The 5 Types of Teeth and Their Characteristics
Teeth are essential on both an evolutionary and social level. Oral health, a concept that also includes a complete and clean set of teeth, is an indicator of physiological well-being and socioeconomic status in equal measure. We’re able to know (to some extent) what a person is like just by looking at their smile. Do you know the types of teeth that characterize our species?
Teeth are structures used by many different vertebrates to break down food (carnivores) or to shred it (ruminant herbivores), which is an essential step for smooth digestion to occur. Keep reading, because in the next few lines, we’ll tell you everything you need to know about the different types of teeth in humans. Don’t miss it!
What are teeth?
The University of Navarra Clinic (CUN) defines the tooth as ‘each of the pieces that occupy the oral border of the mandible and maxilla’. At a biological level, this structure is conceived as a calcified unit found in the mandibular or oral area of various vertebrates. Its primary use is to break down food, but it has many more.
In some animals (particularly carnivores and omnivores), teeth serve to capture and hurt prey, break carcasses, bones, and skin, defend against attacks, and even establish social dominance with the rest of the herd’s congeners. The general structure of the dentition is repeated between taxa, but there are some variations between the teeth of mammals and the rest of vertebrates.
Many living beings are monophiodonts, that is, they only have one denture in the adult stage that isn’t replaced (if the decidua occurs in the fetal period). The diphiodonts are those that have a complex of deciduous teeth, which end up being replaced by a definitive set. Finally, polyphiodonts generate many dental complexes throughout their life.
Beyond the permanence of the pieces and their replacement rate, the dentition of living beings is also categorized into the following groups:
- Homodonts: These have a dentition that’s made up of pieces equal to each other.
- Heterodonts: Living beings within this category have a varied dentition on their jaw. In each taxon, there are different types of teeth, each with a specific function.
This biological introduction was necessary, because now you can understand what it means for human beings to be difiodonts and heterodonts at the same time. In other words, we have two sets of teeth throughout our lives and we carry groups of different teeth simultaneously in our jaw.
Human tooth structure
Now that you know what our teeth are like on a biological level, it’s natural to wonder what teeth are made of. In the following list we’ll show you its layers and the characteristics of each one of them:
- Enamel: As experts tell us, enamel is the hardest tissue in the human body. It contains 96% mineral matter, with the hydroxyapatite crystals being the main components that give it its rigidity. It differs from other hard tissues (such as bones) in that it doesn’t carry collagen in its histological composition. It’s also the outermost layer.
- Dentin: Dentin is the type of tissue that is found immediately under the enamel. It’s made up of 70% inorganic material, while 20% corresponds to organic substances and 10% to water. It’s a connective tissue supported by a collagen matrix and is much more fragile. It has a yellowish hue.
- Cement: This cement is located under the dentin and is composed of 55% calcium hydroxyapatite, 33% collagen, and 22% water.
- Pulp: This is the innermost, centralized layer and is composed of soft connective tissue. The specialized cells that are located in this histological section are known as odontoblasts, whose function is the formation of dentin. The pulp is commonly known as the “nerve” of the tooth.
The structure of permanent teeth is very complex, since humans must carry them (in an ideal setting) throughout their adult life. In any case, the composition of each piece varies greatly according to its function and location in the mouth.
The 5 types of teeth and their role in human biology
Now that we have gone through the biology and histology of teeth, we’re ready to explore what types exist. We divide them according to their permanence, since a deciduous molar (a first, or milk, tooth) has little to do with our second teeth.
1. Deciduous dentition
Dental clinics define deciduous dentition as ‘the first set of teeth that appear in children from 6 months of age’. The appearance of teeth in pediatric age has been very well described, so it’s easy to establish time intervals that are more or less applicable in all cases:
- 6 to 9 months of age: Lower central incisors appear
- 7 to 10 months of age: The upper central incisors and the upper lateral incisors appear
- 15-16 to 21 months: Lower and upper canines appear
- 12 to 16 months: The first molars appear, both lower and upper
- 21 to 30 months: Second molars appear, both lower and upper
The complete dentition of an infant is made up of 20 teeth: 8 incisors, 4 canines, and 8 molars (first and second teeth). During tooth growth, it’s normal for the baby to have certain symptoms, such as irritability, the need to suck or bite on things to press on the gums, decreased appetite, and excessive drooling. All of these signs are normal.
Deciduous teeth are much more fragile than permanent teeth, since the enamel and dentin layers are narrow and the pulp has a greater presence than in the permanent counterparts. However, they perform a series of essential functions in the development of human beings, among which the following stand out:
- Deciduous teeth allow the baby to chew. This mechanical process is essential, as, at this time, exponential growth occurs that requires effective and rapid nutrition.
- They’re the guide for the permanent teeth. The root of each temporary tooth is directed to its permanent counterpart so that the spaces and the location of the teeth are respected.
- They stimulate the growth of the jaws (each of the two bony pieces that make up the mouth) thanks to the mechanical act of chewing.
