Mixed dention ppt

Basics of mixed dention eruption and phases of MD.

1. MIXED DENTITION NAILA SUNBAL PGR ORTHODONTIC DEPARTMENT PESHAWAR DENTAL COLLEGE

2. CONTENT Introduction to mixed dentition Primary dentition Permanent dentition Phases of mixed dentition.

3. Mixed Dentition The period in which both primary and permanent teeth are present in the oral cavity. Usually present between age 6 to 12 years. when some of the primary teeth are being replaced by permanent teeth, starts with the eruption of the first permanent tooth.

4. Eruption Sequence of primary teeth First primary teeth erupt approximately at 6 months of age, up to 6 months of acceleration or delay is within normal range. Mandibular centrals erupt first followed by other incisors. After 3 to 4 month interval the mandibular and maxillary first molars erupt. Followed in another 3 to 4 months interval canine erupt. Primary dentition usually completed at the age of 24 th to 30 th month as the mandibular then maxillary 2 nd molars erupt.

5. Features of primary dentition Duration 6 th month to 12 1/2 years. Generalize spacing proper alignment of permanent teeth. Primate spaces. 20 in numbers (2 incisors ,1 canine ,2 molars). Shorter crown sizes in relation to pulp chamber. No mamelons.

6. Primate spaces : Spaces between maxillary lateral incisor and canines and mandibular canines and 1 st molars .

7. Primary dentition may be type I dentition (spaced dentition) or Type II dentition (closed dentition) also called as Hollywood smile normally leads to future crowding   Shallow overjet & overbite Flush terminal plane is a normal feature. Ovoid arch forms.

8. Features of permanent Dentition Duration 6 th year onwards. 32 in number(2 incisors, 1 canine ,2 premolars, 3 molars). Larger crown sizes in relation to pulp chamber . Mamelons present. Tight contacts. Darker than primary teeth.

9. Mamelons

10. Eruption sequence of permanent teeth Teeth erupt in groups, mandibular first followed by maxillary. A tooth usually emerges when about three-fourth of its root has been completed. It takes 2 to 3 years for root to be completed after a tooth has been erupted into occlusion . Most common sequence is mandibular central incisors at age 6¼ Closely followed by permanent mandibular first molar and maxillary first molar. The beginning of eruption of this group of teeth characterizes dental age 6.

11. Eruption sequence of permanent teeth Dental Age 7 maxillary central incisors and mandibular lateral incisors. Dental Age 8 maxillary lateral incisors after this there is delay of 2 to 3 years. At dental age 9 primary canines, 1st and 2nd molars are present in mouth. At dental Age 11 eruption of mandibular canines ,mandibular first premolars and maxillary first premolars. At dental age 12 maxillary canines and maxillary and mandibular 2 nd premolars. A few months later maxillary and mandibular 2 nd molars.

12. Normal variation in eruption sequence Eruption of 2 nd molars ahead of premolars in mandibular arch. Eruption of canines ahead of premolars in maxillary arch. Unusually large asymmetries in eruption between right and left side.

13. Phases of mixed Dentition First transitional period Inter transitional period Second transitional period

14. 1 st Transitional period 6 to 8 years . Eruption of 1 st permanent molars and the exchange of the deciduous incisors with the permanent incisors. The 1 st permanent molars are guided into the arch by distal surface 2 nd deciduous molars. The mesiodistal relationship between the distal surfaces of upper and lower 2 nd deciduous molars are of three types. 1: Flush terminal plane 2: Mesial step 3: Distal step

15. Flush Terminal Plane : T he distal surfaces of 2 nd deciduous maxillary and mandibular molars are in a straight vertical plane . Most favorable relationship to guide the permanent molars in class I relation. Transition from flush terminal plane to class I requires about 3.5 mm forward movement of lower molars, half is achieved from leeway space half by differential growth of mandible.

16. Flush terminal plane may lead to

17. Mesial step: Distal surface of mandibular 2 nd molar is mesial to distal surface of 2 nd deciduous maxillary molar. Because of this mesial position of lower deciduous molar the permanent 1 st molar erupt directly into class I occlusion. This type of mesial step mainly occurs due to forward growth of mandible but if the differential growth of mandible persists , it can lead to class III in permanent 1 st molars.

18. Mesial step may lead to

19. Distal step : The distal surface of lower deciduous 2 nd molar is distal to the distal surface of upper 2 nd deciduous molar . Distal step leads to class II in permanent 1 st molars .

20. Distal step may lead to

21. The shift in permanent lower molar from flush terminal plane to class 1 relation can occur in 2 ways: 1 . EARLY SHIFT : Eruptive Forces of 1 st per. Molar is sufficient to push the deciduous 1 st and 2 nd molar forward to close the primate spaces & establish a class I relationship, since this occurs in early mixed dentition period its called Early shift.   2. LATE SHIFT : when deciduous 2 nd molar exfoliates the permanent 1 st molar drift mesialy using the leeway space, as this occurs in late mixed dentition its called late mesial shift.

22. Leeway space: The combine mesiodistal width of primary canine 1 st and 2 nd molars is more than that of permanent canine ,1 st and 2 nd premolars and the difference between the two is called Leeway space . Mandible: 2.5 Maxilla :1.5

23. Leeway space

24. 1 st transitional period: Incisors transition The permanent incisors are larger than the deciduous incisors they replace, and this difference between the amount of space needed for the adjustment of permanent incisors and the amount of space available is called incisor liability . Incisor liability at maxilla 7mm and in mandible is 5mm.

25. Incisal liability is overcome by 1: Utilization of primate spaces present in primary dentition. 2: Increase in dental arch width across the canine adds 1 to 2mm. 3: Labial position and inclined permanent incisors adds up to 2mm

26. Inter-transitional phase 8 to 10 years. This is stable phase during the mixed dentition stage and no change occurs during inter-transitional phase. Teeth present are permanent incisors 1 st molars and deciduous canines 1 st and 2 nd molars. Last about 1.5 to 2 years.

27. 2 nd Transitional stage : 10 to 12 years. Replacement of deciduous molars and canines by the premolars and permanent canines 2 nd permanent molars erupt. Eruption of all permanent teeth occur except 3 rd molars.

28. Ugly duckling stage Also called physiological diastema or Broadbents’ phenomena Occurs at 8 to 11 years This stage occurs before eruption of permanent canine. When cuspids are erupting they displaced the roots of lateral incisors mesial transmitting force on the central incisors distally creating a midline diastema . Corrects by itself when canines erupt. Upto 2mm of diastema is self correcting ,further than that requires mx. Describes by Broadbents as ugly duckling as child looks ugly during this phase.

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