Temporary Anchorage Devices in Orthodontics: A Narrative Review of Biomechanical Foundations, Clinical Protocols, and Technological Advances

Abstract

Temporary anchorage devices (TADs) have become integral in contemporary orthodontic biomechanics, providing reliable skeletal anchorage independent of dental support or patient compliance. This narrative review synthesizes the current evidence regarding TADs classification, design parameters, biomechanical principles, clinical insertion protocols, complication management, and technological innovations. We reviewed foundational literature and recent clinical studies with emphasis on factors affecting primary and secondary stability, including insertion torque, angulation, cortical bone characteristics, and soft-tissue considerations. Self-drilling techniques are generally preferred for maxillary sites, while pre-drilling remains indicated in dense mandibular bone to reduce thermal risk and torque overload. Clinical success is optimized when insertion torque is maintained between 5 and 10 N·cm and site-specific anatomy is respected. Reported survival rates exceed 85–95% when proper protocols are followed. While TADs are associated with relatively low complication rates, failures are usually early and linked to excessive torque, poor hygiene, or inflammation. New technologies such as cone-beam computed tomography-guided placement, 3D-printed surgical guides, and AI-based planning tools offer promising avenues for safer and more individualized treatment. In conclusion, TADs represent a predictable and versatile option for skeletal anchorage in orthodontics, provided that mechanical design, biological adaptation, and clinical handling are coherently integrated into patient-specific strategies.

1. Introduction

Anchorage control remains a fundamental principle in orthodontic biomechanics, referring to the ability to resist unwanted reciprocal forces generated during tooth movement. Historically, anchorage has progressed from dental and mucodental methods to extraoral appliances, and ultimately to skeletal anchorage systems that improve force management with minimal reliance on patient cooperation (Figure 1). Contemporary systematic evidence shows that temporary anchorage devices (TADs) offer superior anchorage preservation compared with conventional methods, limiting reciprocal movements and allowing more controlled and complex mechanics [1].

The integration of TADs has reshaped orthodontic biomechanics, enabling stable anchorage units and supporting advanced three-dimensional movements with reduced anchorage loss [2]. Continuous developments in device design, placement protocols, surface technology, and digital-guided insertion have further contributed to improved success rates and biomechanical efficiency [3].

Key biomechanical and device-specific parameters exert a decisive influence on the clinical performance of temporary anchorage devices, primarily through their impact on primary stability and load distribution. The geometry and material characteristics of the mini-implant, such as diameter, length, thread pitch, tip configuration, and alloy composition, directly shape insertion torque dynamics and the quality of mechanical engagement with cortical bone [4,5]. Equally important are the characteristics of the insertion protocol. The choice between self-drilling and pre-drilling techniques, the selection of an appropriate insertion angle, and the control of peak insertion torque collectively determine the magnitude of bone strain and the likelihood of achieving stable fixation [6,7].

Finite-element analyses indicate that perpendicular insertion optimizes stress distribution in dense cortical bone [8], whereas clinical protocols frequently favor oblique (30–45°) insertion in interradicular sites, where anatomical constraints and the cortical–trabecular interface create biomechanical conditions distinct from those observed in thicker cortical regions [9].

Local bone quality further modulates anchorage behavior. Increased cortical thickness and higher trabecular density are consistently associated with enhanced primary stability and reduced risk of failure. In addition, the maintenance of peri-implant soft-tissue health, supported by adequate collar height selection and strict oral hygiene, is essential for long-term stability, as peri-implant inflammation remains a well-documented contributor to elevated failure rates in orthodontic mini-implants [10].

Advances in imaging and digital technologies have substantially refined diagnostic evaluation and placement accuracy for skeletal anchorage. Cone-beam computed tomography (CBCT) facilitates precise assessment of interradicular spacing, cortical thickness, and spatial relationships to adjacent anatomical structures, thus improving site selection and reducing procedural complications [11]. Digital planning integrated with CBCT has been shown to decrease the risk of root contact and enhance placement precision, findings reinforced by cadaveric studies validating fully guided palatal insertion systems [12]. Dynamic navigation technologies further enhance control over insertion angulation and safety, aligning with evidence supporting the accuracy of CAD/CAM-guided insertion protocols in growing patients, albeit with increased technical demands Parallel developments in artificial intelligence now enable automated identification of safe interradicular zones, supporting personalized and risk-aware planning within open digital workflows for guided miniscrew placement [13,14].

Within this evolving landscape, a deeper understanding of how biomechanical principles, anatomical variability, device design, and clinical protocols collectively influence primary and secondary stability is essential. To address this need, the present review provides an integrated, evidence-weighted framework that unifies clinical findings, mechanical experiments, CBCT-derived morphometry, and computational modeling. Rather than offering an instructional overview, the review consolidates these traditionally separate evidence domains into a site-specific, clinically oriented decision framework that supports safe, predictable, and reproducible use of skeletal anchorage in contemporary orthodontics.

2. Methodology of Research

The present work was conducted as a narrative review, designed to synthesize and contextualize the existing evidence on orthodontic TADs, including their biomechanical principles, design characteristics, insertion protocols, and clinical performance.

A narrative format was selected because the topic encompasses highly heterogeneous sources targeting multiple methodological domains, ranging from finite element analyses and in vitro mechanical studies to clinical trials, CBCT-based morphometric studies, retrospective cohorts, randomized clinical trials, case reports and case series, systematic reviews, meta-analyses, umbrella reviews, and textbook chapters, which precludes a unified methodology suitable for a classical systematic review or meta-analysis. Accordingly, no quantitative synthesis or risk-of-bias assessment was performed. The goal was to provide a structured qualitative synthesis integrating multidisciplinary evidence relevant for clinical decision-making.

A comprehensive literature search was performed in the following scientific databases: PubMed, Scopus, Web of Science, ScienceDirect, SpringerLink, and Google Scholar. To ensure adequate methodological depth, both primary research articles (e.g., randomized clinical trials, prospective/retrospective observational studies, CBCT morphometric analyses, in vitro studies, finite element analyses, mechanical testing studies) and secondary sources (systematic reviews, meta-analyses, umbrella reviews, scoping reviews, and narrative reviews), as well as a peer-reviewed orthodontics textbook, were included.

The reference list contains publications from 2006 to 2025, with most sources originating from the last five years, reflecting the rapid expansion of evidence in digital planning, guided insertion techniques, and biomechanical optimization of TADs.

