Table 3.

Data extraction of included studies

	Authors (Year)	Trimline variation	Outcome assessment	Tooth studied	Objectives	Study design	Key findings	Risk of bias
1	Lyu et al. (2022) [33]	1. Scalloped − 2 mm 2. Scalloped 0 mm 3. Scalloped 2 mm 4. Straight − 2 mm 5. Straight 0 mm 6. Straight 2 mm	Tooth movement: En-masse retraction	Whole maxillary arch	To assess the effects of gingival margin design on force expression and stress distribution during upper en-masse retraction in extraction treatment.	Finite element study	Aligners with a margin height of -2 mm showed significantly lower stress, particularly with scalloped cuts. Straight margin aligners generated higher stress than scalloped ones, but the difference was less pronounced at a 2 mm height.	Moderate
2	Elshazly et al. (2023) [34]	1. Scalloped 0 mm 2. Scalloped 2 mm 3. Straight 0 mm 4. Straight 2 mm	Tooth movement: Palatal translation	Tooth 11	To assess the effects of gingival margin designs on forces delivered by orthodontic aligners during the bodily movement of the maxillary central incisor.	Finite element study	Aligners with straight margins exerted higher forces than those with scalloped margins, with force increasing as margin extension increased.	Moderate
3	Elshazly et al. (2024) [23]	1. Scalloped 0 mm 2. Scalloped 2 mm 3. Straight 0 mm 4. Straight 2 mm	Tooth movement: Palatal translation	Tooth 11	To investigate the impact of gingival margin designs on the biomechanical behavior of orthodontic aligners.	Finite element study	Aligners with straight extended margins positively impact force distribution and control of tooth movement.	Moderate
4	Elshazly et al. (2024) [35]	1. Straight 0 mm 2. Straight 2 mm	Tooth movement: Facial translation, distalization, and extrusion	Tooth 11	To investigate the impact of trimming line designs on the biomechanical performance of orthodontic aligners.	Finite element study	Aligners with straight extended margins provide better control of tooth movement and can serve as an alternative to attachments in some cases.	Moderate
5	Karsli et al. (2024) [36]	1. Straight 0.5 mm 2. Straight 2 mm	Tooth movement: Arch expansion	Maxillary first and second molars	To evaluate the effects of different trimline extensions on maxillary first and second molars during arch expansion.	Finite element study	Aligners with high trimline reduced buccal tipping of maxillary molars during arch expansion.	Moderate
6	Karsli et al. (2024) [37]	1. Straight 0.5 mm 2. Straight 2 mm	Tooth movement: Utilization of Class II inter-maxillary elastic	Mandibular anterior teeth and molars	To evaluate the effect of trimline extension of orthodontic aligners when combined with Class II intermaxillary elastics.	Finite element study	Aligners with high trimlines effectively controlled mandibular incisor proclination and mesial tipping of mandibular molars during clear aligner treatment with Class II elastics.	Moderate
7	Gao et al. (2017) [38]	1. Scalloped 0–1 mm 2. Straight 3–4 mm 3. Straight 6–7 mm	Tooth movement: Palatal tipping and intrusion	Tooth 11	To assess the effects of gingival margin height on the force system from orthodontic aligners during tipping and intrusion of the maxillary central incisor.	Force and moment sensors	Aligners with longer margins (3–4 mm and 6–7 mm) deliver significantly greater intrusion force and tipping moment than edgeless aligners. No significant difference in force or moment was observed between the 3–4 mm and 6–7 mm aligners.	Moderate
8	Brown et al. (2021) [39]	1. Scalloped 0 mm 2. Straight 0.75 mm 3. Straight 1.5 mm	Tooth movement: Palatal root movement	Tooth 21	To assess the effects of gingival margin design on strain distribution and force system from orthodontic aligners during labial tipping of the maxillary central incisor.	Force measuring device, and Digital Image Correlation (DIC)	Bucco-lingual force and root torquing moment from aligners vary significantly by margin design, with greater differences between straight and scalloped designs than among straight cut heights. The impact of varying gingival margins on force output is 20–50%.	Low
9	Elshazly et al. (2022) [24]	1. Scalloped 0 mm 2. Scalloped 2 mm 3. Straight 0 mm 4. Straight 2 mm	Tooth movement: Palatal translation	Tooth 11	To assess the effects of gingival margin designs on stress distribution and forces from orthodontic aligners during the bodily movement of the maxillary central incisor.	Pressure-sensitive film	Aligners with straight extended margins exhibited the highest active force, active pressure, and passive pressure, delivering more uniform force transfer and stress distribution compared to scalloped margins. Significant differences in force and pressure were particularly noted at the cervical area of the tooth.	Moderate
10	Traversa et al. (2024) [40]	1. Straight 0 mm 2. Straight 2 mm	Tooth movement: Palatal translation, mesial translation, intrusion	Tooth 11, 13, 16, and neighboring teeth	To report the biomechanical performance of orthodontic aligners with varying trimline heights during three types of translational tooth movements.	Orthodontic force simulator	Aligners with high trimline enhances control over orthodontic movements.	Low
11	Cowley et al. (2012) [22]	1. Scalloped 0 mm 2. Scalloped 2 mm 3. Straight 0 mm 4. Straight 2 mm	Retention	Whole maxillary arch	To evaluate the impact of gingival margin design on orthodontic aligner retention.	Laboratory setting: Retentive pull-off test	Aligners with 2 mm straight margins showed significantly higher retention than scalloped margins at the same height, while 0 mm aligners exhibited no significant difference between straight and scalloped margins.	Low
12	Takara et al. (2022) [41]	1. Straight at HOC 2. Straight 0 mm 3. Straight 2 mm	Retention	Whole maxillary arch	To assess the impact of gingival margin height on orthodontic aligner retention.	Laboratory setting: Specific measuring device	Aligners with longer margins show significantly higher retention.	Low