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Townie Treatment Case: Cant Be Tamed by Dr. Adith Venugopal

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Categories: Orthodontics;
Townie Treatment Case: Cant Be Tamed

A predictable approach to using TADs to correct a steep occlusal cant


by Dr. Adith Venugopal
with Dr. Anand Marya


Asymmetries may pose challenges for orthodontists because of the diverse etiologies, complex mechanics and the uncertain stability of the treatment.1 Occlusal plane canting is one of the asymmetries that usually causes additional treatment complexity.

Diagnosis

A 24-year-old male patient came into the office with a chief complaint of an uneven smile, crooked teeth and excessive gum display when smiling. Clinical examination revealed mild crowding on the upper and lower arches, a Class II canine relationship on the right, a Class I canine relationship on the left, a lower midline shifted to the right by about 2 mm and a severely canted occlusion to the left (Fig. 1).

Dental TADs Case
Fig.1: Pretreatment extraoral and intraoral pictures with radiographs.

The excessive gingival display when smiling was secondary to the cant of occlusion (Fig. 2). Radiographically, the patient displayed a normo-divergent mandible and root canal treatments performed on teeth #14 and #15. Ramal length was found to be a bit longer on the left compared with the right. Frontal extraoral pictures showed a clear asymmetry with the chin positioned toward his right (Fig. 1).

Dental TADs Case
Fig.2: Photographs showing the amount of occlusal cant and subsequent gingival display on smiling.

To diagnose and quantify the occlusal cant, certain reference lines are marked on the photographs, either manually or through basic software such as Keynote or PowerPoint. One of these lines is the bipupilar line, which may be transferred from the original position to the commissure region, the gingival contour or tip of the cusp of one canine, or even the incisal edge of one incisor, depending on the necessity (Fig. 3).

Dental TADs Case
Fig.3: Quantifying the occlusal cant using bipupilar reference lines.

A PA radiograph or CBCT must be used when severe skeletal asymmetries are present and the treatment plan requires an orthognathic surgery as the main corrective measure for the canted occlusal plane.

Once the occlusal cants are defined and quantified, it is essential to identify which side is the “good” side and which side should be intruded or extruded to level the plane. Usually, the upper arch serves as the reference to the diagnosis through the exposure of the crowns and the gingiva, and the orthodontist must know all the aesthetic commandments to interpret the smile.

Orthodontic literature showcases many treatment options for such malocclusions. Some involve altering the bracket heights by placing them more incisal/gingival on the canted side and the opposite on the normal side.2 Others involve using a yin-yang wire that would generate forces in the opposite direction on either side of the arches, thereby flattening the cant.3 Other techniques involve sectional archwires and cantilevers to generate controlled moments to extrude or intrude the segments that need such movements to correct the cant.4

Unfortunately, all of the above methods either involve a reciprocal action on the good/normal side or need anchorage reinforcements in the form of palatal appliances on the molars to counteract the counter-moments generated on the molars through the use of cantilevers/auxiliaries.

Treatment plan

In this case, a biomechanical strategy was devised that required two buccal mini-implants to correct the patient’s severe cant and excessive gingival display. 0.022-inch MBT prescription brackets were bonded on the upper and lower arches. Leveling and alignment were performed on a sequence of NiTi wires ranging from 0.014-inch through 0.016-inch to 0.017-by-0.025-inch NiTi.

After leveling and alignment, two mini-implants were inserted interradicularly between #22–#23 and #24–#25. Because the patient had very limited attached gingiva, the mini-implant placement was mucosal. It was imperative to use a longer implant with a long collar and a bulbous head to reduce chances of inflammation around the neck of the mini-implant; the implants used here were 1.8 by 10 mm.

Intrusion of the left upper posterior segment was initiated on a 0.017-by-0.025-inch NiTi and later continued on a 0.019-by-0.025-inch SS wire using elastic threads from the mini-implant to the base archwire. The distal mini-implant’s position was later placed between #25 and #26 once sufficient intrusion was obtained in the canine to premolar region. The second molars weren’t bonded because they were above the occlusal plane and involving them would lead to unnecessary round-tripping (Fig. 4).


