Why put your patient through a periodontal surgical procedure if it is not needed for periodontal reasons? In many cases the dentist simply wants to have better crown retention by lengthening the mesial, buccal, distal, and lingual walls for greater surface resistance, thus better retention. If there are no periodontal conditions present, such as a degree of pocketing or bone loss, either of which would indicate a periodontal intervention, then why do a periodontal procedure in a periodontally healthy area when the same goal can be achieved with a nonsurgical approach? A periodontal surgical approach may introduce an iatrogenic pocket associated with an adjacent tooth or teeth, which is not a desirable situation. Of course, if a serious periodontal condition exists around the tooth or teeth in question, then a surgical approach would help solve both the periodontal problem and the need for crown lengthening. However, the need for deep scaling, root planing, or curettage may not be a criterion for the surgical approach.
The alternative approach to solve this retention dilemma is called an sTm crown attachment. In most cases, when a tooth needs a crown there has already been previous considerable tooth loss because of earlier caries and the restoration of that tooth. In addition, partial fracture of the tooth may require a stronger type of protective restorative material. The next consideration is 2-fold:
(1) Will the x-ray diagnosis of the tooth prove the tooth worthy of a possible prophylactic endodontic treatment to avoid an endodontic problem later, after the additional irritation of a crown preparation?
(2) Is there enough crown height to have a sufficient retention preparation for the crown using the desired cement?
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| Figure 1. Compromised tooth. | Figure 2. Endodontic therapy performed with post and core. |
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| Figure 3. Preparation for a single sTm crown attachment. | Figure 4. Crown restoration in place with single sTm. |
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| Figure 5. Preparation for a double sTm crown attachment. | Figure 6. Crown restoration in place with double sTm. |
Based on the answer to these two questions, endodontic therapy may be appropriate, and a dual-bonding type composite post and core material may need to be completed, before the crown preparation is done. No metal posts should be inserted for this type of sTm post and core buildup; use as many canals as possible for the core retention (Figures 1 through 6). This type of post and core buildup is extremely strong and retentive, and will avoid any possible stress-related root fractures created by the retention of metal posts (a concept described by Logan in 1884 in Malvin E. Ring’s History of Dentistry). Once the post and core is completed the crown preparation can then be accomplished, achieving parallel walls and any needed retentive boxes.
You can now place one of two long, tapered sTm post holes into the depth of the composite core material. The longer the post hole, the greater the retention of the final crown. The width of the sTm post hole is not as important as length for retention. The sTm tapered post holes must be parallel to each other and the wall preparations for a good path of insertion. Smooth both adjacent contact areas and eliminate any possible filling overhangs.
IMPRESSION
The next critical stage is a good technique for obtaining a perfect impression of your crown preparation and sTm attachment post holes. No bubbles in the impression is an essential goal for a good crown. Either of the following two techniques will work to obtain a good impression: (1) Use an endodontic thin metal- tipped plastic flushing syringe to deliver the viscous light-based impression material down to the base of the sTm post holes, filling them slowly from the bottom up. Then cover all of the preparation as you would normally do with your impression syringe and tray technique. Take your opposing impression and bite relationship as per your usual technique. (2) An alternative impression technique to access your sTm attachment post holes is to use a Duralay plastic post insertion system, as you would use for making a plastic post and core mock-up, before casting the finished product. The only difference would be the allowance for the impression material to grasp the top of the loosely fitted plastic posts and coping, so they can be withdrawn in the impression without shifting position. Once this is poured up in die-cast stone to establish a working model, the lab technician can accurately join the acrylic coping and posts to the final crown wax-up before casting it as one piece.
This sTm attachment technique can he used for any style of crown including full-metal castings, PFM crowns, inlay or onlay crowns, metal, or ceramic. It simply gives you an alternative and perhaps broader approach for better retention when there is not enough traditional crown preparation retention.
CEMENTATION
Always sand blast the internal surface of all metal-coping type crowns. This will provide a clean and microetched surface for bonding with cement. Clean and etch all tooth surfaces that the crown will cover. Using a dual-cure liquid bond and composite cement will result in the best and most complete cementation.
CONCLUSION
I developed the concept described in this article in 1997, and since that time I have used this technique on 12 patients who met the appropriate clinical criteria. All have been successful to date.
Dr. Moody has maintained a general practice in Middletown, RI, since 1989, and was a clinical instructor and a guest lecturer at Tufts University. He is member of the ADA and a past president of the Newport Dental Society. He is also a past president of the New England Dental Society, where he served as a board member and table clinician. He can be contacted at (401) 846-9660.
