Maxillary incisor intrusion with miniscrews

Deep overbite is one of the most challenging occlusal trait to manage during orthodontic correction, probably due to the various contributing aetiologies. Orthodontic correction of deep bites could be accomplished by variety of tooth movements; extrusion of molars, intrusion of incisors, proclination of incisors, and/or more commonly a combination of one or more of these methods. Therefore, careful, thorough and accurate diagnosis of the aetiology is essential for correct management.

True intrusion (or at least near true!) of the maxillary incisors is indicated in adult patients with hyperdivergence. Intrusion is also indicated in the non-surgical management of vertical maxillary excess (VME). VME can be posterior, anterior or total. In some cases, but not all, VME can cause increased gingival exposure i.e. gummy smile which warrants treatment.

In the case of VME, Intrusion of 2-3mm can be achieved with temporary anchorage devices (TADs). Anything more than 3mm falls beyond the realms of orthodontics only and surgery may be considered. We have covered some basic principles related to TADs previously in three parts; I, II and III.

Case

Deep overbite. Aetiology: combination of accentuated Curve of Spee in the mandibular arch and anterior VME.

TADs of 2x8mm dimension inserted just above the mucogingival margins apical to UR2/3 and UL2/3. Approximately 100g of intrusive force was applied via elastomeric powerchain to the base archwire (19”x25” SS).

Full correction of the deep overbite was achieved via intrusion of maxillary incisors and levelling the mandibular Curve of Spee.

Gingival display was reduced by approximately 3mm by ‘near true’ intrusion of maxillary incisors addressing the anterior VME.

Pre-op radiograph showing normal roots of the anterior teeth.

Near end of treatment radiographs confirming no-little resorption of the incisors.

Do we actually get more true intrusion with TADs?

Gupta et al. 2022 in their systematic review found that incisor proclination by TAD-supported incisal intrusion was more than that in the intrusion arch subgroup; however, the difference may not be clinically very relevant. Nevertheless, true intrusion is more obvious when compared to continuous arch mechanics.

Shakti et al. 2022 in a meta-analysis found high certainty of evidence associated with higher association of TADs with incisor intrusion and overbite correction. The review suggests that TADs are superior to the Connecticut intrusion arch with respect to the amount of incisor intrusion and overbite correction.

Is there a higher risk of root resorption associated with TAD supported intrusion?

Solsy et al. 2020 in a systematic review and meta-analysis found that root resorption seems to be an associated adverse effect that occurs regardless of the intrusive mechanics used. Seven RCTs were included in the meta-analysis. When compared with intrusion arches, TADs resulted in a more efficient deep-bite reduction. When TADs were used, a statistically significant difference was observed favouring less maxillary molar extrusion and more incisor intrusion.

Should we use one or two TADs?

This is an interesting clinical question that has significant implications. Fortunately, a recent RCT published in the Angle Orthodontist attempted to answer the question. Manikandan et al. 2024 examined dentoalveolar changes following intrusion of maxillary incisors with one or two anterior TADs in patients with gummy smile and deep bite. Forty-three patients were selected and divided into two groups: group I received one TAD between the upper central incisors, and group II received two TADs between the canines and lateral incisors. Dentoalveolar parameters, including amount of intrusion, root resorption, incisor inclination, alveolar bone thickness, and buccal alveolar crest height, were evaluated using cone-beam computed tomography scans obtained before and after intrusion.

In the present study, when the same total 100g was applied, the degree of intrusion was greater in dual TAD patients than in those with a single TAD. Moreover, root resorption of the maxillary central incisors was greater in patients with one TAD, while maxillary lateral incisor resorption was greater in patients treated with two TADs. This is probably related to the proximity of the TAD to the roots of the central incisors and lateral incisors in the 2 groups.

Should the TADs be placed between lateral and central incisors or lateral incisor and canine?

In our experience, we think that the benefit of placing the TADs between 2s and 3s: 1-there is a natural divergence of the canine and lateral incisor roots meaning there is more inter-radicular bone for safer placement, 2-placing the TADs further apart will allow force dissipation and possibly reduced incidence of root resorption and 3-the mucogingival junction between the 2 and 3 is higher meaning the TAD can be place more apical.

For patients:

Within the realm of orthodontics, the utilisation of bone screws for reducing/eliminating a gummy smile stands out as a highly effective and widely-recognised procedure. This innovative technique involves the strategic placement of bone screws into the jawbone to exert controlled forces, facilitating precise movement of the front teeth and the associated gum. Particularly beneficial for addressing vertical discrepancies such as deep overbites or gummy smiles, bone screws serve as temporary anchorage points that enable targeted tooth movement without impacting neighbouring teeth. By embracing bone screws for treating gummy smiles, we can achieve aesthetically pleasing and functionally optimal outcomes, demonstrating a significant advancement in contemporary orthodontic practices.