Natural head position

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION:
Cephalometrics has given us a different
prespective of interpreting various skeletal
problems in the dentofacial complex.
However, the promise of the cephalometrics as
a diagnostic and prognostic tool is yet to be
fulfilled. www.indiandentalacademy.com

Limitations of cephalometry:
 Errors of projection:
Magnification
Distortion
 Errors of identification
Radiograph quality
Reproducibility
 Unpredictability of growth
 Limitations in suerimpositioning methodswww.indiandentalacademy.com

Errors due to
1.use of intracranial reference planes
2.patient positioning in the cephalostat

Intracranial reference planes:
 Indv. variations in
reference lines -
different
interpretation of
subjects with
similar profiles.

 Variations in the reln. bet. reference lines -
different evaluation of facial skeletal
pattern
 Does not always reflect the clinical
appearance of the individual subject.

CAMPER’S LINE:
First orientation plane to orient cranium
on a horizontal from the middle of EAM
to ANS

Sella- Nasion Plane :
 Antero posterior extent of ant. cranial base.
 Steiner – the S & N points move only
minimally when head deviates from the true
profile position & even when head is rotated
in the cephalostat

Inclination of SN plane:
Bjork AO 1951 – earliest to report unreliability
Drawbacks of S-N plane:
Downward- facial
angles decrease
Upward- facial
angles increase

Mcnamara AO 1981 – Cephalometric
maxillary retrusion in cl.II cases is due to low
inclination of the skull base

The anterior skull base (S-N) is unstable in
growing persons.
• Nasion - landmark on an actively growing suture,
- moves forward, upward, or downward in
growing children
• Sella- its geometric center is unstable since the
pituitary gland enlarges during growth.

• The S-N line may therefore rotate
slightly over time - results in a
considerable back or forward swing of
the chin.

Sella is totally unrelated to the structures of
the face and therefore cannot be used to
measure facial development
( ELLIS & MC NAMARA)

Frankfort horizontal plane
The plane through left and right porion and left
orbitale , (in 1884 by craniologists), - the best
compromise for orientation of crania.

Drawbacks of FH plane:
Downs(1956) - the discrepancies between
Cephalometric and photographic facial
typing disappear when a correction is made
for those persons in whom the "Frankfurt
plane" is not horizontal.

Anatomical location of porion
Machine porion
Anatomic porion
Individual variation
Vertical relationships with other
intracranial landmarks – biologic variation

Occlusal plane:
Drawn thru’ the region of overlapping cusps
of I premolar & I molars (Jacobson Wit’s
Appraisal)
• To eliminate the effect of rotation of the
jaws
• Variation in the A-P relation of the jaws
with respect to cranium

Disadvantages:
• Affected by occlusal plane angle & vertical
alveolar relationships
• Affected by vertical distance between points
A & B

• Any change in occlusal plane during treatment
allows variation
• Growth related changes cannot be determined

Patient positioning in a
cephalogram:
Patient aligned within ear rods of the
cephalostat exerting moderate pressure on
EAM.
Patient’s FH placed parallel to the floor
canthomeatal line placed 10 degrees to floor
Locking nasal positioner against bridge of
nose www.indiandentalacademy.com

Disadvantage of ear rods:
Greenfield et.al. AJO 1989
Fixed position of cephalostat - cannot be
adjusted forward, backward, sidewise, or
rotated.
- The subject moves his head to fit the ear
rods, ( altering the angulation of the
head and neck ).

If the transmeatal axis is not perpendicular
to the midsagittal plane- immobilization of
the head with ear rods introduces asymmetry
Moorrees and Kean(1958).

Definition :
AJO 1994 Moorrees
- A standardized and reproducible
position of the head, in an upright
posture, the eyes focused on a point in the
distance at eye level, which implies that
the visual axis is horizontal.

