Introduction to Reinforcement Fibers🤓

I know that the idea of reading theory is not very exciting-believe me, I understand!

However, Doctors, reinforcement fibers are biomechanically a completely different animal compared to any dental material we have encountered before.

So if you are truly interested in reinforcement fibers and their application in adhesive bridges, I recommend taking four minutes to read this suuuper summarized information that I prepared for you.

Let's begin!

In the early 1990s, a variety of fiber reinforcement materials, known as FRC (Fibre Resin Composites), were introduced, such as Kevlar, carbon fibers, glass fibers, and ultra-high-molecular-weight polyethylene (UHMWPE), which have been used successfully in various clinical applications.

The fibers themselves can be oriented three-dimensionally, and the force they can withstand depends directly on the orientation of the fibers with respect to the direction of the applied force.

Fibers can be continuous unidirectional when all fibers are arranged in parallel, continuous bidirectional, or discontinuous randomly oriented (Fig 1). These variations can cause FRCs to be isotropic, orthotropic, or anisotropic, meaning that their mechanical properties vary.

Fibers with isotropic characteristics exhibit the same reaction regardless of the direction of the applied load. The anisotropic behavior present in continuous unidirectional fibers means they react differently depending on the direction of the applied force. The anisotropy of continuous fibers must be considered when designing prostheses because masticatory movements produce loads and stresses in various directions and magnitudes.

Figure 1: Schematic drawing of unidirectionally oriented continuous fibers (left), bidirectionally woven fibers (middle) and random discontinuous fibers (right).

SYNTHETIC FIBERS USED IN DENTISTRY

FIBERGLASS

These fibers are typically found in a continuous unidirectional orientation and are anisotropic (having different mechanical properties in different directions), exhibiting their maximum strength along the fiber direction. They offer high resistance to water, high resistance to plastic deformation, and a high modulus of elasticity. They can exhibit a high potential for matrix splitting between the fibers after light curing when the loads are not precisely perpendicular to the fiber direction.

Less frequently, they are arranged in bidirectional fibers. These have the same properties in two different directions; however, their strength is considerably lower than that of unidirectional fibers.

The best reinforcement and mechanical properties are achieved only when the fiber and the matrix are well bonded.

Many glass fibers come pre-impregnated with composite resin, which helps to achieve this effect.

CARBON FIBERS

They exhibit better mechanical properties than glass fibers, are biocompatible, have high fracture resistance, and also exhibit high fatigue resistance.

The mechanical properties are very similar to those present in dentin, This is why they are commonly used for the manufacture of endodontic posts. The main limiting factor for their application in dentistry is their aesthetically unacceptable black color.

ARAMID FIBERS

Also known as Kevlar, aramid fibers were introduced in 1962 by DuPont and are commonly used in the automotive industry.

In dentistry, they have been used for temporary periodontal splints, temporary fixed prostheses, and as reinforcement for PMMA in the form of thin woven fibers that increase fracture resistance. One of their most common applications has been reinforcing the bases of acrylic complete dentures. They are difficult to polish when exposed, and their dark color tends to be noticeable on visibly light-colored appliances.

POLYETHYLENE FIBERS

These, along with fiberglass, are the two most commonly used in dentistry. Commonly known as ultra-high-molecular-weight polyethylene (UHMWPE), they are chemically inert and have difficulty adhering to the matrix. Some brands, such as Construct (KERR) and Ribbond (Ribbond), use a high-energy plasma surface treatment to generate free radicals on the fiber surface, which allows for adhesion to the matrix. However, the adhesion effect produced by the plasma is very high initially and decreases rapidly over time.

Many types of fibers and architectures are available; woven fibers offer the highest strength-to-weight ratio with orthotropic behavior.

These fibers are easy for clinicians to handle. Their shape memory is virtually nonexistent, meaning they do not return to their original position. This characteristic allows them to conform closely to the surface to which they will adhere, even if the surface is uneven, and they will not revert to their original shape.

Okay, you're done, now you know a little more about the world of reinforcing fibers.

I will soon be sharing important information on this topic with you.🍻

I hope you find this information useful, best regards!

Dr. Marvin