Structure of Human Teeth - Research Paper Example

Structure of Teeth Bell (2006 defines teeth as “distinct organs of a body structure, attached to the maxillary bones, and formed for the purpose of dividing and communicating the food, preparatory to digestion.” The parts of tooth that form its structure include crown, root, enamel, dentine, pulp cavity, cementum, jaw bone, and gum. Crown is the part of tooth that is visible. It goes inside the gum where it forms the root of the tooth. Enamel is the hardest substance in the body that covers the crown. Beneath the enamel lies the dentine, which is visible in case the crown is damaged. Beneath the dentine lies the pulp cavity which is embedded in the interior of the tooth taking the shape of the tooth itself, being largely located in the crown and then going downwards into the root where it diminishes. This cavity is filled with such pulp that is actually a vascular tissue consisting of nerve endings and blood vessels that enter into the pulp cavity through the root canal that is buried deep inside the root of the tooth. Nerve endings take the message to the brain and we feel pain when the tooth is damaged or is being treated. Blood vessels bring in oxygen for the cells of the pulpy tissue. Cementum is a layer that borders the root and its main purpose is to support the tooth. Jaw bone is the structure that holds the teeth and gum is the part that covers the roots and guards the jaw bone. 2. Enamel Enamel, a covering over the crown of the tooth, is known to be the hardest of all the tissues in the human body. Enamel, which is mainly made up of calcium salts, is hard enough firstly because it has to protect the underlying softer portion of the tooth called the dentin, and secondly because it has to aid in the crushing and chewing of the food. Phinney and Halstead (2003, 96) state in their book on dentistry that “enamel is thicker on the biting surfaces, occlusal cusps, and the incisal edge than in other areas.” If we examine a cross-section of enamel, we come to know that there are enamel rods, also called enamel prisms, embedded inside which are around 4 mm in diameter (Phinney and Halstead). They are cemented together and are of the structure of fish with heads and tails, and they are located inside the enamel in such a way that the head of one enamel rod is touching the tails of the other two. These enamel rods have the lines of Retzius that are marked on the rods as developmental marks. Other than these lines, there are neonatal lines, imbrications lines, and perikymata which are some marks and grooves on enamel rods. The main proteins that are found in the enamel are enamelins and amelogenins. Sometimes, a membrane called the Nasmyth’s membrane is formed by the ameloblasts, which covers the enamel. This membrane gets stained very easily and can easily be removed through polishing sessions. Another problem is tooth decay which starts when the enamel is destroyed by the bacteria that cause plaque which is acidic in nature. 3. Dentin Dentin is another important structure in human tooth and lies beneath the enamel. It is not as harder as enamel although it is another hard structure in the body. It forms most of the tooth structure. The composition of dentin involves “crystals of carbonated apatite together with a small amount of collagen” (Weiner et al. 1999). Dentin contains both organic and inorganic substances. 70% of it is inorganic while 30% is the organic substance (Melfi, Alley and Permar, 2000, p.113). Dentin consists of a number of long micro tubules that “have an internal diameter of 1 micrometer and extend from just below the dentin-enamel junction (DEJ) to the pulp cavity” (Martin 2006, 430). These tubules that run perpendicularly throughout the portion of the dentin are surrounded by peritubular dentin which is a mineral that is contained by the actual dentin that lies beneath the enamel in the crown of the tooth. When compared to the intertubular dentin, the peritubular dentin is found to be much harder and stiffer. The dentinal tubules have cell projections and the whole cell process is going on in these tubules. These cells, called the odontoblasts, line the whole nerve, which is why the dentin, if exposed, is sensitive to touch, sweet or cold things. This sensitivity occurs when these stimuli cause the fluid inside the odontoblasts to move. Towards the root side, the dentin is surrounded by the cementum. Like the enamel, coronal and root dentin also gets exposed due to tooth wear and thus is treated clinically (Lussi 2006, p.94). 