Advantages of NHP:
It provides the use of an extracranial
reference line (true vertical or horizontal) for
cephalometric analysis.
NHP should be the preferred for profile
evaluation as it reflects the everyday true
life appearance of people.
(COOKE 1986)

The natural head position is relatively
constant over time.
(MOORREES &KEAN 1958)
Facial photograph and cephalometric
radiograph in NHP - direct correlation bet.
real-life appearance and tracing.

Natural head posture:
Developed by Molhave for studying the
biodynamics of the human body.
Natural head posture is a physiologic
position -"orthoposition" - characteristic for a
person and reproducible, but differs among
persons.

defined as a small range of positions
oscillating around the subject's mean NHP.
(Lundstrom EJO 1991)
Head posture is a dynamic concept and
ideally its measuration should be performed
in a dynamic and continuous manner.

Postural control of the head is influenced by
Resistance to gravity
Respiration
Deglutition
Sight (visual axis)
Vestibular balance mechanism
Hearing

For Cephalometric analysis, the
standardized NHP is preferable to
natural head posture
(MOORREES)

Ortho position:
―The momentary interim position when
taking the first step forward from a
standing to a moving or walking posture.―
Ortho position is the most reproducible
habitual symmetrical standing position.
Solow and Tallgren

NATURAL HEAD ORIENTATION:
― The head orientation of the subject perceived
by the clinician, based on general
experience, as the NHP in a
standing, relaxed body and head
posture, when the subject is looking at a
distant point at eye level.‖

Lundström and Lundström AJO1995
The NHO related horizontal line
standardized to a line through Sella is the
best reference for clinical cephalometric
analysis when head positions registered at
NHP are unnaturally flexed

Readily registered by instructing the subject
standing or sitting in the cephalostat to look
at a point on the wall in front, exactly at
eye level.
A small mirror (diameter no more than 10
cm), the midpoint of which also at eye
level, can be used also for head orientation.

•The wire plumb line –
record the true vertical
Plumb line bisects the
reflection of the subject's
face in the mirror and
minimize lateral head
rotation.

The location of the central
x-ray beam -determined by
a projected light cross
("+").
Magnification
standardized by the
plumb line bisecting the
reflection of the subject's
face in the mirror.

To prevent the swaying , define the feet
position as "a comfortable distance
apart and slightly diverging―
(Cooke 1986)

Solow & Tallgren
Acta Odontol. Scand. 1971

REHEARSAL PHASE:
• Patients placed facing a neutral wall (nothing
to distract ).
• Carefully observe the patient's posture before
the actual rehearsal takes place,
• The patient walks from the waiting area to the
radiographic room.

BODY POSTURE.
Mølhave(1958) -the most reproducible natural
standing position is the orthoposition
Small children - to place heels together and let
the arms hang.
Older and tense patients - "walk on the spot''
& to raise and drop shoulders to ease
tension.

HEAD POSTURE. - two methods
(SOLOW 1971)
 The subject's own feeling of a natural
head position ―the self-balance position.‖
 Based on visual cues from external
reference

 Positioning according to external reference -
carried out only after the head has been
placed in the self-balance position.
 In adults the head is kept, on the average, 3
degrees higher in the mirror position than in
the self-balance position.

If the earrods are not
aligned, place the
operator’s foot in front
of or behind the patient's
feet and ask the patient
to move slightly until he
hits the operator's foot
POSITIONING OF
THE FEET.

BODY-POSITIONING &
HEAD-POSITIONING.
Patient instructed to
''hold your head so that
you can look into your
own eyes in the miror".
ADJUSTMENT FOR
SYMMETRY.
carried out with guidance
by the light-beam cross

THE FLUID LEVEL DEVICE
AJO 1983 Showfety et.al
The ends of the air bubble aligned with the
ends of an 0.030 inch diameter wire
The fluid consists of a mixture of radiopaque
liquid, blue dye, and a silicone suspension,
rendering the air bubble visible on the
cephalometric radiograph.

