Controv Ersies in Cephalometrics / orthodontic courses by Indian dental academy

Controversies in Cephalometrics

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

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Orthodontics as a science is still very young and a major part of the development of this profession has been raised on trial and error approaches rather than deductive research. Controversies have thus sprung up within the field of Orthodontics.www.indiandentalacademy.com

Natural head position

Natural head position is a standardized and reproducible orientation of the head in space when one is focusing at a distant point at eye level.

German anthropological society in 1884 – Frankfort Agreement. The plane which passes through the left and right porion landmarks and the left orbitale achieved uniformity in craniometric research.


Downs – timely warning. It was he who had shown that discrepancies between cephalometric facial typing and photographic facial typing disappear when the Frankfort plane is not horizontal but tilted up or down.


Bjorks studies of facial prognathism also illustrates the unreliability of intra cranial reference lines on cephalograms.

Two adult Bantu men were selected to represent maximum and minimum facial prognathism relative to the S-N plane.Bjork illustrates the greatest variation in the inclination of the cranial base rather than the greatest differences in prognathism.


The simplest procedure to obtain facial photographs and head radiographs is to instruct patients to sit upright and look straight ahead to a point at eye level on the wall in front of them.

The conventional use of two ear rods to stabilize the head in radiographic cephalometry is based on the assumption that the transmeatal axis of humans is perpendicular to the mid sagittal plane.

The relationship of the left and right ears in their vertical and horizontal relation is frequently asymmetric.


The insertion of ear rods will obviously result in vertical and/or 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 rod should be used in radiographic cephalometry both for the lateral and frontal projection.

The right ear rod should merely be inserted against any part of the ear.


Reliability of Landmark identification and Head Film Measurement.

Head film measurements like all measurements involve error which falls into two categories.

• Errors of Projection

• Errors of Identification


Errors of projection:

Results because headfilm is a two dimensional depiction of a three dimensional object.

Since the rays that produce the image are not parallel and originate from a small source , headfilms are subject to distortion.- the side nearer the x ray source is enlarged more than the side closer to the film.

While meaningful systematic corrections for projection errors are obtainable by using a real time video subtraction stabilization procedure , this is impractical for routine clinical use.


Error of identification:

Involves the process of identifying specific landmarks on headfilms.

To test landmark identification reliability , 4 instructors and 3 orthodontic residents were requested to select and plot four high quality radiographs.

They were provided with a list of landmarks and definitions of each and were asked to identify them using a pencil point on a clean sheet of acetate paper on the radiograph.


The porion, condylion , orbitale and basion were less readily identified than some of the other landmarks.

Condylion was less readily identified and Gnathion more accurately identified.

Baumrind and Frantz demonstrated marked differences in magnitude and configuration of envelope of error found among different landmarks.Other factors that can influence landmark identification are film density and sharpness.


Reliability of cephalometric analyses:

Fundamental to orthodontics is the need to determine the relationship of the various skeletal components, particularly those of the jaws to each other and to the rest of the cranium in the cranio facial complex.

The interpretation of the measurements continues to be the subject of much debate.


Wylie et al compared five analyses in ten individuals who underwent various surgical corrections.Pre treatment cephalometric radiographs of the ten patients were selected to illustrate different dentofacial deformities , each of which was corrected with a different surgical procedure.

The pretreatment cephalometric radiographs were blindly assessed by one investigator who used the criteria for each of five popular analyses.

The results of the analyses ( diagnoses ) were then compared to one another and to the actual surgery performed.


The outcome of the study revealed that performance of the analysis in relation to actual surgery was generally poor.

In the case with mandibular advancement there was 35 % agreement on the surgery performed.

For maxillary advancement - 20 %

For maxillay superior positioning 100%

For maxillary advancement and mandibular reduction- 20%

For bimaxillary protrusion – all analyses agreed that the teeth were protrusive and that the lower third of the face was too long.

This illustrates the unreliability of cephalometric analyses.www.indiandentalacademy.com

Limitations of traditional superimposition methods:

No points or planes in the craniofacial complex are stable and all move relative to each other during growth. Orthodontic analyses, in effect , relates relatively stable areas as depicted by arbitrarily selected points or planes to more remote but less stable landmarks.


While the primary errors are biologically induced , the secondary errors are entirely mathematically defined, since they are related to the primary errors.

Errors in tracing superimposition can be compounded by the method of superimposition used in interpreting the findings.

A study conducted by Ghafari et al demonstrated differences in interpretation of facial changes by comparing four traditional cephalometric methods of superimposition.( best fit on anterior cranial base anatomy,sella-nasion,registration point with bolton nasion planes parallel and basion- nasion plane.


The results of their study showed differences among all paired methods to be statistically significant.

