Introduction

Temporary anchorage devices (TADs) have become a pivotal innovation in contemporary orthodontic practice, offering a reliable solution for achieving effective and predictable tooth movement. These small, screw-like implants, typically made from titanium or other biocompatible materials, are temporarily inserted into the alveolar bone to provide a fixed point of anchorage. This allows for precise application of orthodontic forces without relying on patient compliance or the need for extraoral devices.

According to Cope (2005), the introduction of TADs represents a paradigm shift in orthodontics, allowing for greater control and predictability in treatment outcomes.^[1] Numerous studies have validated the effectiveness and safety of TADs. Papageorgiou, Zogakis, and Papadopoulos (2012) conducted a meta-analysis that demonstrated low failure rates and highlighted various factors influencing the success of miniscrew implants in orthodontics.^[2] Furthermore, Poggio et al. (2006) provided detailed guidelines for the optimal placement of TADs, identifying "safe zones" in the maxillary and mandibular arches to minimize the risk of complications and enhance stability.^[3]

In addition to their effectiveness in routine orthodontic cases, TADs have proven invaluable in complex treatments, such as the correction of Class II malocclusions. Papadopoulos (2014) discusses the versatility of TADs in providing skeletal anchorage, which facilitates significant orthodontic movements that would otherwise be challenging to achieve.^[4] Moreover, Antoszewska-Smith et al. (2017) demonstrated through a systematic review and meta-analysis that TADs significantly improve anchorage control during en-masse retraction, leading to more efficient and effective orthodontic treatments.^[5]

Understanding Implant Sites for TADS

Understanding the sites of implant placement ([Figure 5]) is crucial for ensuring the success of the procedure.

Maxillary buccal alveolar bone

It is the most common site for placing Temporary Anchorage Devices (TADs). A safe spot for miniscrew placement, with sufficient inter-radicular space, is located between the second premolar and first molar. ^[7]

Targeting the most apical region where the cortical bone is thick and dense, it is better to introduce TADs mesiodistally between the first and second molars for the best primary stability. However, the reduced inter-radicular space in this location poses a limitation. Although more apical placement may provide additional inter-radicular space, there is a risk of irritation and discomfort if a TAD is positioned in the movable mucosa. ^[8]

Maxillary palatal alveolar bone

The palatal cortical bone is thicker and denser than the buccal cortical bone. The thickest palatal cortical bone is located between the canine and first premolar, while the densest inter-radicular palatal bone is found between the first and second premolars. ^[9]

Midpalatal suture

In this region, due to the presence of thick and dense bone, pilot drilling is recommended prior to miniscrew placement. Additionally, due to the presence of thick mucosa in this area, longer TADs are preferred. An ideal location for miniscrew placement is 1–2 mm lateral to the mid-palatal suture particularly in growing patients. This is because of the presence of under-ossified bone and soft tissue at the suture site in growing individuals.

Mandibular buccal alveolar bone

The mandibular buccal inter-radicular space is largest between the first and second premolars and increases vertically from the cervical area to the apex. ^[10] The inter-root distance is also found to be greatest between the first and second molar, and noted that the cortical bone thickness tends to increase from the anterior to the posterior region.^[11], ^[12] Theoretically, the denser cortical bone in the mandible should lead to a higher success rate for TADs compared to the upper arch. However, Park et al. found that the success rate of TADs was actually lesser in the mandible than in the maxilla. ^[13]

Buccal shelf area

If placing a Temporary Anchorage Device in the posterior inter-radicular area of the mandible is difficult, buccal shelf area of mandible offers a dependable alternative. This area is beneficial because it allows for the insertion of TADs with increased diameter parallel to the root, minimizing the risk of root injury. A high success rate of 93% for TADs placed at this site has been reported, with no significant difference in success rates whether they were positioned in movable mucosa or attached gingiva. ^[14]

Retromolar area

The retromolar area is another alternative site for implant placement. Although the success rate of TADs in the retromolar pad is quite high, there is a risk of injuring the lingual and inferior alveolar nerves if the TADs shift to the lingual side of the retromolar pad. ^[7]

Factors Affecting Implant Site Selection

Several factors can influence the precise placement of an orthodontic mini-implant ([Figure 6]). The complexity of an insertion site depends on the number of anatomical boundaries present. Ideally, the mini-implant should be placed within the bone volume defined by these boundaries, ensuring that the screw interacts with only one boundary: the cortical plate in which it will be anchored. These boundaries influence the success rate of the mini-implant and the potential for complications. Therefore, a site with fewer boundaries is preferable to one with multiple boundaries. ^[8]

Cortical bone thickness

The cortical bone is crucial for providing stability to the mini-implant and is arguably the most critical anatomical factor to consider when selecting the placement location. A cortical plate that is too thin cannot offer adequate mechanical retention. Conversely, an overly thick plate is also undesirable. It is important to note that the thickness of the cortical plate affects the insertion torque at the implant site, with excessive torque potentially damaging the bone and causing late failures. Therefore, it is advisable to avoid both excessively thin and overly thick cortical bone for optimal implant stability. ^[15] The optimal range for achieving maximum success seemed to be between 1 mm and 1.5 mm. ^[16]

Dental roots

The proximity of the screw to the adjacent dental roots is the second most critical factor influencing the success of TADs. Generally, placing TADs closer to the roots increases the likelihood of screw failure. ^[17], ^[18], ^[19]

To reduce the risk of placing TADs too close to the roots, various strategies can be employed. For instance, anatomical averages can serve as general guidelines. These averages indicate that while buccal insertion space is often limited, several sites on the palate offer ample inter-radicular space. Notably, the area between the maxillary first and second molars provides a favourable inter-radicular distance. ^[3], ^[7], ^[11], ^[20], ^[21], ^[22]

