Extraction of the deciduous canine as an interceptive treatment in children with palatally displaced canines - part II: possible predictors of success and cut-off points for a spontaneous eruption.

Aim: To analyse factors affecting the success rate of palatally displaced canines (PDCs) and eruption time and to find cut-off points to predict when interceptive extraction is beneficial versus unnecessary.

Materials And Methods: Sixty-seven patients, 40 girls, 27 boys (10-13 years) with uni- (45) or bilateral (22) PDCs, persisting deciduous canine and no previous orthodontic treatment were randomly allocated for extraction or non-extraction using the block randomization method. There were no dropped out after the randomization or during the trial. Clinical examination and cone beam computed tomography was performed at 0, 6, and 12 months. Blinded measurements were done on baseline images.

Results: Erupted PDCs had a significantly smaller mesioangular angle, shorter distance of canine cusp tip-dental arch plane, and larger distance of canine cusp tip-midline, and the patients were younger compared to the non-erupted group. Faster eruption was noted of PDCs in the extraction group. Spontaneous eruption was achieved without prior deciduous canine extraction with cut-off points: initial canine cusp tip-midline of 11mm, canine cusp tip-dental arch plane of 2.5mm, or a mesioangular angle of 103 degrees. PDCs with a less favourable position, i.e. an initial cusp tip-midline of 6mm, a canine cusp tip-dental arch plane of 5mm, or a mesioangular angle of 116 degrees, will need surgical exposure despite interceptive extraction of the deciduous canine. The canine cusp tip-midline had the best predictive measure for assessing the outcome.

Limitations: Decision on where to place the cut-off points may differ from one operator to another, therefore results from several studies are needed to get average cut-off points.

Conclusions: Deciduous canine extraction is the variable that affects the spontaneous eruption of the canine most. Canine cusp tip-midline, canine cusp tip-dental arch plane, and mesioangular angle might be useful for distinguishing when an interceptive extraction of the deciduous canine is beneficial or when exposure of the PDC should be implemented without previous interceptive treatment.

Registration: This trial was registered in 'FoU i Sverige' (http://www.fou.nu/is/sverige), registration number: 40921.

Protocol: The protocol was not published before trial commencement.