A short clinical crown is defined as any tooth with less than 2mm of sound, opposing parallel walls. Simply stated they are crowns that don't protrude from the gums very much.
Common causes of short clinical crowns include:
- Disease (caries, erosion, tooth malformation)
- Trauma (fractured teeth, attrition)
- Iatrogenic dentistry (excess tooth reduction, large endodontic access openings)
- Eruption disharmony (insufficient passive eruption, mesially tipped teeth)
- Exostosis, and genetic variation in tooth form
Short clinical crowns can be difficult to treat with clear aligners, because the teeth are simply too small to hold an aligner in position. Short clinical crowns are not bulbous and usually come to a point, much like a triangle, creating a lack of retention points on the tooth. This results in the aligner not being able to fully seat over the tooth, causing it to slide or "pop off".
A helpful way to prevent problems in treatment relating to short clinical crowns is to indicate any short clinical crowns and request engagers on the first or second premolars under the "Additional Instructions" section of your case submission. Please specify to place those engagers during step 1, and we will accommodate your request. Letting us know about short clinical crowns when submitting a case prevents potential fitting problems in the future.
You can also use retention pliers (dimple pliers) to create retention points at the gumline, in order to help the aligners to seat.
Check for short clinical crowns when you evaluate your patient (especially if the first set of aligners don't fit). This way, you can request engagers right away and get your patient into successful treatment.