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too short time we can have these children under our control, and
the necessity for saving many visits to the Clinic, and absences
from school. Let it not be assumed the Clinic keeps its patients
till school leaving age. Many get scholarships and at eleven years
of age pass out of our control to County Schools. The County
Council and other Authorities at present do not treat each others
cases.
Classification of Cases.
As a working basis, the classification of Angle and Lischer
were used. They can be roughly defined as below. A test tooth
had to be taken, and from the relation of all the other teeth in the
arch the classifications were founded. The first permanent molars
were selected as the test teeth. The normal position of these teeth
is that when they are occluded together the anterior (medial) third
of the lower molar will be that amount in front of the upper molar.
From this three classifications are made: —
Class 1 cases.—When the first molars are in normal occlusion
as above stated.
The next two classes depend on the position of this anterior
third of the lower first molar
If it moves back in a distal direction and the anterior part of
the upper first molar is in front of the lower first molar then we
have Class 2—post Normal cases. Should the lower first molar
have moved in a forward direction (medially) to the extent (often)
of its whole width, then the case is a Class 3 Pre-Normal one.
The first and second of these classes have divisions, and all three
have sub-divisions. The correct diagnosis of these classes is helpful
in determining, when aided by Clinical examination and
Orthodontic experience, the type of problem to be solved.
It has always to be kept in mind that the key teeth may be in
normal occlusion, but may have moved forward in the jaw through
the too early extractions of the second temporary molars.
Class 1 cases can be described thus : —
1. The arches of the jaws are in normal relation to each other.
2. The test teeth are in normal occlusion.
3. All teeth anterior to (2) may be in various irregular
positions.