The inclusion criteria consist of peer-reviewed scientific articles or scientific books, or book chapters written in English addressing orthodontic anchorage systems, temporary anchorage devices, biomechanics, TADs design and geometry, CBCT-based insertion site assessment, insertion torque, stability and failure, guided or digital insertion systems, complications, or related clinical, mechanical, or imaging aspects with full-text availability. The exclusion criteria refer to non-English sources, articles outside the scope of orthodontic anchorage or not addressing clinically relevant or mechanical or biomechanical aspects, sources lacking substantive information such as editorials, letters, or reports without data evaluated in-depth, web-only references or non-scientific webpages, and items without accessible full text.

After removal of duplicates, titles and abstracts retrieved from the database searches were screened for relevance by T.C.B. and R.-C.M using the eligibility criteria defined above. Potentially relevant articles underwent full-text evaluation. Disagreements were resolved through discussion and, when necessary, by consultation with G.C.

The search algorithm flow diagram (Figure 2) [15] illustrates the identification, screening, eligibility assessment, and final inclusion of sources in the present narrative review.

Understanding the biomechanics, stability, and clinical performance of temporary anchorage devices requires integrating findings from multiple methodological domains. Each evidence type contributes differently to decision-making, and distinguishing these roles is essential to avoid over-interpreting mechanistic data as clinical proof.

To improve transparency and align this narrative review with research-article standards, the included sources were broadly categorized according to the Oxford Centre for Evidence-Based Medicine hierarchy (OCEBM 2011) [16], based on the study design as reported by the authors of each separate work. High-level syntheses such as umbrella reviews and systematic reviews with or without meta-analysis were considered representative of Level 1 evidence. Randomized clinical trials were mapped to Level 2. Prospective and retrospective clinical studies, CBCT morphometric and other observational imaging studies were regarded as Level 3. In vitro mechanical tests, finite element analyses, and ex vivo models were treated as Level 4. Narrative reviews, scoping reviews, expert-driven overviews, and textbook material were classified as Level 5.

This framework is reflected in table annotations indicating the predominant level of evidence supporting key concepts, without implying a detailed, study-by-study risk-of-bias assessment. In total, 118 peer-reviewed English-language sources were confirmed, validated and included as the evidentiary basis for this review.

3. Types of Anchorage and Biomechanical Principles

3.1. Classification of Orthodontic Anchorage

Orthodontic anchorage is classically divided into intraoral, extraoral, and skeletal categories, each characterized by distinct mechanical properties and clinical limitations. Intraoral anchorage, using dental or dentomucosal units, is among the most widely used modalities. These systems, often based on transpalatal arches, ligatures, or bonded appliances, consolidate tooth groups to resist reciprocal forces [17,18]. While straightforward and cost-effective, intraoral anchorage is prone to anchorage loss, especially when subjected to high or prolonged orthodontic loads. Dentomucosal anchorage, incorporating soft-tissue support, is sometimes used in early orthodontics or mixed dentition phases but is highly variable due to mucosal compliance and hygiene sensitivity [19,20].

Extraoral anchorage, including headgear and facemasks, has traditionally allowed for orthopedic modifications in growing patients, especially in the treatment of Class II and Class III malocclusions. Contemporary reviews indicate that such appliances can be effective for skeletal correction but emphasize limitations related to esthetic concerns, dependency on patient compliance, and occasional safety issues [21].

Skeletal anchorage, primarily delivered through TADs, represents a significant advance, as it can offer absolute anchorage independent of dental support or patient cooperation. Narrative reviews consistently describe that TADs have substantially influenced orthodontic biomechanics by enabling complex tooth movements with minimal anchorage loss and reduced need for extraoral devices [22]. Moreover, clinical studies have reported that TADs can facilitate advanced mechanics such as full-arch anterior retraction, molar intrusion, and complex 3D corrections, which may achieve predictable skeletal and dental effects without relying on patient compliance [23]. The main categories of orthodontic anchorage, along with their representative devices, clinical indications, advantages, and limitations, are summarized in

Table 1. Classification and clinical indications of orthodontic anchorage systems.

Anchorage Type	Typical Devices	Clinical Indications	Main Advantages	Limitations	Ref.
Intraoral (dental)	Consolidated teeth, ligatures, transpalatal arch	Mild space closure, alignment and leveling, limited canine retraction	Simple, low-cost, no external devices	Risk of anchorage loss, reciprocal forces	[24,25]
Dentomucosal	Tooth–mucosa-supported appliances (e.g., acrylic plates, buttons)	Mixed dentition, early transverse control, guidance of eruption	Noninvasive, reinforced soft-tissue support	Variable soft-tissue compliance, reduced force control	[26,27]
Extraoral	Headgear, facemask, chin cup	Growth modification, molar distalization, Class II/III correction in children	High skeletal effects, modulates growth	Compliance-dependent, esthetic concerns, potential safety risks	[28,29]
Skeletal (TADs)	Mini-implants, miniplates	En-masse retraction, molar intrusion, asymmetrical or 3D movements, noncompliant adults	Absolute anchorage, predictable, minimal cooperation	Technique-sensitive, anatomical variability, risk of soft-tissue complications	[30]

TADs, temporary anchorage devices; Ref., references. Evidence base (OCEBM 2011): mainly Level 1–3 evidence from systematic reviews and clinical studies on orthodontic anchorage, complemented by Level 5 narrative reviews and textbook summaries [24,25,26,27,28,29,30].

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3.2. Biomechanical Foundations of Anchorage

At the core of anchorage control lies Newton’s third law, which dictates that every action produces an equal and opposite reaction. In orthodontic terms, the force applied to a moving tooth or segment is mirrored by a reactive force on the anchorage unit. This biomechanical principle underpins all tooth movement, as each applied load generates an equivalent counterforce that must be effectively managed to maintain stability and prevent unintended tooth displacement [31].

Whether that reactive unit consists of a few teeth or a skeletal fixation, the distribution and absorption of force determine the system’s overall stability. Consolidating multiple teeth into a single anchorage block enhances resistance to displacement, yet anchorage loss can still occur if the reactive unit is less rigid or poorly controlled. For instance, a recent finite-element and clinical study found that posterior anchorage units displayed different tipping and anchorage loss patterns depending on extraction patterns and mechanical preparation [32].

Additionally, the vector and moment created by applied forces, especially vertical and transverse components, can unintentionally shift anchorage units, particularly in force systems involving molar intrusion or expansion. A 2023 investigation measured forces and moments during canine bodily movement under different designs and suggested that both moments and complex force vectors must be carefully managed [33].

Frictional mechanics, such as sliding, can further challenge anchorage integrity, while frictionless mechanics (like loops, cantilevers) demand meticulous force calibration. A clinical study comparing anchorage loss after en-masse retraction using friction vs. frictionless mechanics reported significant differences in anchorage outcomes [34].

