How To Prevent Fractures When You Temporize A Post-Core Build Up By: Martin B. Goldstein DMD Official DentalTown Townie

When you bond a prefab endodontic post, there are a number of situations where you may decide to defer prepping the core and taking the impression. Maybe you’re running behind schedule. Or perhaps the patient can’t afford the definitive crown at this point. There may be insurance issues. Or you may want to see how the gingiva heals before you begin C&B.

So you build a direct composite crown build up over the post, and explain to the patient that they must call to schedule the rest of the treatment.

But you don’t hear from them again. Until months later, you get...

The Call
Your overly agitated patient tells you that your crown build up has broken, leaving a toothless gap. To make matters worse, Mrs. Jones has a wedding this weekend and there’s no way she can attend the affair in this state.

Granted, the tooth wasn’t crowned as instructed, but all Mrs. Jones knows is that your handiwork failed very quickly and at the worst possible time. To remain in her good graces, you better find some way to fit her into your already crammed schedule. Looks like lunch is optional today.

So you regroup, send out for something to eat and tell her to come right in, hoping that what’s left of Mrs. Jones’ #10 is salvageable. After several schedule-wrecking, lunch-destroying fractures like Mrs. Jones’, I began over-engineering my post-retained temporary crowns.

And I’ve encountered almost no fractures since.

Consider a typical “at or below the gingivae” coronal fracture that requires a post.

Figure 1

To keep it simple let’s assume an endodontically treated bicuspid has fractured at the gum-line (one that I happen to have clear, illustrative photos of). You’re faced with a partially submerged root surface on one surface with a pink eye of gutta percha peeking out somewhere center-root. Gingivae may have begun to creep into the fractured root recesses. Root caries may be present as well. (Figure 1) You know at a glance that the bicuspid needs a post, core and crown. While my points are illustrated with a bicuspid, the same principles hold true for the typical anterior fracture.

Figure 2 Build up engaging only fractured root interface and post

Your first inclination might be to localize the tissue, blow away the gingiva over the root with a highspeed instrument and remove whatever caries you find. Following placement of the post, you might build the composite crown using a clear former. That way the crown will be retained adhesively by bonding to the root interface as well as mechanically retained by the head of the post (Figure 2).

Figure 3 Two mm collar of root incorporated in core build up

A better alternative
Think back to having read something, somewhere about a “ferrule.” A what?! The ferrule (and I’ve no idea of the origin of the term) refers to 2mm or so of sound root structure apical to the core that the margins of the crown should engage (Figure 3). A ferrule makes post-retained full-coverage restorations significantly more retentive and dramatically strengthens the tooth to resist fracture. It surrounds the circumference of the tooth, holding it together like the metal bands around the head of a wooden mallet.

We encounter the ferrule in other areas of dentistry, such as those small but necessary hex locks that join our implant components.

Apparently, a circumferential, sleeve-like engagement of as little as two mm’s will resist dislodgement and breakage of many things dental. Though the importance of the ferrule is widely acknowledged in literature, it refers primarily to the definitive fixed crown. I’ve found that adding a ferrule to my post- retained temporary crown build-ups has made a dramatic difference in their success.

The walls of the ferrule prep should be as parallel as possible to maximize strengthening. If significant coronal tooth structure remains, that’s not a problem. In some cases, like this bicuspid, we’ll have to accept a certain degree of taper.

Figure 4 Photo courtesy of the Journal of the Canadian Dental Association.

In an ideal situation, we would also like to have a 2mm zone of biologic width apical to the ferrule (Figure 4). Fact is, in a core build-up, we often don’t have enough room. So we’re left with a choice between recommending a crown-lengthening procedure or making do with what’s left. Unless space is a serious problem, I concentrate first on establishing a fracture-resistant build-up and later worry about the biologic zone. Enough said. Here’s how you apply the ferrule rule to temporizing that fractured tooth.

You’ve encountered minimal root decay, cleaned it up and had the wisdom to pick up a perio probe. You’ve found almost 3 mm of sulcus depth surrounding most of the remaining root. You recall the numerous times your patients have not returned for crowns as advised and you remember the ferrule effect. You’re going to play it smart. You’ve decided to expose two mms of submerged root before placing your build up.

First, place your post according to the manufacturer’s instructions.

Figure 5

Pictured here is a Jeneric Pentron FibreKor post that has been fitted and subsequently bonded in place (Figure 5). It’s not unusual to encounter slight bleeding during trough creation so you may as well bond the post in place in as blood free an environment as possible. After bonding the post in place, I stabilize it with college pliers or hemostat and trim it to proper height.

Let’s create space for the ferrule
Do you have an electrosurge unit handy? If there was ever a case that begged for electrosurgery, this is it (precision, nearly bloodless tissue removal performed in just a few minutes.)

