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CEPHALOMETRICS. Diagnostic records for orthodontic purposes may be divided into three major categories : 1. dental casts and occlusal records 2. photographic records 3. radiographic records. Basic radiographic records used in orthodontics are lateral cephalometric radiographs.
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Diagnostic records for orthodontic purposes may be divided into three major categories : 1. dental casts and occlusal records 2. photographic records 3. radiographic records
Basic radiographic records used in orthodontics are lateral cephalometric radiographs. They have two purposes : 1. they reveal details of skeletal and dental relationships that cannot be observed in other ways and 2. they allow a precise evaluation of treatment response
Analysis of lateral skull radiographs allows a more detailed evaluation of facial structures than is possible from a visual assesment of facial appearance. • However, in many instances an adequate orthodontic diagnosis can be made without a cephalometric radiograph, it is practially impossible to assess accurately a patient´s response to treatment without being able to compare cephalometric films before and after treatment. For this reason, even in patient whose dental and skeletal relationships seem perfectly straightforward, a lateral cephalomeric film is needed.
CEPHALOMETRICS – X-RAY TECHNIQUE : • The lateral cephalometric radiograph is taken with the head held in a specially designed holder so that there is a fixed constant relationship between the patient´s head, the film and the anode of the X-ray tube. • Cephalometric head holder fix the patient´s head at two points by the ear rods fitting into the external auditory canals.
CEPHALOMETRICS – X-RAY TECHNIQUE : • The head is in natural relaxed position. Patient gets it by looking at a distant horizont. At this position the midsagittal plane of the head is parallel to film • X-ray beam should run through the external auditory canals and should be perpendicular to midsagittal plane of the head. • The teeth should be held lightly together in centric occlusion. The lips should be relaxed
CEPHALOMETRICS – X-RAY TECHNIQUE : • We have to keep these standard conditions to take standard and comparable cephalometric radiographs. • The midsagittal plane of the head is at a fixed distance from the film - 10 cm. • The distance of the X-ray tube from the head should be more than 1.5 m. This makes the X-rays nearly pararel, not divergent as usual.
CEPHALOMETRIC ANALYSIS – HISTORY AND AIMS : Cephalometric analysis was developed initially by selecting measurements that were most useful in differentiating patients with the various Angle classes. The objective was to produce a reasonably finite number of measurements that would serve as guides in evaluating particular relationships. The original analysis, Down´s, had five skeletal and five dental criteria, each meant to evaluate a particular relationship.
CEPHALOMETRIC ANALYSIS – HISTORY AND AIMS : At present there are many named cephalometric analyses, each based on choosing some specific measurements from the multitude that might be used to evaluate a single relationship. There is not and will not be any single analysis that is ideal for every patient, simply because certain measurements will be useful in providing information about certain patient but not useful for others.
CEPHALOMETRIC ANALYSIS – HISTORY AND AIMS : The goal of cephalometric analysis must be evaluation of the underlying relationships, not recording of any particular set of measurements. The measurements are always a means to this end.
CEPHALOMETRIC ANALYSIS – METHODS OF DATA EVALUATION : Cephalometric analysis may be carried out on the radiograph itself or on the tracing of the radiograph. The tracings have two advantages : 1. they reduce the amount of information on the film to a manageable level ( so they emphasise the relationship of selected points ) 2. they can be better superimposed to show changes caused by growth or treatment.
CEPHALOMETRIC ANALYSIS – METHODS OF DATA EVALUATION : The landmarks used in tracing can be represented as coordinate points on an (x,y) graph, and the digital coordinates can readily be placed into computer memory. An adequate digital model is required, which means that at least 50 and preferably 100 or more points should be digitized. Exellent software programs are available to calculate angles and distances, and to superimpose digitized tracing.
CEPHALOMETRIC ANALYSIS – METHODS OF DATA EVALUATION : In diagnosis, the patient´s facial and dental proportions are compared to a reference group, so that differences between the patient and normal values can be highlighted. Normal dental and facial proportions can be represented in two ways : 1. as tabulated measurements or 2. as a normal tracing produced by averaging the coordinates for the reference sample.
CEPHALOMETRIC ANALYSIS – METHODS OF DATA EVALUATION : Therefore comparison of a patient to reference sample can be done in two ways : 1. by comparing selected measurements for the patient to the same measurements on the reference sample, which is the typical cephalometric analysis aproach or 2. by superimposing the normal tracing on the patient´s tracing and visually comparing the two. This method is called template analysis. It is recomended as an initial step in determining how the patient differs from the norm or in assessing the patient´s response to treatment .
Cephalometric analysis First step in cephalometric analysis is to mark certain points. The following landmarks are used : • Sella (S) – the centre of sella turcica
Cephalometric analysis • Nasion (N) – the most anterior point on frontonasal suture • Menton (Me) – the lowermost point on the mandibular symphysis • Gonion (Go) – it is located on intersection of the tangent to posterior outline of the mandibular ramus and tangent to mandibular body through menton ( mandibular plane ) • Pogonion (Pg) – the most anterior point of the bony chin
Cephalometric analysis • Point A (A) – also known as subspinale, this is the deepest point on the maxillary profile between the anterior nasal spine and the alveolar crest. • Point B (B) – also known as supramentale, this is the deepest point on the concavity of the mandibular profile between the point of the chin and the alveolar crest.
Cephalometric analysis • Anterior nasal spine (ANS) – the point of the bony nasal spine. • Posterior nasal spine (PNS) – the tip of the posterior nasal spine can usually be seen unless unerupted molars obscure it. The outline of the palate gives a good indication of its vertical level. A line through the most inferior point on the pterygo-maxillary fissure, perpendicular to the maxillary plane, indicates the antero-posterior location of PNS.
Cephalometric analysis • Orbitale (Or) – the most inferior point on the margin of the orbit. • Porion (Po) – the highest point on the bony external acustic meatus. • Prostion (Pr) – the lowest point on the alveolar crest labial to the most prominent upper central incisor.
Cephalometric analysis • Infradentale (Id) – the highest point on the alveolar crest labial to the most prominent lower incisor. • Incision superius (IS) – the tip of the crown of the most prominent maxillary incisor. • Incision inferius (II) – the tip of the crown of the most prominent mandibular incisor. • Gnation (Gn) – the most anterior, inferior point on the bony symphysis of the mandible.
Cephalometric analysis • Commonly used reference lines are following : • Facial line (NPog) – nasion-pogonion. It indicates the general orientation of the facial profile. • Frankfort plane (PoOr) – porion-orbitale. This plane is described as being horizontal when the head is in free postural position. In fact, there is considerable individual variation.
Cephalometric analysis • Mandibular plane (Mn) – the line from menton, tangent to the lower border of the mandible at the angle. • Maxillary plane (Mx) – this is line through the anterior and posterior nasal spine. It indicates the orientation of the palate. • Functional occlusal plane – the line following the occlusion of the molar and premolar teeth.