TADs transform this biomechanical equation by externalizing the reactive unit from the dental arch to the cortical bone. This skeletal decoupling facilitates advanced force systems, like direct retraction with torque control or pure intrusion without extrusion, scenarios that would typically overload conventional dental anchorage. Recent reviews suggest that TADs have redefined orthodontic biomechanics by enabling controlled three-dimensional tooth movement while reducing unwanted side effects and dependence on patient cooperation [3]. Moreover, bone-borne anchorage devices may reduce variability linked to dental or mucosal elasticity, and have been associated with consistent and predictable outcomes even in complex combined treatment cases [35].

3.3. Indications and Comparative Use of Anchorage Types

Anchorage selection must align with the magnitude of force required and the complexity of movement planned. In cases of low to moderate anchorage demand (mild space closure or limited retraction) intraoral anchorage can be sufficient and is often preferable, as shown in a randomized clinical trial where transpalatal arches effectively reinforced anchorage during canine retraction [36].

Extraoral anchorage retains value in orthopedic cases, particularly in growing patients, with contemporary clinical evidence supporting facemask use for Class III correction [37], and systematic reviews confirming beneficial orthopedic effects in treated Class III patients versus untreated controls [38].

Skeletal anchorage via TADs is particularly useful when maximum anchorage is required (en-masse anterior retraction with minimal posterior movement), when vertical control is paramount (molar intrusion in open-bite cases), or when complex segmental or asymmetric mechanics would otherwise compromise anchorage integrity. Randomized and clinical evidence has reported that miniscrews provide superior anchorage control compared with conventional intraoral appliances during space closure/retraction [39], and that TADs-supported molar intrusion can achieve effective open-bite correction with stability comparable to surgical approaches [40]. Additionally, a randomized clinical trial on skeletal open-bite adults reported predictable posterior intrusion with miniscrews, underscoring their role when vertical control is critical [41].

In this subsection, clinical outcome data from randomized and prospective studies are therefore presented separately from mechanistic or imaging-based observations, so that indications for anchorage type remain clearly anchored in Levels 1–3 clinical evidence. Clinical decision-making should also consider anatomical feasibility, including cortical bone thickness, interradicular space, soft-tissue environment, and hygiene accessibility. Cone-beam CBCT analyses have demonstrated that cortical bone thickness and interradicular spacing vary significantly across insertion sites, directly influencing primary stability and insertion safety [42].

One study emphasized that correct placement geometry and vector planning are critical to align force systems with the center of resistance of the target segment—minimizing side effects and maximizing efficiency, findings supported by CBCT-based planning studies that have reported optimized biomechanics and reduced root proximity with guided insertion [43].

3.4. Biomechanical Advantages and Limitations of TADs

TADs offer clear biomechanical advantages. By anchoring directly into bone, they provide stable resistance against orthodontic forces, reduce reliance on patient compliance, and allow for force vectors that are otherwise unachievable. Clinical evidence indicates that miniscrew anchorage can enable efficient distalization and en-masse anterior retraction with superior anchorage preservation compared to conventional methods [44].

For vertical control, TADs-supported molar intrusion has been reported to provide effective open-bite correction with stable outcomes [40]. In addition, randomized clinical data comparing retraction mechanics with miniscrew anchorage have described predictable tooth movement while highlighting anchorage considerations during space closure [34].

However, TADs are not biomechanically omnipotent. Their anchorage capacity is finite and highly dependent on device dimensions, insertion angle, cortical bone quality, and insertion torque. Clinical and finite-element studies have shown that insertion angle and cortical bone thickness significantly affect primary stability and stress distribution around miniscrews [45,46]. Moreover, a systematic review on mini-implant failure identified insertion torque, cortical bone thickness and insertion site as significant risk factors for early loosening or failure, confirming that even devices with initial stability can fail if overloaded or mis-angulated [10].

As noted in a study, placement geometry, including vertical height, mesiodistal position, and insertion angulation, affects not only mechanical retention but also the vector of force delivery. Clinical data suggest that insertion angle plays a decisive role in load distribution and failure rates: miniscrews inserted at oblique angles in the maxillary buccal region exhibited higher micromotion and increased risk of loosening compared with those inserted perpendicularly [45]. Similarly, the operator’s precision in determining vertical and mesiodistal positioning strongly influences primary stability and success rates during miniscrew insertion, underscoring the importance of meticulous planning and guided placement [47]. Therefore, skeletal anchorage enhances biomechanical potential but does not simplify it; on the contrary, it demands greater precision in force system design, anatomical planning, and clinical execution.

4. Temporary Anchorage Devices: Design and Selection

4.1. General Design Principles

Orthodontic mini-implants, or TADs, are slender titanium or titanium-alloy screws designed specifically for transient skeletal anchorage during orthodontic movement. Unlike dental implants, which rely on osseointegration to achieve permanent bone bonding for prosthetic support, TADs are intended to maintain mechanical stability without long-term bone adhesion, enabling safe removal upon completion of tooth movement. Clinical and in vitro evidence supports the concept that TADs stability depends on immediate mechanical interlocking with cortical bone rather than osseointegration, allowing predictable removal after treatment [19].

Their design reflects this transient purpose, optimizing primary retention, minimizing invasiveness, and accommodating the variable anatomical constraints of orthodontic sites. Recent experimental studies highlight that parameters such as thread geometry, diameter, and insertion torque significantly influence pull-out strength and success rate [48].

A typical TADs incorporates three structural zones: the head, the transmucosal collar, and the threaded body, each contributing to stability, comfort, and clinical handling. The threaded body is responsible for cortical engagement and primary stability. Finite-element analyses and mechanical studies suggest that design features such as thread pitch, outer and core diameters, and thread depth affect stress distribution, insertion torque, and pull-out resistance, thereby influencing the likelihood of maintaining stability throughout orthodontic loading [8,49]. Moreover, histologic and mechanical analyses have shown that excessive torque or cortical microdamage reduces initial stability and increases failure risk despite adequate geometry [50].

Material selection also contributes to biomechanical performance. Most TADs are manufactured from Ti-6Al-4V alloy due to its tensile strength, corrosion resistance, biocompatibility, and fatigue resistance under cyclic orthodontic forces, performing better than commercially pure titanium in dynamic loading scenarios [51].

