What is crown lengthening?
Crown lengthening referred to the procedure of which the soft and/or hard tissue is removed to expose more clinical crown as to provide more retentive mechanism for the future restoration in a fracture tooth or for more aesthetic appearance in the “gummy smile”. When it is used to expose more clinical crown and reduced the appearance of “gummy smile”, it is referred to as esthetic crown lengthening. (Please see Esthetic Crown Lengthening in the services menu)
This procedure is the most often overlooked or wrongly performed. In many cases, soft tissue crown lengthening was performed with a laser instead of the hard tissue crown lengthening procedure, leaving the crown margin too close to alveolar bone crest and thus causing periodontal breakdown and gingival inflammation (clinical or subclinical) surrounding the new crown.
Why is the bone or soft tissue surrounding the restoration often remove in crown restoration?
There are many concepts to be discussed here involving the construction of a good, long term restoration. They are:
- Biological width
- Crown retention
- Even gingival crest contour
Biological width is a dimension from the crest of alveolar bone to base of the sulcus (2.04mm) and includes connective tissue (1.07) and epithelial attachment (.97mm). If measure form the crest of gingiva, the biological width is measured to be 2.73mm. Any restoration, especially the full crown restoration, needs a biological width of approximately 1mm of tooth structure for connective tissue and 1mm of tooth structure for junctional epithelium, plus 1 or 2mm of tooth structure for the crown margin placement and termination. All together is 3-4mm of tooth surface from the future crown margin must be exposed using hard tissue crown lengthening procedure. The failure of providing the proper biological width may result in restorative infringement on the junctional epithelium and connective tissue attachment, which leads to bone loss and apical migration of the soft tissue complex. This is one of many reason that occasionally, patient with good oral hygiene may experience continuous gingival inflammation, gingival redness, and bleeding even though their newly made crown has good, close margin.
Crown retention is the concept that directly related to the long term function of a crown. Crown retention can be defined as the resistance which prevented dislodgement or movement of the restoration, especially when the restoration is subjected to the forces directed in an oblique or lateral direction. No cements which are compatible with living tooth structure and the biologic environment of the oral cavity possess the adhesive properties required to withstand the repeating lateral or oblique force during mastication. This resistance can be achieved by providing at least 2-3mm of lateral walls at 6 degree taper. Even with the advance of resin bonding cement (much better bond strength than the conventional crown cement) as used with the all ceramic restoration, the lateral wall of the all ceramic crown should be at least 2mm.
In the situation of clinical crown fracture, crown lengthening procedure can be performed to move the margin apically to provide at least 2-3mm of lateral walls. The location of the crown margin should be located at:
- 1-1.5mm below the fracture line as to resist the movement of the build up restoration upon functioning due to shear, lateral force.
- 3mm above the bone crest as to satisfy the biological width
- at the apical level such that the lateral wall of the crown is at least 2-3mm (I preferred 3mm)
In doing so and coupling with optimal ideal occlusion and good oral hygiene care, the crown can last a lifetime.
Finally, the gingival crest contour should be discussed. Even gingival crest contour in width and height should be restored as to aid in food deflection from the dentogingival junction and also in facilitate the oral hygiene effort. Uneven gingival height will cause problem in brushing, as the patient forgot to move the tooth brush following the dentogingival contour. Uneven gingival width will cause food impaction as it prevent food or chew from deflecting away from the dentogingival junction. Both of these phenomena can be achieved with soft tissue crown lengthening with the laser.
What are the steps in the hard tissue crown lengthening procedure?
Treatment technique is varied from the method of which the tissue is removed. They are:
- regular blade
- reposition flap more apically
The best way to approach crown lengthening is first the crow should be prep such that the new crown margin is visuallized. Then the patient can undergo crown lengthening procedure.
We always anesthetized our patient for our hard tissue crown lengthening procedure . Regular blade provides speed and clean steril cut. Electrosurgery provides hemostasis while maintaining the speed efficiency. Laser provides excellent hemostasis, excellent post-operative healing, and excellent tissue control in term of thinning or contouring. However, laser cutting can be very slow and time consuming. Very often I use all three tools with judgement based on the amount of gingiva and the number of teeth involved. Finally, I always combine the removal of gingival tissue with flap reposition more apically as to deepen the vestibule (in many case it help to facilitate oral hygiene effort), to preserve attached gingiva (good protection from localized trauma and bacterial invasion), allow to visualize the alveolar bone crest and determine the need for bone contouring or removal. REMEMBER, tissue growth always followed bone support.
After the tissue is trim and removed to the level of the future crown margin (read about the location of crown margin in the column above), we always reflect the flap to recontour the bone crest. A small round bur should be used and make sure we have adequate water cooling during bone removal (to avoid dehiscence of bone, the cutting temperature should be under 47 degree Celsius). The bone should be removed such that the bone crest is located about 3-4mm from the new crown margin as to satisfy the requirement of biological width. Next the flap is reposition and allow for adaptation at the new gingival crest.. The gingival crest should not demonstrated any pulling movement . In doing so, the flap should be released and readapted prior to suture.
Finally, we suture with either goretex suture or gut suture. I always avoid silk suture because even though it is inexpensive, it always attracted plaque and bacteria harboring to the surgical site. Goretex suture is nonresorbable, very expensive but they are very hygienic, ease of handling, and very strong. Gut suture is weaker but resorbable. Broken suture may lead to reattachment of gingiva at the less optimal location, healing with secondary intention, and subclinical infection due to food/bacteria penetrates the surgical site. I preferred gut suture in this the procedure of hard tissue crown lengthening. Patient will be post-op 1 days, 14 days (tissue heals clinically), and 28 days (tissue heals microscopically). At the end of 28 days, impression of the crown can be made.
These are the protocol of which Dr. Bui follows in his periodontal therapy. It is not necessary the same or equivalent with other operator. Our method may be different, but the final result should be toward achieving that esthetic smile which everyone deserves.
Does the tissue grow back in time?
As mention above, more often we removed or recontour the bone crest as to ensure the biological width is NOT violated and thus the gingival crest will stay where it is placed as long as no other pathological process such as crown margin overhang or periodontal disease occurred. Patient will only have to maintain good oral hygiene with periodic cleaning every six months.
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