Mixed Dentition Occlusion

Question 1

Definition of a Mixed Dentition

Answer 1

4 incisors, 6 buccal segment primary teeth, and 2 permanent 1st molars per arch

in non-crowded: incisors should be well aligned

Question 2

Average Tooth Measurements Ant to First Permanent Molar

Answer 2

Classic mixed dentition has the largest of the incisors (permanent) and the largest of the buccal segment (primary)

Sum total, mesial-distal dimension of the c, d, and e is greater than the 3,4 and 5

Ant to the 1st permanent molar, the most tooth mass is in the mixed dentition

Question 3

Incisor Liability

Answer 3

Permanent incisors are larger than primary incisors

The difference in size is termed “incisor liability”

max: 7.5 mm difference
mand: 5 mm difference

Question 4

Overcoming Incisor Liability

Answer 4

1: Interdental spacing of primary incisors
2: Intercanine arch width growth
3: Labial positioning of the permanent incisors
4: Favorable size ratio b/n the primary and permanent incisors

Question 5

Favorable size ratio b/n the primary and permanent incisors

Answer 5

size ratio b/n the primary and permanent incisors may be favorable or unfavorable

Favorable: large primary, small permanent
Unfavorable: small primary, large permanent

Question 6

Leeway Space

Answer 6

sum of (c,d,e) > sum of (3,4,5)

allows more space for 3,4,5

“leeway space” averages 1.7 mm in the mandibular buccal segment; 0.9 in the maxillary buccal segment

Question 7

Occlusal Changes in Mixed Dentition

Answer 7

Transitional end to end may lead to: class I (LMS), Class II, End to end

Mesial step may lead to: Class I (normally), Class III

Distal step leads to Class II

Question 8

Average Sizes/Growth (Tooth sizes)

Answer 8

L lat = L cen + 0.5
U cen = L cen + 3.5
U lat = U cen - 2.0
U lat = L cen + 1.5
L can = L cen + 1.5
U can = U cen - 1.0
U PM = U cen - 1.8
L PM = L cen + 1.6, 1.9

Question 9

Arch perimeter Changes: Mandibular Arch Perimeter

Answer 9

Inc 2-3 mm b/n 6 and 11

dec 4-7 mm from 11 and 16

Question 10

Arch perimeter changes: Maxillary Arch Perimeter

Answer 10

Inc 4-5 mm b/n 6 and 11

dec 3-4 mm from 11 and 16

Question 11

Typical Radiographs Prescribed per age group for a new Patient: primary dentition

Answer 11

Max ant PA, mandibular anterior PA, BWXs if post teeth in justaposition

Question 12

Typical Radiographs Prescribed per age group for a new Patient: mixed dentition

Answer 12

Panoramic, 2 BWXs

Question 13

Typical Radiographs Prescribed per age group for a new Patient: permanent dentition

Answer 13

Panoramic, 4 BWXs if 2nd permanent molars are in occlusion and have been present long enough to potentially have IP lesion

Question 14

Number Issues when looking in radiograph

Answer 14

Count in 3’s to determine presence of 3,4,5

missing mand 2nd bicuspid
missing max 2nd bicuspid

check for development of second and 3rd molars

check for development of incisors (4 top and bottom)

count erupted molars and cuspids (4 each size)

Question 15

Position/symmetry Issues when looking in radiograph

Answer 15

sides should mirror images of each other (fold X-rays over and match teeth)