Chronology of Dentitions Flashcards
What are lobes?
Tooth development center
What is coalescence?
fusion of lobes
What are mamelons?
3 labial development lobes on incisors
What is the cusp of Carabelli?
5th cusp
When are the earliest signs of tooth development? Where? What, exactly, is developing at this time?
5-6 week old embryo. anterior mandibular region. tiny tooth buds and tooth germs develop in the alveolar bone (tooth germs are clumps of cells that form tooth tissues: enamel, dentin, cementum, pulp)
When does development of permanent teeth occur?
17th week of pregnancy
How many teeth do babies have in development at birth?
44 teeth in various stages of development. enamel formation is well underway on all the primary dentition and the beginning of the permanent first molars
What do primary and permanent dentitions develop from?
Both develop from buds
When do primary teeth begin to calcify? When does this process end?
4th or 5th month of fetal life. this process continues until the 3rd or 4th year after birth for primary teeth, once all the roots have been fully formed
What is calcification?
the hardening of tooth tissues by the deposition of mineral salts within the tissues
What builds enamel?
Ameloblasts
Where does enamel building start from?
Ameloblasts build enamel on the top of the crown at the dentinoenamel junction, and work its way down the sides layer by layer
How long does the calcification process of permanent teeth take?
Begins soon after birth and continues until about 25 years of age, when the 3rd molar roots are fully formed
During enamel and dentin formation, minerals are being deposited while the tooth buds or germs are forming. What can cause improper tooth formation or mineralization?
- high fever
- metabolic dysfuntion
- childhood or nutritional disease
- physical illness
- trauma during formation
Primary eruption rule
begins with mandibular centrals at 6 months of age. mandibular teeth erupt first
Sequence of eruption of primary teeth
A's -- 6-12 months B's -- 9-16 months D's -- 12-18 months C's -- 16-23 months E's -- 24-33 months overall sequence: A, B, D, C, E - usually 20 teeth by the age of 2.5, and all lost by the age of 12
General rules: (not firm and always have exceptions)
- mandibular teeth before maxillary
- erupt in pairs on each arch (one right and one left either on mandible or maxilla)
- permanent teeth in girls erupt slightly earlier than boys. no evidence of difference in primary eruption between the sexes
Primary teeth exfoliation
- mn centrals: erupt around 6 months and exfoliate at 6 years
- mx centrals: erupt 7-8 months and exfoliate 7-8 years
- man laterals: erupt 9 months, exfoliate 8 years
- mn 1st molars: erupts 12 months, exfoliates 10 years
- mx 1st molars: erupts after 12 months, exfoliates 10 years
- canines mx and mn: erupt at 16 months, exfoliates mx at 12, mn at 10 years
- 2nd molars: erupted by 2.5 years old, exfoliates at 12 years
What will occur if a primary tooth is lost prematurely? Why is this?
One side of the jaw will develop differently than the other. Reason: exercise is not divided equally when a tooth is missing
What is the first permanent tooth to erupt?
mandibular 1st molar
What is mesial drift?
the tendency of the permanent molars to erupt towards the midline
When does mesial drift occur? What will happen if this occurs?
- if the primary teeth are lost prematurely, space for permanent teeth will be lost
- the spaces between the primary teeth will close
What does mesial drift cause overall?
Poor eruption of the permanent premolars and canines
What must occur for permanent teeth to erupt?
the teeth of the primary dentition must exfoliate
How does exfoliation occur?
the roots will resorb until the tooth falls out. resorption continues to take place as the permanent tooth erupts
What do odontoclasts do?
destroy the root of the primary tooth
How are odontoclasts activated?
by the pressure of the permanent tooth on the primary tooth
Secondary eruption schedule
Mandibular teeth before maxillary - 1st molars (6): about 6-7 years - 1's: 7-8 years - 2's: 8-9 years - 4's: 10-11 years - 5's: 10-12 years - 3's: 9-12 years - 7's: 12 years - 8's: 17-21 years overall sequence: 6, 1, 2, 4, 5, 3, 7, 8 (mandibular canines may erupt before premolars, in which case the mn schedule is 6, 1, 2, 3, 4, 5, 7, 8
What can occur to stop eruption of 3rd molars?
- can be impacted (totally embedded in bone)
- can be partially erupted (not completely erupted)
- congenitally missing (the tooth bud never develops)
What is attrition? What does it cause?
attrition is the wearing away of tooth surface through functional contact/occlusion. eruptive forces continue throughout the life of a tooth due to attrition
What is the curve of spee?
as the teeth erupt, the meet their partner on the opposing arch and form what is called the occlusal plane. A curved plane is derived from the teeth in both arches occluding with one another and is called the Curve of Spee (anterior teeth are higher than posterior)
When does the primary dentition start and end?
Starts with the eruption of the first primary tooth at 6-9 months and ends with the eruption of the first permanent tooth (around 6 years)
When does the mixed dentition start and when does it end?
Starts with the eruption of the first permanent tooth (around 6 years) and ends with the loss of the last primary tooth
When does the permanent dentition start?
When all primary teeth have been lost.
What does the term edentulous mean?
no teeth
