LO 6 - Development, Form, & Eruption

Question 1

What are tooth germs?

Answer 1

1. Tiny tooth buds
2. Small clumps of cells that have the ability to form tooth tissues (enamel, dentin, cementum, pulp).

Question 2

Describe the beginning of hard tissue development (tooth germs to secondary dentin)

Answer 2

1. Tooth germs (tiny tooth buds) begin to grow within the alveolar process of the fetus at approximately 6 weeks of fetal life. Both the primary and secondary teeth develop from these tooth germs
2. At this time the dental lamina begins to form.
3. The tooth germs grow within an opening in the alveolar bone called a crypt.
4. The crypt later becomes the socket where the tooth is held.
5. At this time the dentin and enamel begin to form, followed later in development by the cementum.
6. Dentin formed at this early stage is called primary dentin, and it occurs before root completion.
7. Secondary dentin is continually formed within the tooth by the same odontoblasts that form regular dentin. This process continues throughout one’s entire lifetime.

Question 3

How do secondary and reparative dentin differ?

Answer 3

Secondary dentin differs from reparative dentin in that reparative dentin is laid down locally as protection for the pulp from irritation, caries, or trauma.

Question 4

Describe calcification of primary teeth

Answer 4

1. 4 or 5 months of fetal life the process of calcification occurs.
2. Calcification - hardening of tooth tissues by the deposition of mineral salts within these tissues.
3. continues until age 3-4 (all deciduous roots are formed).
4. Soon after birth permanent teeth begin to calcify and continue until about 25 when roots of third molars become calcified.
5. The last area of the tooth to become calcified is the apex of the root.

Question 5

Describe eruption

Answer 5

1. Frequently defined as emergence of the tooth through the gingiva.
2. The movement a tooth makes to attain and maintain a relationship with the teeth in the same and the opposing arch.

Question 6

Describe root completion

Answer 6

1. Approximately 50% of the root is formed when eruption begins.
2. Primary roots are completed between 1&1/2 and 3 years of age.

Question 7

Describe developmental lobes

Answer 7

1. Each tooth begins to develop from 4 or more growth centers called developmental lobes.
2. Lobes grow out from tooth germ.
3. The lobes grow and develop within the crypt until they fuse.
4. The junction of the lobes are marked by lines on the tooth called developmental grooves (seen on the tooth after it has erupted).

Question 8

________ is the fusion of lobes

Answer 8

Coalescence

Question 9

How many lobes do anterior teeth have?

Answer 9

1. Four - three facial, one lingual

Question 10

________ are rounded protuberances of the incisal edge of a newly erupted incisor tooth

Answer 10

Mamelons

Question 11

How many lobes and cusps do maxillary premolars have?

Answer 11

1. Four lobes - three facial, one lingual
2. The 3 facial lobes form one high buccal cusp instead of an incisal ridge
3. The lingual lobe forms a large lingual cusp rather than a cingulum.

Question 12

How many lobes and cusps does the mandibular first premolar have?

Answer 12

1. Four - three facial, one lingual
2. Same as maxillary premolar, but the lingual cusp is smaller.

Question 13

how many lobes and cusps does the mandibular second premolar have?

Answer 13

1. May have 2 or 3 cusps
2. 5 Lobe variation - May have one facial cusp and 2 lingual cusps
3. If two lingual cusps mesiolingual cusp bigger than distolingual cusp.
4. 4 Lobe variation – One facial and one lingual cusp. If only one lingual cusp usually quite large.

Question 14

How many lobes and cusps do the maxillary molars have?

Answer 14

1. 2 facial and 2 lingual lobes except:
2. First molars – usually have a fifth minor lobe on the lingual (cusp of carabelli, comes from a 5th lobe)

Question 15

How many lobes and cusps do mandibular first molars have?

Answer 15

1. 5 lobes, 3 facial, 2 lingual
2. 5 cusps

Question 16

How many lobes and cusps do mandibular second molars have?

Answer 16

1. 4 lobes - 2 facial, 2 lingual
2. 4 cusps

Question 17

How many lobes and cusps do 3rd molars have?