The ideal location - between the eyebrow and
the hairline behind the prominent temporal
crest of the frontal bone.
The patient instructed to stand in an ''intention
position‖.
The fluid level is rotated on the pivot until the
bubble is aligned with the ends of the wire.
PROCEDURE:

The patient is placed in the cephalometric head
holder & the patient's head is tilted up or
down until the bubble is aligned with the
wire.
A vertical reference chain & wire in the fluid-
level device will be aligned at 90 degrees to
each other

Inclinometer
AJO 1991 Murphy et.al.
 uses a contactless precision potentiometer to
continuously measure changes in inclination
around a single axis of rotation
 the inclinometer was calibrated
 Spectacles attach the inclinometer to the
head in a stable manner .

AJO1985 Archer and Vig
Wood 1981
Leveling device consisting
of a fluid-filled plastic
ring mounted on a
protractor.

Other methods:
• Schmidt (1876) made use of a frame that encircled
the skull, a plumb line and a protractor.
• Moorrees and Kean projected the image of a plumb
line of stainless steel ligature wire onto
cephalometric radiographs
• Von Baer and Wagner instructed subjects to look
directly at the reflection of their eyes on a a mirror
fixed to a wall.

• Cinefluorography may be used to measure
head posture over a period but exposes
subjects to irradiation for relatively long
periods.(Cleall et.al., AO 1966)

Importance of NHP:
(Solow and Kreiborg 1977)
―Soft tissue stretching hypothesis''
Head extension - stretch of the soft tissues
- increase in the forces of the lips and
other faciocervical muscles .

Extended head posture –
Facial retrognathism
Retroclination of lower incisors
AFH and PFH
A-P craniofacial dimension
Larger inclination of the mandible to SN
Larger cranial base angle
Small nasopharyngeal space
SOLOW & TALLGREN 1976

RESPIRATION &NHP
• Woodside and Linder-Aronson(EJO1976)
- children with nasal obstruction had a more
extended head posture(6°) .
• Extended head posture after induced mouth
breathing - Hellsing et.al.,(EJO1987)

• Oral respiration - produce an altered
mandibular posture and changes in the shape
of the mandible with development of an
anterior open-bite (Harvold et.al.,1973)

Nasal obstruction
Craniocervical postural adaptations
Mandibular postural adaptation
Skeletal growth modification
Dentoalveolar compensation/adaptation

Dentoalveolar height and occlusal plane
inclination showed a set of positive
correlations with the craniocervical and sella
-nasion to vertical angulations
(SOLOW &TALLGREN 1977)

Goldstein and associates(1984)
 Evaluated the mandibular trajectory of
closure with a mandibular kinesiograph
 Four postural attitudes: natural sitting
posture (NP), forward head posture
(FHP), maximal forward head posture
(MFHP), and military posture (MP).

• Alterations of the A-P head and neck posture
have an immediate effect on the trajectory of
mandibular closure.
• As the head moved anteriorly - the vertical
distance of mandibular closure decreased.
• When the head moved posteriorly - the
anterior excursion of the mandible through
the interocclusal space decreased.www.indiandentalacademy.com

DESCRIPTION OF HEAD AND NECK
POSITION ON THE RADIOGRAPH
SOLOW &TALLGREN(1976)

NSL/OPT - represent tilting of the head at
occipitoatloid joint
OPT/CVT -represent change in cervical
curvature
OPT/HOR & CVT/HOR- Cervical
inclination in relation to the true horizontal
NSL/VERT -the total change in head
position

Large craniocervical angle- an extension of the
head -the height of the posterior arc of the
atlas is reduced
-Also related to adenoid airway obstruction
and a vertical facial development
(Huggare et.al., EJO 1985)

Various analysis using
NHP:

Reference planes in NHP:
Down’s & Tweed-
Drop perpendicular thru’ Orbitale
Test difference between true horizontal & FH
& include in the analyses
Bjork & Steiner-
Draw horizontal thru’ nasion
S-N made 10 degrees to horizontal

Growth prediction from posture
Solow & Nielson AJO 1992
41 reference points and 4 fiducial points

Points N and S on the first film - fiducial
points in the anterior cranial base- REFcrb.
In the mandible - fiducial points located
arbitrarily in the middle of the symphysis and
one below the first molars- REFml.

