Table 1.

Characteristics of included studies.

Author and Year	Type of Article	Study Groups	Method	Outcome Measured	Results
Kim et al. 2011 [25]	Prospective randomized animal study with in-vitro analysis	24 tapered mini-implants of 5 mm length 24 cylindrical mini-implants of 7 mm length	Insertion and removal torque test in rabbit bone	Insertion and Removal torque values [N/cm]	Despite the fact that the tapered implants were shorter, they presented higher torque values than cylindrical at each time of the test.
Topcuoglu et al. 2013 [26]	Prospective randomized animal study with in-vitro analysis	4 groups of 20 immediately loaded Ti6Al4V OMIs with interpitch distance of I—0.694 mmm, II—0.721 mm, III—0.693 mm and IV—0.702 mm inserted into rabbit fibula 4 groups of 20 unloaded Ti6Al4V OMIs with interpitch distance of I—0.694 mmm, II—0.721 mm, III—0.693 mm and IV—0.702 mm inserted into rabbit fibula	Removal torque test, SEM, and histomorphometric analyses in rabbit bone	Removal torque values [N/cm]	More frequent thread pitch had a positive effect on stability in every group studied. I—8.50 (2.41–10.05) 8.10 (4.94–9.35) II—6.92 (2.76–8.48) 4.63 (3.53–8.59) III—6.27 (3.99–9.87) 4.59 (2.26–5.57) IV—5.78 (4.17–7.95) 4.10 (2.59–5.53)
Chang et al. 2012 [27]	3D finite element analysis	Four types of titanium grade V OMIs with different design parameters Screw type 1 had a 0.4-mm thread depth and a 7 tapered core at the 5 uppermost threads. Screw type 2 had a 0.4-mm thread depth and a 0 tapered core (cylindrical core). Screw type 3 had a 0.4-mm thread depth and a 7 tapered core at the 3 uppermost threads. Screw type 4 had a 0.32-mm thread depth and a 7 tapered core at the 3 uppermost threads. To evaluate the effect of thread depth on primary stability, the thread depths of the mini-implants were set at 0.16, 0.24, 0.32, 0.40, and 0.48 mm;	Assessment of possible mini-implant insertion torque stress and of displacement within the trabecular bone	Maximum insertion torque [Ncm], Pullout strength (N), Displacement before failure (mm), Stiffness (N/mm)	Mini-implants with greater thread depths, smaller tapers, and shorter taper lengths generated higher maximum stresses on the bone and thread elements. These mini-implants had larger relative displacements, as well. Pullout resistance increased as thread depth increased from 0.16 to 0.32 mm. However, the pullout resistance decreased as thread depth exceeded 0.32 mm. Pullout resistance also decreased as taper degrees and taper lengths decreased. High stresses were distributed on the uppermost threads at the neck of the mini-implants close to the bone margin in all conditions. Maximum insertion torque was observed in the first and the third OMIs.
Shen et al. 2014 [28]	3D finite element analysis	9 samples of titanium grade V mini-implants of thread heigh of 0.1 mm, 0.25 mm and 0.4 mm height and thread pitch of 0.5 mm, 1.20 mm, and 2 mm.	3D finite element analysis of type III bone according to the Lekholm & Zarb classification (maxillary posterior region)	Maximum equivalent stresses	Increased thread height with a thread pitch of 1.20 mm was superior for the maxillary posterior region. Thread height proved more important for reducing maxillary stress and enhancing orthodontic mini-implant stability than the thread pitch.
Dastenaei et al. 2015 [29]	3D finite element analysis	Titanium grade V OMI of diameter 1.6 mm, length 8 mm, thread pitch of 0.75 mm, thread depth of 0.25 mm and thread height of 0.331, tip angle 63°	Assessment of stress points within the implant inserted to trabecular bone	Maximum equivalent stresses	Stress concentration usually occured at the first thread of the implant. Stress decreased when screw pitch decreased from 1 to 0.5 mm; it was concentrated at the apex of the threads. The stress increased when the screw pitch became less than 0.45 mm and the stress distribution pattern was sparse. It seems appropriate to create a new dual miniscrew design that can provide ergonomic aims, with bigger thread pitch at the apex and smaller on threads neck.
Pouyafar et al. 2021 [30]	3D finite element analysis	Series of test leading to optimal design of OMI	Assessment of possible mini-implant displacement within the trabecular bone	The lateral displacement measurement [µm]	The conical section improved the initial stability by creating compressive stress and additional friction in the surrounding bone. With increasing each millimeter and each degree in the conical section’s length and angle, the lateral displacement decreased by 2.3 and 1.8mm, respectively. The length and angle of the non-threaded part does not significantly control the lateral displacement. The higher the pitch of the mini-implant, the higher the lateral displacement (increases by 1.3– 2.2mm). It is necessary to consider the minimum possible value for the pitch according to the threads’ shape.
