Mc Namara / orthodontic courses by Indian dental academy

Mc Namara AnalysisRicketts Analysis

INDIAN DENTAL ACADEMY

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Introduction

Since the introduction of cephalometrics by Broadbent in 1931, a number of different analyses have been devised. Most of the analyses were conceived during the period (1940 to 1970) when significant alterations in craniofacial structural relationships were thought impossible………...


But from 1970’s clinical orthodontics has seen the advent of numerous orthognathic surgery procedures which allow three-dimensional repositioning of almost every bony structure in the facial region. Therefore, a need has arisen for a method of cephalometric analysis that is sensitive not only to the position of the teeth within a given bone but also to the relationship of the jaw elements and cranial base structures one to another.


Mc Namara Analysis

In this method of analysis described by Mc Namara in his article on AJO-DO 1984 represents an effort to relate

• teeth to teeth• teeth to jaws• each jaw to the other • the jaws to the cranial base.


Advantages

1. This method depends primarily upon linear measurements rather than angles, so that treatment planning (particularly treatment planning for the orthognathic surgery patient) is made easier.


Advantages (contd.)

2. This method of analysis is more sensitive to vertical changes than is an analysis which relies on the ANB angle, such as that of Steiner. The use of the ANB angle can be misleading, since it tends to be insensitive to the vertical component of jaw discrepancies. Similarly, changes in growth pattern, which include both horizontal and vertical adaptations, may be completely missed if only a change in the ANB angle is measured.


3. This analytical procedure provides guidelines with respect to normally occurring growth increments. Therefore, the norms derived from the Bolton standards, the Burlington sample, and the Ann Arbor sample and the composite norms presented in this article can be used to evaluate treatment results.

Advantages (contd.)


4. The principles of this analysis are easily explained to nonspecialists and to lay persons such as patients and parents.

Advantages (contd.)


Normative Standards Normative standards were determined by arbitrarily

combining comparable average values of three samples.• The first sample contains normative data derived from

lateral cephalograms of the children comprising the Bolton standards, the longitudinal records of whom were retraced and digitized by Behrents and McNamara to include all the landmarks necessary for the present analysis.


• The second sample contains selected values from a group of normal children from the Burlington Orthodontic Research Centre who also were followed longitudinally.

• The third group considered is the Ann Arbor sample of 111 young adults who had good to excellent facial configurations. Patients in this latter group had a Class I occlusion and good skeletal balance with an orthognathic facial profile.


Contents

1. Relating Maxilla To Mandible 2. Relating Mandible To Maxilla3. Relating the mandible to the cranial base4. Relating the upper incisor to the maxilla5. Relating the lower incisor to the mandible

6. Airway analysis


Relating Maxilla To Mandible

1. Hard Tissue Evaluation2. Soft tissue Evaluation


Hard Tissue Evaluation• The anteroposterior orientation of the

maxilla relative to the cranial base can be determined by measuring the linear distance between Nasion perpendicular and point A.


F-H Plane is drawn from superior aspect of the external auditory meatus to the lower border of the orbit

Nasion Perpendicularis a veritcal line Perpendicular to FHP extending inferiorly from nasion

HARD TISSUE EVALUATION:NASION PERPENDICULAR


Cephalometric values from Ann Arbor sample

Composite Norms

Ajo-Do 1984


Maxillary skeletal protrusion Maxillary skeletal retrusion

Examples


Soft Tissue Analysis

The nasiolabial angle is formed By drawing a line tangent to the

base of the nose and a line tangent to the upper lip

The ideal value is 102° ± 8°


Maxillary protrution Maxillary retrusion Retrusion with normal Nasolabial angle

Examples


The cant of the upper lip Should be slightly forward to form an angle of

14°± 8° in females and 8°± 8° in adult males with the

Nasion perpendicular


Relating Mandible To Maxilla

1. Anteroposterior Relationship2. Vertical Relationship


Anteroposterior RelationshipOf Mandible With Maxilla

A geometric relationship exists between the effective length of the midface and that of the mandible.

