The study “Radiographic predictors for maxillary canine impaction” published in the March 2015 issue (Alqerban A, Jacobs R, Fieuws S, Willems G. Radiographic predictors for maxillary canine impaction. Am J Orthod Dentofacial Orthop 2015;147:345-54) achieves a thorough and detailed cross-sectional analysis of the risk factors for canine impaction. These results are highly useful to planning treatments for impaction. However, it is important to be aware of the predictive limitations of cross-sectional studies: “the primary limitation of the cross-sectional study design is that because the exposure and outcome are simultaneously assessed, there is generally no evidence of a temporal relationship between exposure and outcome.” Without longitudinal data, it is not possible to establish a true cause and effect relationship. For example, some variables that are statistically different on the impacted side (buccal or palatal crown deviation from the arch, increased vertical distance from the occlusal plane) may be a result of the impaction, and not necessarily a cause. Therefore, it is difficult to draw predictive conclusions based on these differences. In the study design, the impaction is diagnosed at the initial cone-beam computed tomography time point and confirmed in all subjects at the 1-year follow-up. Additional data from earlier time points before actual canine impaction would help to clarify the factors that cause canine impaction, rather than result from it.
Limitation of a cross-sectional study
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