24 - Dynamics of tooth development

Question 1

Stage 1 - Initiation of tooth development - BUD stage

Answer 1

This is the formation of Dental germ which begins w/initiation and continues w/proliferation

• Tooth formation starts w/the development of the dental lamina - Over which 20 tooth buds for the 20 primary teeth develop
• The first stage includes Proliferation, Histodifferentiation + 3 stages of tooth development ⇢ BUD - CAP - BELL stages

Note! absence of teeth means disturbance in the chronological period of formation of tooth germ due to lack of info from neural crests

At bud stage begins prevention of dental diseases via nutritional prevention, providing functions of ecto + medoserm.

if there is no dental bud = missing tooth

Question 2

Stage 2 - start of mineralisation

Answer 2

this is the starting point of the apposition + calcification by the 1st deposition + mineralisation of dentin matrix and is immediately deposited the 1st enamel layer

at this point:

• Enamel organ is built
• Differentiation of Ameloblasts + Odontoblasts is completed
• Deposition of organic matrix + mineralisation are performed in parallel

mineralisation starts from the tip of the cusps

Deposition of matrix + mineral - continues until the enamel formation is complete + enamel organ is consumes

Only at this point can appear enamel hypoplasia or any other disturbances in mineralisation

Question 3

Stage 3 - Completion of the crown

Answer 3

At this point:

• Enamel is completely formed
• Enamel organ is now reduced enamel epithelium (REE)
• Dentin is almost completely formed
• Enamel mineralisation is at 50%
• Enamel maturation begins by REE
• Cervical loop ⇢ Hertwig’s epithelial root sheath - beginning of root completion

When the crown is ready it begins the eruption of the tooth by several movements + displacements:

• It begins a bone reabsorption in front of the crown
• and an apposition after the crown

hypomineralisation/hypomaturation may occur in this stage

Question 4

Stage 4 - Eruption

Answer 4

This is the first clinically detectable stage of tooth development

Its the process by which developing teeth emerge through soft tissues of jaws + mucosa to enter the oral cavity

Pre-eruptive phase

• Movements related to tooth eruption begin during crown formation
• they require adjustments relative to the forming bony crypt
• includes all movements of crowns of primary + permanent teeth - from early initiation until formation of tooth’s crown
• this phase ends w/early initiation of root formation

Pre-functional eruptive phase

• starts w/initiation of root formation
• ends when teeth reach occlusal contact
• there are 4 events:

1. root formation
2. movement
3. penetration
4. intraoral occlusal + incisal movements

Functional Eruptive Phase

• Start when teeth start functioning + continues until teeth are present in the mouth

Question 5

Stage 5 - Development of tooth root

Answer 5

Begins after crown formation

1. Start of tooth root development
2. Short root walls - occurs prior + during tooth eruption
3. Root walls close to the final length - visible proliferative zone
4. Constructed root walls but underdeveloped apex - eruption is complete
5. Constructed apex - no proliferative zone

Question 6

Stage 6 - Shedding of Primary Teeth

Answer 6

humans are diphyodont (possess 2 dentitions)

• Primary dentition - 2-6 yrs of age
• Mixed dentition - 6-10/11 yrs
• Permanent dentition - 10/11 until edentulism

The period of tooth shedding follows the mixed dentition period:

Shedding is the loss of primary dentition due to:

• physiologic resorption of roots
• loss of bony supporting structures
• inability of primary teeth to withstand masticatory forces

This resorption of primary teeth is done by the restorative organ attached to the resorbing roots - under the action of eruptive forces of permanent teeth