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==Anatomy of the Enamel Organ==
==Anatomy of the Enamel Organ==
[[Image:Soft Histology of Enamel Organ.jpg|thumb|right|150px|Histology of Enamel Organ - Copyright RVC 2008]]
[[Image:Soft Histology of Enamel Organ.jpg|thumb|right|150px|Histology of Enamel Organ - Copyright RVC 2008]]
[[Image:Enamel Organ Layers.jpg|thumb|right|150px|Enamel Organ Layers - Copyright RVC 2008]]
[[Image:Thomes' Fibres Histology.jpg|thumb|right|150px|Thomes' Fibres - Copywright RVC 2008]]
The main components which form the enamel organ are:
The main components which form the enamel organ are:
*'''Outer epithelium'''
*'''Outer epithelium'''
*'''Stellate reticulum'''- star shaped cells lying between the outer and inner epithelial layers. It has the appearance of connective tissue but is of epithelial derivation.
*'''Stellate reticulum'''- star shaped cells lying between the outer and inner epithelial layers. It has the appearance of connective tissue but is of epithelial derivation.
*'''Inner epithelium''' which becomes the enamel secreting [[Ameloblasts|ameloblast]] layer
*'''Inner epithelium''' which becomes the enamel secreting [[Tooth - Anatomy & Physiology#Ameloblasts|ameloblast]] layer
==Tooth Components==
The enamel organ has many different components. These consist of:
The enamel organ has many different components. These consist of:
===Crown===
===Crown===
The crown of incisors have only one '''cusp'''. The crown of molars have up to 4 cusps for the grinding of food.
The crown of incisors have only one '''cusp'''. The crown of molars have up to 4 cusps for the grinding of food.
===Root===
Teeth may have one or more roots. The furcation angle is the point where roots diverge. The root ends in an apex which is where the nerves, blood vessels and lymphatics travel to the [[Tooth - Anatomy & Physiology#Pulp|pulp]]. '''Hypsodont''' teeth can have open roots (aradicular) e.g. in rabbits which have continued growth. Hypsodont teeth can have closed roots (radicular) e.g. horse where growth decreases with age. '''Brachydont''' teeth have no capacity for growth and so the roots are closed.
'''Species Differences'''
The apex has a single foramen in dogs and cats. It remains open in herbivores. In the horse, the apex closes as the animal ages. Brachiocephalic dogs often have fused roots. Equine incisors have fused roots. In the horse's canines, the size of the root is much larger than the [[Tooth - Anatomy & Physiology#Crown|crown]].
===Alveolar Bone===
[[Image:Enamel Organ Layers.jpg|thumb|right|150px|Enamel Organ Layers - Copyright RVC 2008]]
The alveolar processes of the jaw consists of the '''alveolar bone''', '''trabecular bone''' and '''compact bone'''.
The densest bone called the '''cribiform plate''' lines the alveolus. This appears white on radiographs and is referred to as the '''[[Tooth - Anatomy & Physiology#Lamina Dura|lamina dura]]'''.
===Lamina Dura===
The '''lamina dura''' lines the [[Tooth - Anatomy & Physiology#Alveolar Bone|alveolar bone]]. If uninterrupted, it indicates good dental health.
The '''lamina dura''' is seen as a white line radiographically.
===Enamel===
Enamel has an '''ectodermal''' origin. It is synthesised by [[Tooth - Anatomy & Physiology#Ameloblasts|ameloblasts]]. It is very hard, densly calcified and '''acellular''', therefore cannot regenerate.
Complicated enamel folding occurs in teeth where the '''[[Tooth - Anatomy & Physiology#Crown|crowns]]''' are high. Enamel forming secretions pass through processes of apical cytoplasmic extension called '''Thomes' Fibres'''.
===Dentine===
'''Dentine''' is a calcified, collagen rich matrix. It is synthesised by '''[[Tooth - Anatomy & Physiology#Odontoblasts|odontoblasts]]'''.
'''Secondary dentine''' is produced throughout life and increases with rate of repair. It is darker in colour than '''primary dentine'''.
===Cementum===
'''Cementum''' is synthesised by '''[[Tooth - Anatomy & Physiology#Cementoblasts|cementoblasts]]'''. It is calcified tissue and lacks regular organisation. Collagen fibres extend from the cementum into the '''[[Tooth - Anatomy & Physiology#Periodontal Ligament|periodontal ligament]]''' to fasten the tooth in its socket. '''Cementum''' is relatively immune to pressure erosion, therefore the tooth can be remodelled in its socket.
