Cephalometric analysis : Technique, Aim, Indication, Interpretation
Evaluation and interpretation of both lateral and posteroanterior (PA) radiographs of the head ( usually confined to the former).
Taking the radiograph
Standardised technique to ensure reproducibility and minimise magnification:
Frankfort plane horizontal, ear posts in the external auditory canal with the central X-ray beam directed through them, teeth in centric occlusion,
X-ray source at a fixed distance to the midsagittal plane (about 152.5cm) and to the film (see Fig. 1). Collimate the beam to reduce radiation exposure. An aluminium wedge enables the soft tissues to be demonstrated (Fig. 2).
When anteroposterior and/or vertical skeletal discrepancies are present (Fig. 2); when anteroposterior incisor movement is planned in these cases.
Uses of lateral cephalometric analysis
• To aid diagnosis by allowing dental and skeletal characteristics of a malocclusion to be assessed.
• To check treatment progress during fixed or functional treatments and to monitor the position of unerupted teeth.
• To assess treatment and growth changes by superimposing radiographs or tracings on reasonably stable areas: cranial base or its approximation (S-N line holding at S; Fig. 3); anterior vault of the palate; Bjork’s structures in the mandible.
Aim and objective of cephalometric analysis
To assess the anteroposterior and vertical relationships of the upper and lower teeth with supporting alveolar bone to their respective
maxillary and mandibular bases and to the cranial base.
To compare the patient to normal population standards appropriate for his/her racial group, identifying any differences between the two.
Practice of cephalometric analysis
Ensure that teeth are in occlusion and that the patient is not postured forward.
In a darkened room, by tracing or digitising, calculate angular/linear measurements; identify the points and planes shown in Fig. 4; always trace the most prominent image. For structures with two images (e.g. the mandibular border), trace both and take the average for gonion.
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