1. Mixed Dentition Occlusion and Analysis
Dr S.E.Jabbarifar
Associate Professor
Department of Pediatric Dentistry /Isfahan 2009

2. Dental Efficiency

3. Definition of a Mixed Dentition
6 e d c 2 1
1 2 c d e 6

4. Mixed Dentition

5. Mixed Dentition

6. Mixed Dentition

7. Mixed Dentition
Deep overbite

8. Adequate Spacing

9. Adequate Spacing

10. Average Tooth Measurements Anterior to First Permanent Molar
Most tooth mass
during mixed dentition!!

11. Occlusal Changes in the Mixed Dentition
Flush terminal plane may lead to:
Class I (with late mesial shift)
Class II
End to end
Mesial step may lead to:
Class I (normally)
Class III
Distal step leads to Class II

12. Flush Terminal Plane
Class II
Class I
(desirable)
FTP
ETE

13. Mesial Step
Class III
Class I
(desirable)
Mesial
Step

14. Disto Step
Always
Class II
Disto
Step

15. Class II division 1, transverse dimension
Changes in arch length and width follow same general pattern as normals
Class II, div 1 have relative constriction of the maxillary arch
Constriction present at three stages of dental development, and does not self correct.
Bishara, et al, “Longitudinal comparisons of dental arch changes in normal and untreated Class II, division 1 subjects and their clinical implications” AJO, November 1996.

16. Leeway Space Sum of (c-d-e) > (3-4-5)
This allows more space for 3-4-5
This "leeway space" averages 1.7 mm. in the mandibular buccal segment; 0.9 in the maxillary buccal segment

17. Serial Disking

18. Serial Disking

19. Late Mesial Shift Refers to mandibular permanent molar moving mesially
Good news - if permanent molars are ETE, late mesial shift allows mandibular molar to move into a Class I occlusion
Bad news - the above reduces arch length

20. Late Mesial Shift (cont.)
Molar moves into
this space...
Class I
FTP

21. Late Mesial Shift (cont.)

22. Incisor Liability Permanent incisors are larger than primary incisors
This difference in size is termed "incisor liability"
How does the body create enough room for the larger, permanent incisors?

23. Overcoming Incisor Liability
Interdental spacing of primary incisors
Intercanine arch width growth
Labial positioning of the permanent incisors
Favorable size ratio between the primary and permanent incisors

24. Overcoming Incisor Liability
Interdental spacing of primary incisors Good interdental spacing of primary incisors allows for better alignment of the larger permanent incisors.

25. Primary Spacing

26. Primary Spacing

27. Overcoming Incisor Liability
Intercanine arch width growth
width growth creates more room for the permanent incisors
mandibular intercanine growth occurs mostly during permanent incisor eruption
maxillary intercanine growth occurs during incisor eruption, and continues
unpredictable

28. Intercanine growth

29. Overcoming Incisor Liability
Labial positioning of the permanent incisors
permanent incisors erupt to a more labial position
permanent incisors are angled more labially
the above creates more arch length

30. Labial Positioning

31. Overcoming Incisor Liability
Favorable size ratio between the primary and permanent incisors
size ratio between the primary and permanent incisors may be favorable or unfavorable
favorable: large primary, small permanent
unfavorable: small primary, large permanent

32. Mixed Dentition Analysis
Why: predict amount of crowding after permanent teeth come in
When: during mixed dentition
What: boley guage, models, prediction table
Where: your office
Who: YOU!!!

33. MDA Methodology
Measure mesial-distal diameter of the mandibular incisors and sum
Measure space available for mandibular incisors
Subtract #1 from #2; negative number indicates crowding in the incisor region

34. MDA Methodology (cont.)
Measure space available for on each side of the arch
Calculate from prediction table the size of 3-4-5
Subtract #2 from #1 on each side

35. MDA Methodology (cont.)
At this point, you should have three numbers:
number for incisor crowding or excess space
number for right buccal segment crowding or excess space
number for left buccal segment crowding or excess space
Add the three numbers; negative = crowding, positive = space

36. MDA Methodology (maxillary arch)
Use mandibular incisors to predict the size of the maxillary 3-4-5
Do everything else the same as described for mandibular teeth
REMEMBER!

37. MDA Example Measure 21-12, measure space available for 21-12 Left
Incisors
Right
Space Available
19.8 mm
Tooth Size
23.0 mm
Difference
Measure 21-12, measure space
available for 21-12

38. MDA Example Subtract tooth size from space available Left Incisors
Right
Space Available
19.8 mm.
Tooth Size
23.0 mm.
Difference
-3.2 mm.
Subtract tooth size from
space available

39. MDA Example Measure space available for 3-4-5 on each side Left
Incisors
Right
Space Available
20.1 mm.
19.8 mm.
19.5 mm.
Tooth Size
23.0 mm.
Difference
-3.2 mm.
Measure space available for
3-4-5 on each side

40. Moyer's Prediction Chart

41. MDA Example Calculate size of 3-4-5 from prediction table Left
Incisors
Right
Space Available
20.1 mm.
19.8 mm.
19.5 mm.
Tooth Size
22.2 mm.
23.0 mm.
Difference
-3.2 mm.
Calculate size of from
prediction table

42. MDA Example Subtract tooth size from space available on left and right
Incisors
Right
Space Available
20.1 mm.
19.8 mm.
19.5 mm.
Tooth Size
22.2 mm.
23.0 mm.
Difference
-2.1 mm
-3.2 mm.
-2.7 mm.
Subtract tooth size from
space available on left and right

43. MDA Example Total difference is -8.0 mm. Left Incisors Right
Space Available
20.1 mm.
19.8 mm.
19.5 mm.
Tooth Size
22.2 mm.
23.0 mm.
Difference
-2.1 mm
-3.2 mm.
-2.7 mm.
Total difference is -8.0 mm.

44. Allowance for Late Mesial Shift
If permanent molars are end to end, mandibular molar should move mesially to obtain Class I interdigitation.
This will decrease the arch length available for
Figure 1.7 mm. per side with ETE relationship.

45. Other Factors Influencing Amount of Predicted Crowding
Anterior-posterior position of incisors
Position of molars
Curve of Spee