Natural head posture /certified fixed orthodontic courses by Indian dental academy

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


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Natural head position is a standardized and
reproducible orientation of the head in space when
one is focusing on a distant point at eye level.
after considerable deliberation of the German
anthropological society, support was solicited and
reached in 1884 for the so called Frankfort
agreement i.e the plane through the right and left
porion and left orbitale to achieve uniformity in
craniometric reasearch.

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Frankfort horizontal is a useful compromise for studying
skulls but not for orienting natural head position in the living
because the frankfort plane located in the living is normally
distributed around a true extracranial horizontal.
Timely warning of Downs was completely disregarded. It
was he who had shown in his now classic analysis that
discrepancies between cephalometric facial typing and
photographic facial typing disappear.
When the frankfort plane is not horizontal, but tilted up or
down.

The deviation of the Frankfort horizontal level is ,
+9degrees,middle 0 degree ,right -7 degree


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Bjork’s studies of facial prognathism also illustrate
the unreliability of intracranial reference lines in
cephalograms .
Two adult Bantu men were selected to represent
maximum and minimum facial prognathism
relative to the line nasion –sella turcica [SN].
These two individuals have almost identical
profiles when shown in natural head position and
illustrate the greatest variation in the inclination of
the cranial base rather than the greatest
differences in prognathism.

•These findings illustrate that when SN is markedly
inclined downward, facial angles, such as SNA and
SNPg, become small and facial angles are increased when
SN is inclined upward.
•Therefore, prognathous individuals with a low cranial
base will be grouped in the orthognathous category and
orthognathous individuals with high cranial base in the
prognathous category.
• When various methods of cephalometric analysis are
applied to the study of the same cephalogram results may
differ dramatically depending on the choice of reference
lines.
•


Two bantu subjects have low and high
inclination of sella turcica-nasion line
respectively rather than differeces in
prognathism

•In a 17 year old girl studied by krog man and sassouni in
their exhaustive survey of roentgenographic cephalometry,
the Frankfort horizontal coincided with the physiologic or
true horizontal.
•Hence, the analyses based on the Frankfort horizontal
correctly described this patient as having a maxillary
protrusion and normal mandible because the cranial base
was deflected downward in its dorsal part.
• Analysis using nasion-sella turcica as a reference line
arrived at an opposite and incorrect conclusion, namely a
normal maxilla and a retrusive mandible.
•

A women with a class 2
div 1 malocclusion
suggested a protrusive
maxilla with normal
mandible based on the
FH plane as a reference
line and conversely a
normal maxilla but
retrusive mandible with
sella nasion reference
line.

•A study by Mc Namara shows marked difference in
maxillary development of patients with class II, division I
type malocclusion covers maxillary prognathism to
maxillary retrognathism. The distribution actually
represents variations not only in maxillary prognathism
but also in the inclination of the anterior skull base.
•The left side of the distribution represents individuals
with a low skull base inclination that reduces the SNA
angle for orthognathious maxilla to a retrognathious
status.


ORIENTATION IN NATURAL HEAD
POSITION
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The simplest procedure to obtain facial photographs
and head radiographs in natural head position is to
instruct patients to sit upright and look straight ahead
to a point at eye level on the wall in front of them.
For professional photographers, natural head position
is routinely used for facial photographs.
For the Downs and Tweed analyses, based on the
Frankfort horizontal, a perpendicular line is drawn to
the edge of the film, which is taken to represent an
extracranial or true horizontal.

A boy assuming natural
head position by
looking into the image
of his eyes in a small
mirror located at the
same level as the pupils
of his eyes


A ten year old girl in natural head position , head tipped
slightly up and down.


