Orthodontic Diagnosis and Treatment Planning Essentials

Skeletal Class II and Class III Malocclusions

Causes of skeletal malocclusions include:

• Class II: Hypertrophic maxilla or retrognathic mandible.
• Class III: Hypoplastic maxilla or prognathic mandible.

Functional appliances are typically utilized between ages 11–14 for boys and 10–13 for girls to address Class II issues. Transverse dimension features include compression, crossbite, scissor bite, and midline deviation.

Intramembranous Bone Formation

1. Osteoblasts produce osteoid tissue.
2. Cells and blood vessels become encased.
3. Osteoid tissue is produced by membrane cells.
4. Osteoid calcifies.
5. Essential membrane covers the bone, alongside an internal membrane.

Moyers Method for Mixed Dentition

The Moyers method is used during interarch relationship analysis in mixed dentition. It estimates the size of permanent canines and premolars to calculate the space required for the full permanent dentition. This value is applied in the Tanaka-Johnston equation to determine the discrepancy between space available and space needed.

Andrews' Six Keys to Normal Occlusion

The six keys include: molar relationship, crown angulation, crown inclination, rotations, spaces, and the occlusal plane.

Key I: Molar Relationship

The mesiobuccal cusp of the upper first permanent molar should lie between the mesiobuccal and distobuccal cusps of the lower first molar. If the lower molar is more distal, it is Class II; if mesial, it is Class III. Key V specifies there should be no rotations, as rotated teeth occupy more space.

Orthodontic Model Trimming

• Trim the superior border of the lower model to 35mm in height.
• Draw a line on the upper model down to the palatal raphe.
• Trim the posterior border perpendicular to the palatal raphe line, 5mm distal to the last erupted molars.
• Articulate models with a wax bite in normal occlusion.
• Trim the posterior border of both models using the upper as a guide.
• Trim the upper parallel to the lower to a total height of 70mm.
• Trim the anterior border of the upper model into a V-shape and the lower into a rounded shape; the lingual surface must be flat.

Habits and Equilibrium

Common habits include tongue swallowing, thumb sucking, and mouth instrument use. Tomes' Equilibrium describes equal forces within the vestibule between cheeks, tongue, and teeth, maintaining tooth position. Disturbances, such as excessive tongue force, can disrupt this equilibrium.

Clinical Assessment

Molar Class I, Division 2, Subdivision Right: To assess rotation, draw a line from the distobuccal cusp to the mesiopalatal cusp of the upper first molar. The line should reach the interproximal space between the canine and the first premolar; if it does not, the tooth is rotated.