# Predictability of Maximly Expansion with Invisalign(r) First: Treatment Planning vs. Outcome
## 2 Materials and Methods  
This study has been developed following the ethical standards established in the Declaration of Helsinki in 1975. Every participant provided informed consent and agreed to the privacy policy for the protection of personal data.  
A sample of 64 subjects was required (statistical power set at 0.8). In this retrospective research, the sample consisted of 64 patients treated with Invisalign(r) First (Align Technology Inc., Tempe, AZ, USA) for maxillary expansion. The first aligner was worn for 14 days, and then aligners were changed weekly. The inclusion criteria were as follows: patients between 6 and 12 years old, mixed dentition, fully erupted maxillary first molar, at least 1 mm of maxillary expansion required, and complete diagnostic records. Patients with previous orthodontic treatment, requiring extraction, with craniofacial abnormalities, or with systemic syndromes were excluded.  
Figure 1: Anterior crossbite correction achieved with Invisalign® First clear aligners.  
For all of the patients, digital impressions were recorded with an iTero(r) intraoral scanner (Align Technology Inc., Tempe, AZ, USA) at the beginning and at the end of the treatment. Treatment was planned with the ClinCheck(r) software (Align Technology Inc., Tempe, AZ, USA), and the final desired outcome was digitally designed. To investigate whether the outcome designed with the ClinCheck(r) software was obtained during orthodontic treatment, the.stl files of the predicted outcomes were compared to the final scansion recorded on the patients at the end of the treatment. No further finishing phase was considered.  
The following parameters were considered (Figure 2).  
Deciduous canine gingival diameter: Linear distance measured between the center of the palatal surface of the upper canines in contact with the gingival margin.  
First deciduous molar gingival diameter: Linear distance measured between the center of the palatal surface of the first deciduous upper molars in contact with the gingival margin.  
Second deciduous molar gingival diameter: Linear distance measured between the inner point of the palatal surface of the first deciduous upper molars in contact with the gingival margin.  
First permanent molar gingival diameter: Linear distance measured between the inner point of the palatal surface of the first permanent upper molars in contact with the gingival margin.  
Deciduous canine cuspidal diameter: Linear distance measured between the cusp tips of the upper deciduous canines.  
First deciduous molar cuspidal diameter: Linear distance measured between the cusp tips of the deciduous upper first molars.  
Second deciduous molar cuspidal diameter: Linear distance measured between the mesio-buccal cuspids of the second deciduous upper molars.  
First permanent molar cuspidal diameter: Linear distance measured between the mesio-buccal cuspids of the first permanent upper molars.  
These measurements were taken on the ClinCheck(r), developed at the beginning of the treatment to create the treatment plan, and on the intraoral scansion of the patients recorded at the end of the treatment.  
Statistical analyses was carried out. A Shapiro-Wilk test was used to verify whether the data were normally distributed. All measurements were calculated as average and standard deviations. A paired \(t\)-test was run to report any significant changes between measurements from the planned ClinCheck(r) and the achieved results at the end of the treatment. The statistical significance was set to \(p<0.05\). On 20% of the sample, measurements were taken twice by the same operator after 14 days. The intraclass correlation coefficient  
Figure 2: Linear measurements considered on the ClinCheck® software and on the digital scansions. Transversal diameters were measured at the cuspidal level (in black) and at the gingival level (in green).  
(ICC) was used to assess reliability, showing a high degree of reliability (ICC > 0.98 for all measurements).