Effectiveness of Invisalign® on Correcting Anterior Crowding and Spacing

Limited data are available on the effectiveness of clear plastic aligners (Invisalign®) in resolving maxillary and mandibular anterior crowding and spacing (MMACS). It has previously been demonstrated that Invisalign® effectively closes spaces and corrects anterior rotation. Conversely, data also suggest that Invisalign may be deficient in correcting large anteroposterior discrepancies. Objectives: The aim of this investigation was to study and quantify persistent MMACS after treatment with Invisalign®. Methods: Incisor crowding and spacing on pre- and post-treatment models was measured using OrthoCAD (Cadent; Carlstadt, NJ) and the Irregularity Index (Little, 1975). Cases were drawn from the OSU pre-doctoral and graduate orthodontic clinics. The inclusion criteria included pre-treatment and post-treatment maxillary and mandibular models and treatment plans that included resolving MMACS. Seventeen consecutive cases that met the inclusion criteria comprised the study sample. Pre-, post-treatment changes were analyzed using the Wilcoxon signed-rank test. The protocol was approved by the Institutional Review Board. Results: Reliability (intra-class coefficient, ICC, and 95% confidence intervals) of the repeat measurements on 5 sets of models was 0.99 (0.96-1.00) for total score and maxillary score (0.93-1.00) and 0.98 (0.87-1.00) for mandibular score. Mean overall Irregularity Index (crowding and spacing) was reduced from 6.50 to 0.37 (-94.8%, P<0.0001). Maxillary incisors demonstrated a mean reduction from 6.5 to 0.29 (-95.0%, range -100-56%; N=17, P<0.0001). Mandibular incisors demonstrated a mean reduction from 6.46 to 0.45 (91.4%, range: 100-42%, N=15, P<0.0001). Conclusions: This preliminary cohort demonstrates that clear plastic aligners (Invisalign®) appear to effectively reduce incisor crowding and spacing in most cases to very minor levels.