Growth behavior of an individual as recorded on a sequential set of roentgenograms has been shown to differ greatly when studied using different superimposition methods. Nothing is known of the growth behavior of the individual parts in the continuum of the discrete points studied.

Because of the inability of conventional cephalometry to apprehend curved forms, it is limited to landmark indices.


Reference planes:

The various reference lines still compete with each other.One system is more or less as good or poor as any other and none is completely reliable because each is subject to large individual variability.

What can be done to diminish this problem?

The answer is to choose measurements that are based on different reference planes, in this way it is hoped to compensate for pronounced variations in one or the other reference lines.


True vertical plane:

The problem of a constant reference plane can be solved if the true vertical plane is used. The true vertical is a constant and is perpendicular to the true horizontal.

Some clinicians have acknowledged this fact and developed a cephalometric assessment based on this reference plane.

(Michielis and Tourne,1990;Viazis,1991)

Viazis analysis was based on Bolton standards in which natural head positionwas never a serious consideration.Thus there was a shortcoming of lack of equivalent norm data.www.indiandentalacademy.com

The analysis we feel comfortable at present is divided into four fields or areas.

• Sagittal base relationships

• Vertical base relationships

• Dento alveolar relationships

• Memos ie important evaluations without proper measurements.

A criticism could be that readers do not agree with some of the abbreviations selected. ( SN – SGn instead of Y axis etc ).


Advantages:

• Enhances communication

•Could be speculated that these measurements have some merits since they have been used for a long time.

• Further, it is easy to reckon that the idea of different reference planes was indeed realized: the Steiner angles are related to the SN plane, those of Downs to the FH plane , Wits appraisal to the occlusal plane and the Holdaway soft tissue evaluation like NA-Apog angle to the extension of the skeletal base onto the forehead, the chin and upper lip.


Cross evaluation with different reference planes is important and can be demonstrated with the ANB angle.

If one takes only the ANB angle to measure the relative position of maxilla and mandible to each other ,one must realize that any different horizontal or vertical position of point N and the location of the points A and B in the vertical plane will have an influence on the size of this angle and not on the actual sagittal relation of the two jaws.

( Hussels and Nanda ,1984 ).


The same holds true for a rotation of the occlusal plane: backward rotation of the occlusal plane has a decreasing effect on the ANB angle, though sagittal basal relationships remain constant.


Shortcomings of ANB angle:

Taylor in 1969 pointed out that ANB angle did not always indicate true apical base relationship. Varied horizontal discrepancies of points A and B could give the same ANB measurement because variation in the vertical distance from nasion could compensate for other variation.

Beatty in 1975 reported that ANB angle is not always an accurate method of establishing the actual amount of apical base divergence.As an alternative to ANB angle for measuring apical base discrepancy , he devised the AXD angle,where point x is located by projecting point A on to a perpendicular to SN line.www.indiandentalacademy.com

Point D is located in the bony symphysis as described by Steiner.


-Frankfort horizontal basis for cephalometric analysis Lundström and Lundström- AJO 1995

No difference was found between the variability of the Frankfort horizontal and the sella-nasion line with regard to the horizontal plane. The large variation of both intracranial reference lines, related to NHP, as well as to NHO, confirms their relative unsuitability as cephalometric references for clinical purposes. Findings indicate that a horizontal line, related to natural head position, adjusted to natural head orientation when indicated, presents the most reliable basis for cephalometric analysis.


AJO-DO on -DO, 1980 Variability between the optic plane and Frankfort horizontal – Tremont

Frankfort horizontal is commonly constructed on a lateral cephalogram from the top of the ear rod to orbitale. Ear rod positioning and identification of orbitale present obvious variables with such a reference plane. The optic plane has been proposed as a more accurate representation of Frankfort horizontal.


The optic plane, was significantly different from anthropologic Frankfort horizontal. Also, the optic plane did not vary significantly less from anthropologic Frankfort horizontal than from ear rod to orbitale Frankfort horizontal.


The optic plane was constructed, as defined by Sassouni, by drawing the supraorbitale plane (a line tangent to anterior clinoid and the roof of the orbit), drawing the infraorbital plane (line tangent to the inferior of sella turcica and the floor of the orbit), and then bisecting the angle formed by their intersection to obtain the optic plane.


Cephalometrics for you and me – Steiner – 1953 AJO

Porion and Orbitale are not accurate for our use as we are not dealing with dry skulls.

Points S and N are clearly visible in the X ray pictures and can be located easily and accurately.

Emphasizes that points S and N are located in the mid sagittal plane of the head and therefore they are moved a minimum amount whenever the head deviates from the true profile position and that the points are located on hard non yielding tissue.


Point A revisited – Jacobson- AJO 1980

Point A cannot be accurately identified in all cephalometric radiographs. In instances where this landmark is not clearly discernible, an alternative means of estimating the anterior extremity of the maxillary base is shown.

