An evaluation on the necessity for a cephalogram in natural head position (NHP) for the diagnosis of the severity and direction of malocclusion

Conventional cephalometric analysis, based on intracranial reference line SN and Frankfurt plan, sometimes leads to incorrect diagnostic findings and unpleasant theraputic results, especially in orthosurgery patients, mainly due to the instability of the mentioned references. Natural head position (NHP) is the standardized orientation of the head that its record in lateral cephalometric radiographs, provides us with extracranial references. The aim of this study is to evaluate the necessity for providing a lateral cephalogram in NHP for diagnosis and treatment of severe malocclusion (orthosurgery) in comparison with mild to moderate malocclusions. For this reason, 28 orthodontic and 26 orthosurgery patient's cephalograms, in natural head position, were selected. Diagnosis and treatment planning were based on clinical evaluation and cephalometric analyses especially Harvold and Tweed ones. Each group, based on their growth pattern, was divided vertically and horizontally. The angles between SN and TH planes with TH (True vertical Sine) were measured. Then, the correlation between the angles in two groups and also in relation to the severity of malocclusion, were analyzed in vertical and horizontal directions. The results of two groups were compared by the independent t-test. The findings of this study showed that:1- The SN line was found to be more inclined than FH line and in orthodonthic patients, FH plan is a more reliable reference than SN.2- In orthosurgery patients, the SN-TH and FH-TH angles were strongly different statistically.3- Variation in SN-TH angle, in patients with vertical growth pattern, was high in both groups of patients.These conclusions prove the necessity of a lateral cephalogram in NHP for all orthosurgery patients and those orthodontic patients with vertical growth pattern.