4. Dentine-Enamel Junction (DEJ) Enamel and dentin are connected together through the dentin-enamel junction (DEJ). DEJ is a tissue in the tooth structure that serves as a bonding between the two differently calcified layers namely the enamel and the dentin. It becomes a platform for the hard enamel to work in harmony with the soft dentin that lies beneath. When we look at its structure, we come to know that the convexities of DEJ are toward the dentin whereas the concavities are going toward the enamel. This arrangement of convexities and concavities helps in the bonding between the dentin and enamel. There is very little research on the composition and thickness of DEJ. However, researchers agree that it is high in organic content and is less calcified than other structures of the tooth. DEJ has been known to be a tissue that prevents enamel from entering the dentin due to accidental tooth fracture. The bonding that it provides helps the dentin and enamel to perform at their best in mechanical context. Urabe at al. (2000) measured the cohesive strength of DEJ through a microtensile test. In their experiment, they found that the tensile cohesive strength of DEJ was 51.5 MPa. In bicuspid and molars, the DEJ region is almost straight while in cuspid and incisor, it takes the shape of the tooth. DEJ is also the point where the biomineralization of enamel begins. At DEJ, the proteins of the enamel are deposited on the dentin with collagen. In short, DEJ links enamel and dentin so that both support each other. 5. Properties of Teeth A set of human teeth would contain teeth of different sizes and shapes depending on their functions. Functional Properties Canines and incisors are the types that help us in biting the food and tearing it apart. Premolars and molars are those teeth that help us in chewing the food thus they are made with flat tops so that the food is ground easily into smaller digestible particles. Physical Properties Physical properties include white color of the enamel, its hard nature, yellow color of the dentin and its softness as compared to the enamel. The softness of the dentin helps reduce strain and prevent tooth fracture. When food particles are left uncleaned in the teeth, this gives rise to bacteria that ingest sugars from food and create plaque. This results in cavities in teeth when the enamel is torn down and the dentin is exposed. Enamel is whitest when it is thickest, and with age when enamel worns out, the yellow dentin starts appearing which is why older people mostly have yellow teeth. Mechanical Properties Fluids and meals that the teeth are exposed to have a great impact upon their mechanical properties. Treatments like bleaching and polishing of teeth also affect the mechanical properties. Even the nanostructures of the teeth are affected. The Young’s modulus and the hardness of the enamel varies throughout its cross section, being highest in regions which are the most calcified. An “increase in mechanical properties with increasing distance from the DEJ” is found in the research by Brauer et al. (2011). References Adrian Lussi. “Tooth Structure.” Dental Erosion: From Diagnosis to Therapy. Switzerland: Karger Publishers, 2006. Brauer, Delia S., Joan F. Hilton, Grayson W. Marshall, and Sally J. Marshal. “Nano- and Micromechanical Properties of Dentine: Investigation of Differences with Tooth Side.” Journal of Biomechanics, 44.8(2011): 1626-1629. Donna J. Phinney and Judy H. Halstead. “Tooth Structure.” Delmar’s Dental Assisting: A Comprehensive Approach. USA: Cengage Learning, 2003. John Wilson Martin. Concise Encyclopedia of the Structure of Materials. USA: Elsevier, 2006. Melfi, Rudy C., Keith E. Alley, and Dorothy Permar. Permar’s Oral Embryology and Microscopic Anatomy: A Textbook for Students in Dental Hygiene. USA: Lippincott Williams & Wilkins, 2000. Thomas Bell. The Anatomy, Physiology, and Diseases of the Teeth. UK: Oxford University, 2006. Urabe, I., S. Nakajima, H. Sano, and J. Taqami. “Physical Properties of the Dentin-Enamel Junction Region.” Am J. Dent., 13.3(2000): 129-135. Weiner, Steve, Arthur Veis, Elia Beniash, Talmond Arad, Jerry W. Dillon, Boris Sabsay and Farisa Siddiqui. “Peritubular Dentin Formation: Crystal Organization and the Macromolecular Constituents in Human Teeth.” Journal of Structural Biology, 126.1(1999): 27-41. Read More