Table 4.

Analysis of the results (grouped according to the type of movement).

	Study	Type of Study	Aim	Study Design	Results
Anterior B-L tipping/Root torque	Simon et al. [21]	Retrospective CCT	Verification of the effectiveness of the Invisalign treatment by comparing clin-check with the obtained results. Analysis of the influence of attachments and power-ridges, patient compliance and staging (amount of movement per aligner) on treatment efficacy.	30 patients (11 M–19 F) reduced to 26. Age: 32.9 3 configurations: -Incisors with attachments or power-ridges -Premolars with or without attachments -Molars with or without attachments	Incisor torque showed positive results, both with an horizontal ellipsoid attachment on upper central incisors and with power ridges. A torque loss (up to 50%) is a common finding during incisors retraction.
	Garino et al. [16]	RCT	Verification of the influence of the number of attachments on the amount of upper molar distalization	30 patients with class II malocclusion (12 M–18 F) Age: 30.5 3 configurations: -Group C1—5 attachments per quadrant -Group C2—3 attachments per quadrant -Group C—Control	The greatest distalization of central incisors was obtained in C1 group.
	Dai et al. [23]	Case Series	Comparison between predicted and achieved tooth movements of maxillary first molars and central incisors in extraction cases treated with Invisalign.	30 patients (4 M–26 F) Age: 19.4 ± 6.3 First premolar extraction cases treated with Invisalign. Three variables considered: - Age -Type of attachment -Initial crowding	In case of anchorage loss of posterior teeth, the amount of incisors bodily movement in lingual direction was lower than expected, while inclination increased in the same direction. In particular, 3 mm vertical rectangular attachment, located on the maxillary first molar, showed the least efficacy in anchorage control, compared to horizontal attachments (3 or 5 mm) and optimized G6 attachments.
Intrusion	Durrett [20]	RCT	Analysis of the influence of attachments during: -canine and premolar rotation; -incisors, canines and premolars intrusion and extrusion. Comparison between different attachment configurations.	99 patients reduced to 86 Age: 18+ 6 configurations: -5 groups with different attachments -1 control group (without attachments) 2 groups: -Extraction and non-extraction cases	All the attachment groups showed a greater efficiency compared to the control group. The greatest efficiency and degree of correlation was shown by group F, characterized by a vestibular attachment with a poliedric shape.
	Dai et al. [23]	Case Series	Comparison between predicted and achieved tooth movement of maxillary first molars and central incisors in extraction cases treated with Invisalign.	30 patients (4 M–26 F)Age: 19.4 ± 6.3First premolar extraction cases treated with Invisalign. Three variables considered:- Age- Type of attachment- Initial crowding	First molars achieved greater intrusion than predicted. The group with the optimized G6 attachments showed a greater difference between predicted and achieved tooth movement compared to the other groups.
Extrusion	Durrett [20]	RCT	Analysis of the influence of attachments during: -canine and premolar rotation; -incisors, canines and premolars intrusion and extrusion. Comparison between different attachment configurations.	99 patients reduced to 86 Age: 18+ 6 configurations: -5 groups with different attachments -1 control group (without attachments) 2 groups: -Extraction and non-extraction cases	No statistically significant differences were found among the analyzed groups The group with an ovoid attachment on the buccal face, showed the greatest efficiency. However, the small number of the sample didn’t allow to draw clear conclusions.
Rotation	Simon et al. [21]	Retrospective CCT	Verification of the effectiveness of the Invisalign treatment by comparing clin-check with the obtained results. Analysis of the influence of attachments and power-ridges, patient compliance and staging (amount of movement per aligner) on treatment efficacy.	30 patients (11 M–19 F) reduced to 26. Age: 32.9 3 configurations: -Incisors with attachments or power-ridges -Premolars with or without attachments -Molars with or without attachments	No significant differences were found among the analyzed groups. The effectiveness was reduced for predicted rotations greater than 15° and for movements greater than 1.5° per aligner.
	Kravitz et al. [22]	Prospective CCT	Evaluation of the influence of attachments or IPR on canine rotation (comparison between predicted and achieved results)	38 pazients reduced to 31 (13 M–18 F) Age: 29.4 3 configurations: -Attachment only group (AO) -Interproximal-reduction only group (IO) -Group without attachments (N)	No significant differences were found between groups with and without attachments. The IO group performed better than the other ones, because it allowed the creation of space for movement.
	Durrett [20]	RCT	Analysis of the influence of attachments during: -canine and premolar rotation; -incisors, canines and premolars intrusion and extrusion. Comparison between different attachment configurations.	99 patients reduced to 86 Age: 18+ 6 configurations: -5 groups with different attachments -1 control group (without attachments) 2 groups: -Extraction and non-extraction cases	Conflicting results were found between groups that required or not required a “reboot”. In the non-rebooted patients, group C (without attachments) achieved a greater degree of rotation than group F (with a vestibular attachment). In the rebooted patients, on the other hand, the attachment groups were more effective than the control one, except for the group with a vestibular and a lingual attachment. Larger attachments with sharper edges seem to be more effective.
M-D Movement	Simon et al. [21]	Retrospective CCT	Verification of the effectiveness of the Invisalign treatment by comparing clin-check with the obtained results. Analysis of the influence of attachments and power-ridges, patient compliance and staging (amount of movement per aligner) on treatment efficacy.	30 patients (11 M–19 F) reduced to 26. Age: 32.9 3 configurations: -Incisors with attachments or power-ridges -Premolars with or without attachments -Molars with or without attachments	Molar distalization was more effective than the other movements, regardless to the use of attachments (average accuracy of 88.4% for the attachment group and 86.9% for the group without attachments).
	Dai et al. [23]	Case Series	Comparison between predicted and achieved tooth movements of maxillary first molars and central incisors in extraction cases treated with Invisalign.	30 patients (4 M–26 F)Age: 19.4 ± 6.3 First premolar extraction cases treated with Invisalign. Three variables considered:- Age- Type of attachment- Initial crowding	The study highlighted a loss of posterior anchorage: the 3-mm vertical rectangular attachment showed the worst clinical outcome. On the other hand, the G6-optimized attachments and the horizontal rectangular ones seem to be more effective in counteracting mesial tipping.
	Garino et al. [16]	RCT	Verification of the influence of the number of attachments on the amount of upper molar distalization	30 patients with class II malocclusion (12 M–18 F) Age: 30.5 3 configurations: -Group C1—5 attachments per quadrant -Group C2—3 attachments per quadrant -Group C—Control	The number of attachments seems to play play an important role: group C1 (with attachments bonded on the surface of five teeth) showed greater first molar distalization and central-incisor retraction, compared to the other groups. No significant differences were found regarding the efficacy of second molar distalization among the attachment groups.