Table 2.

Included studies regarding influence of composite attachment presence on movement efficacy.

Authors and Year	Type of the Study	Studied Phenomena	Subjects within the Study	Results and Clinically Relevant Conclusions
Ahmed et al. 2022 [21]	Finite element analysis	The influence of attachment positioning on movement efficiency (incisors intrusion/retrusion) and stress distribution	Model without attachments Model with labial attachments Model with palatal attachments Model with labial and palatal attachments	The most effective retraction was obtained by using palatal attachments. In the labial attachment model, the stress was concentrated in the middle third, while in all other models, this occurred in the cervical third. The model without an attachment generated the highest stresses. Placing the attachments on the labial surface can help avoid uncontrolled tipping.
Ayidağa et al. 2021 [22]	Finite element analysis	The influence of attachment shape on movement efficiency (molar distalization)	Models with no composite attachment Vertical rectangular attachment positioned on the buccal surface of the maxillary 1st molar Guideline attachment positioned on the buccal surface of the first maxillary molar.	All of the models were used to determine the effect on the periodontal ligament and the bone. The “no attachment” model was characterized by the lowest amount of desired translation on the y-axis and by the highest undesired distal tipping movement. In the rectangular attachment model, the tooth moved significantly more along the y-axis, with a smaller component of tipping and distal rotation. In the guided attachment model, the amount of movement along the y-axis was similar; however, there was the smallest range of undesired movements in the form of tipping or rotation. PDL was the point stress concentration in the first 2 groups, while in the guideline attachment group, the stress was equally distributed.
Cortona et al. 2020 [23]	Finite element analysis	The influence of attachment positioning on movement efficiency (molar rotation)	Without attachments Single vertical 3 mm attachment was placed on the buccal surface of element 45 Three vertical 3 mm attachments were placed on the buccal surfaces of teeth 44 to 46. In all three models, the activation of 1.2 degrees and 3 degrees per aligner was considered. In all models, an attempt was made to derotate the second premolar in the fourth quadrant.	The model with a single attachment on 45 and 1.2 degrees of aligner activation was the most efficient, followed by the three-attachment model (at the same degree of activation).Aligner activation should not exceed 1.2 degrees to achieve good control of movement and reasonable stress in periodontal structures.
Costa et al. 2020 [24]	In vitro experimental study	The influence of attachment shape and positioning on movement efficiency (incisor extrusion)	Three models were designed to evaluate which attachment design enables the most effective upper incisor extrusion Rectangle with 8 mm² on its gingival face and a 3 mm thickness from the dental surface to the frontal face A 2 × 4 × 1 mm3 cuboid, associated with two 0.87 × 4 mm2 rectangular planes angled at 45° with the cuboid surface A frontal face without edges and less protrusive, with a vestibular length of 3.32 mm	Different attachment geometries generate forces with significantly different intensities and directions. The third attachment had the best mechanical performance among the three models evaluated for extrusion.
Dai et al. 2019 [25]	Randomized controlled clinical trial	The influence of attachment shape and positioning on movement efficiency (premolar extraction space closure)	G6-optimized attachment on the first molar A 3 mm vertical rectangular attachment on the first molar A 3 mm horizontal attachment on the first molar A 5 mm horizontal attachment on the first molar	G6-optimized attachments, together with horizontal attachments, showed similar efficacy and control in molar angulation. The vertical attachment had the biggest difference between the planned and achieved tooth movement and showed the worst anchorage control (the highest degree of molar tipping).
Dasy et al. 2015 [26]	In vitro experimental study	The influence of attachment shape on aligner retention	Ellipsoid attachments (height: 3 mm, width: 2 mm, depth: 1 mm) Rectangular attachments, which were beveled toward the incisal edge (height: 2 mm, width: 3 mm, depth: 0.25 mm incisally and 1.25 mm gingivally). No attachments	The use of beveled attachments significantly increased retention. Ellipsoid attachments showed no significant effect on aligner retention with regard to an aligner with no attachments.
Fan et al. 2022 [27]	Finite element analysis	The influence of attachment positioning on movement efficiency (molar intrusion)	No attachment Buccal attachment Palatal attachment, Buccal and palatal attachments	The presence of an attachment is essential for clear aligners to intrude on the molars. Combined buccal and palatal attachments could effectively prevent buccal and palatal tipping and showed the best efficiency in terms of intruding on the molars. The second molar showed an unavoidable tendency to tip mesially, regardless of the attachment position. Thus, double attachment is advisable.
