Comparison of bones and teeth
The human bones and teeth are one of the most similar yet different structures within our body. They are both made of living and non-living materials, and both are replaced at some point. However, they have different specialized cells, compositions of calcium and phosphorus, different functions, and different kinds of cells.
Teeth
The hardest substance in the human body are teeth. Teeth are technically considered bones because of their strong crude and tissue surrounding and marrow inside the bone. It is generally assumed that teeth are used only for eating, however it has a bigger impact than what is the notion in this regard (e.g. speech).[1] The anatomy of the teeth is not simple as one may presume, but rather complex. Our teeth are unique as they can be used for both biting and tearing, which is good for tearing food, and grinding and crushing, which are beneficial for chewing and grinding foods.[2]
Types of teeth
We do not have all the same kinds of teeth. We have a variety and it is dependent on our diet. While it is noted most carnivores would have incisors and herbivores would tend to have molars for grinding food.
- Molar (8) – Flat teeth with a unique pattern which are great for macerate plant or animal tissue.[3]
- Incisors (8) – Flat blades best used for cutting.[3]
- Premolars (8) – Intermediate in relation to the function of incisors and molars.[3]
- Canines (4) – Beside the incisors and are generally pointed.[3]
- Wisdom Teeth (4) – Teeth that are not commonly used now, and are surgically removed. They are often referred to as the third molars.[1][3]
The normal human adult has 32 teeth which are generally present (aside from wisdom teeth) by the age of 13.[1] However, scientists predict that we will have fewer teeth with the disappearance of our wisdom teeth.[1] The evolution of the teeth in recent times occurred when the expansion of our size of the brain was occurring. With the increase in size of our jaw became much smaller, and thus the lack of need of our third molars.[1][4] Evolution now favors not having wisdom teeth and thus it is a most favorable trait that would be passed on.[4]
What makes a tooth
The tooth is a complex structure. It has to withstand all the harmful things we may ingest into our body. With such an important structure its components are even more important like:
- Enamel – Composed of primarily calcium phosphate, a hard material. It is generally what gives our teeth the white look and the hardest part of our tooth. Also known as bone or bone marrow.[1]
- Dentin – Layer surrounded by the enamel. It is made up of living cells, which are known to secrete a hard mineral substance (used to maintain the integrity of the enamel)[1]
- Pulp – Living inner structure of the tooth. Within the pulp there are blood vessels and nerves.[1]
- Cementum – Tissue that holds/binds the roots of the teeth against the jaw.[1]
- Periodontal ligament – Tissue that aids in the holding of the teeth to the jaw.[1]
- Crown - Visible part of the tooth. A protective layer (enamel) covers the crown.[2]
- Neck - Area of the tooth between the crown and the root.[2]
- Root - Portion of the tooth which extends to the gum and into the bone of the jaw.[2]
Adult life - changes to the teeth
The primary difference first noticed about the differences in an adults mouth and a babies mouth are the number of teeth. A child's mouth contains 20 temporary teeth, which are called primary teeth, consisting of:[2]
- 4 second molars
- 4 first molars
- 4 cuspids (also called canine or eye teeth)
- 4 lateral incisors
- 4 central incisors
In contrast the adult's mouth contains 32, and it differs from child's teeth as par below:[2]
- 4 third molars (also called wisdom teeth)
- 4 second molars (also called 12-year molars)
- 4 first molars (also called 6-year molars)
- 4 second bicuspids (also called second premolars)
- 4 first bicuspids (also called first premolars)
- 4 cuspids (also called canine or eye teeth)
- 4 lateral incisors
- 4 central incisors
Teeth conditions
While the teeth maybe strong and durable it is still able to decay or breakdown with bad hygiene. Some conditions can occur like:
Cavities – Bacteria that damage the enamel and deeper structures of the teeth. It generally occurs in the molars and premolars.[1]
Tooth Decay – This is the common name for diseases that occur in regards to the teeth, like cavities.
Periodontitis – Inflammation of the deeper structures of the teeth (cementum, periodontal ligament)
Gingivitis – Inflammation of the portion of gums, around the crown of the teeth.