The precise location of this horizontal is immaterial,
but it may be drawn through the lowest point of the
orbital floor that can be fairly clearly ascertained to the
radiograph.
 Thereby, the correspondence between the
extracranial horizontal and the Frankfort horizontal can
be tested. A difference illustrates the effect and extent
of discrepancy between the findings when the
Frankfort horizontal is used for the Downs and Tweed
analyses.
 when using the mesh diagram, the Bjork, or Steiner
analyses, the vertical and a horizontal are drawn
through nasion parallel to the edge of the film.
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• The Bjork polygon is oriented a nasion, and the

nasion-sella turcica line at 10 degrees from the
horizontal or at 80 degrees from the vertical.
•For the Steiner analysis, any difference from the
average (10 degrees) cant of the anterior skull base
(NS) to the horizontal is used as a correction factor,
because a high inclination of the anterior skull base in
the individual studied enlarges the SNA, SNB, and
SNPg angles, while a low inclination reduces these
angles, suggesting greater or lesser amounts of
maxillary or mandibular prognathism than are actually
present.

•A low inclination of the anterior skull base increases
the angles between SN and palatal plane, SN-occlusal
plane and SN-occlusal plane and SN-mandibular
plane, while a high inclination of the anterior skull
base reduces these angles.
•It is easiest to draw a line through nasion at an 80degree inclination from the vertical for all
measurements and to disregard the SN-line on the
tracing.


•The procedure for obtaining natural head position in
cephalometric radiography is particularly pertinent to
obtain a reliable image of the head in the so-called
PA or frontal radiographic projection. These records
register facial asymmetry, the extent of which can be
of critical importance for treatment planning and
prognosis.
•The study of asymmetry is confounded by the
difficulty of defining the midline of the patient’s face
accurately because the midline serves as the origin
for measurements.

Facial symmetry of
eyes ears contour
of lips and
mandible

Assymetry of
eyebrows and
lips


Marked
asymmetry of
eyes ,eyebrows
and ears but
symmetry of lips

•The conventional use of two ear rods to stabilize the
hed in radiographic cephalometry is based on the
assumption that the transmeatal axis of humans is
perpendicular to the midsagittal plane.
• Actually, asymmetry is a general characteristic and
the relationship of the left and right ears in their vertical
and horizontal relation to each other is frequently
asymmetric.
• in these instances, the insertion of ear rods will
obviously result in vertical and / or the horizontal
rotation of the head, which introduces a deficient and
misleading image.

•Thereby, the attempt to determine facial asymmetry
of a patient generally results in a compromise rather
than as an exact definition.
•Only the left ear road should be used in radiographic
cephalometry both for the lateral and particularly for
the frontal projection. The right ear rod should be
merely inserted against any part of the ear, or replaced
by a soft small rubber cup, to prevent sideways
movement of the head after the patient’s facial
midline is aligned with the midline ruler of the
cephalostat.

NATURAL HEAD POSTURE
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In addition to determining natural head position, as
a fixed or standardized orientation of the head for
studying facial morphologic features, efforts have
been made also to determine a functional or
postural position of the head.
This procedure was persued in a renewed effort to
probe the relationship between dentofacial
morphologic features and breathing, which, after a
century of controversy still remains an enigma.

•Although, the head changes its posture continuously
throughout functional activities, Solow and Tallgren
selected the “ortho position” of subjects, name the
momentary interim position when taking the first step
forward from a standing to a moving or walking
posture, which is reproducible acording to Molhave.
•Showfety et al developed a fluid level device to record
head posture prior to exposure of the head film.
•In this way, head posture could be accurately
reproduced for its roentgenographic record and for
cephalometric analysis.

•Instrumentation has also been developed by Murphy
et al as well as Huggare for dynamic measurement of
changing head posture.
•In any case, the terms natural head position and head
posture are not interchangeable, one being a
standardized procedure applied to all individuals for
analysis of dentofacial morphology and the other an
individually characteristic physiologic posture of the
head to study the relation between posture and
morphologic features.