In contrast with restorative implants, TADs require limited surface roughness because extensive surface texturing increases removal torque and may complicate explanation [52,53]. Consequently, design development emphasizes predictability, ease of insertion and removal, minimal soft-tissue irritation, and patient comfort, with innovations such as self-drilling tips and low-profile heads supporting clinical efficiency and user comfort. At the biomaterial level, in vitro work on collagen-coated acrylic bone cements incorporating silver oxide has suggested that combining bioactive protein layers with ion-releasing antimicrobial components can enhance biomineralization and provide sustained antibacterial effects at the bone–material interface, a concept that could inspire future surface engineering strategies for temporary anchorage devices [54]. In a related nanotechnology-based approach, a research developed a nanomodified endodontic sealer in which multi-walled carbon nanotubes loaded with chlorhexidine and silver nanoparticles provided prolonged antibacterial activity while preserving dentin bonding and physicochemical performance, illustrating how carbon-based nanomaterials can be exploited to engineer antimicrobial, mechanically reinforced dental biomaterials [55].

Overall, the design of TADs intentionally balances geometry, material selection, and procedural strategy to achieve reliable temporary skeletal anchorage without promoting long-term biological integration, forming the foundation for subsequent biomechanical considerations.

4.2. Structural Design: Head, Neck, and Thread Geometry

The macro design of orthodontic mini-implants, which includes the head, transmucosal collar, and threaded body, can play a decisive role in achieving primary stability, mechanical reliability, and clinical success. These components have been designed to behave as a coordinated system that integrates anatomical adaptation, mechanical load transmission, tissue compatibility, and ease of clinical manipulation. The head serves as the attachment interface for orthodontic auxiliaries and must provide sufficient clearance from the soft tissues to minimize irritation. Clinical and CBCT-based studies imply that head configuration and the relationship between collar height and mucosal thickness influence comfort, plaque control, and peri-implant health [56].

Configurational variations, such as slotted, button-type, or cross-shaped heads, affect auxiliary engagement and mechanical efficiency, and differences in thread architecture associated with specific commercial systems have been correlated with stability performance, including comparisons between single- and double-thread macro designs [57]. Clinical complications including soft-tissue overgrowth, inflammation, or interference at the head–collar junction have been associated with mismatches between design and the chosen insertion site or with elevated torque values, highlighting the importance of integrating macro design with an appropriate insertion protocol [58].

The transmucosal collar, or neck, serves as the transitional zone between the soft tissue and the osseous anchorage. Its design must account for the variable thickness and quality of oral mucosa across different insertion sites. Smooth, polished collars reduce bacterial adhesion and soft-tissue irritation, promoting healthier peri-implant tissue and lower inflammation scores in vivo [59]. Collar height, generally between 1 and 3 mm, should correspond to the thickness and type of mucosa at the planned insertion site, as CBCT-based evaluations show substantial differences between palatal and buccal regions [56]. When collar height does not match the local gingival profile, soft-tissue hypertrophy, mucositis, or early implant mobility may occur. Patient-specific collar selection, guided through direct clinical inspection or CBCT assessment, may support long-term tissue stability and reduced inflammatory complications.

The threaded body determines bone engagement and primary mechanical stability and is defined through geometric variables such as length, diameter, thread pitch, thread depth, shape, and tip configuration. Clinical reports identify typical dimensions ranging between 1.2 and 2.0 mm in diameter and 6 to 12 mm in length, noting that increased diameter and length are associated with enhanced stability but also with greater space requirements and potential effects on soft tissues [59].

Double-thread designs may offer improved survival and stability over single-thread variants due to superior load transfer characteristics [57]. Tip configuration influences insertion dynamics: current evidence implies that self-drilling designs may provide greater efficiency and primary stability in moderate-density bone, while self-tapping insertion remains advantageous in highly dense cortical sites [19].

The influence of geometry on stress distribution has been highlighted in finite-element analyses, showing that thread parameters and cortical thickness jointly affect insertion torque, load transfer, and primary stability [8]. These FEA-based observations highlight that thread geometry must be interpreted together with local cortical thickness and insertion trajectory, which jointly influence torque and root safety.

Table 2. Influence of macro design features on clinical outcomes.

Design Parameter	Effect on Clinical Behavior	Recommendations
Head profile	Auxiliary versatility; soft-tissue irritation risk	Low-profile, multipoint fixation
Neck height	Muco-gingival adaptation, hygiene, inflammation control	Match to mucosal thickness (1–3 mm)
Outer diameter	Insertion torque, fracture resistance, interradicular compatibility	1.5–2.0 mm
Thread pitch and depth	Retention, insertion resistance, microfracture risk	Fine pitch with moderate depth
Thread shape	Load distribution, stress absorption, ease of removal	Conical in dense bone; cylindrical in soft bone
Tip design	Insertion ease, thermal trauma, bone microdamage	Self-drilling in soft/moderate bone; self-tapping in dense bone

summarizes the influence of key macro-design parameters of orthodontic mini-implants on clinical behavior and outcomes, highlighting their biomechanical and biological implications and providing evidence-based design recommendations.

4.3. Insertion Torque and Stability

The insertion torque required to place TADs is widely accepted as a direct clinical proxy for its primary stability, and higher primary stability predicts short-term mechanical retention [6,60]. This value reflects a complex interplay between screw geometry, bone density, cortical thickness, and insertion technique and serves as a key predictor of short-term mechanical retention [43].

Achieving an appropriate torque level is essential, as insufficient torque values of approximately 3 N·cm or less may reflect inadequate cortical engagement and increase the risk of early displacement, whereas excessive torque exceeding 15 N·cm may cause cortical microdamage, thermal injury, or device fracture, compromising stability despite apparently secure placement [61,62,63].

Numerous studies have proposed a safe and effective insertion torque range between 5 and 10 N·cm for mini-implants of 1.5–1.6 mm in diameter placed in average-density cortical bone, with higher values being tolerated in the mandible and lower values in the maxilla [6,60,61]. For instance, insertion torque increases with cortical bone thickness and density, but also depends on thread pitch, screw length, and diameter [43]. Finer thread pitch or conical designs require greater insertion energy but provide higher pull-out resistance, particularly in dense cortical bone, thereby enhancing mechanical stability [60].

Bone density and anatomical region are key determinants in torque selection. The posterior mandible requires significantly more torque due to high cortical resistance, whereas the posterior maxilla, often characterized by porous cancellous bone, mandates caution to avoid over-insertion and instability.

Table 3. Evidence-stratified insertion torque ranges by anatomical site, bone density, screw diameter, clinical considerations, and primary supporting evidence.