The electrode cauterizes as it cuts, so it minimizes the possibility of blood seeping into the build-up. But if there’s adequate sulcus, I’ll also pack a hemostatic cord prior to tissue removal.

My electrosurge, Parkell’s solid state Sensimatic 600SE has proven to be extremely reliable. I use electrosurgery almost daily–not just for the gingival crown lengthening we’re discussing here, but also to expose root caries and troughing prior to impressing.

In fact, I keep electrosurges in two operatories. That way, a surge will be at the tip of my fingers whenever I want it. The electrosurge must be at arm’s reach or I won’t use it. Take this case for example, if my surge were on a cart in a sterilization area, I’d be more apt to pick up a flame shaped diamond to create space. Bloody as that might become, it would be faster than stopping the show to go fetch the electrosurge.

My advice: (1). Get a surge. (2). Learn to use it. (3). Keep it close at hand!

I prefer the single filament tip for most of my trough creations. It removes very controlled, small amounts of tissue. I keep the device set to the 6 or 7 power range and adjusted to the “cut and coag” mode of operation. I alter the settings based upon the ease of tissue removal. If things aren’t happening fast enough and the electrode is dragging the tissue, I increase the setting (with the converse being true as). Generally, I don’t touch the settings on a day in and day out basis. I just turn it on and go to work.

Non-vital teeth like this one are the most stress-free to work around, as fear of frying a vital pulp isn’t a factor. Certainly I look to keep my cutting edge in tissue but the absence of vital pulp is comforting. When I’m concerned about bone proximity, I carefully identify the depth of the attached gingiva using my perio probe.

Figure 6

Now it’s simply a matter of creating a nice little trough around the root that’s about 1 mm wide and 2 mm deep (Figure 6) In essence, I do what it takes to permit introduction of a flame-shaped diamond into the sulcus without having to wade through tissue. I create a beveled root surface that will mate with the composite. Shoot for a 2mm occluso/gingival prep if possible. Try to keep the bevel as close to parallel as is practical but still slightly beveled.

My favorite technique for creating crown build ups involves a clear strip-off crown form that’s been cut and festooned to closely fit around the newly exposed beveled root. I drill a porthole in the crown former that’s large enough to fit a composite compule tip.

Since I plan to inject the material my composite must have sufficient “flowability.” And since I want it to survive even if the patient doesn’t return as directed, it must have reasonable strength. I use Caulk’s TPH for this application, but if you prefer to use your favorite hybrid you can make it more flowable by heating a compule in warm water. The engagement of the ferrule prep, however, makes the strength of the core material somewhat less critical since this zone of attachment will account for much of the build up’s strength and resistance.

Figure 7

I re-etch the exposed root and apply another coat of my favorite bonding agent. I then seat the crown former over the beveled root and maneuver it until there appears to be close adaptation to the tapered, exposed root. The taper allows a sleeve of composite to encase the root while still being confined to the boundaries of the crown form. Ideally, all of the bevel should be engaged. I then begin to pump composite through the port hole until the crown form is completely filled and excess begins to force its way out at the gingival aspect. (Figure 7)

I digitally stabilize the crown form during injection of the composite paste. I remove as much flash as possible prior to curing.

In some instances, I will have the patient close to full occlusion so long as the crown form won’t be significantly deformed in order to minimize occlusal adjustments. If closure is not an option, I may compress the crown form with fingers placed on the buccal and lingual to achieve better interproximal contacts. Once I’m satisfied that the crown form is in proper position, the build up is zapped with the curing light from four directions, twenty seconds each way.

If you’re concerned about the interproximal contacts, you can create mesial/distal contact ports in the strip crown, but this will make it more difficult to remove the form. Frankly, if the contacts are seriously inadequate I simply add more composite after I’ve finished.

I remove the crown form by slicing it labially top-to-bottom with a #15 blade. This enables me to slip an explorer under the form and pry/peel off the shell.

Figure 8

Occlusion is adjusted, flash trimmed and if really, really necessary, tighter contacts are added. The thickness of the crown form will prevent you from creating normal contacts. Since this is supposed to be an interim restoration, the threat of open contacts is far less critical than the chance of fracture. If you are certain that this build up will remain uncovered for an extended period, feel free to establish better contacts via class two or class three preps accompanied by conventional matrix techniques for contact creation. (Figure 8)

Figure 9

Figure 10

Let’s finish up
This patient did in fact return in a timely fashion for crown preparation. In Figure 9, you can see how the ferrule area has been re-prepped to receive the crown margins formerly occupied by the interim crown build up. Again, I point out the tapered parallel walls that extend well past the post and core/root interface. The impression in Figure 10 assures me that the likelihood of crown failure is minimal given the generous amount of root surface engaged.

