TADs in Orthodontics: Mini Screws, Sites and Success Rates
Temporary anchorage devices (TADs) changed how orthodontists think about anchorage. A small titanium screw placed in the alveolar bone or the palate gives a point of support that does not move in response to the reaction force, or moves very little, and does not depend on the patient wearing headgear or elastics. "Absolute anchorage" is the usual phrase, and it is misleading: mini screws fail, can move, and do not cancel the side effects of the mechanics. This guide covers indications, insertion sites, success and failure rates, complications and anchorage planning.
What are TADs?
TAD is an umbrella term for devices fixed temporarily to bone to serve as orthodontic anchorage and removed at the end of their use. The main families are:
- mini screws (also called miniscrews, mini-implants or microimplants): the most widely used, placed between roots, in the palate or in other bony sites;
- miniplates: fixed to bone with several screws, away from the roots, used for heavier forces or orthopedic purposes;
- palatal implants: short osseointegrated implants in the palate, connected to the teeth by a transpalatal arch.
Our D.U. knowledge base describes mini screws as non-osseointegrated titanium screws, self-tapping or self-drilling, 1.2 to 2 mm in diameter and 6 to 12 mm long, longer where the cortex is thin (Boileau). Thinner screws pass more easily between roots but are more likely to fracture. Osseointegration is not sought; it increases with time, and removal is by simple unscrewing, without anesthesia in most cases (EMC).
In a meta-analysis, self-drilling and self-tapping mini screws had similar success rates; self-drilling screws carried a higher risk of failure when they touched a root (Yi et al., 2017, Eur J Orthod).
Where TADs fit in anchorage planning
Anchorage is the resistance to unwanted tooth movement, the reaction that Newton’s third law guarantees. The course materials rank anchorage methods by increasing strength: conventional intraoral means, then extraoral, then combined (Tweed anchorage preparation, cortical anchorage), then mini screws. Their first rule is that the anchorage need is quantified before the mechanics start: the space analysis (Steiner box or Tweed total space) is compared with the extraction space. If they are equal or the need is greater, anchorage is maximal; if the need is smaller, anchorage loss can be programmed. Our French article on orthodontic anchorage details this reasoning, and our free space analysis tool helps with the arithmetic.
TADs come in at the end of that reasoning, when natural and conventional anchorage are not enough. The courses list situations where the patient’s own anchorage is weak:
| If the patient has… | …natural anchorage is | Direction suggested in the courses |
|---|---|---|
| A hyperdivergent pattern | Weak, sagittally and vertically | Reinforce from the start with non-extrusive means (high-pull headgear, TPA, mini screws) |
| A reduced periodontium | Weak; center of resistance more apical | Lighter forces; conventional intraoral means insufficient, consider skeletal anchorage |
| Missing or small anchor teeth | Reduced | Add teeth to the anchor unit, skeletal or implant anchorage |
| Uncertain cooperation | — | Avoid extraoral devices; mini screws work without cooperation |
| An asymmetric arch | Different needs on each side | Differential anchorage; mini screws strongly recommended for asymmetric mechanics |
For adults, the base adds: non-skeletal means first, and no mini screw when conventional mechanics do as well (overtreatment).
Indications for mini screws
The course and textbook indications cover the three planes:
- Sagittal: en-masse retraction of the anterior teeth after extractions, canine retraction with maximal anchorage, distalization of upper molars in Class II or lower molars in Class III, mesialization of lower molars when incisor retraction would harm the profile, support for Class II or Class III elastics without loading the opposing arch.
- Vertical: molar or incisor intrusion, open-bite closure, reduction of mandibular clockwise rotation; incisor intrusion is described as the hardest movement, and mini screws are preferred to tooth-borne intrusion in hyperdivergent patients.
- Transverse and other: midline correction, occlusal plane cant, impacted tooth traction, molar uprighting before prosthetics, intermaxillary fixation after surgery.
Boileau adds that TADs should not systematically replace conventional anchorage, and describes miniplates for heavier forces, vertical molar control and Class III orthopedics.
Insertion sites
The knowledge base lists the usual sites:
- Maxilla (thin cortex, less dense bone): buccal and palatal alveolar processes, paramedian palate, retromolar area, anterior nasal spine, infrazygomatic crest.
- Mandible (thick cortex, dense bone): buccal alveolar process, retromolar area, symphysis.
Structures to avoid: the sinus, palatine neurovascular bundles, the mental foramen and the roots. The neck of the screw should sit in attached gingiva; in movable mucosa it inflames and the head gets buried. The EMC and Canal add that the palatal side is safer than the buccal side, between the upper second premolar and first molar has the best success, and that in the posterior maxilla the sinus starts about 8 mm above the crest.
