Dentistry

What is the crown?

The top of the tooth, including all the tooth above the gumline. It meets the root at the cemento-enamal junction.

What is the root?

The bottom of the tooth, which is entirely below the gumline. Some teeth, including some premolars and molars have multiple roots. Roots diverge at what is called the furcation angle.

What is the apex of the root?

The very tip of the root, where nerves and blood vessels enter the pulp. In cats and dogs, it has a single foramen which is where the blood vessels and nerves enter the pulp. In herbivores, the formen is open.

What is enamel?

The outer layer of the crown. It is formed by ameloblasts in the tooth bud before eruption, and has little scope for repair once erupted. It consists of rods of hydroxyapetite crystals held within an ECM.

What is dentine?

The second layer of the tooth, which extends throughout the entirety of the root and crown. Primary dentine is formed before tooth eruption. Secondary dentine is continuously formed by odontoblasts on the surface of the pulp, throughout life, and tertiary dentine is formed as a result of trauma to the odontoblasts.

What is the pulp?

The innermost layer of the tooth, located in the pulp chamber. It is well vascularised and innervated by vessels which enter through the apical area of the root.

What is cementum?

Cementum is a mineralised tissue, similiar in composition to woven bone, that covers the roots of tooth, helping to anchor them to the periodontal ligament and jawbone.  is continuously deposited throughout life by epithelial cells called cementoblast.

What is the peridontal ligament (PL)?

A fibrous tissue that connects teeth to the jawbone. It is comprised of collagen fibre bundles which are anchored to the cementum of the tooth and lamina dura. The PL is vascularised and innervated.

What is the lamina dura?

The layer of alveolar bone closest to the tooth, which the peridontal ligament attaches to.

What is alveolar bone?

The bony structure that surrounds and supports the teeth. It can be remodelled by pushing the teeth against it - this is the basis for orthodontic treatment.

What is the gingival sulcus?

The gap between the side of the tooth and the free gingival margin. Its epithelial lining renews every few 5-6 days and it is bathed in crevicular fluid which contains immune cells.

What is the interdental papilla"?

The gingival peak between closely adjacent teeth, which prevents impaction of food and debris.

What is the junctional epithelium (JE)?

A layer of epithelial tissue that attaches the tooth to the gingival tissues via hemidesmosomes. The apical extent of the JE is the CEJ.

What is the cemento-enamel junction?

The junction between the anatomical crown, specifically the enamel, and the root - specifically the cementum.

What is free gingiva?

The part of gingiva that is visible during examination and surrounds the crown of the tooth.

What is attached gingiva?

The part of the gingiva that is tightly adhered to the bone

What is the oral mucosa?

The mucous membrane that lines the inside of the mouth.

What is the mucogingival junction?

The junction between the soft, fleshy mucous membrane of the oral cavity and the tough, collagen rich ginigivia.

What are incisors?

Small, single rooted teeth that are used to cut food.

What are canines?

Single rooted teeth with sharper, pointed crowns. Used to tear and rip food. In carnivorous animals, canine teeth are modified to shear flesh and bone in a scissor-like motion - and are known as carnassial teeth.

What are premolars?

Larger single or double rooted teeth used to tear, grind and crush food.

What are molars?

The largest teeth, with multiple roots. They are used to grind and crush food.

What is diastema?

The gap between teeth which some species, like horses, have.

What are aradicular hypsodont teeth?

Teeth have high crowns and are open rooted, meaning new tooth can continuously erupt as there is reserve crown below the gumline which is constantly growing. This is the case in rabbits.

What are radicular hypsodont teeth?

Teeth have high crowns but are closed rooted. There is reserve crown below the gumline which can continuously erupt, but it does not continuously grow, so as more tooth erupts there is less reserve crown. This is the case in horses, cattle and deer.

What are brachydont teeth?

Teeth have low crowns and well-developed closed roots. There is no scope for further growth once the tooth has erupted.

What are homodont teeth?

All the animal’s teeth are very similiar in shape and size. Examples include frogs, crocodiles and cetaceans (dolphins, sharks)

What are heterodont teeth?

All the animal’s teeth have different shapes, sizes and functions in different parts of the jaw. Examples include humans, dogs, cows, horses.

What is a monophydont?

An animal that has a single set of teeth which lasts its entire life. For example, rats.

What is a diphyodont?

An animal that has two successive sets of teeth. Deciduous (baby) teeth are transient and present during growth, then they fall out and are replaced by permanent teeth. For example, humans, cats, dogs.

What is a polyphodont?

