Lateral Cephalometrics in Orthodontics

First: Class II

Second: Class III

Lateral Cephalogram

• Used in diagnosis and treatment planning

  • Allows assessment of AP and vertical skeletal pattern

  • Incisor positions and angulation

Monitoring of LC

• Antero-posterior

• Movement of the incisors

• Growth modification

• Superimpositions

Cephalometrics

• Cephalometric landmarks/points are located

• Cephalometric planes and relationships are then established using the cephalometric points

Cephalometric Points

• Sella (S) – midpoint of sella turcica (pituitary fossa)

• Nasion (N) – most anterior point on frontonasal suture

• A point (A) – point of deepest concavity anteriorly on the maxillary alveolus

• B point (B) - point of deepest concavity anteriorly of the mandibular symphysis

• Orbitale (O) – most inferior, anterior point of the infraorbital rim

• Porion (Po) – uppermost outermost point on the bony external auditory meatus

• Anterior nasal spine (ANS) – the tip of the anterior nasal spine

• Posterior nasal spine (PNS) – the tip of the posterior nasal spine

• Gonion (Go) – most posterior, inferior point on the angle of the symphysis

• Menton (Me) – most inferior point on the mandibular symphysis

Cephalometric Planes and Relationships

• SN line – line connecting the midpoint of sella turcica with nasion, is taken to resemble the cranial base

• Frankfort Plane – the line joining porion and orbitale

• Mandibular Plane – line joining gonion and menton

• Maxillary Plane – the line joining the anterior nasal spine with the posterior nasal spine

• Functional Occlusal Plane – the line drawn between cusp tips of permanent molars and premolars (or deciduous molars in mixed dentition)

SNA

this angle represents the relative A-P position of the maxilla to the cranial base

SNB

this angle represents the relative A-P position of the mandible to the cranial base

ANB Angle

Subtract SNA and SNB to get the ANB angle

ANB

• ANB – this angle represents the relative A-P position of the maxilla to the mandible and can be used to determine the skeletal class 

  • ANB 2-4⁰ Class I

  • ANB >4⁰ Class II

  • ANB <2⁰Class III

Eastman Correction

• Eastman Analysis assumes cranial base (SN) is a reliable basis for comparison

• Variation in position N can affect SNA and SNB

• Correction made due to varying positions of nasion

  • Provided SN-MP angle b/n5-11⁰

  • SNA inc, for every ⁰ SNA >81, subtract 0.5⁰ from ANB

  • SNA dec, for every ⁰ SNA <81, add 0.5⁰ to ANB

• Alternative avoid cranial base, or in conjunction with use wits analysis and ballards conversion

UI/Max

• Upper incisor to maxillary plane angle (UI/Max) – the angle between the maxillary plane and the axis of maxillary incisors

Average 109⁰ +/- 6

LI/Mand Angle

• Lower incisor to mandibular plane angle (LI/Mand) – the angle between mandibular plane and mandibular incisors

Average 93⁰ +/- 6

Incisal Position

UI/Max and LI/Mand plane angles are used to determine incisal position and if incisors are average inclination, proclined and retroclined

MMPA

• Maxillary – mandibular plane angle (MMPA) angle formed between maxillary plane and mandibular plane

Average MMPA 27⁰ +/4

Wits Analysis

• Compares maxilla and mandible with Functional occlusal plane

• FOP – Line drawn b/n cusp tips of the molars and premolars

To this function, a perpendicular line is drawn from A point to B point.

The difference then when we extract Ao – Bo gives a value for the Wits analysis