In the era of advanced adhesive dentistry and biomimetic dentistry the question is raised – does a post actually improve outcomes? Surprisingly, no. In this article I’ll delve into why they’re no longer necessary in restorative dentistry.
The argument has been made that a post and core can add additional retention and act as a “belt and suspenders.” But, with the advances in adhesive dentistry, do they truly add an advantage? This question is incredibly important to answer. At a minimum, a post is a somewhat costly procedure for the patient. The procedure involved in adding a post may also reintroduce bacteria into the canal system (if the post is placed at a second appointment after the endodontic therapy is completed).
At worst, a post could cause root fracture which could result in a catastrophic failure of the tooth. Dental professionals cannot afford to be ambivalent toward the use of a post and core. 1
Lima et al. concluded in their 2010 study that “The ferrule preparation increased the fracture resistance of endodontically treated teeth. However, the use of glass fiber post showed no significant influence on the fracture resistance.” In effect, it was the ferrule of 2 mm, rather than the post and core that determined fracture resistance.2
Here are the different groups that the study evaluated: Group 1: 2 mm ferrule with a post; Group 2: 2 mm ferrule and without post; Group 3: no ferrule but with post; Group 4: no ferrule and no post.
Surprisingly they found that the fracture resistances were as follows: Group 1: 573.3 N; Group 2: 552.5 N; Group 3: 275.3 N; Group 4: 258.6 N. They then concluded that “significantly higher fracture resistance was found for the groups with a ferrule (p<0.001).”
In effect, this study demonstrates that its the ferrule, not the post, that impacts fracture resistance
In another surprising study, Stricker and Gohring found that the fracture resistance of an endodontically treated tooth, in which the access cavity was restored with composite resin, faired better than the teeth restored with a post, core and crown.3
The ferrule and not necessarily the post is what prevents fracture resistance.
How much ferrule is needed?
In Libman and Nicholls’s classic study they established that a ferrule of 0.5 mm or 1 mm was weaker than a ferrule of 1.5 mm to 2 mm. Whereas Dietschi contends that 1 mm of ferrule is needed.7
The risks and benefits of a cast post and core
The beauty of a cast post and core is that it precise adaptation of the “post significantly increases the fracture resistance of endodontically treated teeth, but upon failure renders the tooth nonrestorable.”8 So in effect, when the post fails, that’s the end of the tooth. I’d like to believe that all dentists are engineers (but not all engineers are dentists…). When we design solutions, we want to ensure they fail the right. way.
What about ceramic posts?
Sadly, Fadag et al.9 reported a higher incidence of catastrophic root fracture with ceramic posts.
What if you don’t have enough ferrule?
As dentists, we’re rarely presented with the ideal restorative conditions. Oftentimes, patients present with teeth fractured at the level of the gingiva. These situations present complex restorative demands.
There are some options available. Crown lengthening or orthodontic extrusion is available to create more ferrule. However, both of these procedures have particular considerations and precautions.
In the case of crown lengthening, it may result in an unfavorable crown to root ratio, and in the case of posterior teeth, it may expose the furcation. What’s more, this procedure may yield an unacceptable esthetic outcome because the gingival zenith is now apical to the adjacent dentition.
On the other hand, orthodontic extrusion may be considered. But, one complication with this procedure is the patient may not want to spend the time and money orthodontic therapy requires. Additionally, orthodontic extrusion may also result in an unfavorable crown-to-root ratio.
The argument could be made that a ferrule could be forcefully created by preparing the margins further gingivally. However, I agree with Stankiewicz that “…overall, it can be concluded that a ferrule is desirable, but should not be provided at the expense of the remaining tooth/root structure.”5 Preparing the tooth subgingivally has the following risks:
1. In some conditions it may invade the biologic width and result in chronic inflammation
2. It makes the crown margins considerably harder for the patient to clean
3. It invades what Milicich describes as the “bio-rim”6
So what should you do if you have a tooth fractured at the level of the gingiva and crown lengthening/orthodontics aren’t an option? Be on the lookout for a future article regarding leveraging adhesive dentistry to create an “internal ferrule.”
P.S. I’d love to be of service. Did you know there’s a way you can earn CE through the Dental Digest Podcast? We’re here to serve. Through the Dental Digest Podcast you can earn CE while you drive to work, walk the dog or just go for a hike. Click here to get started!
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This article was written by your friendly neighborhood dental geek, Dr. Melissa Seibert. Click here to read more.
- Sugaya T, Nakatsuka M, Inoue K, Tanaka S, Miyaji H, Sakagami R, Kawamami M. Comparison of fracture sites and post lengths in longitudinal root fractures. J Endod. 2015 Feb;41(2):159-63. doi: 10.1016/j.joen.2014.09.017. Epub 2014 Oct 30. PMID: 25447503.
- Lima AF, Spazzin AO, Galafassi D, Correr-Sobrinho L, Carlini-Júnior B. Influence of ferrule preparation with or without glass fiber post on fracture resistance of endodontically treated teeth. J Appl Oral Sci. 2010 Jul-Aug;18(4):360-3. doi: 10.1590/s1678-77572010000400007. PMID: 20835570; PMCID: PMC5349065.
- Stricker EJ, Göhring TN. Influence of different posts and cores on marginal adaptation, fracture resistance, and fracture mode of composite resin crowns on human mandibular premolars. An in vitro study. J Dent. 2006 May;34(5):326-35. doi: 10.1016/j.jdent.2005.07.007. Epub 2005 Oct 3. PMID: 16202498.
- Libman WJ, Nicholls JI. Load fatigue of teeth restored with cast posts and cores and complete crowns. Int J Prosthodont. 1995 Mar-Apr;8(2):155-61. PMID: 7575967.
- Stankiewicz NR, Wilson PR. The ferrule effect: a literature review. Int Endod J. 2002 Jul;35(7):575-81. doi: 10.1046/j.1365-2591.2002.00557.x. PMID: 12190896.
- Milicich G. The compression dome concept: the restorative implications. Gen Dent. 2017 Sep-Oct;65(5):55-60. PMID: 28862590.
- Dietschi, D., Duc, O., Krejci, I., & Sadan, A. (2007). Biomechanical considerations for the restoration of endodontically treated teeth: A systematic review of the literature-part 1. composition and micro- and macrostructure alterations. Quintessence International, 38(9), 733-43. Retrieved from https://archive-ouverte.unige.ch/unige:84742
- Sorensen JA, Engelman MJ. Effect of post adaptation on fracture resistance of endodontically treated teeth. J Prosthet Dent. 1990 Oct;64(4):419-24. doi: 10.1016/0022-3913(90)90037-d. PMID: 2231450.
- Fadag, Abdulrahman et al. “Fracture Resistance of Endodontically Treated Anterior Teeth Restored with Different Post Systems: An In Vitro Study.” European endodontic journal vol. 3,3 174-178. 7 Sep. 2018, doi:10.14744/eej.2018.70299