19
Transversal Problems: Symmetric and Asymmetric Expansion

It is commonly accepted that, in the transverse dimension, normal occlusion is when the palatine cusps of the upper molars and premolars occlude in the fossa of lower molars and premolars.

This is also related to arch expansion, which is mostly defined by the patient’s skeletal condition, and is one of the key factors in success with aligners, as it is possible to expand asymmetrically with the archform tool – something that has been never possible with standard preformed NiTi archwires.

Schematic illustration of classic NiTi archwires were only available on standard sizes and shapes, now, with aligners, we can define exactly the best archform for every patient — **Fig. 19.1** Classic NiTi archwires were only available on standard sizes and shapes, now, with aligners, we can define exactly the best archform for every patient.

This is especially important in order to avoid gingival recessions associated with excessive dental expansions, and this is the reason why it is so important to use the archform tool to decide whether to have a regular expansion or more posterior/anterior sector one.

Schematic illustration of expansion can be defined in a precise way, with the decision about whether if it is more or less on anterior/posterior made according to patient’s available bone — **Fig. 19.2** Expansion can be defined in a precise way, with the decision about whether if it is more or less on anterior/posterior made according to patient’s available bone.

Schematic illustration of expansion with aligners can be defined in between Fa point (blue line) and Wa point (yellow line) — **Fig. 19.3** Expansion with aligners can be defined in between Fa point (blue line) and Wa point (yellow line).

That said, a crossbite is a commonly seen discrepancy in the buccolingual relationship of the upper and lower teeth, when the lower teeth are in a buccal or labial position with regard the upper teeth, in a unilateral, bilateral, anterior and/or posterior manner.

Schematic illustration of dentoalveolar expansion can be achieved with aligners, as with braces and wires, to solve crossbites — **Fig. 19.4** Dentoalveolar expansion can be achieved with aligners, as with braces and wires, to solve crossbites.

Crossbite malocclusion can have a skeletal or dental component or a combination of both. For this reason, when facing transversal problems, the first thing needed is a careful diagnosis, in order to determine the protocol to follow:

Checking the occlusal view with the occlusal grid if there is a symmetric arch in shape, torque and size.
In the frontal view, check the posterior lateral torques to see if torque in both sides is symmetric or asymmetric.

Schematic illustration of in this situation, if we ask for the same amount of expansion in both sides, the left side with correct torque at the beginning will end up with premolars and molars tipped to labial and the labial cusp of those teeth would rise altering the Wilson curve. — **Fig. 19.5** In this situation, if we ask for the same amount of expansion in both sides, the left side with correct torque at the beginning will end up with premolars and molars tipped to labial and the labial cusp of those teeth would rise altering the Wilson curve.

Smile analysis: check if the patient displays more gum on one side than on the other. Normally, if there is a side with less torque it will be accompanied by an increase in gum exposure on the same side.

Photo depicts check smile — **Fig. 19.6** Check smile In unilateral masticatory side the patient will expose more gummy posterior smile in the non‐masticatory side. We will need to achieve a final alternate bilateral mastication and to make the torque of posterior teeth equal at the end of the treatment.

For symmetric expansion ask for labial crown torque to the laterals, canines, premolars and molars until they become perpendicular to the bone (0 degrees of final torque).

Photo depicts asymmetric expansion — **Fig. 19.7** Asymmetric expansion.

For asymmetric expansion: teeth on the side with correct torque in the posterior area should not be moved until correcting the side with altered torque. In this way, one hemiarch is being used as an anchorage to correct the other.

Photo depicts proper posterior torque, white ones show arch to be developed transversally — **Fig. 19.8** Blue arrows indicate proper posterior torque, white ones show arch to be developed transversally.

If patients need asymmetric expansions they should be informed that a final open bite in the posterior zone will require using intermaxillary elastics to close it.
Protrusion: in patients with upper protrusion, in order to get a bigger expansion, the clinician should request the technician to apply a simultaneous movement of expansion and arch length reduction. In that way, retracting the incisors at the same time as expanding will provide us with very predictable and very effective transversal development of the arches.

19.1 Things to Consider in Expansion Cases

Plan ahead for anchorage attachments to provide labial root torque to the premolars and molars during the expansion. AT HBG bevelled attachment to gingival of 4 mm in first premolars and first molars provide an effective anchorage during the expansion.
Maintain third upper molars if possible and do not move them during the expansion.
If second and third molars are not in posterior crossbite, for better posterior anchorage, do not move them during the expansion.
Soften the contact points with metal strips if posterior contact points are tightened before the expansion.
Consider how much overjet there is before doing the expansion: if there is not enough overjet, the moment the expansion is made, even if we do not see the retraction in the ClinCheck, the incisors will move backward (pearl necklace effect).

