Tooth Eruption and Dental Development Flashcards
What are the characteristics of a newborn baby’s gum pads and tooth development at birth?
- Upper gum pad is rounded
- Lower gum pad is ‘U’ shape
- Often appear very ‘Class II’
- Present with anterior open bite (AOB)
All primary tooth crowns are well into calcification at birth
First permanent molar crowns are starting to calcify
Describe the eruption pattern of primary teeth, including timing and sequence.
Eruption occurs between 6 months and 2.5 years
Sequence follows the pattern: a-b-d-c-e (central incisor, lateral incisor, first molar, canine, second molar)
Lower teeth typically erupt before upper teeth
First tooth appears around 6 months of age
What are the key occlusal characteristics of the primary dentition?
- Incisors are positioned more upright
- Presence of Anthropoid spaces (mesial to maxillary canines and distal to mandibular canines)
- May present with generalized spacing
- Incisors may tend toward edge-to-edge occlusion after period of wear
- Terminal molars (E’s) should have distal edges flush in vertical plane for proper Class I development
How does spacing in the primary dentition predict crowding in permanent dentition?
- No spacing: 66% chance of crowding
- Less than 3mm space: 50% chance of crowding
- 3-6mm space: 20% chance of crowding
- Greater than 6mm space: No crowding likely
What is the most common natal tooth?
lower incisors
When is extraction of natal/neo-natal teeth indicated?
- mobile and present a risk of inhalation
- causing difficulty with breastfeeding
What are the three main phases of tooth eruption?
- Pre-eruptive phase: From crown formation start until root formation begins
- Eruptive phase: From root formation start until tooth reaches occlusal plane (divided into intra-osseous and extra-osseous stages)
- Post-eruptive phase: Continuous minor movements throughout life as root forms
What occurs during the pre-eruptive phase?
- Developing crowns move constantly within the jaws
- Small mesial and distal tooth movements occur
- Crowns reposition in response to jaw growth
- Movement contained within bony crypts
What occurs in the eruptive phase?
Permanent tooth germs develop on lingual side of primary teeth
Movements respond to:
Changes in neighboring crown positions
Maxillary and mandibular growth
Deciduous tooth root resorption
Describe the stages of the eruptive phase in sequence.
intra/extra osseous
Intra-osseous
1.Root formation begins with epithelial root sheath proliferation
2.Developing tooth moves in occlusal/incisal direction
3.Reduced enamel epithelium fuses with oral epithelium (forms junctional epithelium)
Extra-osseuous
4.Crown tip penetrates epithelial layers
5.Crown moves through mucosa toward occlusal plane
6.Final position influenced by cheek, lip, and tongue muscle forces
What is the role of the gubernacular cord in tooth eruption?
- Forms from dental lamina remnants (within eruption pathway)
- Creates fibrous tissue strand in eruptive pathway
- Allows developing permanent teeth to maintain connection with oral mucous membrane’s lamina propria
- Helps guide the tooth along its eruption path
What is the eruption pathway?
Within the Dental follicle degeneration occurs.
Blood vessels decrease in number
Nerve fibres break up into pieces
What have experiments revealed about the mechanism of tooth eruption?
- Dental follicle is crucial for eruption (tooth will not erupt if follicle is removed)
- Metal replicas can erupt if placed within dental follicle
- Bone resorption is the rate-limiting factor
- Root formation not essential for eruption process
- Blocked occlusal movement can cause root dilaceration
- Blood flow changes affect eruption in extra-osseous phase
- Most eruption occurs between 8 PM and 1 AM
What is primary failure of eruption?
What gene is affected
Teeth are not mechanically prevented from eruption and there is no evidence of ankylosis but the propulsive mechanism that moves teeth along the eruptive path is defective.
Recent evidence suggest this is under genetic influence : mutation in the PTHR1 gene (
parathyroid hormone receptor gene )
Very Rare
Posterior teeth affected
Teeth do not respond to orthodontic force
What is cleidocranial dysplasia?
