Long‐term stability of curve of Spee depth among orthodontically treated patients: A retrospective longitudinal study

Abstract Objective The curve of Spee is deemed important characteristic of the dentition for a balanced occlusion and distribution of masticatory forces, while orthodontic levelling of an accentuated curve of Spee is generally included as a treatment goal for deepbite correction. However, relapse is often seen and can be problematic. Methods A retrospective longitudinal study of predominantly young patients with a deep curve of Spee, who had been treated orthodontically with 0.018”‐slot Edgewise fixed appliances, was performed. The depth of the curve of Spee was digitally measured before treatment (T1), at debond (T2), and an average of 7 years post‐debond (T3) and analysed statistically at 5%. Results A total of 157 patients were included (56.7% female; 11.6‐year‐old at T1), 16.6% of which were treated with premolars extractions. Non‐extraction treatment reduced the curve of Spee at the first premolar from 1.87 mm (T1) to 0.22 mm (T2), which relapsed 0.12 mm (T3; P = .04). The respective depths for the second premolar were 2.0 mm (T1), reduced to 0.80 mm (T2). No significant relapse was seen for the second premolar (0.08 mm; P > .05) or the first permanent molar (0.06 mm; P > .05). No overall significant differences in absolute relapse were seen between extraction and non‐extraction patients, but premolar extractions were associated with less clinically relevant relapse at the first molar (odds ratio 0.27; 95%‐confidence interval 0.08‐0.88; P = .003). Conclusion Steep curves of Spee can be satisfactorily levelled orthodontically with satisfactory stability in the long term, while premolar extractions might be associated with less relapse.