Anatomical Site	Bone Density	Screw Diameter	Recommended Torque (N·cm)	Clinical Notes	Ref.
Anterior maxilla	Low–moderate	1.4–1.6 mm	5–7	Pre-drilling often unnecessary; avoid overtightening to prevent early mobility	[64,65,66]
Posterior maxilla	Low density	1.6–2.0 mm (conical)	4–6	Use conical or larger-diameter screws; high failure risk if over-torqued	[64,65,67]
Anterior mandible	Moderate–high	1.4–1.6 mm	8–10	Good cortical support; monitor torque to avoid microfracture	[65,67]
Posterior mandible	High density/thick cortex	1.6–2.0 mm	10–12	Self-tapping preferred; consider a pilot hole to reduce heat generation	[67,68,69]
Midpalatal suture	High density	1.6–2.0 mm	7–10	Excellent primary stability; digital torque drivers recommended	[70,71]
Zygomatic crest	Very high density	≥1.8 mm	10–15	Risk of overheating; CBCT evaluation essential for depth and trajectory planning	[61,65,72,73]

Evidence base (OCEBM 2011): predominantly Level 3–4 evidence derived from observational clinical and torque-removal studies, CBCT-based assessments and in vitro mechanical analyses, supported by comprehensive narrative reviews on insertion torque and miniscrew stability [61,64,65,66,67,68,69,70,71,72,73].

summarizes the clinically reported insertion-torque ranges across anatomical sites. These values reflect broad trends reported in the literature rather than strict prescriptive thresholds. The torque intervals reported in Table 3 should be interpreted as evidence-informed reference ranges rather than prescriptive guidelines, as they derive from heterogeneous sources including observational torque–removal studies, CBCT-based cortical thickness assessments, in vitro pull-out tests, and finite-element simulations. Because insertion torque is sensitive to screw diameter, thread geometry and local cortical density, the table stratifies values by these parameters and indicates the corresponding OCEBM evidence level supporting each range.

Recent biomechanical studies have emphasized the role of cortical bone thickness as a dominant factor in predicting both insertion torque and implant stability [42,74,75].

Deguchi et al. (2006) first demonstrated a direct correlation between cortical thickness and pull-out strength, particularly in posterior maxillary and mandibular insertion sites [66], and these findings have since been confirmed and refined by newer CBCT-based and experimental analyses [76]. As a result, preoperative CBCT evaluation has increasingly been used and is considered important for assessing local bone characteristics and selecting appropriate screw dimensions to achieve optimal insertion torque and primary stability.

The technique of torque application also influences stability. Excessive rotational speed, lack of pilot drilling when indicated, or suboptimal insertion angulation may generate excessive frictional heat and microtrauma, compromising the surrounding cortical bone, whereas inadequate engagement in low-density bone may promote micromovement and early loosening [48,62,74].

Technological advancements have recently introduced digital torque drivers and guided insertion systems, which have the potential to improve reproducibility and reducing the risk of over- or under-torquing. These tools provide real-time feedback on torque delivery and enable clinicians to respect material limits while achieving the desired anchorage level [68,77,78]. Moreover, smart navigation systems integrating CBCT and intraoral scanning offer improved control over insertion angle and depth, particularly in anatomically constrained regions [79,80].

In clinical practice, insertion torque is more than a mechanical threshold—it is an indicator of biological compatibility and surgical precision. Understanding the relationships between torque, geometry, and bone biology may help clinicians to optimize primary stability without compromising peri-implant health. To reconcile biomechanical and clinical evidence regarding insertion angle, it is important to recognize that optimal angulation is site-specific and depends on local bone characteristics. Perpendicular (90°) insertion is advantageous in dense cortical regions where minimizing peak stress is critical, as supported by finite-element and in vitro evidence showing reduced peak cortical stress and more favorable load distribution at near-perpendicular trajectories [48,49]. In contrast, oblique angulation (30–45°) improves cortical purchase, insertion safety, and root avoidance in interradicular sites with limited spacing, as consistently demonstrated by clinical survival studies and CBCT-based investigations [44,81]. This distinction harmonizes the evidence streams and clarifies the biomechanical rationale for angle selection.

4.4. Device Selection Criteria

The selection of TADs must integrate multiple clinical, anatomical, and biomechanical factors in a structured decision-making framework. As shown in Figure 3, five core domains inform optimal device selection: anatomical site, biomechanical demand, bone quality, soft-tissue environment, and operator-specific variables. These domains are interdependent, and neglecting any of them may compromise primary stability, increase the risk of failure, or limit the efficiency of applied force systems.

The anatomical site dictates spatial availability, cortical thickness, and proximity to adjacent structures. CBCT mapping studies show that interradicular dimensions and buccal or palatal cortical thickness vary by region and skeletal pattern, directly informing miniscrew planning [42,82]. Interradicular space, especially in the posterior maxilla or mandible, must accommodate the selected screw diameter (typically 1.5–2.0 mm) without risking root proximity or impingement, as confirmed by posterior maxilla safe-zone analyses on CBCT cohorts [83].

Cortical bone thickness at the insertion site is positively correlated with insertion torque and pull-out strength, influencing both initial retention and long-term success [84,85].

The biomechanical demand refers to the direction and magnitude of forces that the implant must withstand. Clinical and finite element studies have demonstrated that load direction significantly influences miniscrew stability and stress distribution within the cortical bone [6,46]. For example, intrusive forces require greater torque stability and deeper cortical engagement, while distalizing forces demand directional alignment with the applied vector to minimize bending moments and micromotion [86]. These findings support the frequent use of insertion torques in the 5–10 N·cm range to balance primary stability and bone preservation during high-load mechanics [6]. Furthermore, the choice between direct and indirect anchorage determines whether the TADs bear the active orthodontic force directly or supports a reactive anchorage unit; recent randomized trials have shown that direct miniscrew anchorage provides superior control and reduced anchorage loss compared with indirect systems during en-masse retraction [39,87].

Bone quality further influences device selection. In regions of denser cortex such as the anterior mandible or midpalatal suture, self-drilling TADs can be placed without predrilling, producing high primary stability with lower heat generation [42,46]. In contrast, the posterior maxilla, characterized by lower trabecular density and thinner cortex, may benefit from pilot drilling to minimize insertion torque and avoid cortical microfractures or overheating [88].

CBCT-based studies have further confirmed that mandibular bone density and cortical thickness are significantly higher than in the maxilla, justifying site-specific torque adjustments during TADs placement [78].

The soft-tissue environment, specifically the type and thickness of mucosa, also guides collar height and transmucosal design. Recent CBCT and ultrasonographic evaluations have demonstrated that mucosal thickness varies considerably between palatal and buccal regions, directly influencing peri-implant tissue response and stability [56,89].

