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

Categories: Orthodontics;
Townie Treatment Case: Small But Mighty 

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).

Townie Treatment Case TADs
Fig. 1: Pretreatment extraoral and intraoral pictures and radiographs.


Extraction of #14, #24 and #34 was proposed. The upper and lower canine-to-canine segments would then be retracted into the available extraction spaces using interradicular implants placed between the upper and lower second bicuspids and first molars.

This strategy was offered to the patient, but he declined because of aesthetic concerns; he worried about the bicuspid extraction spaces being visible for several months. Because of this, it was decided to extract the third molars and insert four extraradicular miniscrews (two IZC and two BS) in an attempt to distalize the entire maxillary and mandibular dentition at the same time.

Treatment progress

Upper and lower arches were bonded with 0.022-inch MBT prescription brackets. A sequence of NiTi wires, varying in size from 0.014 inch to 0.016 inch to 0.018-by-0.025 inch, was used to level and align the arches. After the upper and lower arches were perfectly aligned, teeth #18, #28 and #38 were extracted and two IZC and two BS implants were placed to begin whole-arch distalization. A powerchain was extended from the implant head to hooks inserted distal to the lateral incisor brackets on a 0.019-by-0.025-inch stainless steel archwire for whole-arch distalization (Fig. 2).

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


A force of 350 g per side was applied. Because the miniscrews are clear off the roots of the dentition, it is possible to achieve an uninhibited mesiodistal movement of the whole arch (Fig. 3). The rate of distalization was approximately 0.5 mm per month for both the arches, which is slower because of the increased resistance offered by many teeth.

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


According to studies, the average amount of distalization on the lower arch is less than 3 mm.2 That is because once the second molar’s distolingual root contacts the mylohyoid ridge, further distalization is impossible. Further distal force would simply tip the second molar distally, increasing the likelihood of relapse. Before deciding on entire-arch distalization as a treatment option, it is best to measure the distance between the distolingual root of the second molar and the mylohyoid ridge on an apical section—not coronal—of a CBCT image (Figs. 4a and 4b).

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


The application of force dictates the line of force and, ultimately, the movement of the occlusal plane while retracting the upper anterior segment. Typically, the force system involves anterior retraction induced by the force generated by a NiTi spring or chain elastics, which connects the mini-implant to a hook affixed to the archwire. Similar to our case, when retraction force is provided by a force that passes below the CR, anterior teeth tend to rotate clockwise, resulting in torque loss and a vertical extrusion force on the incisors.1 To counteract this, more positive crown torque on the wire in the anterior region was incorporated. The resultant force vector caused an upward and backward movement of the incisors, resulting in incisor intrusion and retraction (Figs. 5a–c).3

Townie Treatment Case TADs
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


All resultant spaces were substantially closed by retraction after 30 months of active treatment. Distalization was achieved in all quadrants, with retraction and intrusion of the upper incisors and uprighting of the lower incisors. The patient demonstrated improved aesthetics, a satisfactory occlusion and lip competence after orthodontic therapy (Figs. 6–8).

Townie Treatment Case TADs
Fig. 6: Posttreatment extraoral and intraoral pictures and radiographs.
Townie Treatment Case TADs
Fig. 7: Before and after profile comparison.
Townie Treatment Case TADs
Fig. 8: Superimpositions of pre- (black) and posttreatment (red) cephalometric tracings.


Conclusion

With clinical experience, it is possible to suggest that:
  • 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.



Author Bio
Dr. Adith Venugopal
Dr. Adith Venugopal is a clinical instructor and associate professor of orthodontics and dentofacial orthopedics at the University of Puthisastra, Phnom Penh, Cambodia, and an adjunct professor of orthodontics at Saveetha Dental College and Hospitals in Chennai, India. He also has a private practice at Pachem Dental Clinic in Phnom Penh. Venugopal has published several scientific studies and clinical reports in international peer-reviewed scientific journals, and has been an invited keynote speaker at many international orthodontic congresses. He has held courses and workshops on TAD-based biomechanics worldwide. His current research and clinical interests are on TAD-assisted biomechanics for tooth movement, adult Class III correction and gummy smile corrections.

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