There was not a statistically significant difference between the ages of the Invisalign and braces groups. The mean age in the Invisalign group was greater than that in the braces group by almost 3 years. This discrepancy was expected because young adults are more likely to be interested in treatment with greater esthetics and comfort. However, tooth movement should be similar regardless of age with all other things being equal, such as periodontal condition and patient compliance.
Fixed appliances should have an advantage because of the ability to make precise wire adjustments within 0.5 mm to intrude or extrude teeth as necessary; it has been thought that removable aligners cannot be this accurate. Fixed appliances produced better treatment outcomes than Invisalign in orthodontist’s hands, given his level of expertise. Particularly important to the outcome of Invisalign is proficiency in using Align Technology’s Clincheck program that allows the practitioner to accept or modify the treatment plan of tooth movements before the aligners are actually fabricated (11
Interestingly, there was not a statistically significant difference between the treatment durations of the groups: 1.8 years for both patients. These data suggest that Invisalign treatment cannot be somewhat faster than fixed appliances. Moreover the final occlusion might not be as ideal (12
Arch form development and posterior expansion of the dental arches have been indicated as effects of low-friction mechanics with self-ligating brackets during the initial phases of treatment with superelastic nickel-titanium .014-in wires (13
). Our findings showed statistically more significant increases in maxillary arch perimeter with low-friction brackets than invisalign during treatment. No differences were found in maxillary arch depth between two groups. Statistically significant increases were found for all width measurements between the lateral and posterior teeth, with the exception of the first molars measured lingually only in braces group.
Increases in arch width that used lingual points for measurement were consistently smaller than the increases recorded by using points located at cusps or occlusal fossae.
The self-ligating system consent a significant increase in Intercanine widths (cusp) during treatment (3.15 mm), whereas the measurements at the lingual point was not statistically significant. The first interpremolar widths (lingual and cusp) had significant increases, while the changes in intermolar width at the lingual point and at the fossa were not statistically significant (0.90 mm and 0.30 mm, respectively). The arch dept and arch perimeter had not a statistically significant T2-T1 increase (1.30 mm and 1.90 mm).
This indicates that expansion of the maxillary arch in self-ligating group was achieved with a component of buccal inclination of canines and posterior teeth (14
The greatest transverse increases were recorded at the level of the premolars and the canines, whereas smaller increases were found at the level of the molars. A possible reason for this differential effect might be the shape of the archwires used for alignment of the maxillary teeth (Tru-Arch form); these have an accentuated width in the canine first premolar region (15
The significant increases in the transverse widths of the maxillary arch led to a statistically significant increase in maxillary arch perimeter (on average 3.5 mm), a clinically favorable result for nonextraction treatments.
The invisalign group showed not statistically significant changes in intercanine widths (lingual and cusp), and in the first interpremolar widths (lingual and cusp). The change in the second intermolar width at the lingual point was not statistically significant (0.30 mm).
A significant change in intermolar widths at the fossa was found (0.50 mm), while the measurement at lingual point was not significant (0.05 mm). The arch dept and arch perimeter had not a statistically significant T2-T1 increase (−0.05 mm and 0.00 mm).
No significant differences were found between the 2 groups for the intercanine widths at lingual point (0.75 mm), whereas the change at the cusp was significantly larger in the self-ligating group (2.65 mm).
The changes in arch dept and arch perimenter were not significantly different from T1 to T2.
In invisalign subjects there was not expansion in maxillary arch in all measurements considered.
Interproximal reduction was performed as prescribed, but no other modifications were made to augment tooth movement (16
). Therefore, the pass rate for Invisalign cases might be higher if more sophisticated techniques, such as auxiliaries, interarch elastics, or combination treatment with braces had been used. On the other hand, the braces patients were treated with tip-edge fixed appliances, which can make fine adjustments with uprighting springs, rotation springs, interarch elastics, and other auxiliaries in addition to the tooth movements made possible by the bracket prescription (17
However, there are several reasons that Invisalign might not be as effective as fixed appliances. Primary among them is compliance. Because the aligners are removable, the orthodontist must rely on the patient’s motivation and dependability to achieve the desired results. The removability of Invisalign is an advantage to the patient but not to the clinician. Another reason that Invisalign fails to compare with braces is that Invisalign minimally addresses the occlusion (18). Boyd et al. (16
) admitted that, when evaluating the occlusal outcome of an Invisalign case, it was evident that the same or an even better result could have been achieved with conventional braces in arguably less time.
Therefore, the major advantages of Invisalign over braces are that the aligners are esthetic, removable, and comfortable, but there are no biomechanical advantages.