If fence posts in the Wild West were as reliable as today's endodontic posts, cattle rustlers would have had to find "real" jobs.
It's a challenge just to get your hands around the huge variety of products available for supporting restorations in endodontically treated teeth that have insufficient coronal structure. Recently, though, one type of post -- fiber-reinforced -- has begun to stand out from the others.
For many years, labor-intensive, custom-cast gold posts and cores were the de facto standard in posts. When used with traditional cements such as zinc phosphates, these posts continue to have a high success rate. However, metal posts, whether custom or cast, are more likely to cause root fractures because of their stiffness, which concentrates forces at the end of the posts. Manufacturers have given dentists many choices for simpler custom and prefabricated posts that place less stress on the root.
The 2008 Henry Schein dental catalog contains eight pages of prefabricated post systems ranging from gold-plated composite to titanium, stainless steel, zirconia-enriched, and the increasingly popular fiber-reinforced.
For those who favor custom-made, CAD/CAM fabricated posts are preferred by dentists like Chris Farrugia, D.D.S., a private practitioner in Pensacola, FL, who believes, "For most clinical situations, a custom-fitting ceramic bonded post and core should be considered" (General Dentistry, January/February 2008, Vol. 56:1, pp. 42-50).
With their milliseconds of spare time, doctors must also choose among additional features, such as parallel or tapered, screw-type or passive, flexible or stiff, hollow or solid, tooth-colored or dark, and biocompatible or toxic. A Schein sales representative consulted for guidance on which are bestsellers told DrBicuspid.com, "They all sell well. It just depends on what you like." Such remarks leave one wondering: Does it even matter?
Yes, it does. When posts fail, dentists face time-consuming and expensive retreatment at best and, in the worst cases, catastrophic root fracture.
Custom-made posts may seem to offer a more perfect fit. But they are costly to order from a lab, and making your own requires bulky and expensive equipment. Meanwhile, recent research shows that prefabricated posts bond well to dentin and exhibit high fracture resistance -- especially fiber-reinforced ones.
For example, after comparing glass fiber to zirconia and titanium in their lab, Turkish researchers wrote in the November issue of the Journal of Contemporary Dental Practice that "Glass fiber posts exhibited a modulus of elasticity much better matched to that of teeth" when used with new-generation adhesives (November 2008, Vol. 9:7, pp. 33-40).
(The researchers recommend self-etching adhesives for cementation because these adhesives contain "self-etching primers and do not require acid etching procedures. Therefore, the risk of overetching the dentin is decreased.")
Excellent aesthetics
Steve Weinberg, D.M.D., a University of Pennsylvania assistant professor who oversees most of the aesthetic dentistry performed in his clinic, agrees that fiber-reinforced posts are an excellent choice for most situations. Glass fiber posts are tooth-colored, which is of great aesthetic importance when using all-ceramic crowns because a dark substructure can show through, he said.
Today, posts can fit passively because of the adhesive system. "The retention is from the bond," he said. "A good adhesive system is more important than the post." Unlike traditional cements, self- or dual-curing resin cements and dual-cure bonding agents create a chemical bond to the dentin that actually "pulls the tooth inward, like an internal splint, so it's fracture-resistant."
Additionally, attention to the little details during preparation and cementation increases the likelihood of success. A ferrule of 1-2 mm on coronal tooth structure allows the crown to reinforce the tooth externally. To get the best bond, the post space must be free of temporary material, gutta-percha, and eugenol. Also, the post space should be at least as long as the crown, but no less than 3-4 mm from the apical seal.
According to Dr. Weinberg, one reason for fiber post failure is "a lot of doctors still don't know that you can't bond a self-cured composite to a light-cured bonding agent. That's why they developed dual-cure bonding agents."
Overall, prefabricated fiber-reinforced polymer posts satisfy the five most important criteria for posts: aesthetics, physical properties similar to tooth structure, excellent adhesion to resin cement, biocompatibility, and easy removal when necessary. (They are easier to remove than metal posts when bonded with resin cement.)
Still, there's plenty of room for individual preference, as long as you can hold down the core without fracturing the root.
Perhaps the day is not far off when an easy-to-use, all-in-one "bondable" file actually shapes, obturates, and serves as the core.
Stay tuned, we'll keep you posted.
Monica "Dr. mOe" Anderson, D.D.S., is a general dentist, writer, and motivational speaker in Austin, TX.
