our patient calls the office on Monday morning and tells your receptionist that her crown fell off her front tooth. You know the truth before she walks in the door – the post and core that was in the tooth, is still inside the crown that is inside the ziplock bag, that is inside your patient’s purse! Your dental team thinks that this is going to be a quick recement, but you’re already worried that there isn’t going to be enough tooth structure to even recement the post/core/crown temporarily! Sure enough, there is hardly any tooth structure above the gum line, and what is there, is decayed ;(. If you haven’t had an anterior crown that you placed on a patient fall off yet, it’s probably only a matter of time. Losing a front crown is one of the most sensitive issues for our patients…and when it is dentistry that we’ve placed, the patients can be particularly unhappy.
What do we know about treating anterior teeth with crowns?
Two prosthetic considerations will give us the highest chance for success with the definitive restorations. The first is ‘ferule.’ Ferule is the amount of tooth structure that the crown can grab. The ferule is the facial, palatal, and interproximal tooth structure that is available with our preparation. We all know that the more natural tooth structure that we have, the better off we are for long term cementation of our crowns. OK – here’s the important part - even with our wonderful adhesive dental cements, we must have 2 mm of tooth structure to bond our restorations. Less than 2 mm of tooth structure, the crown cementation will become less secure and stable.
The second consideration besides ferule, is the total tooth structure to secure our crown. Now adhesive dentistry has helped us significantly with this issue; however, we still need 4-5 mm of tooth structure, or tooth structure + build-up, to have ideal retention of our bonded crown. This then leads us to the discussion of post and cores for the endodontically treated tooth. When do we need to place a post on endodontically treated teeth.
Dentistry has changed in our understanding and approach to placing posts in endodontically treated teeth. Through research, we have come to understand that posts, especially if the canal system is over instrumented and the canal space is artificially enlarged to support a post, this can lead to fracture of the root down the road. In fact, many dentists have shied away from placing posts because of this concern, but the reality is that there are still indications for placing posts. In my practice, I place posts when I am concerned about the ability of the core build-up to maintain bonded to the tooth structure. Posts do not strengthen roots; posts help us secure, or anchor, the core build-up restoration to reduce the risk of build-up material separation from the tooth structure. But please remember - posts do not strengthen roots!
The technique for placing posts is not particularly complicated, but there are several important factors to consider.
First, we were taught in dental school that the post needs to extend down the root system leaving about 3 mm of apical gutta percha. This technique was related to the cements that we had available at the time, but now that we have the opportunity to chemically bond the posts, perhaps we can reduce the length of the post so that the terminal end of the post is in a thicker area of the root system. With the end of the post in thicker root structure, the risk of root fracture in the future is reduced.
The second issue to consider with the posts is the type of post that we use. There are several options currently for direct posts – metal posts, fiber posts, and fiber reinforced zirconia posts. I definitely do not want to use a metal post when restoring an anterior tooth. Even with our ability to opaque the post and core with our composites, we will need to use a more opaque crown material to block out the low value of the tooth that is common with metal posts. So, I absolutely know that it will be easier for my ceramist to create an esthetic crown if I use a tooth-colored post with a tooth-colored build-up material.
That leaves the choice between an all-fiber post or a zirconia/fiber post. How do you choose? Research suggests that stiff posts, bonded into the root, gives us the most stability in our direct post systems. The flexibility of the all-fiber posts can lead to future breakdown of the adhesive interface. So, given the choice, I am going to choose an esthetic, stiff post, like the DentaPost from Brassler.
The third and final critical issue to consider is how are you going to cement the post. The best, most predictable, and turns out the most simplified technique that I have found is to use my core build-up material as the post cement. My technique is as follows:
1. Create post space – I like to have about 5 mm of post into the root canal system. This would typically give me a 10 mm post – 5 mm into the canal system, 2 mm of tooth structure (ferule) and 3 mm extension of the post beyond the ferule
2. Etch the canal system and tooth structure with 37% phosphoric acid for 15 seconds, using a microbrush to lightly ‘scrub’ the etchant (alternatively, you can use a self-cure self etch adhesive system)
3. Rinse and make sure all phosphoric acid is removed
4. Remove excess water so that the dentin is left moist, but no pools of water
5. This is critical – you must use a self-cure adhesive – if you use a light cured adhesive, the effect of the light down into the canal system is going to be limited (I use Cosmedent Complete with the self-cure activator), air thin and use microbrushes to remove excess adhesive
6. Inject tooth colored core build-up material into canal system (I use Cosmecore A2 with the metal Centrix syringe tip), place post into the canal, and continue to use the Cosmecore build-up material around the post and onto the tooth structure.
7. Light cure for a full minute. Now your tooth is ready for the final preparation!
To get a fuller explanation of ferule and all issues related to placing the direct esthetic post and core, check out mycourse on dental online training. I hope that this review is helpful and I look forward to sharing more techniques with you down the road!
Yours for better dental health,
Dennis Hartlieb, DDS, AAACD
DOT Founder
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Day 1 (8 - 4 pm CST)
Erosion and wear – the why and the how
Adding length to teeth – when is it safe
Opening VDO to compensate for lost tooth structure – where to begin
Records visit and key points you need to understand before you start
The smile – the 7 strategic points to consider when evaluating the smile