Ferlias et al. 2022 [28]	In vitro experimental study	The influence of attachment shape and positioning on movement efficiency (premolar rotation)	A total of 11 different types of attachment and one with no attachment Invisalign® “Bevelled” (Bevelled, 3.5 × 1.5 × 1 mm), “Horizontal Ellipsoid” (HEllipsoid, 3 × 2 × 1 mm), “Vertical Ellipsoid” (VEllipsoid 3 × 2 × 1 mm), “Elliptical Pair” (ElliPair, 2 × 2 × 1 mm/each), “Hemi-elliptical Right” (HemiEllipR, 2 × 2 × 1 mm), “Hemi-elliptical Left” (HemiEllipL, 2 × 2 × 1 mm), “Horizontal Rectangular Left” (HRecL, 3.5 × 1.5 × 1 mm), “Horizontal Rectangular Right” (HRecR, 3.5 × 1.5 × 1 mm), “Vertical Rectangular Down” (VRecDOWN, 3.5 × 1.5 × 1 mm), “Vertical Rectangular Up” (VRecUp, 3.5 × 1.5 × 1 mm). “3Shape® Box” (3Shape, 3.5 × 1.5 × 1 mm) “No Attachment”	The rotations above 1° generate moments that are too high from a clinical point of view. Aligner steps of no more than 1–1.5° should be recommended for effective derotation of a premolar. The vertical rectangular attachments perform best when derotating a premolar due to their large flat active surface but receive the most side effects in terms of tipping, torque and intrusive force. Derotation of a premolar without any attachment was less efficient despite showing the least side effects. When a premolar was mesially rotated, the attachment producing the highest intrusive force was 3Shape. When the tooth was rotated distally, most attachments again received an intrusive force, while the 3Shape attachment displayed an extrusive force. When the tooth was rotated mesially, all setups received a buccal root torque, with the highest seen with the vertical rectangular attachment and the smallest with the beveled one. In the other direction, for the distally rotated tooth, a moment of lingual root torque was observed in all setups.
Garino et al. 2016 [29]	Randomized clinical trial	The influence of attachment shape and positioning on movement efficiency (molar movement along a different axis)	A total of 30 non-growing patients in need of distalization after third-molar extraction. Rectangular composite attachments were placed on all distalized teeth from canine to second molar (five attachments per quadrant) Rectangular attachments were used only on the first and second premolars and the first molar (three attachments per quadrant)	Although the groups did not differ in the amount of distalization, minimizing distal crown tipping and preventing molar extrusion, minimizing anterior anchorage loss and reducing undesirable changes in lower facial height were more effective in patients with all five teeth bonded with attachments. This approach seems promising in patients in need of 2–3 mm of distalization.
Gomez et al. 2015 [30]	Finite element analysis	The influence of attachment presence on stress distribution (canine distalization)	No attachment model Two optimized ellipsoid optimized attachment models from a random Invisalign case	The displacement of the model with attachments was equivalent to typical distal bodily movement. The displacement of the model without attachments was equivalent to typical uncontrolled distal crown tipping, with almost no reaction of the root.
Karras et al. 2021 [31]	Retrospective cross-sectional study	The influence of attachment type (optimized vs. conventional) on movement efficacy	Included a total of 120 teeth arches, from which 163 teeth qualified for optimized rotation attachments (43%): 72 conventional rotation attachments (19%), 81 optimized extrusion attachments (21%) and 66 conventional extrusion attachments (17%)	For all tooth movements and attachment types, the mean predicted values were significantly larger than the mean achieved values. The least accurate tooth movement was mandibular canine extrusion with a conventional attachment (16.1%). The most accurate tooth movement was the extrusion of the maxillary central incisor with a conventional attachment (73.9%), followed closely by the rotation of the maxillary premolar with an optimized attachment (72.8%). Overall, the optimized attachments enabled achieving better results in terms of rotation movement, while conventional attachments performed better in extrusion movements.
Kim et al. 2020 [32]	Finite element analysis	The influence of attachment shape and positioning on movement efficiency and stress distribution (lower canine rotation)	A virtual model with two attachments on the lower canine. The shape of the attachment for rotation had a plane perpendicular to the direction of rotation with the surfaces to which the load was applied. The models were classified as having angles of 90 degrees, 65 degrees and 45 degrees to the attachment surface of the teeth. There were four types of attachments for the torque tested; four shapes were half round, half round at the cross-section, half round at the cross-and longitudinal sections, and a lower bevel of 45°.	A desirable stress distribution was observed when there was a high contact area between the attachment and the aligner. Torque control and intended movement were achieved when the attachments were positioned on the lingual surface rather than on the buccal surface of the canines; thus the attachment used in the aligner treatment of the rotated canine is a cylinder form bonded to the lingual surface of the canine. In intrusion, a better control of the movement is achieved by bonding attachments to both the buccal and lingual surfaces of the canine.
Kravitz et al. 2008 [33]	Randomized clinical trial	The influence of attachment shape and positioning on movement efficiency (canine rotation)	No attachments Interproximal reduction without attachments Canines with attachments without IPR	Vertical, ellipsoid attachments and interproximal reduction do not significantly improve the accuracy of canine rotation with the Invisalign system.