Dental TADs Case
Fig.4: Biomechanics involved in the correction of the occlusal cant using 1.8-by-10mm MIs.

Usually, when such force vectors are used, the most common side effect is buccal tipping of the segment being intruded.5 This is obvious, because there is no counteracting force on the palatal aspect. Usually such a treatment would involve the placement of a transpalatal arch or mini-implants on the palatal alveolar ridge to counteract the buccal tipping forces.

In this case, the buccal tipping forces on the left side were counterbalanced by making the arch a single unit by lacing all the maxillary teeth together, incorporating a palatal crown torque on the archwire distal to the #2 and the use of minimal forces of intrusion (60g per elastic thread).

After about six months of active intrusion, a posterior open bite was forming on the left side. This was resolved with light 5⁄16-inch, 2 oz box elastics to extrude the lower left segment and close the bite. The intrusive forces were continued while using the box elastics to prevent the upper posteriors from extruding back (Fig. 4). As the cant was corrected and the lower left posteriors segment erupted, the mandible repositioned itself into a more natural position and the midlines were coincident with the facial midlines.

After 17 months of active orthodontic treatment, the cant was corrected and the canines and molars on the left and right sides were on a Class I relationship (Fig. 5). Most of the soft-tissue asymmetry was corrected after the cant correction (Fig. 6). With the subsequent intrusion on the left posterior segment, substantial correction in the gingival display on smile was noticed (Figs. 7 and 8).



Dental TADs Case
Fig. 5: Posttreatment extraoral and intraoral pictures with radiographs.

Dental TADs Case
Fig.6: Comparative pictures showing correction of the soft-tissue chin asymmetry.

Dental TADs Case
Fig.7: Comparative pictures showing correction of occlusal cant and gingival exposure maintaining the same inter-lip distance.

Dental TADs Case
Fig.8: Sequential follow-up pictures showing the gradual correction of the occlusal cant.

Conclusion


Gummy smile correction is one of orthodontist’s most overestimated treatments and the “after” smiles are usually never as animated as the “before” smiles. Cants and gingival smile displays are usually diagnosed with photographs with maximum elevation of the upper lip. Because a smile is such a dynamic process and a person never smiles the same at any one given point of time, a video would be the best way to gauge the level of gained correction.6 One could also measure the interlip distance (Fig. 7) and keep it constant in the before and after smiles photographs.

All in all, the improvement of soft-tissue chin deviation, steep occlusal cant and a severe gingival exposure through orthodontic management without surgical intervention makes us wonder if the envelope of discrepancy has indeed expanded.

References
1. Burstone, CJ. Diagnosis and treatment planning of patients with asymmetries. Semin Orthod 1998;4:153-64.
2. Anhoury PS. Nonsurgical treatment of an adult with mandibular asymmetry and unilateral posterior crossbite. Am J Orthod Dentofacial Orthop 2009;135:118-26.
3. Liou EJW, Mehta K, Lin JCY. An archwire for non-invasive improvement of occlusal cant and soft tissue chin deviation. APOS Trends Orthod 2019;9(1):19-25.
4. Farret, Marcel Marchiori. (2019). Occlusal plane canting: a treatment alternative using skeletal anchorage. Dental Press Journal of Orthodontics, 24(1), 88-105.
5. Takano-Yamamoto T, Kuroda S. Titanium screw anchorage for correction of canted occlusal plane in patients with facial asymmetry. Am J Orthod Dentofacial Orthop. 2007;132(2):237-42.
6. Lee MS, Chung DH, Lee JW, Cha KS. Assessing soft-tissue characteristics of facial asymmetry with photographs. Am J Orthod Dentofacial Orthop. 2010;138(1):23-31.


 

Author Bio
Adith Venugopal Dr. Adith Venugopal is a clinical instructor and assistant professor of orthodontics and dentofacial orthopedics at the University of Puthisastra, PhnomPenh, 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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