Simultaneous Bilateral Intrusion of Supra-Erupted Maxillary Molars using Miniscrew Implants

Case report

Diagnosis and treatment plan

A 28-year-old adult female patient reported to the Department of Prosthodontics at SDM College of Dental Sciences and Hospital, Dharwad, Karnataka, India, with the chief complaint of missing teeth posteriorly in both upper and lower arches for which she wanted replacement. On preliminary intra-oral examination, it was found that the upper second molars on both sides and the upper third molar on the right side were supra-erupted and in contact with the lower alveolar ridge (Figures 1 and 2). Thus she was referred to the Department of Orthodontics and Dentofacial Orthopedics for orthodontic intrusion of the upper molars so as to facilitate prosthetic replacement in the lower posterior regions. In addition, she had generalized interdental spacing in the upper anteriors, which she wanted closed.

Thus, we outlined the following treatment objectives for her:

To level and align the upper and lower arches;

To close all spaces in the upper anterior region; and

To carry out orthodontic intrusion of the supra-erupted maxillary molars on both sides using miniscrew implants.

Treatment

Both the upper and lower arches were bonded with 0.022” x 0.028” slot MBT brackets, and the upper molars were banded. After initial levelling and aligning with 0.016” nickel-titanium archwires, 0.018” stainless steel wires were placed in the upper and lower arches, and a customized transpalatal arch was fabricated for the patient (Figure 3), from a 0.9 mm diameter stainless steel wire (LeoWire, Leone SpA, Via P a Quaracchi, 50, 50019 Sesto Fiorentino, Firenze, Italy; www.leone.it), with shortened arms ending as hooks suspended from the roof of the palate, instead of double back bends which are inserted into the palatal sheaths of the first molar bands (Figure 3).

Two minscrew implants of dimension 1.3 mm diameter and 8 mm length (AbsoAnchor Microimplant, Small Head Type, Dentos Inc, Daegu, Korea) were inserted in the attached gingiva of the buccal dento-alveolus on each side, 1 mm below the mucogingival junction, between the roots of the molars to be intruded, on the right side, and mesial to the mesiobuccal root of the second molar where the first molar was missing, on the left side (Figure 3). Only topical anaesthetic was used for all implant placement procedures.

A bracket-head implant of dimension 1.6 mm diameter and 6 mm length (AbsoAnchor Microimplant, Bracket Head Type, Dentos Inc, Daegu, Korea) was inserted 3 mm paramedian to the midpalatal suture, the reasons for which have been discussed later. The central U-loop of the transpalatal arch was bonded to the bracket-head implant (Figure 4d) by light-cured composite resin material (Transbond XT, 3M Unitek, Monrovia, CA, USA).

Elastomeric power chains were engaged from the hooks of the transpalatal arch, running across the occlusal surface of the molars to be intruded, to the miniscrew implants placed on the buccal aspect (Figure 4). On the right side where the second and third molars were present, a segment of 0.019” x 0.025” stainless steel wire was bonded onto the occlusal surfaces of the molars, and the elastomeric chain was passed over this piece of wire. An intrusive force of 100 grams was applied on each side, and the elastomeric chains were changed every 3 weeks to provide a constant intrusive force on the molars and bring about simultaneous bilateral intrusion in the posterior region (Figure 5).

Results

Sufficient intrusion of maxillary molars was achieved on both sides in a period of 6 months (Figure 6). Cephalometric superimpositions of pre- and post-intrusion lateral cephalograms registered on the Basion-Nasion plane at CC point, and on the palatal plane at anterior nasal spine, show true molar intrusion of 4 mm with molar uprighting (Figure 9). Comparison of pre- and post-intrusion orthopantomograms shows improved bone support and periodontal condition around the intruded molars, with no detectable apical root resorption (Figures 2 and 8). Currently, the patient is undertaking treatment for prosthodontic rehabilitation of the lower molars with prosthetic implants, and has been given a lower temporary removable partial denture with instructions to wear it full time, to prevent relapse of the intruded upper molars (Figure 7). She will be debonded at the time of placement of the lower fixed prosthesis, so that the orthodontic corrections achieved are maintained till then.

