Why choose a fiber post instead of metal or ceramic? The main reason is mechanical properties. Fiber posts simply behave and perform differently. In addition to the obvious esthetic advantages, fiber posts cannot corrode , like base metals (including stainless steel) can. Because the stiffness (Elastic Modulus) of fiber posts is like the tooth structure, they function WITH the tooth instead of against it, in helping to prevent fractures and other problems. While some fiber posts are stronger (Flexural/Transverse and Tensile) than other fiber posts and metal posts, fiber posts are stronger than dentin , and therefore, adequate for this restorative task. All of the components used in the manufacture of RTD fiber posts are proven to be biocompatible (ISO standards), while stainless steel contributes Nickel and Chromium, and non-precious casting alloys contain other suspect elements. In independent studies, RTD fiber posts have been proven to be as retentive as metal posts . Good quality fiber posts tend to resist fatigue better than rigid metal posts, and RTD posts specifically demonstrate fatigue resistance superior to stainless steel, titanium and other fiber posts.

The information below illustrates these points, supporting the choice of fiber posts over ANY metal version.

RTD fiber posts are a genuine industrial composite.
In other words, it is made of 1) spacially- oriented reinforcement of continuous elongated fibers, 2) a matrix of a proprietary epoxy resin and 3) an interface: a bonding system between the matrix and the fiber. The reinforcement fibers represent at least 80% of the volume (>60% wt.) of the post, and are pre-tensed during manufacture, to consistently achieve the ideal mechanical properties; THE most distinguishing attribute of the RTD fiber post.

The fibers are uni-directional and equally pre-tensed along the long axis of the post. For a lateral force applied on a given material, at say 45 degrees, the material will endure different stresses at once: tension on one side, compression on the other side and shearing in the middle. High mechanical values in tension – compression - shearing are, thus, of extreme importance.

Since RTD patented and introduced the original Carbon Fiber COMPOSIPOST in 1989, several companies have attempted to copy our products. Independent studies have proven that the quality, type, and volume of fibers, the way the fibers are silanated, and the pre-tension of the fibers during manufacture all influence the performance of the end product.    

These important properties are addressed here:

The Elastic Modulus (relative rigidity) of all of our fiber posts systems is probably their greatest mechanical distinction from metal and Zirconium posts. The ability of our posts to absorb and dissipate stress is the primary attribute responsible for their ability to prevent root fracture. Elastic Modulus is a property inherent to a given material, and does not

interaction between the fiber post and the tooth, and appears to prevent root fractures.
A plethora of published independent IN VITRO TESTING , which includes Photoelastic, Finite Element Analysis and compressive Fracture Resistance protocols, all support this conclusion.

These simplified drawings illustrate the distribution of stresses, a function of Elastic Modulus:
On the LEFT: distribution in a natural tooth.
In the CENTER: distribution of stress in a tooth with a LOW-modulus reconstruction. The pattern is very close to that of the natural tooth.
On the RIGHT: are 2 HIGH-modulus metallic post/cores, which redistributes the stresses in a specific and dangerous way.

This post, made of quartz fibers, has demonstrated his excellent biological behavior.

Composipost®, R.T.D. carbon fiber post, was the first fiber post approved by the U.S. Food and Drug Administration (FDA) and was subjected to biological evaluation during this procedure.

CORROSION:

According to the textbook Contemporary Fixed Prosthodontics, “Of 468 teeth with vertical or oblique root fractures, 72% are attributed to electrolytic action of dissimilar metals used for the post and core; reaction between the tin in the amalgam core and the stainless steel post.” . Fiber posts simply cannot corrode.

Radiographic density is also an important CLINICAL property.
The first generation and most of the second generation of fiber posts were not radiopaque. The current ISO standard (#4049) for radiopacity of a composite requires equivalence to the equivalent thickness of Aluminum. Most RTD fiber posts (except Aestheti-Plus and MatchPost) are radiopaque according to ISO 4049. The radiopacity has been documented by independent institutions. The challenge for the chemist and fabricator is to achieve maximum radiopacity without sacrificing translucency.

The primary purpose of the post is to retain the core / crown assembly. Metal prefabricated posts all feature some sort of macro-retention features, threads, knurling, retention form heads, etc. These features can often adversely influence the shape and size of the core. RTD has developed and adapted special equipment into its manufacturing that places a specific amount of retentive roughness on the post, increasing the surface area, which is IDEAL for the retention process. The combination of a retentive post surface, a cleaned internal dentin surface and contemporary bonding adhesives and resin cements (which are virtually insoluble) create retentive capability EQUAL TO OR GREATER THAN that of metal posts.

There is a great deal of such IN VITRO TESTING confirming this important feature of fiber posts, assessing such varied aspects as excess film thickness, post shape, cement type, depth of post insertion, post diameter, ferrule effect and even operator experience levels! Here is the result of one recent study (Borer, Quintessence, 2007) comparing the comparative retention of RTD’s tapered DT LIGHT-POST compared to the well-known parallel Stainless Steel ParaPost Plus, at both 5mm and 10mm depth.

The in vitro test that most realistically approximates the oral conditions that universally take their destructive toll on natural teeth and restorations is FATIGUE.

All materials fatigue when under function. Their failure is a result of repeated loading by a load well below its ultimate flexural strength limits.

Knowing this, RTD uses a customized fatigue machine to test EVERY production run of raw material made for use as posts. The long rods of raw materials must survive 10 million cycles without rupture to pass this test and to proceed to the shaping process.

The test inspired some professors visiting RTD facility to conduct and publish the same testing on various brands of fiber posts (from different manufacturers, and compositions)

This protocol tests ONLY the post, eliminating all the variables introduced with extracted teeth, bonding techniques, operator skill, etc. The posts are tested at 3 Hz, at 900, because that angle allows even the poorest post to flex at its best (lowest Elastic Modulus) for as long as possible, before rupture.

Conclusions of the study: "Different types of fiber posts give very dissimilar results when undergoing a fatigue test. From a statistical point of view, the DT Light-Post (RTD) resists the fatigue tests significantly better than the other posts tested in this study. A correlation can probably be made between the fatigue test (results) and the structural integrity of the post".

Here are microscopic views of typical specimens for several of the posts after testing.

The fatigue resistance of the posts can also be assessed when the post is imbedded inside the extracted tooth, and this testing is considerably (and predictably) more complicated.

Wiskott, HW, Meyer, M, Perriard, J, Scherrer, SS. Rotational fatigue-resistance of seven post types anchored on natural teeth. Dent Mater. J 2007 Jan 29; [Epub ahead of print]

Conclusions:" In increasing order of magnitude, the resistances to fatigue loading were as follows: Biopost, Unimetric-Ti, Unimetric-SS, Composipost, Easypost, Everstickpost, DT Light-Post. Significance: The fatigue resistance of the two fibrous posts with the highest fatigue resistance (DT Light-Post and Everstick) was twice that of any of the ceramic or metal posts."