Kim et al. 2009 [31]	In-vitro study	Titanium grade V (10 of each group) 6 mm cylindrical, 8 mm cylindrical, 6 mm taper, 8 mm taper, 6 mm dual-thread and taper and 8 mm dual-thread and taper	Mechanical assessment of toque in artificial bone block from polyurethane foam block	Insertion torque (MIT), maximum removal torque (MRT), torque ratio (TR; MRT/MIT), insertion angular momentum (IAM), removal angular momentum (RAM)	The removal torque of the taper shape was lower than the removal of torque of the dual-thread shape. The dual-thread shape showed a low insertion torque and a gentle increase of insertion torque. The dual-thread shape also showed a higher removal torque on the broad range than the cylindrical and taper shapes. Long mini-implants need higher insertion torque than short mini-implants. Dual-thread shape may need improvement for reducing the long insertion time to decrease the stress to the surrounding tissue.
Gracco et al. 2012 [32]	In-vitro study	35 OMIs (7 in each group) five different designs in thread shape (reverse buttress, buttress, 75° joint profile with flutes, trapezoidal and rounded)	Pull out strength form artificial bone block from polyurethane foam block	Pull out strength [N]	The thread shape influenced the resistance to pullout and, therefore, the primary stability of miniscrews. The buttress reverse thread shape (about 192.8 N) had consistently higher pullout strength values than the other designs. They fared worse in turn rounded, trapezoidal, 75° joint profile design and buttress profile)
Migliorati et al. 2012 [33]	In-vitro study	Three types of OMIs—one stainless steel, two titanium grade V of thread depth of 0.1735 mm, 0.1926 mm, 0.2757 mm and thread pitch of 0.9172 mm, 0.8255 mm and 0.1043 mm	Mechanical assessment of toque and screw mobility in artificial bone block with different densities from polyurethane foam	Peak load at the pull out tests [KN]	Increased thread shape factor (depth/pitch) is positively correlated with resistance to extraction.
Migliorati et al. 2013 [34]	In-vitro study	30 titanium grade V OMIs in 3 groups: (10 in each group) of thread depth of 0.345, 0.216, 0.114mm and thread pitch of 0.826, 0.894, 0.574	Mechanical assessment of toque and screw mobility in artificial bone block with different densities from polyurethane foam	Maximum insertion torque [Ncm], peak load at the pull out tests [KN]	There is a direct positive correlation between the increase in TSF (depth/pitch), the miniscrew pull-out strength and maximum insertion torque
Da Cunha et al. 2015 [35]	In-vitro study	20 titanium grade V OMIs in 2 groups (10 in each group) G1 of thread pitch 30 × 0.6 mm and G2 45 × 0.8 mm	Mechanical assessment of torque and screw mobility in artificial bone block with different densities of polyurethane foam	Maximum insertion torque, removal torque, loss of torque [Ncm], implant stability [x]	The mini-implants with a shorter pitch distance and an insertion angle of 30° presented a better primary stability (torque) in artificial bone of a higher density. The mini-implants with a longer pitch distance and an insertion angle of 45° were found to be more stable in artificial bone of lower density, when performing evaluation with the Periotest.
Walter et al. 2013 [36]	In-vitro study	240 self-drilling titanium Titanium Grade V OMIs of 12 types from 8 manufacturers The authors did not provide exact geometrical characteristics for every type od the screw—only correlations	Mechanical tests of pull-out strength, torsional fracture and insertion torque in artificial bone block of polyurethane foam, SEM inspection	Maximum insertion torque, Torsional Fracture [Ncm], pull-out strength [N]	Within the medium diameter OMI group, conical screws had higher insertion torque and torsional fracture values than cylindrical OMIs. Greater thread depth was related to higher pull-out strength values, although OMIs with similar pull-out strength values may have different insertion torque values. Thread depth and pitch had some impact on pull-out strenght. Torsional fracture depended mainly on the OMI inner and outer diameters. A thread depth to outer diameter ratio close to 40% increased torsion fracture risk.
Cha et al. 2015 [37]	In-vitro study	Titanium grade V OMIs with single-thread (thread pitch 0.7) and dual-thread design (lower part pitch 0.7 and 0.35 upper pitch part)	Insertion torque test and strain of bone-implant interface in artificial bone block from polyurethane foam block	Strain in [µstrains] and Insertion torque in [Nm]	The strain between the single-thread and dual-thread type miniscrews was similar at a cortical bone thickness of 1.0mm, but the discrepancy between miniscrew types widened to >10,000 μstrain with increasing cortical bone thicknesses. Self-drilling dual-thread miniscrews provide better initial mechanical stability, but their design may cause excessive strain that is over the physiological bone remodeling level (>1mm cortical bone) at the bone-implant interface of thick cortical bone layers.