An animal that has multiple sets of teeth which are continously replaced throughout its life. For example, kangaroos, elephants, manatees, sharks.

What is the first stage of tooth development (Bud stage)?

The oral epithelium thickens and the mesenchymal layer beneath it condenses to form a horseshoe ridge.

What is the second stage in tooth development (Cap stage)?

Tooth buds form in the dental lamina and develop into enamel organs. Within the enamel organ is the dental papilla with produces dentine and the dental pulp. Surrounding the enamel organ is the dental follicle, which consists of ectomesenchyme tissue. It later develops into the cementum, periodontal ligament and alveolar bone. These structures collectively comprise the tooth germ.

What is the third stage of tooth development (Bell stage)?

The inner layer of the enamel organ differentiates into ameloblasts, which make enamel. Cells in the dental papilla differentiate into odontoblasts, which make dentine. Dentine surrounds the pulp to produce tooth rot. Epithelial cells near the distal part of the tooth are called cementoblasts and secrete cementum around the tooth root.

What type of tissue is the enamel organ derived from?

Ectoderm - the top germ layer of the epiblast which develops into the outer layer of the body including the skin.

What type of tissue are the dental papilla and follicle derived from?

Neural crest cells which have broken off the neural tube and travelled along predestined migratory pathways.

What is the stellate epithelium/reticulum?

A group of cells located within the enamel organ during Bell stage that act as a supportive structure between the inner enamel epithelium and the outer enamel epithelium.

How does a temporary tooth erupt?

After the crown is fully formed, but before the root is - as eruption provides space for completion of the root. Upon eruption, the epithelial covering is continuous with the gums but wear removes this epithelium.

How does a permanent tooth erupt?

When a temporary tooth has eupted, the permanent tooth moves into the socket left behind. The temporary tooth is no longer anchored to underlying bone and looses, before being shed and replaced with the permanent tooth.

What are the three distinct compartments that make up the sinuses?

• the external nose

• the nasal cavities

• the paransasal cavities

What is the external nose?

Consists of paired nasal cavities separated by a nasal septum. It is flexible and cartilagenous, and extends into the vestibule which is the most rostral part of the internal nasal cavity.

What is the nasolacrimal duct?

The tear duct. It is a small tube with drains tears and mucus from the eyes into the nose, via the inferior meatus.

What are the nasal cavities?

They contain turbinate bones which are covered by mucosa. Each nasal cavity is divided into three sections - the ventral meatus (front/rostral), middle meatus, and dorsal meatus. Conchae are foldings of the inner nasal wall that compartmentalise the nasal cavity. They are separated by narrow clefts.

What are the paranasal sinuses?

Hollow, air-filled spaces in the bones of the face that surround the nose. There are 4 pairs of paranasal sinuses named after the bones they are located in - maxillary sinuses, ethmoid sinuses, sphenoid sinuses, frontal sinuseses. They are connected to the nasal cavity by small openings and primarily drain into the middle meatus via the nasomaxillary aperture.

Which three muscles are used to close the jaw?

Temporalis

Masseter

Lateral and Medial Pterygoids

Temporalis muscle

Origin: Temporal fossa on the lateral surface of the cranium

Insertion: Coronoid process on the mandible.

Function: Pulls mandible dorsally, rostrally and caudally. Carnivores have a larger temporalis than herbivores as it is used to generate a strong force to bite through muscle.

Masseteric Muscle

Origin: Maxillary region of the skull and zygomatic arch.

Insertion: Lateral aspect of the mandible.

Function: Protrudes the jaw. Herbivores have a larger masseter than carnivores as it is used to facilitate grinding plant material.

Lateral and Medial Pterygoid Muscle

Origin: Pterygopalatine region of the skull.

Insertion: Medial aspect of the madible.

Function: Closes the jaw (one sided). Herbivores have larger pterygoids than carnivores.

Which muscle is used to open the jaw?

Digastricus Muscle

Digastricus Muscle

Origin: Mastoid process of the temporal bone.

Insertion: Hyoid bone.

Function: Used to open the jaw. Carnivores have a large digastricus than herbivores.

What is the mandibular symphysis?

An amphiarthroses (partly-moving) joint where the two halves of the mandible meet. This joint allows the two halves to move independently to prevent the mandible breaking when one side of the jaw is chewing something harder than the other.

What is the temporomandibular joint (TMJ)?

The hinge joint between the temporal bone and lower jaw. In herbivores, the TMJ is more complex than in herbivores, allowing for significant lateral jaw movements allowing them to grind plant material.