A backward inclination of the cervical column
& small craniocervical angle
 reduced backward displacement of TMJ
 increased growth in maxillary length,
 increase in max. and mand. prognathism,
 forward true rotation of the mandible .

Upright position of the cervical column &
large craniocervical angle
 large backward displacement of TMJ
 reduced growth in maxillary length
 reduction of max.and mand. Prognathism
 less forward true rotation of the mandible

A small craniocervical angle was associated
with a horizontal facial growth pattern
A large craniocervical angle was associated
with a vertical facial development.

Five-factor cephalometric
summary analysis
Horizontal line Reference-
 drawn parallel to the border of the radiograph
constructed at right angles to the registered true
vertical.
 drawn in any vertical position.
 BEST -close to the Frankfort plane
Cooke and Wei AJO 1988

Angle 1 - anteroinferior angle bet. Y axis &
true horizontal.
Angle 2 - angle bet. upper incisor & true
horizontal.
Angle 3 - NHP equivalent of the facial angle
Angle 4 - angle bet. AB line & true
horizontal.
Angle 5 - angulation of the lower incisor &
true horizontal.www.indiandentalacademy.com

"Normal" AB/horizontal values for clinical use
 Skeletal Class I 12° to 18°
 Skeletal Class II > 18°
 Skeletal Class III < 12°

Advantages:
Requires no new sets of "norms" or figures.
 Only the reference plane has been changed
to eliminate the errors inherent in analyses.
Conventional methods are subject to errors
in describing true life appearance.

Normal - focus on the profile from the nose
down
The A-P position of the forehead -not a major
factor
The size of the nose -alter clinician's
impression of the convexity of the profile &
the position of the lips.
A new measurement of profile
esthetics JCO, 1991 VIAZIS

A line drawn through
the middle of the nose
(No), parallel to the true
vertical- the ― V‖ line.
The ― V‖ angle - the
angle between this line
and Steiner's ― S‖ line.
for adults - -12.5°
for adolescents -13.0 °

FCA - + 3° prognathic
― E‖ line -normal lower
lip
V‖ angle - -1.5° -
supports clinical
impression of prognathic
profile .

FCA - -8° indicates
retrognathic profile.
― E‖ line I- retrusive
― V‖ angle - -11° in
accordance with
clinical impression of
orthognathic profile.

Cephalometric Analysis based on
NHP: JCO 1991 VIAZIS
Defines the A-P & vertical position of the
maxilla and mandible relative to the true
horizontal plane, then relates the position of
the dentition to its skeletal substrate.
Only two soft-tissue measurements.
No linear measurements.

Comprehensive Assessment of
Anteroposterior Jaw Relationships
JCO1992 VIAZIS
Describe an assessment of the
anteroposterior position of the jaws based
on measurements that use TH as their
reference line.

 Size of Mand. relative to Ant. Cranial Base (SN-
GoGn)
 Maxillomandibular Ratio (PNS-ANS:ArGn)
 Linear and Angular Measurements (A, B, Pg to
N^TH; NA, NB, NPg to TH)
 Relative A-P Position ( TH Wits & ANB)
 Anteroposterior Chin Position (Chin Length and
BNPg)

1. Size of Mandible Relative to Anterior
Cranial Base (SN-GoGn)
1:1 ratio -indicate a
well-balanced mandible
relative to the cranial
base . SN should be 0-
5mm greater than GoGn
before puberty, and
about 0-5mm less than
GoGn after puberty.

