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Mc NAMARA ANALYSIS


INTRODUCTION Dr James. A. McNamara.. described a method of cephalometric analysis which is used in the evaluation and treatment planning of orthodontic and orthognathic surgery patients The analysis represents an effort to relate… 

Teeth to teeth

Teeth to jaws

Each jaw to the other

Jaws to the cranial base


Composite Normative Standards Are Based On.. Bolton's

Standards

Burlington Ann

Orthodontic Research Centre

Arbor sample of 111 young adults

(Female – 26 yrs 8 mon, Male – 30 yrs 9 mon )

The analysis method is derived in part from the principles of cephalometric analyses of Ricketts and Harvold


Why Another Analysis ? 1940 – 1970 : Significant alteration in the craniofacial relationship were thought impossible In the decade from 1970 - 1980 Advent

of numerous Orthognathic surgery procedures which allow three dimensional repositioning of almost every bony structure in the facial region

Functional

appliance therapy which present new possibilities in the treatment of skeletal discrepancies


Landmarks And Planes : Nasion- Most anterior point on Nasofrontal Suture Porion- Superior aspect of the external auditory meatus

N

s po

Co

Ptm Or

Ba A

Orbital- lowermost point on the orbit Basion- lowest point on the foramen magnum in the median plane Ptm-

ANS

Go Pog Me Gn


Landmarks And Planes : ANS- Tip of the bony anterior nasal spine Point A- Deepest point on the curved bony outline ( subspinale ) Pogonion- Most anterior point on the bony chin Menton- Lowest point on the outline of the symphysis Gonion- Constructed by intersection of the lines tangent to the posterior margin of the ascending ramus

N

s po

Co

Ptm Or

Ba A

ANS

Go Pog Me Gn


Landmarks And Planes : Gnathion- Constructed by intersecting a line drawn perpendicularly to the line connecting Me and Pog Condylion- Most posterosuperior point on the outline of the condyle

N

s po

Co

Ptm Or

Ba A

ANS

Mandibular plane – Go – Me Go Pog

Facial axis – Ptm – Gn

Me Gn


Craniofacial Skeletal Complex Is Divided Into Five Major Sections… 

Maxilla to Cranial base

Maxilla to Mandible

Mandible to Cranial base

Dentition

Airway


Relating Maxilla To The Cranial Base N

Hard tissue evaluation: po

Linear distance is measured

FH

or

1 mm

Between nasion perpendicular to point A 0 mm – in mixed dentition 1 mm – in adults


Maxillary Skeletal Protrusion

Maxillary Skeletal Retrusion With Obtuse Nasolabial Angle


Relating Maxilla To The Cranial Base Soft Tissue Evaluation: Nasolabial Angle: Formed by line drawn tangent to the base of the nose and a line tangent to the upper lip


Relating Maxilla To The Cranial Base Soft Tissue Evaluation: N Perpendicular

Cant Of Upper Lip : Female – 14 degree Male – 8 degree ( SD 8 0 )


Relating Maxilla To The Mandible: Anteroposterior Relationship: Effective Midfacial Length : Measured from Condylion to point A

Effective mandibular length : Measured from Condylion to gnathion


Effective lengths are not age or sex related but are related to size of component parts Small - Mixed dentition Medium - Adult female Large - Adult male Any given effective midfacial length corresponds to a given effective mandibular length Mandibular length – Midfacial length = Maxillomandibular differential


Small : 20 mm

Medium : 25 to 27 mm

Large : 30 to 33 mm


CLASS II DIV 1 Mandible 12 mm deficient


Relating Maxilla To The Mandible: Vertical Relationship : Lower Anterior Face Height : ď śMeasured

from ANS to Menton

ď śIncreases

with age and is correlated

With effective midfacial length


66 – 68 mm

60 – 62 mm

70 – 74 mm


Vertical

maxillary excess can cause a downward and backward rotation of mandible resulting in an increase in lower anterior face height and vice – versa An

increase or decrease in the lower anterior face height can have a profound effect on the horizontal relationship of the maxilla and mandible If

the lower anterior face height is increased then the mandible will appear to be more retrognathic and vice - versa


Mandibular Plane Angle : Angle between FH plane and the Mandibular plane ( Gonion – Menton ) 220 + 40


Facial Axis Angle : Angle between a line from basion to nasion and the facial axis i.e. PTM to Gn 900 < 900 â&#x20AC;&#x201C; ( -ve value ) excessive vertical development > 900 â&#x20AC;&#x201C; ( +ve value ) deficient vertical development


Relating Mandible To The Cranial Base Distance from Pog to the nasion Perpendicular


- 8 mm to â&#x20AC;&#x201C; 6 mm

- 4 mm to 0 mm

- 2 mm to 2 mm


Mandibular Skeletal Retrusion

Mandibular Prognathism


Dentition : In

cases of malrelationship between the maxillary and mandibular skeletal structures, errors may result if the position of the upper incisor is determined by any measurement that uses mandible as a reference point e.g. A – pogonion line

A

measurement of upper incisor to the N – A line is valid only if the maxilla is in neutral position anteroposteriorly relative to the cranial base


N

A


Relating upper Incisor to Maxilla : Anteroposterior position Position of the upper incisor can be located by using measurement that relate dental portion of maxilla to the skeletal portion Line parallel to nasion perpendicular through point A Distance from point A er To the facial surface of upper incisor is measured


Vertical position : The incisal edge of the upper incisor lies 2 â&#x20AC;&#x201C; 3 mm below the upper lip at rest

Vertical position of the upper lip is best determined at the time of clinical examination


Relating Lower Incisor To Mandible : Anteroposterior position : Measurement of the facial surface of the lower incisor to the A â&#x20AC;&#x201C; Pog line Normal : 1 mm to 3 mm anterior

A

Pog


ď śIf

there is a discrepancy in Anteroposterior or vertical positioning of the maxilla and the mandible then modifications in this measurement procedure is necessary

ď śTo

predict Anteroposterior position of the incisor after functional or surgical intervention


A second tracing of the mandible and the incisor is made The tracing is moved so that the mandible is in the desired position relative to the maxilla A new A â&#x20AC;&#x201C; Pog line is drawn The incisor is expected to lie 1 â&#x20AC;&#x201C; 2 mm anterior to the constructed line


Estimate the number of mm that the mandible will be brought forward relative to the maxilla at the end of the treatment Then a new point A is constructed the same number of mm in the opposite direction Post treatment A â&#x20AC;&#x201C; Pog line


Vertical Position Of The Lower Incisor : Relating the lower incisor tip to the functional occlusal plane Evaluated on the basis of existing lower anterior facial height Excessive Curve of Spee… LAFH is normal or excess – Intruded LAFH is inadequate – Eruption of the Molars


Airway : Upper pharynx Width is measured from a point on the posterior outline of the soft palate to the closest point on the posterior pharyngeal wall Average : 15 - 20 mm


2 mm


Airway : Lower pharynx Width is measured from intersection of the posterior border of tongue and the inferior border of the mandible to the closest point on the posterior pharyngeal wall Average : 10 â&#x20AC;&#x201C; 12 mm


Advantages : Linear measurements rather than angles Provides guidelines with respect to normally occurring growth increments The method is more sensitive to the vertical changes Easily explained to non specialist and lay persons such as patients and parents


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