A point plotted 3.0 mm. labial to a point between the upper third and lower two thirds of the long axis of the root of the maxillary central incisor was found to be a suitable point - (estimated point A) through which to draw the NAE line and one which most closely approximates the true NA plane.


Steiners analyses:

Acceptable compromises:

Steiner clearly recognized that cephalometric standards are merely gauges by which to determine more favorable compromises as a treatment goal.He developed a chart that reflects a number of average measurements of normal dentofacial relationships.

Steiner recognized variations in antero posterior jaw relations to each other.

The compromise describes the anticipated axial inclinations of the maxillary and mandibular incisors to the NA and NB lines at various ANB relationships.


The Steiner compromises are geometric resultants of morphogenetic variations and their resulting treatment possibilities.


Method of appraisal of jaw disharmony- Witts

The Witts appraisal is the extent to which the jaws are related to each other.

The occlusal plane is drawn through the region of the overlapping cusps of the first premolars and first molars.The point of contact on the occlusal plane from points A and B are labeled AO and BO respectively.

The average jaw relationship according to Witts is – minus 1 mm for men and 0 mm for women.


Schudy described the occlusomandibular plane angle (OM angle )as another method of evaluating skeletal divergency and thus an indication of skeletal pattern.A variation in the range of OM angles is from 7 to 21 degrees.

As the OM angle approaches 21 degrees,hyperdivergency of skeletal pattern is more likely.

Smaller OM angles indicate hypodivergency.


A-Po line and cephalometric correction- Ricketts

The A-Po line is another method used in cephalometric analyses to assess the position of mandibular incisor tooth.

A range of –2mm to +3mm is considered a satisfactory incisor position,with + 0.5 mm lower incisor tip to A-Po line being an idealized position.

Downs credits Ricketts for suggesting relating the lower incisor to the profile,specifically the lower face using A-Po.


Cephalometric correction describes a method to determine mandibular dental arch crowding or spacing by assessing mandibular incisor position on a cephalometric radiograph in concert with mesiodistal dimensions of mandibular teeth and mandibular arch circumference.

The rationale is that by advancing or retracting the mandibular incisor 1mm will result in a 2mm gain or a 2 mm reduction in the available space for mandibular arch.


Calculations have indicated that tipping the lower incisor tooth forward by 3 degrees results in total dental arch length increase of 2.5mm.

Conversely, retracting the mandibular incisor 3 degrees will encroach on the lower arch length by 2.5mm.

Ricketts stresses the significance of utilizing linear as well as angular measurements in these assessments.

All cephalometric measurements must be evaluated in concert with other measurements and must include clinical and diagnostic judgement.


Mc Namara analyses:

For determining the anteroposterior relationship to maxilla and mandible , mid facial length is measured from condylion to point A. The effective length of the mandible is measured from condylion to gnathion.

Birte Melsen suggests that there are displacements of condyle,pogonion,menton and point B relative to superimposition on implants at a study done on annaual intervals between 8.5 yrs and 15.5 yrs of age.


Soft tissue analyses- Holdaway

Legan and Burstone suggest using a constructed horizontal.This is a line drawn through nasion at an angle of 7 degrees to the SN line.

A vertical reference line can be traced passing through sub nasale (SnV) or glabella.

Naso labial angle – formed by two lines namely the columella tangent and an upper lip tangent.Arbitrary value is 90 to 110 degrees.

Legan and Burstone report a mean value of 102 +/- 4 degrees.


Scheidman et al drew a postural horizontal line through subnasale and further divided the naso labial angle into columella tangent to postural horizontal ( -25 degrees)and upper lip tangent to postural horizontal ( -85 degrees).

They argue that each of these angles must be assessed individually in as much as they vary independently.


E line: Drawn from tip of nose to soft tissue pogonion.Normally the upper lip is about 4 mm behind this reference line while the lower lip lies about 2 mm behind it.

Ricketts admits that considerable variation exists in terms of age and sex.He therefore advises that adult lips should be contained with nose – chin lip line.

S line:- Steiner line is a line drawn from soft tissue pogonion to the mid point of the S shaped curve between sub nasale and tip.


H line: The harmony line is tangent to the chin point and the upper lip. The H line angle formed between this line and the soft tissue nasion – pogonion line.The H line angle measures either the degree of upper lip prominence or the amount of retrognathism of the soft tissue chin.


A combination of various cephalometric norms and variables should be compiled to arrive at a proper diagnosis.Although innumerable controversies exist in the field of cephalometrics, it is still a very significant & effective diagnostic tool.

Conclusion:


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Controv Ersies in Cephalometrics / orthodontic courses by Indian dental academy

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