Keratinized mucosa, often found in palatal regions, is more tolerant of shorter collars, while nonkeratinized, mobile mucosa (buccal vestibule) requires longer collars to reduce inflammation and facilitate oral hygiene access. Maintaining an appropriate transmucosal profile has been associated with lower the risk of peri-implant mucositis and enhances long-term stability [78,90].

Lastly, operator experience and access conditions must be considered. In sites with limited visibility or access, such as the infra-zygomatic crest or posterior mandible, clinicians may benefit from prefabricated guides or computer-assisted navigation tools that enhance precision in angulation and depth control. Recent in vitro and clinical investigations have reported that CBCT-based static guidance can significantly improve positional accuracy and reduces the risk of root proximity compared with freehand insertion [79]. Dynamic navigation systems, which provide real-time visual feedback during drilling, further appear to enhance precision in challenging anatomical areas, although they require greater technical expertise and equipment cost [91].

Digital workflows combining CBCT with intraoral scanning may support the fabrication of customized three-dimensional printed guides, achieving angular deviations below 2° even in sites with limited interradicular space [88]. These technological adjuncts may help to compensate for variations in operator experience and provide reproducible, safe, and minimally invasive TADs placement in clinical orthodontics.

Selecting appropriate TADs is not merely a matter of size or shape. It is a complex integration of mechanical demands, anatomical realities, and clinician capabilities. These five domains function as decision nodes in a clinical algorithm that, when applied thoughtfully, enhance both the predictability and the longevity of skeletal anchorage systems.

4.5. Clinical Implications

A thorough understanding of mini-implant design parameters is important for translating biomechanical theory into clinical predictability. TADs can be considered dynamic interfaces between patient-specific anatomy, desired tooth movement, and the applied forces. Thread shape and pitch influence insertion torque and primary stability, with comparative data indicating better stability profiles for certain macrodesigns such as double-thread versus single-thread screws and for optimized thread geometries [57,92].

Implant diameter and length must balance interradicular clearance with mechanical retention, while the transmucosal collar height should match local mucosal thickness to limit inflammation and ensure hygiene access, palatal and site-specific CBCT maps help select collar/neck dimensions and head clearance [56,93].

Head configuration also modulates stress transfer and soft-tissue tolerance, with recent analyses comparing bracket, button, cross and other heads showing meaningful differences in stress/displacement under load [94].

In terms of materials, titanium alloy Ti-6Al-4V remains widely used due to its tensile strength and superior fatigue resistance under cyclic orthodontic loads, supporting durable clinical performance when combined with appropriate macro-geometry and surface characteristics [95,96].

Larger diameters and deeper threads increase insertion torque capacity and mechanical retention, particularly in dense cortical bone, although careful spatial planning is required to prevent root contact or anatomic interference. Recent CBCT-based and mechanical analyses confirm that TADs with diameters of 1.8–2.0 mm can generate higher insertion torque and pull-out strength when interradicular spacing permits their use [46,78]. Finite element simulations and in vitro mechanical testing further indicate that deeper or double-threaded designs distribute stress more evenly and reduce micromotion under load, enhancing overall stability [92].

Another in vitro/FEA model comparing single-threaded vs. double-threaded implants reported that double-threaded designs produced different strain patterns and comparable insertion torque under specific angulations [97]. The transmucosal collar plays a critical role in maintaining peri-implant tissue health, as insufficient collar height may lead to mucosal impingement and inflammation, whereas excessive collar height may act as a lever arm that increases bending stress and mobility risk [56,90].

Selecting collar height according to mucosal thickness (typically 1–3 mm) appears to optimize both hygiene and soft-tissue stability. Similarly, the geometry of the screw tip, whether self-drilling or self-tapping, should match the local bone density to minimize trauma and heat generation during insertion. In moderate-density maxillary bone, self-drilling designs often shorten procedure time and may increase primary stability, whereas in dense mandibular bone, pre-drilling and self-tapping can help reduce torque overload and thermal injury [6,60,62].

4.6. Soft-Tissue Response, Patient Comfort, Hygiene, and Inflammation: Critical Appraisal

Soft-tissue behavior around miniscrews is widely recognized as a major determinant of long-term success, on par with torque and bone-related variables. Prospective peri-implant evaluations suggested that plaque accumulation, bleeding on probing, and pocketing around TADs are strongly associated with local mucositis and, when persistent, with reduced stability over time [90].

Similarly, a recent clinical and radiographic study reported that miniscrews with poorer periodontal indices and inadequate soft-tissue adaptation were more likely to exhibit radiographic bone changes and clinical signs of inflammation, underlining the importance of peri-implant periodontal monitoring in orthodontic practice [98].

Hygiene feasibility is a modifiable risk factor. A 2024 narrative review specifically addressing hygiene around miniscrews showed that accumulation of biofilm is common, but that structured hygiene protocols (mechanical cleaning with soft brushes or interdental brushes, alcohol-free chlorhexidine or essential-oil rinses, and regular reinforcement of instructions) can reduce mucositis and early mobility, particularly when miniscrews are placed in non-keratinized, difficult-to-clean areas [89].

In support of the clinical relevance of inflammation control, in a 2023 prospective split-mouth study, miniscrews exhibited significantly higher plaque accumulation and gingival inflammation indices over time compared with adjacent control teeth, highlighting that peri-implant soft-tissue status around temporary anchorage devices may be highly susceptible to biofilm-related changes and requires strict maintenance to avoid early complications [99].

Beyond conventional hygiene strategies, adjunctive photodynamic approaches have been investigated for biofilm control around orthodontic devices. An in vitro study on fixed orthodontic systems indicated that riboflavin-mediated photodynamic disinfection significantly reduced viable counts of Streptococcus mutans and other cariogenic species on bracket surfaces, suggesting potential benefits for controlling biofilms in areas where mechanical cleaning is limited [100].

A more recent translational review highlighted riboflavin broad antimicrobial spectrum, favorable safety profile, and possible applicability for managing plaque-associated conditions in orthodontic and implant settings [101].

These findings align with systematic reviews showing that antimicrobial photodynamic therapy can provide an effective adjunct to mechanical debridement in peri-implant and periodontal disease, particularly in high-risk or refractory cases [102].

Patient-reported outcomes add another dimension to these biological findings. In a randomized prospective clinical trial on mandibular buccal shelf miniscrews, larger 2.0 mm–diameter devices achieved significantly higher long-term stability but were associated with higher rates of mucosal inflammation (about 50%) and pain persisting beyond 48 h (about 60%), compared with smaller screws [59].

