C axis & g axis

C- Axis :
A growth vector for the Maxilla.
Stanley Braun :
Angle Orthod : 1999
www.indiandentalacademy.com

Introduction
•Cephalometric analysis is important in orthodontics because
it helps the clinician to understand the factors that may
contribute to malocclusion .
•Downward & forward migration often used in describing
maxillary growth but imprecisely used.
Nanda & Merill proposed “M” point constructed point
representing the centre of largest circle that is tangent to the
superior anterior & palatal surfaces of the maxilla in sagittal
plane.

• “M” point - A geometrically defined point
within the maxillary complex, would permit
a description of the natural loci of this
complex in relation to craniofacial
structures during growth & development.

C axis :
> A linear line from sella to M point.
> The purpose of this investigation was to study
the natural changes in position of M point in
relation to anterior cranial base (S-N) using polar
coordinates in combination with the palatal plane.
Objective :
It provides a quantitative description of the
anterior & downward migration of the maxilla
associated with growth.

C-Axis
M-point
Angle θ
Angle α

Materials and Methods :
• Lateral ceph 19 males & 20 females,
• Age group 7.4 to 18.75 years from Mooseheart growth
study, Chicago, illinois
• no history of orthodontic intervention
• “M” point determined on transparent template
containing a no of circle whose diameter increased in
1mm increments.
• The best fit circle was selected.

Results :

Discussion :
Chronological growth along the C axis
Based on slope of linear regression formula. upto age 14.
C Axis in males increased at a rate of 1.14 mm /year. C axis in females increased at rate of 1.13mm/year
Regression formula suggest growth along C axis tends to cease at age 16 years in females.
In males increased through out the age of selected age group.

Increases for both males and females throughout the
age studied.
It is relatively small.
For males - 3.980
Females - 2.250
Linear regression formula suggests no statistically
significant difference in growth axis angle.
Growth axis angle (C axis - SN) V/s Chronological
age.

Conclusion
•C axis permits the quantification of complex maxillary growth in Cephalometric terms relative to
various craniofacial structures in the sagittal plane.
C axis angle is independent of gender within the chronological age studied.
>

• C axis however are related to gender up to age 14 in
males and females display average yearly growth
increments of 1.14mm and 1.13 mm per year
respectively .
• After age 14 growth increments in females tends to
diminish and cease at the age of 16 years.
• In males growth along the C axis continues linearly
throughout the age range studied.

∝ angle =
θ - Ǿ

• Single point “M” cannot by itself summarized
the growth of the dento maxillary in the sagittal
plane
• However when associated with the palatal
plane the downward and forward migration is
more accurately described than previously
possible.

∀∝ angle tends to flatten the palatal plane
with respect to the C axis during growth
and development.

• The C-axis incremental growth change & its
vector offer a means of quantifying
complex maxillary growth in the sagittal
plane via cephalometric measurements
relative to & co-ordinated with other
craniofacial structures

The G axis ; A growth vector for the mandible: Stanley Braun
et al.
Angle Orthod : 2004

Growth of the mandible :
> Expressed through the resorption & deposition at
periosteal & endosteal surfaces.
> Cartilage replacement by bone at the condyle &
dental eruption accompanied by growth of alveolar
bone.
> Net result for this is the downward & forward
displacement of the mandible.
> This displacement quantified to a degree through
the description of the Y-Axis (S-GN)
Introduction :

It is noted that usefulness of the Y-axis has been
questioned because of extensive remodeling of the
external symphyseal area.
> This study was undertaken to establish an improved
descriptive growth axis for the mandible.
> Length of the axis is determined by sella to G point
> G point is defined as a point representing the center
of the largest circle that is tangent to the internal
inferior, anterior & posterior surfaces of the
mandibular symphyseal region.

• G Axis vector (Direction) is defined by the angle α which
G axis establishes relative to the sella-nasion.
∀ θ angle: It is the angle between the mandibular plane to
the S-G point.
• Use of the three dimensions ∝, θ, & length of the G axis
provides a quantitative description of the anterior &
downward migration of the mandible related to growth &
maturation.

Methods & Materials :
> Serial lateral ceph of 24 males & 24 females.
> Age group 6 to 19.25 years without orthodontic
intervention.
> ANB angle – 1 to 5o
.
> Ratio of N-ANS to ANS to GN 0.80 to 0.09 for
males & 0.82 to0.09 for females.
> G-point was established using specially designed
transparent template containing a number of circles
whose diameter increased in 1mm increments.
> The best fit circle is selected

• G axis length increases in males 2.3mm / year.
• G Axis length increases in females 1.6mm/year.
• Growth velocities of G- axis length are
determined by the slope of the mean linear
regression formula.
• Mean velocity of G - axis length increase for both
genders is relatively constant within the age range
studied.
Discussion :

• The low correlation coefficients of growth
vector axis angle for age range studied
shows little change in magnitude
• Slope of both graphs are relatively shallow.

• Angular relationship of mandibular plane
to the “G” axis.
• Mean value increases 0.4º/year for males.
0.3º/year for females.

From a clinical viewpoint, the mandibular plane angle is
commonly measured relative to S-N. This angle, herein
referred to as the angle ǿ, bears a geometric relationship
to the angles α and θ. It is ǿ =(α – θ)

Conclusion :
“G” Axis (S-G point) allows quantification of the complex mandibular growth process in
relation to various craniofacial structures in Sagittal plane.

C axis & g axis

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