Any given effective midfacial length corresponds to a given effective mandibular length.


The effective midfacial length is determined by measuring a line from condylion to point A

Condylon is the most posterosuperior point on the outline of the mandibular condyle

The effective mandibular length is derived by constructing a line from condylion to anatomic gnathion

Gnathion is the most anteroinferior aspect of the mandibular symphysis


Composite Norms Ajo-Do 1984


Bolton StandardsAjo-Do 1984


Burligton ValuesAjo-Do 1984


• The effective lengths of midface and mandible described in the analysis is not age or sex dependent but related to size of the component parts. So the term "small” "medium," and "large" are used rather than "mixed dentition," "adult female" and "adult male."


Retrusive mandible

Examples

Protrusive mandibleRetrusive maxillaProtrusive mandible


Vertical Relationship

lower anterior facial height is measured from anterior nasal spine to menton.

This linear measurement increases with age and is correlated to the effective length of the midface


Composite Norms

Adult Male

Adult Female

Mixed dentition

Ajo-Do 1984


ExamplesIncrease in vertical height Decrease in vertical height


26° ± 4.5° at 9 years and decreases by 1° every 3 years

The Mandibular Plane Angle


The Facial Axis

Average value is 90 °± 3.5 ° .

Excessive vertical development is indicated by negative values (values less than 90°), and deficient vertical facial development is indicated by positive values (values greater than 90°).


Examples

Retrusive Mandible Protrusive mandible


Relating the mandible to the cranial base


• The relationship of the mandible to the cranial base is determined by measuring the distance from Pogonion to the Nasion perpendicular.




Composite Norms

Ajo-Do 1984


EXAMPLESRetrusive Protrusive


Relating the upper incisor to the maxilla

1. Anteroposterior position2. Vertical position


Anteroposterior position

• The position of the upper incisor can be located by using measurements that relate the dental portion of the maxilla to the skeletal portion of the maxilla.


The measurement from point A to the facial surface of the upper incisor horizontally is 4 to 6 mm

This is accomplished by drawing a vertical line through point A, parallel to the nasion perpendicular. The distance from this constructed point A perpendicular to the facial surface of the upper incisor is measured.

Ajo-Do 1984



Composite Norms

Ajo-Do 1984


Vertical

• The vertical position of the upper incisor is best determined at the time of the clinical examination.

• Typically, the incisal edge of the upper incisor lies 2 to 3 mm below the upper lip at rest.


It is in the range of 2 to 3 mm. Women show more within this range


Relating the lower incisor to the mandible

1. Anteroposterior position2. Vertical position


Anteroposterior position

• The anteroposterior position of the lower incisor can be determined by using a measurement of the facial surface of the lower incisor to the A-pogonion line


Composite Value is 1 to 3 mm

Ajo-Do 1984


Airway analysis

1. Upper pharynx2. Lower pharynx


Upper pharynx.

• The upper pharyngeal width is measured from a point on the posterior outline of the soft palate to the closest point on the posterior pharyngeal wall.

• This measurement is taken on the anterior half of the soft palate outline because the area immediately adjacent to the posterior opening of the nose is critical in determining upper respiratory patency.


Average Value is approximately15 to 20 mm in width


Lower pharynx.

Lower pharyngeal width is measured from the intersection of the posterior border of the tongue and the inferior border of the mandible to the closest point on the posterior pharyngeal wall.


Average Value is 11 to 14 mm.

A greater than average value suggests anterior positioning of the tongue


Ricketts Analysis


Relation of the Mandible

1. Facial axis2. Facial(depth)angle3. Mandibular plane


1. Facial Axis

• The angle formed between the basion-nasion plane and the plane from foramen rotundum (PT) to gnathion.


