This piece will focus on crown lengthening for functional reasons only—stay tuned for a future installment about possible aesthetic reasons.
“Many practitioners never crown-lengthen teeth, so why do I need to bother?” you may be asking. This added procedure will certainly add cost and healing time to a patient’s treatment plan, but there are some fundamental reasons why certain teeth will need to be crown-lengthened.
More surface needed!
The first reason to crown-lengthen a tooth is if there simply isn’t enough clinical crown remaining to receive a crown. A patient who has occlusal wear may have lost enough occlusal tooth structure so that by the time the tooth is prepped, there isn’t enough axial height to retain the crown. Every practitioner has his or her comfort zone; my rule of thumb is to have at least 4 millimeters of axial height to support a crown. Obviously, luting agents have evolved and we often can get away with less, but I shoot for a minimum of 4mm.
Anatomically, there are also going to be areas in the mouth where excess tissue will lead to short clinical crowns. Second molars are commonly shorter as a result. Have you ever run into that situation where by the time you prep #31, the tooth is just so short that the crown keeps coming uncemented?
In such scenarios, we usually need to crown-lengthen 360 degrees or close to it.
But there are also other situations where maybe only a portion of the tooth requires crown lengthening. Those situations might include:
• A fractured portion of the tooth offers minimal crown height or even extends subgingivally.
• Decay extending to minimal crown height or even subgingivally.
• Removal of an older crown, only to find that any of the previously mentioned situations exist.
• Placement of a subgingival root restoration.
• A resorptive lesion that extends subgingivally.
It goes without saying that prepping margins subgingivally is challenging because of lessened visibility, increased bleeding (which will also make getting a good impression tougher), and more difficulty in packing cord and having a readable margin.
The second main reason to lengthen a tooth’s crown is to avoid invading the biologic width. Harken back to your dental school days and you’ll most certainly remember hearing about the holy biologic width; in general terms, this refers to the space from the free gingival margin to the crestal bone.
Sulcus depth varies, depending on which tooth you’re probing and where you’re probing it. Assuming that we’re dealing with a periodontally healthy situation, normal limits for a sulcus depth would be 1–3mm. We then would assume the epithelial attachment to be about 1mm, and the connective tissue attachment to be about 1mm as well. According to the original biologic width studies by Gargiulo,¹ this 2mm of tissue is where we want to avoid having a preparation end.
As a periodontist, my preference is to not have preps end subgingivally, but that’s not realistic in 100 percent of the cases. If the margin ends in the sulcus, we’re going to be safe most of the time—85 percent of the time, according to Kois.² Violate this principle by having your margin end in the 2mm of tissue attachment, however, and you’ll face an untimely death. OK, maybe that was an exaggeration, but you risk having chronic inflammation, bleeding and discomfort, as well as possible gingival recession.
The best course of treatment is to prep the tooth for the ideal location of your margin and then crown-lengthen from the anticipated margin location.
There are also some less common reasons for crown lengthening teeth, such as to aid in placement of a rubber dam or for those with excess tissue that creates pseudo-pockets. (This may be more of a gingivectomy, though, if bone removal is not required.)
Healing on these cases is usually only six to eight weeks. Studies have shown that the tissues are stable as early as six weeks. That said, I will wait longer to be on the safe side, if the case is aesthetic in nature (Bragger³, et al).
When should I not
As dental implants have become routine and predictable treatment options, there are instances when crown lengthening may not be worthwhile, in my opinion:
• If the aesthetics in the smile zone would be sacrificed.
• If we may have to expose (or further expose) the furcation opening of the affected or adjacent tooth.
• If the tooth would need endodontic therapy in addition to osseous crown lengthening.
• Patients with high caries rates are not good candidates for osseous crown lengthening, because this makes them even more susceptible to caries.
1. Gargiulo, AW, Wentz FM, Orban B. Dimensions and relations of the dentogingival junction in humans. J Perio 1961;32:261–267.
2. Kois J. Altering gingival levels: The restorative connection, Part 1: Biologic variables. J Esthet Dent. 1994;6:3–9.
3. Bragger U, Lauchenauer D, and Lang NP: Surgical lengthening of the clinical crown. J Clin Perio 19: 58-63, 1992
Discover when to refer cases
to a perio specialist
In which situations should clinicians refer cases
to a periodontist? Dr. Brian S. Gurinsky’s article for Dentaltown discusses some of the factors and flags where it makes sense to refer out. To read it, go to dentaltown.com/gurinsky-on-perio.