Relationship between incisor irregularity and ectopic position of permanent canines : A 3D model-based...

The aim of this study was to investigate whether the severity of incisor irregularity is associated with the buccal, palatal/lingual, or normal positions of fully erupted upper or lower permanent canines in three dimensional (3D) digital models.

This cross-sectional study included 288 individuals aged 13.2-15.3 years with skeletal class I malocclusion. Incisor irregularity was assessed using Little's irregularity index (LII), which quantifies the linear displacement of anterior contact points. Canine eruption positions in the upper and lower jaw were classified as normal, buccal or palatal/lingual. All measurements were performed digitally on calibrated 3D intraoral scans. Associations between canine position, irregularity severity, and gender were analyzed using χ² tests. A priori power analysis was conducted (effect size w = 0.51, α = 0.05, power = 0.95).

In the maxilla, normally positioned canines were most frequently associated with 0-3 mm of incisor irregularity (59.6%), and this proportion decreased progressively as irregularity increased. Buccal displacement became more common at higher irregularity levels, particularly ≥ 7 mm. In the mandible, 69.8% of normally positioned canines were also observed in the 0-3 mm group, whereas buccal displacement was mainly associated with 4-6 mm (60%) and 7-9 mm (32%) irregularity; lingual displacement was rare. Although the distribution patterns differed between arches, no significant gender-related differences were identified (p > 0.05).

The severity of incisor irregularity is significantly associated with ectopic canine eruption, especially when irregularity exceeds 4 mm. Early diagnosis and monitoring of anterior irregularities of more than 4 mm may require specific clinical monitoring and timing of orthodontic assessment.