G axis

The G-Axis: A growth vector
for the Mandible
www.indiandentalacademy.com

Introduction
The growth of the mandible express through the
resorption and deposition at the numerous
periosteal and endosteal surfaces.
Cartilage replacement bone at the condyle and
dental eruption accompanied by growth of
alveolar bone.
Net result for this is the downward and forward
displacement of the mandible.
This displacement quantified to a degree
through the description of the Y-axis.

G-axis vector is defined as the angle
alpha to the sell nasion.
Use of 3-dimensions alpha theta and G-
axis provides a quantitative description of
the anterior and downward migration of
the mandible related to growth and
maturation.

Extensive remolding of the external
symphysial area makes the usefulness of
the Y-axis has been questioned.
For improving the descriptive growth axis
for the mandible G-axis was evolved.
G-axis is the length of the sella to G-
point.
G point is defined as a point representing
center of the largest circle that is tangent
to the internal inferior anterior and lingual
surfaces of the mandibular symphysial
region in sagital viewwww.indiandentalacademy.com

Material and Methods
• Serial lateral cephalograms of 24 males and
females.
Criteria for selection
• Age group -6-9.25years.
• ANB angle – 5 degree.
• Ratio of N-ANS to ANS-Gn – 0.080 ± 0.09 for
males and 0.82 ± 0.08 for females.
• G point is established using a specially designed
transparent template containing number of
circles who’s diameter is increased 1 mm in
increments.

θ
α
G-POINT

Discussion
• G-axis length increases in females 1.6 mm per
year.
• G-axis length increases in males 2.3 mm per
year.
• Growth velocity of G-axis length determined by
slop of the mean linear regression formula.
• Mean velocity of G-axis length increases for both
gender is relatively constant with in the age
range studied.

G-AXIS VECTOR α
The low correlation coefficient angle α and
age for age range studied shows the little
change in magnitude.
Slope of both graphs are relatively
shallow.
θ angle
Mean value increases at the rate of 0.4
degree per year for males and 0.3 degree
per year in females.

Mandibular plane angle Ø
It occurs between SN to Mandibular plane.
For females and male subjects decreases
at a annual rate of 0.42 degree and 0.014
degree respectively.
It is measured by θ – α.

Conclusion
G-axis (S-G point) allows for the
quantification of complex mandibular
growth process in cephalometric relative
to various craniofacial structures in the
sagittal plane. This has been achieved for
ages six through years for each sex.

C-AXIS-GROWTH FACTOR FOR THE
MAXILLA
Stanley Braun, Roert T. Rudman, Hug J.
Murdoch, Shaun Hicken, Russell
Kittleson, Donald J . Ferguson.
Angle Orthodontist: 1999; 69; 539-542.

Introduction
Cephalometric analysis help the clinician
to understand the factors that may
contribute to malocclusion, to evaluate
facial esthetics and treatment effects and
forecast and understand changes
associated with growth and development.
Maxilla is altered during growth and
development.
No anatomic area viewed in the sagittal
plane to determine a suitable point for the
growth and development.

Downward and forward migration of
maxilla often used and imprecisely is
used.
Nanda and Merill proposed a M point.
M point is a constructed point
representing the center of largest circle
that is tangent to the superior anterior and
parallel surfaces of the maxilla in sagittal
plane.

• It is geometrically defined point with in the
maxillary complex would permit a
description of the natural loci of this
complex in relation to craniofacial
structures during growth and
development.
C-axis
Sella to M point

θ
α
M-POINT

Aim of the study
The purpose of this study is to find natural
changes in position of M point in relation
to anterior cranial base in combination
with palatal plane.
Objective:-
Provide a quantitative description of the
anterior and downward migration of the
maxilla.

Materials and Methods
Lateral cephalograms of 19 males and
females.
Age group 7.4 to 18.75 years.
Cephalometric values and planes were
digitized.
M point determined on transparent
template containing a number of circles
who’s diameter increased by 1mm
increment. The best fit circle is selected.

Results

Discussion
C-axis in males increased linearly and
continuously at a rate of 1.14 mm per year. It is
based on linear regression formula.
In females increased at a rate of 1.31 mm per
year.
Linear regression formula suggest that growth
along the C-axis tends to cease at age of 16
years in females.
T test comparing males with females reveals the
statistical significance decrease in female
growth velocity at age 14.

The mean growth axis angle for both
males and females tends to increase
through the age range studied.
It is relatively small for males 3.98 degree
and for females 2.25 degree.
Growth axis angle
Linear regression formula suggest that no
statistically difference in the growth axis
angle.

Conclusion

It represents relationship of ANS-PNS to
SN plane between the age of 7 to 16.
Since the C-axis vector is related to SN
plane the palatal plane geometrically
related to C-axis.
([ANS-PNS]/C-axis angle = [C-axis/SN]
angle – [ANS-PNS]/SN angle)

It explains the relationship of palatal plane
angle to the C-axis for each gender from
age 7 to 16.
In females the angular relation between the
palatal plane and the C-axis tends to
increase from 35.4 degree at age 6 to 37.4
degree at age 16.
In males it increases from 39.3 degrees to
41.6 degrees.
These changes tend to flatten the palatal
plane with C-axis during growth and
development. www.indiandentalacademy.com

Points To Be Raised
1. This article has inadequate sample size.
2. The study is a cross sectional study.
3. Peak growth velocity is different for
different individuals.

G axis

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G axis