Pt pointThe junction of the pterygomaxillary fissure and the foramen rotundum

The outline of the foramen rotundum can be approximated at the 10.30 (face of a clock) position on the circular outline of the superior border of the pterygomaxillary fissure

Facial axis is a line extending from the foramen rotundum (Pt) to gnathion

The angle formed between the basion-nasion plane and the plane from foramen rotundum (PT) to gnathion is 90 ± 3.5°

•A lesser angle suggests a retropositioned chin, whereas an angle greater than a right angle suggests a protrusive or forward growing chin


2.Facial(depth)angle

• The angle between the facial plane (N-Pog) and the Frankfort horizontal.

• This angle provides some indication of the horizontal position of the chin.

• It also suggests whether a skteletal Class II or III pattern is due to the position of the mandible


Facial planeExtends from Nasion to Pogonion

Facial angle is formed between facial plane (N-Pog) and the Frankfurt horizontal line

This angle is 87 ± 3° at 9 years of age and it has to be increased by 1 every 3 years


3.Mandibular Plane

• A high or steep mandibular plane angle implies that an open bite may be due to the skeletal morphologic characteristics of the mandible. A low mandibular plane suggests the opposite (ie, a deep bite).


Mandibular planeExtends from gnathion to gonion

26. 60° ± 4.5° at 9 years and decreases by 1° every 3 years


Convexity


The convexity of the middle face is measured from Point A to the facial plane (N-Pog).

The clinical norm at 9 years of age is 2.0 mm and decreases 1 degree every 5 years

Convexity At Point A


II.Convexity At Point A

• High Convexity implies a Class II skeletal pattern. Negative Convexity suggests a Class III skeletal pattern.


Dentition


Lower incisor to A-Pog

• The A-Pog plane is referred to as the denture plane and is a useful reference line from which to measure the position of the anterior teeth.


A-Pog LineExtends from point A to Pogonion

Ideally, the lower incisor should be located 1.0 ± 2 mm ahead of the A- Pog line . This measurement is used to define the protrusion of the lower arch.


A-Pog Line

• If the measured value of lower incisor to A-Pog line is more than the average value

then extraction is indicated.


Upper Molar To PtV

• This measurement assists in determining whether the malocclusion is due to the position of the upper or lower molar. It is also useful in deciding whether extractions are necessary.


Pterygoid Vertical(PtV)A vertical line drawn throgh distal radiographic outline of the pterygomaxillary fissure and perpendicular to FHP

The distance from the pterygoid vertical (back of the maxilla) to the distal of the upper molar. On average is measured, This measurement should equal the age of the patient +3.0 mm (eg, a patient 11 years of age has a norm of 11 + 3 = 14 mm).


Lower incisor to A-Pog

• This measurement provides some idea of lower incisor procumbency


The angle between the long axis of the lower incisor and the A-PO plane (1 to A-PO) is measured. On the ayerage, this angle should be 28 ± 4°.


Profile


Lower lip to E-plane

• The distance between the lower lip and the esthetic (nose-chin) plane is an indication of the soft tissue balance between the lips and the profile


Esthetic line (E-line)Extends from soft tissue tip of nose(En) to soft tissue Chin point(DT)

• The average norm for this measurement is -2.0 mm at 9 years of age. The positive values are those ahead of the E-line.


Condylar Axis andCorpus Axis

• These are used to describe the morphology of the mandible


Xi Point

Locate FHP and Draw PtV Plane perpendicular to the FHP and locate four R1, R2, R3, & R4R1 is the deepest point on the anterior border of the ramusR2 is located on the posterior borderof the ramus ,opposite R1R3 is the deepest point of the sigmoid notchR4 is opposite R3 on the inferior border of the mandibleConstruct four Planes tangent to thes points and it forms a rectangle enclosing the ramus

Xi point can be located at the center of the rectangle at the intersection of the diagonals


Condyle (Dc) pointThe point In the center of the the condyle neck along the Ba-N plane

Suprapogonion (PM) pointThe point at which the shapeof the symphysis mentalis changes from convex to concave

Condylar Axis extends from Xi to Dc

Corpus axis extends fromXi to PM point


Thank you


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Mc Namara / orthodontic courses by Indian dental academy