Occlusal interferences in orthodontic patients before and after treatment, and in subjects with minor orthodontic treatment need.

Different opinions have been expressed concerning the effect of orthodontic treatment on mandibular function. One factor discussed is occlusal interferences. The aim of this study was to establish the prevalence of occlusal interferences in 210 orthodontic patients before (mean age 12 years 8 months) and after (mean age 16 years 10 months) treatment and to compare them with subjects with minor orthodontic treatment need. The results showed a decrease in retruded contact position/intercuspal position (RCP/ICP) interferences in all morphological deviations, age, and gender groups. The prevalence of mediotrusion interferences decreased in some types of malocclusions whilst in others there was no change. One reason for this is that treatment was started when the majority of the patients had no second or third molars erupted. At the final registration, the second molars were erupted in all patients, and the third molars were erupted in approximately 25 per cent. Mediotrusion interferences were more consistent with basal morphological deviations, for example, Class III relationships and anterior open bite were more consistent in the same person, and more difficult to eliminate than RCP/ICP interferences. RCP/ICP interferences, often caused by dental deviation in position, size, and shape, were easier to correct. Optimal orthodontic treatment, if necessary, including selective grinding, will decrease the prevalence of occlusal interferences.