Lesson 3

Subject:  1. Teeth.

                2  Revision of grammar.            

              3. Teeth and gums. Surfaces of the teeth.

 

Structure of the Teeth

     Every tooth consists of a crown, a neck and one or more roots. The crown is the part visible in the mouth and the root is the part hidden inside the jaw. The junction of crown and root is called the neck and the end of the root is called the apex (Fig. 1). Every tooth is composed of enamel, “dentine, cementum and pulp.

 

     Enamel

     This is the outer covering of the crown and is the hardest substance in the body. It is insensitive to pain. Unlike most other body tissues it can­not undergo repair; thus any damage caused by decay or Injury is per­manent. The microscope shows that it consists of long solid rods, called enamel prisms, cemented together by the interprismatic substance. The prisms run roughly at right angles to the surface.

 

     Cementum

     This is the outer covering of the root and is similar in structure to bone. Cementum meets enamel at the neck of the tooth.

 

     Dentine

     This occupies the interior of the crown and root, and is very sensitive to pain. Dentine from elephants’ tusks is commonly known as ivory but is exactly the same dentine as that found in human teeth.

 

     Pulp

     Unlike enamel, dentine and cemen­tum, the pulp is purely soft tissue. It con­tains blood vessels and nerves, and oc­cupies the centre of the dentine, vessels and nerves of the pulp enter the root apex through the apical foremen ma pass up the root canal into the crown, where the space occupied by the pulp is called the pulp chamber. The nerves of the pulp are responsible for pain felt when dentine is drilled or toothache occurs. The outermost layer of the pulp, next to the dentine, is lined with the spe­cial cells which formed the dentine. Under the microscope fine prolonga­tions of these cells can be seen passing through tubes in the dentine. They run throughout the full thickness of dentine and, by their origin from the pulp, are associated with its repair processes and sensitivity to pain.

 

     Supporting Structures

     Every tooth is inserted into the jaw by its root. The part of the jaw containing the teeth is known as the alveolar process  and is covered with a soft tissue called gum. The jaw bones consist of a dense outer layer known as compact bone  and a softer interior called spongy bone.

     A tooth is attached to its socket in the jaw by a soft fibrous tissue called the periodontal membrane. This acts as a shock absorber and is attached to the cementum of the root and the compact bone lining the socket. The periodontal membrane contains nerves and blood vessels, but consists mainly of bundles of fibres which pass obliquely from ce­mentum to bone.

 

 

 

 

 

 

 

 

 

 

 

Surfaces of the Teeth

     The biting surface of molars and premolars is called the occlusal surface. On incisors and canines it is called the incisel edge. The occlusal surface of molars and premolars is raised up into mounds called cups. Between the cusps are crevices known as fissures.

The outer surface of molars and premolars — the surface facing the cheeks — is called the buccal surface. In the case of incisors and canines this surface is called labial as it faces the lips instead of the cheeks.

     The inner surface of every lower tooth faces the tongue so it is called the lingual surface. This surface in all upper teeth is known as the palatal surface.

     The remaining surfaces are those between adjoining teeth. The surface facing towards the front of the mouth is called mesial and that facing backwards is called distal.

     The adjective cervical is used for the neck of the tooth.

 

Teeth and Gums

     Six months or so after birth, the first deciduous teeth (baby teeth, milk teeth) erupt through the gums. A normal child will eventually have twenty “baby” teeth, each jaw holding ten teeth: four incisors (for cutting), two canines (for tearing), and four molars (for grinding). The deciduous teeth are lost when the permanent teeth are ready to emerge. Both sets of teeth are usually present in the gums at birth, or shortly afterward, with the permanent teeth lying under the deciduous teeth. By the time a perma­nent tooth is ready to erupt, the root of the deciduous tooth above it has been completely resorbed by osteoclasts. The six permanent molars in each jaw hare no deciduous predecessors. The shedding of deciduous teeth and the appearance of permanent teeth follow a fairly consistent pattern.

     The thirty-two permanent teeth (sixteen in each jaw holds four inci­sors (cutting teeth), two canines (cuspid, with one point or cusps), and six molars (millstone teeth). Because the upper incisors are wider than the lower ones, the lower grinding teeth are usually aligned slightly in front of the upper grinders. This arrangement enhances the grinding motion between the upper and lower teeth.

     The teeth are held in their sockets by bundles of connective tissue called periodontal ligaments. The collagenous fibers of each ligament extent from the alvelar bone into the cement of the tooth, and allow for some normal movement of the teeth. Nerve endings in the ligaments monitor the pressures of chewing and relay the information to the brain centers involved with chewing movements.

 

Why Are Canine Teeth Called “Eyeteeth”

     Early anatomical schemes ofteamed body parts according to their relation to other structures or functions. Eyeteeth were named so proba­bly because they lie directly under the eyes. (As another example, peo­ple in the Western world wear wedding rings on the fourth finger of the left hand, because it was believed that this finger was connected directly to the heart).

 

     Chewing

     Although chewing can certainly be voluntary, most of the chewing we do during a meal is an automatic rhythmic reflex that is triggered by the pressure of food against the teeth, gums, tongue and hard palate. Such pressure causes the jaw muscles to relax and the jaw to drop slightly; then, as opposite muscles contract in an attempt to balance the relaxation the jaw is pulled up again

 

LITERATURE:

 

a) Юдіна Є.Є., Потяженко Л.В. Підручник англійської мови. – К., Вища школа, 1994.

b) Гурська А.І. Англійська мова для студентів-медиків. Львів: Світ, 2003.

c) Демченко О. Й., Костяк Н.В. Англійська мова для студентів-медиків. Тернопіль: Укрмедкнига, 2001.

d) Мухіна В. В. Англійська мова для студентів-стоматологів.-М., 2003.

TEST SAMPLE:

Тема: Structure of the teeth

Варіант 1

1. Виберіть еквівалент слова “речовина“

A. chamber                                   

B. solid

C. structure

D. surface

E. substance

 

2. Виберіть синонім слова “apex”

A. crown

B. pulp

C. root

D.top

E. neck

 

3. Виберіть антонім слова “sensitive”

A. unlike                                           

B. insensitive

C. hidden

D. painful

E. injury

 

4. Виберіть еквівалент слова “jaw”

A. щелепа                      

В. ясна

С. з’єднання             

D. камера

Е. зуб

 

5. Виберіть правильний варіант написання слова “цемент”

A. cementem                    

B. cementum

C. simentem             

D. ciment

E. cementum