Lateral Cephalometrics in Orthodontics

Orthodontic Radiographs

Radiographic Assessment

• Radiographs – if appropriate must be justified

• For the teeth, bone levels and skeletal pattern

Cephalometric

First: Class II

Second: Class III

Images assess the skeletal pattern and the underlying dentition

• Lateral Cephalogram

• Used in diagnosis and treatment planning

  • Allows assessment of AP and vertical skeletal pattern

  • Incisor positions and angulation

• Monitor the progress of treatment

  • Antero-posterior

  • Movement of the incisors

  • Growth modification

  • Superimpositions

Used in Diagnosis and Treatment Planning

• Profile image

• Lateral cephalogram

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)

• Anteroposterior relationship

• 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

Cephalometric

• Subtract SNA and SNB to get the ANB angle

• 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 <2⁰ Class 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

Cephalometrics

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

  • Average 109⁰ +/- 6

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

  • Average 93⁰ +/- 6

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

• Vertical skeletal relationship

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

• Average MMPA 27⁰ +/4

Therefore this patient has:

• A skeletal II pattern.

• Eastman correction cannot be done.

• Upper incisors are within normal limits

• Lower incisors are proclaimed

Average LI/MAND is 93^o and MMPA of 27^o = 120⁰ total

• >120^o = proclaimed

• <120^o = retroclined

Wits Analysis

• Compares maxilla and mandible with Functional occlusal plane

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

• Wits appraisal and application – Jacobson 1975

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