Interradicular space
The textbooks ask for at least 1.5 mm of bone between the screw and each periodontal ligament, which means at least 4.5 mm of interradicular width for a 1.5 mm screw. When that width exists only apically, in movable mucosa, the options are to open the space first with second-order bends, or to distalize the molars and place the screw mesial to them. The screw’s position at the end of the planned tooth movement must also be anticipated.
Failure rate by site
A meta-analysis of 61 studies gave failure rates by site (Mohammed et al., 2018, Prog Orthod):
| Site | Failure rate (95% CI) |
|---|---|
| Midpalatal | 1.3% (0.3-6) |
| Paramedian palate | 4.8% (1.6-13.4) |
| Parapalatal | 5.5% (2.8-10.7) |
| Maxillary buccal, between second premolar and first molar | 9.2% (7.4-11.4) |
| Maxillary buccal, between lateral incisor and canine | 9.7% (5.1-17.6) |
| Infrazygomatic (zygomatic buttress) | 16.4% (4.9-42.5) |
| Mandibular buccal, between second premolar and first molar | 13.5% (7.3-23.6) |
| Mandibular buccal, between canine and first premolar | 9.9% (4.9-19.1) |
Root contact multiplied the risk of failure by about 8.7. The quality of evidence was very low to low for most sites and moderate for the effect of root contact.
Success rate and failure factors
What meta-analyses report
- 13.5% overall failure (95% CI 11.5-15.8) for 4,987 mini screws in 2,281 patients; failure was not associated with sex, age or side, but was associated with the jaw of insertion (Papageorgiou et al., 2012, AJODO).
- 13.5% again (95% CI 11.5-15.9) for about 3,250 mini screws in 41 studies; diameter, length, design, age and jaw had minimal effect, while the type of gingiva and smoking had a significant effect (Alharbi et al., 2018, Eur J Orthod).
- 16.4% for mini screws, against 7.3% for miniplates and 10.5% for palatal implants, in an older review of 27 studies; torque-resisting devices failed about half as often (Schätzle et al., 2009, Clin Oral Implants Res).
- An umbrella review of 17 systematic reviews found success rates of 90% or more in most of them, with large methodological gaps and heterogeneity (Ramírez-Ossa et al., 2020, J Evid Based Dent Pract).
Our course materials give a similar order of magnitude: failure from under 10% to 30% depending on the studies (Boileau), about 8 to 12% (Canal, EMC).
Causes of failure named in the knowledge base
- root contact, the first cause of failure, especially in the mandible;
- lack of primary stability;
- inflammation around the screw, often linked to movable mucosa or poor hygiene;
- placement technique: overheating or an oversized pilot hole, "whipping" the screw during insertion, a screw too short, poorly corticalized bone;
- excessive load, or a screw disturbed by the tongue, cheek or a frenum;
- fracture of thin screws.
A slightly mobile screw has not necessarily failed: the EMC advises loading it more gradually and keeping it while it still anchors, never screwing, unscrewing and rescrewing the same site. A new screw can be placed after about 3 weeks, or in a neighboring site.
Age
The initial-training course sets bone maturity over 15 years as a condition for mini screws, together with good hygiene, and this remains the rule shown in our knowledge base. Boileau gives no age and names other contraindications instead: bone in remodeling (resorbing primary teeth, recent extraction), insufficient bone, poor cooperation or hygiene, and the general contraindications of implants. Miniplates are described around 12 years in Class III. The two meta-analyses above found no clear effect of age on failure. The age threshold is therefore a course rule, not a finding from these reviews; for a young patient, bone and hygiene are the criteria to assess.
Loading and placement protocol
The knowledge base reports a protocol from Boileau, with variants among authors:
- Imaging: panoramic plus long-cone periapical radiograph, or tomography; control radiograph after placement (Boileau; Canal does not make it systematic).
- Light mucosal anesthesia, so that the patient still feels the periodontal ligament if the screw approaches a root.
- Pilot hole of 2 to 3 mm in thick cortex, even with self-drilling screws; manual insertion; primary stability is indispensable.
- Loading immediately at about 50 g, or after healing, then progressively. Other authors give 50 to 200 g, 150 g at most without any couple, or 25 to 50 g; all agree on starting light, without a couple, and increasing gradually.
- Postoperative care: chlorhexidine for about 10 days, no routine antibiotics (Canal).
Under heavy, prolonged loads, screws can drift by 0.5 to 1.5 mm: keep about 2 mm of margin from any structure.
Complications
A systematic review of 24 articles, of low methodological quality, found root injury to be the most frequent adverse event, with periradicular lesions, loss of vitality, pink discoloration of the tooth and transient loss of pulp sensitivity. Other events included chronic inflammation with mucosal overgrowth, buccal mucosa lesions, soft tissue necrosis, perforation of the nasal floor or maxillary sinus, and, after removal, bleeding, screw fracture, scars and exostosis (Giudice et al., 2021, Korean J Orthod).
