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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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• “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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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. www.indiandentalacademy.com
Angle θ C-Axis M-point
Angle α
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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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Results :
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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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Growth axis angle (C axis - SN) V/s Chronological age. 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.
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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. > www.indiandentalacademy.com
• 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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∝ angle =
θ
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-
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.
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∀ � angle tends to flatten the palatal plane with respect to the C axis during growth and development.
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• 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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The G axis ; A growth vector for the mandible: Stanley Braun et al. Angle Orthod : 2004
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Introduction : 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) www.indiandentalacademy.com
ďƒ˜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. www.indiandentalacademy.com
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• 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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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 www.indiandentalacademy.com
Results
:
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Discussion : • 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.
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• 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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• 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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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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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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