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1. C- Axis :
A growth vector for the Maxilla.
Stanley Braun :
Angle Orthod : 1999
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2. 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.
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3. • “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.
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4. 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.
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6. 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.
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8. 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.
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10. 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.
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11. 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.
>
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12. • 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.
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15. • 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.
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17. ∀∝ angle tends to flatten the palatal plane
with respect to the C axis during growth
and development.
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18. • 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
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19. The G axis ; A growth vector for the
mandible: Stanley Braun et al.
Angle Orthod : 2004
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20. 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 :
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21. 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.
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23. • 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.
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24. 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
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26. • 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 :
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28. • 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.
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30. • Angular relationship of mandibular plane
to the “G” axis.
• Mean value increases 0.4º/year for males.
0.3º/year for females.
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31. 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)
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32. Conclusion :
“G” Axis (S-G point) allows
quantification of the complex
mandibular growth process in relation
to various craniofacial structures in
Sagittal plane.
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