This illustrates a clinically relevant trade-off between maximum anchorage and soft-tissue morbidity that should be explicitly discussed with patients. More broadly, systematic reviews and meta-analyses on orthodontic treatment have shown that oral-health-related quality of life (OHRQoL) typically deteriorates during the initial phase of appliance therapy due to pain, ulceration, and functional limitations, and gradually improves as patients adapt [103].

Mechanistic findings from in vitro biofilm and photodynamic studies are thus interpreted as supportive of biological plausibility, whereas peri-implant soft-tissue behavior and patient-reported outcomes are derived from clinical investigations and periodontal assessments (Levels 2–3).

Taken together, these findings support a more critical, patient-centered view of soft-tissue and comfort outcomes in TADs-based mechanics.

Table 4. Clinical relevance of soft-tissue, hygiene, and comfort outcomes around TADs: evidence-to-practice summary.

Domain/Variable	Clinical Impact	Practical Implication	Ref.
Peri-miniscrew tissue indices (plaque, bleeding on probing, PD)	Strongly associated with mucositis and progressive instability risk, even in clinically asymptomatic but inflamed sites	Integrate periodontal index charting at each follow-up; manage inflammation as early risk rather than benign sign	[90,98]
Soft-tissue phenotype and collar adaptation	Inadequate adaptation correlates with radiographic bone changes and inflammation	Prioritize keratinized mucosa; measure mucosal thickness for collar-height matching	[98]
Hygiene feasibility and protocol type	Structured hygiene protocols reduce mucositis and risk of early mobility	Routine interdental brushing + alcohol-free chlorhexidine/essential oils rinse + reinforcement at each visit	[89]
Adjunctive antimicrobial photodynamic strategies	Proven biofilm reduction on orthodontic surfaces in vitro and promising safety profile, but limited TADs-specific clinical data	Consider only in high-risk or maintenance-resistant cases; currently considered adjunctive rather than routine therapy	[100,101,102]
Screw dimension vs. comfort	Larger screws increase stability but also pain & inflammation	Match screw diameter to anchorage need, not default preference	[59]
OHRQoL impact (pain domain)	Early deterioration in OHRQoL mainly related to pain and ulceration	Discuss expected discomfort trajectory & provide supportive strategies	[103,104,105]

PD, Probing depth; a periodontal parameter reflecting soft-tissue health around miniscrews; OHRQoL, Oral Health–Related Quality of Life; a patient-reported outcome measuring the functional, emotional, and social impact of oral conditions; TADs, Temporary Anchorage Devices; a skeletal anchorage mini-implant used in orthodontics; Evidence base (OCEBM 2011): mixed evidence ranging from Level 1 to Level 5, with predominance of Level 3 data from observational clinical studies on peri-miniscrew tissue health, soft-tissue adaptation, screw dimensions and OHRQoL [59,90,98,104,105], complemented by Level 4–5 evidence from in vitro and expert-opinion studies on hygiene protocols and photodynamic adjuncts [89,100,101], and supported by isolated Level 1 data regarding antimicrobial PDT and patient-reported outcomes [102,103].

summarizes the key clinical implications derived from current evidence, emphasizing modifiable factors relevant to soft-tissue health, hygiene feasibility, and patient-reported outcomes.

5. Clinical Technique, Stability, and Evidence-Based Outcomes

5.1. Insertion Techniques, Protocols, and Decision Pathways

The clinical success of TADs depends on the use of appropriate insertion protocols. Two primary techniques exist: self-drilling, which uses a sharp cutting tip to penetrate cortical bone directly, and pre-drilling, which involves creating a pilot hole prior to screw placement. The former is commonly preferred in moderate-density bone (e.g., maxilla), while the latter is generally recommended in dense bone (e.g., mandibular posterior) to prevent thermal damage and torque overload.

A clear comparison between self-drilling and pre-drilling techniques, highlighting their procedural characteristics, biomechanical implications, and clinical indications, is presented in

Table 5. Comparison of self-drilling vs. pre-drilling techniques.

Parameter	Self-Drilling	Pre-Drilling	Ref.
Technique	No pilot hole; sharp-cutting tip	Pilot hole (0.2–0.3 mm smaller)	[52,60,106,107]
Indicated Bone Type	Moderate to soft (maxilla)	Dense (mandibular posterior)	[59,106,108,109]
Insertion Torque	Higher; may need torque control	Lower; smoother path	[6,106,110]
Heat Generation Risk	Low	High if >1000 rpm or poor irrigation	[62,111,112]
Primary Stability	Higher	Slightly lower	[42,109]
Clinical Advantage	Faster, less instrumentation	Safer in dense bone	[52,62,106]

Evidence base (OCEBM 2011): mixed Level 2–5 evidence, including randomized controlled trials on miniscrew stability and pre-drilling, CBCT-based and navigation-related observational studies, in vitro and ex vivo mechanical and thermal experiments, and narrative or scoping reviews on miniscrew complications and heat generation [6,42,52,59,60,62,106,107,108,109,110,111,112].

.

Optimal clinical protocols rely on an integrated evaluation across biological, mechanical, and procedural dimensions. The biological component involves assessing cortical thickness, bone density, and mucosal characteristics using CBCT or probing, all of which substantially influence insertion torque and primary stability [42,43]. Mechanically, the screw design must be compatible with the torque requirements and the type of orthodontic movement planned. Procedurally, clinicians must adapt insertion angle, pre-drilling strategy, and torque delivery to avoid overheating, root proximity, and torque overload.

Finite element and in vitro findings support maintaining insertion torque within the 5–10 N·cm range, as this level optimizes load transfer, minimizes micromotion, and promotes stability at the bone–implant interface [60]. Guided or computer-assisted placement further enhances accuracy by refining angulation and depth control and reducing the risks of root contact or thermal damage [79,91]. Predictable outcomes arise when implant design, patient-specific anatomy, and surgical execution are approached as interdependent factors. Their interaction is depicted in Figure 4.

5.2. Stability Determinants, Complications, and Risk Management

Primary stability results from the mechanical interlocking of the screw within the cortical bone, and is influenced by bone density, cortical thickness, screw geometry, and insertion angle. Secondary stability, by contrast, reflects the biological adaptation that occurs after placement and is dependent on controlled micromotion, appropriate force levels, and healthy peri-implant soft tissues. Excessive loading or inadequate oral hygiene can compromise this phase, particularly during the early healing period.