2. Maxillomandibular Ratio (PNS-
ANS:ArGn)
The length of the
mandible is exactly
double the length of
the maxilla for all age
groups and both sexes

3. Linear and Angular Measurements (A,
B, Pg to N^TH; NA, NB, NPg to TH)
Three linear measurements— from A, B,
and Pg to nasion perpendicular to TH
The angles between NA and NPg and TH -
evaluate the anteroposterior position of the
jaws . NB provides an additional
assessment

4. Relative Anteroposterior Position (TH
Wits and ANB)  Points A and B
projected on
perpendiculars to
TH, (a and b). The
distance ab - "TH
Wits‖ - provides a
clearer picture of the
anteroposterior
relationship of the
jaws

5. Anteroposterior Chin Position
(Chin Length and BNPg)
The BNPg angle
assesses the
prominence of
the chin relative
to the body of
the mandible

 Projections of B and
Pg to a line parallel
to TH and tangent
to the mandible at
menton define the
chin length,- bp

Optic plane: SASSOUNI
the supraorbitale plane (a line tangent to
anterior clinoid and the roof of the orbit)
the infraorbital plane (line tangent to the
inferior of sella turcica and the floor of the
orbit)
 bisect the angle formed by their intersection
- the optic plane

Natural head position in
photographs

Camera - mounted on a tripod & leveled with
the optical axis of the lens horizontal and the
film plane vertical.
20 × 100 cm mirror mounted at eye level on the
wall
Subject – camera –150 cm 2.55 m.
Mirror- subject – 120cm.
Recording of NHP:

Assume and maintain a "natural and normal"
erect posture of head and shoulders, with
both arms hanging free beside the trunk.
On each photograph, a reference line placed
perpendicular to the ground by using a small
spirit level (true vertical) was drawn.

AJO 1994 Ferrario et.al.,
Developed a photographic technique -
associated with standard radiograph &
a computerized method allowing an easy
and fast superimposition of the two
recordings was introduced

the angle between the N'-Pg' line and the true
vertical was calculated on the photograph &
cephalometric films
The difference - compute the position of the
soft and hard tissue Frankfurt planes, and of
the sella-nasion plane in NHP.
These new values were compared with the
values observed in the standard cephalometric
orientation.

 Angle N'-Pg' line/true
vertical was fed to a
computer program -
provided a rotation of all
the landmarks until the
cephalometric N'-Pg' line
coincided with the
photographic one.
Rotation was performed around the
Bolton point

Craniofacial morphometry by
photographic evaluation
AJO 1993 –Ferrario et.al.
 Frontal standing, rest & clenching a Fox plane
 Lateral standing, rest &clenching a Fox plane
 Lateral sitting, rest
16 points were located by careful inspection &
palpation and traced on the face of each
subject www.indiandentalacademy.com

 Median points -soft tissue nasion ,nasal
apex ,soft tissue subnasale ,upper lip ,lower
lip ,soft tissue pogonion .
 Lateral points - supraorbital foramen
, infraorbital foramen , soft tissue orbitale
, soft tissue gonion .

 Face center of gravity (CG) coordinates--- used as
the new origin of coordinate axes - the points
were translated.
on the frontal image using the areas of eyes ,nose
and mouth
on the lateral image as center of the polygon N-
Pog-Go-Tr
 In the frontal plot, the N-CG axis -used as a new
reference y-axis - points were rotated.

A proportional analysis of the soft
tissue facial profile
Lundström et.al, AO 1992

DISADVANTAGE OF NHP
AJO 1980 Frankel
 Functional appliance treatment- changes in
posture ( functional and physiologic)- distorts data
base
 Fu.A. alters muscle form and function. Adjoining
muscle groups experience reciprocal changes and
treatment-related head posture changes could
result.

Did not consider NHP modifications
during treatment, but proposed to refer all
longitudinal radiograms to the first NHP
recording – missed the important
information. Ferrario et.al., AJO 1994

CONCLUSION:
― THE SEARCH FOR AN IDEAL‖
-Cephalometrics is constantly undergoing
refinements in its techniques & analyses to
improve the clinical applications. NHP , a
long proposed modification, yet not fully into
practice, can be an ―ideal‖ reference for us to
improve our cephalometric interpretation……

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Natural head position

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