Molecular composition of teeth
A research done by the University of Michigan showed that the inorganic part of human teeth contain three chemical formulas:[5]
- Tricalcium phosphate and calcium carbonate – Ca2(PO4)2 + CaCO3
- Carbonate apatite – Ca10(PO4)6CO3
- Hydroxyl apatite – Ca5(PO4)3OH + CaCO3
Study has shown however that there is more organic carbon within the dentine than in the enamel. It is seen that the concentrations of magnesium, carbonate, and chloride concentration increased from the surface to the interior of the enamel.[6] Carbonate and density distribution patterns are easily predictable as they tend to follow the histological and morphological features of the tooth section.[6]
Importance of the jaw
We generally cannot talk about teeth without mentioning the jaw. The jaw is what holds the teeth in place, and prevents them from shattering. If the jaw is unaligned when taking bites it can damage the teeth. Additionally, proper alignment of the teeth and the jaw is crucial for mating in other animals. It has been noted that it is considered that you are immunological weak if your jaw is not aligned.[3]
Evolution and development of teeth
The evolution of teeth is extraordinary. They contain the hardest biological substance known (enamel).[7] Paleontologists and anthropologists have been using fossils to further understand the evolution of teeth. From an evolutionary-developmental perspective there are four things that make it such a compelling model to use:[7]
- The Cusp patterns, which are the tooth shapes and their arrangement which are highly unique to each species.
- Tooth patterns determine the diet it had in the past and its feeding niches
- Tooth development involves just two embryonic cell types
- They can be easily cultured in vitro to recapitulate normal development
Two proposed hypotheses for the evolution of teeth
- Teeth evolved independently from jaws from pharyngeal denticles, which is found in many extant species like the zebrafish[7]
- Teeth evolved at the same time, or after, jaws by internalization of skin denticles. This is seen in modern-day sharks.[7]
Research has shown as well that tooth morphogenesis shares many key genes with jaw skeletal morphogenesis.[7] However, this would suggest that the two tissues evolved independently but the evolution of heterodonty (teeth that has different shapes) from homodonty (teeth with an 'all in one' purpose shape) had to directly interact with the jaw morphogenesis.[7]
Bones
Bones in the human body provide the necessary foundation to support the body. However, many people presume that bones are living tissue, which is not entirely true. While it is composed of bone cells, fat cells, and blood vessels, it is also home to nonliving materials such as water and minerals.[8][9] The cells help them grow and repair themselves. A person is born with 300 soft bones and the cartilage grows and is then replaced with a harder more durable material. Additionally, bones fuse together, and eventually the adult skeleton has 206 bones.[9][10]
The functions of the bones are to provide structural support for the body, as well as protection of the vital organs, an environment for marrow (white blood cells), and a storage area for minerals like calcium.[11]
During childhood and adolescence bones are sculpted by a process called bone remodeling, which is formation of new bone and the removal of the old bone.[10] This is partially thanks to the bones being such a great reservoir to hold essential minerals. The adult skeleton is generally replaced every 10 years.[8][11]
The growth of the skeleton is in a response to mechanical forces, and its ability to be a massive mineral storage which is important for the proper functioning of systemic or circulating hormones which respond to change within the calcium and phosphorus levels.[8][10] For example if the Ca/P levels are low then the body transmits signals to take them out of the bones to serve other vital processes within the body.[8] Due to the dual roles with support and regulation of calcium and phosphorus the bone is constantly changing. It requires specialized cells to communicate with the body in order for this to occur.[8][10] The cells have to respond to different signals from internal to the external, and mechanical and hormonal, to the systemic (the whole skeleton) to the local (specific region).[8]
Composition of Bones
Types of Bones
There are commonly two types of bones and it can be identified through examining the pattern of collagen forming the osteoid:[11]
- Woven bone which is a haphazard organization of the collagen fibers and it is mechanically weak
- Lamellar bone is the regular parallel alignment of collagen into sheets (lamellae) and is mechanically strong
The Woven bone is made when osteoblasts produce osteoid rapidly which initially occurs in all fetal bones, but then due to the process of remodeling it is changed to lamellar bones.[8][11] Woven bones are found in adults when osteoblasts have to repair something rapidly such as the repair of a fracture. It would eventually revert to the lamellar bone.[11]
Types of Tissue that make up bones
- A hard outer layer called cortical (compact) bone, which is extremely strong, dense, and durable.[11]
- A spongy inner layer called trabecular (cancellous) bone. Comparative to the other layer it is much lighter and less dense.[11]
Composition on a micro-level
- Bone forming cells, such as osteoblasts, and osteocytes[11]
- Bone resorbing cells (osteoclasts)[11]
- Non-mineral matrix of collagen and non-collagenous proteins (osteoid)[11]
- Inorganic mineral salts deposited within the matrix[11]
Bone cells
The cells that make up bone are very specialized and serve a crucial role.