What are additional features of the syndrome
Patients have a failure of bone resorption and resorption of deciduous tooth roots so
permanent teeth do not erupt.
This condition also includes presence of multiple supernumeraries and thick fibrous gingivae.
Once all obstructions are removed teeth can erupt and can be respond to orthodontic force.
What is the mechanism behind
tooth eruption?
multifactoiral - likely combination
- Remodelling of the alveolar bone
- Root formation ( but note : rootless teeth still erupt )
- Development of the periodontal ligament (membrane)
- contractile fibroblasts
- Crosslinking of collagen fibres ( likely only applies once tooth has emerged into oral cavity)
- Alteration in pulpal blood pressure or blood flow around the developing tooth
- Alteration in the extracellular ground substance in the periodontal ligament
(thixotropic gel effect) - Gubernacular cord ?
What controls tooth eruption at the molecular level?
- Dental follicle modulates cellular activity
- Signaling cascade includes:
Interleukin-1
CSF 1
RANKL/Osteoprotegerin pathway - Signaling occurs between dental follicle and reduced enamel epithelium
- Eruptive movement results from balance between:
Tissue destruction (bone, connective tissue, epithelium)
Tissue formation (bone, PDL, root)
Roles of Dental Follicle?
- Initiates resorption of the bone overlying the tooth
- Facilitates connective tissue degradation and creates the eruption pathway
- Promotes alveolar bone growth at the base of the tooth
- Provides traction forces within the periodontal ligament (special fibroblasts with contractile properties)
- Ectomesenchymal cells from dental follicle contribute to root formation (cementoblasts and cementum)
What occurs during the extra osseous eruptive phase?
premolars and PDL
Once it has emerged into the oral cavity the tooth
initially erupts very rapidly (1-2 weeks) then at a
slower rate (many months) until it reaches occlusion
with the opposing arch
In humans the eruption of premolars in the extraosseous phase has been shown to be affected by
changing blood flow in the apical area
Collagen cross-linking in the PDL is now more
prominent than in the intra-osseous phase and may
What occurs during the post-eruptive phase?
what is it in response to
movement occurs after tooth has already reached occlusal plane
In response to increases in height of the growing alveolar bone and jaws
In response to attrition and abrasion
* teeth erupt slightly to compensate for wear on occlusal surfaces
* proximal surface tooth wear leads to mesial drift
In response to loss of opposing teeth = over-eruption
What is interceptive orthodontic treatment?
- Can be used to minimize developing malocclusion
- Timing for extraction of deciduous teeth: when permanent successor has 1/2 to 2/3 root development
- Ectopic upper permanent canines can be managed by extracting deciduous canines between ages 10-13
- Treatment utilizes natural eruption process to guide tooth position
What is the typical sequence and timing of permanent tooth eruption?
- First molars (6’s): 6 years
- Central incisors (1’s): 7 years
- Lateral incisors (2’s): 8 year
- First premolars (4’s): 10 years
- Canines (3’s) and second premolars (5’s): 11-12 years
- Second molars (7’s): 12-13 years
How is additional space gained to accommodate larger permanent teeth?
4 mechanisms
- Increase in intercanine width through lateral jaw growth
- Upper incisors erupting onto wider arc (more proclined)
- Primary canines moving back into anthropoid spaces (mandible)
- Utilization of leeway space
What is the leeway space and how does it differ between arches?
- Upper arch: 1 to 1.5mm difference between primary and permanent teeth
- Lower arch: 2 to 2.5mm difference between primary and permanent teeth
Represents difference in combined widths of:
Primary canine + first molar + second molar versus
Permanent canine + first premolar + second premolar
What is the pattern of midline diastema presence through development?
- At 6 years: 96% have diastema
- At 12 years: 7% have diastema (after canines erupt)
Diastemas less than 2.5mm typically close naturally
Frenectomy has little effect on long-term closure
