Tooth Eruption

• What are the main differences between primary & permanent teeth?

  Primary teeth:

  - Thin, uniform layer of enamel

  - Thin layer of dentin

  - Larger pulp chamber and closer to the surface

  - Broad proximal contact areas

  - smaller whiter

  - mesio-distal diameter of a primary molar crown is greater than cervico-occlusal dimension

  - buccal and lingual surfaces converge towards the occlusal

  - Cervical enamel rods slope occlusally, ending abruptly at the cervix rather than being oriented gingivally and gradually becoming thinner as in permanent teeth

  - primary teeth contact areas are broad and flattened, rather than being small distinct circular contact points, as in permanent teeth

  - shorter clinical crown heights of primary teeth

  - Deciduous molar roots diverge to allow space for the developing permanent premolars

  -Crown is short relative to the length of root In primary teeth

  
  

  Permanent teeth:

  - Variable thickness of enamel

  - Thicker layer of dentine

  - Proportionally smaller pulp

  - Deeper fissures
• tooth development

  
  

  what is the importance of dental development?

  • Disturbances of eruption/exfoliation

  
  

  • Occusal development

  - normal/abnormal

  
  

  • Management of dental trauma

  ( trauma of the deciduous tooth can affect the development, mineralisation, and shape of the permanent tooth).

  
  

  • Treatment planning

  - Types of restorations, extraction Vs. restoration Vs. monitoring

  
  

  • Disturbances of tooth form

  - E.g. Hypoplasia, hypomineralisation
• tooth development

  
  

  when does root formation complete for permanent teeth?

  maxillary central incisor- 8.6-9.8 years of age

  mandibular central incisor- 7.7-8.6 years of age

  maxillary lateral incisor- 9.6-10.8 years of age

  mandibular lateral incisor- 8.5-9.6 years of age

  maxillary canines- 11.2- 13.3 years of age

  mandibular canines- 10.8-13.0 years of age

  maxillary first premolars- 11.2-13.6 years of age

  mandibular first premolars- 11.0-13.4 years of age

  maxillary second premolars- 11.6-14.0 years of age

  mandibular second premolars- 11.7-14.3 years of age

  maxillary first molar- 9.3-10.8 years of age

  mandibular first molar- 7.8-9.8 years of age

  maxillary second molar- 12.9-16.2 years of age

  mandibular second molar- 11.0-15.7 years of age

  maxillary third molar- 19.5-19.6 years of age

  mandibular third molar- 20.0-20.8 years of age
• tooth development

  
  

  when does crown formation complete for permanent teeth?

  maxillary central incisor- 3.3-4.1 years of age

  mandibular central incisor- 3.4-5.4 years of age

  maxillary lateral incisor- 4.4-4.9 years of age

  mandibular lateral incisor- 3.1-5.9 years of age

  maxillary canines- 4.4-5.8 years of age

  mandibular canines- 4.0-4.7 years of age

  maxillary first premolars- 6.3-7.0 years of age

  mandibular first premolars- 5-6 years of age

  maxillary second premolars- 6.6-7.2 years of age

  mandibular second premolars- 6.1-7.1 years of age

  maxillary first molar- 2.1-3.5 years of age

  mandibular first molar- 2.1-3.6 years of age

  maxillary second molar- 6.9-7.4 years of age

  mandibular second molar- 6.2-7.4 years of age

  maxillary third molar- 12.8-13.2 years of age

  mandibular third molar- 12.0-13.7 years of age
• tooth development

  
  

  when does hard tissue formation begin for permanent teeth?