- Osteoblasts – The cells are derived from the mesenchymal stem cell. They are responsible for the synthesis of the bone matrix and subsequent mineralization.[11] Within the adult skeleton, majority of the bone surfaces are not going undergoing formation or resorption (no remodeling) are lined by bone lining cells.[8][11]
- Osteocytes – Cells that are osteoblasts however have been incorporated within the newly formed osteoid, which would become the calcified bone. They are situated deep within the bone matrix, where it would maintain contact with the osteoid, osteoblasts, and bone lining cells on the surface through an extensive network of cell processes (bone canaliculus).[11] They are examined to be the intermediary to the changes in physical forces and to transmit messages to the cells on the surface, whether to initiate in resorption or formation responses.[9][11]
- Osteoclasts – They are large multinucleated cells, much like macrophages, which are from the hematopoietic lineage.[11] Osteoclasts are found attached to the bone surface at the sites of active bone resorption. They function in the resorption of mineralized tissue and are characteristic feature of a ruffled edge where active resorption takes place by bone-resorbing enzymes which digest to the bone matrix.[9][11]
Molecular Composition of Bones
The process of determining the mineral and non-collagenous organic components of the bone were examined following powdering, demineralization with EDTA and digestion with bacterial collagenase.[12]
The protein, hexose, sialic acid, and uronic acid contents of the bone matrix were determined. It was found that neonatal bone had lower levels of mineral and calcium and higher levels of organic material sialic acid than adult bones.[12] This would suggest glycoprotein is higher in neonatal bone.[12]
The heterogeneous composition of the bone is:[13]
- Hydroxyapatite – Ca5(PO4)3OH + Ca CO3
- Organic phase – contains ~90% type I collagen, ~5% noncollagenous proteins (NCPs), ~2% lipid by weight
- Water
Proteins in the extracellular matrix of the bone can also be broken down into:[13]
- Structural Proteins – Collagen and Fibronectin[13]
- Proteins with specialized functions – serve as signaling molecules, serve as growth factors, serve as enzymes, and others[13]
This is all again dependent on a variety of factors like age, site, gender, ethnicity, and health status. Comparing to other species by examining the human iliac crest our bone is predominantly mineral and organic, as seen in the image.[10][11][12][13]
Adult life – changes within the bone structure
We are born with about 300 soft bones.[8][11] During childhood and adolescence, the cartilage grows and is slowly replaced by hard bone (lamellar bone).[11] The factors that play a role are both genes and the environment for bone development.[8] Errors in gene can result in birth defects. Ideally, the adult’s diet is a large part of bone health throughout life.[8] Eventually, with proper care bones would later fuse together so it can become more durable, with the end result being adult’s skeletons have 206 bones.[8][10][11] Humans tend to grow during their childhood and adolescent years, and their bones get denser continuously.[11] Generally in humans we reach something called the peak bone mass where we will have the highest amount of bone mass, which generally occurs between the ages of 18 and 25.[10] It has been shown that with the higher mass you have the less likely you are to break a bone or to get osteoporosis later on.[8][10]
Fundamental components of a bone
Bones are made of three major components that make them flexible and strong:[14]
- Collagen, a protein that gives bones a flexible framework
- Calcium-phosphate mineral complexes that make bones hard and strong
- Living bone cells that remove and replace weakened sections of bone
Evolution and development of bone
The use of fossil records and genetic information from modern species have aided in figuring the origins of how bones developed.[15] The key issues in determining the past are the primitive examples of mineralization belong to extinct lineages. It has been dependent towards fossil record. It is also to be noted that it coincides with the origin of vertebrates.[15][16]
It is hypothesized that vertebrates were likely to be descended from amphioxus-like forms with a notochord.[15] It was then followed by jaw-less creatures with a cartilage-like endoskeleton, which are like the hagfish or lamprey.[15] The next major event would have been the mineralized skeletal parts - which brought upon the rise of the vertebrate lineage.[15]
In order to understand why bones developed the way they did, many factors have to be taken into account. The environment is one prime example, so take for example 1.5 billion years ago.[15] Tectonic plates were violently moving, and huge amounts of minerals like CaCO3, were washed into the oceans.[15] This could have been the premise of developing bones.[15] This is just one of many proposed ideas on the origins of bones.