- They allow the correct development of speech. Deciduous teeth open the way for the infant to begin to make its first sounds and to develop language in later stages.
2. Permanent dentition
The permanent dentition is the one that appears after the decidua and is maintained throughout the person’s life. They begin to appear around 6 years of age; this set consists of a total of 32 teeth.
Each permanent tooth is essential to understanding phonation and chewing in humans. We’re going to give you some detailed insight into each type.
1. Incisors (8 teeth)
The incisor teeth correspond to the teeth located in the anterior area of both dental arches (4 above and 4 below). Each maxilla contains 2 central and 2 lateral incisors. Upper centrals are also known as paddles, as they resemble a shovel and are larger than other teeth.
The upper central incisors are conceived as the most important teeth in individual aesthetics. Each dental unit has a trapezoidal crown (partly covered by enamel), a single root, and greater height than width. As a whole, they occupy a large part of the space formed during the act of smiling, so their absence causes facial problems.
In humans, the incisors are powerful and allow the breakdown of food into smaller pieces (the act of biting and chewing). In addition, they’re essential for the development of speech and phonation, as they serve as a fulcrum for the tongue and prevent air from “escaping” when saying certain words. In summary, it can be said that its function is approximately 10% masticatory and 90% phonetic-aesthetic.
Not all mammals have 8 incisors. For example, possums have 18 in all.
2.2 Canines (4 teeth)
As indicated by the Statpearls medical portal, the canine teeth are considered to be the corners of each dental arch, as they separate the anterior section (incisors) from the posterior section (molars). This group represents a total of 4 teeth – 2 above and 2 below, on each side.
From a physiological point of view, they’re the most important teeth (together with the first molars) as they play an essential role in mandibular guidance and function. The term canine guide refers to the control that these teeth exert when performing lateral chewing movements. Without them, this mechanical act becomes very complicated.
Canines are large at both the crown and the root level. The tip is pentagonal and sharp, which helps a lot to break up the food into smaller pieces. In any case, in our species, it can be generalized that they have a chewing function of 20% and an aesthetic-phonatory function of 80%.
In humans, these teeth aren’t too developed, but other carnivorous vertebrates have very pronounced canines. It should be noted that, in nature, canines are usually a clear indication of sexual dimorphism, since the males of many species have larger ones than the females (either adapted for hunting or fighting).
2.3 Premolars (8 teeth)
Premolar teeth are those that grow where a deciduous molar used to be. There are a total of 8 – 4 in the upper jaw and 4 in the lower jaw, and 2 on each side of the body plane respectively. They have at least 2 cusps (bicuspid), although the second lower premolar has 3 (tricuspid), and a pentagonal crown. These teeth only appear in the final adult teeth.
The premolars are responsible for the fine grinding during the act of chewing. In human beings, their function is 60% chewing and 40% aesthetic-phonatory, as they aren’t seen when we smile, and the tongue doesn’t rely on them as much to produce sounds.
2.4 Molars (12 teeth)
The molar teeth are a total of 12 – 6 in each jaw and 3 on each side of the body plane. The third and final molar in the dental arch is known as the wisdom tooth, and is the last piece to appear (at between 18 and 25 years of age). Wisdom teeth are considered vestigial and unused today, but our hominid ancestors used them to chew plant tissue.
The molars are located at the back of the mouth and are the ones with the largest surface area. They’re named in order of appearance as first molar, second molar, and third molar (upper or lower). Here are the traits of the first molars:
- Upper first molars: These have 4 functional cusps (mesiobuccal, distobuccal, mesiopalatine and disto-palatine) and an accessory. Its crown has a rhomboid shape.
- Lower first molars: These have 5 functional cusps (mesiobuccal, distobuccal, distal, mesio-lingual and disto-lingual). The crown has a rectangular shape.
In humans, the function of the molars is more than 90% chewing and less than 10% aesthetic. In any case, it’s considered that the functionality of the third molars or wisdom teeth is almost nil and they’re usually extracted due to the problems that they give in the long term.
Ruminant herbivorous mammals have highly developed molars to “liquefy” plant matter.
A world after human teething
So, these are the 5 types of teeth that exist in humans (deciduous plus 4 permanent), but you must bear in mind that this dental plane (32 = 8 + 4 + 8 + 12) isn’t the same in all species of mammals or vertebrates. Each living being is specialized in a type of diet, but being omnivores, we have a great variety and dental adaptability.
In any case, it’s necessary to bear in mind that the function of teeth goes far beyond chewing. For example, the incisors and canines have essential speech functions ranging from the development of basic sounds to the formation of complex words. Nor should its aesthetic work be neglected, since the lack of incisors can create great insecurity and complexes.
For all these reasons, it’s vital to look after our second teeth from the moment they appear, as they’ll accompany us for the rest of our lives. Mouth rinses, regular brushing, and limiting sugar intake will help these all-important pieces remain healthy and viable until the later stages of life.
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