Maxillary expansion with clear aligners in the mixed dentition: a preliminary study with invisalign® first system

Maxillary transverse discrepancy is one of the most common and detrimental problems associated with facial growth and the overall integrity of the dentoalveolar structure. It is characterized by posterior cross-bite that may be unilateral or bilateral, total or partial. Problems such as crowding, deep and narrow palate, and dark spaces in the buccal corridor are frequently associated with transverse maxillary deficiency.

As with most skeletal deformities of the craniofacial region, transverse discrepancies are also a challenge to rehabilitate and almost impossible to do in adults without the combined intervention of orthodontics and surgery. This is a major reason why experts recommend maxillary deficiencies be detected and treated before or during the adolescent growth spurt.

For over a century, these maxillary deficiencies have been corrected with the help of a procedure known as maxillary expansion. As can be relayed from the name, this procedure uses an external appliance to expand the arch perimeter and alter the anatomy so that the discrepancy is corrected. In the last decades, an increasing number of individuals, mainly teens have been seeking a more aesthetic approach to orthodontics.

As if on cue, in 2018, Align Technology Inc., the company behind the sensational Invisalign® aligners introduced their newest product specifically targeting younger patients in the early mixed dentition phase. The Invisalign® First clear aligners were originally designed to allow orthodontists to perform phase I orthodontic treatment, including the correction of a narrow maxillary arch.

But no literature before now has ever evaluated maxillary expansion with this treatment option, especially in patients with early mixed dentition. This study strives to change that.

This study was conducted by a team from Italy and published in the Europen Journal of Paediatric Dentistry.

Maxillary expansion with clear aligners in the mixed dentition: A preliminary study with Invisalign® First system

Levrini L, Carganico A, Abbate L.

Eur J Paediatr Dent. 2021 Jun;22(2):125-128. doi: 10.23804/ejpd.2021.22.02.7.

What they asked

The authors aimed:

“To evaluate dentoalveolar changes in patients treated with Invisalign® First clear aligners in the mixed dentition focusing on maxillary arch width, arch perimeter, arch depth, molar inclination and alveolar expansion.”

What they did

This was a retrospective study with:

• Participants: 20 patients (12 females and 8 males) between 6 and 12 years (mean age was 8.9 years) with mixed dentition.
• Intervention: Planned arch expansion with Invisalign® First treatment.

The first aligner was worn for 14 days and then aligners were changed weekly. The mean number of aligners used in this study was 33 and the average treatment time was 8 months.

Pre-treatment (T0) and post-treatment (T1) dental digital models were obtained using an iTero® intraoral scanner in order to compare arch changes. The following measurements were recorded:

1. Arch width

(i) Canine gingival width (PC)

(ii) First deciduous molar gingival width (PD)

(iii) Second deciduous molar gingival width (PE)

(iv) First permanent molar gingival width (P6)

(v) Canine dental width (DC)

(vi) First deciduous molar dental width (DD)

(v) Second deciduous molar dental width (DE)

1. Arch perimeter (AP)
2. Arch depth (AD)
3. Intermolar angle (IMA)

The superimposition of 3D digital maxillary models was performed using palatine rugae in order to evaluate the alveolar expansion.

What they found out

They also calculated the average and standard deviations for all measurements. Paired t-test was run to report significant changes between T0 and T1. All measured values showed a statistically significant variation between T0 and T1 (p-value<0.05). In particular, the intercanine width showed an average increase of 2.8 mm at the cusp tips and 2.01 mm at the gingival level.

Overall, there were significant increases in all measurements pertaining to the arch width and arch perimeter. However, they found that the arch depth and molar inclination significantly decreased. The alveolar expansion was recorded at all of the reference points and the Shapiro-Wilk test was done to check normal distribution.

What we can conclude

This review highlighted the advantages of clear aligner systems like Invisalign®, especially in terms of correcting mild crowding or limited transverse maxillary deficiency. Invisalign® First clear aligners could be a reasonable alternative to traditional slow maxillary expanders, however, further studies are required to confirm these findings.