DENTALK h a l e e l A l y a h y a , P h D , M E d

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Mastering Medical Technology

Essential of Human Anatomy & Physiology

Mosby’s Dictionary

KENHUB

By Sue Walker, Maryann Wood and Jenny Nicol

By Elaine Marieb and Suzanne Keller

By Mosby

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Introduction▪ The role teeth play in processing food needs little introduction.

▪ We masticate, or chew, by opening and closing our jaws and moving them fromside to side while continuously using our tongue and cheek muscles to keep thefood between our teeth.

▪ In the process, the teeth tear and grind the food, breaking it down into smallerfragments.

▪ Ordinarily, by the age of 21, two sets of teeth have been formed.

▪ The first set are primary teeth or temporary teeth or baby teeth or milk teeth.

▪ The primary teeth begin to erupt around 6 months; the first teeth to appear arethe lower central incisors.

▪ A baby has a full set (20 teeth) by the age of 2 years.

▪ As the second set of teeth, the deeper permanent teeth, enlarge and develop,the roots of the milk teeth are reabsorbed, and between the ages of 6 and 12years they loosen and fall out.

▪ All the permanent teeth but the (third molars) have erupted by the end ofteenage.

▪ The third molars, also called wisdom teeth, emerge between the ages of 17 and25.

▪ Although there are 32 permanent teeth in a full set, the wisdom teeth often fail toerupt; sometimes they are completely absent.

Khaleel Alyahya, PhD, MEd 3

Classifications ▪ We classify the teeth according to shape and function as incisors,

canines, premolars, and molars.

▪ The incisors are adapted for cutting; canines (eyeteeth) are for tearingor piercing.

▪ The premolars (bicuspids) and molars have broad crowns withrounded cusps (tips) and are best suited for crushing and grinding.

▪ The human dentition is composed of two sets of teeth:

• Primary

• Permanent

▪ Teeth are organized into two opposing arches:

• Maxillary (upper)

• Mandibular (lower)

▪ These can be divided down the midline (mid-sagittal plane) into left andright halves.

▪ Teeth are positioned in alveolar sockets and connected to the bone bya suspensory periodontal ligament.

Khaleel Alyahya, PhD, MEd 4

Primary & Permanent ▪ The primary dentition

• Composed of 20 teeth, with 10 in each arch.

• There are five teeth in each quadrant, composed of two incisors(central and lateral), a canine, and two molars.

• These teeth are referred to as letters A, B, C, D and E.

• The primary teeth begin to erupt at 6 months of age.

▪ The permanent teeth

• Begin to erupt, and replace the primary teeth, at 6 years of age.

• The permanent teeth complete eruption by approximately age 13years – with the exception of the 3rd molar ‘wisdom’ teeth, whichusually erupt by the age of 21 years.

• The permanent dentition is composed of 32 teeth with 16 in eacharch.

• There are eight teeth in each quadrant, composed of two incisors(central and lateral), a canine, two premolars, and three molars.

• These teeth are referred to as numbers, 1 (central incisor) to 8 (3rd

molar or ‘wisdom’ tooth).

Khaleel Alyahya, PhD, MEd 5

Structures ▪ A tooth can be divided into two main parts – the crown and the root.

▪ The part of a tooth which is visible in the mouth is referred to as theclinical crown, while the part which is not visible is, by definition, theclinical root.

▪ Anatomically, the crown and root can be distinguished based on theirstructure and the type of hard tooth tissue covering the external surface.

▪ Generally, the anatomic crown is covered by enamel, while the anatomicroot is covered by cementum:

• Enamel is a solid, avascular hard tissue with a high mineral content. It is, ineffect, designed to provide thermal insulation for a tooth, and to protect theinternal vital tissues from destruction. Enamel is susceptible to dental caries,tooth wear and acid dissolution.

• Cementum is a softer, more sensitive tissue. It becomes visible if a tooth isextruded from the alveolar socket during a traumatic dental injury, and whenperiodontal disease (disease of the tooth supporting tissues) causes rootexposure; a person becomes “long in the tooth”.

Khaleel Alyahya, PhD, MEd 6

Dental Parts ▪ A layer of dentine lies beneath the enamel and cementum, throughout

the crown and root.

▪ Dentine is a vital, innervated tissue that accounts for the majority of thehard tooth structure.

▪ The part of the tooth where the dentine and enamel meet is called thedentineo-enamel junction (DEJ).

▪ The boundary where the anatomic crown meets the anatomic root (wherethe enamel meets the cementum) is called the cemento-enameljunction (CEJ).

▪ The pulp cavity is the space within a tooth root that is filled with the vitaldental pulp, a pink mass of innervated, vascular tissue.

▪ The end of the root is called the apex.

