Crowding

Question 1

Tooth size discrepancy

Answer 1

• In instances where there is tooth size discrepancy where the proportions of the upper and lower teeth don’t match, either the wider teeth will need to be reduced with IPR, or the narrower teeth will need to be widened with restorations. If the tooth size discrepancy is too large, the extraction of a single lower incisor should also be considered.
• Assuming a Class I occlusion, a tooth size discrepancy may manifest either by presenting excess overjet when the teeth are completely aligned if the upper teeth are proportionally wider than the lower teeth, or by presenting upper spaces when the teeth are completely aligned since the lower teeth are wider than the upper; the alternative is for the lower teeth to be crowded if no spaces are present on the upper arch.

Question 2

Crowding and tooth inclination

Answer 2

• When the patient has lingually tipped anterior and/or posterior teeth, increasing the arch length will help to alleviate crowding. The arch length can be increased by proclination of the anterior teeth and expansion of the posterior teeth (buccal crown tipping movements). Note that proclination of the anterior teeth will create relative intrusion, which will help reduce the overbite; if there is a Deep Bite present, additional absolute anterior intrusion may be required to create the necessary overjet space to further procline the lower anterior teeth to align them.
• With crowding with normally inclined anterior teeth or flared anterior teeth, IPR and arch or specifically posterior expansion will be the only means to create space to address the crowding; if this is not enough to prevent excessive proclination of the anterior teeth, distalisation or a more complex extraction treatment plan may be considered.

Question 3

• The three basic options to address crowding are

Answer 3

anterior proclination (buccal crown tipping),

posterior dental expansion (buccal crown tipping) and

interproximal reduction (IPR).

Question 4

With severe crowding, extractions may be needed. Please note that…

Answer 4

this may increase the complexity of the treatment and may require auxiliary techniques to be used in combination with the aligners.

Question 5

On adult patients where there is significantly more lower anterior crowding than upper crowding and the posterior occlusion very tightly interdigitated,

Answer 5

the extraction of a single lower incisor instead of doing extensive lower anterior IPR should be evaluated.

Question 6

On treatments with posterior crowding,

Answer 6

careful consideration to determine whether space may be created to bring into alignment the teeth positioned outside the arch will be required. If space is insufficient and cannot be created, extractions may be considered, as well as leaving the posterior crowding/crossbite untreated.

Question 7

When analysing the Bolton index, this patient showed a 0.6 mm anterior Maxillary excess.

Answer 7

0.6 mm of IPR on the upper arch was planned on provider’s request to achieve the goals.

Question 8

Complexity assessment of a potential Crowding patient with the Invisalign system:

Answer 8

Question 9

Patients with crowded teeth can be treated most predictably when the following conditions are present:

Answer 9

Anterior teeth are upright or retroclined

Patient has narrow arches where posterior teeth are tipped lingually; particularly cuspids and bicuspids

Clinical crowns are not short