Cartilage and bone - the big confusion
The table shows the differences and similarities of cartilage and bones[17][18][19]
| Bone[18][19] | Cartilage[18][19] | |
|---|---|---|
| Types | They are compact or spongy (woven or lamellar). They are considered to be hard, inelastic, and tough | They are in the categories of hyaline cartilage and fibrocartilage, and are generally flexible, soft, and elastic tissue |
| Function | It is used to support the body, in movement, store minerals, and a site of red and white blood cells | They help in reducing the friction at joints, they are between, weight-bearing bones, and holds the integrity of the shape and flexibility of the fleshy appendages |
| Structure | They are made up of osteoblasts, osteocytes, and osteoclasts. The matrix is both organic and inorganic, with large amounts of calcium present | They have chondroblasts, chondrocytes, and their matrix is non-vascular, completely organic, does not contain any lamellae, and minerals like calcium do not need to be present there |
| Location | They are found throughout the axial and appendicular skeleton | Due to the natural strength of the cartilage is much softer, it is found between joints of bones, and where flexibility is required |
These a common misconception is they are considered the same. To bring it into perspective the mesenchymal cells which can differentiate into cartilage (can also become bone cells directly, called intramembranous ossification) and is then replaced by bone.[17]
Bones and teeth are complex and composite structures. Bones can be classified based on their shape and the distinct functions they perform. While long bones have a marrow cavity surrounded by an outer cylinder, flat bones have diverse structures and varying amount of cancellous bone ranging from lower amounts in skull to one mainly consisting of cancellous bone in the spine.[20] Tooth, on the other hand have three different components dentin, enamel, cementum and is connected to the jawbone by a periodontal ligament via cementum.[20] At the microscopic level, bones structural unit comprises distinct struts which connect the bone structure, the thin plates and bones originating about the blood vessels.[20] In the tooth, it is made up of tubules that pass through the dentin and the intertubular dentins.[20]
At the ultra-structural level, bones and teeth are both made up of cells, an organic and an inorganic matrix.[20] While the organic matrix of bone is mainly made up of protein and collagen, in tooth too collagen is primary part of the dentin and cementum, but is non-existent in enamel.[20] The presence of collagen in the two dentin and cementum gives them the desired flexibility.[20] However, it is the presence of mineral that makes them inflexible and strength to bear greater loads and stresses.[20]
Human teeth and bones both contain mineral family, apatites that give both the strength and the hardness.[21] However, the difference being in their composition and the structure of the apatites which gives them different physical attributes such as hardness, density, solubility and brittleness etc.[21] The biological apatites are distinct forms of calcium hydroxyapatite.[21] For the apatite to form all the components such as calcium, phosphorus, etc. need to be present and in appropriate quantity, however, the exact structure and composition of the apatite is quite flexible.[21] The channel site in the hydroxyapatite can be occupied by (OH-,F-) and/or Cl-.[21] While hydoxyapatite is of great relevance, the chlorapatite and fluorapatite, the other two are also very common amongst the apatite group.[21] While the composition of apatite in bones can be varied but the flexibility on this regard is very limited unlike other chemicals.[21] However, it may be noted that much less substitutions are possible in biological apatites because of the limited number of elements available in the body plus also on account of structural limits.[21] While substitution of fluoride takes palace readily and rapidly even at room temperature, the substitution of Chlorine ion does not take place because of its large ionic size.[21] While in the enamel the Ca/P molar ratio is around the normal ratio 1.67, in bones and in dentin the ratio is much different from this ratio as enamel apatite allows for very limited substitutions.[20]