▪ The apical foramen is the space at the apex through which bloodvessels and nerves enter the dental pulp, and through which pulpinfection may enter the alveolus and surrounding soft tissues.

Khaleel Alyahya, PhD, MEd 7

Identifying Teeth ▪ There are four main types of teeth:

• Incisors

• Canines

• Premolars

• Molars

▪ The premolars are only present in the permanent dentition.

▪ Note: There is an accepted order that is used when naming teeth:

• Dentition, arch, quadrant, tooth type.

• E.g. permanent mandibular right lateral incisor.

Khaleel Alyahya, PhD, MEd 8

Incisors▪ There are 8 incisors in both the primary and permanent dentition;

• 4 maxillary and 4 mandibular.

▪ Central and lateral incisors have straight edges that are designed toincise into food.

▪ They are located at the front of mouth with central incisors nearest themidline, and lateral incisors between the central incisors and thecanines.

▪ Incisor teeth, particularly in the maxilla, are at risk of damage duringa traumatic dental injury, due to their relatively unprotected position, andtheir size and shape.

▪ Traumatic dental injuries are common in childhood (at least 1 in 10children are affected).

▪ The consequences of traumatic dental injuries can be significant in termsof function, good looking, dental anxiety, and quality of life for affectedchildren and their carers.

Khaleel Alyahya, PhD, MEd 9

Canines ▪ There are 4 canines in both the primary and permanent dentition;

2 maxillary and 2 mandibular.

▪ They are located at corners of the mouth and have an incisal edgethat has a sharp, triangular shaped projection.

▪ The function of the cusp is to pierce and hold food.

▪ They are sometimes referred to as cuspid teeth.

▪ Canines have long stable roots that withstand greater forces thanincisors.

▪ Teenagers who experience dental crowding (the total width of theteeth exceeds the available width of the arch for the teeth to eruptin to) may present with unerupted canines.

▪ These are frequently located radiographically in the palate, or highthe buccal sulcus.

▪ Oral surgery may be required to aid the eruption of these teeth.

Khaleel Alyahya, PhD, MEd 10

Premolars ▪ The permanent dentition has 8 premolars that generally have 2 cusps,

but this is not always the case.

▪ They are sometimes referred to as bicuspid teeth.

▪ They are located between the canines and the molars, and they sharesome of the characteristics of these teeth.

▪ There are no premolars in the primary dentition.

▪ Premolar teeth are frequently extracted by dentists to relieve dentalcrowding, particularly prior to orthodontic treatment.

Khaleel Alyahya, PhD, MEd 11

Molars ▪ There are 8 molars in the primary permanent dentition; 4 maxillary and

4 mandibular.

▪ There are 12 molars in the permanent dentition; 6 maxillary and 6mandibular.

▪ The number of cusps varies between 3 and 5.

▪ They are located at the back of the mouth, and are designed to crush andchew food, prior to swallowing.

▪ Molar teeth are particularly at risk of dental caries (decay) due to thepresence of deep grooves that run across the top surface of the teeth,and due to the presence of a relatively wide point of contact betweenadjacent molars.

▪ These sites are more difficult to clean than the smooth walls of the labial(lip), buccal (cheek), lingual (tongue), and palatal (palate) surfaces ofteeth.

Khaleel Alyahya, PhD, MEd 12

Pathology& Diseases

Impacted Teeth ▪ When teeth remain embedded in the jawbone, they are said to be

impacted.

▪ Impacted teeth can exert pressure and cause a good deal of pain, sothey usually must be removed surgically.

▪ Wisdom teeth are the most commonly impacted.

Khaleel Alyahya, PhD, MEd 14

Dental Caries▪ Dental caries is the medical term for the common condition of tooth

decay.

▪ Bacteria in the mouth cause a film on the teeth called plaque.

▪ This in turn converts starches in food to acid.

▪ The acid erodes the enamel of the teeth causing caries.

▪ A high standard of oral hygiene is the best preventative measure.

Khaleel Alyahya, PhD, MEd 15

Orthodontics ▪ Orthodontics is a specialty of dentistry that deals with the diagnosis,

prevention and correction of malpositioned teeth and jaws.

▪ It can also focus on modifying facial growth, known as dentofacialorthopedics.

▪ Abnormal alignment of the teeth and jaws is common, nearly 30% of thepopulation has malocclusions severe enough to benefit from orthodontictreatment.

▪ Treatment can take several months to a few years; it involves the useof dental braces and other appliances to slowly move the teeth and jawsaround.

▪ If the malocclusion is very severe, jaw surgery may be used.

▪ Dental braces are devices used in orthodontics that align andstraighten teeth and help position them with regard to a person's bite, whilealso aiming to improve dental health. Braces also fix gaps

▪ Treatment is usually started before a person reaches adulthood since bonescan more easily be moved around in children.

Khaleel Alyahya, PhD, MEd 16

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