Incisal Gaps

There is a gap between the incisal edge of the tooth and the aligner. If this should occur, there is no need for concern, as the progression of movement will continue.

Causes Incisal gaps can be a result of any of the following:

  • Non-compliant patient
  • Wear schedule is inadequate to achieve desired tooth movement
  • Tooth movements have not occurred due to insufficient pressure or lack of space
  • Amplifiers are not lining up with the spaces created for the amplifier in the aligner


  • increase wear time
  • check with Doctor at next visit
  • use Chewies as directed

Too Big or Too Small aligners

An aligner too big for the patient when it is too wide or too long for the patient’s arch. An aligner that is too big fails to remain in place when the patient speaks or opens mouth. An aligner is too small when it cannot easily be placed into the patients mouth. An aligner that is too small may need to be trimmed or forcibly placed in order to fit properly.

Causes Aligners can appear too big,

  • The impressions used to make the aligners had minor distortions
  • Patient’s molars have not moved distally (backwards) in the arch as expected
  • Patient’s arch has not expanded as expected
Aligners can appear too small,
  • Mesial (toward the middle of the front of the jaw along the curve of the dental arch) translations have not happened as anticipated
  • Patient’s teeth are too round for the aligner to properly move them
  • undesirable undercuts resulting too much retention
  • Over crowding of teeth resulting too much retention
  • Teeth have moved lingually as expected


  • For Aligners that seem too big
    • Backtracking by using the previous aligner
    • Request a case revision to have more amplifiers added
  • For Aligners that seem too small
    • Get the distal half of the aligner trimmed
    • Request for undercuts to be blocked at either at the beginning of the case, or in the middle/end of the case by requesting a case revision
    • Request a case revision asking for an adjustment to the trim line

Short Clinical Crowns

A short clinical crown is defined as any tooth with less than 2 mm of sound, opposing parallel walls remaining after occlusal and axial reduction. (Clinical crown is the visible portion of the tooth)


  • Diseases - dental cavities, erosion, malformation of teeth
  • Trauma (fractured teeth, wearing away by friction & abrasion)
  • Excess tooth reduction (iatrogenic)
  • Disharmony in eruption of teeth
  • Thickening of bone around the teeth (Exostosis)


  • Because the short clinical crowns are too small to hold an aligner in position properly it can be difficult to treat this condition using clear aligners. Owing to its small size short clinical crowns have less retention points. As a result, the aligner will not fully seat over the tooth, causing it to slide.
  • Indicate any short clinical crowns and request amplifiers when submitting a case to prevents possible fitting problems in the future.

Undesirable undercuts

  • Undercut - the portion of a tooth that lies between its height of contour and the gingiva, only if that portion is of less circumference than the height of contour.
  • Undercuts occur naturally due to tooth morphology and contours. Aligners depend on these desirable undercuts for its normal retention. However undesirable undercuts are too retentive. They make it too difficult to remove/insert aligners or remove impressions. 


  • Anomaly in tooth morphology.
  • Gingival recession (exposure in the roots of the teeth caused by a loss of gum tissue and/or retraction of the gingival margin from the crown of the teeth.)
  • Under restored dental implants and bridges
  • Over contoured restorations


  • Fill in the undesirable undercuts (with wax). This will make the impression easier to remove, and stop those undercuts from going in to the 3D model, making the aligners easier to remove and insert.
  • Trim the medium body material - Between the first and second steps of a two-step impression, trim the impression 2 millimeters above the gingival margin in the medium body material.