Fig. 19.9 Pearl necklace effect.
For staging:
1. Define staging
2. Expansion and rotation corrections: move simultaneously
3. Symmetric expansion: move simultaneously both sides
4. Asymmetric expansion: sequential movement, first the side with negative torque or posterior crossbite and then the anchorage side.
In the posterior view check in the final position of the ClinCheck that the palatal upper cusp of the molars occludes in the fossae of the lower molars.

The key to effective transversal development of the arches is the staging of movements:

Symmetric expansion and provide a parabolic arch: this movement can be done simultaneously to
- Incisor retrusion (arch length reduction)
- Rotation of molars and premolars
- Minor corrections of molars through distalization
Proclination
Vertical goals: extrusion or intrusion of incisors.
If we need to expand and distalize , we can make at the same time the expansion, the mesial‐out rotation of first molars and the sequential distalization.

If we need to expand and procline: first expand (transversal compensation), second procline (sagittal compensation) and third, intrude or extrude (vertical compensation).
Attachments: in the asymmetric expansion the key attachments are on the anchorage side, which is the side that is not going to move until the posterior crossbite on the contralateral side is corrected.
- In the anchorage side ask for rectangular attachments of 4 mm in first premolars and molars.
- In the side with negative torque or with posterior crossbite ask for horizontal attachments bevelled to gingival that provide a labial root torque to the root during the expansion.

Photo depicts a patient with smile. — **Fig. 19.10** Smile picture.

19.2 Symmetric Expansion

19.2.1 Symmetric Compression Causing Anterior Open Bite

Photo depicts symmetric compression causing anterior open bite — **Fig. 19.11** Symmetric compression causing anterior open bite.

Diagnosis

A 26‐year‐old woman with a normodivergent skeletal class I presented with narrow arches and symmetric compression. She had a class I relationship with negative torque of posterior canines, premolars and molars, wisdom teeth erupted, labially flared maxillary lateral incisors and mild lower crowding, with a posterior gummy smile resulting from the inadequate posterior torque.

Treatment Plan

Open space by upper expansion and sequential distalization
In the lower arch, as the initial dental relationship was a class I, a sequential lower distalization was also planned
All four wisdom teeth were extracted 2 weeks before the treatment start

Requirements for the Technician

In the upper arch, make a symmetric expansion by changing torque applying labial crown torque to canines and premolars simultaneously to the sequential upper distalization of 1.5 mm.
Sequence the movement on the incisors, first proclining 11 and 21 to make torque equal to 12 and 22 and to make space for the correction of the upper lateral and then making an IPR and applying a simultaneous movement of distal‐tipping of the crown in 12 and 22 and retrusion (relative extrusion). Horizontal attachments to be placed on the lateral incisors for better control.
In the lower arch, make a sequential distalization, maintaining the class I molar relationship during the treatment.

Treatment Summary

The total treatment was 18 months.
The patient wore a set of 38 aligners used in a 10‐day change interval protocol.
An additional aligners set was planned to settle the posterior occlusion.
A final bilateral class I was obtained with adequate overbite and overjet, after uprighting posterior teeth, which provided the patient with a final beautiful smile and a stable occlusion.

Photos depict pretreatment extraoral and intraoral views — **Fig. 19.12** Pretreatment extraoral and intraoral views.

Photos depict initial panoramic X-ray, teleradiograph and cephalometry — **Fig. 19.13** Initial panoramic X‐ray, teleradiograph and cephalometry.

Schematic illustration of interproximal reduction — **Fig. 19.14** Interproximal reduction.

Schematic illustration of upper superposition — **Fig. 19.15** Upper superposition.

Schematic illustration of lower superposition — **Fig. 19.16** Lower superposition.

Schematic illustration of initial right ClinCheck view, with
CAD designer instructions. — **Fig. 19.17** Initial right ClinCheck view, with CAD designer instructions.

Schematic illustration of initial left ClinCheck view, with
CAD designer instructions. — **Fig. 19.18** Initial left ClinCheck view, with CAD designer instructions.

Photos depict comparison of initial and final occlusion — **Fig. 19.19** Comparison of initial and final occlusion.

Photos depict comparison of initial and final occlusal — **Fig. 19.20** Comparison of initial and final occlusal.

Photos depict comparison of initial and final smile overjets — **Fig. 19.21** Comparison of initial and final smile overjets.

Photos depict comparison of initial and final smiles — **Fig. 19.22** Comparison of initial and final smiles.

Photos depict final panoramic X-ray and teleradiograph — **Fig. 19.23** Final panoramic X‐ray and teleradiograph.