Natural Head Posture / orthodontic courses by Indian dental academy

NATURAL HEAD POSTURE

INDIAN DENTAL ACADEMY

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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.


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


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.

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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.

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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

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.


• 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 80-degree 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

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

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

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

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

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

Solow B. Siersboeck-Nielsen S. Cervical and craniocervical posture as predicators of craniofacial growth. Am J Orthod Dentofac Orthop 1992;101 :449-458.

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;25:172-181

• 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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Natural Head Posture / orthodontic courses by Indian dental academy

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