Tooth enamel is the hardest part of the body[6] and is and is made up of 96% mineral which gives it the necessary hardness but on the other hand makes it more brittle too.[22] Dentin, the part of the teeth in the crown of the teeth under the enamel has a different composition of hydoxyapatite which allows it to be flexible and thus absorb all the pressures without breaking.[22] Cementum which separates the dentin from the jawbone is a blend of bone and dentin material.[20]
Bones on the other hand are highly calcified, intercellular mixture of three types of cells - Osteocytes, osteoblasts and osteoclasts.[23] All the cells are embedded in glycans, which is a mixture of collagen fibres, bone proteins and carbohydrates.[22] The bone matrix is made up of 1/3rd organic and 2/3rd inorganic matter.[21] While osteoblasts manage and regulate the mineralization of collagen matrix, osteocytes help in communicating throughout the tissue, osteoclasts remove the bone mineral and matrix.[20]
The distinct composition and structure of minerals results in the contrasts observed in the bone and the tooth enamel. While bone apatite has twice the concentration of carbonate than it is in enamel apatite, the bone crystallites are much smaller compared to the enamel crystallites.[21] While the initial shape of crystals of both the bones and the tooth are round but with age the tissue become elongated and develop differently.[20] The crystal in bone and also in dentin usually are 20-50 nm and width of 12-20 nm, the crystals in enamel are almost 10 times large both in length and width.[20] Both the above attributes of high carbonate concentration and smaller crystallite size result in higher solubility of bone apatite vis-a-vis enamel apatite.[21] In addition the respective structures of the bone and enamel apatites also lead to different morphologies.[20] While in the case of bone it supports a morphology that interfaces very well with collagen fibrils, for enamel very little organic chemicals get associated with it.[20] The properties above blend extremely well with the needs of the two.[21] While bones need to continually form, absorb and precipitate again and again to control the levels of calcium, phosphorus, and magnesium in the body which is one of the key functions of the bones which is not related to the motion, the enamels need to oppose dissolution.[21]
The composition of bone changes with age because of remodeling, health and environmental factors.[20] As a result the unit structure of bone undergoes change in its chemical composition, crystal size and the percentage of minerals present in it.[20] Similarly the organic matrix of the enamel also gets degraded with as enamel does not have a collagen matrix.[20] However, dentin and cementum are not remodeled as such the changes in them are only in terms of changes of minerals present in them with age.[20]
| Cell[20] | Tissue[20] | Composition, structure and function[20] |
|---|---|---|
| Osteoblast | Bone | Round or flat bone forming cells. Regulate mineralization of collagen matrix |
| Osteocyte | Bone | Formed when osteoblasts surrounded by mineral. Help in communicating and sending messages throughout the tissue |
| Osteoclast | Bone | Bind to bone surface and release acids and enzymes. Remove bone mineral and bone matrix |
| Cementoblast | Cementum | Cells engaged in synthesis of cementum minerals |
| Ameloblast | Enamel | Cell involved in producing enamel |
| Odontoblast | Dentin | Cells involved in production of dentin matrix |
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 "Oral Care". The Teeth (Human Anatomy). WebMD. Retrieved 15 March 2015.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 "Your Teeth From Birth to Adulthood". WebMD. WebMD. Retrieved 4 April 2015.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Shubin, Neil (2008). Your inner fish : a journey into the 3.5-billion-year history of the human body (1st ed.). New York: Pantheon Books. ISBN 9780375424472. Search this book on
- ↑ 4.0 4.1 Douglas, Main. "Ancient Mutation Explains Missing Wisdom Teeth". Why Some People Lack Wisdom Teeth. livescience. Retrieved 15 March 2015.