  maxillary central incisor- 3-4 months after birth

  mandibular central incisor- 3-4 months after birth

  maxillary lateral incisor- 10-12 months after birth

  mandibular lateral incisor- 14.7-16.5 months after birth

  maxillary canines- 4-5 months after birth

  mandibular canines- 4-5 months after birth

  maxillary first premolars- 18-24 months after birth

  mandibular first premolars- 18-24 months after birth

  maxillary second premolars- 24-30 months after birth

  mandibular second premolars- 24-30months after birth

  maxillary first molar- 7-8 months after ovulation

  mandibular first molar- 7-8 months after ovulation

  maxillary second molar- 30-26 months after birth

  mandibular second molar- 30-26 months after birth

  maxillary third molar- 7-9 years after birth

  mandibular third molar- 8-10 years after birth
• tooth development

  
  

  when does root formation complete for primary teeth?

  maxillary central incisor- 33 months after birth

  mandibular central incisor- 33 months after birth

  maxillary lateral incisor- 33 months after birth

  mandibular lateral incisor- 30 months after birth

  maxillary canines- 43 months after birth

  mandibular canines- 43 months after birth

  maxillary first molars- 37 months after birth

  mandibular first molars- 34 months after birth

  maxillary second molars- 47 months after birth

  mandibular second molars- 42 months after birth
• what is an easy way to determine root formation ages if you know the eruption ages?

  root formation is usually 1.5-3 years after eruption so if you know eruption then you know root formation
• tooth development

  
  

  when does crown formation complete for primary teeth?

  maxillary central incisor- 1.5 months after birth

  mandibular central incisor- 2.5 months after birth

  maxillary lateral incisor- 2.5 months after birth

  mandibular lateral incisor- 3 months after birth

  maxillary canines- 9 months after birth

  mandibular canines- 8-9 months after birth

  maxillary first molars- 6 months after birth

  mandibular first molars- 5-6 months after birth

  maxillary second molars- 11 months after birth

  mandibular second molars- 8-11 months after birth
• tooth development

  
  

  when does hard tissue formation begin for primary teeth?

  maxillary central incisor- 13-16 weeks after ovulation

  mandibular central incisor- 13-16 weeks after ovulation

  maxillary lateral incisor- 14.7-16.5 weeks after ovulation

  mandibular lateral incisor- 14.7-16.5 weeks after ovulation

  maxillary canines- 15-18 weeks after ovulation

  mandibular canines- 16-18 weeks after ovulation

  maxillary first molars- 14.5-17 weeks after ovulation

  mandibular first molars- 14.5-17 weeks after ovulation

  maxillary second molars- 16-23.5 weeks after ovulation

  mandibular second molars- 17-19.5 weeks after ovulation
• tooth development

  
  

  Are the stages of tooth development the same for both primary & permanent teeth?

  Yes, although the progression through stages occurs at different times
• tooth development

  
  

  For how long does tooth development continue after it first starts forming?

  Until the roots of the third permanent molars are completed (about 20 yrs of age)
• tooth development

  
  

  When do teeth start forming?

  During week 5 of embryonic life
• What is mixed dentition?

  Combination of primary and permanent teeth
• which took in the permanent teeth does not have a predecessor (deciduous tooth before its eruption)?

  first permanent molar
• what are the eruption and shedding ages of permanent teeth?

  
• what are the eruption and shedding ages of primary teeth?

  
• clinical consideration: abnormalities of shedding

  
  

  What are pre-deciduous teeth?


  • teeth that are already present at birth

  • Known as "natal" or "rootless teeth"

  • Rare condition in newborn infants

  • May cause eryption cyst

  • Danger of inhaling

  • Cause of discomfort when breastfeeding

  
• clinical consideration: abnormalities of shedding

  
  

  What are remnants of deciduous teeth?

  As the deciduous teeth are worn away and permanent teeth erupt to replace them, the occlusal remnants of the deciduous teeth are referred to as deciduous caps. The caps are normally shed as part of the eruptive process and do not cause problems however sometimes they remain:

  
  

  • Roots of deciduous teeth, specially molars (can interfere with eruption path of permanent teeth).

  • Usually due to more diverged roots of the deciduous teeth and smaller premolar size.

