A simple guide to orthodontic miniscrews. Part 3: possible complications

In the previous 2 blogs we looked at the history and success rates of TADs as well as some evidence of their effectiveness in providing anchorage. Now it is time to explore their complications and side effects.

Complications are RARE! We have to admit that in our experience of placing TADs, our failure rate is approximately 5% mostly due to complications in the form of loosening of the TAD. In hindsight, certain basic principles weren’t adhered to, resulting in loss of primary stability and failure or mucosal overgrowth.

A thorough understanding of the following basic principles is essential for successful TAD placement: proper placement techniques, understanding bone density requirements, peri-implant soft tissue and regional anatomical structures. As with any ‘surgical’ procedure, complications are not uncommon, however. Complications may occur at any of the following stages: during insertion, during loading and/or during removal.

There are potential complications that patients should be aware of. These should be discussed with the patient to form the basis of informed consent. Some of the complications associated with TADs may include:

1. Failure to achieve adequate anchorage: In some cases, TADs may not provide sufficient support for the desired tooth movement, leading to ineffective treatment outcomes.

2. Infection: Like any ‘surgical’ procedure, there is a risk of infection at the site where the TAD is placed. We have not seen this in our patients.

3. Tissue damage: Improper placement of TADs can result in damage to surrounding tissues such as gingiva and roots of adjacent teeth. This can lead to pain, inflammation, and other complications.

4. Loosening or loss of TADs: They can sometimes become loose or even dislodged due to factors such as poor bone quality, inadequate screw size, or incorrect placement.

5. Allergic reactions: While rare, some individuals may experience allergic reactions to the titanium material used in TADs.

6. Root resorption: Prolonged TAD placement or excessive forces applied during orthodontic treatment can contribute to root resorption.

7. Patient discomfort: Some patients may experience discomfort or pain at the TAD insertion site, especially in the initial days after placement. This discomfort typically subsides as the area heals.

A great systematic review by Lo Giudice and colleagues summarised the evidence nicely. The authors concluded that “the most frequent adverse event reported was root injury with an associated periradicular lesion, vitality loss, pink discoloration of the tooth, and transitory loss of pulp sensitivity. Chronic inflammation of the soft tissue surrounding the miniscrew with mucosal overgrowth was also reported. The other adverse events reported were lesion of the buccal mucosa at the insertion site, soft-tissue necrosis, and perforation of the floor of the nasal cavity and maxillary sinus. Adverse events were also reported after miniscrew removal and included secondary bleeding, miniscrew fracture, scars, and exostosis”.

From the abovementioned complications, mucosal overgrowth is probably the most common, particularly in the mandible. It tends to be more common if the TAD is placed in an area of unattached mucosa i.e. apical to the mucogingival junction.

Mucosal overgrowth around the TAD in lower right region.

Sometimes we are limited anatomically by the soft tissue boundaries and we have to make a choice of whether to place the TAD in attached keratinised gingiva, accepting that it is not ideal or place in the ideal position even if it is in unattached mucosa. Coronal placement of the TAD risks root contact and injury given that there is less interradicular clearance coronally and more root divergence apically.

The TAD was placed too coronal in order to keep it within keratinised gingiva.

In the case of interradicular placement, some clinicians recommend pre-TAD placement orthodontics in order to diverge the roots. We don’t feel this is needed in the vast majority of cases. However, we do recommend inserting the TAD at 40-45 degrees apically and 5-10 degrees distally in order to avoid root contact of the upper second premolar and first molar.

The TAD is inserted at 40-45 degrees to the occlusal plane.

The TAD is inserted at 5-10 degrees distally.

Trauma to the dental roots or periodontal ligament can theoretically lead to ankylosis (rare), root resorption (rare), root fracture (rare), loss of vitality (really rare) or osteosclerosis (really rare). Clinicians should not rely solely on radiographs as an assessment tool, as radiographs are usually unreliable in predicting the proper site of insertion. During insertion, if resistance is encountered or if patient feels a sudden sharp pain, then it can be assumed that the screw has come in contact with a root.