Figure 11

As you can see from Figure 11 taken when my patient has returned for cementation, the tissue has fully recovered from the electrosurge procedure. The gingival contour made possible by the beveled root had enabled placement of a physiologic crown build up with proper emergence profile that was followed by a similarly contoured temporary crown. Both were well received by the surrounding tissue as well be the finished restoration. The gingivae was happy! (OK, maybe just content) and the resulting crown is well supported.

So what’s the big deal? Well, there are four things I hope you’ll take away from this article. For many reasons, your patient may not have the definitive crown placed as soon as you recommend. This poses particular dangers for teeth with endodontic posts. Therefore, it makes sense to design a provisional crown build up that will withstand prolonged use. Doing so will reduce the number of lunch hours you forfeit.

Teeth with posts will hold up much better if the provisional crown engages a long beveled root surface. Remember the ferrule effect!!!

An electrosurge offers a fast, almost blood-free way to create working room for the ferrule prep. The surge should be located just as conveniently as your favorite handpiece. If it’s at hand, chances are you’ll use it every day.

If you place the crown form first and then inject into it, you’ll get a more reliable crown orientation. This also assures that the composite will fully engage the root taper to create a ferrule.

Dr. Goldstein is a 1977 graduate of the University of Connecticut School of Dental Medicine and practices general dentistry in a group setting in Wolcott, Conn. He enjoys promoting the cosmetic side of his practice and has found it helpful to incorporate digital photography into his daily routine as a practice builder.

He is available for speaking engagements on both digital imaging in dentistry and the use of high tech methodology to further the cosmetic practice, including the use of direct bonded veneers as an alternative to porcelain laminates.

Martin can be contacted by email at martyg924@cox.net or at his office at 203-879-4649.

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Townies Discuss Build-Ups

I think the advantages to your build-up technique are not with the fact that there’s a ferrule for the BU: at least IMO. BU materials possess insufficient rigidity to enhance resistance-form of the BU overall just from inclusion over a ferrule-prepped root surface. I’m sure the additional surface-area for bonding does add to the retention of the bulk of BU material, but is it offset by the diminished resistance form caused by decreased cervical cross-sectional diameter to the tooth? Who knows. Might be a “wash.”

However, after giving this technique some thought, the big benefit (it seems to me, at least) is that one can determine the degree of crown-lengthening one WILL need for the ferrule of the final restoration. Place the post, do initial BU per your method, then prep for the proper ferrule with gingivectomy bur or in conjunction with electrosurge or whatever. Obtain hemostasis and BAM, finish up the BU with that crown form thingy. The tissue heals in the interim with attachment at a level just apical to the crown-margin-to-be, and one knows (come final crown-prep time) exactly where to place the previously-determined margin just by prepping away the BU axially until dentin is met. I’d think getting a crisp result like your final pic would be that much easier with an impression that isn’t hampered by blood ‘n’ serous fluid, etc., as might well occur if attempted at the time of the CL. Think I’ll try it for that reason.
marshall_white_dmd,
Official Townie

Marshall is very correct about the ferrule created by build-up material. You need a material or system that is good in tension and a design that translates tension to compression. I think all that would happen is the BU material will abfract at the finish line of the ferrule joint. The larger the ferrule joint’s circumference the more translative resistance you have. Just like the larger amount of leather thongs you have on your tomahawk the more you can whack your enemies with. The DEJ is mother natures ferrule to prep below that only reduces retention and increases strain on the joint.

When you move the finish line below the DEJ then you have to have a material that has more than twice the tensile strength of the original ferrule. IMHO composite won’t cut it.

T1xD1/T2xD2 should equal 1 if your new ferrule is to be effective. In severely broken down teeth this is not always possible. This is why I choose internal ferrules in these cases.
daniel,
Official Townie

You raise some good points to be sure. My contention that the gingivally extended core build-up will stay the course better, is really just based upon clinical experience. The article was spurred by an associate of mine that brought in a film of a failed post and core that she did...looking at the film, it was apparent that the build up never went past the point of fracture...As do many of us (what I’ve done in the past as well), post was placed, everything cleaned up, etched, bonded...and built up to the butt joint of the fracture...and that’s just where it gave way. I experienced similar for years until the light went off...quite accidentally.

I also believe that today’s core materials are rigid enough to make a difference particularly when they encircle the root form. I can’t remember the last time I did one like this that failed. And, as pointed out in the article, ferrules seem to make a big difference in “many things dental”. Consider the 1 mm external hex in a 3I attachment.

At any rate, thank you for your thoughtful input...it’s appreciated.
martingoldstein,
Official Townie

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