Laohachaiaroon et al. 2022 [34]	Finite element analysis	The influence of attachments shape on movement efficiency and stress distribution (upper central incisors extrusion)	Without any composite attachment Rectangular beveled attachment on the labial surface of the central and lateral incisors Ellipsoid attachment on the labial surface of the central and lateral incisors Horizontal rectangular attachment on the labial surface of the central and lateral incisors	When considering the incisal edge as a reference, the model with the horizontal rectangular attachment had the greatest extrusive movement (0.037991 mm) followed by the model with the ellipsoid attachment (0.037606 mm) and the model with the rectangular beveled attachment (0.036786 mm). The model without a composite attachment demonstrated little intrusive movement (0.000105 mm). The differences were very small and were not clinically significant. The stress patterns were also similar in all three attachment models.
Rossini et al. 2020 [35]	Finite element analysis	The influence of attachment use on movement efficiency and stress distribution (maxillary second molar distalization)	No attachments Vertical 3 mm vertical attachments from the canine to the first molar Vertical 3 mm vertical attachments from the canine to the second molar	The attachments are mandatory to control the bodily movement of a second molar. Attachments should be used to reinforce the anchorage units and to function as active units on sequential distalizing molars. The configuration of attachments in the whole segment, from the canine to the 2nd molar, represents the most promising model for Class II correction via maxillary molar distalization.
Rossini et al. 2021 [36]	Finite element analysis	The influence of attachment presence on movement efficiency and stress distribution (incisors extrusion)	Without attachments Horizontal rectangular attachments only on incisors Rectangular attachments from the second molar to the canine Rectangular attachments from the second molar to the canine used together with optimized extrusion attachments on incisors Rectangular attachments from the second molar to the canine used together with rectangular buccal horizontal attachments on the incisors Rectangular attachments from the second molar to the canine used together with rectangular palatal horizontal attachments on the incisors	The presence of 3 mm rectangular horizontal attachments on the buccal or palatal surface of the upper incisors with additional rectangular vertical attachments in the lateral from the canine to the second molar seemed to produce the most efficient force system to extrude incisors with minimal aligner deformation. Standard attachments seem to be more accurate than optimized ones. The most efficient configurations showed the need for the use of attachments on posterior teeth in order to obtain better anchorage.
Savignano et al. 2019 [37]	Finite element analysis	The influence of attachments on movement efficiency and stress distribution during upper incisors extrusion	Without attachments Horizontal rectangular palatal attachment Horizontal rectangular buccal attachment Ellipsoid buccal attachment	The extrusion of an upper central incisor cannot be achieved without any attachment. There was no clear difference between the rectangular and ellipsoid attachments. The position of the attachment showed a stronger influence on the outcome compared to the shape (palatal instead of buccal).
Simon et al. 2014 [38]	Retrospective cross-sectional study	The influence of attachment shape and positioning on movement efficiency (incisors torque, lateral teeth derotation and distalization)	Patients treated with the use of an attachment Patients with no auxiliaries were used (except incisor torque, in which Power Ridges were applied)	The use of attachments can significantly improve the efficiency of planned tooth movement. However, clinically planned movements are rarely completed. The crucial factors that influence the efficiency of aligner therapy are patient compliance and the reasonable, split staging of planned moves <1.5° of rotation per aligner, 1° aligner for incisor torque and up to 0.25 mm/aligner for distalization. Invisalign treatment usually needs refinements to achieve planned positions of the teeth.
Smith et al. 2022 [39]	Retrospective cross-sectional study	The influence of attachments on tooth movement efficiency (lower incisor tipping)	66 lower incisors in 42 non-extraction aligner patients A total of 21 incisors with vertical attachments A total of 45 incisors without any attachments	It is possible to move roots using Invisalign® but not as predictably as ClinCheck® suggests. Moreover, the average amount of root movement achieved was substantially less than predicted. Vertical rectangular attachments are recommended when a large range of root movement is planned. Attachments improve the possibility of translating the root apex.
Takara et al. 2022 [40]	In vitro experimental study	The influence of attachment shape on aligner retention	A total of 22 different models with 11 different types of attachments were placed on the lateral incisors or the first premolars and included a model with no attachments	Attachments significantly increase aligner retention. The easiest way to remove an aligner is from the lingual side of the first molar. It is difficult to remove the aligner by trying to lift it in the area of the incisors. However, the attachment on the lateral incisor may not contribute to the gripping force of the aligner when it is removed by lifting on the labial surface of the upper first molar. The retention of the aligner is influenced by the height, width and angulation of the attachment. The retention is superior when the bevel angle is close to the right angle.
Yokoi et al. 2019 [41]	Finite element analysis	The influence of attachment shape and positioning on movement efficiency (diastema closure)	No attachment Double contrary attachments on the labial surface of the central incisor	The use of attachments limited unplanned root movement and tooth tipping, increasing the effectiveness of diastema closure. In the aligner used with the attachments, the incisor overlapped completely on the target position in FEM, meaning that the efficacy of movement was almost 100%. However, the attachment did not influence the initial movement of the tooth, showing significant differences with an ongoing time simulation.