PREFABRICATED POST-AND-CORE SYSTEMS
An alternative consideration is the prefabricated post-and-core system. Prefabricated post-and-core systems are classified according to their geometry (shape and configuration) and method of retention. The methods of retention are designated as active or passive. Active posts engage the dentinal walls of the preparation upon insertion, whereas passive posts do not engage the dentin, relying instead on cement for retention.1 The basic post shapes and surface configuration are tapered, serrated; tapered, smooth-sided; tapered, threaded; parallel, serrated; parallel, smooth-sided; and parallel, threaded. While active or threaded posts are more retentive than the passive posts, the active posts create high stress during placement and increase the susceptibility of root fracture when occlusal forces are applied. Parallel-sided serrated posts are the most retentive of the passive prefabricated posts, and the tapered smooth-sided posts are the least retentive of all designs.2
Prefabricated Metal Posts
Traditional prefabricated metal posts are made of platinum-gold-palladium, brass, nickel-chromium (stainless steel), pure titanium, titanium alloys, and chromium alloys.2,4 Although stainless steel is stronger, the potential for adverse tissue responses to the nickel has motivated the use of titanium alloy.12 Also, contributing factors to root fracture such as excessive stiffness (modulus of elasticity)13 and post corrosion2 from many of these metal posts have stimulated concerns about their use.
Prefabricated Nonmetallic Posts
 |
 |
 |
 |
|
Figures 8a to 8d. (8a) A dual-curing self-etch adhesive (Futurabond DC) was applied to the remaining dentin surface and light-cured for 10 seconds. (8b) A dual-cure, radiopaque flowable core-build-up composite material (Rebilda) was injected over the coronal aspect of the post, (8c), sculpted with a long bladed interproximal instrument, (8d) and smoothed with a No. 2 sable brush to an ideal coronal preparation geometric shape and dimension and light-cured for 40 seconds. |
The nonmetallic prefabricated posts have been developed as alternatives, including ceramic (white zirconium oxide) and fiber-reinforced resin posts. Zirconium oxide posts have a high flexural strength, are biocompatible, and are corrosion resistant. However, this material is difficult to cut intraorally with a diamond, and to remove from the canal for retreatment.4 The fiber-reinforced composite resin post-and-core system offers several advantages: a one appointment technique, no laboratory fees, no corrosion, negligible root fracture, no designated orifice size, increased retention resulting from surface irregularities, conserved tooth structure, and no negative effect on aesthetics.