Ortho module 2 part C

Question 1

What do infant mandibles look like and how do they make the overall child’s face look like?

Answer 1

All infants have a small, under-developed mandible that gives them a very convex profile. As growth progresses, the mandible will grow forward more than the maxilla and this will lead to a straighter face profile and increased mandibular projection compared to the maxilla.

Question 2

What do infants look like intra-orally?

Answer 2

The maxillary and mandibular arch forms have different shapes in the edentulous infnat.

The maxillary arch is ovoid in shape while the mandibular arch is V-shaped. The alveolar ridges contain the developing primary and permanent tooth buds.

Question 3

What do infants look like intra-orally?

Answer 3

The maxillary and mandibular arch forms have different shapes in the edentulous infant.

Question 4

What shape is the dentition in infants?

Answer 4

The maxillary arch is ovoid in shape while the mandibular arch is V-shaped. The alveolar ridges contain the developing primary and permanent tooth buds.

Question 5

How is space made for the eruption of primary teeth?

Answer 5

Vertical growth takes place where initially the upper and lower gum pads were touching with no vertical space and eventually the vertical growth of the maxilla leads to an increase in face height which accomodates eruption of the primary teeth

Question 6

How is space made for the eruption of primary teeth?

Answer 6

Vertical growth takes place where initially the upper and lower gum pads were touching with no vertical space and eventually the vertical growth of the maxilla leads to an increase in face height which accomodates eruption of the primary teeth.

TL;DR: The erupting teeth don’t push the jaws apart, the jaws move apart and this creates space for the eruption of the teeth.

Question 7

When is primary tooth eruption completed?

Answer 7

Usually by 24 - 30 months of age.

Question 8

What does spacing indicate about developing primary dentition?

Answer 8

Spacing is common and desirable in the primary dentition and is usually noticeable in 2 locations called the primate spaces.

These spaces are also found in non-human primates.

Question 9

What does spacing indicate about developing primary dentition?

Answer 9

Spacing is common and desirable in the primary dentition and is usually noticeable in 2 locations called the primate spaces.

Question 10

Why are primate spaces called that?

Answer 10

These spaces are also found in non-human primates.

Question 11

Where are primate spaces located?

Answer 11

In the maxillary arch it is between the lateral incisors and the canines.

In the mandibular arch it is between the canine and the first molar.

Question 12

What does a lack of spacing in primary dentition indicate?

Answer 12

Potential future crowding problems in the transitional and permanent dentitions as the larger permanent incisors erupt.

Question 13

What is the incisor liability?

Answer 13

The combined mesiodistal width of the permanent incisors is larger than that of the primary incisors.and is approximately 7.5mm greater.

In the mandible the permanent incisors are 6mm wider.

Question 14

How is incisor liability overcome in the maxillary arch?

Answer 14

In the maxillary arch the larger permanent incisors are accommodated by:

Utilization of any interdental spaces between the laterals and centrals. (image 1)
Utilization of the maxillary primate spaces between the laterals and canines. (image 2)
Labial eruption of the incisors increasing arch length and circumference. (image 3)
Increase in width of the dental arch across the canines (intercanine width)

Question 15

How is incisor liability overcome in the mandibular arch?

Answer 15

Utilization of any developmental spaces between incisors.

Increase in intercanine width.

Question 16

What are the categories of molar occlusion that take place in the primary dentition?

Answer 16

Flush terminal plane: distal surfaces of opposing primary second molars are in the same vertical plane.

Mesial step terminal plane: Mandibular primary second molar terminal plane is located mesial to the terminal plane of the maxillary primary second molar. (corresponds to class 1 occlusion)

Distal step terminal plane: Mandibular primary second molar is located distal to the terminal plane of the maxillary primary second molar. (corresponds to class 2 occlusion)

Question 17

What are the types of canine relationships in the primary dentition?

Answer 17

End to end: Canines point in the same vertical line.

Class 1 canine relationship: The cusp tip of the upper canine occludes in the embrasure between the lower canine and lower first molar.

Class 2: Cusp tip of ujpper canine occludes mesial to the lower canine in the space between the lower canine and the lateral incisor.

Class 3: Cusp tip of upper canine occludes distal to the embrasure between mandibular first primary molar and canine.

Question 18

What is the leeway space?

Answer 18

The primary canine, first molar and second molar occupy more space in their quadrants than their permanent successors. The space they leave over is called the leeway space.

Question 19

What is the leeway space of the maxillary and mandibular arches?

Answer 19

Maxillary arch: 1.5mm per side

Mandibular arch 2.5mm per side

This is highly variable due to the variability in tooth size

Question 20

What is the early mesial shift?

Answer 20

Patients with a flush terminal plane molar relationship in the primary dentition can and often develop a class 1 permanent molar relationship

Question 21

Why does early mesial shift happen?

Answer 21

Primate spaces exist distal to the mandibular primary canines so at 6 years of age when the permanent molars erupt they can use that space to shift forward and close the mandibular primate space.

Question 22

What is the late mesial shift?

Answer 22

With exfoliation of all primary second molars, the permanent maxillary and mandibular molars shift mesially into the leeway space. The mandibular leeway space is larger than the maxillary space meaning that mandibular molars shift more mesially than maxillary molars and this causes a shift mesially that is more prominent.

Question 23

How does jaw growth influence the mesial shift?

Answer 23

Differential growth of mandible relative to maxilla due to the cephalocaudal gradient is an important contributor to the molar position.

Growth of the jaws carries the dentition along with it and due to difference in rate between maxilla and mandible growth there is an overall affect on how upper and lower teeth will be related in space.

Generally, the mandible grows forward relative to the maxilla during the transition from mixed dentition to the early permanent dentition, carrying the lower teeth with it and this aids in development of normal occlusion of the permanent teeth.

Question 24

What are the possible shifts in occlusion between primary and secondary teeth based on growth differential of mandible and maxilla?

Answer 24

Distal step leads to class 2 occlusion whereas a forward growth of the mandible leads to end-to-end occlusion.

Flush terminal plane with minimal growth differential leads to end-to-end occlusion whereas forward mandible growth leads to class 1 occlusion.

Mesial step with minimal growth differential leads to class 1 occlusion whereas forward growth of mandible leads to class 3 occlusion.

Question 25

What percentage of children with flush terminal plane in the primary dentition develop into a class 1 relationship in permanent dentition?

Answer 25

~75% of children with a flush terminal plane.

Question 26

What is the best case scenario to expect from a distal step in primary dentition when transitioning into the permanent dentition?

Answer 26

An end-to-end relationship because the distance from distal step to class 1 occlusion is too far.

This means that distal step patients require orthodontic intervention most likely

Question 27

What does a mesial step transition into if the mandible grows excessively?

Answer 27

Into a class 3 occlusal relationship