Another consideration is to diverge the roots orthodontically in the sites that lacks adequate space of implant placement. ^[3]

Bone depth

Bone depth is the distance from the cortical plate, which provides screw retention (the first anatomical boundary), to the opposite cortical plate or another anatomical structure that may restrict insertion. ^[23]

Engaging or even penetrating the contralateral cortex generally does not raise the risk of screw failure. While single cortex engagement is standard and offers adequate retention for orthodontic purposes, some clinicians advocate for bicortical engagement in orthopedic applications, such as rapid palatal expansion (RPE) or protraction facemask use. ^[24]

Most perforations of the nasal cavity cause no issues, apart from possible discomfort or irritation. However, perforation of the maxillary sinus can lead to more serious complications due to inadequate drainage. ^[8]

Soft tissue

Attached gingiva refers to the gingiva located between the alveolar crest and the mucogingival junction. This area provides the most suitable soft tissue for mini-implant insertions because it is firmly attached and therefore remains stable, minimizing movement around the TAD. ^[25]

Various safe zones for implant placement are mentioned in [Table 1]

Safe zones for implant placement
Posterior region	Anterior region	Palate	Other locations
In both maxilla and mandible, MSI can be safetly placed between the roots of second premolar and first molar and between first molar and second molar through buccal cortical plate	Maxilla - Between central and lateral incisors at an approximate distance of 6 mm from the CEJ	The interradicular space between first and second premolar, second premolar and first molar, first molar and second molar	Maxillary tuberosity
	One MSI can be placed in the midline just below the anterior nasal spine	Midpalatal raphe - Non growing	Infra zygomatic
	Mandible - Inter radicular bone between lateral incisor and canine	Para-median position - 3 to 6 mm laterally and 6 to 9 mm posterior to incisive foramen	Retromolar area
			Buccal shelf area

Table 1 Safe zones for implant placement

Technique of Miniscrew Placement

Case selection

Proper medical history should be taken prior to miniscrew insertion – Patient having any systemic diseases affecting bone and patient under medication that affects bone metabolism.

Radiographs should be taken to evaluate the bone quality, inter-radicular space, crestal bone level, and mesio-distal angulation.

Informed consent

Oral cavity should be free from gingival inflammation and periodontal diseases. Oral prophylaxis and oral hygiene intructions should be given to the patient.

Miniscrew selection

Screw length

The miniscrews are available in the length of 5 to 12 mm. (Figure 6) Factors affecting the selection of miniscrew length includes;

Bone quantity and bone quality

Good cortical bone – Small screws can be used

Trabecular bone – Long screws might be needed

Minimum contact of screw with the bone should be 6mm in maxilla and 4 mm in mandible. So, the commonly used screw length is 7-8mm in maxilla and 5 to 7mm in mandible.

Soft tissue thickness

Thick soft tissue – Long screws should be used. Example – Thick mucosa covering palate usually requires long screws of 10-12 mm. However, in the Midpalatal suture the soft tissue thickness is less and small screw can be used in this area.

Screw thickness/Diameter

Available thickness – 1.2 to 2.7 mm.

The screw diameter is selected based on the inter-radicular space. A miniscrew intended to be placed between roots should be narrow enough to get accommodated and should have at least 1 mm bone around its maximum diameter.

Commonly used miniscrew thickness is 1.5mm. The miniscrew thickness of 1.2 mm is used between the lower incisors because of minimal inter-radicular space.

The primary stability of miniscrew depends mainly on screw thickness. ^[26], ^[27] However, there is no significant difference in the stability of TADS of greater than 1.5mm diameter and screw of greater than 2mm thickness was found to be less stable and might cause root injury. ^[28]

Miniscrew placement guide can be fabricated on a recent plaster model that helps in accurate placement of miniscrew.

Additionally, the patient is advised to begin taking 250 mg of amoxicillin or another appropriate antibiotic the night before the procedure. Patients who appear to be less pain-tolerant may also be given a safe painkiller one hour prior to the procedure.

The patient is asked to rinse with 10 ml of 0.12% chlorhexidine gluconate mouthwash for 1 min. ^[6]

Administration of local anaesthesia.

The maxillary buccal miniscrew (Self-drilling) is then inserted between the roots of premolar and molar at an angle of 45 to 60 degree ([Figure 8]) to the long axis of teeth and at an angle of 10 to 30 degree in the mandibular buccal region ([Figure 9]).

In case of self-tapping miniscrew, the pilot drilling is required before screw insertion ([Figure 10], [Figure 11])

A course of antibiotics, stringent oral hygiene care, and avoidance of hard meals would all be necessary during the postoperative phase to prevent damage to the miniscrew. It is possible to take the painkillers as needed.

After a week, there should be another follow-up to thoroughly examine for any symptoms of inflammation and mobility.

Loading of Implant

Research conducted at AIIMS examines the stability and peri-implant inflammation by analyzing the peri-miniscrew crevicular fluid (PMICF) and found that the inflammatory markers gradually decrease to baseline levels over a three-week period. Consequently, Dr. Kharbanda's protocol recommends delayed loading after three weeks. ^[6]

S.No.	Miniplate	Miniscrew
1	More invasive	Less invasive
2	More expensive	Less expensive
3	Post-operative pain and discomfort present	Less post-operative pain and discomfort
4	No interference from dental roots as they are placed away from dental arch	Inter-radicular placement might increase the risk of root damage
5	Overall success rate is better than miniscrew.	In situations when intermittent inter-arch elastic traction is employed, a single miniscrew is more prone to failure.

Table 2 Miniscrew vs miniplate

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