Dentistry: Mixed Dentition Period Lecture 6

Molar Eruption and Occlusion

• First permanent molars typically erupt between 6-7 years old.

Anteroposterior Positioning of Permanent Molars

• The anteroposterior positioning of permanent molars is influenced by the terminal plane of the second deciduous molars.

Role of First Permanent Molars in Occlusion

• First permanent molars play a crucial role in occlusion, as they establish the posterior occlusal plane.

Influence of Terminal Plane on Permanent Molars

• A flush terminal plane of the second deciduous molars allows for a more mesial eruption of the permanent first molars.

Leeway Space and Occlusion

• The Leeway space contributes to the development of occlusion by providing room for the permanent teeth to erupt.

Emergence and Transition Period

• The emergence of the first permanent molars and transition of incisors occur during the early mixed dentition period (6-12 years old).

Distal and Mesial Steps

• A distal step in the deciduous second molars results in a Class II molar relationship.
• A mesial step relationship of primary second molars leads to a Class III molar relationship in the mixed dentition.

Early and Late Shift

• Early shift occurs during the early mixed dentition period, where the molars shift mesially to close any spaces between the primary molars.
• The late mesial shift of molars occurs later in the mixed dentition period.

Nance's Description and Arch Length

• Nance described in 1947 that the combined mesiodistal width of the primary canines and molars equals the combined mesiodistal width of the permanent canines and premolars.
• The expected arch length in the maxilla is 38 mm based on Nance's description.
• The expected arch length in the mandible is 34 mm based on Nance's description.

Class II Malocclusion

• Class II malocclusion can occur despite Leeway space and differential growth due to other factors such as genetics, habits, or other environmental influences.