Assessing treatment effectiveness of removable and fixed orthodontic appliances with the occlusal index.

Orthodontists from different backgrounds may have different opinions about removable and fixed orthodontic appliances, but there have been few objective comparisons of their relative treatment effectiveness. It is the purpose of the present study to analyze objectively the effectiveness of these two types of appliances. Eighty cases involving patients who had been treated with removable appliances and 67 cases of patients treated with fixed appliances were studied with respect to the Occlusal Index (OI). Scores indicating severity of malocclusion were obtained from pretreatment and posttreatment study casts. The effectiveness of the fixed appliance (represented by average reduction in OI score) was much greater than that of the removable appliance. The result of treatment with the fixed appliance was also found to be much better than that of the treatment with the removable appliance (indicated by the much lower posttreatment OI score in the fixed-appliance cases). The Occlusal Index was designed to measure features of basic malocclusion and is not a very sensitive index for assessing symptoms of a developing malocclusion. The fact that both the treatment effectiveness and the treatment results of the removable appliance were found to be inferior to those of the fixed appliance may indicate that the removable appliance has been used largely to correct "symptoms" rather than basic malocclusion.