- ↑ Asgar, Kamal (October 1956). "Chemical Analysis of Human Teeth" (PDF). University of Michigan: 742–748. Retrieved 1 April 2015.
- ↑ 6.0 6.1 6.2 Weatherell, JA; Robinson, C; Hallsworth, AS (1974). "Variations in the chemical composition of human enamel". Journal of dental research. 53 (2): 180–92. PMID 4591966.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 McCOLLUM, MELANIE; SHARPE, PAUL T. (July 2001). "Evolution and development of teeth". Journal of Anatomy. 199 (1–2): 153–159. doi:10.1046/j.1469-7580.2001.19910153.x.
- ↑ 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 Office of the Surgeon General, (US) (2004). "Bone Health and Osteoporosis: A Report of the Surgeon General" (Bone health and Osteoporosis). PMID 20945569.
- ↑ 9.0 9.1 9.2 9.3 "Medical Specializations, Medical Dictionary". Mediways. Retrieved 18 March 2015.
- ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 "Bone Basics". National Institute of Arthritis and Musculoskeletal and Skin Diseases. NIH Osteoporosis and Related Bone Diseases National Resource Center. Retrieved 18 March 2015.
- ↑ 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19 11.20 11.21 "Introduction to Bone Biology: All About Our Bones". International Osteoporosis Foundation. International Osteoporosis Foundation. Retrieved 15 March 2015.
- ↑ 12.0 12.1 12.2 12.3 Quelch, KJ; Melick, RA; Bingham, PJ; Mercuri, SM (1983). "Chemical composition of human bone". Archives of oral biology. 28 (8): 665–74. PMID 6314948.
- ↑ 13.0 13.1 13.2 13.3 13.4 Boskey, Adele L (4 December 2013). "Bone composition: relationship to bone fragility and antiosteoporotic drug effects". BoneKEy Reports. 2. doi:10.1038/bonekey.2013.181.
- ↑ "Bone Basics". NOF. National Osteoporosis Foundation. Retrieved 15 March 2015.
- ↑ 15.0 15.1 15.2 15.3 15.4 15.5 15.6 15.7 Wagner, Darja Obradovic; Aspenberg, Per (August 2011). "Where did bone come from?". Acta Orthopaedica. 82 (4): 393–398. doi:10.3109/17453674.2011.588861.
- ↑ Pietsch, Ted. "Biology of Fishes" (PDF). FISH/BIOL 311. University of Washington. Retrieved 2 April 2015.
- ↑ 17.0 17.1 Gilbert, Scott F. (2000). Developmental biology (6. ed.). Sunderland, Mass.: Sinauer Assoc. ISBN 978-0878932436. Search this book on
- ↑ 18.0 18.1 18.2 "Bone vs Cartilage". Diffen. Diffen. Retrieved 6 April 2015.
- ↑ 19.0 19.1 19.2 "Difference between Bone and Cartilage". Major Differences. Major Differences. Retrieved 6 April 2015.
- ↑ 20.00 20.01 20.02 20.03 20.04 20.05 20.06 20.07 20.08 20.09 20.10 20.11 20.12 20.13 20.14 20.15 20.16 20.17 20.18 20.19 20.20 20.21 Boskey, Adele (2007). "Mineralization of Bones and Teeth" (PDF). Elements. 3 (6): 385–391.
- ↑ 21.00 21.01 21.02 21.03 21.04 21.05 21.06 21.07 21.08 21.09 21.10 21.11 21.12 21.13 Wopenka, Brigitte; Pasteris, Jill D. (April 2005). "A mineralogical perspective on the apatite in bone". Materials Science and Engineering: C. 25 (2): 131–143. doi:10.1016/j.msec.2005.01.008.
- ↑ 22.0 22.1 22.2 "Bone and Tooth Minerals". Science Learning. Science Learning. Retrieved 1 April 2015.
- ↑ "Bones and Teeth, Histology of (marine mammals)". What When How. Retrieved 30 March 2015.
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