  
• clinical consideration: abnormalities of shedding

  
  

  What are submerged deciduous teeth?

  • the affected teeth do not come to the level of adjacent normal occluding teeth (slightly lower from the occlusal plane)

  • Ankylosed deciduous teeth (often because of trauma)

  • Mostly see in lower E

  • The permanent is either impacted or out of alignment

  
• clinical consideration: abnormalities of shedding

  
  

  What are retained deciduous teeth?

  • Persist (stay) beyond their shedding time (most common: upper B and lower E)

  • Usually due to congenital missing or impaction of permanent ones or ankylosis due to trauma.

  • Appears normal and persists for a while, till resorption occurs due to heavy masticatory forces.

  
• shedding

  
  

  Where does resorption initiate in deciduous molars?

  On the inner surface where the permanent premolars initially develop. Later, the premolars come to lie beneath the deciduous molars. The shift in position may be the reason for intermittent nature of resorption
• shedding

  
  

  where does the growing permanent tooth become?

  With subsequent movement and relocation of the teeth in the

  growing jaws, the growing permanent tooth becomes directly

  below the deciduous tooth.
• shedding

  
  

  Where does resorption initiate for all anterior deciduous teeth?

  At the lingual side of the root
• shedding

  
  

  What is the pattern of shedding?

  - It happens symmetrically (R;L)

  - lower teeth shed before upper

  - Shedding happens slightly faster in girls

  - Sequence of shedding in mandible follows anterior to posterior order, while in the maxilla, the first molar sheds before the canine
• shedding

  
  

  What are factors which can affect shedding?

  Local factors:

  - Pressure from permanent successional tooth

  - Growth of face & jaw and enlargement of masticatory muscles, increase the forces applied to deciduous teeth

  
  

  --> pressure and growth and enlargement loss of supporting tissue= exfoliation ( shedding)

  
  

  
  

  Genetic factors:

  - Apoptosis in PDL fibers

  - Initiation of root resorption might be inherent developmental process
• eruption

  
  

  what is eruption?


  The process whereby a tooth moves from its developmental position within the jaws to emerge in the oral cavity

  
  

  - developmental and adaptive process, and continues throughout life
• eruption

  
  

  what is the clinical relevance of tooth eruption?

  Eruptive tooth movements are involved in primary eruption,

  supraeruption, impaction, alveolar compensation following wear, as well as failure of eruption.
• eruption

  
  

  what are the 4 possible mechanisms of eruption?

  1• Root formation, during which space for the growing root is accommodated by occlusal movement of the tooth crown.

  2• Hydrostatic pressure within the periapical tissues pushing the tooth occlusally.

  3• Bone remodelling

  4• Pulling of the tooth in an occlusal direction by the cells and fibres of the periodontal ligament.
• eruption

  
  

  in what direction does tooth eruption occur?

  This is usually in an axial direction, but may also occur in other planes during the life of the tooth.
• shedding

  
  

  What is shedding?

  The physiological process for elimination of deciduous teeth by resorption of their roots prior to eruption of their permanent successors
• what does polyphyodont mean?

  A polyphyodont is any animal whose teeth are continually replaced.

  -> e.g. fish and reptiles
• what does monophyodont mean?

  A monophyodont is an animal that has only one set of teeth. They are permanent teeth in nature.

  -> e.g. in mice
• What does thecodont mean?

  The type of teeth attachment where each tooth is embedded in a socket of the jaw bone
• Why are humans classed as heterodont?

  a heterodont is an animal which possesses more than a single tooth morphology.

  
  

  an adult human has 32 teeth which are of 4 different types, hence heterodont.

  -> 4 different types: incisors, canine, premolars, and molars
• what is a diphyodont?

  A diphyodont is any animal with two sets of teeth, initially the deciduous set (20 teeth) and consecutively the permanent set (28-32 teeth).
• what are teeth like in humans?

  diphyodont, thecodont, and heterodont