Townie Treatment Case: Small But Mighty by Dr. Adith Venugopal

Whole-arch distalization using extraradicular miniscrews to correct lip incompetence and bidental protrusion

by Dr. Adith Venugopal

Temporary anchorage devices play a crucial part in anchorage management, which is critical for orthodontic success. Mini-implants, often known as miniscrews, are a valuable absolute anchorage solution in orthodontics. Although they are most commonly placed in areas of the alveolar process between the roots of adjacent teeth, other locations, known as extraradicular sites, have been suggested.

Miniscrews in the infrazygomatic crest (IZC) and mandibular buccal shelf (BS) areas offer unique benefits, including reduced risk of root damage, larger quantities of cortical bone at insertion points, no interference with mesiodistal movement of teeth or groups of teeth, and low failure rates when compared with interradicular miniscrews. This allows the use of miniscrews with larger diameter and length, and allows simultaneous movement of the entire dentition. This makes them suitable for a wide range of orthodontic movements that require an effective and safe anchorage system, thereby expanding the horizons of treatment options.¹

Case selection for placement of extraradicular screws

Extraradicular screws may be employed in patients requiring maximum anchorage for tooth movement such as protraction, retraction, intrusion, extrusion, uprighting, segmental or full-arch therapy, and asymmetric tooth movement. Though it can be used in the treatment of various malocclusions, in my practice I limit the use to distalization of entire maxillary or mandibular dentition cases, especially for subjects who have relapsed and have already had their premolars previously extracted. It may also be a good method to use in patients who refuse to have therapeutic premolar extractions performed.

Diagnosis and treatment plan

A 24-year-old patient came to the office complaining about incompetent lips and protruding teeth and jaws. A missing lower right first molar was noticed during clinical examination, as well as a Class III molar and canine relationship on the left and a Class I canine relationship on the right. The lower midline was moved to the right by 2 mm. The patient had a steep mandibular plane on a Class III skeletal base, as seen on radiographs. Root canal therapy was performed on tooth #21. On #36, there was a significant decay. The existence of a mesially inclined #38 with proclined upper incisors was noted (Fig. 1).

Fig. 1: Pretreatment extraoral and intraoral pictures and radiographs.

Fig. 2: Whole-arch distalization of the maxillary and mandibular arches using infrazygomatic crest and mandibular buccal shelf miniscrews, respectively.

Fig. 3: Midtreatment radiographs illustrate the placement of extraradicular screws clear off the roots of the dentition.

Fig. 4a: CBCT slice shows the coronal section of the dentition. Note the sufficient space available for distal movement of the second molars.

Fig. 4b: CBCT slice shows the apical section of the dentition. Note the proximity of the distolingual root to the mylohyoid ridge, making distal movement of the second molars impossible.

Fig. 5: Schematic comparison among Burstone’s incisor root spring (5a), continuous arch with lever arm (5b), and combined use of miniscrews and continuous arch with additional torque on the archwire (5c).³

Fig. 6: Posttreatment extraoral and intraoral pictures and radiographs.

Fig. 7: Before and after profile comparison.

Fig. 8: Superimpositions of pre- (black) and posttreatment (red) cephalometric tracings.

• It is hard to achieve further lip retraction once lip competence is achieved.
• Premolar extractions cannot be substituted for whole-arch distalization, because of anatomical limitations as mentioned earlier.
• Line of force control is crucial to get desired vertical changes.
• Incorporation of torque (labial crown) helps maintain positive inclination while retracting, and also aids in intrusion of incisors.

References
1. Almeida MR. Biomechanics of extra-alveolar mini-implants. Dental Press J Orthod. 2019 Sep 5;24(4):93-109. doi: 10.1590/2177-6709.24.4.093-109.sar. PMID: 31508712; PMCID: PMC6733231.
2. Kim SH, Cha KS, Lee JW, Lee SM. Mandibular skeletal posterior anatomic limit for molar distalization in patients with Class III malocclusion with different vertical facial patterns. Korean J Orthod. 2021 Jul 25;51(4):250-259. doi: 10.4041/kjod.2021.51.4.250. PMID: 34275881; PMCID: PMC8290085.
3. Kim SJ, Kim JW, Choi TH, Lee KJ. Combined use of miniscrews and continuous arch for intrusive root movement of incisors in Class II division 2 with gummy smile. Angle Orthod. 2014 Sep;84(5):910-8. doi: 10.2319/080713-587.1. Epub 2014 Feb 7. PMID: 24512532.