Development of the curve of Spee in Class II subdivision malocclusion: a longitudinal study

To compare the depth of curve of Spee (COS) in Class I and II sides of Class II subdivision malocclusion longitudinally and to describe the changes in the COS in relation to dental arch over time.

The study group comprised 17 subjects exhibiting Class II subdivision malocclusion. The depth of COS, intermolar width, distances from mesial anatomic contact points of the first permanent molars to the contact point of the central incisors in Class I and II sides and arch length in mandible were analysed on digital models in three different time points based on cervical vertebral maturation (T1; mean age: 12.4 years, T2; mean age: 15.1 years, and T3: mean age: 19.1 years). Pearson's correlation coefficients were calculated and linear multiple regression analysis with enter method was carried out.

No significant differences were found in the depth of COS between Class I and II sides in all time periods. The mesiobuccal cusp of the first molar was the deepest part of COS in both sides and in all time periods, with a maximum depth of 2.37±0.83mm in T1 and a minimum depth of 1.91±0.66mm in T3. Between baseline and final follow-up; the depth of COS, ach length, and distance in Class I side decreased significantly. Arch length had a significant correlation with the depth of COS (r = 0.471) in T3.

As the depth of COS did not differ between either the Class II or I sides, the same mechanics can be used to level the COS in either sides of the mandibular arch.