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

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Presentation on theme: "Mixed Dentition Occlusion and Analysis Dr S.E.Jabbarifar Associate Professor Department of Pediatric Dentistry /Isfahan 2009."— Presentation transcript:

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

3 Dental Efficiency

4 Definition of a Mixed Dentition 6 e d c c d e 6

5 Mixed Dentition

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8 Deep overbite

9 Adequate Spacing

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

12 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

13 Flush Terminal Plane FTP Class II Class I (desirable) ETE

14 Mesial Step Mesial Step Class III Class I (desirable)

15 Disto Step Disto Step Class II Always

16 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.

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

18 Serial Disking

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20 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

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

22 Late Mesial Shift (cont.)

23 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?

24 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

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

26 Primary Spacing

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28 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

29 Intercanine growth

30 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

31 Labial Positioning

32 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

33 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!!!

34 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

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

36 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

37 REMEMBER! MDA Methodology (maxillary arch) Use mandibular incisors to predict the size of the maxillary Do everything else the same as described for mandibular teeth

38 MDA Example LeftIncisorsRight Space Available 19.8 mm Tooth Size 23.0 mm Difference Measure 21-12, measure space available for 21-12

39 MDA Example LeftIncisorsRight Space Available 19.8 mm. Tooth Size 23.0 mm. Difference -3.2 mm. Subtract tooth size from space available

40 MDA Example LeftIncisorsRight Space Available 20.1 mm.19.8 mm.19.5 mm. Tooth Size 23.0 mm. Difference -3.2 mm. Measure space available for on each side

41 Moyer's Prediction Chart

42 MDA Example LeftIncisorsRight Space Available 20.1 mm.19.8 mm.19.5 mm. Tooth Size22.2 mm.23.0 mm.22.2 mm. Difference -3.2 mm. Calculate size of from prediction table

43 MDA Example LeftIncisorsRight Space Available 20.1 mm.19.8 mm.19.5 mm. Tooth Size22.2 mm.23.0 mm.22.2 mm. Difference-2.1 mm-3.2 mm.-2.7 mm. Subtract tooth size from space available on left and right

44 MDA Example LeftIncisorsRight Space Available 20.1 mm.19.8 mm.19.5 mm. Tooth Size22.2 mm.23.0 mm.22.2 mm. Difference-2.1 mm-3.2 mm.-2.7 mm. Total difference is -8.0 mm.

45 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.

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


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