Photometry in orthodontics is one of the common diagnostic methods needed to plan orthodontic treatment and examine changes that have occurred due to treatment or an individual's growth.
The Department of Orthodontics has developed a computer program that performs efficient photometric analysis of patients' faces to assess the condition of their dentofacial systems. The input data for the program are digital photos of patients' faces in profile.
Obtaining a photograph of the patient's face for photometric examination requires a clear orientation of the subject's head in the sagittal, frontal, and transversal (horizontal) planes; failure to do so compromises the reliability of the results of facial photographs analysis (Fig. 12.1).
In modern diagnostics, it is generally accepted that the most physiological for a photoand cephalometric examination is the natural position of the head.
The NHP (Natural Head Position) is the position that is observed in an individual in normal life and is optimal for cephalometric and photometric studies. The variability of the NHP in the population is insignificant and is about 4°, whereas the variability of the Frankfurt horizon is 26° (Fig. 12.2).
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Fig. 12.1. Head orientation in three planes
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Fig. 12.2. Natural position of the head for photometry.
In the natural head position, the pupils are centered in the middle of the eyes, and the gaze line defines a line along the true horizontal (TH). This head position can be achieved by using the «mirror technique», where the patient looks «into his own eyes» while standing against the mirror. The true horizontal is perpendicular to the true vertical (TV or TVL - true vertical line), i.e. the line of gravity which can easily be marked with a plumb line (Fig. 12.3).