Answer 17

1. The most unpredictable of all teeth.
2. # of lobes (cusps) varies.
3. As a general rule the farther back the molar the smaller the crown and cusps.
4. The roots are also generally smaller.

Question 18

What are the 3 general rules of eruption?

Answer 18

1. Mandibular teeth erupt before max. teeth.
2. Teeth in both jaws erupt in pairs.
3. Permanent teeth usually erupt slightly earlier in girls than in boys.

Question 19

What are some important things to remember about formation/eruption?

Answer 19

1. First teeth to emerge are the deciduous/primary teeth.
2. Calcification begins around fourth month of fetal life, by the end of the sixth month all deciduous teeth have begun to develop.
3. Crown forms first then root.
4. Any fever, metabolic dysfunction, childhood or nutritional disease, or physical illness or trauma can alter the formation of teeth and even stop their formation or mineralization completely.
5. All of the deciduous teeth are expected to have erupted by the time the child is 2.5 years old.
6. For the next 36 months the child and jaw continues to grow.
7. The teeth do not become larger but spaces between the teeth may become apparent by age 5 caused by the increased growth of the jaws.

Question 20

Describe the importance of deciduous teeth

Answer 20

1. Important or normal jaw growth
2. Spacing (enough room for permanent teeth)
3. Help guide permanent teeth especially first permanent molar into normal position. The first molars act as the foundation for the rest of the permanent dentition.

Question 21

Describe the eruption of the permanent dentition

Answer 21

1. First teeth to erupt are the mandibular first molars frequently called the sixth year molars.
2. Mandibular and maxillary molars act as the foundation for the rest of the permanent dentition.
3. The first molar cannot appear without sufficient jaw growth.
4. Mesial drift – Tendency of the permanent molars to have an eruptive force forward towards the midline. This helps close the spaces between the deciduous teeth.
5. If deciduous teeth are prematurely lost, the permanent first molar moves into the available space, blocking out the premolars and canines.
6. When a retained deciduous tooth is finally lost, pressure from the tongue forces the permanent tooth facially until it occupies its correct position in a balance between the lingual forces of the tongue and the facial forces of the lips.

Question 22

_________ is the process by which the roots of a baby tooth are resorbed and dissolved until so little root remains that the baby tooth falls out.

Answer 22

Exfoliation

Question 23

Define resorption

Answer 23

As a permanent tooth erupts osteoclastic cells destroy the root of the deciduous tooth.

Question 24

Describe exfoliation

Answer 24

1. The pressure on the deciduous root by the eruption of the permanent tooth triggers the body to activate certain bone destroying cells called osteoclasts. The roots of deciduous teeth are destroyed and the tooth loses its anchorage, tooth becomes loose and falls out (exfoliates).
2. During this process, the permanent tooth moves into the space that was occupied by the deciduous tooth.

Question 25

Describe the eruption of permanent incisors

Answer 25

1. It is not uncommon for the permanent incisor to erupt **lingually** to the deciduous incisors. 2. Sometimes the central incisors are still in place, with the permanent central incisors located immediately lingual to the deciduous teeth.

Question 26

Define impacted teeth

Answer 26

Teeth that do not completely erupt but remain embedded in bone or soft tissue. Example - third molars

Question 27

Define attrition

Answer 27

1. The wearing away of the tooth through contact of its functioning surfaces. 2. Teeth erupt until they meet their antagonist in the opposing arch. 3. Eruption continues throughout life because of attrition.

Question 28

Define the primary dentition

Answer 28

1. Begins with the eruption of the first deciduous tooth. 2. Lasts as long as all deciduous teeth are present. 3. When first permanent molar erupts, period ends.

Question 29

Define the mixed dentition

Answer 29

1. Occurs at about 6 years old 2. When both primary and permanent teeth are simultaneously present. 3. Ends when the last primary tooth is exfoliated and only permanent teeth are present.

Question 30

Define the permanent dentition

Answer 30

1. Begins when the last deciduous tooth is lost around 12 years. 2. Ends when the last permanent tooth is lost.

Question 31

Define succedaneous teeth

Answer 31

Permanent teeth that replace deciduous teeth.

Question 32

Define non succedaneous teeth

Answer 32

Teeth that do not replace deciduous teeth. i.e. permanent molars.