Written by: Dennis Kwan, Edited by Ivan Suen
In this article, you will take a glimpse into the structural changes of teeth due to evolution and environmental factors.
In order to learn more about the evolution of teeth, it is vital to first examine the structure of human teeth.
Figure 1 on the structure and layers of human teeth.
Real teeth are made up of three layers and have the same general structure. In mammals, an outer layer of enamel covers part or all of the crowns of the tooth, which is entirely inorganic and the hardest tissue in the body. The primary mineral in enamel is hydroxyapatite, which is crystalline calcium phosphate.
Dentine is the tooth's intermediate layer, which is softer than enamel and has a comparable composition to bone. Dentine is the primary mass, or core, of each tooth and runs practically the whole length of the tooth, with enamel covering the crown and cementum covering the roots. Dentine is nourished by the pulp, which is the tooth's deepest layer.
The pulp, which is made up of cells, tiny blood vessels, and a nerve, is housed in a cavity at the center of the tooth. The pulp canal is long and narrow, with an enlargement at the coronal end known as the pulp chamber. The pulp canal runs practically the entire length of the tooth and connects to the body's general nutritional and neurological systems via the apical foramina (holes) at the root's end (AF Dental, n.d.).
The root of the tooth extends below the gum line and is at least partially covered by cementum. The latter has a structure that is similar to bone but is less dense than dentine. Cementum provides a thin covering for the root and acts as a medium for the fibers that hold the tooth to the surrounding tissue to bind to (periodontal membrane). Each tooth's cementum is connected to the surrounding alveolar bone by gum (How Did Teeth, n.d.).
The function of Teeth:
Teeth aid animals in getting food and breaking it down so that it may be digested efficiently. Animals who have lost their teeth are usually unable to eat enough food to survive. The mechanical activities that teeth must fulfill are determined by the food source of the animal. The animal may be required to penetrate the skin and tear meat, grind fibrous vegetables, or do a combination of both (15.1 Digestive, n.d.).
To help them take down prey and eat fresh meat, predators generally have sharp, pointed, or even serrated teeth. Herbivores, on the other hand, have long, pointed incisors at the front of their mouths to aid in cutting bite-sized pieces from plants, as well as molars with broad, rough surfaces in the back of the mouth that crush and break down plant matter for easier stomach digestion.
Consequently, adaptations of types of teeth to assist digestion include:
1. The incisors or front teeth break food into bite-sized portions.
2. Jagged, sharp canine teeth that can be used to break meat and other meals into bits.
3. Molars and premolars, which pulverize vegetable matter and other meals.
Figure 2 on the function of incisors, cuspids, and molars.
Tooth Form:
Throughout our lives, we have two sets of teeth. The primary, or deciduous, teeth are the first set, while the permanent teeth are the second. Humans have 32 permanent teeth and 20 primary teeth. In simpler words, humans have two sets of teeth; baby teeth that loosen and fall out before age and adult teeth that remain in place throughout adulthood (Structure and Composition, n.d.).
Because teeth can be lost due to injury or disease, certain animals have the ability to replace them throughout their lives. The quantity and shape of an animal’s teeth change via folding and growth patterns to suit their distinct diets. For example, cows have flat molar teeth with parallel ridges for grinding tough grasses, pigs have blunt, thick teeth useful for crushing hard roots and seeds.
Edward Drinker Cope’s Theory:
The myriad molars or teeth structures of modern mammals can be unearthed back to a common form called ‘tribosphenic,’ which first appeared during the dinosaur age. In the 19th century, a paleontologist, Edward Drinker Cope brainstormed and came up with the simplistic model for how this form evolved. He hypothesized that it began with a cone-shaped tooth seen in fishes and reptiles. He soon believed small cusps were then added so the teeth had three in a row aligned front to back and connected by crests. Over time, the cusps were pushed out of line to make triangular crowns, and adjacent teeth formed continuous zig-zag crests for slicing and dicing. Next, a low shelf then formed at the back of each set of teeth, becoming a medium for crushing (Teeth, n.d.).
Figure 3 on small cusps adding to the teeth.
Although many scientists of that era disagreed with Cope’s hypothesis, visual examples of teeth from the fossil record looked just like Cope’s predictions. Through his hypothesis, scientists and researchers today are able to conduct experiments to further understand the structure of teeth (Tooth, n.d.).
References
AF Dental. (n.d.). https://af-dental.business.site/posts/7471169218679054449
How did teeth evolve? - Peter S. Ungar. (n.d.). https://ed.ted.com/lessons/how-did-teeth-evolve-peter-s-ungar
15.1 Digestive Systems. (n.d.). https://opentextbc.ca/biology/chapter/15-1-digestive-systems/
On the evolutionary advantage of multi-cusped teeth. (n.d.). https://www.researchgate.net/figure/Tooth-types-of-two-early-mammals-a-Triconodont-tooth-from-an-early-mammal-from-India_fig1_306532681
On the evolutionary advantage of multi-cusped teeth. (n.d.). https://www.researchgate.net/figure/Tooth-types-of-two-early-mammals-a-Triconodont-tooth-from-an-early-mammal-from-India_fig1_306532681
Structure and composition of a human tooth. (n.d.). https://www.researchgate.net/figure/Structure-and-composition-of-a-human-tooth_fig4_209233992
Teeth. (n.d.). https://biologydictionary.net/teeth/
Tooth. (n.d.). https://www.britannica.com/science/tooth-anatomy
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