The knowledge base gives clinical signs: a screw touching the periodontal ligament causes pain on percussion and chewing; a touched root becomes sensitive to hot and cold, and the screw should then be removed. On the patient side, pain after insertion was mild to moderate on the first day and mild by the fifth to seventh day, and speaking, chewing and cleaning were more problematic with TADs than with conventional anchorage (Mousa et al., 2023, Cureus).
Do TADs actually anchor better?
The meta-analyses agree on the direction and differ on the size of the effect:
- En-masse retraction: 1.86 mm more anchorage preservation than conventional methods, 14 studies, 616 patients, moderate quality (Antoszewska-Smith et al., 2017, AJODO).
- Maximum anchorage cases with bimaxillary protrusion: less mesial molar movement and more incisor retraction with mini-implants, 12 studies (Liu et al., 2020, J Evid Based Dent Pract).
- Canine retraction: about 1.6 mm more anchorage preservation in each jaw, very low-quality evidence (Tian et al., 2020, BMC Oral Health).
- Incisor intrusion in adults with deep bite: 0.78 mm more upper incisor intrusion than segmented arches, statistically significant but judged not clinically relevant by the authors (Atalla et al., 2019, Contemp Clin Dent).
Soft tissue follows the teeth: greater retraction with TADs came with a larger increase of the nasolabial angle in two meta-analyses, about 4.7° more than two-step retraction with conventional anchorage in one of them, which matters when the profile is already flat (Khlef et al., 2018, Contemp Clin Dent; Liu et al., 2019, J Evid Based Dent Pract). The evidence on these soft tissue effects is of low quality (Mohan et al., 2022, J Orofac Orthop). Before-and-after incisor positions can be checked with our free cephalometric analysis tool.
"Absolute" anchorage is not side-effect free
The knowledge base is explicit on this point: mini screws prevent neither arch tipping nor vertical effects. A distal force applied below the center of resistance tips the occlusal plane clockwise; a unilateral force tips the arch toward that side; a vertical component flares the molars buccally. Even with mini screws, transverse control of the maxilla remains unpredictable. Success depends on bone, hygiene and technique, and above all on biomechanics. Our French article on the biology of tooth movement and orthodontic forces covers the force systems involved.
In practice: a checklist
- Quantify the anchorage need from the space analysis before choosing any device.
- Check whether conventional anchorage would do the job; if so, a mini screw is overtreatment.
- Assess bone maturity, hygiene, periodontium, smoking and the general contraindications of implants.
- Choose the site on imaging: interradicular width (at least 4.5 mm for a 1.5 mm screw), attached gingiva, distance from the sinus, roots and nerves, and the screw’s position at the end of the movement.
- Start with a light load and increase gradually; check stability at each visit.
- Predict the side effects of the force system (occlusal plane cant, arch tipping, vertical changes) and plan their control.
Frequently asked questions
What is the success rate of orthodontic mini screws?
Two large meta-analyses found a mean failure rate of 13.5%, so roughly 86 to 87% success, with wide variation by site: about 1% in the midpalatal region against more than 13% in the posterior mandible (Papageorgiou et al., 2012; Alharbi et al., 2018; Mohammed et al., 2018).
Does placing a TAD hurt?
Placement is done under light local anesthesia. In a review of patient-reported outcomes, pain was mild to moderate on the first day and mild by the end of the first week (Mousa et al., 2023). For a specific case, the orthodontist in charge can explain what to expect.
How long do mini screws stay in?
As long as the mechanics need them. The EMC gives an average use of 3 to 8 months; removal is usually done by unscrewing, often without anesthesia, and the site heals within about a week.
Is there a minimum age for TADs?
Our course materials set bone maturity over 15 years for mini screws, while Boileau sets no age and looks at bone quality and hygiene instead; meta-analyses found no clear link between age and failure. Miniplates are used earlier in some Class III protocols.
What is the difference between TADs and dental implants?
Dental implants osseointegrate and stay for life. Mini screws are thinner, are not meant to osseointegrate, can be loaded early and are removed after use. A prosthetic implant can also serve as anchorage, but the restorative plan fixes its position.
With GS Ortho
In GS Ortho, the diagnostic studio takes the case through 12 panels, so the anchorage need is reasoned from the clinical examination, photos, cephalometrics and the space analysis of the same patient before any device is chosen. AI places 29 landmarks on the lateral cephalogram for you to check and correct, and the Steiner and Tweed analyses follow. When the choice between conventional and skeletal anchorage is unclear, "Request an opinion" sends the question, with the panel attached, to a colleague or supervisor you choose; the answer stays in the record. The decision stays yours. The GS Ortho interface is currently available in French.