Structure and function of the components of teeth
The crystalline structure of salt makes enamel extremely hard, much harder than dentin. In addition, the special protein mesh, although only about 1 percent of the mass of enamel, makes teeth resistant to acids and enzymes.
The figure is a longitudinal section of a tooth, depicting the main parts of the tooth: crown, enamel, dentin, cementum, and pulp. Teeth can also be divided into crowns, which are the protrusions from the gums into the mouth, and legs, which are the inside of the jawbone. The part of the neck between the crown and the root surrounded by gums is called the neck.
Figure. Structure of teeth
The outer surface of the tooth is covered by a layer of enamel that is formed before teething by special epithelial cells called ameloblasts. Once the tooth has erupted, the enamel is no longer formed. Enamel is densely composed of large crystals of hydroxyapatite and adsorbed carbonate, magnesium, sodium, potassium, and other ions embedded in a network of strong and insoluble protein components that are similar in physical (but not chemically similar) properties. identical) to the keratin of the hair.
The crystalline structure of salt makes enamel extremely hard, much harder than dentin. In addition, the special protein mesh, which makes up only about 1 percent of the mass of enamel, makes teeth resistant to acids, enzymes and other erosive agents since this protein is one of the insoluble proteins. and most durable.
The bulk of the tooth is dentin, which is a strong bony structure. Dentin is made up mainly of hydroxyapatite crystals similar to those found in bone but denser. The crystals are embedded in a network of collagen fibres, in other words, the major components of tooth enamel are the same as bone. The main difference is in histology because the dentin does not contain any osteoclasts, osteoblasts, osteoclasts, or spaces for blood vessels or nerves. Instead, it is deposited and nourished by a layer of cells called odontoblasts, the inner layer along the pulp cavity.
The calcium salts in the dentin make it extremely resistant to squeezing, and the collagen walls help resist and withstand the stresses that can occur when teeth collide with solid objects.
Cement is a bony substance secreted by the cells of the periodontal membrane, which is located at the dental acupoint. collagen fibres pass directly through the jawbone, through the dental lamina, and then into the cementum. The collagen and cementitious fibres hold the teeth firmly in place. When teeth are exposed to excessive traction, the cement layer becomes thicker and stronger. In addition, it also increases in thickness and strength with age, helping teeth become stronger in the jaw in adulthood and beyond.
The cavity of each tooth contains the pulp inside, which includes connective tissue containing nerves, blood vessels, lymphatic system and lymphocytes. The pulp cavity is lined with odontoblasts; during the formative years of the tooth, dentin occupies more and more of the pulp chamber, making it smaller. After some time, the dentin stops growing and the pulp cavity remains largely unchanged in size. However, the odontoblasts remain active, producing small dentinal tubules that penetrate the dentin; It plays an important role in the exchange of calcium, phosphate, and other minerals with dentin.
Humans and most other mammals develop two sets of teeth throughout their lives. The first teeth are called deciduous teeth, or baby teeth, there are 20 in humans. Teething begins between July and 24 months and lasts until 6 or 13 years of age. When 1 baby tooth falls out, the Permanent Teeth replace it and an additional 8-12 molars appear behind in the jaw, bringing the total number of permanent teeth 28-32, depending on whether 4 wisdom teeth erupt, which is not happening in everyone.
Figure. A. primitive teeth; B. tooth development; C. milk teeth.
Formation of teeth
The figure shows the formation and eruption of teeth. The figure depicts the self-rolling of the oral epithelium into the dental lamina, resulting in the formation of a tooth producing organ. The upper epithelial cells produce ameloblasts, which later form the outer enamel layer of the tooth. The inferior epithelial cells roll between the teeth to form the pulp cavity and odontoblasts secrete dentin. Thus, the enamel is formed on the outside of the tooth and dentin is formed on the inside, creating a primary tooth, as shown in the figure.
During adolescence, teeth begin to protrude from the bone through the epithelium into the mouth. The cause of the "grow" is unknown, although many theories have been put forward in an attempt to explain the phenomenon. The most likely theory is that the growth of the root and bone beneath the tooth gradually pushes the tooth upward.
The development of permanent teeth
During the embryonic period, a tooth-forming organ also develops in the dental lamina for each permanent tooth, which plays an important role once the primary teeth have fallen out. These tooth forming organs slowly form permanent teeth during the first 6-20 years of life. When each permanent tooth is fully formed, it, like a baby tooth, pushes outward through the bones.
In doing so, it wears down the root of the baby tooth and eventually makes it lose and broken. Not long after that, permanent teeth grew to take up the place.
Metabolic factors affecting tooth development
The rate of teething can be accelerated by both thyroid and growth hormones. In addition, the deposition of salts in the early tooth form is significantly influenced by various factors of metabolism, such as dietary calcium and phosphate availability, vitamin D , and the rate of PTH secretion. When all these factors are normal, the dentin and enamel will be healthy respectively, but when deficient, the calcification of the teeth can also be faulty and the teeth will be abnormal throughout life.
Mineral exchange in teeth
Salt, like bone, is composed of hydroxyapatite with absorbed carbonate and various cations bound together in a hard crystalline substance. In addition, new salts are continuously deposited as old salts are reabsorbed from the teeth, as occurs in bone. Deposit and resorption occur mainly in dentin and cementum and to a limited extent in enamel. In enamel, these processes occur mainly in mineral exchange with saliva rather than with body fluids and the marrow cavity. The rate of reabsorption and deposition of minerals in cement is similar to that in bone marrow, while the rate of deposition and reabsorption of minerals in dentin is only one-third of bone.
Cement has nearly identical characteristics to normal bone, including the presence of osteoblasts and osteoclasts, whereas dentin lacks these features, as explained earlier. This difference certainly explains the difference between mineral exchange rates
In summary, the mineral exchange continues to occur in dentin and cementum, although the mechanism of this exchange in dentin is unclear. However, yeast metabolizes minerals very slowly, so it maintains most of its original mineral intake throughout its life.