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The norm concept and cephalometrics

1956; Elsevier BV; Volume: 42; Issue: 12 Linguagem: Inglês

10.1016/0002-9416(56)90190-7

1557-8488

Ernest H. Hixon,

dental development and anomalies

1. Most available cephalometric norms describe faciodental traits with reference to the variability of the trait in a population. 2. Clinical use of these norms is thus appropriate for describing or ranking the patient in terms of the norm. It is abusing the norm to use it alone for evaluation in diagnosis, or to use the average as an objective in treatment planning. A norm is not a substitute for professional judgment. 3. A norm is not a single value, but a range of values. Thus, norms constructed in terms of percentiles, such as the ones used in height and weight norms, have certain advantages. They are easy to use and understand. They are usable whether there is a normal or an asymmetrical distribution. Since variability is emphasized, use of percentiles probably reduces a natural tendency to think of the average as a treatment goal. 4. Until we can construct a larger body of knowledge, our normative use of present cephalometric data should recognize some limitations. Sample sizes of most studies are too small to represent fully the variability of a population. Also, the samples have usually been subjectively selected; for example, on the basis of normal occlusion. The importance of this, as well as differences due to age, sex, and race, is yet to be adequately explored. 5. When using cephalometric data, it is very important to recognize that two persons will seldom duplicate each other exactly in tracing or measuring. Individual orthodontists, and also the same orthodontist on different occasions, will often disagree by several degrees. 6. There is such wide variability between individual persons that most cephalometric measures are not diagnostic within themselves. It is abusing normative data to set arbitrary diagnostic limits of abnormality at one or even two standard deviations from the mean. 7. Some children with normal occlusion will have angulation measurements similar to the malocclusion cases. Many aspects of facial pattern do not appear to be related to the presence of a good occlusion or a malocclusion. 8. Individual deviations from the average pattern of growth are marked. Thus, the ability to predict facial growth in different persons varies considerably and does not provide a stable basis for treatment planning on the basis of present knowledge for the period between the ages of 5 years and 13 years.