METHODS OF MEASUREMENT
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A number of methods of measuring and recording head
posture, each with its advantages and limitations.
A straight edge ruler and protractor have been used in
some craniometric studies to measure natural head
position relative to a true vertical reference line.
The procedure described by Vig et al relates points
marked on the soft tissues of the face to a gravity
defined vertical.

•Repeated measurements could record variations in
head posture over a few hours.
•A true vertical, provided by a radio opaque plumb
line, has also been used in radiographic cephalometric
studies of head posture.
•Although less accurate, photographic methods have
also been useful in the study of facial features relative
to extracranial reference lines.
•Bjerin transferred true horizontal lines from profile
photographs of subjects to their lateral skull
radiographs.

•Measurements were made on these radiographs
with reference to the true horizontal.
•Electromyographic techniques have also been used
in attempts to determine specific physiologic head
positions, such as dorsiflexion and ventroflexion.
•These studies have provided no definite standards
against which head posture can be measured.
•Lundstrom defined natural head posture as a small
range of positions oscillating around the individual’s
mean NHP.

•In terms of this definition, head posture is not static
and, ideally, its study requires a method that makes
it possible to measure and record postural changes
continuously.
•The observation also makes evident the need to
draw a distinction between the concepts of position
(static) and posture (dynamic).
•Cleall el al recorded dynamic changes in head
posture by means of cinefluorography, a procedure
that exposed their subjects to radiation for relatively
long periods.

•They found the technique to be unreliable and the
images produced not completely suitable for
detailed frame-by-frame analysis.
•Murphy et al also recognized merit in developing
an accurate measuring device capable of the
continuous recording of head position as it may
change over extended periods.
•Such a measuring device would be valuable in the
study of head posture during normal daily activities,
and specifically, in the measurement of NHP during
oral functions such as mastication and swallowing.

INSTRUMENTATION
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An inclinometer consisting of a contactless precision
potentiometer measuring single axis inclinations was
selected for the accurate measurement of inclinations
and declinations of the head.
The first version of this instrument weighted just less
than 30g and the latest version weighs less than 9g.
The response time to changes in position was 0.3
seconds with a tilt sensibility, including hysteresis, of
0.01 degrees.

•The inclinometer was attached to one arm of a pair
of spectacles in a position as close to the ear as
comfort would allow.
•This reduced the force moment acting on the
occipital condyles.
•A small switchbox containing a size AA battery
provided the power source.
•A Rustrak Ranger (Gulton Industries East
Greenwich, Conn) adaptive data logger was used to
record the flow of analog output emanating from the
inclinometer.

Array of instruments
assembled for recording
head posture

A subject wearing the spectacle
array


The Rustrak Ranger
adaptive data logger may
readily be carried in a
pocket


•Downloaded to a computer, the data reflected the
postural positions of the head in the sagittal plane,
within the range of 0 to 60 degrees relative to a
gravity defined vertical.
•Lundstrom and Lundstrom studied the
reproducibility of NHP as well as the variability of
three standard cephalometric reference lines.
•The three lines varied greatly in their relationshp to
sa true horizontal line drawn through the sella
turcica with the head held in NHP.


•Lundstrom and Lundstrom concluded that this
constructed line provided a better and more stable
reference base line for cephalometric analysis.


A STUDY OF STATIC AND CONTINUOUS
HEAD POSTURE
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MATERIAL AND METHODS:
The sample consisted of a volunteer group of 30 male
dental students, 20 to 30 years old, all of whom were
free of neck pathosis, chronic respiratory infections, or
severe allergies, which could have influenced the
outcome of the study.
They were predominantly nose breathers with
competent lips and no obvious postural deformities.
The study was approved by the Committee for
Research on Human Subjects, University of
Witwatersrand, Johannesburg.

•The inclinometer was first used to record
measurements of the mean static natural head
position for each of the students in the sample,
determined according to the techniques described by
Molhave and by Sandham.
•The continuous measurement and recording of head
posture in walking subjects was conducted in a large
hall with bland walls, no direct vision to the outside,
and good artificial lighting.
•A route of approximately 25m was provided along
which the subjects could walk in an unobstructed
manner.

