|TƯƠNG QUAN HÀM TRÊN VÀ HÀM DƯỚI|

* ANB: 3 +/- 2
Thể hiện tương quan vị trí của hàm trên so với hàm dưới. Thường từ 1- 5 độ, >5 độ biểu thị tương quan xương loại II, dưới 1 độ biểu thị tương quan xương loại III.
* SN- MP: 32 +/- 5
Sử dụng như là một giá trị đánh giá phát triển hàm dưới và hướng phát triển tầng mặt dưới.
* FH- MP: 24 +/- 3
Đánh giá độ khó của điều trị
* Trục Y- SN: 66 +/- 3
Tiên lượng hướng tăng trưởng hàm dưới.
* Trục Y- FH: 59 +/- 3
Tương tự trục Y- SN

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* ANB
The ANB angle measures the relative position of the maxilla to mandible. The ANB angle can be measured or calculated from the formula: ANB = SNA – SNB.
• A positive ANB angle indicates that the maxilla is positioned anteriorly relatively to the mandible (Class I or Class II malocclusion cases). 
• A negative ANB angle indicates that the maxilla is positioned posteriorly relative to the mandible (Class III malocclusion cases).
The normal range is 1- 5. 
>5 indicates a Class II skeletal jaw relationship, protrusive maxilla or retrognathic mandible.
<1 indicates a Class III skeletal jaw relationship, deficient maxilla or prognathic mandible.
* SN – MP
Reference Line: Sella – Nasion
The mandibular plane is represented by a line which bisects the distance between the left and right mandibular lower borders and connects anteriorly with Menton. The mandibular plane can also be used as a measure of mandibular growth and lower facial growth direction.
* FH – MP
Reference Plane: Frankfort Horizontal (Orbitale – Porion)
Also known as Frankfort Mandibular-Plane Angle (FMA) many orthodontists prefer to use Frankfort Horizontal than SN.
They consider the mandibular plane angle to be a measure of difficulty of treatment, the greater (higher) the angle, the more vertical the growth direction and the more complicated the treatment.
* Y Axis – SN
Reference Line: Sella – Nasion
The Y axis ( the line connecting Sella to Gnathion) is an estimate of mandibular growth direction. A larger angle indicates a more downward and vertical growth direction of the mandible. A smaller angle indicates a more horizontal and anterior growth direction of the mandible. It also indicates the degree of downward and forward position of the chin in relation to the upper face.
• Class II division 1 cases usually have an average to high Y-axis.
• Class II division 2 cases usually have a smaller Y-axis.
• High Y-axis is usually seen with a high mandibular plane angle.
• As the mandibular plane and the Y-axis increase, the relative chin prominence decreases.
* Y Axis – FH
Reference Plane: Frankfort Horizontal (Orbitale – Porion)
The same interpretation as above using Sella-Nasion. Many orthodontists prefer to use Frankfort Horizontal than SN.