Mixed Dentition Occlusion and Analysis Dr S E

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

Dental Efficiency

Definition of a Mixed Dentition 6 edc 21 12 cde 6

Mixed Dentition

Mixed Dentition

Mixed Dentition

Mixed Dentition Deep overbite

Adequate Spacing

Adequate Spacing

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

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

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

Mesial Step Class III Class I (desirable) Mesial Step

Disto Step Always Disto Step Class II

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.

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

Serial Disking

Serial Disking

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

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

Late Mesial Shift (cont. )

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?

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

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

Primary Spacing

Primary Spacing

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

Intercanine growth

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

Labial Positioning

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

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!!!

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

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

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

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!

MDA Example Left Incisors Space Available 19. 8 mm Tooth Size 23. 0 mm Right Difference Measure 21 -12, measure space available for 21 -12

MDA Example Left Incisors Space Available 19. 8 mm. Tooth Size 23. 0 mm. Difference -3. 2 mm. Subtract tooth size from space available Right

MDA Example Left Space Available 20. 1 mm. Incisors 19. 8 mm. Tooth Size 23. 0 mm. Difference -3. 2 mm. Right 19. 5 mm. Measure space available for 3 -4 -5 on each side

Moyer's Prediction Chart

MDA Example Left Incisors Right Space Available 20. 1 mm. 19. 8 mm. 19. 5 mm. Tooth Size 22. 2 mm. 23. 0 mm. 22. 2 mm. Difference -3. 2 mm. Calculate size of 3 -4 -5 from prediction table

MDA Example Left Incisors Right Space Available 20. 1 mm. 19. 8 mm. 19. 5 mm. Tooth Size 22. 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

MDA Example Left Incisors Right Space Available 20. 1 mm. 19. 8 mm. 19. 5 mm. Tooth Size 22. 2 mm. 23. 0 mm. 22. 2 mm. Difference -2. 1 mm -3. 2 mm. -2. 7 mm. Total difference is -8. 0 mm.

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 3 -4 -5. • Figure 1. 7 mm. per side with ETE relationship.

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