10 Average Tooth Measurements Anterior to First Permanent Molar Most tooth massduring mixed dentition!!
11 Occlusal Changes in the Mixed Dentition Flush terminal plane may lead to:Class I (with late mesial shift)Class IIEnd to endMesial step may lead to:Class I (normally)Class IIIDistal step leads to Class II
15 Class II division 1, transverse dimension Changes in arch length and width follow same general pattern as normalsClass II, div 1 have relative constriction of the maxillary archConstriction 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 3-4-5This "leeway space" averages 1.7 mm. in the mandibular buccal segment; 0.9 in the maxillary buccal segment
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 occlusionBad news - the above reduces arch length
20 Late Mesial Shift (cont.) Molar moves intothis space...Class IFTP
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 incisorsIntercanine arch width growthLabial positioning of the permanent incisorsFavorable 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.
29 Overcoming Incisor Liability Labial positioning of the permanent incisorspermanent incisors erupt to a more labial positionpermanent incisors are angled more labiallythe above creates more arch length
31 Overcoming Incisor Liability Favorable size ratio between the primary and permanent incisorssize ratio between the primary and permanent incisors may be favorable or unfavorablefavorable: large primary, small permanentunfavorable: small primary, large permanent
32 Mixed Dentition Analysis Why: predict amount of crowding after permanent teeth come inWhen: during mixed dentitionWhat: boley guage, models, prediction tableWhere: your officeWho: YOU!!!
33 MDA MethodologyMeasure mesial-distal diameter of the mandibular incisors and sumMeasure space available for mandibular incisorsSubtract #1 from #2; negative number indicates crowding in the incisor region
34 MDA Methodology (cont.) Measure space available for on each side of the archCalculate from prediction table the size of 3-4-5Subtract #2 from #1 on each side
35 MDA Methodology (cont.) At this point, you should have three numbers:number for incisor crowding or excess spacenumber for right buccal segment crowding or excess spacenumber for left buccal segment crowding or excess spaceAdd the three numbers; negative = crowding, positive = space
36 MDA Methodology (maxillary arch) Use mandibular incisors to predict the size of the maxillary 3-4-5Do everything else the same as described for mandibular teethREMEMBER!
37 MDA Example Measure 21-12, measure space available for 21-12 Left IncisorsRightSpace Available19.8 mmTooth Size23.0 mmDifferenceMeasure 21-12, measure spaceavailable for 21-12
38 MDA Example Subtract tooth size from space available Left Incisors RightSpace Available19.8 mm.Tooth Size23.0 mm.Difference-3.2 mm.Subtract tooth size fromspace available
39 MDA Example Measure space available for 3-4-5 on each side Left IncisorsRightSpace Available20.1 mm.19.8 mm.19.5 mm.Tooth Size23.0 mm.Difference-3.2 mm.Measure space available for3-4-5 on each side
41 MDA Example Calculate size of 3-4-5 from prediction table Left IncisorsRightSpace Available20.1 mm.19.8 mm.19.5 mm.Tooth Size22.2 mm.23.0 mm.Difference-3.2 mm.Calculate size of fromprediction table
42 MDA Example Subtract tooth size from space available on left and right IncisorsRightSpace Available20.1 mm.19.8 mm.19.5 mm.Tooth Size22.2 mm.23.0 mm.Difference-2.1 mm-3.2 mm.-2.7 mm.Subtract tooth size fromspace available on left and right
43 MDA Example Total difference is -8.0 mm. Left Incisors Right Space Available20.1 mm.19.8 mm.19.5 mm.Tooth Size22.2 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 forFigure 1.7 mm. per side with ETE relationship.
45 Other Factors Influencing Amount of Predicted Crowding Anterior-posterior position of incisorsPosition of molarsCurve of Spee