===Pulp===
Pulp fills the dental cavity. It is a delicate connective tissue bordering the [[Tooth - Anatomy & Physiology#Odontoblasts|odontoblast]] layer. It is highly vascularised and contains a lymphatic plexus.
Pulp allows pain sensation to thermal, mechanical and chemical stimulants. Most of the nervous supply is sensory, with some vasomotor input.
===Periodontal Ligament===
The collagen fibre bundles are called '''Sharpey's fibres'''. The fibres insert into the [[Tooth - Anatomy & Physiology#Alveolar Bone|alveolar bone]] and [[Tooth - Anatomy & Physiology#Cementum|cementum]] of the tooth.
There are 3 categories: gingival, trans-septal and alveolodental. There are evenly distributed blood vessels and nerve fibres transmitting thermal, pain and pressure sensation. Some species can also sense proprioception in the periodontal ligament.
==Main Cells==
[[Image:Ameloblast Histology.jpg|thumb|right|150px|Ameloblast Histology - Copywright RVC 2008]]
===Ameloblasts===
'''Ameloblasts''' are cells in the enamel organ which forms the tooth. They secrete '''[[Tooth - Anatomy & Physiology#Enamel|enamel]]'''.
Epithelial cells line the inner surface of the enamel organ. '''Ameloblasts''' are derived from epithelium and form a single layer of very long columnar cells that are hexagonal in cross section. They have elongated, basally sited nuclei. They synthesise '''[[Tooth - Anatomy & Physiology#Enamel|enamel]]''' which forms the '''[[Tooth - Anatomy & Physiology#Crown|crown]]''' of each tooth. They maintain connections with the newly synthesised '''[[Tooth - Anatomy & Physiology#Enamel|enamel]]''' through cellular projections called '''Thomes' fibres'''.
'''[[Tooth - Anatomy & Physiology#Enamel|Enamel]]''' is acellular so once the connection with the ameloblasts via the '''Thomes' fibres''' is lost (upon eruption), the [[Tooth - Anatomy & Physiology#Enamel|enamel]] matrix cannot be remodelled.
===Odontoblasts===
The '''odontoblasts''' are cells in the '''enamel organ''' which forms the tooth. They secrete '''[[Tooth - Anatomy & Physiology#Dentine|dentine]]'''.
'''Odontoblasts''' are derived from mesenchyme and are composed of a single layer of elongated columnar cells. They are at the '''dental-pulp border'''. They secrete '''[[Tooth - Anatomy & Physiology#Dentine|dentine]]''' which is a mineralised matrix of collagen I, [[Tooth - Anatomy & Physiology#Dentine|dentine]] and proteins.
The first layer of [[Tooth - Anatomy & Physiology#Dentine|dentine]] is formed on the enamel organ. As production increases, the odontoblasts are displaced from the [[Tooth - Anatomy & Physiology#Enamel|enamel]]. It is a major part of the tooth structure and is produced continually by the odontoblasts. The rate of [[Tooth - Anatomy & Physiology#Dentine|dentine]] synthesis is increased during repair as it is innervated (but still acellular).
===Cementoblasts ===
'''Cementoblasts''' are cells in the '''[[Tooth - Anatomy & Physiology#Enamel|enamel]]''' organ which forms the tooth. They secrete '''[[Tooth - Anatomy & Physiology#Cementum|cementum]]'''.
Epithelial cells are present near the distal end of the cup. They become follicle cells. '''Cementoblasts''' synthesise [[Tooth - Anatomy & Physiology#Cementum|cementum]] which mostly contains '''collagen I'''.
[[Tooth - Anatomy & Physiology#Cementum|Cementum]] surrounds the '''[[Tooth - Anatomy & Physiology#Dentine|dentine]]''' of the [[Tooth - Anatomy & Physiology#Root|root]]. [[Tooth - Anatomy & Physiology#Cementum|Cementum]] is acellular and not readily absorbed.
{{Template:Learning
|flashcards = [[Teeth and Gingiva Flashcards]]
|powerpoints = [[Oral Cavity Histology resource|Interactive tutorial on development of teeth]]
|dragster = [[Oral Cavity Histology Resource (I)]]
|Vetstream = [https://www.vetstream.com/canis/search?s=teeth Teeth]
}}
{{OpenPages}}
[[Category:Teeth - Anatomy & Physiology]]
[[Category:Teeth - Anatomy & Physiology]]