to produce strong and lasting non-functional contraction, which makes the teeth rattle. Generally divided into three types: molar type, clench type and mixed type.

People are in the period of changing teeth from 6 years old to 13 years old, and there will be molars to adapt to the running-in of upper and lower teeth. But for teenagers and adults who have passed the tooth changing period, frequent grinding is morbid.

There are several types of molars.

1. Molar type: People often grind their teeth after falling asleep at night, which is often called night molars. During sleep, patients grind their teeth or clench their teeth, which is often called "grinding teeth" because of the creaking sound. Also, it is also called "night grinding" because it mostly happens during sleep at night. Patients don't know it themselves, and it is often said by others that it is more valued because it affects others, especially their spouses.

2. Occlusal type: The teeth often clench unconsciously during daytime concentration, but there are no molars of the upper and lower teeth.

3. Mixed type: There is the phenomenon of grinding teeth at night and grinding teeth during the day.

According to oral physiology and psychology, the oral cavity is the first source of human excitement and a channel to communicate with the outside world. The oral cavity has the function of expressing tension and pessimism.

Nowadays, the pace of people's life is getting faster and faster, and the competition is becoming more and more fierce. Everyone tries his best to relieve all kinds of pressures in life or work. One of the effective methods is physical exercise and mental transfer, while some people grind their teeth.

Some researchers made a comparative study on 80 pairs of patients with molars and those without bruxism, and tested each person's personality. The results show that introversion and depression, especially emotional instability and tension, are important factors of bruxism.

In other words, bruxism patients are more pessimistic than non-bruxism patients. Many scholars have found that in the pathogenesis of bruxism, oral diseases are not important, and psychological factors occupy the primary position.

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