Radwan et al. 2017 [38]	In-vitro study	40 orthodontic miniscrews of same diameter and length and different taper designs randomly inserted into pilot holes	Mechanical assessment of pull-out test and periotest in 10 embalmed human maxillae	Pull-out strength estimation [N], implant stability [x]	Larger pitch width, flank, thread angle, apical face angle, and/or lead angle led to a higher primary stability, while a smaller thread shape factor (depth/width) improved primary stability.
Katić et al. 2017 [39]	In-vitro study	In each tested group there were 10 cylindrical self-drilling titanium grade 5 Ortho Easy® (FORESTADENT®, Pforzheim, Germany), 1.7 × 6 mm and 1.7 × 8 mm; Aarhus Anchorage System (MEDICON eG, Tuttlingen, Germany), 1.5 × 6 mm and 1.5 × 8 mm; and Jeil Dual Top™ Anchor System (Jeil Medical Corp., Seoul, Korea), 1.4 × 6 mm, 1.6 × 6 mm, 2.0 × 6 mm, 1.4 × 8 mm, 1.6 × 8 mm, and 2.0 × 8 mm	Maximum insertion torque test in rabbit bone	Maximum insertion torque [Nmm], Vertical Force [N], Torsion [Nmm]	The multiple linear regression model showed that significant predictors for higher maximum insertion torque were: a larger implant diameter, a higher insertion angle, and thicker cortical bone. Manufacturers should consider increasing the insertion angle of the implant to improve the implant design and achieve a better primary stability in cases where the operator cannot use a larger implant diameter.
Yashwant et al. 2017 [40]	In-vitro study	50 OMIs (10 in each group) of five different designs in thread shape (reverse buttress, buttress, 75° joint profile with flutes, trapezoidal and trapezoidal fluted)	Pull out strength in artificial bone block from polyurethane foam block	Pull out strength [N]	Trapezoidal fluted mini implants showed twice as higher pull out strength then mini implants of other thread designs used in this study (about 61N), followed by reverse buttress (about 27N), (buttress, 75° joint profile with flutes) which showed similar values (about 26N). A trapezoidal design presented the lowest value (13N).
Sana et al. 2020 [41]	In-vitro study	3 Titanium grade V OMIs— ORTHOImplant (3M Unitek, Monrovia, CA, USA): 1.8-mm diameter and 8-mm length, TOMAS (Dentaurum): 1.6-mm diameter and 8-mm length, VECTOR TAS (Ormco): 1.4-mm diameter and 8-mm length.	Pull out strength in artificial bone block from polyurethane foam block	Pull out strength [N]	Orthoimplant type with a larger diameter, smaller pitch and shorter taper length has a better primary stability, and lower stresses within the mini-implants and surrounding comparing to other groups tested. The favorable insertion angulation found was 90°, as it provides better primary stability and low stresses in the mini-implant and surrounding bone under orthodontic loading.
Watanbe et al. 2022 [42]	In-vitro study	Cylindrical vs. classic thread shape vs. novel thread shape Titanium grade V OMIs The authors did not provide exact geometrical characteristics for every type od the screw—only correlations	Mechanical assessment of toque, screw mobility and stiffness in artificial bone block from polyurethane foam	Values of maximum insertion torque, removal torque, torque ratio, [Ncm} screw mobility, [mm] static stiffness, dynamic stiffness [N/mm} and energy dissipation	Compared to miniscrews of a regular thread shape, the novel miniscrew of a different thread shape showed a higher torque ratio, a lower stiffness and screw mobility. These features seem important for the initial stability.
Budasbong et al. 2022 [43]	In-vitro study	60 custom made titanium Grade V OMIs	Mechanical assessment of toque in 10 embalmed human maxillae	Maximum insertion torque [Nm], implant stability [x]	The maximum insertion torque and implant stability tests demonstrated a pitch-dependent decrease. The pitch had a strong negative correlation with maximum insertion torque and implant stability, while the cortical bone thickness had a strong positive correlation with these outcomes.
Redžepagić-Vražalica et al. 2022 [44]	In-vitro study	40 Titanium grade V OMIs of which 20	Mechanical assessment of toque in 40 pork ribs	Maximum insertion torque [Nm], Pull out strength [N]	The design of the mini-implant affects the insertion torque and pulling force. The bone quality at the implant insertion point is important for primary stability; thus, the increase in the cortical bone thickness significantly increases the pulling force.