How are permanent teeth classified according to their shape and function?

Oct 18, 2025 Source: Cainiu Health

Dr. Liu Chao

Introduction

Under normal circumstances, permanent teeth can be classified into four types according to their shape and function: incisors, canines, premolars, and molars. Incisors are located in the front of the oral cavity, with four in the upper jaw and four in the lower jaw, making a total of eight. They have a shovel-like shape. The morphological differences among these four types of teeth directly determine their specific roles in the mastication process, working together to cut, tear, and grind food.

Under normal circumstances, permanent teeth can be divided into four types according to their shape and function: incisors, canines, premolars, and molars. A detailed analysis is as follows:

1. Incisors

Incisors are located in the front of the oral cavity, with four in the upper jaw and four in the lower jaw, totaling eight. Their shape is shovel-like, with a flat and broad crown and a sharp cutting edge at the border, similar to the blade of scissors. Their main function is to cut food—for example, when biting into solid foods such as apples or bread, incisors quickly separate pieces from the whole. Additionally, because they are positioned at the front of the mouth, incisors play a role in maintaining facial aesthetics and assisting with speech.

2. Canines

Canines are located on either side of the incisors, with two in the upper jaw and two in the lower jaw, totaling four. They are also known as cuspids or dog teeth. The crown is pointed and the root is thick and long—making them the teeth with the longest roots in the mouth. The sharp cusp effectively pierces food and is especially suited for tearing tough foods such as meat and fibrous vegetables. Due to their strong root structure, canines also help support the corners of the mouth and maintain facial contours.

3. Premolars

Premolars are situated between the canines and molars, with four in the upper jaw and four in the lower jaw, totaling eight. They are also called bicuspids. Their crown shape is intermediate between that of canines and molars, with two or more cusps on the occlusal surface and shallow grooves and pits. Their primary function is to assist canines in tearing food and to help molars grind food, serving as a transitional link. Premolars usually have one or two roots, providing good stability and enabling them to withstand moderate chewing pressure.

4. Molars

Molars are located at the back of the oral cavity, with six in the upper jaw and six in the lower jaw, totaling twelve. They have the largest crown volume among all teeth, with broad occlusal surfaces covered with complex grooves, pits, and cusps, giving them the largest chewing surface area of the four tooth types. Their main function is to thoroughly grind and crush food, further breaking down torn pieces into small particles to facilitate digestion and absorption in the gastrointestinal tract. Molars have multiple thick roots capable of withstanding high chewing forces, making them the primary teeth responsible for mastication.

The morphological differences among these four types of teeth directly determine their specific roles in the chewing process, working together to complete the cutting, tearing, and grinding of food.

View All

How long does it take for teeth to grow in after losing baby teeth?

In general, when children are losing baby teeth and permanent teeth are erupting, there is no fixed timeframe for the process from baby tooth loss to full eruption of the permanent tooth. It usually takes 1 to 3 months, with the exact duration influenced by individual development rate, the manner in which baby teeth fall out, and the oral environment. In daily life, attention should be paid to children's oral hygiene—brushing teeth morning and night, rinsing after meals to prevent decay of baby teeth. During the tooth-replacement period, children should avoid using their tongue to lick the gums or biting hard foods.

View Full Answer

Will a 6-year-old child's decayed permanent molar be replaced by another tooth?

A 6-year-old child has four primary molars in the mouth, one each in the upper left, upper right, lower left, and lower right positions. These are part of the primary dentition and are typically replaced by permanent teeth between the ages of 9 and 12. Even if a primary molar develops a cavity, as long as the tooth root is not severely damaged and the permanent tooth germ is unaffected, the primary tooth will naturally exfoliate when the permanent tooth erupts. However, dental caries still require treatment to prevent pain or infection that could affect the child's eating habits and the eruption of permanent teeth.

View Full Answer

Can teeth regenerate?

In general, whether teeth can regenerate depends on age and tooth type. In children, when primary (baby) teeth fall out, permanent teeth will naturally grow in their place. However, if adult teeth are lost due to shedding, decay, or injury, they cannot naturally regenerate. It is important to protect teeth through daily care, including brushing teeth morning and night, using dental floss to clean between teeth, and having regular dental check-ups and professional cleanings.

View Full Answer

How many teeth do normal people have?

Human tooth development occurs in stages: during the primary dentition stage (from 6 months after birth to around age 6), 20 primary teeth erupt, responsible for chewing and the development of the jaw and face. Starting at around age 6, the permanent tooth replacement phase begins; by approximately age 12, all 20 primary teeth have been replaced, and the number of permanent teeth stabilizes at 28. Between ages 17 and 26, some individuals may develop 1 to 4 wisdom teeth, while others may never grow wisdom teeth—both scenarios are considered normal.