We recommend applying minimal local anaesthetic infiltration directly over the site of insertion. The aim should be to anaesthetise the superficial soft tissue without anesthetising the bone or roots. In this way any contact with the roots will be noticed by the patient.

What if the TAD comes in contact with the root, what is going to happen? complete repair of the injury usually takes place within 12 weeks. In fact, healing of the cementum can take place within 8 weeks in some cases.

In the case of perforation of the root (uncommon), there are reports to suggest that spontaneous repair takes place upon removal of the screw.

To avoid root damage when placing interradicular TADs, clinicians should be aware of the safe zones in both the maxilla and mandible.

Safe zones in the maxilla.

Safe zones in the mandible.

Clinicians should also be familiar with the anatomy of relevant nerves and blood vessels prior to TAD insertion. When placing a palatal TAD, there is a small theoretical risk of damage to greater palatine nerve and blood vessels. The palatine foramen is usually lateral to the third molar or between second and third molars. It runs anteriorly 5–15 mm from the gingival margin. Therefore, TADs should be placed in a more mesial site in the palatal slopes if it is clinically decided to be inserted in the third molar region.

In the mandibular buccal shelf, there is a risk of damage to the inferior alveolar nerve which runs in the mandibular canal. It is most buccally placed just distal to the second molar and around the apex of the second premolar.

In the retromolar region, there is a risk of damage to two main nerves. The long buccal nerve, which runs buccally and crosses high in the retromolar area; whilst the lingual nerve runs lingually and lies immediately under the floor of the mouth. Thus, TADs of less than 8 mm length are recommended in these regions.

It is also not uncommon to perforate the maxillary sinus when placing TADs in the buccal cortical bone, the risk is higher if the region is edentulous although perforations usually heal without any complications. It is believed that the stability of immediately loaded miniscrews that perforate the sinus is not compromised. In these cases, it is recommended to continue the orthodontic therapy as there is no need for repositioning of the miniscrew. However, careful monitoring is required.

A further complication that the clinician should be aware of is bending and even fracture of the TADs during insertion or indeed removal. TADs fracture due to either high torsional stress or cyclic fatigue. This was a significant weakness of earlier versions, fracture is less likely with the newer types of TADs. If fracture occurs, it occurs most likely between the head and the collar. It is recommended to avoid excessive pressure and over tightening of the miniscrews to eliminate the risk of cyclic fatigue.

Bone quality should be assessed adequately as dense bone may require pre-drilling. If a self-drilling TAD is used in dense cortical bone, then a diameter of 1.6 mm or greater is recommended. If breakage occurs, it is recommended to remove the broken part if possible (artery forceps can be useful). Generally, if the broken screw is deep and sterile, it can be left in-situ; however, careful monitoring is required.

Finally, poor oral hygiene can lead to mucosal irritation which may cause peri-implantitis. Poor oral hygiene can also cause soft tissue hypertrophy as described above which in turn may lead to partial or complete coverage of the TAD head. Thus, it is recommended for patients to have meticulous oral hygiene.

Final remarks: placement of TADs is relatively straightforward and complications are unlikely. In the event of any complications arising, dealing with the complications is simple as long as the clinician adheres to the basic principles as described above.

For patients:

Bone screws are commonly used in orthodontic treatment to provide extra support for moving teeth. Despite being effective, they can lead to issues such as loosening, moving in the bone, infection, or harm to nearby teeth. Proper placement and monitoring by your orthodontist are crucial to prevent problems. Regular check-ups are vital to ensure the bone screws work well and address any concerns promptly. If you feel pain, discomfort, or see changes near the bone screw, contact your orthodontist right away to prevent complications from getting worse. Collaboration with your orthodontist is key to minimizing risks and achieving the best results in your orthodontic treatment.