Complications related to TADs placement may arise intraoperatively, such as root contact, screw fracture, or excessive torque, or postoperatively, including mucositis, early mobility, and peri-implant inflammation. Although uncommon, more severe events, such as sinus perforation, subcutaneous emphysema, or neurovascular injury, may occur in anatomically complex areas. Preventive measures include thorough CBCT-based planning, the use of torque-limiting drivers, avoidance of excessively deep insertions, and reinforcement of hygiene protocols. Stability-related outcomes and common complications are predominantly supported by clinical and CBCT-derived evidence (Levels 1–3), whereas insights into thermal damage, torque-induced microcracks, and stress distribution originate from finite element models and in vitro experiments (Level 4), which provide important mechanistic context without representing direct clinical evidence. A summary of the main complications and preventive strategies is provided in

Table 6. Complication management summary.

Complication Type	Examples	Preventive Measures	Ref.
Intraoperative	Root contact, excessive torque, fracture	CBCT planning, optimized insertion angle, torque-limited driver	[11,60,68,79,113]
Postoperative	Mucositis, early mobility, inflammation	Hygiene, correct collar height, force control (<200 g)	[47,56,89,98,114]
Rare/Severe	Sinus perforation, emphysema, neurovascular injury	Avoid deep insertions, air-driven tools, monitor anatomical landmarks	[115,116,117,118]

Evidence base (OCEBM 2011): intraoperative and postoperative complications are mainly informed by Level 1–3 evidence from systematic reviews, randomized or prospective clinical studies, and CBCT-based observational analyses, whereas rare and severe events draw primarily on Level 4–5 sources such as in vitro modeling, case series, case reports and expert-based reviews [11,47,56,60,68,79,89,98,113,114,115,116,117,118].

.

5.3. Clinical Guidelines and Evidence-Based Recommendations

On the basis of the available evidence synthesized in this review, several clinical recommendations may help support the safety and predictability of TADs use. These include the frequent preferential use of self-drilling screws in the maxilla and pre-drilling in denser mandibular regions. Maintaining insertion torque within 5–10 N·cm, selecting appropriate transmucosal collar heights, and enforcing hygiene protocols are all considered important to help reduce the risk of complications. CBCT imaging can improve placement accuracy and may help identify anatomical safety zones. Evidence-based clinical recommendations for optimizing the safety, stability, and predictability of TADs placement and use are outlined in

Table 7. Clinical best practices summary.

Recommendation	Justification	Ref.
Use self-drilling in maxilla	Less dense bone, faster insertion	[59,62,109]
Use pre-drilling in dense mandible	Prevent overheating and torque overload	[6,60,68]
Maintain 5–10 N·cm torque	Ensures stability without damage	[47,60]
Apply force ≤ 200 g post-insertion	Avoids overload during healing	[47,114]
Use CBCT for planning	Increases safety and predictability	[79,88,91]
Enforce hygiene protocols	Prevents mucositis and late mobility	[56,89,98]

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To assist clinicians in interpreting the heterogeneous evidence supporting the key decisions discussed in this section,

Table 8. Evidence-to-decision summary for key clinical recommendations regarding TADs.

Clinical Question/Decision	Predominant Evidence Types (OCEBM Levels)	Effect Direction and Consistency	Clinical Applicability	Overall Certainty
Recommended insertion angle (perpendicular vs. 30–45°)	Clinical survival studies, CBCT geometric mapping, FEA	Perpendicular insertion reduces peak stress in dense cortical bone; 30–45° angulation improves root safety in narrow interradicular sites	Site-specific angle selection	Low–moderate
Optimal insertion torque range (5–10 N·cm for 1.5–1.6 mm screws)	Clinical torque–removal studies, CBCT-derived cortical thickness data, in vitro mechanical tests	Consistent association between moderate torque and higher primary stability with reduced microdamage risk	Routine torque selection for most alveolar sites	Moderate
Hygiene protocols and inflammation control	Clinical studies, periodontal assessments, narrative reviews, in vitro biofilm work	Consistent reduction of mucositis with structured hygiene	Universal applicability; intensified for high-risk patients
Self-drilling vs. pre-drilling (maxilla vs. dense mandible)	RCTs, clinical comparative studies, thermal/mechanical in vitro experiments	Convergent evidence: self-drilling suitable for moderate-density maxilla; pre-drilling safer in dense mandibular cortex	Widely applicable for routine placement	Moderate–high
Collar height and soft-tissue management	Prospective clinical studies, CBCT soft-tissue thickness assessments, periodontal evaluations	Consistent association between matched collar height and lower inflammation/mobility	Routine device selection; critical in non-keratinized mucosa

CBCT, cone-beam computed tomography; RCTs, randomized clinical trial; FEA, finite element analysis; OCEBM, Oxford Centre for Evidence-Based Medicine.

synthesized the principal findings into an evidence-to-decision summary. This overview integrates the predominant evidence types, OCEBM levels, effect consistency, and clinical applicability for the main technical and biomechanical considerations related to TADs placement.

6. Conclusions and Perspectives

TADs have substantially expanded the biomechanical possibilities in orthodontic treatment by enabling controlled, non-compliant-dependent tooth movements and expanding the range of correctable malocclusions. When appropriately selected and placed, mini-implants can offer a reliable anchorage source with minimal invasiveness and high clinical versatility. As detailed throughout this review, optimal outcomes depend on a delicate interplay between implant design, anatomical site characteristics, insertion technique, and post-placement protocols.

Nonetheless, several limitations temper the current evidence base. Much of the literature is derived from observational studies with heterogeneous methodologies, and there is a relative scarcity of long-term, high-quality clinical trials. Variability in outcome definitions, insertion protocols, and biomechanical strategies makes direct comparisons challenging. Moreover, key factors such as patient comfort, soft-tissue adaptation, esthetic concerns, and compliance behavior remain underrepresented in published research, despite their impact on clinical success.

Looking forward, the field of skeletal anchorage stands to benefit significantly from technological advances. Integration of AI-assisted planning, CBCT-guided insertion, and customized 3D-printed TADs holds potential for more precise, patient-specific anchorage solutions. Likewise, the development of smart torque sensors and in situ biomechanical feedback systems could improve safety and real-time control during placement and loading. Research should also aim to better characterize tissue responses over time, particularly regarding soft-tissue health, inflammation, and the transition from primary to secondary stability.

To fully realize the potential of TADs in modern orthodontics, future studies will need to bridge current knowledge gaps through standardized protocols, robust multicenter trials, and broader inclusion of patient-reported outcomes. With such evidence-based refinement, mini-implants may evolve from a powerful adjunct to a cornerstone of personalized, digitally guided orthodontic biomechanics.