Discussion

The largest amount of maxillary interradicular bone in the buccal dentoalveolus is between the second premolar and first molar.⁶ To intrude the supra-erupted maxillary molars, the buccal miniscrew was placed on the right side between the second and third molars, as a vertically upward directed force was required passing through the centre of resistance of the right posterior unit, which was located in the interproximal area between these two molars. On the left side, the buccal miniscrew was placed mesial to the second molar, so that the elastomeric chain from the hook of the transpalatal arch would run diagonally across the occlusal surface of the left second molar, that is, from the distopalatal to the mesiobuccal surface. Adequate interradicular space and attached gingiva were present on both sides to allow for placement of the miniscrews.

Intrusion of molars by only applying an apically directed force to the buccal tooth attachment will tip the molars to the buccal. Sherwood et al used a constricted overlay round the archwire to provide a counterbalancing moment and control the buccal crown tipping.⁶ However, the most efficient control may result from simultaneous application of intrusive force from buccal and palatal aspects.

The paramedian area of the palate has been previously recommended for miniscrew insertion in adult patients due to its thin keratinized soft tissue, compact bone and distance from the palatine artery.^7,8-9 The median-sagittal area may be characterized by relatively low vertical bone support, so the paramedian region is a good alternative to place the palatal implants.^10,11 Bernhart et al¹² reported a success rate of 85.7% for paramedian palatal implants, while Zuger et al,¹³ in a retrospective cohort study, reported a high success rate (95.2%) of paramedian palatal implants in adolescent and adult orthodontic patients, and showed that paramedian palatal implants are highly reliable and effective devices to obtain skeletal anchorage for orthodontic treatment. The palatal bracket-head implant was placed 3 mm paramedian to the midpalatal suture. It is particularly preferable to leave the suture area undisturbed in growing patients because ossification of the suture is incomplete before the age of 23 years. Also, as the bone thickness in this region is limited, the nasal cavity may be perforated if the miniscrew used is too long. Bone in the region lateral to the midpalatal suture line is thickest in the posterior palate,¹⁴ specifically within 3 mm from the midpalatal suture.¹⁵

There is no agreement in the literature on the optimum force to be used for intrusion. Some authors suggest forces ranging from 15 to 50 grams,^16,17 whereas others have recommended using much greater forces for intrusion (150–500 grams).^9,18 Andreasen and Bishara¹⁹ suggested using 40% more than the optimum force when the elastic is first applied, to compensate for the loss of force that occurs in the first 24 hours. With this assumption, an intrusive force of 100 grams was used on each side. The elastic chain was activated every 3 weeks to maintain a constant application of force.

Whether overerupted maxillary molars can be intruded within the maxillary sinus floor without apical root resorption is controversial. Ari-Demirkaya et al²⁰ reported that the amount of resorption after molar intrusion with skeletal anchorage was not clinically different from control groups treated without intrusion mechanics. Daimaruya et al²¹ intruded maxillary second premolars into the nasal floor of six beagle dogs and reported only 0.18 + 0.18 mm (mean + SD) of apical root resorption after 7 months of intrusion. The sinus floor membrane lifted intranasally, and a thin layer of newly formed cortical bone covered the intruding roots. Park et al²² reported two cases of successful maxillary molar intrusion using skeletal anchorage, without notable root resorption.

Conclusion

This case demonstrated that substantial intrusion of supra-erupted maxillary molars could be achieved in a well-controlled manner using temporary anchorage devices to create adequate vertical clearance for restorations. The results showed that the biological response of the teeth and the surrounding bony structures to the intrusion appeared normal and acceptable. It can therefore be concluded that this technique is an effective, safe and reliable way to bring about simultaneous bilateral upper molar intrusion.