•Once a subject was comfortable with what was
expected of him, a 5 minute recording session of
head posture commenced.
•Care was taken to ensure that the experiment was
repeated at about the same time and in the same
manner on each of the 5 days.
•A Kruskal-Wallis one-way analysis by ranks was
conducted to determine whether there were
significant differences (P<.05)between the head
postures determined on the different days.

Mean static vs mean walking
head posture

Mean= - 2.01 deg
S.D= 3.12 deg
Range= - 7.70 to 4.13 deg


5 measurement of NHP a
static position identified on
the continuous recording by
the five vertical dotted lines


NATURAL HEAD POSITION vs NATURAL
HEAD POSTURE
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Statistically significant differences found between
the means of the measurements of natural head
position (static) and of the dynamically recorded
walking head position and head posture.
The distinction was emphasized by Moorrees, who
identified natural head posture as being physiologic
in character and determined by the orthoposition
technique suggested by Molhave.

•Moorrees followed the concept of Cooke and Wel
in describing natural head position as “a
standardized and reproducible position of the head in
an upright posture, the eyes focused on a point in the
distance at the eye level”.
•Orthodontists include in their treatment objectives
the desire to match physiologic, functional, and
esthetic ideals.

•Yet, great reliance is still placed on diagnosis and
treatment planning based on analyses of
cephalometric radiographs that have been taken while
the patient is constrained by a cephalostat to a
position that brings the Frankfort plane to a true
horizontal.
•An effective, convenient, and accurate means of
recording natural head posture as a dynamic entity
has now been developed.
•Serious consideration could be given to utilizing this
technology in cephalometric radiology.

•Here it may be argued that natural head posture is that
attitude of the head and face in which the patient
predominantly lives and which he or she presents to
the world.
•Since orthodontists are vitally concerned with
physiological totality, it may even be an advantage to
have the cephalometric means to monitor postural
changes occurring in response to physiologic changes.

A patient wearing the
recording apparatus and
positioned in the cephalostat


•Various researchers have continued to examine
factors that may affect head posture.
•All of these studies have been based on purely
static recordings of cranial posture.
•If natural head posture does indeed oscillate around
the individual’s mean natural head position, the
question arises as to whether static recordings of
head posture are appropriate.


REFERENCES
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Solow B. Siersboeck-Nielsen S. Cervical and
craniocervical posture as predicators of craniofacial
growth. Am J Orthod Dentofac Orthop 1992;101 :449458.
Murphy KE, Preston CB,Evans Wg. The development
of instrumentation of the dynamic measurement of
changing head posture. Am J Orthod Dentofac
Orthoped 1991;99:520-526.

• Huggare JAV. A natural head position technique for
radiographic cephalometry. Dentomaxillofac Radiol
1993;22:74-76
• Moorrees CFA. Natural head position-a revival.
Am J Orthod dentofac Orthop 1994;105:512-513
• Viazis AD. A cephalometric analysis based on
natural head position. J Clin Orthod 1991;25:172181
• Viazis AD. Atlas of Orthodontics: Principles and
clinical Applications. Philadelphia: WB Saunders:
1993;74

•Lundstrom F, Lundstrom A. Natural head position
as a basis for cephalometric analysis. Am J Orthod
Dentofac Orthop 1992;101:244-247
•Lundstrom A, Forsberg CM, Westergren H,
Lundstrom FA. A comparison between estimated
and registered natural head posture. Eur J Orthod
1990;13:59-64
•Murphy KE, Preston CB, Evans WG. The
development of instrumentation for the dynamic
measurement of changing head posture. Am J
Orthod Dentofac Orthop 1991;99:520-526

•Moorrees CF. Natural head position-a revival. Guest
editorial. Am J Orthod Dentofac Orthop
1994;105:512-513.


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